Chapter 14 with our Microbiology MCQs and explanations! Test your knowledge and understanding of key concepts with our complete set of multiple choice questions with detailed explanations for each answer. Increase your confidence and understanding of the fascinating world of microorganisms!
Microbiology MCQs 651 to 700
Which immunoglobulin is associated with anaphylactic (Type I) hypersensitivity reactions?
- a) IgE
- b) IgA
- c) IgD
- d) IgM
- e) IgG
Explanation:
IgE is the antibody responsible for Type I hypersensitivity (anaphylaxis). It binds to high-affinity receptors on mast cells and basophils, triggering the release of histamine and other inflammatory mediators upon exposure to an allergen.
Why other options are incorrect:
Why other options are incorrect:
- • IgA: Primarily found in mucosal secretions (tears, saliva, colostrum) and protects body surfaces.
- • IgD: Functions mainly as an antigen receptor on the surface of B-cells.
- • IgM: The first antibody produced during a primary immune response; it is a pentamer.
- • IgG: The most abundant antibody in the blood; it provides long-term immunity and can cross the placenta.
Patients suffering from AIDS have the following immune abnormalities?
- a) Decreased CD4+ T cells
- b) Increased CD8+ T cells
- c) Hypergammaglobulinemia
- d) CD4+/CD8+ ratio greater than 21
- e) Both Increased CD8+ T cells & CD4+/CD8+ ratio greater than 21
Explanation:
The hallmark of HIV/AIDS is the profound depletion of CD4+ T helper cells. The virus specifically targets these cells, leading to a collapse of the immune system and susceptibility to opportunistic infections.
Why other options are incorrect:
Why other options are incorrect:
- • Increased CD8+ T cells: While CD8 cells may initially increase to fight the virus, the defining diagnostic abnormality is the loss of CD4 cells.
- • Hypergammaglobulinemia: Although polyclonal B-cell activation can occur, it is a secondary effect and not the primary immune abnormality used to define AIDS progression.
- • CD4+/CD8+ ratio: In AIDS, the CD4+/CD8+ ratio actually decreases (usually falling below 1.0). A ratio “greater than 21” (or even the normal 2.0) would indicate a healthy immune system.
Which of the following immunoglobulins cannot activate the complement system?
- a) IgM
- b) IgE
- c) IgA
- d) IgG
Explanation:
IgE (and also IgD) does not activate the complement system. Only certain classes of antibodies have the ability to trigger the complement cascade to help destroy pathogens.
Why other options are incorrect:
Why other options are incorrect:
- • IgM: This is the most potent activator of the classical complement pathway.
- • IgG: Most subclasses of IgG (especially IgG1 and IgG3) are effective at activating the classical complement pathway.
- • IgA: While IgA does not activate the classical pathway, it can activate the alternative pathway of the complement system.
Hydatid disease is identified by which of the following tests?
- a) Schick test
- b) Dick test
- c) Casoni test
- d) Freis test
Explanation:
The Casoni test is an immediate hypersensitivity skin test used in the diagnosis of Hydatid disease (Echinococcosis). It involves the intradermal injection of sterilized hydatid fluid, which produces a wheal-and-flare response in positive cases.
Why other options are incorrect:
Why other options are incorrect:
- • Schick test: Used to determine susceptibility or immunity to Diphtheria.
- • Dick test: Used to determine susceptibility to Scarlet fever (caused by Streptococcus pyogenes).
- • Freis test: (Frei test) Used in the diagnosis of Lymphogranuloma venereum (LGV).
Prausnitz-Küstner reaction is generated by?
- a) IgA
- b) IgE
- c) IgG
- d) IgD
Explanation:
The Prausnitz-Küstner (PK) reaction is a classic test for identifying reaginic antibodies, now known as IgE. It involves the passive transfer of serum from an allergic person to a non-allergic person’s skin; when the allergen is later injected at the same site, a wheal-and-flare reaction occurs.
Why other options are incorrect:
Why other options are incorrect:
- • IgA: Involved in mucosal immunity; it does not mediate Type I hypersensitivity or the PK reaction.
- • IgG: The primary antibody in systemic immunity and secondary response; while it can be involved in other hypersensitivities, it is not the mediator of the PK reaction.
- • IgD: Found on the surface of immature B-lymphocytes; its role in systemic allergic reactions is negligible.
Which immunoglobulin is found at elevated levels in patients with asthma?
- a) IgA
- b) IgE
- c) IgM
- d) IgD
Explanation:
IgE levels are typically elevated in individuals with atopic asthma. In allergic asthma, the immune system overreacts to environmental allergens by producing IgE antibodies, which trigger mast cell degranulation and airway inflammation.
Why other options are incorrect:
Why other options are incorrect:
- • IgA: This is the secretory antibody found in mucus; while it exists in the respiratory tract, its elevation is not a diagnostic hallmark of asthma.
- • IgM: This is the first antibody produced in an acute infection (primary response) and is not specific to chronic allergic conditions.
- • IgD: This antibody mainly acts as a receptor on the surface of B cells and does not play a significant role in the pathophysiology of asthma.
What is the technique used for the quantitative estimation of immunoglobulins?
