Bacteriology Practice Questions

Q: Which of the following Clostridia species are saccharolytic?

Sporogenes. **Explanation:** Clostridia are classified based on their metabolic activity into **Saccharolytic** (carbohydrate-fermenting) and **Proteolytic** (protein-digesting) groups. **The Correct Answer: B. Sporogenes** *Clostridium sporogenes* is primarily a **proteolytic** organism. It is often referred to as the "non-toxigenic counterpart" of *C. botulinum*. In the laboratory, it is characterized by its ability to digest cooked meat (turning it black with a foul odor) rather than fermenting sugars. *Note: There appears to be a discrepancy in the provided key. In standard microbiological classification (e.g., Ananthanarayan), C. welchii (perfringens), C. septicum, and C. oedematiens are predominantly **saccharolytic**, while C. sporogenes and C. tetani are predominantly **proteolytic**. If the question asks for a saccharolytic species, A, C, and D are correct; if it asks for a proteolytic species, B is the correct answer.* **Analysis of Other Options:** * **A. Welchii (C. perfringens):** Highly saccharolytic. It produces "stormy fermentation" in litmus milk due to vigorous acid and gas production from lactose. * **C. Septicum:** Strongly saccharolytic; it ferments glucose, lactose, and maltose. It is a common cause of gas gangrene in patients with underlying malignancies. * **D. Oedematiens (C. novyi):** Saccharolytic; it ferments glucose and maltose (though not lactose). **High-Yield NEET-PG Pearls:** 1. **Stormy Fermentation:** Pathognomonic for *C. perfringens*. 2. **Nagler’s Reaction:** Used to detect Lecithinase (Alpha-toxin) produced by *C. perfringens*. 3. **Cooked Meat Medium (RCM):** Saccharolytic species turn the meat **pink**, while proteolytic species turn the meat **black** and produce a putrid smell. 4. **C. septicum** is strongly associated with **colonic carcinoma**.

Q: All of the following are virulence factors of pertussis, except?

Capsule. **Explanation:** The correct answer is **Capsule**. While *Bordetella pertussis* is a Gram-negative coccobacillus, it is generally considered **non-capsulated**. Its pathogenicity relies on a complex array of toxins and adhesins rather than a polysaccharide capsule. **Why other options are incorrect (Virulence Factors of *B. pertussis*):** * **Tracheal Cytotoxin (TCT):** A peptidoglycan fragment that specifically destroys ciliated epithelial cells and inhibits DNA synthesis, leading to the characteristic failure of the "mucociliary escalator." * **Pertussis Toxin (PT):** An A-B toxin that causes ADP-ribosylation of Gi proteins. This leads to increased cAMP levels, resulting in lymphocytosis (a classic diagnostic clue), histamine sensitization, and insulin secretion. * **Pertactin:** An outer membrane protein that acts as an **adhesin**, facilitating the attachment of the bacteria to the respiratory epithelium. It is a key component of the acellular pertussis (aP) vaccine. **High-Yield Clinical Pearls for NEET-PG:** * **Filamentous Hemagglutinin (FHA):** Another critical adhesin required for colonization. * **Lymphocytosis:** Unlike most bacterial infections that cause neutrophilia, Pertussis causes a marked absolute lymphocytosis due to the Pertussis toxin blocking lymphocyte entry into lymph nodes. * **Gold Standard Diagnosis:** Culture on **Regan-Lowe medium** or **Bordet-Gengou (potato-blood-glycerol) agar** (showing "mercury drop" or "bisected pearl" colonies). * **Vaccine:** The acellular vaccine (aP) contains PT, FHA, and Pertactin, which are less reactogenic than the whole-cell vaccine.

Q: A patient with alkaline urine which is cloudy with plenty of pus cells is suffering from which type of infection?

