FMGE 2023 - Microbiology Practice Questions

Q: Which among the following parasites directly invade the skin?

Schistosoma mansoni. ***Schistosoma mansoni***- The infectious stage, the **cercariae**, actively penetrate the intact skin of the human host when swimming or wading in contaminated water. - This stage bypasses the need for an insect vector and directly initiates infection, often causing **'swimmer's itch'** at the site of entry.*Dracunculus medinensis*- This infection is acquired by the oral route through ingestion of **copepods** (water fleas) containing the larval stage in drinking water.- While the mature female worm creates a painful **blister** to exit the skin, it does not invade the skin to initiate the infection.*Wuchereria bancrofti*- This parasite is transmitted by the bite of an **infected mosquito** (e.g., *Culex*), which deposits infective larvae near the bite site.- The larvae enter the host through the **puncture wound** created by the mosquito bite, not by actively penetrating intact dermal layers.*Onchocerca volvulus*- The transmission involves the bite of an infected **blackfly** (*Simulium* species), which transmits the infective larvae (microfilariae) into the host.- The larvae enter through the **wound site** created by the fly bite and subsequent manipulation of the wound by the vector (not direct skin invasion).

Q: Which of the following hepatitis viruses is likely to get transmitted via fecal-oral route?

Hepatitis A. ***Hepatitis A***- Hepatitis A virus (HAV) is primarily spread through the **fecal-oral route**, typically via consumption of food or water contaminated with feces.- It causes an **acute**, self-limiting infection that rarely results in chronic liver disease.*Hepatitis B*- Hepatitis B virus (HBV) is transmitted mainly through **parenteral** (exposure to infected blood), sexual contact, or perinatal (mother-to-child) routes.- Unlike HAV, HBV is a major cause of **chronic hepatitis**, cirrhosis, and hepatocellular carcinoma.*Hepatitis C*- Hepatitis C virus (HCV) transmission is predominantly **parenteral**, most commonly associated with intravenous drug use, blood transfusions (historically), and shared needles.- HCV is the leading cause of chronic viral hepatitis globally and frequently establishes persistent infection.*Hepatitis D*- Hepatitis D virus (HDV) is a defective RNA virus that requires **Hepatitis B surface antigen (HBsAg)** for its replication and assembly.- HDV is transmitted parenterally (same routes as HBV) and not via the fecal-oral route.

Q: A 70-year-old patient with a smoking history presents with high-grade fever, cough, confusion, and diarrhea. Chest X-ray shows bilateral infiltrates in bilateral lower lung fields. On sputum gram stain, no organisms were detected. Laboratory results reveal Na: 126mEq/L, AST:62, ALT:56, RBS:112 mg/dl, serum bilirubin of 0.8mg%, and a positive HIV test. Which of the following organisms is responsible?

Legionella. ***Legionella***- This clinical picture, characterized by **high fever**, **atypical pneumonia** (bilateral infiltrates), and systemic symptoms including **confusion** (CNS involvement), **diarrhea** (GI involvement), **hyponatremia** and mildly elevated **LFTs**, is highly suggestive of **Legionella pneumophila** (Legionnaires' disease) [1].- *Legionella* is an **atypical bacterium** that requires specialized culture media and therefore typically results in a Gram stain showing **no organisms detected** through standard methods [1].*Streptococcus*- *Streptococcus pneumoniae* (the most common cause of typical community-acquired pneumonia) typically presents with an abrupt onset, pleurisy, and a consolidation pattern (**lobar pneumonia**) on CXR, differentiating it from this diffuse, atypical presentation.- It is a readily detectable **Gram-positive diplococcus** on sputum Gram stain, which contrasts with the microbiological report of no organisms seen [1].*Pneumocystis jeroveci*- While highly relevant in HIV-positive individuals, **Pneumocystis pneumonia (PJP)** typically presents with subacute onset, severe **hypoxemia**, and diffuse **interstitial infiltrates**, not typically associated with prominent hyponatremia or severe diarrhea [2].- PJP is diagnosed via special staining (e.g., silver stain) on induced sputum or bronchoalveolar lavage, and it does not usually cause the multisystem failure (hyponatremia and transaminitis) characteristic of Legionnaires' disease [2].*Klebsiella*- **Klebsiella pneumoniae** typically causes destruction and necrosis leading to classic **lobar pneumonia** (often in the upper lobes), classically associated with **currant jelly sputum** in immunocompromised individuals, especially alcoholics.- *Klebsiella* is a large encapsulated **Gram-negative rod** that would be easily visible and identifiable on a standard sputum Gram stain.

