Bacteriology Practice Questions

Q: Q-fever is caused by which bacterium?

Coxiella burnetii. **Explanation:** **Coxiella burnetii (Option B)** is the causative agent of **Q-fever**. Although it was historically classified under the family Rickettsiaceae, it is now recognized as a distinct genus. It is an obligate intracellular, Gram-negative bacterium that is highly resistant to environmental stressors due to its ability to form **spore-like variants**. **Why the other options are incorrect:** * **Rochaemelia quintana (Option A):** Now known as *Bartonella quintana*, this organism causes **Trench Fever**, which is transmitted by the human body louse. * **Mycoplasma hominis (Option C):** This is a cell-wall-deficient bacterium associated with urogenital tract infections, pelvic inflammatory disease (PID), and postpartum fever, but not Q-fever. **High-Yield Clinical Pearls for NEET-PG:** * **Transmission:** Unlike other Rickettsial diseases, Q-fever is **not** transmitted by an arthropod vector. It is primarily a **zoonosis** transmitted via inhalation of contaminated aerosols from birth products (placenta), urine, or feces of infected livestock (sheep, goats, cattle). * **Diagnosis:** The **Weil-Felix test is negative** in Q-fever (a common MCQ trap). Diagnosis is usually confirmed via Serology (IFA). * **Antigenic Variation:** It undergoes **Phase Variation**. Phase I is the highly infectious, "smooth" form found in nature; Phase II is the "rough" form produced after repeated laboratory subcultures. * **Clinical Presentation:** Presents as an atypical pneumonia or hepatitis (acute) or culture-negative endocarditis (chronic). * **Treatment:** Doxycycline is the drug of choice.

Q: Neisseria infection is associated with which of the following conditions?

Deficiency of late complements. **Explanation:** The correct answer is **B. Deficiency of late complements.** **Underlying Medical Concept:** The complement system is a vital component of innate immunity. The "late" or "terminal" complement components (**C5, C6, C7, C8, and C9**) assemble to form the **Membrane Attack Complex (MAC)**. The MAC is essential for the lysis of Gram-negative bacteria, particularly those with thin peptidoglycan layers like *Neisseria* species (*N. meningitidis* and *N. gonorrhoeae*). Patients with deficiencies in these terminal components cannot form the MAC effectively, making them highly susceptible to recurrent, invasive infections by *Neisseria*. **Analysis of Options:** * **Option A (Early Complements):** Deficiencies in early components (C1, C2, C4) are primarily associated with **immune complex diseases** like Systemic Lupus Erythematosus (SLE) and pyogenic infections (e.g., *S. pneumoniae*), but not specifically with *Neisseria*. C3 deficiency is severe and leads to susceptibility to various encapsulated bacteria. * **Option C & D:** These are incorrect because there is a well-documented, specific clinical association between the terminal pathway and *Neisseria* susceptibility. **NEET-PG High-Yield Pearls:** * **C5-C9 Deficiency:** Classic association with recurrent **Meningococcal** meningitis and disseminated **Gonococcal** infections. * **C1, C2, C4 Deficiency:** Most common presentation is **SLE-like autoimmune disease**. * **C3 Deficiency:** The most severe complement deficiency; presents with recurrent infections by **encapsulated bacteria** (e.g., *H. influenzae*, *S. pneumoniae*). * **Properdin/Factor D Deficiency:** Also associated with *Neisseria* infections due to impairment of the alternative pathway. * **CH50 Assay:** Used to screen for total complement activity; it will be low/zero in terminal component deficiencies.

Q: Orientia Tsutsugamushi causes which of the following diseases?

