Bacteriology Practice Questions

Q: The most frequent cause of scalded skin syndrome is?

Staphylococci. ***Staphylococci*** - **Staphylococcus aureus** produces an **exotoxin (exfoliatin)** that targets desmosomes, leading to epidermal cleavage and the characteristic blistering seen in **staphylococcal scalded skin syndrome (SSSS)**. - SSSS is primarily seen in **infants and young children** due to their immature renal clearance of the exfoliatin toxin and lack of protective antibodies. *Meningococci* - **Neisseria meningitidis** is known to cause **meningitis** and **meningococcemia**, which can present with a **purpuric rash** but not typically widespread blistering characteristic of scalded skin syndrome. - The skin manifestations of meningococcal disease are usually due to **vasculitis** and **coagulopathy**, not exotoxin-mediated epidermal separation. *Pneumococci* - **Streptococcus pneumoniae** is a common cause of **pneumonia**, **otitis media**, and **meningitis**. - It does not produce exotoxins that cause the characteristic skin peeling seen in scalded skin syndrome. *Enterococci* - **Enterococci** are opportunistic pathogens primarily associated with **urinary tract infections**, **bacteremia**, and **nosocomial infections**. - They are not known to produce toxins that cause epidermolysis or scalded skin syndrome.

Q: 45 yrs old Ramlal has intra-abdominal sepsis. The causative organism was found to be vancomycin, gentamicin and ampicillin resistant. It grows well in presence of 6.5% NaCl and arginine. Bile esculin hydrolysis is positive. Which of the following is the organism? -

Enterococcus fecalis. ***Enterococcus fecalis*** - *Enterococcus fecalis* is commonly associated with **intra-abdominal sepsis** and can exhibit resistance to **vancomycin, gentamicin, and ampicillin**. - Its ability to grow in **6.5% NaCl**, hydrolyze **bile esculin**, and utilize **arginine** are classic biochemical characteristics distinguishing it from streptococci. *Streptococcus bovis* - While *Streptococcus bovis* can hydrolyze **bile esculin**, it typically **does not grow in 6.5% NaCl** and is usually susceptible to **ampicillin**. - It is more commonly associated with **bacteremia in patients with colon cancer** or endocarditis, rather than multi-drug resistant intra-abdominal sepsis. *Streptococcus pneumoniae* - *Streptococcus pneumoniae* is known for causing pneumonia and meningitis but **does not grow in 6.5% NaCl** and has a **negative bile esculin test**. - It is also typically **penicillin-sensitive** (though resistance exists) and does not exhibit the multi-drug resistance profile described. *Streptococcus agalactiae* - *Streptococcus agalactiae* (Group B Strep) is known for causing neonatal sepsis and meningitis, but it **does not grow in 6.5% NaCl** and is **bile esculin negative**. - It is generally susceptible to **ampicillin** and does not fit the described multi-drug resistance pattern or biochemical profile.

Q: Infection occurring after human bite is?

Anaerobic streptococci. **Anaerobic streptococci** - Human bite infections are characteristically **polymicrobial**, with **anaerobic bacteria being the most predominant** organisms isolated from these wounds. - **Anaerobic streptococci** (including *Peptostreptococcus* species) are commonly found in the human oral flora and are frequently implicated in infections resulting from human bites. - These bacteria thrive in the **anaerobic (low oxygen)** environment created in deep puncture wounds caused by bites. - Other important anaerobes include *Fusobacterium*, *Prevotella*, and *Porphyromonas* species. *Spirochetes* - **Spirochetes** are spiral-shaped bacteria, and while some (*Treponema denticola*) are part of the normal oral flora, they are not the primary cause of acute infections following human bites. - They are more commonly associated with conditions like **syphilis** (*Treponema pallidum*) or **Lyme disease** (*Borrelia burgdorferi*), which are not typically transmitted via human bites in this manner. *Staphylococcus* - **Staphylococcus aureus** is commonly isolated from human bite wounds and can cause significant soft tissue infections. - However, human bite infections are characteristically **polymicrobial with predominance of anaerobic bacteria**, making anaerobic streptococci more characteristic than staphylococci alone. - Note: ***Eikenella corrodens*** is considered pathognomonic for human bite infections but is an **aerobic** organism. *Candida* - **Candida** is a genus of yeast (fungus) and a common cause of fungal infections (e.g., thrush, candidiasis). - While *Candida* can be found in the mouth, it is **not a primary pathogen** causing acute bacterial infection following a human bite wound.

