MicroBiology MCQs with Answer and Explnation | Chapter 65

Answer: 2%

The most commonly used concentration of agar in agar medium is 2%. This concentration provides a good balance between solidity for isolating colonies and allowing for diffusion of nutrients and oxygen.

The other options are incorrect:

• 10%: This concentration is too high and would create a very firm gel, hindering nutrient diffusion and potentially impacting microbial growth.
• 5%: While usable in some specific cases, 5% agar creates a softer medium that might not be ideal for isolating single colonies.
• 15%: Similar to 10%, 15% is excessively high and would result in a very rigid medium unsuitable for most microbial cultures.

Answer: Discovery of M. Tuberculosis

Louis Pasteur is not associated with the discovery of M. Tuberculosis. Instead, this discovery is credited to Robert Koch in 1882.

The other options are incorrect:

• Introduction of complex media: Louis Pasteur is associated with the introduction of complex media in microbiology. He developed various culture media and techniques for studying microorganisms.
• Discovery of Rabies Vaccine: Louis Pasteur is famously known for developing the rabies vaccine. His work in this area was groundbreaking and led to significant advancements in vaccination and immunology.
• Disproved spontaneous generation theory: Louis Pasteur played a key role in disproving the theory of spontaneous generation, showing through his experiments that living organisms do not arise spontaneously from non-living matter.

Answer: Robertson cooked meat medium

Robertson cooked meat medium is specifically designed for cultivating anaerobic bacteria. It provides a meat-based nutrient source and includes a reducing agent, like sodium thioglycolate, to create an oxygen-depleted environment for anaerobic growth.

The other options are incorrect:

• L-J medium: L-J medium, also known as Levinthal-Jennings medium, is formulated for culturing pathogenic Neisseria species, which are typically aerobic or require increased CO2.
• Loeffler’s medium: This medium is suitable for cultivating aerobic bacteria, particularly fastidious ones requiring enriched media. It might not be ideal for anaerobes due to the presence of oxygen.
• Sabouraud agar: Sabouraud agar is commonly used for growing fungi and yeasts. While some fungal species can tolerate low-oxygen environments, they aren’t strictly anaerobic and wouldn’t necessarily require the anaerobic conditions provided by Robertson cooked meat medium.

Answer: Protein polysaccharide complex

Exotoxins are primarily proteins, not a combination of protein and polysaccharide. They exert their toxic effects through their protein structure and enzymatic activity.

The other options are incorrect:

• Heat labile: Exotoxins are often heat labile, meaning they can be deactivated by high temperatures. This property helps with some food preservation methods.
• Highly potent: Exotoxins are frequently very potent, even in small quantities, causing significant damage to host cells.
• Has specific tissue affinity: Many exotoxins have a high degree of specificity for certain tissues or cell types. This targeted action contributes to the specific symptoms associated with different bacterial infections.

Answer: Sabouraud’s agar

Sabouraud’s agar is a specifically formulated culture medium ideal for growing a wide variety of fungi. It contains a good balance of nutrients, including simple sugars like dextrose, which fungi readily utilize for growth. Additionally, it has a slightly acidic pH that favors fungal growth over bacterial growth.

The other options are incorrect:

• Blood agar: This medium is enriched with sheep or horse blood and is primarily used for cultivating fastidious bacteria, particularly those requiring blood components for growth.
• Tissue culture: Tissue culture refers to the methods used to grow and maintain animal or plant cells in a controlled environment. It’s not typically used for fungi.
• Thioglycollate medium: This medium is designed for culturing a variety of bacteria, including both aerobic and anaerobic types. It wouldn’t be the optimal choice for most fungi.

Answer: Clostridia

Robertson’s cooked meat medium is best suited for the cultivation of Clostridia, which are anaerobic bacteria commonly found in soil, water, and the gastrointestinal tract. This medium provides an anaerobic environment and a nutritious substrate for the growth of Clostridia species.

The other options are incorrect:

• S. epidermidis: Staphylococcus epidermidis is a facultative anaerobe, meaning it can grow with or without oxygen. While it can tolerate some reduced oxygen environments, it wouldn’t necessarily require the strictly anaerobic conditions provided by Robertson cooked meat medium.
• Choleria: Vibrio cholerae, the bacteria responsible for cholera, is a facultative anaerobe as well. Standard bacteriological media would be sufficient for its cultivation.
• Mycobacterium: Mycobacterium species, including Mycobacterium tuberculosis (which causes TB), are typically aerobic and require oxygen for growth.

Answer: Oxidation

Dry heat destroys microorganisms primarily through oxidation. The high temperatures cause essential cellular components, particularly proteins and lipids, to denature and break down due to oxidation reactions. This disrupts the cell structure and function, leading to cell death.