Q: A soldier presents to a referral hospital one day after sustaining a high-velocity shrapnel injury to his right thigh. He complains of severe pain at the wound site. On examination, crepitus is present. Which of the following organisms is the most likely cause of his condition?

Clostridium perfringens. ***Clostridium perfringens*** - *Clostridium perfringens* is the most common cause (80-90%) of **gas gangrene** (clostridial myonecrosis), especially following severe penetrating trauma such as that caused by a high-velocity shrapnel injury, which creates **anaerobic** conditions in deep tissue. - The organism produces potent toxins, primarily **alpha toxin** (a lecithinase), which causes rapid tissue necrosis, hemolysis, and the production of gas that manifests clinically as **crepitus**. *Incorrect: Clostridium septicum* - This organism is primarily associated with **spontaneous, non-traumatic gas gangrene**, often occurring in patients with underlying conditions like **colonic malignancy**, diabetes, or neutropenia. - While it can cause traumatic gas gangrene, it is significantly less frequent than *C. perfringens* in established wound infections. *Incorrect: Clostridium difficile* - *C. difficile* is the principal cause of **antibiotic-associated diarrhea** and **pseudomembranous colitis**. - It causes localized disease in the colon by producing **Toxin A (enterotoxin)** and **Toxin B (cytotoxin)** and does not typically cause myonecrosis or gas gangrene in penetrating wounds. *Incorrect: Clostridium novyi* - *C. novyi* is a recognized cause of gas gangrene but is less common than *C. perfringens* in traumatic settings and is sometimes associated with **intravenous illicit drug use**. - It is known for producing large amounts of **edema** compared to other clostridial species, causing a characteristic "malignant edema" syndrome rather than the primarily necrotizing and gas-producing infection seen with *C. perfringens*.

Question 1

Which among the following parasites directly invade the skin?

Accepted Answer

Schistosoma mansoni

Answer

Wuchereria bancrofti

Answer

Onchocerca volvulus

Answer

Dracunculus medinensis

Question 2

Which of the following hepatitis viruses is likely to get transmitted via fecal-oral route?

Accepted Answer

Hepatitis A

Answer

Hepatitis B

Answer

Hepatitis C

Answer

Hepatitis D

Question 3

A 70-year-old patient with a smoking history presents with high-grade fever, cough, confusion, and diarrhea. Chest X-ray shows bilateral infiltrates in bilateral lower lung fields. On sputum gram stain, no organisms were detected. Laboratory results reveal Na: 126mEq/L, AST:62, ALT:56, RBS:112 mg/dl, serum bilirubin of 0.8mg%, and a positive HIV test. Which of the following organisms is responsible?

Accepted Answer

Legionella

Answer

Klebsiella

Answer

Streptococcus

Answer

Pneumocystis jeroveci

Question 4

A soldier presents to a referral hospital one day after sustaining a high-velocity shrapnel injury to his right thigh. He complains of severe pain at the wound site. On examination, crepitus is present. Which of the following organisms is the most likely cause of his condition?

Accepted Answer

Clostridium perfringens

Answer

Clostridium novyi

Answer

Clostridium difficile

Answer

Clostridium septicum

FMGE 2023 — Microbiology