Bacteriology Practice Questions

Q: Outbreak of abscess following vaccine injection can be caused by which mycobacteria?

M. fortuitum. **Explanation:** The correct answer is **M. fortuitum**. This organism belongs to the group of **Rapidly Growing Mycobacteria (RGM)**, which are classified under Runyon Group IV. **Why M. fortuitum is correct:** * **Mechanism:** *M. fortuitum* and *M. chelonae* are environmental saprophytes commonly found in soil and water. They are notorious for causing **post-injection abscesses** and surgical site infections (especially following cosmetic surgery, liposuction, or vaccinations) due to the use of contaminated needles, syringes, or skin antiseptics. * **Characteristics:** They grow rapidly on routine laboratory media (like Lowenstein-Jensen or blood agar) within **3 to 7 days**, unlike slow-growing mycobacteria which take weeks. **Why other options are incorrect:** * **M. scrofulaceus (Group II):** A scotochromatogen primarily associated with **cervical lymphadenitis** (scrofula) in children. * **M. avium (Group III):** Part of the *M. avium-intracellulare* complex (MAC), it typically causes disseminated disease in **HIV/AIDS patients** or chronic pulmonary disease, not localized post-vaccination abscesses. * **M. hordinae:** This is a non-pathogenic environmental mycobacterium and is not associated with human clinical outbreaks. **High-Yield Clinical Pearls for NEET-PG:** * **Runyon Classification:** Remember that Group IV (Rapid Growers) includes *M. fortuitum, M. chelonae,* and *M. abscessus*. * **Clinical Association:** If a question mentions "abscesses following tattooing," "pedicure-associated furunculosis," or "post-surgical wound infection" failing standard antibiotic therapy, always suspect Rapidly Growing Mycobacteria. * **Diagnosis:** They are unique because they can grow on **MacConkey agar** (without crystal violet), appearing as small, pin-point colonies.

Q: Which of the following does NOT cause meningitis?

Streptococcus type A. The correct answer is **Streptococcus type A** (Group A Streptococcus or *S. pyogenes*). ### **Explanation** **Streptococcus type A (*S. pyogenes*)** is primarily a pathogen of the upper respiratory tract and skin. It is the leading cause of bacterial pharyngitis, impetigo, cellulitis, and non-suppurative sequelae like Rheumatic Fever and Glomerulonephritis. While it can cause invasive diseases like necrotizing fasciitis or toxic shock syndrome, it is **not** a recognized or common cause of meningitis. ### **Analysis of Other Options** * **Listeria monocytogenes:** A significant cause of meningitis in specific populations, including neonates, the elderly, and immunocompromised individuals. It is unique as a gram-positive motile rod. * **Pneumococcus (*S. pneumoniae*):** Currently the **most common cause** of bacterial meningitis in adults and children (following the decline of *H. influenzae* due to vaccination). It is characterized by lancet-shaped diplococci. * **Beta-Streptococci (specifically Group B):** *Streptococcus agalactiae* (Group B Streptococcus) is the **leading cause of neonatal meningitis**, typically transmitted during childbirth from the maternal vaginal flora. ### **NEET-PG High-Yield Pearls** * **Most common cause of meningitis overall:** *Streptococcus pneumoniae*. * **Most common cause in neonates (0–28 days):** Group B Streptococcus (GBS), followed by *E. coli* and *Listeria*. * **Most common cause in adolescents/young adults:** *Neisseria meningitidis* (often associated with outbreaks in dormitories). * **Listeria hint:** If the question mentions "tumbling motility" at 25°C or meningitis in a renal transplant patient, think *Listeria*. * **CSF Findings in Bacterial Meningitis:** Increased neutrophils, markedly low glucose, and high protein.

Q: Vincent's angina is caused by Borrelia vincentii along with which other microorganism?