Q: All of the following organisms are known to survive intracellularly except

Neisseria meningitidis. ***Neisseria meningitidis*** - While *Neisseria meningitidis* can be found in the **phagosomes of neutrophils** in infected individuals, it is not considered a classic intracellular pathogen that replicates significantly or survives for extended periods within host cells. - Its primary mechanism of pathogenesis involves replication extracellularly and the production of a capsule to evade phagocytosis. *Legionella pneumophila* - *Legionella pneumophila* is a **facultative intracellular pathogen** known to replicate within **macrophages** and **amoebae** in aquatic environments. - Its ability to survive and multiply inside host cells is crucial for its virulence and persistence. *Streptococcus pyogenes* - *Streptococcus pyogenes* (Group A Streptococcus) can **invade and survive within non-phagocytic cells** such as epithelial cells, which may contribute to persistent infections and immune evasion. - This intracellular survival mechanism can make it more challenging for antibiotics and the immune system to eradicate the bacteria. *Salmonella Typhi* - *Salmonella Typhi* is a well-known **intracellular pathogen** that survives and replicates within **macrophages and other phagocytic cells** in the host. - This intracellular lifestyle allows it to evade immune surveillance and disseminate throughout the body, leading to systemic infections like typhoid fever.

Q: Incubation period of Lymphogranuloma venereum is:

10-30 days. ***10-30 days*** - The incubation period for **Lymphogranuloma venereum (LGV)**, caused by specific serovars of *Chlamydia trachomatis*, typically ranges from **10 to 30 days**. - This period aligns with the presentation of the primary lesion, often a transient, painless papule or ulcer. *60-90 days* - An incubation period of **60-90 days** is excessively long for the primary stage of LGV. - Such an extended period is more typical for diseases with a very slow progression or long latency, not the initial manifestation of LGV. *5-7 days* - While some sexually transmitted infections (STIs) have an incubation period of **5-7 days**, this is too short for LGV. - This shorter timeframe is more characteristic of diseases like **genital herpes** or **chancroid**. *1-5 days* - An incubation period of **1-5 days** is very short and not consistent with LGV. - This rapid onset suggests infections like **gonorrhea** or early stages of some bacterial infections.

Q: Not true about gas gangrene:

Cl perfringens produce heat-labile spores. ***Cl perfringens produce heat-labile spores*** - *Clostridium perfringens* spores are, in fact, **heat-resistant**, allowing them to survive harsh conditions and subsequently germinate into vegetative cells causing infection. - This heat resistance is a crucial factor in food poisoning outbreaks and wound infections, as spores can survive cooking temperatures. *Metronidazole is the drug of choice* - While metronidazole can be used as an adjunct, **penicillin G** is generally the primary antibiotic of choice for gas gangrene, often in combination with other agents like clindamycin. - **Surgical debridement** and **hyperbaric oxygen therapy** are also critical components of treatment, as antibiotics alone are often insufficient. *Most common cause is Cl perfringens* - **_Clostridium perfringens_** is indeed the most frequent cause of gas gangrene (clostridial myonecrosis), accounting for approximately 80-95% of cases. - This bacterium produces potent **exotoxins** that cause rapid tissue destruction and gas formation, leading to the characteristic symptoms. *Extensive necrosis of muscles* - Gas gangrene is characterized by **rapid and extensive necrosis of muscle tissue**, which is caused by the potent toxins produced by clostridial species, particularly alpha-toxin. - This muscle destruction leads to systemic toxicity, pain, and the production of gas within the tissues.