The other options are incorrect:

• Lysis: Lysis refers to the bursting of a cell membrane. While dry heat can damage cell membranes, oxidation is the more prominent mechanism for killing microbes in this context.
• Hydrolysis of DNA: Dry heat can damage DNA to some extent, but oxidation is a more general and efficient way to inactivate microorganisms through protein denaturation.
• Coagulation of proteins: Coagulation is a specific type of protein denaturation caused by heat. However, it’s just one aspect of the broader oxidative damage that dry heat inflicts on microbial cells.

Answer: Robert koch

Robert Koch is credited with introducing the first practical and widely used solid media for growing bacteria in 1881. He experimented with various solidifying agents and found agar, a gelatinous substance derived from red algae, to be particularly effective.

The other options are incorrect:

• Louis Pasteur: While Louis Pasteur made significant contributions to microbiology, including germ theory and pasteurization, he wasn’t directly involved in developing the first solid media.
• Hensen: Although Friedrich Hensen, a German botanist, conducted early experiments with solidified media using gelatin, it wasn’t as practical as the agar-based method developed by Koch.
• Ogston: Alexander Ogston, a Scottish surgeon, also played a role in the development of early culture media. However, his contributions focused on using liquids for bacterial growth, not the introduction of solid media.

Answer: Nucleic acids

Nucleic acids, primarily DNA and RNA, are the most susceptible components to UV irradiation in bacteria and viruses. UV light disrupts the structure of these molecules by causing mutations or breaks in the sugar-phosphate backbone, which can render them nonfunctional. This damage inhibits the microorganism’s ability to replicate and can ultimately lead to cell death.

The other options are incorrect:

• Lipids: While UV radiation can damage lipids to some extent, it’s not the primary target for microbial inactivation.
• Carbohydrates: Similar to lipids, carbohydrates are less susceptible to UV damage compared to nucleic acids.
• Inorganic salts: Inorganic salts are generally not affected by UV irradiation in the context of microbial disinfection.

Answer: Sterilization kills all spores but disinfection does not

The main difference between sterilization and disinfection is that sterilization kills all forms of microbial life, including bacterial spores, while disinfection typically does not kill bacterial spores, although it eliminates most other microbial forms.

The other options are incorrect:

• Disinfection kills all spores but sterilization does not: This option is incorrect. Sterilization kills all forms of microbial life, including spores, while disinfection typically does not kill bacterial spores.
• Sterilization involves chemicals and disinfection involves physical methods: This option is incorrect. Both sterilization and disinfection can involve either physical methods (such as heat or radiation) or chemical agents, depending on the specific process and requirements.
• Sterilization is easier to achieve: This option is incorrect. Sterilization is generally more challenging to achieve than disinfection because it requires the complete elimination of all microbial life, including spores, from an object or environment.

Answer: Enriched media

Blood agar is an enriched media because it contains added nutrients, specifically sheep or horse blood, to support the growth of fastidious bacteria. These bacteria have complex nutritional requirements and may not thrive on basic media formulations.

The other options are incorrect:

• Simple media: Simple media contains only the basic nutrients required for most bacteria to grow. It wouldn’t have the additional enrichments like blood found in blood agar.
• Transport media: Transport media is designed to preserve and transport bacterial specimens from the collection site to the laboratory for further analysis. It doesn’t necessarily aim to promote bacterial growth.
• Differential media: Blood agar can be considered a type of differential media in some contexts. The presence of blood allows for the differentiation of certain bacteria based on their hemolytic properties (ability to lyse red blood cells).

Answer: Stationary phase

The stationary phase of the bacterial growth curve is characterized by a zero net growth rate. While some bacterial cells might still be dividing, the rate of cell death balances out the rate of cell division, resulting in no overall increase in population size.

The other options are incorrect:

• Lag: The lag phase is the initial adaptation period where bacteria adjust to the new environment and prepare for division. There’s minimal growth during this phase, but it’s not zero.
• Exponential growth: The exponential growth phase, also known as the log phase, is characterized by rapid bacterial multiplication. The population size increases exponentially during this time.
• Decline: The decline phase occurs when nutrients become depleted, waste products accumulate, and the environment becomes unfavorable for bacterial growth. The number of viable cells starts to decrease in this phase.

Answer: Clothes

Clothes are typically made from fabrics that can melt, burn, or deform at the high temperatures (up to 300°C) used in hot air ovens for sterilization. This would damage the clothes and potentially render them unusable.

The other options are incorrect:

• Instruments: Hot air ovens are a common method for sterilizing heat-resistant instruments like scalpels, forceps, and scissors.
• Culture media: While not the most common method (autoclaves using steam are preferred), culture media can be sterilized in a hot air oven at specific temperatures and durations depending on the media type.
• Needles: Similar to instruments, needles made of heat-resistant materials can be sterilized in a hot air oven.

