Bacteriology Practice Questions

Q: Which component of tubercle bacilli produces granuloma?

Surface glycolipids. ### Explanation The correct answer is **Surface glycolipids**, specifically **Cord Factor** (Trehalose 6,6'-dimycolate). **1. Why Surface Glycolipids are correct:** The hallmark of *Mycobacterium tuberculosis* infection is the formation of a **granuloma**. This is primarily mediated by **Cord Factor**, a surface glycolipid found in the cell wall of virulent strains. It inhibits neutrophil migration and induces the release of TNF-α (Tumor Necrosis Factor-alpha) from macrophages. TNF-α is the critical cytokine responsible for the recruitment of lymphocytes and macrophages, leading to the formation of organized granulomas and caseating necrosis. Under the microscope, virulent strains grow in parallel "serpentine cords" due to this factor. **2. Why the other options are incorrect:** * **Sulfatides (Sulfolipids):** While also surface glycolipids, their primary role is to **prevent phagosome-lysosome fusion**, allowing the bacilli to survive intracellularly within macrophages. They do not directly initiate granuloma formation. * **Hetero polysaccharide:** These are structural components of the cell wall (like arabinogalactan) but do not possess the specific immunomodulatory properties required to trigger a granulomatous response. * **Sulfadase:** This is not a recognized virulence factor of *M. tuberculosis*. **Clinical Pearls for NEET-PG:** * **Cord Factor:** Responsible for virulence and granuloma formation; causes "serpentine cord" appearance in liquid media. * **Sulfatides:** Responsible for intracellular survival (prevents phagolysosome fusion). * **Wax D:** The component responsible for the **delayed hypersensitivity reaction** (positive Mantoux test) and acts as an adjuvant. * **Lipoarabinomannans (LAM):** Involved in macrophage signaling and inhibiting host immune response.

Q: Which of the following organisms produces signs and symptoms that mimic acute appendicitis?

Yersinia enterocolitica. ### Explanation **Correct Answer: D. Yersinia enterocolitica** **Why it is correct:** *Yersinia enterocolitica* is a Gram-negative coccobacillus known for causing **Pseudoappendicitis** (also called mesenteric adenitis). The organism frequently involves the terminal ileum and mesenteric lymph nodes. Inflammation of these nodes causes sharp pain in the **Right Lower Quadrant (RLQ)**, fever, and leukocytosis, which clinically mimics the presentation of acute appendicitis. In many cases, patients are taken to surgery, only to find a normal appendix but significantly enlarged mesenteric lymph nodes. **Why other options are incorrect:** * **A. Enteropathic E. coli (EPEC):** Primarily causes watery diarrhea, especially in infants and children in developing countries. It does not typically cause localized RLQ pain or mesenteric lymphadenitis. * **B. Enterobius vermicularis (Pinworm):** While it can occasionally be found inside a surgically removed appendix, its primary clinical manifestation is perianal pruritus (itching), not an acute abdomen mimicking appendicitis. * **C. Trichomonas hominis:** This is generally considered a non-pathogenic commensal of the human large intestine and does not cause clinical syndromes like pseudoappendicitis. **High-Yield Clinical Pearls for NEET-PG:** * **Transmission:** Often associated with the consumption of contaminated pork products (chitterlings) or untreated water. * **Cold Enrichment:** *Yersinia* is unique because it can grow at low temperatures (**4°C**), a property used in labs for "cold enrichment" to isolate it from fecal flora. * **Bipolar Staining:** Shows a characteristic **"safety-pin appearance"** with Wayson or Giemsa stain. * **Other Mimics:** Apart from *Yersinia*, **Campylobacter jejuni** and **Non-typhoidal Salmonella** can also occasionally present with pseudoappendicitis.

Q: Which organism is not easily culturable but is well visualized and used in epidemiology?

