Bacteriology Practice Questions

Q: Which of the following is true about Enteropathogenic E. coli?

Causes diarrhea in infants. **Explanation:** **Enteropathogenic *E. coli* (EPEC)** is a major cause of infantile diarrhea, particularly in developing countries. 1. **Why Option A is correct:** EPEC is classically associated with **outbreaks of diarrhea in nurseries and daycare centers**. It primarily affects infants (children <2 years old). The hallmark of its pathogenesis is the **"Attaching and Effacing" (A/E) lesion**. It uses **Bundle-Forming Pili (BFP)** for initial attachment and the **Intimin** protein for intimate adhesion to intestinal epithelial cells, leading to the destruction of microvilli and malabsorptive diarrhea. 2. **Why other options are incorrect:** * **Option B:** EPEC is **non-invasive**. Invasion of intestinal epithelial cells is the characteristic mechanism of **Enteroinvasive *E. coli* (EIEC)**, which mimics Shigellosis. * **Option C:** Adults are rarely affected because they have usually developed acquired immunity. EPEC is a pediatric pathogen. * **Option D:** While immunocompromised hosts are at risk for many infections, EPEC is specifically defined by its predilection for the **pediatric/infant population** regardless of immune status, rather than being an opportunistic infection of the immunocompromised. **High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic:** **EPEC** = **P**ediatric/**P**ili (Bundle-forming). * **Pathogenesis:** Mediated by the **LEE (Locus of Enterocyte Effacement)** pathogenicity island. * **Diagnosis:** Characterized by "stacked-brick" appearance is NOT EPEC (that is EAEC); EPEC shows **localized adherence** on HeLa or HEp-2 cells. * **Toxins:** EPEC does **not** produce Shiga-like toxins or Enterotoxins (LT/ST).

Q: Anthrax bacilli differs from anthracoid bacilli by being:

Non-motile. ### Explanation The differentiation between *Bacillus anthracis* (Anthrax bacilli) and *Bacillus anthracoides* (Pseudoanthrax/Anthracoid bacilli) is a classic high-yield topic in NEET-PG Microbiology. **Why "Non-motile" is correct:** *Bacillus anthracis* is characteristically **non-motile**. In contrast, almost all anthracoid bacilli (like *B. cereus* or *B. subtilis*) exhibit active motility (peritrichous flagella). This lack of motility is a key diagnostic feature used to identify the pathogen in a laboratory setting. **Analysis of Incorrect Options:** * **A. Non-capsulated:** Incorrect. *B. anthracis* is **capsulated** (polypeptide capsule made of D-glutamic acid), which is essential for its virulence. Anthracoid bacilli are generally non-capsulated. * **B. Strict aerobe:** Incorrect. Both *B. anthracis* and anthracoid bacilli are **aerobes and facultative anaerobes**. * **D. Haemolytic colonies:** Incorrect. *B. anthracis* is **non-haemolytic** (gamma-haemolysis) on blood agar. Anthracoid bacilli typically produce strong beta-haemolysis. **High-Yield Clinical Pearls for NEET-PG:** | Feature | *B. anthracis* | Anthracoid Bacilli | | :--- | :--- | :--- | | **Motility** | **Non-motile** (Statue-like) | **Motile** | | **Haemolysis** | Non-haemolytic | Usually Beta-haemolytic | | **Capsule** | Present (Polypeptide) | Absent | | **Medusa Head** | Present (on Agar) | Absent/Irregular | | **Salicin Fermentation** | Negative | Positive | | **Penicillin** | Sensitive (McFadyean's reaction) | Resistant | * **Mnemonic:** *B. anthracis* is "Lazy and Boring" (Non-motile, Non-haemolytic). * **McFadyean’s Reaction:** Uses polychrome methylene blue to visualize the **M**auve-colored capsule of *B. anthracis*. * **String of Pearls Reaction:** Seen when *B. anthracis* is grown on agar containing low concentrations of penicillin.

Q: Which organism is known to cause epidemics of puerperal sepsis?

