Bacteriology Practice Questions

Q: Which of the following is true about H. pylori?

Produces Vacuolating cytotoxin. **Explanation:** *Helicobacter pylori* is a microaerophilic, Gram-negative spiral bacterium primarily associated with peptic ulcer disease and gastric carcinoma. **Why Option A is Correct:** *H. pylori* possesses several virulence factors, the most significant being the **Vacuolating cytotoxin (VacA)** and the **Cytotoxin-associated gene A (CagA)**. VacA induces the formation of large cytoplasmic vacuoles in gastric epithelial cells, leading to cell death and tissue damage. Strains expressing both VacA and CagA (Type I strains) are more strongly associated with severe inflammation and malignancy. **Why Other Options are Incorrect:** * **Option B:** While Type I strains are more virulent, **Anti-CagA antibodies** (not antiurease) are the specific markers used to identify these aggressive strains. Urease is produced by almost all *H. pylori* strains to neutralize gastric acid; therefore, antiurease antibodies lack specificity for Type I. * **Option C:** *H. pylori* specifically colonizes the **gastric mucosa** (primarily the antrum). It does not inhabit the jejunum, as it requires the specific pH environment and mucosal receptors found in the stomach. * **Option D:** Treatment involves **Triple Therapy** (Clarithromycin, Amoxicillin/Metronidazole, and a Proton Pump Inhibitor). Al(OH)₃ is an antacid used for symptomatic relief but has no curative or antimicrobial effect against the infection. **High-Yield Clinical Pearls for NEET-PG:** * **Urease Breath Test:** The non-invasive "Gold Standard" for monitoring treatment success. * **Biopsy Urease Test (RUT):** A rapid invasive test (color change from yellow to pink). * **MALToma:** *H. pylori* is a Class I carcinogen; its eradication can lead to the regression of low-grade gastric MALT lymphoma. * **Culture:** Uses Skirrow’s medium or Chocolate agar.

Q: 'Bull neck' in Diphtheria is due to which of the following?

Lymphadenopathy. **Explanation:** The hallmark clinical feature of **Diphtheria** (caused by *Corynebacterium diphtheriae*) is the formation of a greyish-white pseudomembrane. The characteristic **'Bull neck' appearance** is primarily due to massive **cervical lymphadenopathy** and associated periadenitis (inflammation of the tissues surrounding the lymph nodes) and edema in the soft tissues of the neck. **Analysis of Options:** * **D. Lymphadenopathy (Correct):** The diphtheria toxin causes local tissue destruction and intense inflammation. This leads to significant enlargement of the cervical lymph nodes. When combined with surrounding soft tissue edema, it obliterates the angle of the jaw, resulting in the "Bull neck" deformity. * **A. Retropharyngeal abscess:** While this can cause neck swelling, it is typically a complication of pyogenic infections (like *S. aureus*) or TB (Pott’s spine), not the primary cause of the classic diphtheritic bull neck. * **B. Laryngeal edema:** This occurs in laryngeal diphtheria and leads to airway obstruction and stridor, but it does not manifest as external "bull neck" swelling. * **C. Cellulitis:** Although there is inflammation of the subcutaneous tissues (periadenitis), the primary pathological driver and clinical descriptor for this specific sign is the profound lymph node involvement. **High-Yield Clinical Pearls for NEET-PG:** * **Schick Test:** Used to demonstrate immunity/susceptibility to diphtheria. * **Culture Media:** Loeffler’s Serum Slope (rapid growth) and Potassium Tellurite agar (black colonies). * **Microscopy:** Gram-positive bacilli showing **Chinese letter pattern** (cuneiform) and **Volutin/Metachromatic granules** (Albert’s stain). * **Virulence:** Mediated by an exotoxin (fragment A inhibits Protein Synthesis via EF-2). * **Complications:** Myocarditis (most common cause of death) and neurological deficits (palatal paralysis).

Q: Stalactite growth in a ghee broth culture is characteristic of which bacterium?