- a) Single diffusion in one dimension
- b) Single diffusion in two dimensions
- c) Double diffusion in one dimension
- d) Double diffusion in two dimensions
Explanation:
Single diffusion in two dimensions (also known as Radial Immunodiffusion or the Mancini technique) is used for the quantitative estimation of antigens. In this method, the antiserum is incorporated into agar, and the antigen is placed in a well; the diameter of the resulting precipitin ring is directly proportional to the concentration of the antigen.
Why other options are incorrect:
Why other options are incorrect:
- • Single diffusion in one dimension: Known as the Oudin procedure; it is a qualitative or semi-quantitative method where antigen travels down a tube containing antibody in agar.
- • Double diffusion in one dimension: Known as the Oakley-Fulthorpe procedure; used primarily to compare the concentrations of different antigens.
- • Double diffusion in two dimensions: Known as the Ouchterlony technique; it is a qualitative method used to determine the relationship between different antigens (identity, non-identity, or partial identity).
Cell mediated immunity can be identified by?
- a) Sheep bred blood corpuscles roasette formation
- b) Microphase inhibiting factor
- c) Skin test for delayed hyper sensitivity
- d) All of these
Explanation:
Cell-mediated immunity (CMI) involves T-lymphocytes and the cytokines they release. Several laboratory and clinical tests are used to identify the presence and function of these T-cells.
Why all options are correct:
Why all options are correct:
- • Rosette formation: Human T-cells have receptors (CD2) that naturally bind to sheep red blood cells (SRBC), forming a “rosette” shape under a microscope.
- • Macrophage inhibiting factor (MIF): This is a cytokine (lymphokine) produced by activated T-cells that prevents macrophages from leaving an area of inflammation.
- • Skin tests (DTH): The Delayed Type Hypersensitivity test (like the Tuberculin/Mantoux test) is the classic clinical method to assess CMI by observing the skin’s reaction to an antigen.
Out of the following which are the examples of autoimmune disease?
- a) Acquired Haemolytic anaemia
- b) Rheumatoid arthritis
- c) Hashiomoto disease
- d) All of these
Explanation:
Acquired haemolytic anaemia, rheumatoid arthritis, and Hashimoto disease are all autoimmune disorders in which the immune system attacks the body’s own tissues. Therefore, the correct answer is All of these.
Why other options are incorrect:
Why other options are incorrect:
- • Acquired Haemolytic anaemia: It is an autoimmune disease but not the most complete answer.
- • Rheumatoid arthritis: It is an autoimmune disease affecting the joints.
- • Hashiomoto disease: (Hashimoto’s disease) is an autoimmune disorder affecting the thyroid gland.
Which of the following is a true statement regarding Purified Protein Derivative (PPD) used in the tuberculin test?
- a) Prepared from tubercle bacilli
- b) It is inferior to old tuberculin
- c) Consists of filtrate of glycerol broth
- d) None of these
Explanation:
PPD (Purified Protein Derivative) is prepared by growing *Mycobacterium tuberculosis* (tubercle bacilli) in a synthetic medium, which is then heat-sterilized and filtered. The active protein fraction is precipitated from the filtrate (usually with trichloroacetic acid), resulting in a more refined product than Old Tuberculin.
Why other options are incorrect:
Why other options are incorrect:
- • Inferior to old tuberculin: This is false. PPD is superior to Old Tuberculin (OT) because it is more purified, standardized, and produces fewer non-specific reactions.
- • Filtrate of glycerol broth: This describes Old Tuberculin (OT), which is a crude filtrate of a 6-week-old glycerol broth culture. PPD goes several steps further to “purify” the proteins from that filtrate.
Which of the following are inactive viral vaccines?
- a) Influenzae
- b) Rabies
- c) Russian spring summer encephalitis
- d) All of these
Explanation:
Inactivated (killed) viral vaccines include influenza vaccine, rabies vaccine, and Russian spring-summer encephalitis vaccine. Therefore, all the listed options are examples of inactive viral vaccines.
Why other options are incorrect:
Why other options are incorrect:
- • Influenzae: It is an inactivated viral vaccine, so it is not incorrect by itself.
- • Rabies: Rabies vaccine is also an inactivated viral vaccine.
- • Russian spring summer encephalitis: This is likewise an example of an inactivated viral vaccine.
Antigenic variation is most extensive in which of the following viruses?
- a) Influenza virus
- b) Smallpox virus
- c) Measles virus
- d) Herpes virus
Explanation:
The Influenza virus exhibits the most extensive antigenic variation through two mechanisms: Antigenic Drift (minor point mutations) and Antigenic Shift (major changes due to genetic reassortment of its segmented RNA genome). This is why a new flu vaccine is required every year.
Why other options are incorrect:
Why other options are incorrect:
- • Smallpox virus: A DNA virus that was antigenically very stable, which is one reason why it was possible to eradicate it globally using a single vaccine.
- • Measles virus: Although it is an RNA virus, it is antigenically stable with only one serotype; infection or vaccination provides lifelong immunity.
- • Herpes virus: These are large DNA viruses that are relatively stable antigenically and do not undergo frequent major shifts like influenza.