Group A beta-hemolytic streptococci. **Explanation:** **Puerperal sepsis** is defined as an infection of the genital tract occurring at any time between the onset of rupture of membranes or labor and the 42nd day postpartum. **Why Group A beta-hemolytic streptococci (GABS) is correct:** Historically, *Streptococcus pyogenes* (Group A Strep) is the most notorious cause of **explosive epidemics** of puerperal sepsis. It is highly virulent and can be introduced into the birth canal via the hands or respiratory droplets of healthcare workers or the patient herself. While modern hygiene has reduced its frequency, it remains the primary organism associated with rapidly progressing, life-threatening outbreaks in obstetric wards. **Analysis of Incorrect Options:** * **Group B beta-hemolytic streptococci (GBS):** While *S. agalactiae* is the most common cause of neonatal sepsis and a frequent cause of sporadic postpartum infections, it typically exists as normal vaginal flora and does not usually cause the "epidemic" patterns seen with Group A. * **Cytomegalovirus (CMV):** This is a viral pathogen primarily associated with congenital infections (TORCH syndrome) rather than acute postpartum maternal sepsis. * **Toxoplasma gondii:** This is a protozoan parasite. While it can cause congenital toxoplasmosis via transplacental transmission, it is not a causative agent of puerperal sepsis. **High-Yield Clinical Pearls for NEET-PG:** * **Ignaz Semmelweis:** Known as the "Father of Infection Control," he famously discovered that handwashing could drastically reduce the mortality of puerperal sepsis caused by GABS. * **Most common overall cause:** While GABS causes epidemics, **anaerobic bacteria** (e.g., *Bacteroides*, *Peptostreptococcus*) and *E. coli* are common causes of sporadic polymicrobial puerperal infections today. * **Clinical Presentation:** Sudden high fever, pelvic pain, and foul-smelling lochia are classic signs.

Q: Trachoma is one of the leading causes of blindness. Which of the following best typifies the disease?

It is caused by Chlamydia trachomatis. **Explanation:** **1. Why Option A is Correct:** Trachoma is a chronic keratoconjunctivitis caused by specific serotypes of **_Chlamydia trachomatis_ (Serotypes A, B, Ba, and C)**. It is the leading infectious cause of blindness worldwide. The pathogenesis involves repeated cycles of infection leading to subepithelial follicular inflammation, conjunctival scarring (Arlt’s line), trichiasis (inward turning of eyelashes), and eventual corneal opacity. **2. Why the Other Options are Incorrect:** * **Option B:** The WHO-recommended treatment for Trachoma follows the **SAFE strategy**. The medical treatment of choice is a **single dose of oral Azithromycin** (macrolide) or topical Tetracycline. Cephalosporins are not the standard of care for Chlamydial eye infections. * **Option C:** While Trachoma is a global health issue, it is most hyperendemic in the **arid areas of Africa** (Sub-Saharan Africa), the Middle East, and parts of Asia, rather than being specifically characterized by 400 million cases in the Pacific Rim. * **Option D:** Trachoma is a disease of the **conjunctiva and cornea** (keratoconjunctivitis). Uveitis involves the middle layer of the eye (iris, ciliary body, and choroid), which is not the primary site of pathology in Trachoma. **3. NEET-PG High-Yield Pearls:** * **SAFE Strategy:** **S**urgery (for trichiasis), **A**ntibiotics (Azithromycin), **F**acial cleanliness, **E**nvironmental improvement. * **Inclusion Bodies:** Look for **Halberstaedter-Prowazek (HP) bodies** (intracytoplasmic inclusions) in conjunctival scrapings. * **Clinical Signs:** **Herbert’s pits** (scarred limbal follicles) are pathognomonic for Trachoma. * **Serotypes:** Remember **A-C** cause Trachoma; **D-K** cause inclusion conjunctivitis and NGS; **L1-L3** cause Lymphogranuloma Venereum (LGV).

Q: A wound shows crepitation in the subcutaneous tissue and muscle with foul-smelling discharge. Pus culture shows Cl. perfringens. All of the following features about Cl. perfringens are TRUE, EXCEPT?

The most important toxin is hyaluronidase.. **Explanation:** The clinical presentation of crepitation, foul-smelling discharge, and muscle involvement is classic for **Gas Gangrene (Clostridial Myonecrosis)**. **1. Why Option C is the correct answer (The False Statement):** While *Clostridium perfringens* does produce hyaluronidase (an enzyme that aids tissue spread), it is **not** the most important toxin. The primary virulence factor responsible for the pathogenesis of gas gangrene is **Alpha (α) toxin**. Alpha toxin is a **lecithinase (phospholipase C)** that degrades cell membranes, leading to massive tissue necrosis, hemolysis, and toxemia. **2. Analysis of Incorrect Options (True Statements):** * **Option A:** *Cl. perfringens* Type A is indeed the most common cause of gas gangrene worldwide (responsible for 80-90% of cases). * **Option B:** The **Nagler’s reaction** is a biochemical test used to detect Alpha toxin. When the organism is grown on egg yolk agar, the lecithinase activity creates a zone of opalescence around the colonies, which is inhibited by adding specific antitoxin. * **Option D:** Strains causing gas gangrene produce **heat-resistant spores**, which allow the bacteria to survive in soil and dust before entering a traumatic wound. (Note: Food poisoning strains of *Cl. perfringens* also produce highly heat-resistant spores). **Clinical Pearls for NEET-PG:** * **Target Hemolysis:** On blood agar, *Cl. perfringens* shows a "double zone of hemolysis" (inner zone of complete hemolysis due to Theta toxin; outer zone of incomplete hemolysis due to Alpha toxin). * **Stormy Fermentation:** In litmus milk media, it produces acid and gas, leading to a "stormy" appearance of the clot. * **Non-motile:** Unlike most Clostridia, *Cl. perfringens* is non-motile.