Scrub typhus. **Explanation:** **Correct Answer: C. Scrub typhus** *Orientia tsutsugamushi* is the causative agent of **Scrub typhus**. It belongs to the family Rickettsiaceae but is genetically distinct from the genus *Rickettsia* (lacking a lipopolysaccharide cell wall). It is transmitted to humans through the bite of the larval stage (chigger) of **Leptotrombidium mites**. Clinically, it is characterized by high fever, lymphadenopathy, and a pathognomonic **black eschar** at the site of the mite bite. **Analysis of Incorrect Options:** * **A. Epidemic typhus:** Caused by ***Rickettsia prowazekii*** and transmitted by the **human body louse**. It typically occurs in crowded, unsanitary conditions. * **B. Endemic typhus:** Also known as Murine typhus, it is caused by ***Rickettsia typhi*** and transmitted by **rat fleas** (*Xenopsylla cheopis*). * **C. Q fever:** Caused by ***Coxiella burnetii***. Unlike other rickettsial diseases, it does not cause a rash and is usually transmitted via inhalation of contaminated aerosols from livestock. **High-Yield Clinical Pearls for NEET-PG:** * **Vector:** Chigger-borne (Mite). * **Diagnosis:** The **Weil-Felix test** shows agglutination with **OX-K** antigens (negative for OX-19 and OX-2). * **Drug of Choice:** **Doxycycline** is the gold standard treatment for all rickettsial infections, including Scrub typhus. * **Reservoir:** The mite acts as both the vector and the reservoir (via transovarial transmission).

Q: Chlamydial infection is associated with which of the following?

All of the above. **Explanation:** The genus *Chlamydia* consists of obligate intracellular bacteria that cause a wide spectrum of human diseases. The correct answer is **"All of the above"** because different species and serovars of Chlamydia are implicated in each of these conditions. 1. **Coronary Heart Disease (CHD):** *Chlamydia pneumoniae* has been linked to atherosclerosis and CHD. Seroepidemiological studies and the detection of the organism within atherosclerotic plaques suggest that chronic inflammation triggered by this bacterium may contribute to the pathogenesis of coronary artery disease. 2. **Lymphogranuloma Venereum (LGV):** This is a sexually transmitted infection caused by *Chlamydia trachomatis* **serovars L1, L2, and L3**. It is characterized by primary genital lesions followed by painful regional lymphadenopathy (buboes) and potential proctitis. 3. **Ophthalmia Neonatorum:** *Chlamydia trachomatis* (**serovars D-K**) is a leading cause of neonatal conjunctivitis, transmitted from the mother’s infected birth canal. It typically presents 5–14 days after birth, later than gonococcal ophthalmia. **High-Yield Clinical Pearls for NEET-PG:** * **Trachoma:** Caused by *C. trachomatis* serovars **A, B, Ba, and C** (leading cause of preventable blindness). * **Inclusion Conjunctivitis/Urethritis:** Caused by serovars **D-K**. * **Diagnosis:** **Nucleic Acid Amplification Test (NAAT)** is the gold standard. * **Microscopy:** Look for **Halberstaedter-Prowazek (HP) inclusion bodies** (intracytoplasmic) on Giemsa stain. * **Treatment:** Azithromycin (single dose) or Doxycycline (7 days) are the drugs of choice. For neonatal ophthalmia, oral Erythromycin is preferred to prevent subsequent pneumonia.

Q: Which of the following organisms is catalase positive, coagulase positive, non-motile, facultative anaerobe, and does not form spores?

Staphylococcus aureus. ### Explanation The question describes the classic biochemical and morphological profile of **Staphylococcus aureus**. **1. Why Staphylococcus aureus is correct:** * **Catalase Positive:** Staphylococci produce catalase, which differentiates them from Streptococci. * **Coagulase Positive:** This is the definitive test for *S. aureus*, distinguishing it from Coagulase-Negative Staphylococci (CoNS) like *S. epidermidis*. * **Morphology & Physiology:** It is a Gram-positive coccus (non-motile, non-spore-forming) and a facultative anaerobe, meaning it can grow in both aerobic and anaerobic conditions. **2. Why the other options are incorrect:** * **Streptococcus viridans & Pneumococcus (S. pneumoniae):** Both belong to the *Streptococcus* genus, which is characteristically **catalase-negative**. Furthermore, *S. pneumoniae* is bile soluble and optochin sensitive, unlike Staphylococci. * **Pseudomonas aeruginosa:** This is a Gram-negative bacilli. While it is catalase positive, it is an **obligate aerobe** (not facultative) and is highly **motile** via polar flagella. **3. NEET-PG High-Yield Pearls:** * **Gold Standard Test:** The **tube coagulase test** detects "free coagulase" and is the definitive test for *S. aureus*. * **Culture:** On Blood Agar, it typically shows **beta-hemolysis**. On Mannitol Salt Agar (MSA), it ferments mannitol, turning the medium yellow. * **Protein A:** A key virulence factor of *S. aureus* that binds to the Fc portion of IgG, inhibiting phagocytosis. * **Common Infections:** It is the most common cause of osteomyelitis, septic arthritis (in general population), and acute bacterial endocarditis.