Yersinia. **Explanation** The correct answer is **Yersinia pestis**. **1. Why Yersinia is Correct:** *Yersinia pestis*, the causative agent of plague, exhibits a unique growth pattern in liquid media containing a layer of oil or fat. When grown in **Ghee broth** (clarified butter) or broth with oil, the bacteria grow as delicate, hanging filaments or "icicle-like" structures extending downwards from the surface. This is known as **Stalactite growth**. This occurs because the organism is non-motile and prefers the interface between the lipid and the broth for optimal growth. **2. Why Other Options are Incorrect:** * **Bacillus:** *Bacillus anthracis* typically shows a "Medusa head" appearance on agar plates and a "inverted fir tree" appearance in gelatin stabs, but not stalactite growth. * **Legionella:** This is a fastidious organism that requires buffered charcoal yeast extract (BCYE) agar supplemented with L-cysteine and iron. It does not show specific growth patterns in ghee broth. * **Leptospira:** These are spirochetes that require specialized media like EMJH (Ellinghausen-McCullough-Johnson-Harris). They are highly motile and do not form stalactites. **3. High-Yield Clinical Pearls for NEET-PG:** * **Safety Note:** *Y. pestis* is a Tier 1 Select Agent; laboratory diagnosis requires extreme caution (BSL-3). * **Microscopy:** Shows characteristic **"Safety-pin" appearance** (bipolar staining) with Wayson or Giemsa stain. * **Culture:** On blood agar, it forms "fried egg" colonies. * **Vector:** Transmitted by the rat flea (*Xenopsylla cheopis*). * **Virulence Factor:** F1 antigen (capsular) and V/W antigens.

Q: What is the most common sensitive causative organism for Traveller's diarrhoea?

E. coli. **Explanation:** **Traveller’s Diarrhoea (TD)** is defined as the passage of three or more unformed stools in a 24-hour period, often accompanied by abdominal cramps, nausea, or bloating, occurring in individuals traveling from developed to developing regions. **Why E. coli is correct:** The most common causative agent worldwide is **Enterotoxigenic *Escherichia coli* (ETEC)**. It accounts for approximately 30–50% of cases. ETEC colonizes the small intestine and produces two types of enterotoxins: **Heat-labile (LT)**, which increases cAMP, and **Heat-stable (ST)**, which increases cGMP. Both lead to the hypersecretion of water and electrolytes, resulting in watery diarrhea. **Analysis of Incorrect Options:** * **Shigella:** While a common cause of bacterial dysentery (bloody diarrhea), it is less frequent than ETEC in travelers. It typically presents with high fever and mucoid stools. * **Norwalk virus (Norovirus):** This is the leading cause of epidemic gastroenteritis and is frequently associated with **cruise ships** and institutional outbreaks, but it ranks behind ETEC for general traveler’s diarrhea. * **Rotavirus:** This is the most common cause of severe diarrhea in **infants and young children** globally, but it is not the primary cause of traveler's diarrhea in adults. **NEET-PG High-Yield Pearls:** * **Most common bacterial cause:** ETEC (Enterotoxigenic *E. coli*). * **Most common parasite:** *Giardia lamblia*. * **Drug of choice (Prophylaxis):** Fluoroquinolones (e.g., Ciprofloxacin) or Rifaximin. * **Mechanism of ETEC LT toxin:** Similar to Cholera toxin (ADP-ribosylation of Gs protein → ↑cAMP). * **Clinical Tip:** If the question specifies "bloody diarrhea in a traveler," consider *Campylobacter* or *Shigella*.

Q: A 14-year-old girl with cystic fibrosis is admitted to the hospital with fever and shortness of breath, diagnosed with pneumonia. During a respiratory therapy session, she coughs up mucus that is distinctly greenish in color. Which of the following organisms should be suspected?

Pseudomonas aeruginosa. **Explanation:** The correct answer is **Pseudomonas aeruginosa**. This case highlights a classic clinical presentation involving a patient with **Cystic Fibrosis (CF)** and the production of **greenish sputum**, both of which are hallmark associations with *Pseudomonas*. **Why Pseudomonas aeruginosa is correct:** * **Cystic Fibrosis Link:** *P. aeruginosa* is the most common cause of chronic pulmonary infections in CF patients due to its ability to form thick biofilms in the viscous mucus of the lungs. * **Pigment Production:** The distinct green color of the sputum is due to the production of water-soluble pigments: **Pyocyanin** (blue-green) and **Pyoverdin** (yellow-green/fluorescent). These pigments also contribute to the organism's virulence by generating reactive oxygen species. **Why other options are incorrect:** * **A. Klebsiella pneumoniae:** Typically causes "currant jelly" sputum (thick and blood-tinged) and is more common in alcoholics or diabetics. * **B. Mycoplasma pneumoniae:** Causes "walking pneumonia" characterized by a dry, non-productive cough and interstitial infiltrates on X-ray, rather than green purulent sputum. * **C. Pneumocystis carinii (jirovecii):** An opportunistic fungus seen in immunocompromised patients (like HIV/AIDS). It typically presents with a non-productive cough and ground-glass opacities. **High-Yield Clinical Pearls for NEET-PG:** * **Culture Characteristics:** *Pseudomonas* is a Gram-negative, non-fermenting motile rod that produces a characteristic **fruity/grape-like odor** on culture. * **Oxidase Test:** It is **Oxidase positive**, which helps differentiate it from members of the Enterobacteriaceae family. * **Virulence Factor:** Exotoxin A (inhibits EF-2, similar to Diphtheria toxin). * **Ecthyma Gangrenosum:** A characteristic skin lesion (necrotic eschar) seen in *Pseudomonas* septicemia.