Q: What is the most common organism causing cerebrospinal fluid shunt-related infections?

Coagulase-negative Staphylococcus aureus. **Explanation:** The correct answer is **Coagulase-negative Staphylococcus aureus (CoNS)**, specifically **Staphylococcus epidermidis**. **Why CoNS is the correct answer:** Cerebrospinal fluid (CSF) shunt infections are primarily caused by skin flora introduced during the surgical procedure or via retrograde migration along the shunt tract. *Staphylococcus epidermidis* (a CoNS) is the most common culprit because of its unique ability to produce an **extracellular polysaccharide biofilm (slime layer)**. This biofilm allows the bacteria to adhere firmly to the synthetic material of the shunt (silicone/plastic) and protects them from both the host’s immune response and systemic antibiotics. **Analysis of Incorrect Options:** * **A. Streptococcus agalactiae (GBS):** This is a leading cause of neonatal meningitis (acquired during birth), but it is not typically associated with prosthetic device infections. * **B. E. coli:** While a common cause of neonatal meningitis and UTIs, it only accounts for a small percentage of shunt infections, usually in the immediate postoperative period or via hematogenous spread. * **C. Enterococcus:** These are enteric organisms. While they can cause healthcare-associated infections, they are far less common than skin commensals in the context of neurosurgical hardware. **Clinical Pearls for NEET-PG:** * **Most common organism:** *Staphylococcus epidermidis* (>50% of cases). * **Second most common:** *Staphylococcus aureus*. * **Pathogenesis:** Biofilm formation is the key virulence factor. * **Management:** Successful treatment usually requires **removal of the infected shunt** in addition to targeted intravenous antibiotics (often Vancomycin due to high rates of methicillin resistance in CoNS). * **Timing:** Most shunt infections occur within 6 months of placement or revision.

Q: Which Streptococcus toxin is responsible for connective tissue breakdown?

Hyaluronidase. **Explanation:** **Correct Answer: A. Hyaluronidase** Hyaluronidase is an enzyme secreted by *Streptococcus pyogenes* (Group A Strep) that degrades **hyaluronic acid**, a critical component of the ground substance in mammalian connective tissue. By breaking down this "intercellular cement," the enzyme facilitates the rapid lateral spread of the bacteria through tissue planes. This is why it is historically referred to as the **"Dreading Factor."** **Incorrect Options:** * **B. Streptolysin O:** This is an oxygen-labile, highly antigenic hemolysin that creates pores in cell membranes, leading to the lysis of RBCs, WBCs, and platelets. It is the basis for the ASO (Antistreptolysin O) titer. * **C. Streptolysin S:** This is an oxygen-stable, non-antigenic hemolysin responsible for the zone of beta-hemolysis seen on blood agar plates. * **D. Streptococcus pyogenic exotoxin (Spe):** Also known as erythrogenic toxins, these act as **superantigens**. They are responsible for the clinical manifestations of Scarlet Fever (rash) and Streptococcal Toxic Shock Syndrome (STSS). **High-Yield NEET-PG Pearls:** * **Spreading Factors:** Other streptococcal enzymes that aid spread include **Streptokinase** (fibrinolysin) which dissolves clots and **DNase (Streptodornase)** which liquefies viscous pus. * **Clinical Correlation:** The action of Hyaluronidase is a major reason why streptococcal skin infections like **cellulitis** are characterized by diffuse, spreading inflammation rather than localized abscesses (unlike *Staphylococcus aureus*). * **M Protein:** Remember that M protein is the chief virulence factor of *S. pyogenes*, primarily acting as an anti-phagocytic agent.

Q: What is the most common causative organism for lobar pneumonia?

