Bacteriology Practice Questions

Q: Which of the following doesn't cause urethritis in males?

H. Ducreyi. ***H. Ducreyi*** - *Haemophilus ducreyi* is the causative agent of **chancroid**, a sexually transmitted infection characterized by painful **genital ulcers** and **lymphadenopathy**. - It does not primarily cause **urethritis**, which is inflammation of the urethra. *Trichomonas vaginalis* - **Trichomonas vaginalis** is a protozoan parasite that commonly causes **trichomoniasis**, a sexually transmitted infection. - In males, it can lead to **urethritis** with symptoms such as dysuria and urethral discharge. *Chlamydia trachomatis* - **Chlamydia trachomatis** is a very common bacterial cause of **urethritis** in males, often presenting with a **mucopurulent discharge** and dysuria. - It is frequently asymptomatic, making it a significant cause of undiagnosed sexually transmitted infections. *N. gonorrhoeae* - **Neisseria gonorrhoeae** is the bacterium responsible for **gonorrhea**, a well-known cause of **purulent urethritis** in males. - Symptoms typically include a profuse, **purulent urethral discharge** and painful urination.

Q: True about lepra bacilli is

Mycobacterium leprae can be grown in foot pad of mice. ***Mycobacterium leprae can be grown in foot pad of mice*** - **M. leprae** cannot be cultured on artificial media; therefore, it is grown in vivo, typically in the **footpads of mice** or armadillos. - This method allows for the study of the bacterium's growth, drug susceptibility, and the pathogenesis of **leprosy**. - This is the most distinctive laboratory characteristic of M. leprae. *Antileprosy vaccine does not provide lifelong protection* - While this statement is technically true (there is no specific leprosy vaccine, and **BCG vaccine** offers only partial protection with 20-80% efficacy that doesn't provide lifelong immunity), this is not a unique characteristic of lepra bacilli. - BCG reduces the risk but is not a complete preventative measure. *Incubation period is 3-5 years* - The **average incubation period** for leprosy is indeed **3-5 years**, making this statement technically accurate. - However, the incubation period is highly variable and can range from as short as 6 months to over 20 years. - This statement is **acceptable but less specific** than the culture characteristic. *INH does not inhibit their growth* - While this statement is true (**Isoniazid (INH)** is ineffective against **Mycobacterium leprae**), this is not the most defining characteristic of lepra bacilli. - The cell wall structure and metabolic pathways of M. leprae differ from **M. tuberculosis**, rendering INH ineffective against leprosy. - Leprosy is treated with dapsone, rifampicin, and clofazimine instead.

Q: Which of the following is the aetiological agent most often associated with Epiglottitis in children -

Haemophilus influenzae type b. ***Haemophilus influenzae type b*** - Historically, **_Haemophilus influenzae_ type b (Hib)** was the most common cause of **epiglottitis** in children. - The introduction of the **Hib vaccine** has significantly reduced its incidence, but it remains a crucial consideration. *Neisseria sp* - **_Neisseria_ species** are typically associated with infections like **meningitis** and **gonorrhea**, not primary causes of epiglottitis. - While **_Neisseria meningitidis_** can cause invasive disease, it's not a common pathogen for epiglottitis. *Moraxella catarrhalis* - **_Moraxella catarrhalis_** is a common cause of **otitis media**, **sinusitis**, and **bronchitis**, especially in children. - It is not a principal cause of acute epiglottitis. *Streptococcus pneumoniae* - **_Streptococcus pneumoniae_** is a major cause of **pneumonia**, **otitis media**, **meningitis**, and **sepsis**. - While it can cause respiratory infections, it is not the most frequent pathogen associated with epiglottitis compared to Hib pre-vaccine era.

Q: A 9 years old child presented to OPD with complaints of high grade fever, vomiting, one episode of seizure. CSF examination was done and Gram staining of the culture showed the following finding. What is the probable causative agent?