Mycobacterium tuberculosis. **Explanation:** The correct answer is **Mycobacterium tuberculosis (MTB)**. This question focuses on the practical diagnostic and epidemiological characteristics of common bacterial pathogens. **1. Why Mycobacterium tuberculosis is correct:** * **Culturing Challenges:** MTB is a "fastidious" and extremely slow-growing organism. On traditional solid media like Lowenstein-Jensen (LJ), it takes **3–6 weeks** to show visible colonies. Even with rapid liquid systems (MGIT), it takes 1–2 weeks. This makes culture impractical for immediate clinical decisions. * **Visualization:** It is easily visualized using the **Ziehl-Neelsen (ZN) stain** or fluorescent Auramine-Rhodamine stain. Because it is an Acid-Fast Bacillus (AFB), microscopy is the primary tool for rapid diagnosis. * **Epidemiology:** Sputum microscopy (visualization) is the cornerstone of global TB control programs (like NTEP in India) to identify "open cases" (infectious individuals) and monitor treatment response. **2. Why the other options are incorrect:** * **Staphylococcus (Option A), E. coli (Option C), and Salmonella (Option D):** These are all **rapidly growing bacteria**. They can be easily cultured on standard media (Blood Agar or MacConkey Agar) within 18–24 hours. While they can be visualized via Gram stain, culture is the gold standard for their identification and antibiotic sensitivity testing. **High-Yield Clinical Pearls for NEET-PG:** * **Generation Time:** MTB has a long generation time of **12–20 hours** (compared to 20 minutes for *E. coli*). * **Culture Media:** LJ medium (egg-based) is the classic solid medium; Middlebrook is agar-based. * **Molecular Epidemiology:** While microscopy is used for routine surveillance, **NAAT (CBNAAT/GeneXpert)** is now the preferred initial diagnostic test for its speed and ability to detect Rifampicin resistance.

Q: Which of the following conditions is more strongly associated with Klebsiella pneumoniae than Escherichia coli?

Lobar pneumonia in an alcoholic patient. **Explanation:** **Correct Option: D. Lobar pneumonia in an alcoholic patient** *Klebsiella pneumoniae* is a classic cause of severe, necrotizing lobar pneumonia, particularly in individuals with compromised host defenses, such as those with **chronic alcoholism** or diabetes mellitus. Alcoholics are predisposed due to an impaired cough reflex and increased risk of aspiration of oropharyngeal flora. A high-yield clinical feature of *Klebsiella* pneumonia is the production of **"currant jelly" sputum**, which results from significant tissue necrosis and hemorrhage. On X-ray, it may present with the **"bulging fissure sign"** due to the heavy mucoid inflammatory exudate. **Analysis of Incorrect Options:** * **A. Pneumonia in a hospitalized patient:** While *Klebsiella* is a common cause of Nosocomial (Hospital-Acquired) Pneumonia, *E. coli* is also a frequent isolate in hospital settings. However, the association with alcoholism is much more specific to *Klebsiella*. * **B. Endotoxic shock:** Both are Gram-negative bacilli containing Lipid A (Endotoxin). *E. coli* is actually the most common cause of Gram-negative sepsis and endotoxic shock globally. * **C. Hemolytic uremic syndrome (HUS):** This is strongly associated with **Enterohemorrhagic *E. coli* (EHEC)**, specifically the O157:H7 strain, which produces Shiga-like toxins. It is not typically associated with *Klebsiella*. **NEET-PG High-Yield Pearls:** * **Morphology:** *Klebsiella* is a Gram-negative, non-motile, encapsulated bacillus. * **Culture:** It produces large, **mucoid colonies** on MacConkey agar due to its prominent polysaccharide capsule (lactose fermenter). * **Urease Test:** *Klebsiella* is typically urease positive (weak), whereas *E. coli* is urease negative. * **IMViC Profile:** *Klebsiella* is (- - + +), while *E. coli* is (+ + - -).

Q: Red leg disease in amphibians is caused by which organism?