Streptococcus pneumoniae. **Explanation:** **Streptococcus pneumoniae (Pneumococcus)** is the most common cause of community-acquired pneumonia (CAP) and specifically **lobar pneumonia** across all age groups. The underlying medical concept involves the organism's ability to reach the alveoli, where its polysaccharide capsule inhibits phagocytosis. This leads to an intense inflammatory exudate that spreads rapidly through the **Pores of Kohn**, resulting in the consolidation of an entire lobe (lobar distribution) rather than patchy involvement. **Analysis of Incorrect Options:** * **Staphylococcus aureus:** Typically causes **bronchopneumonia** (patchy consolidation), often following a viral prodrome like Influenza. It is notorious for causing complications like lung abscesses and pneumatoceles. * **Streptococcus pyogenes:** A rare cause of pneumonia; it more commonly causes pharyngitis, skin infections, and post-streptococcal sequelae (RHD/PSGN). * **Haemophilus influenzae:** A common cause of CAP, particularly in patients with underlying **COPD** or cystic fibrosis, but it usually presents as bronchopneumonia rather than classic lobar consolidation. **High-Yield Clinical Pearls for NEET-PG:** * **Classic Presentation:** Sudden onset high-grade fever, productive cough with **"rusty sputum"** (due to altered blood in the alveolar exudate). * **Pathology Stages:** Congestion → Red Hepatization → Gray Hepatization → Resolution. * **Diagnosis:** Gram-positive lancet-shaped diplococci; **Quellung reaction** positive; Bile solubility positive; Optochin sensitivity positive. * **Vaccination:** PPSV23 (capsular polysaccharide) and PCV13 (conjugate) are used for prevention in high-risk groups.

Question 1

Which of the following is true about Enteropathogenic E. coli?

Accepted Answer

Causes diarrhea in infants

Answer

Acts by invasion of intestinal epithelial cells

Answer

Adults are mostly affected

Answer

Affects immunocompromised hosts

Question 2

A 22-year-old male presented with fever and increasing dyspnea. He has a history of frequent episodes of hemoptysis, sinusitis, pneumothorax, and fatty stools, for which he has been hospitalized multiple times. Investigations revealed deranged renal and liver function tests, cirrhotic changes in the liver with multiple renal calculi on USG abdomen, signs of necrotizing pneumonia on X-ray chest, and sputum culture showing non-fermenting, mucoid, oxidase-positive colonies. Which of the following drugs can be used to treat the identified organism?

Accepted Answer

IV Meropenem + inhaled tobramycin

Answer

IV plus inhaled colistin

Answer

IM Streptomycin

Answer

IV Ceftriaxone

Question 3

Anthrax bacilli differs from anthracoid bacilli by being:

Accepted Answer

Non-motile

Answer

Non-capsulated

Answer

Strict aerobe

Answer

Haemolytic colonies on blood agar

Question 4

Which organism is known to cause epidemics of puerperal sepsis?

Accepted Answer

Group A beta-hemolytic streptococci

Answer

Cytomegalovirus

Answer

Group B beta-hemolytic streptococci

Answer

Toxoplasma gondii

Question 5

Trachoma is one of the leading causes of blindness. Which of the following best typifies the disease?

Accepted Answer

It is caused by Chlamydia trachomatis

Answer

It is best treated with systemic cephalosporins and ophthalmic tetracycline

Answer

It affects 400 million people in the Pacific Rim

Answer

It is a form of chronic uveitis

Question 6

A wound shows crepitation in the subcutaneous tissue and muscle with foul-smelling discharge. Pus culture shows Cl. perfringens. All of the following features about Cl. perfringens are TRUE, EXCEPT?

Accepted Answer

The most important toxin is hyaluronidase.

Answer

It is the most common cause of gas gangrene.

Answer

Can be detected by Nagler's reaction.

Answer

Gas gangrene strains produce heat-resistant spores.

Question 7

All of the following statements about El-Tor vibrios are true, except?

Accepted Answer

Enterotoxin can have direct effects on other tissues besides intestinal epithelial cells

Answer

Humans are the only reservoir

Answer

Can survive in ice-cold water for 2-4 weeks

Answer

Killed by boiling for 30 seconds

Question 8

What is the most common organism causing cerebrospinal fluid shunt-related infections?

Accepted Answer

Coagulase-negative Staphylococcus aureus

Answer

Streptococcus agalactiae

Answer

E. coli

Answer

Enterococcus

Question 9

Which Streptococcus toxin is responsible for connective tissue breakdown?

Accepted Answer

Hyaluronidase

Answer

Streptolysin O

Answer

Streptolysin S

Answer

Streptococcus pyogenic exotoxin

Question 10

What is the most common causative organism for lobar pneumonia?

Accepted Answer

Streptococcus pneumoniae

Answer

Staphylococcus aureus

Answer

Streptococcus pyogenes

Answer

Haemophilus influenzae

Bacteriology — MCQs

Bacteriology — MCQs

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