Gram-positive diplococci (e.g., Streptococcus pneumoniae). ***Gram-positive diplococci (e.g., Streptococcus pneumoniae)*** - The image displays small, purple (Gram-positive) cocci arranged in pairs (**diplococci**). - *Streptococcus pneumoniae* is a common cause of **bacterial meningitis** in children, and its characteristic morphology on Gram stain is Gram-positive diplococci. *Gram-negative coccobacilli (e.g., Haemophilus influenzae)* - While *Haemophilus influenzae* can cause meningitis in children, its Gram stain morphology would show **pink-stained coccobacillary forms**, not purple cocci. - The bacteria in the image are clearly cocci, not coccobacilli, and stain Gram-positive (purple). *Gram-negative diplococci (e.g., Neisseria meningitidis)* - *Neisseria meningitidis* is a significant cause of meningitis and appears as **Gram-negative (pink) diplococci**. - The organisms in the image are stained purple, indicating they are Gram-positive. *Gram-positive cocci in chains (e.g., Streptococcus pyogenes)* - *Streptococcus pyogenes* typically forms **chains of Gram-positive cocci**, which is not the predominant arrangement seen in the image. - Although it is Gram-positive, the characteristic arrangement in the image is diplococci, not chains.

Q: A 12 year old boy presents with vomiting within 3 hours of consumption of food at a party. What is the likely causative organism responsible for the symptoms?

Staphylococcus aureus. ***Staphylococcus aureus*** - **Vomiting occurring within 1-6 hours of food consumption** is highly characteristic of preformed toxin ingestion, commonly associated with *S. aureus*. - *S. aureus* produces **heat-stable enterotoxins** that cause rapid onset nausea, vomiting, and abdominal cramps. *Clostridium perfringens* - This bacterium typically causes symptoms like **abdominal cramps and diarrhea**, with vomiting being less common. - The onset of illness from *C. perfringens* is usually **8-16 hours** after consumption, which is longer than the 3-hour window in this case. *Clostridium botulinum* - *C. botulinum* causes **botulism**, a neuroparalytic illness, which may include nausea and vomiting in its early stages but is primarily characterized by **flaccid paralysis**. - Symptoms usually appear **12-36 hours** after exposure, which is much longer than the presentation described. *Salmonella* - **Salmonellosis** typically has an incubation period of **6-72 hours**, with symptoms including diarrhea, fever, and abdominal cramps; vomiting may occur but is not as immediate or predominant as with *S. aureus* toxin. - The illness is caused by bacterial colonization and invasion, not preformed toxins, leading to a longer onset compared to the 3-hour presentation.

Q: A 29 year old male was brought to ED with complaints of nausea, vomiting and abdominal cramps 3-4 hours after eating meat at dinner. What is the likely cause of this condition?

Staphylococcus aureus. ***Staphylococcus aureus*** - The rapid onset of symptoms (3-4 hours) after eating meat, characterized by **nausea**, **vomiting**, and **abdominal cramps**, is highly suggestive of preformed toxin-mediated food poisoning, with **Staphylococcus aureus** being a common culprit. - *S. aureus* produces heat-stable enterotoxins that, when ingested, cause prompt gastrointestinal symptoms due to their direct irritant effect on the gut. *Clostridium perfringens* - This bacterium typically causes food poisoning with an incubation period of **8-16 hours** and symptoms primarily include **abdominal cramps** and **diarrhea**, with vomiting being less common. - Symptoms arise from toxins produced *in vivo* after spore ingestion, not preformed toxins, which leads to a longer incubation time. *Clostridium botulinum* - While *Clostridium botulinum* produces a potent neurotoxin, its food poisoning primarily manifests as **neurological symptoms** (e.g., flaccid paralysis, diplopia, dysphagia), not acute gastrointestinal upset like vomiting and cramps. - The incubation period is typically **12-36 hours**, longer than the reported 3-4 hours, and it is usually associated with improperly canned foods. *Salmonella Enteritidis* - *Salmonella* infections usually have a longer incubation period of **6 hours to 6 days**, and while they can cause nausea, vomiting, cramps, and diarrhea, the rapid onset in this case makes *S. aureus* more likely. - Infection typically leads to **inflammatory gastroenteritis**, sometimes with fever, which is not mentioned as a prominent symptom here.