Answer: Leumenhoek

Antonie van Leouwenhoek, a 17th-century Dutch scientist, is credited with coining the term “animalcule” to refer to the microscopic organisms he observed, including bacteria found in his own mouth scrape.

The other options are incorrect:

• Wd Miller: While Wd Miller (Willoughby Dayton Miller) was a prominent microbiologist who made significant contributions to our understanding of oral health and dental caries, he did not originate the term “animalcule.”
• Robertson: Similar to Miller, microbiologist Robertson likely wouldn’t be credited with the term “animalcule” as it predates their work.
• Socranci: Just like the previous two options, Socranci (likely referring to Janet K. Setlow Sochancrati) is a microbiologist whose contributions wouldn’t encompass naming such a historical term.

Answer: Deactivate all spores and dill pathogenic organism

Sterilization is a rigorous process aimed at eliminating all forms of microbial life, including both vegetative cells (active, growing microbes) and spores (dormant, highly resistant forms of some bacteria). This ensures the complete absence of any microbial growth, pathogenic (disease-causing) or not.

The other options are incorrect:

• Kill all pathogenic micro-organisms: While eliminating pathogens is a crucial aspect of sterilization, it’s not enough. Non-pathogenic microbes can still be present and potentially cause spoilage or contamination even if they don’t directly cause disease.
• Kill all non-pathogenic micro-organisms in the environment: This describes disinfection, a process that significantly reduces but doesn’t necessarily eliminate all microbes. Disinfection is often used for surfaces and objects where complete sterility isn’t essential.
• Deactivate all pathogens not spores: This is partially correct as sterilization targets all pathogens, but it also needs to inactivate spores, the highly resistant form that can survive harsher conditions and germinate later, causing new growth.

Answer: Mycobacterium tuberculosis

Mycobacterium tuberculosis has a unique cell wall structure rich in waxy substances like mycolic acid. This thick and complex wall makes it difficult for the crystal violet stain used in Gram staining to penetrate during the staining process.

The other options are incorrect:

• Actinomyces israelii: This bacterium possesses a typical Gram-positive cell wall with a thick peptidoglycan layer, allowing it to retain crystal violet and appear Gram-positive.
• Candida albicans: This fungus doesn’t have a cell wall like bacteria but has a cell membrane. Gram staining is not typically used for fungi, but Candida albicans can be identified through other staining methods.
• Streptococcus mutans: This bacterium has a classic Gram-positive cell wall structure and retains crystal violet during Gram staining, appearing Gram-positive.

Answer: Gamma rays

Cold sterilization refers to the process of sterilization using chemical agents or ionizing radiation, particularly gamma rays. Gamma rays can penetrate materials deeply, effectively killing microorganisms by damaging their DNA and disrupting cellular functions.

The other options are incorrect:

• Ultra violet rays: While ultraviolet (UV) rays can be used for disinfection purposes, they are not typically used for cold sterilization. UV rays have limited penetration and are less effective for sterilizing materials compared to gamma rays.
• Ultrasonic vibrations: Ultrasonic vibrations are not typically used for cold sterilization. Ultrasonic cleaners are commonly used for cleaning instruments through the action of high-frequency sound waves, but they do not achieve sterilization.
• Infrared rays: Infrared rays are not used for cold sterilization. Infrared radiation is primarily used for heating purposes and does not possess the necessary properties for achieving sterilization.

Answer: Growing bacteria in unconventional host

Attenuation refers to weakening a microorganism, often a pathogen, to create a live vaccine. This process typically involves manipulating the bacteria’s ability to cause disease while retaining its ability to trigger an immune response. Unconventional hosts wouldn’t be a standard method for attenuation.

The other options are incorrect:

• Growing bacteria in adverse environment: Exposing bacteria to stressful conditions like extreme temperatures, limited nutrients, or certain chemicals can introduce mutations that reduce virulence (disease-causing ability).
• Growing bacteria in a different but natural host: Passing a pathogen through a different natural host, like switching from humans to animals, can sometimes lead to attenuation as the bacteria adapts to the new host and loses some of its ability to infect humans.
• Repeated cultures in artificial media: Serial passage involves repeatedly culturing bacteria in a lab under controlled conditions. Over time, mutations can arise, potentially leading to attenuated strains that are less virulent.

Answer: Mitochondria

Bacterial cells are prokaryotic, meaning they have a simpler structure compared to eukaryotic cells like animal or plant cells. Mitochondria are membrane-bound organelles found in eukaryotes responsible for cellular respiration, a process bacteria carry out differently in their cytoplasm without a dedicated organelle.

The other options are incorrect:

• DNA: Bacterial cells do contain DNA, typically a single circular chromosome, which stores their genetic information.
• Ribosome: Ribosomes are present in both prokaryotic and eukaryotic cells. They are responsible for protein synthesis, a crucial process for all life forms.
• Cell Wall: Most bacteria possess a cell wall made of peptidoglycan, which provides shape, support, and protection for the cell.

