MicroBiology MCQs with Answer and Explnation | Chapter 17

Answer: All of the above

Penicillin, bacitracin, and cyclosporin are all antibiotics that act on the cell wall of bacteria.

• Penicillin is a β-lactam antibiotic that inhibits the synthesis of peptidoglycan, a major component of bacterial cell walls. Without peptidoglycan, the bacterial cell becomes osmotically fragile and bursts.
• Bacitracin is a cyclic polypeptide antibiotic that also inhibits the synthesis of peptidoglycan. It is effective against a wide range of Gram-positive bacteria.
• Cyclosporin is a cyclic peptide antibiotic that is not commonly used as an antibiotic. It is more often used as an immunosuppressant drug to prevent organ rejection. However, it can also act as an antibiotic by inhibiting the synthesis of cell wall precursors in bacteria.

Answer: Macrolides

Macrolides are a class of antibiotics characterized by a large lactone ring containing 12- to 16-membered atoms. Erythromycin is a representative member of this class. Macrolides inhibit bacterial protein synthesis by binding to the 50S ribosomal subunit, preventing the translocation of the tRNA and thereby blocking the elongation of the polypeptide chain.

The other options are incorrect:

• β-lactose: This is a typographical error. The correct term is “β-lactams,” which include antibiotics like penicillins and cephalosporins. Erythromycin does not belong to this class.
• Tetracyclines: Tetracyclines are a different class of antibiotics that inhibit bacterial protein synthesis by binding to the 30S ribosomal subunit.
• Aminoglycosides: Aminoglycosides, such as streptomycin and gentamicin, are another class of antibiotics that interfere with bacterial protein synthesis, but they do so by binding to the 30S ribosomal subunit.

Answer: Plasmids

Plasmids are small, circular DNA molecules that can carry genes, including those encoding antibiotic resistance. Bacteria can acquire resistance to antibiotics through the horizontal transfer of plasmids between individual bacterial cells. This transfer can occur through mechanisms such as conjugation, where plasmids are directly transferred from one bacterium to another.

The other options are incorrect:

• Transduction: Transduction involves the transfer of genetic material via bacteriophages (viruses that infect bacteria) and is not the primary mechanism for transmitting antibiotic resistance genes.
• Transformation: Transformation is the process by which bacteria take up free DNA from their environment, but it is not the primary mechanism for transmitting antibiotic resistance genes.
• Mutation: While mutations can lead to antibiotic resistance, it is not the primary means of transmission between bacteria. Mutation is a random, spontaneous change in the DNA sequence of an individual bacterium. Horizontal gene transfer, often mediated by plasmids, is more common in spreading resistance across bacterial populations.

Answer: Attaching to 50 S unit or ribosome

Erythromycin, a macrolide antibiotic, interferes with bacterial protein synthesis by binding to the 50S ribosomal subunit. It specifically binds to the 23S rRNA of the 50S subunit, preventing the translocation of the tRNA and inhibiting the elongation of the polypeptide chain during protein synthesis.

The other options are incorrect:

• Attaching to the 30S ribosomal subunit: Erythromycin primarily targets the 50S ribosomal subunit, not the 30S subunit.
• By the attachment to t-RNA: Erythromycin does not directly attach to tRNA. Its primary binding site is the 50S ribosomal subunit.
• By the attachment to m-RNA: Erythromycin’s mode of action is not by directly attaching to mRNA (messenger RNA). It interferes with the ribosome and the process of translation rather than mRNA itself.

Answer: Both Amino acid synthesis and Thymidine synthesis

Tetrahydrofolic acid (THFA) is a coenzyme involved in various metabolic pathways, including:

• Amino Acid Synthesis: THFA serves as a coenzyme in the synthesis of amino acids, playing a crucial role in providing one-carbon units for the synthesis of purines and certain amino acids.
• Thymidine Synthesis: THFA is involved in the synthesis of thymidine, a component of DNA. It provides one-carbon units necessary for the synthesis of thymidylate, a precursor of thymidine.

The other options are incorrect:

• Protein Synthesis: While THFA is involved in amino acid synthesis, it is not directly involved in protein synthesis. Protein synthesis involves the translation of mRNA into polypeptide chains at ribosomes.

Answer: Mutation

Drug resistance in tuberculosis, including resistance to antibiotics like isoniazid and rifampin, often develops through mutations in the bacterial genome. Mutations can lead to changes in the target sites of the drugs or alterations in the metabolic pathways, rendering the bacteria less susceptible or resistant to the effects of the drugs.

The other options are incorrect:

• Transduction: Transduction involves the transfer of genetic material via bacteriophages (viruses that infect bacteria) and is not the primary mechanism for the development of drug resistance in tuberculosis.
• Transformation: Transformation is the process by which bacteria take up free DNA from their environment, but it is not the primary mechanism for the development of drug resistance in tuberculosis.
• Conjugation: Conjugation involves the direct transfer of genetic material, often in the form of plasmids, between bacterial cells. While this can contribute to the spread of drug resistance genes, it is not the primary mechanism for the development of drug resistance through mutations.