Q: Which E. coli pathotype is depicted in the image?

All of the above. ***All of the above*** - **ETEC**, **EPEC**, and **EHEC** are all recognized **diarrheogenic E. coli pathotypes** that cause distinct forms of gastrointestinal illness. - Each pathotype has unique **virulence mechanisms** and **clinical presentations**, making them all legitimate E. coli variants associated with diarrheal diseases. *Enterotoxigenic E. coli (ETEC)* - Causes **traveler's diarrhea** through production of **heat-labile (LT)** and **heat-stable (ST) toxins** that increase cAMP/cGMP levels. - Results in **watery diarrhea** without invasion or inflammation of intestinal mucosa. *Enteropathogenic E. coli (EPEC)* - Causes **infantile diarrhea** through **attaching and effacing (A/E) lesions** that destroy intestinal microvilli. - Leads to **watery diarrhea** in children under 2 years, particularly in developing countries. *Enterohemorrhagic E. coli (EHEC)* - Produces **Shiga toxins (Stx1/Stx2)** causing **bloody diarrhea** and potential **hemolytic uremic syndrome (HUS)**. - Associated with **hemorrhagic colitis** and severe complications including kidney failure and neurological symptoms.

Q: Which of the following is NOT true about ASO titre?

Is a major Jones criterion.. **Explanation:** The ASO (Antistreptolysin O) titre is a serological marker used to detect a recent infection with Group A Streptococcus (GAS). **Why Option B is the correct answer (The "False" statement):** In the **Revised Jones Criteria** for Acute Rheumatic Fever (ARF), an elevated ASO titre (or other streptococcal antibodies) is considered **evidence of a preceding streptococcal infection**, which is a mandatory requirement for diagnosis. However, it is **not** a Major or Minor criterion. Major criteria include Carditis, Polyarthritis, Chorea, Erythema marginatum, and Subcutaneous nodules (mnemonic: **J♥NES**). **Analysis of other options:** * **Option A:** ASO titres can be positive in normal individuals (healthy carriers) because the "normal" range depends on age and geographical prevalence of streptococcal infections. * **Option C:** ASO titres may be negative in **Post-Streptococcal Glomerulonephritis (PSGN)**, especially if the preceding infection was a skin infection (impetigo). In skin infections, the ASO response is poor because cholesterol in the skin inhibits Streptolysin O. Anti-DNase B is a better marker for skin-related PSGN. * **Option D:** ASO titres peak 3–5 weeks after infection. If a patient presents with isolated carditis or chorea months after the initial infection, the ASO titre may have already declined to normal levels. **NEET-PG High-Yield Pearls:** * **Standard Value:** A titre >200 units is generally considered significant in adults. * **Best marker for Pyoderma/Impetigo:** Anti-DNase B (ASO is unreliable here). * **Mechanism:** Streptolysin O is oxygen-labile and highly antigenic; ASO antibodies neutralize its hemolytic activity. * **False Positives:** Can occur in liver disease (due to hypercholesterolemia) and bacterial contamination of serum.

Q: Hansen's bacillus is cultured in which of the following?