Answer: Optochin sensitivity

The organism described in the scenario is likely Streptococcus pyogenes, also known as Group A Streptococcus. Optochin sensitivity testing is used to differentiate between Streptococcus pneumoniae (which is optochin sensitive) and other alpha-hemolytic streptococci. Streptococcus pyogenes is optochin sensitive, while other streptococci are resistant.

The other options are incorrect:

• Bile solubility: Bile solubility testing is typically used to differentiate Streptococcus pneumoniae (which is bile soluble) from other alpha-hemolytic streptococci. Streptococcus pyogenes does not typically undergo bile solubility.
• Bacitracin sensitivity: Bacitracin sensitivity testing is used to differentiate Group A Streptococcus (S. pyogenes) from other beta-hemolytic streptococci, particularly Streptococcus agalactiae (Group B Streptococcus). Group A Streptococcus is bacitracin sensitive, but this test is not the best choice for identifying it in the scenario described.
• Catalase positive: Catalase testing is typically used to differentiate between catalase-positive organisms (such as Staphylococcus species) and catalase-negative organisms (such as streptococci). Streptococcus pyogenes is catalase negative.

Answer: Spore formers

The purpose of sterilization is to eliminate all forms of microbial life, including bacterial spores, which are highly resistant structures formed by certain bacteria. Sterilization ensures that an object or environment is completely free from viable microorganisms, reducing the risk of contamination or infection.

The other options are incorrect:

• Bacteria: While sterilization does aim to eliminate bacteria, its scope is broader and includes the eradication of all forms of microbial life, not just bacteria.
• Viruses: Sterilization targets viruses along with other microorganisms, but its primary focus is on eliminating bacteria and spores rather than specifically targeting viruses.
• Fungus: Sterilization aims to eliminate fungi as well as other microorganisms, but its primary goal is to eradicate bacterial spores and other forms of microbial life to ensure complete decontamination.

Answer: Mycoplasma

Mycoplasma are a type of bacteria that naturally lack a cell wall. This unique characteristic allows them to be resistant to certain antibiotics that target cell wall synthesis.

The other options are incorrect:

• Escherichia Coli (E. coli): This is a common bacterium found in the intestines of humans and animals. E. coli has a cell wall and can be beneficial or harmful depending on the strain.
• Staphylococci: These are spherical bacteria that often form clusters. They also possess a cell wall and can cause various infections.
• Spirochetes: These are spiral-shaped bacteria with a unique structure that includes a cell wall. They are known for causing diseases like syphilis and Lyme disease.

Answer: Coxiella burnetti

Moist heat is a very effective sterilization method that can eliminate most bacteria, viruses, and fungi.Coxiella burnetii is the causative agent of Q fever, a respiratory illness. It forms highly resistant spores that can withstand moist heat sterilization at boiling temperatures (100°C).

The other options are incorrect:

• Brucella: This bacteria causes brucellosis, a zoonotic disease transmitted through contact with infected animals or their products. Moist heat effectively kills Brucella.
• Mycobacterium: This genus includes bacteria like Mycobacterium tuberculosis, which causes tuberculosis. Moist heat sterilization methods like autoclaving (high pressure steam) are effective against Mycobacterium.
• Salmonella: This common foodborne pathogen responsible for food poisoning can be eliminated by moist heat sterilization.

Answer: Boivin antigen

The Boivin antigen is a lipopolysaccharide (LPS) molecule found in the outer membrane of Gram-negative bacteria. It plays a crucial role in the bacterium’s interaction with the host’s immune system and contributes to virulence (disease-causing ability).

The other options are incorrect:

• Region I: This option does not provide sufficient context to determine its relevance to the cell wall. Without additional information, it is unclear what “Region I” refers to in this context.
• Region II: Similar to the previous option, “Region II” lacks context to determine its significance regarding the cell wall.
• Region III: Without further information, “Region III” does not specify any particular component or structure of the cell wall. It is an ambiguous option.

Answer: Cell wall of Gram positive organisms

Teichoic acid is a key component of the cell wall in Gram-positive bacteria. It contributes to several functions, including cell wall stability, shape maintenance, and interaction with the environment.

The other options are incorrect:

• Cell wall of Gram negative organisms: Teichoic acid is not present in the cell wall of Gram-negative organisms. Gram-negative cell walls primarily consist of lipopolysaccharides (LPS) in the outer membrane, which are structurally distinct from the cell walls of Gram-positive bacteria.
• Cytoplasm of Gram positive organisms: Teichoic acid is not found in the cytoplasm of Gram-positive organisms. It is a component of the cell wall, specifically in the peptidoglycan layer or associated with it.
• Cytoplasm of Gram negative organisms: Teichoic acid is not found in the cytoplasm of Gram-negative organisms. It is a component of the cell wall, which is external to the cytoplasmic membrane in both Gram-positive and Gram-negative bacteria.