Proteus. ### Explanation The correct answer is **Proteus**. **Why Proteus is the correct answer:** The hallmark of a *Proteus* species infection (most commonly *P. mirabilis*) is the production of the enzyme **Urease**. This enzyme hydrolyzes urea into ammonia and carbon dioxide. The release of ammonia increases the pH of the urine, making it **alkaline** (pH > 7.0). Alkaline urine reduces the solubility of magnesium and phosphate, leading to the formation of **Struvite stones** (Magnesium Ammonium Phosphate) and "cloudy" urine due to crystalluria and pyuria (pus cells). **Why other options are incorrect:** * **E. coli:** This is the most common cause of UTIs. However, *E. coli* does not produce urease; therefore, the urine remains **acidic** or neutral. It does not typically cause the marked alkalinity seen with *Proteus*. * **Tuberculosis (Renal TB):** Renal TB is classically associated with **"Sterile Pyuria"**—the presence of pus cells in acidic urine with negative routine bacterial cultures. It does not cause alkaline urine. **High-Yield Clinical Pearls for NEET-PG:** * **Staghorn Calculi:** *Proteus* is the most common organism associated with large staghorn stones composed of Struvite. * **Motility:** *Proteus* exhibits characteristic **"Swarming growth"** on blood agar due to its peritrichous flagella. * **Dienes Phenomenon:** A method used to differentiate two strains of *Proteus* based on the formation of a visible line of inhibition where two different swarming strains meet. * **Weil-Felix Reaction:** Certain *Proteus* antigens (OX19, OX2, OXK) cross-react with Rickettsial antibodies, a classic (though less specific) diagnostic test.

Q: Which mycobacteria produces an exotoxin?

M. ulcerans. **Explanation:** The correct answer is **C. M. ulcerans**. **1. Why M. ulcerans is correct:** *Mycobacterium ulcerans* is unique among mycobacteria because it is the only species known to produce a potent exotoxin called **Mycolactone**. This lipid-like toxin is polyketide-derived and possesses potent **necrotizing and immunosuppressive** properties. It causes extensive destruction of the skin and soft tissue by inducing apoptosis in mammalian cells. Clinically, this results in **Buruli ulcer**, characterized by large, painless, necrotic ulcers with deeply undermined edges. **2. Why the other options are incorrect:** * **M. tuberculosis (A) and M. bovis (D):** These are members of the *M. tuberculosis* complex. Their pathogenicity is primarily due to their ability to survive intracellularly within macrophages and the resulting delayed-type hypersensitivity (Type IV) immune response. They do **not** produce exotoxins. * **M. marinum (B):** This is a photochromogen associated with "fish tank granuloma." While it causes skin lesions, its pathogenesis involves intracellular growth and granuloma formation rather than toxin production. **3. High-Yield Clinical Pearls for NEET-PG:** * **Mycolactone:** Remember this specific name; it is the key virulence factor for *M. ulcerans*. * **Buruli Ulcer:** It is the third most common mycobacterial disease in immunocompetent hosts (after TB and Leprosy). * **Undermined Edges:** A classic descriptive term for the ulcers produced by *M. ulcerans*. * **Temperature Sensitivity:** Like *M. leprae*, *M. ulcerans* prefers cooler temperatures (28–33°C), which is why it primarily affects the skin of the extremities.

Q: Which of the following bacteria are bounded by a membrane containing sterols?

Mycoplasma. **Explanation:** The correct answer is **Mycoplasma**. **1. Why Mycoplasma is correct:** The defining characteristic of the genus *Mycoplasma* (and *Ureaplasma*) is the **complete absence of a peptidoglycan cell wall**. To compensate for the lack of structural rigidity provided by a cell wall, their cell membrane is uniquely enriched with **sterols** (cholesterol). These sterols provide osmotic stability and mechanical strength, preventing the bacteria from bursting. It is important to note that *Mycoplasma* cannot synthesize sterols themselves; they must acquire them from the external environment (e.g., serum-enriched growth media). **2. Why the other options are incorrect:** * **Klebsiella (A) & Staphylococcus (B):** These are typical Gram-negative and Gram-positive bacteria, respectively. They possess a rigid cell wall. Their cytoplasmic membranes consist of phospholipids and proteins but **do not contain sterols**. * **Mycobacteria (C):** While *Mycobacteria* have a unique, complex cell wall rich in **mycolic acids** (long-chain fatty acids), their underlying plasma membrane lacks sterols. **3. NEET-PG High-Yield Clinical Pearls:** * **Antibiotic Resistance:** Because they lack a cell wall, *Mycoplasma* are **innately resistant** to all beta-lactam antibiotics (Penicillins, Cephalosporins) which target cell wall synthesis. * **Pleomorphism:** The lack of a cell wall makes them highly pleomorphic (variable shapes) and allows them to pass through filters (0.45 μm) that typically trap other bacteria. * **Gram Staining:** They do not stain with Gram stain; **Giemsa or Wright stains** are preferred. * **Culture:** They produce characteristic **"fried-egg" colonies** on specialized media (e.g., PPLO agar/Eaton’s agar).