Answer: Methicillin

Methicillin is a penicillinase-resistant penicillin that is also acid-labile. This means that it is not destroyed by stomach acid and can be taken orally. Methicillin is effective against a wide range of Gram-positive bacteria, including Staphylococcus aureus (Staph) and Streptococcus pneumoniae (pneumococcus).

The other options are incorrect:

• Amoxycillin: Amoxycillin is a penicillinase-resistant penicillin, but it is not acid-labile. This means that it is destroyed by stomach acid and must be taken intravenously. Amoxycillin is effective against a wide range of Gram-negative and Gram-positive bacteria.
• Cloxacillin: Cloxacillin is a penicillinase-resistant penicillin, but it is not acid-labile. This means that it is destroyed by stomach acid and must be taken intravenously. Cloxacillin is effective against a wide range of Gram-positive bacteria, including Staphylococcus aureus (Staph).
• Carbenicillin: Carbenicillin is a penicillinase-resistant penicillin, but it is not acid-labile. This means that it is destroyed by stomach acid and must be taken intravenously. Carbenicillin is effective against a wide range of Gram-negative bacteria.

Answer: Amikacin

Amikacin is an aminoglycoside antibiotic that inhibits bacterial protein synthesis by binding to the 30S ribosomal subunit. It does not inhibit cell wall synthesis.

The other options are incorrect:

• Penicillin: Penicillin is a β-lactam antibiotic that inhibits the synthesis of peptidoglycan, a major component of bacterial cell walls. Without peptidoglycan, the bacterial cell becomes osmotically fragile and bursts.
• Carbenicillin: Carbenicillin is another β-lactam antibiotic that inhibits the synthesis of peptidoglycan. It is effective against a wide range of Gram-negative bacteria.
• Vancomycin: Vancomycin is a glycopeptide antibiotic that inhibits the synthesis of cell wall precursors in bacteria. It is effective against a wide range of Gram-positive bacteria, including methicillin-resistant Staphylococcus aureus (MRSA).

Answer: The DNA structure & function

Anti-tumor antibiotics, such as anthracyclines (e.g., doxorubicin) and bleomycin, primarily target the DNA structure and function. They interfere with DNA replication and transcription processes, leading to DNA damage and inhibition of cell division. These antibiotics are often used in the treatment of various cancers to disrupt the growth and proliferation of cancer cells.

The other options are incorrect:

• Cell Wall Synthesis: Antibiotics targeting cell wall synthesis, like penicillins and cephalosporins, are not classified as anti-tumor antibiotics.
• RNA Synthesis: While some antibiotics may interfere with RNA synthesis, it is not the primary target of anti-tumor antibiotics.
• Cell Membrane Synthesis: Anti-tumor antibiotics do not primarily target cell membrane synthesis. They are more focused on disrupting DNA-related processes.

Answer: β-lactamase enzymes

Amoxycillin is a penicillin-type antibiotic that works by inhibiting the synthesis of bacterial cell walls. However, some bacteria produce enzymes called β-lactamases that can break down amoxycillin, making it ineffective. Clavulanic acid is a β-lactamase inhibitor, which means that it prevents bacteria from producing β-lactamases. As a result, the combination of amoxycillin and clavulanic acid is effective against a wider range of bacteria than amoxycillin alone.

The other options are incorrect:

• DNA gyrase is an enzyme involved in DNA replication. Amoxycillin and clavulanic acid do not target DNA gyrase.
• Cell synthesis is a general term for the processes by which cells make new proteins, lipids, carbohydrates, and other molecules. Amoxycillin and clavulanic acid specifically target bacterial cell wall synthesis.
• Protein synthesis is the process by which cells make new proteins. Amoxycillin and clavulanic acid do not target protein synthesis.

Answer: Vancomycin

Vancomycin is the drug of choice for treating infections caused by methicillin-resistant Staphylococcus aureus (MRSA). It is a glycopeptide antibiotic effective against Gram-positive bacteria, including those resistant to β-lactam antibiotics like methicillin.

Incorrect Options:

• Ampicillin: Ampicillin is a β-lactam antibiotic and is not effective against MRSA. MRSA is resistant to many β-lactam antibiotics, including methicillin.
• Erythromycin: Erythromycin is a macrolide antibiotic and is not typically the first-line drug for MRSA infections. Vancomycin is preferred.
• Neomycin: Neomycin is an aminoglycoside antibiotic and is not the drug of choice for MRSA. Vancomycin is more effective against MRSA infections.