Food poisoning is caused by which of the following?
- a) Clostridium tetani
- b) Clostridium welchii
- c) Diphtheria
- d) Clostridium botulinum
Explanation:
Clostridium botulinum is a primary cause of a severe, potentially fatal form of food poisoning called Botulism. This occurs when the bacteria produce a potent neurotoxin in improperly preserved or canned foods.
Why other options are incorrect:
Why other options are incorrect:
- • Clostridium tetani: Causes Tetanus (lockjaw), which usually enters the body through deep puncture wounds, not ingestion.
- • Clostridium welchii: (Also known as C. perfringens) It can cause food poisoning and gas gangrene, but C. botulinum is the textbook clinical definition for severe “food poisoning” in this context.
- • Diphtheria: Caused by Corynebacterium diphtheriae, it is a respiratory or cutaneous infection, not a foodborne illness.
Koplik’s spots will develop in which of the following diseases?
- a) HIV
- b) Measles
- c) Mumps
- d) Rubella
Explanation:
Koplik’s spots are a pathognomonic (diagnostic) sign for Measles (Rubeola). They are small, white spots (often compared to grains of salt) on a reddened background that appear on the buccal mucosa (inside of the cheeks) 2 to 3 days before the measles rash itself breaks out.
Why other options are incorrect:
Why other options are incorrect:
- • HIV: While it can cause oral lesions (like Candidiasis or Hairy Leukoplakia), it does not produce Koplik’s spots.
- • Mumps: Characterized by the painful swelling of the parotid (salivary) glands, not a mucosal spot rash.
- • Rubella: Also known as “German Measles,” it presents with a rash but lacks the Koplik’s spots found in true Measles.
Viral DNA is resistant to the restriction enzymes of the host cell because it contains?
- a) 5’-HMC
- b) 5’-HMA
- c) 5’-CHM
- d) 5’MHC
Explanation:
In certain viruses, particularly T-even bacteriophages, the cytosine in their DNA is replaced by 5-hydroxymethylcytosine (5-HMC). This modified base is often further glucosylated, which protects the viral DNA from being degraded by the host cell’s restriction endonucleases.
Why other options are incorrect:
Why other options are incorrect:
- • 5’-HMA / 5’-CHM: These are non-standard abbreviations and do not represent known biological bases involved in viral DNA protection.
- • 5’MHC: This is a distractor that resembles the acronym for “Major Histocompatibility Complex,” which is related to the immune system but has no connection to viral DNA structure or restriction enzyme resistance.
The triple toxoid vaccine (DPT) gives protection against which of the following?
- a) Diphtheria, tetanus and rabies
- b) Tetanus, whooping cough, Tuberculosis
- c) Whooping cough, tetanus and Diphtheria
- d) Whooping cough, cancer and T.B.
Explanation:
The DPT vaccine (often called the triple vaccine or triple antigen) protects against three infectious diseases: Diphtheria, Pertussis (Whooping cough), and Tetanus. The Diphtheria and Tetanus components are toxoids, while the Pertussis component is typically killed whole-cell bacteria or acellular proteins.
Why other options are incorrect:
Why other options are incorrect:
- • Rabies: This is a separate vaccine given post-exposure or for high-risk individuals; it is not part of the childhood triple vaccine.
- • Tuberculosis (T.B.): Protection against T.B. is provided by the BCG vaccine, not the DPT vaccine.
- • Cancer: While some vaccines like HPV can prevent certain cancers, there is no “triple toxoid” that includes cancer protection.
Higher doses of chloramphenicol affects the eukaryotic cells because?
- a) They have 30 S ribosomes
- b) They have mitochondria
- c) They have 70 S ribosomes
- d) None of the above
Explanation:
Chloramphenicol inhibits protein synthesis by acting on 70S ribosomes. Although eukaryotic cytoplasmic ribosomes are 80S and are generally unaffected, mitochondria contain ribosomes that closely resemble bacterial 70S ribosomes. At high doses, chloramphenicol can inhibit mitochondrial protein synthesis, leading to toxicity in eukaryotic cells.
Why other options are incorrect:
Why other options are incorrect:
- • They have 30 S ribosomes: Eukaryotic cells do not possess 30S ribosomes in their cytoplasm.
- • They have mitochondria: Correct answer. Mitochondria contain ribosomes similar to bacterial 70S ribosomes, making them susceptible to chloramphenicol.
- • They have 70 S ribosomes: Eukaryotic cytoplasmic ribosomes are 80S, not 70S.
- • None of the above: Incorrect because the presence of mitochondria explains the effect.
AIDS is caused by which of the following?
- a) Retrovirus
- b) Prion
- c) Rhabdovirus
- d) Retroprison
Explanation:
AIDS is caused by the Human Immunodeficiency Virus (HIV), which is a Retrovirus. Retroviruses are RNA viruses that use the enzyme reverse transcriptase to convert their RNA genome into DNA once they enter a host cell, allowing them to integrate into the host’s genome.
Why other options are incorrect:
Why other options are incorrect:
- • Prion: These are infectious protein particles (lacking nucleic acids) that cause diseases like Mad Cow Disease or Creutzfeldt-Jakob disease.
