Bacteriology Practice Questions

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: Gas gangrene can be caused by all Except

Clostridium difficile. ***Clostridium difficile*** - *Clostridium difficile* is primarily known for causing **pseudomembranous colitis** and **antibiotic-associated diarrhea**, not gas gangrene. - Its pathogenic mechanisms involve **toxins A and B** which cause colonic inflammation and damage, distinct from the tissue destruction and gas production seen in gas gangrene. *Clostridium sporogenes* - *Clostridium sporogenes* is an anaerobic bacterium that can produce **gas** and contribute to **tissue necrosis** in mixed infections, including gas gangrene. - While not one of the most common causes, it possesses enzymatic capabilities that can degrade tissues and support the anaerobic environment characteristic of gas gangrene. *Clostridium septicum* - *Clostridium septicum* is a significant cause of **spontaneous gas gangrene**, especially in patients with **hematological malignancies** or **colonic pathologies**. - It is highly invasive and can rapidly spread through tissues, producing potent toxins that lead to extensive myonecrosis and gas formation. *Clostridium bifermentans* - *Clostridium bifermentans* is one of the less common species of *Clostridium* that can cause **gas gangrene**, particularly in **polymicrobial infections**. - It is capable of producing **proteolytic enzymes** that contribute to tissue destruction and the characteristic foul-smelling discharge associated with clostridial myonecrosis.

Q: Which of the following is not a biovar of Corynebacterium diphtheriae?

Meningitidis. ***Meningitidis*** - **Meningitidis** is the species name for *Neisseria meningitidis*, a bacterium known for causing **meningitis** and other invasive diseases. - It is **not a biovar** or strain type of *Corynebacterium diphtheriae*, the causative agent of diphtheria. *Belfanti* - **Belfanti** is one of the recognized **biovars of *Corynebacterium diphtheriae***, known for its biochemical characteristics differentiating it from other strains. - While it can cause diphtheria, it is generally associated with milder symptoms compared to other biovars. *Gravis* - **Gravis** is a clinically significant **biovar of *Corynebacterium diphtheriae***, historically associated with severe forms of diphtheria. - It is known for its ability to produce potent toxins and cause widespread outbreaks. *Intermedius* - **Intermedius** is another established **biovar of *Corynebacterium diphtheriae***, exhibiting biochemical traits that differentiate it from Gravis and Mitis. - It is also capable of causing diphtheria, although its clinical presentation can vary.

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: The term 'leathery' appearance in medical terminology is characteristically used to describe:

Diphtheria. ***Diphtheria*** - The term "leather" in medical terminology is commonly used to describe the **pseudomembrane** found in diphtheria, which is tough, leathery, and firmly adherent. - This **pseudomembrane** is composed of fibrin, bacteria, inflammatory cells, and necrotic tissue, and its removal can cause bleeding. *Anthrax* - Anthrax typically causes a **black eschar** with surrounding edema, which is distinct from the leathery pseudomembrane of diphtheria. - The characteristic lesion is often referred to as a **malignant pustule** and is not described as "leather." *Neisseria* - Infections caused by *Neisseria* species, such as **meningitis** or **gonorrhea**, do not involve the formation of a leathery pseudomembrane. - *Neisseria meningitidis* can cause **purpuric rash** and petechiae, while *Neisseria gonorrhoeae* typically causes mucopurulent discharges. *Proteus* - *Proteus* species are common causes of **urinary tract infections** and wound infections. - These infections do not produce a "leathery" appearance or pseudomembrane and are known for their strong **ammonia-like odor** in urine.

Q: In a patient of the nephrotic syndrome with spontaneous bacterial peritonitis, which one of the following micro-organisms is most commonly involved?

Pneumococcus. ***Pneumococcus*** - **Streptococcus pneumoniae (Pneumococcus)** is the **most common** causative organism of **spontaneous bacterial peritonitis (SBP)** in patients with **nephrotic syndrome**, especially in children. - Nephrotic syndrome causes loss of **immunoglobulins (IgG)** in the urine, leading to **opsonization defects** that increase susceptibility to **encapsulated organisms** like Pneumococcus. - The organism typically reaches the peritoneal cavity via **hematogenous spread** from respiratory or other primary sites. - This contrasts with SBP in **cirrhotic ascites**, where gram-negative enteric organisms predominate. *Escherichia* - **Escherichia coli (E. coli)** is the most common cause of SBP in **cirrhotic patients** with ascites (due to bacterial translocation from the gut). - In **nephrotic syndrome**, E. coli is a less common cause compared to Pneumococcus, as the immune defect specifically affects defense against encapsulated organisms. - The pathophysiology differs between cirrhosis (portal hypertension, bacterial translocation) and nephrotic syndrome (immunoglobulin loss). *Proteus* - **Proteus mirabilis** is an uncommon cause of spontaneous bacterial peritonitis in nephrotic syndrome. - Proteus is more frequently associated with **urinary tract infections**, especially in patients with structural abnormalities or catheterization. *Staphylococcus* - **Staphylococcus** species are rare causes of primary spontaneous bacterial peritonitis in nephrotic syndrome. - When present, Staphylococcus usually suggests **secondary peritonitis** from perforation, surgical complications, or catheter-related peritonitis (e.g., peritoneal dialysis).