Fusobacterium. **Explanation:** **Vincent’s Angina** (also known as Trench Mouth or Acute Necrotizing Ulcerative Gingivitis - ANUG) is a classic example of a **synergistic infection**. It is characterized by painful, bleeding gums and the formation of a "pseudomembrane" on the tonsils and pharynx. The condition is caused by the symbiotic proliferation of two specific organisms: 1. **Borrelia vincentii:** A large, Gram-negative motile spirochete. 2. **Fusobacterium fusiforme:** A Gram-negative, anaerobic, spindle-shaped (fusiform) bacillus. This combination is often referred to as the **"fusospirochetal complex."** These organisms are part of the normal oral flora but become pathogenic under conditions of poor oral hygiene, malnutrition, or extreme physical stress. **Analysis of Options:** * **C. Fusobacterium (Correct):** As stated above, it works synergistically with *Borrelia vincentii* to cause tissue necrosis and ulceration. * **A & B. Lactobacillus:** These are Gram-positive rods that are part of the normal flora of the mouth, gut, and vagina. They are primarily associated with dental caries and maintaining vaginal pH, not necrotizing angina. * **D. Bacteroides:** While *Bacteroides* are common oral anaerobes involved in periodontal disease and abscesses, they are not the specific diagnostic partner in the classic description of Vincent’s Angina. **High-Yield Clinical Pearls for NEET-PG:** * **Diagnosis:** Usually made via a Gram stain of the ulcerated lesion showing the characteristic "fusospirochetal" morphology. * **Clinical Presentation:** Punched-out interdental papillae, halitosis (fetid breath), and a greyish pseudomembrane. * **Treatment:** Penicillin is the drug of choice, along with metronidazole and surgical debridement. * **Related Condition:** If the infection spreads to the cheeks and face, it is called **Cancrum Oris (Noma)**, typically seen in severely malnourished children.

Q: Which organism commonly causes early-onset neonatal septicemia?

Streptococcus agalactiae. **Explanation:** **Early-Onset Neonatal Sepsis (EONS)** occurs within the first 72 hours of life and is typically caused by the vertical transmission of pathogens from the maternal genital tract during labor or delivery. **Correct Option (A): Streptococcus agalactiae** Also known as **Group B Streptococcus (GBS)**, this is the most common cause of EONS worldwide. It colonizes the maternal vagina and rectum; during birth, the neonate can aspirate infected amniotic fluid or vaginal secretions, leading to pneumonia, septicemia, or meningitis. In developing countries like India, while GBS remains significant, Gram-negative organisms like *Klebsiella* and *E. coli* are also frequently isolated. **Incorrect Options:** * **B. Streptococcus bovis:** Now reclassified as *S. gallolyticus*, it is a Group D Strep associated with endocarditis and colorectal cancer in adults, not neonatal sepsis. * **C. Streptococcus pyogenes:** Known as Group A Strep (GAS), it causes pharyngitis, skin infections, and rheumatic fever. While it can cause puerperal sepsis in mothers, it is a rare cause of neonatal sepsis. * **D. Streptococcus viridans:** These are normal commensals of the oropharynx. They are low-virulence organisms usually associated with subacute bacterial endocarditis or dental caries. **High-Yield Clinical Pearls for NEET-PG:** * **Definition of EONS:** Onset 18 hours), and maternal fever. * **Drug of Choice:** Empirical treatment is a combination of **Ampicillin and Gentamicin**.

Q: Where does Neisseria gonorrhoeae initially infect the female reproductive tract?