Answer: Lowenstein Jensen medium

Lowenstein Jensen medium is a selective medium specifically designed for the isolation and cultivation of Mycobacterium species, particularly Mycobacterium tuberculosis. It contains malachite green, which inhibits the growth of contaminants while allowing the growth of mycobacteria.

The other options are incorrect:

• Sabourauds medium: This medium is formulated for the growth of fungi and yeasts. It wouldn’t be suitable for Mycobacterium, which is a type of bacteria.
• Agar-agar: This is a basic solidifying agent used in many microbiological media but lacks the specific nutrients and selective properties needed for Mycobacterium growth.
• Loeffler’s serum slope: This medium is typically used for the cultivation of fastidious bacteria, but it’s not selective for Mycobacterium and lacks the specific nutrients they require.

Answer: Slide flocculation test

The VDRL (Venereal Disease Research Laboratory) test is a slide flocculation test used for syphilis screening. It detects antibodies produced by the body in response to a syphilis infection. In this test, a serum sample is mixed with a specific antigen on a slide. If antibodies are present, they will clump together (flocculate) with the antigen, indicating a potential syphilis infection.

The other options are incorrect:

• Tube flocculation test: While flocculation can occur in tubes, the VDRL test is specifically designed as a slide test for faster results and easier observation.
• Tube agglutination test: Agglutination also involves clumping, but it refers to the specific clumping of antigens (usually with antibodies). The VDRL test detects antibody-antigen complexes.
• Latex agglutination test: This is a different type of rapid test that uses latex beads coated with antigens. While some rapid tests exist for syphilis, the VDRL test is a slide-based flocculation test.

Answer: Both First and Second

Plasmids are extrachromosomal DNA molecules found in some bacteria. They offer bacteria several advantages:

• Multidrug resistance transfer: Plasmids can carry genes for antibiotic resistance, allowing bacteria to acquire resistance to multiple drugs. This is a significant concern in the rise of superbugs.
• Conjugation: Plasmids can facilitate conjugation, a process where a plasmid is transferred from one bacterium to another, allowing for the spread of genetic traits like antibiotic resistance among bacterial populations.

The other options are incorrect:

Imparts capsule formation: Capsule formation is typically associated with chromosomal genes or specific virulence plasmids, not all plasmids in general.

Answer: Sarcina

Sarcina is a genus of bacteria known for their unique arrangement. They are gram-positive cocci (round-shaped bacteria) that typically cluster in regular packets of eight cells, forming a cube-like structure. This specific arrangement is a distinguishing feature of Sarcina.

The other options are incorrect:

• Staphylococcus: Staphylococcus bacteria are also gram-positive cocci, but they typically cluster in irregular groups or pairs. They don’t form the cubical packets characteristic of Sarcina.
• Micrococcus: Similar to Staphylococcus, Micrococcus are gram-positive cocci that usually form irregular clusters or tetrads (groups of four). They lack the specific cubical arrangement of Sarcina.
• Aerococcus: Aerococcus is another genus of gram-positive cocci. However, they typically grow in pairs or short chains, not the cubical packets seen in Sarcina.

Answer:

Sporulation typically occurs during the stationary phase of bacterial growth. During this phase, nutrient depletion and accumulation of waste products trigger certain bacterial species, particularly spore-forming bacteria like Bacillus and Clostridium, to undergo sporulation as a survival mechanism.

The other options are incorrect:

• Lag phase: The lag phase is the initial phase of bacterial growth characterized by slow growth as bacteria adjust to the new environment and synthesize essential molecules. Sporulation does not occur during this phase.
• Log phase: The log phase, also known as the exponential phase, is characterized by rapid and exponential growth of bacterial population. Sporulation does not typically occur during this phase as bacterial growth is focused on replication rather than survival mechanisms like sporulation.
• Decline phase: The decline phase, also known as the death phase, is characterized by a decrease in bacterial population due to factors such as nutrient depletion and accumulation of waste products.

Answer: Spirochetes

Smith-Noguchi medium is a specific type of culture media designed to support the growth of certain bacteria, particularly nonpathogenic (not causing disease) strains of Spirochetes. These are spiral-shaped bacteria with unique nutritional needs.

The other options are incorrect:

• Salmonella: This is a type of bacteria commonly associated with foodborne illness. Smith-Noguchi medium wouldn’t be the ideal choice for culturing Salmonella.
• Klebsiella: This is another type of bacteria often found in the environment and human respiratory tract. It has different growth requirements compared to Spirochetes and wouldn’t thrive in Smith-Noguchi medium.
• Bacillus: This genus includes a diverse group of bacteria, some of which can form spores. Smith-Noguchi medium isn’t specifically designed for spore-forming bacteria and may not be suitable for all Bacillus species.