Aeromonas. **Explanation:** **Aeromonas hydrophila** is the primary causative agent of **"Red Leg Disease"** in amphibians (frogs, toads, and salamanders). This condition is a form of bacterial septicemia characterized by subcutaneous hemorrhages, particularly on the ventral surface of the legs and abdomen, giving them a distinct reddish appearance. * **Why Aeromonas is correct:** *Aeromonas* species are Gram-negative, facultatively anaerobic bacilli commonly found in freshwater environments. They are opportunistic pathogens; in amphibians, stress or poor water quality allows the bacteria to invade the bloodstream, leading to capillary fragility and systemic bleeding. In humans, *Aeromonas* is high-yield for causing gastroenteritis (diarrheal disease) and cellulitis following exposure to contaminated water. **Analysis of Incorrect Options:** * **Pseudomonas:** While *Pseudomonas* can cause various opportunistic infections in aquatic animals, it is not the classic etiologic agent associated with the specific "Red Leg" syndrome. * **Histoplasmosis:** This is a fungal infection (*Histoplasma capsulatum*) primarily affecting the pulmonary system in humans via inhalation of bird or bat droppings; it does not cause septicemic skin changes in amphibians. * **Shigella hemolyticus:** This is a distractor. *Shigella* species cause bacillary dysentery in humans. There is no recognized species named *Shigella hemolyticus* associated with amphibian pathology. **High-Yield Clinical Pearls for NEET-PG:** * **Aeromonas hydrophila** is oxidase-positive (distinguishing it from Enterobacteriaceae) and resistant to the vibriostatic agent O/129 (distinguishing it from *Vibrio*). * In humans, it is a rare but serious cause of **necrotizing fasciitis** following freshwater trauma. * Always associate **freshwater exposure + cellulitis/diarrhea** with *Aeromonas*.

Q: Which drug is used in the treatment of resistant gonorrhoea?

Spectinomycin. **Explanation:** **Why Spectinomycin is correct:** Spectinomycin is an aminocyclitol antibiotic that inhibits protein synthesis by binding to the 30S ribosomal subunit. It is specifically indicated for the treatment of acute gonorrheal urethritis and proctitis, particularly in cases caused by **PPNG (Penicillinase-Producing Neisseria gonorrhoeae)** or in patients allergic to penicillins/cephalosporins. While Ceftriaxone is currently the first-line treatment for uncomplicated gonorrhea, Spectinomycin remains a high-yield answer for "resistant" cases in the context of classical microbiology questions. **Analysis of Incorrect Options:** * **A. Penicillin:** Historically the drug of choice, it is no longer used due to the widespread emergence of PPNG strains and plasmid-mediated resistance. * **B. Cotrimoxazole:** This combination (Sulfamethoxazole + Trimethoprim) is not effective against *N. gonorrhoeae* and is primarily used for UTIs or respiratory infections. * **C. Erythromycin:** While used for neonatal prophylaxis (ophthalmia neonatorum) or in pregnancy when other drugs are contraindicated, it is not the standard treatment for resistant adult gonorrhea due to poor efficacy and resistance. **NEET-PG High-Yield Pearls:** * **Current CDC/WHO Guidelines:** The current gold standard for uncomplicated gonorrhea is a single IM dose of **Ceftriaxone** (often combined with Azithromycin to cover potential Chlamydia co-infection). * **Spectinomycin Limitation:** It is **ineffective against pharyngeal gonorrhea** and does not treat syphilis (unlike Penicillin). * **Culture Media:** *N. gonorrhoeae* is fastidious and grows on **Thayer-Martin Medium** (Selective VCN medium: Vancomycin, Colistin, Nystatin). * **Gram Stain:** Look for Gram-negative kidney-shaped diplococci within polymorphonuclear leukocytes (intracellular).

Q: All are true about Gonococci except?

Vaginal swab is done for diagnosis in females. **Explanation:** The correct answer is **B**, as vaginal swabs are **not** the preferred specimen for diagnosing Gonorrhoea in females. 1. **Why Option B is the Correct Answer (The Exception):** In adult females, *Neisseria gonorrhoeae* primarily infects the **endocervical canal** because the organism has a predilection for columnar epithelium. The adult vagina is lined by stratified squamous epithelium, which is resistant to infection. Therefore, an **endocervical swab** is the specimen of choice. A vaginal swab is only used in cases of prepubertal vulvovaginitis (where the vaginal mucosa is thin) or when using NAAT-based screening. 2. **Analysis of Other Options:** * **Option A:** The incubation period for Gonorrhoea is typically short, ranging from **2 to 7 days**, making this statement true. * **Option C:** In males, the primary site of infection is the urethra. A **purulent urethral discharge** or a urethral swab is the standard specimen for microscopy and culture. * **Option D:** *N. gonorrhoeae* is a fastidious organism. **Thayer-Martin (TM) medium** is a selective medium (Chocolate agar base + Vancomycin, Colistin, Nystatin) specifically designed to inhibit normal flora and allow the growth of Gonococci. **High-Yield Clinical Pearls for NEET-PG:** * **Microscopy:** Gram-negative, kidney-shaped **intracellular diplococci** (found within polymorphonuclear leukocytes). * **Transport Media:** If processing is delayed, use **Stuart’s or Amies medium**. * **Biochemical Test:** Gonococci are **Oxidase positive** and ferment only **Glucose** (G for Gonococci, G for Glucose). * **Treatment:** Due to rising resistance, the current CDC/WHO recommendation is usually a single dose of **Ceftriaxone** (IM). * **Complications:** In females, untreated infection can lead to Pelvic Inflammatory Disease (PID) and Fitz-Hugh-Curtis Syndrome.