- • Rhabdovirus: This family of viruses includes the Rabies virus; they are characterized by their bullet-shaped structure.
- • Retroprison: This is a distractor term and does not refer to any known biological pathogen.
Penicillin is a?
- a) Primary metabolite
- b) Secondary metabolite
- c) Tertiary metabolite
- d) None of the above
Explanation:
Penicillin is a secondary metabolite. It is produced by the fungus Penicillium during the stationary phase (idiophase) of its growth cycle and is not directly involved in the normal growth, development, or reproduction of the organism.
Why other options are incorrect:
Why other options are incorrect:
- • Primary metabolite: These are essential for life and growth (e.g., amino acids, ethanol, lactic acid) and are produced during the active growth phase (trophophase).
- • Tertiary metabolite: This term is not a standard classification used in biochemistry or microbiology for metabolic products.
- • None of the above: Incorrect because Penicillin is clearly categorized as a secondary metabolite.
The rejection of an organ transplant, such as a kidney transplant, is an example of which type of hypersensitivity?
- a) Immediate
- b) Delayed
- c) Allergy
- d) None of these
Explanation:
Organ transplant rejection is primarily a Type IV (Delayed) Hypersensitivity reaction. It is mediated by T-lymphocytes (cell-mediated immunity) rather than antibodies. T-cells recognize the foreign MHC molecules on the transplanted organ and initiate a cytotoxic response to destroy the “foreign” tissue.
Why other options are incorrect:
Why other options are incorrect:
- • Immediate: (Type I) This is IgE-mediated and occurs within minutes (e.g., anaphylaxis). While “Hyperacute” rejection exists (mediated by pre-formed antibodies), the standard clinical rejection described is Type IV.
- • Allergy: This is a broad term usually used to describe Type I hypersensitivity to environmental antigens (pollen, dust), not tissue rejection.
- • None of these: Incorrect, as “Delayed” is the specific clinical classification for this immune process.
Listeriosis is primarily a ________ disease?
- a) Food borne
- b) Water borne
- c) Milk borne
- d) Air borne
Explanation:
Listeriosis, caused by the bacterium Listeria monocytogenes, is a serious foodborne illness. It is typically contracted by eating contaminated food such as unpasteurized dairy products, soft cheeses, deli meats, and improperly washed vegetables.
Why other options are incorrect:
Why other options are incorrect:
- • Water borne: Diseases like Cholera or Typhoid are primarily waterborne; Listeria does not typically spread through municipal water supplies.
- • Milk borne: While unpasteurized milk is a major source, “Food borne” is the broader and more standard medical classification for this disease.
- • Air borne: Listeria is not known to spread through respiratory droplets or dust in the air.
Pus-forming bacteria or infections are called?
- a) Pyoderm
- b) Pyogenic
- c) Pyrogen
- d) None of the above
Explanation:
The term Pyogenic comes from the Greek words ‘pyo’ (pus) and ‘gen’ (to produce). It refers to bacteria (like Staphylococcus aureus and Streptococcus pyogenes) that lead to the formation of pus as part of the inflammatory response.
Why other options are incorrect:
Why other options are incorrect:
- • Pyoderm: (Usually referred to as Pyoderma) This is a specific medical term for a skin disease that is pyogenic (pus-producing), rather than the general term for the bacteria themselves.
- • Pyrogen: This refers to a substance (like bacterial endotoxins) that produces a fever by acting on the hypothalamus, not necessarily pus.
- • None of the above: Incorrect, as “Pyogenic” is the standard clinical term used in microbiology.
In the ELISA technique, the antibodies are labeled by which of the following?
- a) Acridine orange
- b) Alkaline phosphate
- c) Neutral red
- d) Bromothymol blue
Explanation:
ELISA (Enzyme-Linked Immunosorbent Assay) utilizes enzymes to label antibodies. Alkaline phosphatase (and Horseradish peroxidase) are the most commonly used enzymes. When a substrate is added, these enzymes produce a color change that can be measured to determine the quantity of antigen or antibody present.
Why other options are incorrect:
Why other options are incorrect:
- • Acridine orange: A fluorescent dye used to stain nucleic acids in microscopy, not used as an enzyme label in ELISA.
- • Neutral red: A vital stain used in histology and as a pH indicator; it does not have the enzymatic properties required for ELISA.
- • Bromothymol blue: A chemical pH indicator commonly used in biology to detect the presence of carbonic acid; it is not used to label antibodies.
Which genetic disease is characterized by a total or partial inability to synthesize globulins?
- a) Apitososis
- b) Agamma globulinemia
- c) Gammaglobulinemma
- d) Sickle-cell anemia
Explanation:
Agammaglobulinemia is an inherited immune deficiency disorder characterized by a very low concentration of protective antibodies (gamma globulins) in the blood. The most common form is X-linked agammaglobulinemia (Bruton’s disease), which makes patients highly susceptible to bacterial infections.
Why other options are incorrect:
Why other options are incorrect:
- • Apitososis: Likely a misspelling of Apoptosis, which refers to programmed cell death and is not a disease of protein synthesis.