Foot pad of mice. **Explanation:** **Hansen’s bacillus (*Mycobacterium leprae*)**, the causative agent of leprosy, is unique because it is an **obligate intracellular pathogen** that has never been grown on artificial (in vitro) culture media. This is due to its massive reductive evolution and loss of essential metabolic genes. 1. **Why Option C is correct:** Since *M. leprae* cannot grow on agar, researchers use **animal models** for cultivation. The **mouse footpad** (Shepard’s method) is the standard model because the bacteria prefer cooler temperatures (approx. 30°C) found in the extremities. For large-scale production of the bacilli (e.g., for lepromin antigen), the **nine-banded armadillo** is used as it develops systemic infection. 2. **Why other options are incorrect:** * **Option A (LJ Medium):** Lowenstein-Jensen medium is the classic egg-based medium used for *Mycobacterium tuberculosis*, but it does not support the growth of *M. leprae*. * **Option B (RCM Medium):** Robertson’s Cooked Meat medium is used for the cultivation of **anaerobes** (e.g., *Clostridium* species). * **Option C (Sabouraud’s Agar):** SDA is a selective medium used for the cultivation of **fungi**. **High-Yield Clinical Pearls for NEET-PG:** * **Generation Time:** *M. leprae* is the slowest-growing human pathogen, with a doubling time of approximately **12–13 days**. * **Staining:** It is Acid-Fast (Ziehl-Neelsen stain) but **less acid-fast** than *M. tuberculosis*; hence, 5% sulfuric acid is used for decolonization instead of 20%. * **Target Cells:** It has a specific tropism for **Schwann cells** and macrophages. * **Viability:** The **Morphologic Index (MI)** measures the percentage of uniformly stained (viable) bacilli in a smear, used to monitor treatment response.

Question 1

Which of the following is NOT true about Helicobacter pylori?

Accepted Answer

The Cag-A gene is not associated with an increased risk of duodenal ulcers.

Answer

It splits urea to produce ammonia for survival.

Answer

It is associated with an increased risk of gastric cancer.

Answer

It presents as Gram-negative curved rods.

Question 2

Q-fever is caused by which bacterium?

Accepted Answer

Coxiella burnetii

Answer

Rochaemelia Quintana

Answer

Mycoplasma hominis

Answer

None of the above

Question 3

Neisseria infection is associated with which of the following conditions?

Accepted Answer

Deficiency of late complements

Answer

Deficiency of early complements

Answer

There is no such association

Answer

Any complement deficiency can be associated

Question 4

Orientia Tsutsugamushi causes which of the following diseases?

Accepted Answer

Scrub typhus

Answer

Epidemic typhus

Answer

Endemic typhus

Answer

Q fever

Question 5

Chlamydial infection is associated with which of the following?

Accepted Answer

All of the above

Answer

Coronary heart disease

Answer

Lymphogranuloma venereum (LGV)

Answer

Ophthalmia neonatorum

Question 6

Which of the following organisms is catalase positive, coagulase positive, non-motile, facultative anaerobe, and does not form spores?

Accepted Answer

Staphylococcus aureus

Answer

Streptococcus viridians

Answer

Pneumococcus

Answer

Pseudomonas aeruginosa

Question 7

Which E. coli pathotype is depicted in the image?

Accepted Answer

All of the above

Answer

Enterotoxigenic E. coli (ETEC)

Answer

Enteropathogenic E. coli (EPEC)

Answer

Enterohemorrhagic E. coli (EHEC)

Question 8

Which of the following is NOT true about ASO titre?

Accepted Answer

Is a major Jones criterion.

Answer

May be positive in normal individuals.

Answer

May be negative in post-streptococcal glomerulonephritis.

Answer

May not be elevated in the presence of carditis.

Question 9

Which one of the following organisms is the most frequent cause of acute pyogenic meningitis in adults?

Accepted Answer

Streptococcus pneumoniae

Answer

Neisseria meningitidis

Answer

Haemophilus influenzae

Answer

Listeria monocytogenes

Question 10

Hansen's bacillus is cultured in which of the following?

Accepted Answer

Foot pad of mice

Answer

LJ medium

Answer

Robertson’s cooked meat medium

Answer

Sabouraud’s agar

Bacteriology — MCQs

Bacteriology — MCQs

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