Q: Absence of Vi-antibody in a typhoid patient indicates what regarding prognosis?

Bad prognosis. **Explanation:** The **Vi-antigen** (Virulence antigen) is a surface polysaccharide capsular antigen found in *Salmonella Typhi*. Its primary role is to mask the O-antigen, thereby protecting the bacterium from phagocytosis and complement-mediated lysis. 1. **Why it indicates a Bad Prognosis:** In the context of an active infection, the production of Vi-antibodies is a protective immune response. These antibodies assist in opsonization and the killing of the bacteria. If a patient fails to produce Vi-antibodies during the course of the disease, it suggests an inadequate immune response against the virulence factor of the pathogen, leading to uncontrolled bacterial multiplication and a higher risk of complications or a fatal outcome. Hence, the absence of Vi-antibody in a clinically diagnosed typhoid patient signifies a **bad prognosis**. 2. **Analysis of Incorrect Options:** * **Option A:** A good prognosis would typically be associated with a robust antibody response (High titers of Anti-O and Anti-H) and clinical improvement. * **Option C:** Vi-antibody status is a recognized prognostic marker; therefore, it is directly related to the clinical outlook. * **Option D:** The Widal test measures antibodies against O and H antigens, not Vi. A separate agglutination test is required for Vi-antibodies. **High-Yield Clinical Pearls for NEET-PG:** * **Carrier Status:** The most common use of the Vi-antibody test is for **screening typhoid carriers**. Persistent high titers of Vi-antibodies (even in the absence of symptoms) indicate a chronic carrier state (usually in the gallbladder). * **Vaccination:** The Vi-capsular polysaccharide vaccine is a common parenteral vaccine used for typhoid prophylaxis. * **Disappearance:** Vi-antibodies disappear early during convalescence; their persistence is the hallmark of the carrier state.

Q: A boy presented with multiple non-suppurative osteomyelitic dactylitis with sickle cell anaemia. What is the likely causative organism?

Salmonella typhi. **Explanation:** In patients with **Sickle Cell Anemia (SCA)**, there is a unique predisposition to osteomyelitis. While **Staphylococcus aureus** remains the most common cause of osteomyelitis in the general pediatric population, **Salmonella species** (specifically *S. typhi* and *S. typhimurium*) are the most common pathogens isolated in children with SCA. **Why Salmonella?** 1. **Hyposplenism:** Functional asplenia in SCA reduces the clearance of encapsulated organisms. 2. **Bowel Infarction:** Micro-infarctions in the gut mucosa allow *Salmonella* to translocate into the bloodstream. 3. **Bone Infarction:** Vaso-occlusive crises create areas of ischemic bone (infarcts), which act as a nidus for hematogenous seeding of *Salmonella*. 4. **Dactylitis (Hand-Foot Syndrome):** This is often the first manifestation of SCA in infants, presenting as symmetrical, non-suppurative swelling of the short tubular bones of the hands and feet. **Analysis of Incorrect Options:** * **B. S. aureus:** Although it is the #1 cause of osteomyelitis in healthy children, it is statistically surpassed by *Salmonella* in the specific context of Sickle Cell Anemia. * **C. H. influenzae:** Previously a common cause of septic arthritis/osteomyelitis in children, its incidence has plummeted due to the Hib vaccine. * **D. Peptococcus magnus:** This is an anaerobic organism occasionally associated with prosthetic joint infections or chronic osteomyelitis, but it is not a primary pathogen in SCA dactylitis. **Clinical Pearls for NEET-PG:** * **Radiology:** In *Salmonella* osteomyelitis, look for **diaphyseal involvement** and extensive involucrum formation. * **Dactylitis vs. Osteomyelitis:** Dactylitis is often due to infarction (ischemia), but if it presents with fever and systemic symptoms in an SCA patient, *Salmonella* must be ruled out. * **Treatment:** Third-generation cephalosporins (Ceftriaxone) or Fluoroquinolones are preferred.

Q: A 40-year-old woman presented with complaints of profuse vaginal discharge. There was no discharge from the cervix on speculum examination. The microscopy image of the vaginal discharge is shown above. Which of the following is NOT a diagnostic criterion for bacterial vaginosis?