Answer: The inhibition of DNA synthesis

Nalidixic acid belongs to the class of antibiotics known as quinolones, and its primary mechanism of action is the inhibition of DNA synthesis in bacteria.

The other options are incorrect:

• Inhibition of Protein Synthesis: Nalidixic acid does not primarily inhibit protein synthesis. Its main target is the bacterial DNA gyrase enzyme involved in DNA replication.
• The Inhibition of Cell Wall Synthesis: Nalidixic acid does not inhibit cell wall synthesis. Antibiotics that target cell wall synthesis include penicillins and cephalosporins.

Answer: Both Tube-dilution test and Paper-disc test

• Tube-Dilution Test: This method involves preparing a series of tubes with varying concentrations of the antibiotic. The minimum inhibitory concentration (MIC), which is the lowest concentration of the drug that inhibits visible growth of the microorganism, can be determined.
• Paper-Disc Test (Disk Diffusion Test): This test involves placing paper discs containing a known amount of antibiotic on the surface of an agar plate inoculated with the microorganism. The zone of inhibition around each disc is measured, and the size of the zone correlates with the susceptibility of the microorgan

Answer: MIC (minimum inhibitory concentration)

MIC is the lowest concentration of a chemotherapeutic agent (such as an antibiotic) that inhibits the visible growth of a microorganism in vitro.

The other options are incorrect:

• Thermal Death Point (TDP): TDP refers to the lowest temperature at which all microorganisms in a liquid suspension will be killed in a specified time.
• Death Rate: Death rate typically refers to the rate at which organisms die and is not specifically related to the concentration of a chemotherapeutic agent.

Answer: Lysis of the bacterial cells surrounding the disc

• In the paper-disc diffusion test (also known as the disk diffusion test), clear zones (zones of inhibition) around the antibiotic disc indicate that the bacteria in that area have been inhibited or killed by the antibiotic.
• The antibiotic diffuses into the agar medium from the disc. If the bacteria are susceptible to the antibiotic, their growth will be inhibited, leading to clear zones.

The other options are incorrect:

• Growth of the Bacterium Surrounding the Disc: Clear zones indicate the opposite – inhibition of bacterial growth, not growth.
• The Destruction of Paper Disc (Antibiotic): The clear zones are not due to the destruction of the paper disc but rather to the inhibitory effect of the antibiotic on bacterial growth.

Answer: B. subtilis

Bacitracin is an antibiotic produced by the bacterium Bacillus subtilis. It is effective against Gram-positive bacteria and is commonly used in topical preparations to prevent bacterial infections.

The other options are incorrect:

• B. anthracis: Bacillus anthracis is a different species of bacterium. It is known for causing anthrax but does not produce bacitracin.
• B. cereus: Bacillus cereus is another bacterium, and it is not the source of bacitracin.
• B. anthracoid: “B. anthracoid” is not a recognized species or term in bacteriology. The correct source is Bacillus subtilis.

Answer: Streptomyces orientalis

ancomycin is obtained from the soil bacterium Streptomyces orientalis. It is a glycopeptide antibiotic that is used to treat serious infections caused by Gram-positive bacteria.

The other options are incorrect:

• Streptococcus species are a group of Gram-positive bacteria that can cause a variety of infections, including strep throat and pneumonia. However, they do not produce vancomycin.
• Aspergillus niger is a fungus that is commonly found in soil and decaying organic matter. It is not known to produce vancomycin.
• Bacillus anthracis is a Gram-positive bacterium that causes anthrax, a serious and potentially fatal disease. It does not produce vancomycin.

Answer: Both Penicillin & Cephalosporin

β-lactam antibiotics are a large class of antibiotics that contain a β-lactam ring in their chemical structure. The β-lactam ring is essential for the activity of these antibiotics, as it interferes with the synthesis of bacterial cell walls.

• Penicillin was the first β-lactam antibiotic to be discovered, and it is still one of the most widely used antibiotics today. Penicillin is effective against a wide range of bacteria, including Staphylococcus aureus, Streptococcus pneumoniae, and Neisseria gonorrhoeae.
• Cephalosporin is another broad-spectrum β-lactam antibiotic that is similar to penicillin in many ways. However, cephalosporins are generally more resistant to β-lactamases, which are enzymes that bacteria can produce to break down β-lactam antibiotics. This makes cephalosporins effective against a wider range of bacteria than penicillin, including some that are resistant to penicillin.

Answer: Group B cox sack virus

These viruses, belonging to the Enterovirus genus of the Picornaviridae family, are responsible for various infections. Epidemic pleurodynia is characterized by sudden onset of fever and pleuritic chest pain, while myocarditis in newborn infants can lead to serious heart-related complications.