Q: All of the following statements about cholera are true except -

O & H antigens measure carrier state. ***O & H antigens measure carrier state*** - **O and H antigens** are primarily involved in serotyping *Vibrio cholerae* and are crucial for the initial classification of different strains, particularly differentiating between toxigenic and non-toxigenic strains. - The detection of **carrier states** in cholera is typically achieved through culturing stool samples for the presence of *Vibrio cholerae*, rather than by measuring O and H antigens, as these antigens reflect the bacterial surface components. *Culture medium is TCBS Agar* - **Thiosulfate-citrate-bile salts-sucrose (TCBS) agar** is a selective and differential medium widely used for isolating *Vibrio* species, including *Vibrio cholerae*, from clinical samples and environmental sources. - It works by inhibiting the growth of most enteric bacteria while allowing *Vibrio* species to grow and produce distinct colonies (e.g., yellow colonies for sucrose-fermenting *V. cholerae*). *Produces indole and reduces nitrate* - *Vibrio cholerae* is biochemically characterized by its ability to **produce indole** from tryptophan and to **reduce nitrates** to nitrites, which are important diagnostic markers. - These metabolic activities are part of the standard battery of biochemical tests used to identify and confirm the presence of *Vibrio cholerae* in laboratory settings. *Synthesize neuraminidase* - *Vibrio cholerae* produces **neuraminidase**, an enzyme that cleaves **sialic acid** residues from mucin, potentially enhancing the binding of cholera toxin to intestinal epithelial cells by exposing GM1 ganglioside receptors. - This enzyme contributes to the pathogen's virulence by modifying the host's intestinal environment, although its direct role in disease pathogenesis is still under investigation.

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 pneumophilia* - While *Legionella* can cause **atypical pneumonia** with similar systemic symptoms and a dry cough, it often presents with **gastrointestinal symptoms** (diarrhea) or **neurological symptoms** (confusion) which are not described here. - *Legionella* usually infects via **aerosolized contaminated water sources** and is often associated with outbreaks. *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.

Q: A 4-year-old male child presents with fever, anemia and azotemia after an episode of dysentery 9 days earlier. The commonest organism responsible for this condition is?

E. coli. ***E. coli*** - **Enterohemorrhagic E. coli** (EHEC), particularly O157:H7, is the most common cause of **hemolytic uremic syndrome (HUS)**, which presents with the triad of **fever, anemia (hemolytic)**, and **azotemia (acute kidney injury)** following bloody diarrhea (dysentery). - The incubation period of about 7-10 days between the diarrheal episode and the onset of HUS symptoms is consistent with the timeline described. *Meningococcus* - **Neisseria meningitidis** typically causes **meningitis** and **meningococcemia**, characterized by fever, headache, neck stiffness, and a petechial rash. - It is not associated with dysentery or the subsequent development of hemolytic uremic syndrome. *E. histolytica* - **Entamoeba histolytica** causes **amebic dysentery** and can lead to complications such as **liver abscesses**. - While it causes dysentery, it does not typically lead to the systemic complications of hemolytic anemia and azotemia characteristic of HUS. *Staphylococcus* - **Staphylococcus aureus** can cause a wide range of infections, including **skin infections**, **food poisoning**, and **sepsis**, but it is primarily a gram-positive coccus. - It is not a common cause of dysentery leading to HUS; EHEC, a gram-negative rod, is the usual culprit in this clinical scenario.

Question 1

Fermentation of glycerol is the basis for classification of:

Accepted Answer

Yersinia

Answer

Neisseria

Answer

Enterobacteriaceae

Answer

Streptococci

Question 2

Gas gangrene can be caused by all Except

Accepted Answer

Clostridium difficile

Answer

Clostridium sporogenes

Answer

Clostridium septicum

Answer

Clostridium bifermentans

Question 3

Which of the following is not a biovar of Corynebacterium diphtheriae?

Accepted Answer

Meningitidis

Answer

Belfanti

Answer

Gravis

Answer

Intermedius

Question 4

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 5

The term 'leathery' appearance in medical terminology is characteristically used to describe:

Accepted Answer

Diphtheria

Answer

Anthrax

Answer

Neisseria

Answer

Proteus

Question 6

In a patient of the nephrotic syndrome with spontaneous bacterial peritonitis, which one of the following micro-organisms is most commonly involved?

Accepted Answer

Pneumococcus

Answer

Proteus

Answer

Escherichia

Answer

Staphylococcus

Question 7

All of the following statements about cholera are true except -

Accepted Answer

O & H antigens measure carrier state

Answer

Culture medium is TCBS Agar

Answer

Produces indole and reduces nitrate

Answer

Synthesize neuraminidase

Question 8

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

Legionella pneumophilia

Answer

Streptococcus pneumoniae

Answer

Parainfluenza virus

Question 9

“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

Question 10

A 4-year-old male child presents with fever, anemia and azotemia after an episode of dysentery 9 days earlier. The commonest organism responsible for this condition is?

Accepted Answer

E. coli

Answer

Meningococcus

Answer

E. histolytica

Answer

Staphylococcus

Bacteriology — MCQs

Bacteriology — MCQs

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