Answer: Borrelia

Noguchi’s medium, though not as widely used today, was historically employed for cultivating Borrelia species, specifically those causing relapsing fever. These are spiral-shaped bacteria with specific nutritional needs.

The other options are incorrect:

• Bordetella: This genus includes bacteria like Bordetella pertussis, which causes whooping cough. Bordetella has different growth requirements and wouldn’t necessarily be cultured using Noguchi’s medium.
• Brucella: This genus encompasses bacteria responsible for brucellosis, a zoonotic disease. Brucella has distinct growth needs compared to Borrelia and wouldn’t be the primary target for Noguchi’s medium.

Answer: India ink preparation

India ink preparation is a negative staining technique used for visualizing capsules surrounding some bacteria and fungi. In negative staining, the background gets stained while the specimen itself remains unstained, creating a halo effect around the capsule.

The other options are incorrect:

• Gram’s staining: This is a differential staining method that separates bacteria into two groups based on their cell wall structure. It uses a series of dyes to directly stain the bacteria itself.
• Fontana’s staining: This is a histological staining technique used to identify melanin, a pigment, in tissues. It wouldn’t be used for bacteria or fungi.
• Ziehl-Neelsen staining: This is another differential staining method specifically designed to identify acid-fast bacteria like Mycobacterium tuberculosis. It directly stains the bacteria.

Answer: Lophotrichate

Bacteria with a tuft of flagella at one end are called lophotrichate. “Lophotrich” comes from the Greek words “lophos” meaning crest and “thrix” meaning hair, referencing the tufted arrangement.

The other options are incorrect:

• Monotrichate: This refers to bacteria with a single flagellum at one end, not a tuft.
• Peritrichate: These bacteria have flagella distributed all over their cell surface, not just at one end.
• Bipolar: This term isn’t commonly used in bacterial flagellation. Some bacteria might have flagella at both ends, but wouldn’t be called bipolar specifically.

Answer: Increased Virulence

Exaltation refers to an increase in the virulence of a microorganism, particularly a pathogen. This means the microbe becomes more capable of causing disease. Exaltation can occur through various mechanisms, such as mutations that enhance toxin production, or adaptation to a new host environment.

The other options are incorrect:

• Decreased virulence: This is the opposite of exaltation and is called attenuation.
• No change: Exaltation is a specific process leading to an increase in virulence.
• None of the above: While the term “none” isn’t technically incorrect, it doesn’t describe the specific phenomenon of exaltation.

Answer: activate complement by the alternate pathway

Endotoxins, a part of the outer membrane of gram-negative bacteria, can directly interact with components of the immune system, including activating the complement system through the alternate pathway. This triggers a cascade of immune responses.

The other options are incorrect:

• are proteins: Endotoxins are lipopolysaccharides (LPS), a complex molecule with sugar and lipid components, not solely proteins.
• are heat labile: Endotoxins are generally heat-stable, meaning they can withstand high temperatures without being destroyed.
• are highly antigenic: Endotoxins can be weakly antigenic, meaning they may not always elicit a strong immune response compared to exotoxins.

Answer: Treponema

A darkfield microscope is a specialized tool that illuminates objects with light scattered at an oblique angle. This allows visualization of unstained, transparent structures like Treponema pallidum, the bacterium that causes syphilis.

The other options are incorrect:

• Actinomyces: These are filamentous bacteria that can be visualized with routine brightfield microscopy after staining.
• Streptococcus: Streptococcus is a genus of spherical bacteria. They are easily stained and observed under a brightfield microscope.
• Mycobacterium: While some Mycobacterium species might require specialized staining techniques, they generally have a cell wall structure that allows visualization under a brightfield microscope.

Answer: Selenite F Broth

Selenite F Broth is an enrichment medium used to selectively enrich for Salmonella species from clinical specimens. It contains selective agents that inhibit the growth of competing bacteria while allowing for the growth of Salmonella, thus facilitating their isolation.

The other options are incorrect:

• Blood agar: This is an enriched medium that provides additional nutrients for a wider range of bacteria, but it doesn’t selectively favor a specific type.
• MacConkey agar: This is a differential and selective medium that allows differentiation between lactose fermenting and non-fermenting bacteria. It’s not specifically designed for enrichment.
• Nutrient Broth: This is a basic all-purpose medium that supports the growth of many different bacteria, but it doesn’t enrich for any particular type.

Answer: Lysozyme

Lysozyme is an antibacterial enzyme found in eggs (particularly egg white) and saliva. It works by breaking down the cell walls of certain bacteria, particularly those with peptidoglycan walls (common in gram-positive bacteria). This disrupts the bacteria’s structure and leads to cell death.