The other options are incorrect:

• Reovirus: Reoviruses are another group of viruses, but they are not typically associated with epidemic pleurodynia or myocarditis in newborn infants.
• Polyomavirus: Polyomaviruses, such as JC virus and BK virus, are not known to cause epidemic pleurodynia or myocarditis in newborn infants.
• Cytomegalovirus: Cytomegalovirus (CMV) is a herpesvirus and is not a common cause of epidemic pleurodynia or myocarditis in newborn infants.

Answer: All of these

• Acute Self-Limited Illness: Many viral infections cause acute illnesses with symptoms such as fever, fatigue, respiratory symptoms, etc. These infections often resolve on their own over time.
• No Apparent Symptoms: Some viral infections may be asymptomatic, meaning individuals may carry the virus without showing any noticeable symptoms. However, they can still spread the virus to others.
• Chronic Infection with Persistent Viral Shedding: Certain viruses can establish chronic infections, where the virus persists in the body for an extended period. During chronic infection, individuals may shed the virus continuously.

Answer: Retroviruses

Retroviruses are a group of viruses that carry their own RNA genome instead of a DNA genome. When a retrovirus infects a cell, it uses its own reverse transcriptase enzyme to convert its RNA genome into DNA. This DNA is then inserted into the cell’s DNA, where it can be used to produce new copies of the virus.

The other options are incorrect:

• Hepatitis B virus carries its own DNA genome, so it does not need to reverse transcribe its RNA genome into DNA.
• Poxviruses carry their own DNA genome, so they do not need to reverse transcribe their RNA genome into DNA.
• Heepes simplex virus carries its own DNA genome, so it does not need to reverse transcribe its RNA genome into DNA.

Answer: All of these

• Adenovirus: Adenoviruses can establish latent infections in lymphoid tissues.
• Varicella-Zoster Virus (VZV): VZV, responsible for chickenpox and shingles, establishes latent infections in sensory nerve ganglia.
• Cytomegalovirus (CMV): CMV is known for establishing latent infections in various tissues, including salivary glands and leukocytes.
• Herpes Simplex Virus (HSV): Both HSV-1 and HSV-2 can establish latent infections in sensory nerve ganglia.

Answer:

Herpes simplex virus (HSV) can cause birth defects if a pregnant woman contracts the virus for the first time during pregnancy. The most common birth defect caused by HSV is microcephaly, which is a condition in which the baby’s head is abnormally small. HSV can also cause eye problems, intellectual disability, and seizures.

Cytomegalovirus (CMV) is the most common cause of congenital viral infections in the United States. CMV can cause a variety of birth defects, including hearing loss, vision problems, and intellectual disability. In some cases, CMV infection can also lead to stillbirth or premature birth.

Rubella virus is the virus that causes German measles. Rubella infection during pregnancy can cause a variety of birth defects, including heart defects, cataracts, and deafness. Rubella can also cause miscarriage or stillbirth.

Answer: Most prevalent in Japan and Hawaii

This is an acute febrile illness that primarily affects children. It is more prevalent in Japan and Hawaii, although cases have been reported worldwide.

The other options are incorrect:

• Patients Show Rickettsia-Like Bacteria in Skin Biopsies: Kawasaki Syndrome is not associated with rickettsia-like bacteria.
• Strain Involved May Be Propionibacterium: Propionibacterium is not implicated in Kawasaki Syndrome. The exact cause of Kawasaki Syndrome is not yet fully understood.

Answer: Inhibition of DNA gyrase

Quinolone antibiotics are a class of antibiotics that inhibit the action of DNA gyrase, an enzyme that is essential for bacterial DNA replication. By preventing DNA gyrase from working, quinolone antibiotics prevent bacteria from replicating their DNA and growing.

The other options are incorrect:

• Inhibition of β-lactamase: Quinolones do not inhibit β-lactamase. Their primary target is DNA gyrase.
• Prevention of the Cross-Linking of Glycine: Quinolones do not affect the cross-linking of glycine. This statement is not related to their mechanism of action.
• Inhibition of Reverse Transcriptase: Quinolones do not inhibit reverse transcriptase. Reverse transcriptase is primarily associated with retroviruses, not bacteria.

Answer: Accidental intruder in rat flea cycle

Accidental Intruder in Rat Flea Cycle: Humans are not a natural part of the plague life cycle. In the natural cycle, plague is maintained in rodent populations, particularly rats, and transmitted by fleas that infest these rodents.

The other options are incorrect:

• Secondary Reservoir: Humans are not considered a reservoir for plague. Rodents, especially rats, serve as the primary reservoir.
• Primary Transmission Vector: Fleas, particularly rat fleas like Xenopsylla cheopis, are the primary vectors transmitting the plague bacteria between rodents and, in rare cases, to humans.
• Primary Host: The primary hosts in the plague life cycle are rodents, with fleas acting as vectors.