Q: A patient with HIV presents with diarrhea and acid-fast bacilli (AFB) positive in stool. What is the most likely causative organism?

Mycobacterium avium intracellulare. **Explanation:** The correct answer is **Mycobacterium avium intracellulare (MAC)**. In patients with advanced HIV/AIDS (typically with CD4 counts <50 cells/mm³), **Mycobacterium avium complex (MAC)** is the most common cause of disseminated opportunistic bacterial infection. While MAC primarily affects the reticuloendothelial system, it frequently involves the gastrointestinal tract, leading to chronic diarrhea, abdominal pain, and malabsorption. A key diagnostic feature is the presence of **Acid-Fast Bacilli (AFB)** in the stool or biopsy, representing the organism's acid-fast nature due to mycolic acid in its cell wall. **Why other options are incorrect:** * **Mycobacterium tuberculosis (MTB):** While MTB is common in HIV patients, it usually presents with pulmonary symptoms or ileocecal tuberculosis (causing constipation or obstruction rather than simple chronic diarrhea). It is less likely than MAC to show positive AFB in a stool sample unless there is active intestinal TB. * **Mycobacterium leprae:** This organism causes Leprosy, affecting the skin and peripheral nerves. It does not cause gastrointestinal disease or diarrhea. * **Mycoplasma:** These are the smallest free-living organisms and **lack a cell wall**; therefore, they are not acid-fast and cannot be detected via AFB staining. **High-Yield Clinical Pearls for NEET-PG:** * **Prophylaxis:** Azithromycin or Clarithromycin is indicated for MAC prophylaxis in HIV patients when CD4 <50 cells/mm³. * **Diagnosis:** Gold standard is blood culture (using BACTEC) or bone marrow culture. * **Stain:** MAC appears as short, coccobacillary acid-fast bacilli, often found within macrophages (foamy histiocytes). * **Differential Diagnosis:** If a stool AFB is positive in an HIV patient, also consider **Cryptosporidium parvum**, but these appear as acid-fast **oocysts**, not bacilli.

Q: A traveler drinks a glass of fruit juice with ice cubes made from tap water. E. coli contaminating the water supply grow in the traveler's intestine and synthesize a protein that causes his intestinal epithelium to overproduce cyclic AMP, resulting in a watery diarrhea. Which pathogenic strain of E. coli is typically responsible for this syndrome?