The other options are incorrect:

• Secretozyme: This term isn’t a recognized antibacterial substance. It might be a misspelling of “secretome,” which refers to the collection of secreted proteins by an organism.
• Albumin: Albumin is the major protein component of egg white, but it doesn’t have specific antibacterial properties.
• Isozyme: Isozymes are different forms of the same enzyme with slightly varying structures and functions. While lysozyme might have isozymes, the term itself doesn’t indicate an antibacterial substance.

Answer: Remove microbes

The major antiseptic value of soap lies in its ability to remove microbes from the skin or surfaces rather than killing them. Soap functions by emulsifying oils, dirt, and microorganisms, allowing them to be rinsed away with water.

The other options are incorrect:

• Kill microbes: While soap can damage some bacterial membranes, it’s not as effective as disinfectants or antiseptics that directly kill a broad spectrum of microbes.
• Inhibit microbial growth: Soap doesn’t have a long-lasting inhibitory effect on microbial growth in the same way some antiseptics do.
• Dehydrate microbial cells: Dehydration can be a method of killing microbes, but soap doesn’t specifically dehydrate them. It disrupts their cell membrane structure.

Answer: Resistance transfer factor (RTF)

Multiple drug resistance of bacteria often depends on the presence of resistance transfer factors (RTFs), also known as R factors. These are extrachromosomal genetic elements (plasmids) that carry genes encoding resistance to multiple antimicrobial agents. Bacteria can acquire these plasmids through horizontal gene transfer, enabling them to withstand the effects of various antibiotics.

The other options are incorrect:

• Colicigenic factor (Col): Colicigenic factors are not directly associated with multiple drug resistance. They are plasmids that carry genes responsible for the production of colicins, which are bacteriocins produced by certain strains of Escherichia coli and related bacteria.
• Fertility factor (F+): Fertility factors, also known as F factors or sex factors, are plasmids that contain genes necessary for bacterial conjugation. They are not directly involved in conferring multiple drug resistance to bacteria.
• All of the above: While resistance transfer factor (RTF) is indeed crucial for multiple drug resistance, colicigenic factors and fertility factors are not directly related to antibiotic resistance in bacteria. Therefore, “All of the above” is incorrect.

Answer: Refrigerator

Refrigerators are not typically used for the cultivation of anaerobic organisms. Anaerobic organisms require an oxygen-free environment for growth, which is provided by specialized methods such as anaerobic jars or anaerobic chambers. These methods create an oxygen-depleted atmosphere conducive to the growth of anaerobes.

The other options are incorrect:

• Incubator: Essential for maintaining optimal growth temperature for anaerobes.
• Anaerobic jar: Creates an oxygen-free environment crucial for strict anaerobes.
• Centrifuge: Can be a helpful tool in certain steps during anaerobic culturing.

Answer: Disinfectant

The Rideal-Walker test, though no longer widely used, was a historical method for determining the disinfecting efficiency of a substance. It compared the dilution of the disinfectant needed to kill a specific bacteria (often Staphylococcus aureus or Salmonella enterica serovar Typhi) to the dilution of phenol required to achieve the same effect under controlled conditions.

The other options are incorrect:

• Moist heat sterilization: This is a physical method using steam or autoclave to achieve sterilization, a process that eliminates all viable microorganisms, not just some. The Rideal-Walker test focused on the effectiveness of disinfectants, which may not achieve complete sterilization.
• Antibiotics: These are medications that target and inhibit the growth or kill specific bacteria, not disinfectants used on inanimate surfaces.
• Dry heat sterilization: Similar to moist heat sterilization, this method uses high dry heat to achieve sterilization, not disinfection measured by the Rideal-Walker test.

Answer: All pathogenic and non-pathogenic microorganisms killed

Sterilization refers to the complete elimination or destruction of all forms of microbial life, including bacteria, viruses, fungi, and bacterial endospores, as well as their spores. It ensures the absence of viable microorganisms, both pathogenic and non-pathogenic, in a given environment or on an object.

The other options are incorrect:

• Pathogens killed but spores are not affected: This describes disinfection, not sterilization. Disinfection reduces the number of microorganisms but may not eliminate all spores.
• Only pathogenic micro-organisms killed: Sterilization eliminates all microorganisms, regardless of their pathogenic potential.
• Non-pathogenic killed: Sterilization targets all forms of life, not just non-pathogenic ones.

Answer: Time-consuming

Compared to autoclaving, the use of a dry heat oven for sterilization is typically more time-consuming. Dry heat sterilization requires longer exposure times and higher temperatures to achieve sterilization compared to autoclaving, which uses steam under pressure to achieve rapid sterilization.