Q: Superantigen is produced by which of the following?

Streptococcus pyogenes. ***Streptococcus pyogenes*** - *Streptococcus pyogenes* produces **superantigens** such as **streptococcal pyrogenic exotoxins (SPE-A, SPE-B, SPE-C)**. - These superantigens cause massive non-specific T-cell activation, leading to **toxic shock syndrome** and **scarlet fever**. - Superantigens bypass normal antigen processing by directly binding MHC class II molecules to T-cell receptors. *Clostridium perfringens* - *Clostridium perfringens* primarily produces **alpha-toxin** (phospholipase C) and other toxins causing **gas gangrene** and **food poisoning**. - It does not produce superantigens. *Vibrio cholerae* - *Vibrio cholerae* produces **cholera toxin**, an **enterotoxin** that causes massive fluid secretion in the intestine, leading to profuse watery diarrhea. - Cholera toxin is not a superantigen; it acts by activating adenylate cyclase through ADP-ribosylation. *Staphylococcus epidermidis* - *Staphylococcus epidermidis* is a common skin commensal that can cause infections related to **medical devices** and **biofilm formation**. - Unlike *Staphylococcus aureus* (which produces TSST-1 and enterotoxins), *S. epidermidis* does not produce superantigens.

Q: Urethritis in males is not caused by:

H. ducreyi. ***H. ducreyi*** - *Haemophilus ducreyi* is the causative agent of **chancroid**, a sexually transmitted infection characterized by **genital ulcers** [1] with painful regional lymphadenopathy. - It does not typically cause urethritis as its primary site of infection is the **skin and mucous membranes** of the external genitalia, forming ulcers rather than urethral inflammation. *Chlamydia* - **Chlamydia trachomatis** is a common cause of **non-gonococcal urethritis** in males [1]. - It often presents with **dysuria**, **urethral discharge**, and sometimes can be asymptomatic [1]. *Gonococcus* - **Neisseria gonorrhoeae** (gonococcus) is a well-known cause of urethritis, often referred to as **gonococcal urethritis** [1]. - It typically causes a **purulent urethral discharge** and **dysuria** [1]. *Trichomonas* - **Trichomonas vaginalis** can cause **urethritis** in males [1], although it is less common than in females. - Males may experience **dysuria**, **urethral discharge**, or can be asymptomatic carriers.

Q: Gram stain of CSF shows gram-negative diplococci. Culture grows on Thayer-Martin medium. Most likely organism?

N. meningitidis. ***N. meningitidis*** - The presence of **gram-negative diplococci** in CSF is a hallmark feature of *Neisseria meningitidis*. - **Thayer-Martin medium** is a selective medium specifically designed for the isolation and growth of *Neisseria* species, inhibiting other bacterial and fungal contaminants. *L. monocytogenes* - *Listeria monocytogenes* is a **gram-positive rod**, which contradicts the gram stain finding of gram-negative diplococci. - It typically causes meningitis in neonates, elderly, and immunocompromised individuals, but its morphology is distinct. *S. pneumoniae* - *Streptococcus pneumoniae* is a **gram-positive coccus**, often appearing in pairs (diplococci) or short chains, but it is gram-positive, not gram-negative. - It is a common cause of bacterial meningitis but does not grow readily on Thayer-Martin medium. *H. influenzae* - *Haemophilus influenzae* is a **pleomorphic gram-negative coccobacillus**, not a diplococcus, and it requires specific growth factors (X and V factors) found in chocolate agar. - While it can cause meningitis, its characteristic morphology and growth requirements differ from the description.

Q: Which microorganism causes pseudomembranous colitis?