Q: Fermentation of glycerol is the basis for classification of:

Yersinia. ***Yersinia*** - Fermentation of **glycerol** to produce acid (seen as a color change in specific media) is a key biochemical test used to differentiate and classify species within the **Yersinia** genus. - This metabolic characteristic, along with other biochemical reactions, helps in identifying pathogenic species. **Yersinia pestis** is glycerol-**negative**, while **Yersinia pseudotuberculosis** is glycerol-**positive**, making this test crucial for species differentiation. *Neisseria* - **Neisseria** species are primarily classified by their ability to ferment various **sugars** (glucose, maltose, sucrose, lactose), not glycerol. - They are typically Gram-negative cocci that are oxidase-positive, and their sugar fermentation patterns are critical for species identification (e.g., *N. gonorrhoeae* ferments glucose, *N. meningitidis* ferments glucose and maltose). *Enterobacteriaceae* - The **Enterobacteriaceae** family is a large and diverse group of Gram-negative rods, and while they can ferment many carbohydrates, glycerol fermentation is not a primary or sole basis for their classification. - Classification within **Enterobacteriaceae** relies on a wide array of biochemical tests including lactose fermentation, indole production, citrate utilization, H2S production, and urease activity. *Streptococci* - **Streptococci** are Gram-positive cocci classified primarily by their **hemolytic patterns** on blood agar (alpha, beta, gamma) and by **Lancefield serogrouping** based on cell wall antigens. - While they ferment various carbohydrates, glycerol fermentation is not a standard or distinguishing feature used for their classification.

Q: Bacteria most commonly involved in prosthetic valvular heart disease within 2 months of surgery is:

Staphylococcus epidermidis. ***Staphylococcus epidermidis*** - This coagulase-negative staphylococcus is a common cause of **early-onset prosthetic valve endocarditis (PVE)**, occurring within 2 months of surgery. - It is a normal skin flora, and infections are often related to **intraoperative contamination** during valve replacement surgery. *Streptococcus viridans* - This group of streptococci is a leading cause of **late-onset PVE** and **native valve endocarditis (NVE)**, often following dental procedures. - Infections typically occur more than 2 months post-surgery, differentiating it from early-onset cases. *Enterococci* - Enterococci can cause both **NVE** and **PVE**, but they are more commonly associated with infections in patients with **nosocomial acquisition** or those undergoing genitourinary or gastrointestinal procedures. - While they can occur post-surgery, they are not the most common causative agent within the first 2 months compared to *Staphylococcus epidermidis*. *Hemophilus* - *Haemophilus species* are considered part of the **HACEK group** (Haemophilus, Aggregatibacter, Cardiobacterium, Eikenella, Kingella), which are known for causing **culture-negative endocarditis**. - While they can cause endocarditis, they are rare causes of early-onset PVE and are more associated with subacute or chronic forms of endocarditis.

Q: A 40-year-old woman complained of unrelenting headache, accompanied by fever, chills, and malaise. After 3 to 4 days, a dry cough developed. Her white cell count was normal. Chest x-ray and CT scan were done. A pathogen I suspected which produces colonies like the ones given below. Which of the following is the most likely diagnosis?

Mycoplasma pneumoniae. ***Mycoplasma pneumoniae*** - This presentation of **unrelenting headache, fever, chills, malaise**, followed by a **dry cough** and a **normal white cell count**, is classic for "walking pneumonia" caused by *Mycoplasma pneumoniae*. - Its colonies often have a **fried egg appearance** (although not explicitly stated, this is a common association with suspected pathogens shown colonially) and it's a common cause of **atypical pneumonia**. *Legionella pneumophila* - While *Legionella* can cause **atypical pneumonia** with similar systemic symptoms and a dry cough, it is often associated with **gastrointestinal symptoms** (diarrhea), **neurological symptoms** (confusion), **hyponatremia**, and a history of exposure to **aerosolized contaminated water sources**; none of these additional features are present here, making *Mycoplasma* a more likely diagnosis in this clinical context. - *Legionella* is often associated with outbreaks and the absence of gastrointestinal symptoms alone does not exclude it. *Streptococcus pneumoniae* - This bacterium typically causes **lobar pneumonia** with a **productive cough**, **purulent sputum**, and often an **elevated white cell count**. - Its onset is usually more acute and severe than described, and it is a **typical pneumonia** pathogen. *Parainfluenza virus* - Parainfluenza viruses primarily cause upper and lower respiratory tract infections, often presenting as **croup** in children or **bronchiolitis**. - While it can cause pneumonia, it typically does not present with such a prominent and unrelenting headache, nor the specific systemic pattern common in atypical bacterial infections.