Cervix. **Explanation:** The correct answer is **B. Cervix**. *Neisseria gonorrhoeae* is a Gram-negative diplococcus that specifically targets **columnar and cuboidal epithelium**. In the female reproductive tract, the **endocervix** is the primary site of initial infection because it is lined by simple columnar epithelium, which provides the necessary receptors (pili and Opa proteins) for bacterial attachment and invasion. **Why other options are incorrect:** * **A. Vagina:** In adult females, the vagina is lined by **stratified squamous epithelium**. This thick, multi-layered surface is resistant to gonococcal invasion. (Note: In pre-pubertal girls, the vaginal mucosa is thin and can be infected, leading to vulvovaginitis). * **C. Uterus & D. Fallopian tubes:** While the infection can ascend to the endometrium and fallopian tubes causing Pelvic Inflammatory Disease (PID), these are **secondary sites** of infection. The bacteria must first establish a colony in the cervix before ascending. **High-Yield Clinical Pearls for NEET-PG:** * **Most common site of asymptomatic infection:** The cervix (up to 50-70% of women are asymptomatic). * **Gold Standard Diagnosis:** Nucleic Acid Amplification Test (NAAT). Culture on **Thayer-Martin medium** is used for sensitivity testing. * **Fitz-Hugh-Curtis Syndrome:** A complication where the infection spreads to the liver capsule, causing "string-bread" adhesions. * **Treatment:** Due to increasing resistance, the current recommendation is often a combination therapy (e.g., Ceftriaxone IM + Azithromycin/Doxycycline) to cover co-infection with *Chlamydia trachomatis*.

Q: A 32-year-old female presents with watery diarrhea, hyponatremia, and hypokalemia. She is diagnosed with cholera. What is the mechanism of action of the heat-labile toxin of Vibrio cholerae?

Increased cAMP. ### Explanation **Correct Option: A. Increased cAMP** The pathogenesis of cholera is mediated by the **Cholera Toxin (Choleragen)**, a classic A-B subunit exotoxin. The 'B' subunit binds to the **GM1 ganglioside receptor** on enterocytes, allowing the 'A' subunit to enter the cell. The A subunit causes **permanent activation of Gs (stimulatory) protein** via ADP-ribosylation. This leads to the constitutive activation of **adenylate cyclase**, resulting in a massive increase in intracellular **cyclic AMP (cAMP)**. High cAMP levels trigger the active secretion of chloride ions ($Cl^-$) and inhibit the absorption of sodium ($Na^+$), leading to the osmotic movement of water into the intestinal lumen, manifesting as "rice-water stools." **Why Incorrect Options are Wrong:** * **B. Increased cGMP:** This is the mechanism of the **Heat-Stable (ST) toxin** of *Enterotoxigenic E. coli* (ETEC). (Mnemonic: **S**table = **G**MP; **L**abile = **A**MP). * **C. Inhibition of acetylcholine release:** This is the mechanism of **Botulinum toxin** (*Clostridium botulinum*), leading to flaccid paralysis. * **D. Inhibition of protein synthesis (EF-2):** This is the mechanism of **Diphtheria toxin** (*C. diphtheriae*) and **Exotoxin A** of *Pseudomonas aeruginosa*. **NEET-PG High-Yield Pearls:** * **Stool Appearance:** "Rice-water" (non-inflammatory, no blood/pus). * **Electrolyte profile:** Profound hypokalemia, hyponatremia, and metabolic acidosis (due to bicarbonate loss). * **Gold Standard Diagnosis:** Culture on **TCBS (Thiosulfate-Citrate-Bile Salts-Sucrose) agar**, where *V. cholerae* produces yellow colonies (sucrose fermenter). * **String Test:** Used to identify *Vibrio* species (positive). * **Treatment:** Aggressive rehydration (ORS/IV fluids) is the mainstay; Azithromycin or Doxycycline can reduce shedding.

Q: Which of the following statements about Yaws is not true?