Enterotoxigenic. **Explanation:** The clinical presentation describes **Traveler’s Diarrhea**, which is most commonly caused by **Enterotoxigenic *E. coli* (ETEC)**. **Why the correct answer is right:** ETEC causes watery diarrhea through the production of two types of enterotoxins: 1. **Heat-labile toxin (LT):** This toxin acts similarly to the Cholera toxin. It ADP-ribosylates the Gs protein, leading to the permanent activation of adenylate cyclase. This results in **increased levels of intracellular cyclic AMP (cAMP)**, which triggers the secretion of chloride ions and water into the intestinal lumen. 2. **Heat-stable toxin (ST):** This toxin increases **cyclic GMP (cGMP)** by activating guanylate cyclase. The question specifically mentions the overproduction of cAMP, which is the hallmark mechanism of ETEC's LT toxin. **Why incorrect options are wrong:** * **Enteroaggregative (EAEC):** Associated with persistent diarrhea in children and HIV patients; it uses "stacked-brick" adhesion but does not primarily act via cAMP. * **Enterohemorrhagic (EHEC):** Causes bloody diarrhea (hemorrhagic colitis) and Hemolytic Uremic Syndrome (HUS). It produces **Shiga-like toxin**, which inhibits protein synthesis (60S ribosome). It does not increase cAMP. * **Enteroinvasive (EIEC):** Invades the colonic mucosa, causing a dysentery-like syndrome (fever, cramps, blood/pus in stool) similar to *Shigella*. **High-Yield NEET-PG Pearls:** * **ETEC:** Most common cause of Traveler’s Diarrhea. Mnemonic: **L**abile increases **A**MP (**L**A), **S**table increases **G**MP (**S**G). * **EHEC:** Most common serotype is **O157:H7**. It does *not* ferment sorbitol (distinguishing it from other *E. coli* on Sorbitol-MacConkey agar). * **EPEC:** Causes pediatric diarrhea in developing countries; characterized by "attaching and effacing" lesions (destruction of microvilli).

Question 1

Which component of tubercle bacilli produces granuloma?

Accepted Answer

Surface glycolipids

Answer

Sulfatide

Answer

Hetero polysaccharide

Answer

Sulfadase

Question 2

Which of the following organisms produces signs and symptoms that mimic acute appendicitis?

Accepted Answer

Yersinia enterocolitica

Answer

Enteropathic Escherichia coli

Answer

Enterobius vermicularis

Answer

Trichomonas hominis

Question 3

Which organism is not easily culturable but is well visualized and used in epidemiology?

Accepted Answer

Mycobacterium tuberculosis

Answer

Stapp

Answer

Escherichia coli

Answer

Salmonella

Question 4

Which of the following conditions is more strongly associated with Klebsiella pneumoniae than Escherichia coli?

Accepted Answer

Lobar pneumonia in an alcoholic patient

Answer

Pneumonia in a hospitalized patient

Answer

Endotoxic shock

Answer

Hemolytic uremic syndrome in children

Question 5

Red leg disease in amphibians is caused by which organism?

Accepted Answer

Aeromonas

Answer

Pseudomonas

Answer

Histoplasmosis

Answer

Shigella hemolyticus

Question 6

A 34-year-old female patient presented with left leg pain. On examination, the area was erythematous, warm, and tender with indistinct borders. The doctor suspected cellulitis and started her on IV oxacillin. The doctor noted that the pain was disproportionate to the level of cellulitis, and hence admitted the patient. During the night, the patient developed hypotension, deranged renal function tests, and a deranged coagulation profile. X-ray and CT of the leg were conducted. Which is the most common organism causing the condition described?

Accepted Answer

Group A Streptococcus

Answer

Staphylococcus aureus

Answer

Pseudomonas aeruginosa

Answer

Group D Streptococcus

Question 7

Which drug is used in the treatment of resistant gonorrhoea?

Accepted Answer

Spectinomycin

Answer

Penicillin

Answer

Cotrimoxazole

Answer

Erythromycin

Question 8

All are true about Gonococci except?

Accepted Answer

Vaginal swab is done for diagnosis in females

Answer

Incubation period is 2-7 days

Answer

Urethral swab for diagnosis in males

Answer

Culture media is Thayer Martin media

Question 9

A patient with HIV presents with diarrhea and acid-fast bacilli (AFB) positive in stool. What is the most likely causative organism?

Accepted Answer

Mycobacterium avium intracellulare

Answer

Mycobacterium tuberculosis

Answer

Mycobacterium leprae

Answer

Mycoplasma

Question 10

A traveler drinks a glass of fruit juice with ice cubes made from tap water. E. coli contaminating the water supply grow in the traveler's intestine and synthesize a protein that causes his intestinal epithelium to overproduce cyclic AMP, resulting in a watery diarrhea. Which pathogenic strain of E. coli is typically responsible for this syndrome?

Accepted Answer

Enterotoxigenic

Answer

Enteroaggregative

Answer

Enterohemorrhagic

Answer

Enteroinvasive

Bacteriology — MCQs

Bacteriology — MCQs

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