Q: “Hundred day cough” is the name of

Cough due to Bordetella pertussis. ***Cough due to Bordetella pertussis*** - **Whooping cough**, caused by **Bordetella pertussis**, is colloquially known as the "hundred-day cough" due to its prolonged duration. - The cough can last for weeks to months, especially in unvaccinated individuals, characterized by severe paroxysms followed by a characteristic "whoop" inspiration. *Cough due to Haemophilus influenzae* - **Haemophilus influenzae** can cause respiratory infections like bronchitis or pneumonia, with cough as a symptom, but it is not specifically known as the "hundred-day cough." - This bacterium is more commonly associated with **otitis media**, sinusitis, epiglottitis, and meningitis, rather than a prolonged, distinctive coughing illness. *Cough due to respiratory syncytial virus* - **Respiratory syncytial virus (RSV)** is a common cause of respiratory infections, particularly in infants and young children, leading to bronchiolitis and pneumonia. - While RSV can cause a persistent cough, it is not referred to as the "hundred-day cough"; its symptoms are typically more acute and can involve wheezing and difficulty breathing. *Cough due to adenovirus* - **Adenoviruses** can cause various respiratory illnesses ranging from the common cold to pneumonia, with cough being a frequent symptom. - However, the cough associated with adenovirus infections is generally not as prolonged or severe as "whooping cough" and does not typically fit the "hundred-day cough" description.

Question 1

The most frequent cause of scalded skin syndrome is?

Accepted Answer

Staphylococci

Answer

Meningococci

Answer

Pneumococci

Answer

Enterococci

Question 2

45 yrs old Ramlal has intra-abdominal sepsis. The causative organism was found to be vancomycin, gentamicin and ampicillin resistant. It grows well in presence of 6.5% NaCl and arginine. Bile esculin hydrolysis is positive. Which of the following is the organism? -

Accepted Answer

Enterococcus fecalis

Answer

Streptococcus bovis

Answer

Streptococcus pneumoniae

Answer

Streptococcus agalactiae

Question 3

Infection occurring after human bite is?

Accepted Answer

Anaerobic streptococci

Answer

Spirochetes

Answer

Staphylococcus

Answer

Candida

Question 4

All of the following organisms are known to survive intracellularly except

Accepted Answer

Neisseria meningitidis

Answer

Legionella pneumophila

Answer

Streptococcus pyogenes

Answer

Salmonella Typhi

Question 5

Incubation period of Lymphogranuloma venereum is:

Accepted Answer

10-30 days

Answer

60-90 days

Answer

5-7 days

Answer

1-5 days

Question 6

Not true about gas gangrene:

Accepted Answer

Cl perfringens produce heat-labile spores

Answer

Metronidazole is the drug of choice

Answer

Most common cause is Cl perfringens

Answer

Extensive necrosis of muscles

Question 7

Fermentation of glycerol is the basis for classification of:

Accepted Answer

Yersinia

Answer

Neisseria

Answer

Enterobacteriaceae

Answer

Streptococci

Question 8

Bacteria most commonly involved in prosthetic valvular heart disease within 2 months of surgery is:

Accepted Answer

Staphylococcus epidermidis

Answer

Streptococcus viridans

Answer

Enterococci

Answer

Hemophilus

Question 9

A 40-year-old woman complained of unrelenting headache, accompanied by fever, chills, and malaise. After 3 to 4 days, a dry cough developed. Her white cell count was normal. Chest x-ray and CT scan were done. A pathogen I suspected which produces colonies like the ones given below. Which of the following is the most likely diagnosis?

Accepted Answer

Mycoplasma pneumoniae

Answer

Streptococcus pneumoniae

Answer

Legionella pneumophila

Answer

Parainfluenza virus

Question 10

“Hundred day cough” is the name of

Accepted Answer

Cough due to Bordetella pertussis

Answer

Cough due to Haemophilus influenzae

Answer

Cough due to respiratory syncytial virus

Answer

Cough due to adenovirus

Bacteriology — MCQs

Bacteriology — MCQs

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