Answer: Perform dark field microscopy for treponemes

Dark field microscopy is the most appropriate method for diagnosing syphilis in the primary stage, where a painless chancre is present. Treponemes, the causative bacteria of syphilis, are visible under dark field microscopy.

The other options are incorrect:

• To Take Rest at Home: Rest is not the appropriate action for diagnosing or treating syphilis.
• To Swab the Chancre and Culture on Thayer-Martin Agar: Thayer-Martin agar is used for culturing Neisseria gonorrhoeae, not Treponema pallidum, which causes syphilis.
• To Gram Stain the Chancre Fluid: Treponema pallidum is difficult to visualize using Gram staining.
• To Repeat VDRL Test in 10 Hours: VDRL (Venereal Disease Research Laboratory) test is a blood test for syphilis, but repeating it in a short time frame is not necessary. Dark field microscopy is more appropriate for the primary stage.

Answer: Brucella melitensis

Brucella melitensis is a bacterium that can infect goats and other animals. Humans can contract brucellosis, a zoonotic infection, by coming into contact with infected animals or their products. This infection can lead to symptoms such as fever, joint pain, and fatigue.

The other options are incorrect:

• Treponema pallidum: This bacterium is responsible for syphilis, not a fever associated with dealing with goats.
• Mycobacterium tuberculosis: Tuberculosis is caused by Mycobacterium tuberculosis and is not associated with dealing specifically with goats.
• Clostridium novyi: This bacterium is associated with certain types of infections in livestock but is not typically linked to fever in individuals dealing with goats.

Answer: Lysogenic for β prophase

Only lysogenic strains of Corynebacterium diphtheriae produce diphtheria toxin. Lysogeny is a state in which a bacteriophage, or virus that infects bacteria, inserts its DNA into the bacterial chromosome. The phage DNA, called a prophage, can remain dormant in the bacterial chromosome for many generations without causing any harm to the bacterium. However, under certain conditions, the prophage can become active and produce new phage particles, which can then lyse (break open) the bacterial cell.

The other options are incorrect:

• Encapsulated: Encapsulation is a type of bacterial virulence factor that helps bacteria to evade the immune system. Encapsulated strains of C. diphtheriae are not more likely to produce diphtheria toxin than non-encapsulated strains.
• Sucrose fermentors: Sucrose fermentation is a type of carbohydrate metabolism. Sucrose fermenting strains of C. diphtheriae are not more likely to produce diphtheria toxin than non-sucrose fermenting strains.
• Of the mitis and strain: Mitis strain is a type of C. diphtheriae that is less likely to produce diphtheria toxin than gravis strain.
• Glucose fermentors: Glucose fermentation is another type of carbohydrate metabolism. Glucose fermenting strains of C. diphtheriae are not more likely to produce diphtheria toxin than non-glucose fermenting strains.

Answer: Nonhemolytic staphylococci

The skin of a healthy person has a normal microbial flora, which is a community of microorganisms that live on the skin. This normal flora helps to protect the skin from infection by preventing harmful bacteria from colonizing. The normal microbial flora of the skin includes bacteria, fungi, and viruses.

The bacteria that are most commonly found on the skin are nonhemolytic staphylococci, such as Staphylococcus epidermidis. These bacteria are not usually harmful, but they can sometimes cause infections if the skin is broken.

The other options are incorrect:

• Enterobacteriaceae are a family of bacteria that can cause a variety of infections, including urinary tract infections, pneumonia, and sepsis. Enterobacteriaceae are not normally found on healthy skin.
• Aerobic diphtheria bacilli are bacteria that cause diphtheria, a serious infection of the throat that can be fatal. Aerobic diphtheria bacilli are not normally found on healthy skin.
• Anaerobic diphtheriae bacilli are bacteria that are closely related to aerobic diphtheria bacilli. Anaerobic diphtheriae bacilli are not normally found on healthy skin.

Answer: Both Trichinella spiralis and Taenia solium

Trichinella spiralis causes trichinosis, a parasitic infection that occurs when raw or undercooked meat containing the larvae of the parasite is consumed.
Taenia solium is responsible for causing cysticercosis. The infection occurs when humans ingest undercooked pork that contains the larval stage of the tapeworm.

The other options are incorrect:

Taenia saginata: Causes beef tapeworm infection in humans.
Typically transmitted by consuming raw or undercooked beef.

Diphyllobothrium latum: Causes fish tapeworm infection in humans.
Usually contracted by consuming raw or undercooked freshwater fish.

Answer: Necatur americanes

Ancylostoma duodenale and Necator americanus are both hookworm species that can infect humans. They attach to the lining of the small intestine, causing ancylostomiasis or hookworm infection.