C. difficile. ***C. difficile*** - **Clostridioides difficile** (formerly Clostridium difficile) infection is the most common cause of **pseudomembranous colitis**, characterized by inflammation of the colon and formation of pseudomembranes. - This infection often occurs after **antibiotic use**, which disrupts the normal gut flora, allowing C. difficile to proliferate and produce toxins. *Shigella* - **Shigella** species cause **shigellosis**, a type of dysentery characterized by bloody diarrhea, fever, and abdominal cramps. - While it can cause severe colitis, it typically does not lead to the distinct pseudomembranous lesions seen in C. difficile infection. *E. coli* - Various strains of **Escherichia coli** can cause different gastrointestinal illnesses, such as traveler's diarrhea (enterotoxigenic E. coli) or hemorrhagic colitis (enterohemorrhagic E. coli O157:H7). - However, E. coli is not the causative agent of **pseudomembranous colitis**. *Salmonella* - **Salmonella** species cause salmonellosis, which can manifest as **gastroenteritis** (food poisoning) or **typhoid fever**. - While it causes enterocolitis, it does not typically result in the formation of **pseudomembranes** that characterize C. difficile infection.

Question 1

Which of the following doesn't cause urethritis in males?

Accepted Answer

H. Ducreyi

Answer

Trichomonas vaginalis

Answer

Chlamydia trachomatis

Answer

N. gonorrhoeae

Question 2

True about lepra bacilli is

Accepted Answer

Mycobacterium leprae can be grown in foot pad of mice

Answer

Antileprosy vaccine does not provide lifelong protection

Answer

Incubation period is 3-5 years

Answer

INH does not inhibit their growth

Question 3

Which of the following is the aetiological agent most often associated with Epiglottitis in children -

Accepted Answer

Haemophilus influenzae type b

Answer

Neisseria sp

Answer

Moraxella catarrhalis

Answer

Streptococcus pneumoniae

Question 4

A 9 years old child presented to OPD with complaints of high grade fever, vomiting, one episode of seizure. CSF examination was done and Gram staining of the culture showed the following finding. What is the probable causative agent?

Accepted Answer

Gram-positive diplococci (e.g., Streptococcus pneumoniae)

Answer

Gram-negative coccobacilli (e.g., Haemophilus influenzae)

Answer

Gram-negative diplococci (e.g., Neisseria meningitidis)

Answer

Gram-positive cocci in chains (e.g., Streptococcus pyogenes)

Question 5

A 12 year old boy presents with vomiting within 3 hours of consumption of food at a party. What is the likely causative organism responsible for the symptoms?

Accepted Answer

Staphylococcus aureus

Answer

Clostridium perfringens

Answer

Clostridium botulinum

Answer

Salmonella

Question 6

A 29 year old male was brought to ED with complaints of nausea, vomiting and abdominal cramps 3-4 hours after eating meat at dinner. What is the likely cause of this condition?

Accepted Answer

Staphylococcus aureus

Answer

Clostridium perfringens

Answer

Clostridium botulinum

Answer

Salmonella Enteritidis

Question 7

Superantigen is produced by which of the following?

Accepted Answer

Streptococcus pyogenes

Answer

Clostridium perfringens

Answer

Vibrio cholerae

Answer

Staphylococcus epidermidis

Question 8

Urethritis in males is not caused by:

Accepted Answer

H. ducreyi

Answer

Chlamydia

Answer

Gonococcus

Answer

Trichomonas

Question 9

Gram stain of CSF shows gram-negative diplococci. Culture grows on Thayer-Martin medium. Most likely organism?

Accepted Answer

N. meningitidis

Answer

L. monocytogenes

Answer

S. pneumoniae

Answer

H. influenzae

Question 10

Which microorganism causes pseudomembranous colitis?

Accepted Answer

C. difficile

Answer

Shigella

Answer

E. coli

Answer

Salmonella

Bacteriology — MCQs

Bacteriology — MCQs

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