Spread by sexual transmission. **Explanation:** **Yaws** is a chronic, non-venereal treponematosis caused by the bacterium *Treponema pallidum pertenue*. 1. **Why Option A is correct:** Unlike Syphilis, Yaws is **not** a sexually transmitted infection. It is primarily a disease of childhood (usually under 15 years) and is transmitted through **direct skin-to-skin contact** with infectious lesions. It thrives in warm, humid, tropical environments where poor hygiene and overcrowding are prevalent. 2. **Why the other options are wrong:** * **Option B:** This is a true statement. The causative agent is *T. pallidum pertenue*, which is morphologically identical to the agent of syphilis. * **Option C:** This is true. Infection with Yaws provides a degree of **cross-immunity** against syphilis, which is why venereal syphilis was historically less common in areas where Yaws was endemic. * **Option D:** This is true. Because the organisms are so closely related, standard serological tests (both non-treponemal like **VDRL/RPR** and treponemal like **TPHA/FTA-ABS**) cannot distinguish between Yaws and Syphilis. Diagnosis relies on clinical presentation and epidemiological history. **High-Yield Clinical Pearls for NEET-PG:** * **Stages:** Primary (Mother Yaw/Frambesioma), Secondary (Daughter Yaws), and Tertiary (Goundou – swelling of nasal bones; Gangosa – destructive rhinopharyngitis). * **Bone Involvement:** Saber shin (periostitis) is a common late feature. * **Treatment:** A single dose of **Oral Azithromycin** is now the preferred treatment (WHO Morges Strategy), replacing injectable Penicillin G Benzathine. * **Target:** Yaws is targeted by the WHO for global eradication.

Q: Which poisoning can be prevented by an antitoxin?

Clostridium botulinum. **Explanation:** The correct answer is **Clostridium botulinum**. This is because Botulism is a classic example of **pre-formed toxin ingestion** (intoxication) where the pathology is mediated entirely by a potent neurotoxin. **1. Why Clostridium botulinum is correct:** Botulinum toxin is a heat-labile protein that acts at the neuromuscular junction to block the release of acetylcholine, leading to flaccid paralysis. Since the disease is toxin-mediated rather than an active infection in adults (foodborne botulism), the primary treatment and prevention of progression is the administration of a **specific antitoxin** (Equine Heptavalent Antitoxin). The antitoxin works by neutralizing the circulating toxin before it binds to nerve endings. **2. Why the other options are incorrect:** * **Staphylococcus aureus:** While it causes food poisoning via a pre-formed enterotoxin, the condition is self-limiting (resolving within 24 hours). Treatment is purely supportive (rehydration); no antitoxin is indicated or available. * **Salmonella typhimurium:** This causes an invasive infection (enterocolitis), not a toxin-mediated poisoning. Management involves fluid replacement and, in severe cases, antibiotics. * **Bacillus cereus:** Similar to S. aureus, it produces toxins (emetic and diarrheal types) that cause self-limiting symptoms. Management is supportive; no antitoxin exists. **Clinical Pearls for NEET-PG:** * **Botulinum Toxin:** Cleaves SNARE proteins (synaptobrevin), preventing vesicle fusion. * **Infant Botulism:** Unlike adults, infants ingest **spores** (often from honey), which germinate in the gut (colonization). * **High-Yield Tip:** Remember the "D's" of Botulism: Diplopia, Dysarthria, Dysphagia, and Dyspnea with descending paralysis. * **Therapeutic use:** Botox (Toxin A) is used for achalasia, strabismus, and focal dystonias.

Q: An inhibitor was designed to block a biologic function in H. influenzae. If the goal of the experiment were to reduce the virulence of H. influenzae, what would be the most likely target?