The other options are incorrect:

• Wuchereria bancrofti: Causes lymphatic filariasis, a condition leading to swelling of body parts due to the blockage of lymphatic vessels by the adult worms.
• Loa loa: Causes loiasis or African eye worm disease. Adult worms migrate through subcutaneous tissues and occasionally across the eye.
• Trichinella spiralis: Causes trichinosis, a parasitic infection resulting from the consumption of undercooked meat containing the larvae of the Trichinella spiralis worm.

Answer: Entamoeba gingivalis

Entamoeba gingivalis is the amoeba that does not primarily inhabit the large intestine. Instead, it is commonly found in the oral cavity, particularly in the gingival (gum) crevices and periodontal pockets of the mouth.

The other options are incorrect :

• Entamoeba coli and Endolimax nana are non-pathogenic amoebas that can inhabit the large intestine of humans. They are generally considered harmless commensals.
• Entamoeba histolytica is a pathogenic amoeba that can cause amoebic dysentery and liver abscesses in humans. It primarily resides in the large intestine.

Answer:

Aneurysm is a weakening in the wall of an artery or vein that can cause it to bulge or balloon out. It is not a symptom of congenital syphilis.

The other options are incorrect:

• Saddle nose is a deformity of the nose that can be caused by congenital syphilis.
• Stillbirth is the death of a fetus before delivery. Congenital syphilis can increase the risk of stillbirth.
• Hutchinson’s teeth are peg-shaped teeth with a notch at the biting edge. They are a sign of congenital syphilis.

Answer: Salmonella cholerasuis

Among the options provided, Salmonella cholerasuis is known for causing a prolonged and severe form of septicemia in humans and animals. Septicemia refers to a systemic infection in which bacteria are present and multiplying in the bloodstream, leading to a potentially life-threatening condition.

The other options are incorrect:

• Salmonella anatum: Salmonella anatum is known to cause various infections in humans, but it is not particularly associated with prolonged septicemia.
• Salmonella typhimurium: Salmonella typhimurium is a common cause of gastroenteritis in humans. While it can cause systemic infections, it is not typically associated with prolonged septicemia to the extent seen with Salmonella cholerasuis.
• Salmonella enteritidis: Salmonella enteritidis is often associated with foodborne gastroenteritis and is not known for causing prolonged septicemia at the same level as Salmonella cholerasuis.

Answer: Both Exotoxins and Endotoxins

E. coli can produce both exotoxins and endotoxins. Exotoxins are proteins that are secreted by the bacteria into the surrounding environment. They can cause a variety of symptoms, including diarrhea, vomiting, and abdominal cramps. Endotoxins are part of the outer membrane of E. coli bacteria. They are released when the bacteria die and can also cause a variety of symptoms, including fever, chills, and shock.

The other options are incorrect:

• Leucocidin: Leucocidins are toxins that can destroy white blood cells. While some bacteria produce leucocidins, E. coli is not particularly known for producing leucocidins. The primary toxins associated with E. coli are exotoxins and endotoxins.

Answer: Cl.perfringens

Gas gangrene is a serious and potentially fatal bacterial infection that destroys muscle and other soft tissues. It is most commonly caused by the bacterium Clostridium perfringens, which is found in soil, water, and the intestines of humans and animals. Gas gangrene typically develops in deep wounds that have been contaminated with bacteria and have poor blood flow. The bacteria produce toxins that destroy tissue and release gas, which causes the skin to swell and become discolored.

The other options are incorrect:

• B.anthrax is a bacterium that causes anthrax, a disease that can affect humans and animals. Anthrax can be contracted through contact with contaminated skin, inhalation of spores, or ingestion of contaminated food or water.
• Clostridium tetani is a bacterium that causes tetanus, a disease that affects the nervous system and can lead to muscle spasms and lockjaw. Tetanus is typically contracted through puncture wounds that are contaminated with the bacteria.
• Cl.deficile is a bacterium that causes Clostridium difficile (C. diff) infection, a type of diarrhea that can be difficult to treat. C. diff infection is typically acquired in healthcare settings, such as hospitals and nursing homes.

Answer: Bordetella pertussis

Bordetella pertussis is a gram-negative, aerobic bacterium that is the primary cause of whooping cough, also known as pertussis. It is a highly contagious respiratory infection that primarily affects infants and young children. The bacteria attach to the cilia, tiny hair-like extensions that line the respiratory tract, and produce toxins that cause inflammation and coughing.

The other options are incorrect:

• Bordetella parapertussis is a gram-negative, aerobic bacterium that can cause a mild form of whooping cough that is more common in adolescents and adults.
• Bordetella bronchiseptica is a gram-negative, aerobic bacterium that is primarily a pathogen of animals, particularly dogs and cats. It can rarely cause infections in humans, but these infections are typically mild and do not include whooping cough symptoms.