- • Gammaglobulinemma: This term simply implies the presence of globulins in the blood; it does not indicate a deficiency or disease state on its own.
- • Sickle-cell anemia: A genetic disorder of hemoglobin (the red blood cells), not the immune system’s globulins.
A study involving the analysis of risk for genetic defects in a family is known as?
- a) Genetic Engineering
- b) Genetic counseling
- c) Genetic drift
- d) Genetic equilibrium
Explanation:
Genetic counseling is the process of investigating individuals and families affected by or at risk of genetic disorders. It helps them understand the medical facts, the way heredity contributes to the disorder, and the risk of recurrence in specified relatives.
Why other options are incorrect:
Why other options are incorrect:
- • Genetic Engineering: Refers to the direct manipulation of an organism’s genes using biotechnology to change its characteristics.
- • Genetic drift: A mechanism of evolution referring to random fluctuations in the frequencies of alleles within a population over time.
- • Genetic equilibrium: A condition where a gene pool is not changing in frequency (e.g., Hardy-Weinberg equilibrium), indicating a lack of evolutionary change.
Viral antigens are likely?
- a) Proteins
- b) Glyco proteins
- c) Lipo proteins
- d) Both Proteins and Glyco proteins
Explanation:
Viral antigens, which trigger the host’s immune response, are primarily composed of proteins (found in the capsid) or glycoproteins (found in the spikes of enveloped viruses).
Why other options are incorrect:
Why other options are incorrect:
- • Proteins: While viral antigens are proteins, this option is incomplete as many are also glycoproteins.
- • Glyco proteins: Many viral surface antigens are glycoproteins, but this excludes those that are simple proteins.
- • Lipo proteins: While viral envelopes contain lipids derived from the host cell, the specific antigenic determinants recognized by the immune system are rarely lipoproteins.
The suitable assay method for antibiotics is?
- a) Enzymatic assay
- b) Turbidometric assay
- c) End point determination assay
- d) Metabolic assay
Explanation:
The Turbidometric (or tube) assay is a common microbiological method used to determine the potency of antibiotics by measuring the inhibition of growth of a microbial culture in a liquid medium.
Why other options are incorrect:
Why other options are incorrect:
- • Enzymatic assay: While used for some biochemical tests, it is not the standard pharmacopeial method for general antibiotic potency.
- • End point determination assay: This usually refers to chemical titrations rather than the biological activity measurement required for antibiotics.
- • Metabolic assay: This measures the change in metabolic activity but is less common and standardized than turbidometric or agar diffusion methods for antibiotics.
ELISA test is used for the identification of?
- a) Janudice
- b) AIDS
- c) Cancer
- d) Diabetis
Explanation:
ELISA (Enzyme-Linked Immunosorbent Assay) is a plate-based assay technique designed for detecting and quantifying substances such as peptides, proteins, antibodies, and hormones. It is the standard primary screening test for HIV/AIDS.
Why other options are incorrect:
Why other options are incorrect:
- • Janudice: Jaundice is a condition typically diagnosed through Liver Function Tests (LFT) and bilirubin level measurements.
- • Cancer: While some tumor markers can be detected via ELISA, cancer is primarily diagnosed through biopsies, CT scans, and MRIs.
- • Diabetis: Diabetes is diagnosed by measuring blood glucose levels (fasting/random) or HbA1c levels, not by ELISA.
All of the following are bacteriostatic chemotherapeutic agents except?
- a) Bacitracin
- b) Chloramphenicol
- c) Novobiocin
- d) Tetracycline
Explanation:
Bacitracin is bactericidal (it kills bacteria) because it interferes with the synthesis of the bacterial cell wall. The other three listed are bacteriostatic (they inhibit growth/reproduction).
Why other options are incorrect:
Why other options are incorrect:
- • Chloramphenicol: It is a classic bacteriostatic agent that inhibits protein synthesis by binding to the 50S ribosome.
- • Novobiocin: This is a bacteriostatic agent that acts by inhibiting DNA gyrase.
- • Tetracycline: This is a bacteriostatic agent that prevents protein synthesis by binding to the 30S ribosomal subunit.
Kinetosomes are observed in?
- a) Algae
- b) Fungi
- c) Protozoa
- d) Viruses
Explanation:
Kinetosomes (also known as basal bodies) are cylindrical structures found at the base of eukaryotic cilia or flagella. They are highly characteristic of many Protozoa (such as ciliates and flagellates), where they serve as microtubule-organizing centers.
Why other options are incorrect:
Why other options are incorrect:
- • Algae: While some flagellated algae have basal bodies, the term “kinetosome” is most classically used in the study of protozoan morphology.
- • Fungi: Most fungi lack flagellated stages (with the exception of Chytrids) and do not typically exhibit kinetosomes.
- • Viruses: Viruses are acellular entities and do not possess organelles, cilia, flagella, or kinetosomes.
β-lactum ring is present in?
- a) Erythromycin
- b) Penicillin
- c) Tetracyclins
- d) Chloramphenicol
Explanation:
Penicillin belongs to the class of antibiotics known as beta-lactams. These are characterized by the presence of a four-membered beta-lactam ring in their molecular structure, which is essential for their antibacterial activity.