The other options are incorrect:

• Less effective: Dry heat sterilization is generally considered to be as effective as autoclaving for certain heat-resistant materials. While it may require longer exposure times, it can achieve sterilization under appropriate conditions.
• Causes instruments to rust: Dry heat sterilization does not introduce moisture to instruments, so it is less likely to cause rust compared to autoclaving, which involves steam. Rusting is typically associated with exposure to moisture rather than dry heat.
• Causes sharp instruments to dull: Dry heat sterilization does not directly cause sharp instruments to dull. Dulling of instruments may occur due to factors such as mechanical wear over time or improper handling, but it is not a direct consequence of dry heat sterilization.

Answer: Autoclave

Bacterial spores are effectively destroyed by autoclaving, which involves subjecting them to high-pressure saturated steam at temperatures typically ranging from 121°C to 134°C. The combination of heat and moisture under pressure is highly effective in killing bacterial spores, making autoclaving one of the most reliable methods for sterilization.

The other options are incorrect:

• Boiling at 100°C: Boiling at 100°C is not sufficient to consistently destroy bacterial spores. While it may kill vegetative cells and some less resistant forms of microorganisms, it is generally not reliable for sterilization as it does not reach the temperatures required to kill bacterial spores.
• Disinfection by hypochlorite solution: Disinfection by hypochlorite solution, such as bleach, is effective against many vegetative bacteria and viruses but may not reliably kill bacterial spores. It is typically used for disinfection rather than sterilization.
• Pasteurization: Pasteurization involves heating a substance to a specific temperature for a defined period to reduce the microbial load, but it is not intended to sterilize.

Answer: Spirochaetes

Darkfield microscopy is particularly useful for visualizing transparent or translucent specimens, such as spirochaetes, against a dark background. The dark background enhances the contrast, making the thin, spiral-shaped spirochaetes visible.

The other options are incorrect:

• Mycoplasma: These are the smallest bacteria and lack a cell wall. While they are also difficult to visualize with brightfield due to their size, dark ground microscopy is not the preferred method for identification. Specialized staining techniques or electron microscopy are typically used.
• Chlamydiae: These are obligate intracellular parasites, meaning they can only live inside host cells. Dark ground microscopy cannot visualize them within host cells. Specific staining techniques or cell culture techniques are needed for Chlamydiae identification.
• Rickettsiae: Similar to Chlamydiae, Rickettsiae are obligate intracellular parasites and require alternative methods for identification.

Answer: 3 minutes 11

The minimum time required for the sterilization of surgical instruments by moist heat at 134°C (autoclaving) is typically 3 minutes and 11 seconds. This specific duration ensures adequate exposure to high temperature and steam under pressure, effectively killing microbial contaminants including bacterial spores.

The other options are incorrect:

• 15 minutes: This duration is longer than necessary for the sterilization of surgical instruments by autoclaving at 134°C. Autoclaving for 15 minutes at this temperature would be excessive and may lead to unnecessary energy consumption and potential damage to heat-sensitive instruments.
• 30 minutes: Autoclaving for 30 minutes at 134°C would be significantly longer than the minimum required time for sterilization. This extended duration would not provide additional benefits in terms of sterilization efficacy and may increase processing time and resource utilization.
• 60 minutes: Sterilizing surgical instruments for 60 minutes at 134°C would be excessively long and impractical. It far exceeds the minimum time required for effective sterilization by autoclaving at this temperature, leading to unnecessary delays in instrument turnaround time and increased energy consumption.

Answer: Autoclave

An autoclave is a pressurized chamber that utilizes steam under pressure to achieve sterilization. This method effectively eliminates all microorganisms, including bacteria, viruses, and spores, making it ideal for sterilizing surgical instruments, laboratory equipment, and other materials requiring complete sterility.

The other options are incorrect:

• Pasteurization: Pasteurization involves heating liquids to a specific temperature for a short period to eliminate some, but not all, microorganisms. It is not a sterilization method and is commonly used for preserving food products like milk.
• Koch’s sterilizer: This term is not widely used in modern microbiology. Historically, some early sterilization techniques involved hot air ovens or flaming implements. However, these methods are less reliable and efficient compared to autoclaves.
• Hot air oven: While hot air ovens can be used for sterilization at very high temperatures for extended periods, they are generally not preferred for medical applications. 

Answer: Person to person transmission

Legionella pneumophila is not directly transmitted from person to person. It thrives in water environments and spreads through the inhalation of aerosolized droplets contaminated with the bacteria.

The other options are incorrect:

• Aquatic bodies are main habitat: Legionella pneumophila is naturally found in freshwater environments like lakes and rivers.
• It can replicate in amoeba: This bacterium can indeed live and multiply within amoeba, a type of single-celled organism, found in water.
• Urine test is not a reliable method: While not the only diagnostic tool, a urine antigen test can be a reliable method for detecting Legionella pneumophila in some cases.