Answer: Vibrio cholerae

Out of the given options, only Vibrio cholerae is associated with the Pfeiffer phenomenon. The Pfeiffer phenomenon is an immunological reaction that occurs when antibodies specific to a certain bacterium are introduced to the bacterium in a live animal. The antibodies cause the bacterium to lyse, or break down. This phenomenon was first observed by Richard Pfeiffer in 1894, who used it to demonstrate the presence of Vibrio cholerae in cholera patients.

The other options are incorrect:

• B. anthracis is the bacterium that causes anthrax, a serious and potentially fatal infectious disease. It is not known to be associated with the Pfeiffer phenomenon.
• Rickettsialpox is a disease caused by the bacterium Rickettsia akari. It is not known to be associated with the Pfeiffer phenomenon.

Answer: Dark ground microscopic examination

Dark ground microscopy is a diagnostic technique used for the direct visualization of Treponema pallidum, the bacterium that causes syphilis. This method is particularly useful for examining samples from syphilitic lesions, such as a chancre during the primary stage of syphilis. The dark ground microscopy allows the visualization of live spirochetes, enhancing the chances of detecting Treponema pallidum in clinical specimens.

The other options are incorrect:

• VDRL test: The Venereal Disease Research Laboratory (VDRL) test is a blood test used for the screening of syphilis, but it is not specific for the primary stage. It is often used for detecting antibodies against Treponema pallidum.
• Treponema pallidum immobilization test: This is a laboratory test that measures the ability of patient serum to immobilize Treponema pallidum. While it is used in the diagnosis of syphilis, it may not be as commonly used as other methods.
• Kahn’s test: Kahn’s test, also known as Kahn’s precipitation reaction, is a serological test used for the diagnosis of syphilis. It measures the precipitation of antibodies in response to Treponema pallidum, but it is not as commonly used today.

Answer: Lepra bacilli

Biological false-positive reactions in the VDRL test can occur in individuals with leprosy (Hansen’s disease) due to the presence of lepra bacilli (Mycobacterium leprae). Leprosy is known to cause cross-reactivity in syphilis serological tests, leading to false-positive results.

The other options are incorrect::

• Lepra bacilli: This is the correct answer. Individuals with leprosy may experience biological false-positive reactions in the VDRL test due to cross-reactivity with lepra bacilli.
• Corynebacterium diphtheriae: Corynebacterium diphtheriae is not typically associated with biological false-positive reactions in the VDRL test.
• Cl. welchii (Clostridium welchii): Clostridium welchii, also known as Clostridium perfringens, is not known to cause biological false-positive reactions in the VDRL test.

Answer: Corn steep liquor

Corn steep liquor, a byproduct of corn wet milling, is a commonly used medium for the production of Penicillin. It provides essential nutrients, including nitrogen and carbon sources, for the growth of the Penicillium mold, which is used in the industrial production of Penicillin. The mold produces Penicillin as a secondary metabolite during its growth, and the nutrient composition of the medium plays a crucial role in optimizing the yield of Penicillin.

The other options are incorrect::

• Nutrient agar: Nutrient agar is a general-purpose medium used for the cultivation of a wide range of microorganisms. However, it may not be optimized for the specific needs of Penicillin production.
• Sulfite waste liquor: Sulfite waste liquor is not typically used as a medium for Penicillin production. The choice of medium is crucial for the optimal growth of the Penicillium mold and the subsequent production of Penicillin.
• Whey: Whey, a byproduct of cheese production, is also used as a medium for Penicillin production. It contains lactose and other nutrients that support the growth of the Penicillium mold. While both whey and corn steep liquor are suitable, the specific choice may depend on factors such as cost and availability.

Answer: Serial dilution method

The serial dilution method is commonly used in microbiology to isolate and culture microorganisms. In the context of isolating antibiotic-producing organisms, the serial dilution method involves diluting a sample containing various microorganisms to obtain individual colonies. The diluted samples are then plated onto agar plates, and the colonies that develop are isolated for further study.

The other options are incorrect::

• Disk plate method: The disk plate method is used for antibiotic susceptibility testing, where paper disks containing antibiotics are placed on a bacterial lawn to determine the sensitivity of the bacteria to specific antibiotics. It is not typically used for isolating antibiotic-producing organisms.
• Direct plate method: The direct plate method involves directly plating a sample on agar without prior dilution. While it may be used for certain purposes, it may not be as effective as the serial dilution method for isolating specific organisms.
• Crowded plate method: The crowded plate method, also known as the streak plate method, involves streaking a sample onto an agar plate in a way that separates individual bacterial cells to form isolated colonies. While this is a common method for isolation, the specific term “crowded plate method” is not standard in microbiology.

Answer: Bottom yeast

Top yeast, also known as ale yeast or top-fermenting yeast, refers to yeast strains that float on the surface during fermentation. These yeast strains are commonly used in the production of alcoholic beverages such as beer. The specific strain often depends on the type of beer being brewed.