Capsule formation. ### Explanation **1. Why Capsule Formation is Correct:** The primary virulence factor of *Haemophilus influenzae* is its **polysaccharide capsule**. The capsule allows the bacteria to resist phagocytosis by host immune cells and inhibits complement-mediated lysis. While there are six serotypes (a-f), **Type b (Hib)**—which contains a Polyribosylribitol Phosphate (PRP) capsule—is historically the most invasive, causing meningitis, epiglottitis, and septic arthritis. Inhibiting capsule formation effectively "disarms" the pathogen, making it susceptible to the host's innate immune system and significantly reducing its virulence. **2. Analysis of Incorrect Options:** * **A. Exotoxin liberation:** *H. influenzae* does **not** produce exotoxins. Its pathogenicity is derived from structural components and invasive capabilities rather than toxin secretion. * **B. Endotoxin assembly:** While *H. influenzae* possesses Lipooligosaccharide (LOS) in its cell wall (which acts as an endotoxin causing inflammation), the **capsule** is the definitive factor that determines systemic invasiveness and high-grade virulence. * **C. Flagella synthesis:** *H. influenzae* is **non-motile**. It does not possess flagella; therefore, targeting flagella synthesis would have no biological effect on this organism. **3. High-Yield Clinical Pearls for NEET-PG:** * **Quellung Reaction:** Used for serotyping *H. influenzae* based on capsular swelling. * **Vaccine:** The Hib vaccine is a **conjugate vaccine** (PRP conjugated to a protein carrier like tetanus toxoid) to induce a T-cell dependent immune response, crucial for infants. * **Culture:** Requires **Factors V (NAD)** and **X (Hemin)**. It shows the **"Satellitism phenomenon"** when grown near *Staphylococcus aureus* on blood agar. * **Nontypable H. influenzae (NTHi):** Strains without a capsule; these primarily cause localized mucosal infections like otitis media, sinusitis, and COPD exacerbations.

Question 1

Outbreak of abscess following vaccine injection can be caused by which mycobacteria?

Accepted Answer

M. fortuitum

Answer

M. scrofulaceus

Answer

M. hordinae

Answer

M. avium

Question 2

Which of the following does NOT cause meningitis?

Accepted Answer

Streptococcus type A

Answer

Listeria

Answer

Pneumococcus

Answer

Beta-Streptococci

Question 3

Vincent's angina is caused by Borrelia vincentii along with which other microorganism?

Accepted Answer

Fusobacterium

Answer

Lactobacillus

Answer

Lactobacillus

Answer

Bacteroides

Question 4

Which of the following most accurately describes the therapy available for the prevention and treatment of C. diphtheriae?

Accepted Answer

Antimicrobial therapy and prophylaxis, antitoxin, and toxoid (DPT)

Answer

Antimicrobial therapy for prophylaxis only

Answer

Diphtheria toxoid (DPT) booster vaccination only

Answer

Antitoxin only

Question 5

Which organism commonly causes early-onset neonatal septicemia?

Accepted Answer

Streptococcus agalactiae

Answer

Streptococcus bovis

Answer

Streptococcus pyogenes

Answer

Streptococcus viridans

Question 6

Where does Neisseria gonorrhoeae initially infect the female reproductive tract?

Accepted Answer

Cervix

Answer

Vagina

Answer

Uterus

Answer

Fallopian tubes

Question 7

A 32-year-old female presents with watery diarrhea, hyponatremia, and hypokalemia. She is diagnosed with cholera. What is the mechanism of action of the heat-labile toxin of Vibrio cholerae?

Accepted Answer

Increased cAMP

Answer

Increased cGMP

Answer

Inhibition of acetylcholine release from nerves

Answer

Inhibition of protein synthesis by inactivating EF-2

Question 8

Which of the following statements about Yaws is not true?

Accepted Answer

Spread by sexual transmission

Answer

Caused by Treponema pallidum pertenue

Answer

Has cross immunity with syphilis

Answer

Cannot be differentiated serologically from T. pallidum

Question 9

Which poisoning can be prevented by an antitoxin?

Accepted Answer

Clostridium botulinum

Answer

Staphylococcus aureus

Answer

Salmonella typhimurium

Answer

Bacillus cereus

Question 10

An inhibitor was designed to block a biologic function in H. influenzae. If the goal of the experiment were to reduce the virulence of H. influenzae, what would be the most likely target?

Accepted Answer

Capsule formation

Answer

Exotoxin liberation

Answer

Endotoxin assembly

Answer

Flagella synthesis

Bacteriology — MCQs

Bacteriology — MCQs

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