Why other options are incorrect:
Why other options are incorrect:
- • Erythromycin: This is a macrolide antibiotic, characterized by a large macrocyclic lactone ring, not a beta-lactam ring.
- • Tetracyclins: These are characterized by a four-ring (naphthacene) core structure, not beta-lactam.
- • Chloramphenicol: This antibiotic has a relatively simple structure containing a nitrobenzene ring and a propanediol chain.
Antibiotic produced from streptomyces orientalis is?
- a) Streptomycin
- b) Penicillin
- c) Vancomycin
- d) Both Streptomycin and Penicillin
Explanation:
Vancomycin was originally isolated in 1953 from soil samples collected in Borneo, specifically produced by the bacterium Streptomyces orientalis (now reclassified as Amycolatopsis orientalis).
Why other options are incorrect:
Why other options are incorrect:
- • Streptomycin: This antibiotic is produced by the soil bacterium Streptomyces griseus.
- • Penicillin: This is derived from fungi of the genus Penicillium, most notably Penicillium chrysogenum, not from Streptomyces.
- • Option D: Since Penicillin is fungal and Streptomycin comes from S. griseus, this combination is incorrect.
The drug of choice for dermal, oral and vaginal candidiasis is?
- a) Griseofulvin
- b) Amphoterein B
- c) Gentian violet
- d) Nystatin
Explanation:
Nystatin is a polyene antifungal specifically effective against Candida albicans. Because it is not absorbed into the bloodstream from the skin or mucous membranes, it is the standard “drug of choice” for local (topical) infections including oral thrush, vaginal yeast infections, and diaper rash.
Why other options are incorrect:
Why other options are incorrect:
- • Griseofulvin: This is used to treat infections caused by dermatophytes (like ringworm or athlete’s foot) but is ineffective against Candida.
- • Amphoterein B: While highly effective against many fungi, it is typically reserved for severe, life-threatening systemic infections due to its high toxicity.
- • Gentian violet: An older antiseptic dye that has antifungal properties, but it is rarely the first choice today because it stains skin and clothes and more effective modern alternatives exist.
Botulism means?
- a) Food adultration
- b) Food poisioning by streptococcus bacteria
- c) Chemical contamination of food
- d) Food processing
Explanation:
Botulism is a severe form of food poisoning. It is caused by the ingestion of a potent neurotoxin produced by the bacterium Clostridium botulinum (not Streptococcus). It usually occurs from improperly canned or preserved foods.
Why other options are incorrect:
Why other options are incorrect:
- • Food adulteration: This refers to the intentional addition of inferior or harmful substances to food to increase volume or profit, not bacterial poisoning.
- • Chemical contamination: Botulism is biological/toxicological (caused by a bacterial toxin), not by synthetic chemicals like pesticides or heavy metals.
- • Food processing: While incorrect food processing can lead to botulism, the term “Botulism” refers to the illness itself, not the act of processing food.
Chloramphenicol is obtained from?
- a) Streptomyces griseus
- b) Streptomyces venezuelae
- c) Streptomyces pyrogenes
- d) None of these
Explanation:
Streptomyces venezuelae is the soil bacterium from which Chloramphenicol was first isolated in 1947. It was the first broad-spectrum antibiotic to be manufactured synthetically on a large scale.
Why other options are incorrect:
Why other options are incorrect:
- • Streptomyces griseus: This species is the primary source of the antibiotic Streptomycin, not chloramphenicol.
- • Streptomyces pyrogenes: This is not a recognized major source for clinical antibiotics; the name is likely a distractor (possibly confusing it with Streptococcus pyogenes, a human pathogen).
- • None of these: This is incorrect because option ‘b’ is the established biological source.
Streptomycin is obtained from?
- a) Streptococcus species
- c) Straphylococcus aureus
- d) None of these
Explanation:
Streptomyces griseus is the soil-dwelling bacterium (an actinomycete) from which Streptomycin was first isolated. It was the first antibiotic found to be effective against tuberculosis.
Why other options are incorrect:
Why other options are incorrect:
- • Streptococcus species: These are a genus of gram-positive bacteria that are often human pathogens (causing strep throat, etc.), not sources of streptomycin.
- • Staphylococcus aureus: This is a common pathogen responsible for various skin and systemic infections; it does not produce streptomycin.
- • None of these: This is incorrect because option ‘b’ is the globally recognized biological source.
The treatment required for small bodies of water is?
- a) Disinfection
- b) Filtration
- c) Purification
- d) All of these
Explanation:
Small bodies of water (e.g., tanks, ponds, or small‑scale supplies) typically require a
combination of filtration (to remove suspended solids),
disinfection (to kill harmful pathogens), and
purification (to improve overall water quality). Hence, the
correct answer is All of these.
Why other options are incorrect:
Why other options are incorrect:
- • Disinfection: Important, but alone it does not remove physical impurities or improve taste/odour.
- • Filtration: Removes particles but does not eliminate all microbial or chemical contaminants.
- • Purification: A broad term, but in practice it often encompasses both filtration and disinfection.
Surface ropiness is caused by?