The other options are incorrect::

• Top yeast: This is the correct answer. Top yeast is commonly used in the production of industrial alcohol, particularly in the brewing of beer.
• Middle yeast: There is no specific category known as “middle yeast” in the context of brewing or industrial alcohol production.
• Feeder yeast: There is no specific category known as “feeder yeast” in the context of brewing or industrial alcohol production.

Answer: Ethanol fermentors

This reaction is a key step in alcoholic fermentation, where pyruvate is decarboxylated to produce acetaldehyde and carbon dioxide. Subsequently, acetaldehyde is reduced to ethanol in the presence of alcohol dehydrogenase. This process is commonly employed by certain microorganisms, including yeast, during ethanol fermentation.

The other options are incorrect::

• Lactic acid fermentors: Lactic acid fermentation does not involve the conversion of pyruvate to acetaldehyde and carbon dioxide. Instead, pyruvate is directly reduced to form lactic acid.
• Algae: Algae typically do not carry out alcoholic fermentation as a primary means of energy production. Algae may use other metabolic pathways for energy generation.
• Plants: While plants can undergo fermentation under certain conditions, the specific pathway involving pyruvate decarboxylase and the formation of acetaldehyde and carbon dioxide is more commonly associated with ethanol-fermenting microorganisms like yeast rather than plants.

Answer: Strictly anaerobic bacteria

The pyruvate dehydrogenase complex is an important enzyme complex involved in aerobic respiration. It catalyzes the conversion of pyruvate to acetyl-CoA, which is a key step in the citric acid (Krebs) cycle. Strictly anaerobic bacteria typically lack this complex since they primarily rely on anaerobic pathways for energy production, and the pyruvate dehydrogenase complex is associated with aerobic metabolism.

The other options are incorrect::

• Aerobic bacteria: The pyruvate dehydrogenase complex is present in aerobic bacteria, playing a crucial role in linking glycolysis to the citric acid cycle.
• Microphilic bacteria: The term “microphilic bacteria” is not standard, but if it refers to microaerophilic bacteria, these bacteria can have the pyruvate dehydrogenase complex since they can tolerate low levels of oxygen.
• Facultative anaerobic bacteria: Facultative anaerobic bacteria are capable of both aerobic and anaerobic metabolism. They can have the pyruvate dehydrogenase complex and adapt their metabolism based on the availability of oxygen.

Answer:Corn steep liquor

Corn steep liquor is a commonly used component in the production media for penicillin. It is a byproduct of the corn wet milling process and contains nutrients such as amino acids, vitamins, and minerals that support the growth of the Penicillium mold used in the industrial production of penicillin.

The other options are incorrect::

• Corn meal: While corn meal is derived from corn, it is not typically a major ingredient in penicillin production media. Corn steep liquor is more commonly used.
• Cane steep liquor: Cane steep liquor is not as commonly used in penicillin production media. Corn steep liquor is more prevalent in this context.

Answer: Vinegar

The outstanding example of a traditional microbial fermentation product is vinegar. Vinegar has been produced for centuries using a natural fermentation process that involves the action of acetic acid bacteria on various substrates, such as wine, cider, or grain alcohol. Acetic acid bacteria convert the ethanol in the substrate into acetic acid, which gives vinegar its characteristic sour flavor.

The other options are incorrect:

• Penicillin is an antibiotic that is produced by the fungus Penicillium chrysogenum. It is a relatively recent invention, dating back only to the early 1940s.
• Citric acid is an organic acid that is produced by the fungus Aspergillus niger. It is a common ingredient in food and beverages, as well as in industrial applications.
• Tetracycline is an antibiotic that is produced by the bacterium Streptomyces aureofaciens. It was first discovered in the 1940s and has since become one of the most widely used antibiotics in the world.

Answer: Nitrification

Nitrification is the process of converting ammonia (NH3) into nitrate (NO3-). It is a two-step process that is carried out by two different groups of bacteria. The first group of bacteria converts ammonia into nitrite (NO2-), and the second group of bacteria converts nitrite into nitrate.

The other options are incorrect:

• Ammonification: The process of converting organic nitrogen into ammonia (NH3).
• Denitrification: The process of converting nitrate (NO3-) into nitrogen gas (N2).
• Nitrogen fixation: The process of converting atmospheric nitrogen (N2) into ammonia (NH3).

Answer: Hepatitis B

The first genetically engineered and biotechnologically produced vaccine was against Hepatitis B. It was developed in the 1980s and is produced by recombinant DNA technology. The vaccine is made by inserting the gene for the hepatitis B surface antigen into a yeast cell. The yeast cells then produce the surface antigen, which is purified and used to make the vaccine.

The other options are incorrect:

• AIDS is a viral infection that does not have a vaccine.
• Smallpox is a viral infection that has been eradicated through vaccination.
• Herpes simplex is a viral infection that does not have a vaccine.