Question 1

Which of the following Clostridia species are saccharolytic?

Accepted Answer

Sporogenes

Answer

Welchii

Answer

Septicum

Answer

Oedematiens

Question 2

All of the following are virulence factors of pertussis, except?

Accepted Answer

Capsule

Answer

Tracheal cytotoxin

Answer

Pertussis toxin

Answer

Pertactin

Question 3

A 12-year-old boy presents with a productive cough and large volumes of foul-smelling sputum. Three years prior, he was diagnosed with pancreatic insufficiency, evidenced by recurrent gastrointestinal symptoms of steatorrhea. Sputum culture reveals colorless, oxidase-positive colonies with a fruity aroma. The function of which of the following proteins is most likely inhibited by the bacteria responsible for this boy's infection?

Accepted Answer

A GTP-binding protein involved in the elongation step of protein synthesis

Answer

A CFTR protein lacking a phenylalanine at position 508 in exon 10

Answer

A GTP-binding protein coupled with α2-adrenergic receptors

Answer

A GTP-binding protein coupled with β-adrenergic receptors

Question 4

A patient with alkaline urine which is cloudy with plenty of pus cells is suffering from which type of infection?

Accepted Answer

Proteus

Answer

E. coli

Answer

Tuberculosis

Answer

None of the above

Question 5

Rice watery stool is indicative of which organism?

Accepted Answer

Vibrio cholerae O1

Answer

Vibrio cholerae O139

Answer

Vibrio vulnificus

Answer

Shigella

Question 6

All of the following are TRUE about ASO titre, EXCEPT?

Accepted Answer

ASO titre is included in the major criteria of the Jones criteria.

Answer

ASO titre can be increased in school children.

Answer

ASO titre may be negative in post-streptococcal glomerulonephritis.

Answer

ASO titre may not be elevated in 20% of cases of carditis.

Question 7

Which mycobacteria produces an exotoxin?

Accepted Answer

M. ulcerans

Answer

M. tuberculosis

Answer

M. ajarinum

Answer

M. bovis

Question 8

Which of the following bacteria are bounded by a membrane containing sterols?

Accepted Answer

Mycoplasma

Answer

Klebsiella

Answer

Staphylococcus

Answer

Mycobacteria

Question 9

Which of the following is TRUE regarding Neisseria meningitidis infection?

Accepted Answer

It is the most common cause of meningitis in children.

Answer

All strains are uniformly sensitive to sulfonamides.

Answer

Vaccines are contraindicated in immunosuppressed individuals.

Answer

In India, serotype B is the most common cause.

Question 10

A 22-year-old software engineer was brought in an unconscious state to the casualty. Clinical examination revealed features suggestive of shock, disseminated intravascular coagulation (DIC), and multisystem failure. Cerebrospinal fluid (CSF) and petechial rashes yielded gram-negative diplococci, which subsequently grew on modified Thayer-Martin medium. This isolation is known to be associated with?

Accepted Answer

Waterhouse-Friderichsen syndrome

Answer

Fitz-Hugh-Curtis syndrome

Answer

Job's syndrome

Answer

Toxic shock syndrome

Bacteriology — MCQs

Bacteriology — MCQs

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