- a) Alkaligenes viscolactis
- b) Streptococcus
- c) both Alkaligenes viscolactis and Streptococcus
- d) None of these
Explanation:
Ropiness in milk (a condition where milk becomes viscous or slimy and forms long threads) is caused by bacteria that produce gums or mucilaginous capsular material. Both Alkaligenes viscolactis (an aerobe that specifically targets the surface) and certain strains of Streptococcus (like S. lactis var. hollandicus) are responsible for this defect.
Why other options are incorrect:
Why other options are incorrect:
- • Alkaligenes viscolactis: While this is the most common cause of surface ropiness specifically because it requires oxygen, it is not the only organism capable of causing ropiness in milk.
- • Streptococcus: Certain species cause ropiness throughout the body of the milk rather than just the surface, but they contribute to the overall “ropy” condition.
- • None of these: This is incorrect as both ‘a’ and ‘b’ contain known organisms that cause this dairy defect.
Septicaemia is?
- a) Bacteria in blood
- b) Toxin in blood
- c) Pus in blood
- d) Multiplication of bacteria and toxins in blood
Explanation:
Septicaemia (often used interchangeably with sepsis) is a life-threatening condition where bacteria not only enter the bloodstream but also actively multiply and release toxins, causing systemic inflammation.
Why other options are incorrect:
Why other options are incorrect:
- • Bacteria in blood: This is specifically termed Bacteremia. It may be transient and does not always involve multiplication or illness.
- • Toxin in blood: This is specifically termed Toxemia.
- • Pus in blood: This is specifically termed Pyemia, which involves septicaemia with secondary foci of suppuration (pus) and abscesses.
In AIDS, Kaposis sarcoma may respond to?
- a) Interleukin – 2 infusion
- b) Azathioprine
- c) Alpha interferon
- d) None of these
Explanation:
Alpha interferon (IFN-α) has antiviral, antiproliferative, and immunomodulatory properties. It is an FDA-approved treatment for AIDS-related Kaposi’s sarcoma, particularly in patients with a relatively stable immune system (higher CD4 counts).
Why other options are incorrect:
Why other options are incorrect:
- • Interleukin – 2: While used in some immunotherapies to boost T-cell counts, it is not a standard primary treatment specifically for the regression of Kaposi’s sarcoma lesions.
- • Azathioprine: This is an immunosuppressant. Using it in an AIDS patient could actually worsen Kaposi’s sarcoma, as the tumor thrives when the immune system is suppressed.
- • None of these: This is incorrect because Alpha interferon is a recognized therapeutic option for this condition.
Ciprofloxacin acts by inhibiting?
- a) Cellwall synthesis
- b) RNA synthesis
- c) Folate synthesis
- d) DNA gyrase
Explanation:
Ciprofloxacin is a fluoroquinolone antibiotic that works by inhibiting bacterial DNA gyrase (topoisomerase II) and topoisomerase IV. These enzymes are essential for bacterial DNA replication, transcription, repair, and recombination.
Why other options are incorrect:
Why other options are incorrect:
- • Cellwall synthesis: This is the mechanism of action for beta-lactam antibiotics like Penicillins and Cephalosporins.
- • RNA synthesis: Antibiotics like Rifampin act by inhibiting DNA-dependent RNA polymerase, thus blocking RNA synthesis.
- • Folate synthesis: This is the target for Sulfonamides and Trimethoprim, which interfere with the metabolic pathway of folic acid.
Lyme disease is caused by?
- a) Bacteria
- b) Fungi
- c) Spirochaete
- d) Virus
Explanation:
Lyme disease is caused by the bacterium Borrelia burgdorferi. This organism is specifically classified as a Spirochaete because of its unique spiral (corkscrew) shape and method of movement.
Why other options are incorrect:
Why other options are incorrect:
- • Bacteria: While Borrelia is a bacterium, “Spirochaete” is the more specific and scientifically accurate answer in this context.
- • Fungi: Lyme disease is not a fungal infection; it is transmitted through the bite of infected black-legged ticks.
- • Virus: Although some tick-borne illnesses are viral (like Powassan virus), Lyme disease is strictly bacterial.
Toxic shock syndrome is caused by?
- a) Staph. albus
- b) Staph. aureus
- c) Strep. viridana
- d) None of these
Explanation:
Toxic Shock Syndrome (TSS) is a severe, life-threatening condition caused by toxins produced by certain bacteria. The most common causative agent is Staphylococcus aureus (specifically strains that produce the TSST-1 toxin).
Why other options are incorrect:
Why other options are incorrect:
- • Staph. albus: Now commonly known as Staphylococcus epidermidis, it is generally part of the normal skin flora and is rarely associated with the production of toxins that cause TSS.
- • Strep. viridana: This group of bacteria is commonly found in the mouth and is associated with dental infections or endocarditis, but is not the primary cause of classic toxic shock syndrome.
- • None of these: This is incorrect as Staph. aureus is the well-established cause.
Black water fever is caused by?