Abundance of polymorphs. ***Abundance of polymorphs*** - Bacterial vaginosis is a **non-inflammatory condition**, characterized by the **absence of polymorphonuclear leukocytes (PMNs)** on microscopy. - The presence of abundant **polymorphs** would suggest an **inflammatory vaginitis** like trichomoniasis or cervicitis, not bacterial vaginosis. *Abundance of gram-variable coccobacilli* - **Gardnerella vaginalis** appears as gram-variable coccobacilli and is a key finding in bacterial vaginosis. - These organisms are seen adhering to **vaginal epithelial cells**, forming the characteristic clue cells. *Absence of lactobacilli* - Normal vaginal flora is dominated by **Lactobacillus species**, which maintain acidic pH and prevent pathogen overgrowth. - In bacterial vaginosis, there is a marked **reduction or absence of lactobacilli**, leading to pH elevation above 4.5. *Presence of clue cells* - **Clue cells** are vaginal epithelial cells covered with gram-variable coccobacilli, giving them a stippled appearance. - They are pathognomonic for bacterial vaginosis and represent one of the **Amsel criteria** for diagnosis.

Question 1

Which of the following is true about H. pylori?

Accepted Answer

Produces Vacuolating cytotoxin

Answer

Antiurease antibody detection is specific for type I strains

Answer

Inhabits the jejunum

Answer

Treatment involves Al(OH)2

Question 2

'Bull neck' in Diphtheria is due to which of the following?

Accepted Answer

Lymphadenopathy

Answer

Retropharyngeal abscess

Answer

Laryngeal edema

Answer

Cellulitis

Question 3

Bilateral tonsillectomy is performed on an otherwise healthy 11-year-old female with recurrent upper respiratory tract infections. On pathological examination of the tonsils, numerous small, yellow granules are noted. A granule crushed between two slides reveals a dense, gram-positive center and numerous branching filaments at the periphery. The granules are most likely composed of which of the following organisms?

Accepted Answer

Actinomyces israelii

Answer

Aspergillus fumigatus

Answer

Blastomyces dermatitidis

Answer

Candida albicans

Question 4

Stalactite growth in a ghee broth culture is characteristic of which bacterium?

Accepted Answer

Yersinia

Answer

Bacillus

Answer

Legionella

Answer

Leptospira

Question 5

What is the most common sensitive causative organism for Traveller's diarrhoea?

Accepted Answer

E. coli

Answer

Shigella

Answer

Norwalk virus

Answer

Rotavirus

Question 6

A 14-year-old girl with cystic fibrosis is admitted to the hospital with fever and shortness of breath, diagnosed with pneumonia. During a respiratory therapy session, she coughs up mucus that is distinctly greenish in color. Which of the following organisms should be suspected?

Accepted Answer

Pseudomonas aeruginosa

Answer

Klebsiella pneumoniae

Answer

Mycoplasma pneumoniae

Answer

Pneumocystis carinii

Question 7

A 68-year-old male patient with 3rd-degree burn wounds affecting 25% TBSA was admitted to the hospital and treated with intravenous fluids and analgesics. After 8 days of hospital admission, the patient develops fever and leukocytosis. On examination, there is erythema and swelling around the wound. Exudate from this wound is positive for gram-negative, oxidase-positive bacilli which do not ferment sugars. What is the drug of choice for this infection?

Accepted Answer

Cefepime

Answer

Amoxicillin-clavulanic acid

Answer

Ceftriaxone

Answer

Streptomycin

Question 8

Absence of Vi-antibody in a typhoid patient indicates what regarding prognosis?

Accepted Answer

Bad prognosis

Answer

Good prognosis

Answer

No relation with prognosis

Answer

Indicates Widal negative

Question 9

A boy presented with multiple non-suppurative osteomyelitic dactylitis with sickle cell anaemia. What is the likely causative organism?

Accepted Answer

Salmonella typhi

Answer

S. aureus

Answer

H. influenzae

Answer

Peptococcus magnus

Question 10

A 40-year-old woman presented with complaints of profuse vaginal discharge. There was no discharge from the cervix on speculum examination. The microscopy image of the vaginal discharge is shown above. Which of the following is NOT a diagnostic criterion for bacterial vaginosis?

Accepted Answer

Abundance of polymorphs

Answer

Abundance of gram-variable coccobacilli

Answer

Absence of lactobacilli

Answer

Presence of clue cells

Bacteriology — MCQs

Bacteriology — MCQs

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