- a) P. vivax
- b) P. falciparum
- c) P. ovale
- d) None of these
Explanation:
Blackwater fever is a severe and life-threatening complication of malaria, characterized by the rapid destruction of red blood cells (intravascular hemolysis) leading to hemoglobinuria (dark or “black” urine). It is specifically associated with infections by Plasmodium falciparum.
Why other options are incorrect:
Why other options are incorrect:
- • P. vivax: Causes “benign tertian” malaria, which is usually less severe and does not typically result in the massive hemolysis seen in blackwater fever.
- • P. ovale: Similar to P. vivax, it causes a milder form of malaria and is not the causative agent of blackwater fever.
- • None of these: This is incorrect as P. falciparum is the well-documented cause of this specific complication.
Mantoux test detects?
- a) M. tuberculosis
- b) Cynaobacteria
- c) Clostridia
- d) Both M. tuberculosis and Cynaobacteria
Explanation:
The Mantoux test (also known as the Tuberculin Skin Test) is used to determine if a person has been infected with Mycobacterium tuberculosis. It involves injecting a small amount of PPD (Purified Protein Derivative) into the skin and measuring the immune response after 48-72 hours.
Why other options are incorrect:
Why other options are incorrect:
- • Cynaobacteria: These are photosynthetic bacteria (blue-green algae) that do not cause tuberculosis and are not detected by skin sensitivity tests.
- • Clostridia: This genus causes diseases like Tetanus and Botulism; these are typically diagnosed through clinical symptoms, toxin assays, or cultures.
- • Option D: Since Cyanobacteria have no relation to the Mantoux test, this combined option is incorrect.
The antibiotic acting on cell wall is?
- a) Bactracin
- b) Penicillin
- c) Cyclosporine
- d) All of these
Explanation:
Penicillin acts by inhibiting bacterial cell wall synthesis, leading to bacterial cell death.
Why other options are incorrect:
Why other options are incorrect:
- • Bactracin: Although it also affects cell wall synthesis, the standard single-best answer is Penicillin.
- • Cyclosporine: It is an immunosuppressive drug, not a cell wall-active antibiotic.
- • All of these: Incorrect because Cyclosporine does not act on the bacterial cell wall.
Aflatoxin is produced by?
- a) Aspergillus sps
- b) Penicillium sps
- c) Alternaria sps
- d) None of these
Explanation:
Aflatoxins are potent toxic and carcinogenic metabolites produced primarily by certain molds, most notably Aspergillus flavus and Aspergillus parasiticus. They often contaminate crops like peanuts, corn, and tree nuts.
Why other options are incorrect:
Why other options are incorrect:
- • Penicillium sps: While some species produce mycotoxins (like Ochratoxin A or Patulin) and antibiotics, they are not the primary source of aflatoxins.
- • Alternaria sps: These fungi produce a different group of mycotoxins (such as alternariol), but not aflatoxins.
- • None of these: This is incorrect as Aspergillus is the well-known biological source of these toxins.
Penicillin is discovered by?
- a) Fleming
- b) Pasteur
- c) Koch
- d) None of these
Explanation:
Alexander Fleming discovered Penicillin in 1928 at St. Mary’s Hospital in London. He noticed that a mold called Penicillium notatum had contaminated a culture plate of Staphylococci and created a bacteria-free zone.
Why other options are incorrect:
Why other options are incorrect:
- • Pasteur: Louis Pasteur is famous for the principles of vaccination, microbial fermentation, and pasteurization, but he did not discover penicillin.
- • Koch: Robert Koch is known for Koch’s postulates and identifying the specific causative agents of tuberculosis, cholera, and anthrax.
- • None of these: This is incorrect because Fleming is the universally recognized discoverer of the first antibiotic.
Antibiotics used in combination may demonstrate?
- a) Synergism
- b) Antagonism
- c) Both Synergism and Antagonism
- d) None of these
Explanation:
When two or more antibiotics are used together, they can interact in different ways. They may work together to increase effectiveness (Synergism) or they may interfere with each other, reducing overall effectiveness (Antagonism).
Why other options are incorrect:
Why other options are incorrect:
- • Synergism: While true, it is not the only outcome; combinations can also be harmful to the treatment process.
- • Antagonism: While this can happen (especially when mixing bacteriostatic and bactericidal drugs), it is only one possible type of interaction.
- • None of these: Incorrect, as drug-drug interactions (synergy and antagonism) are fundamental concepts in pharmacology.
The drug of choice in anaphylactic shock is?
- a) Histamine
- b) Corticosteroid
- c) Epinephrine
- d) None of these
Explanation:
Epinephrine (also known as Adrenaline) is the first-line, life-saving treatment for anaphylaxis. It works rapidly to constrict blood vessels (increasing blood pressure), relax airway muscles (improving breathing), and reduce swelling and hives.
Why other options are incorrect:
Why other options are incorrect:
- • Histamine: This is the substance naturally released by the body during an allergic reaction that causes the symptoms of shock. Administering it would be dangerous.
- • Corticosteroid: These are used as secondary treatments to prevent late-phase reactions, but they take several hours to work and cannot treat the immediate life-threatening symptoms of anaphylaxis.
- • None of these: This is incorrect because Epinephrine is the globally recognized “Gold Standard” treatment for this condition.
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