Bacteriology Practice Questions

Q: All of the following cause hemolytic uremic syndrome except

Vibrio cholera. ***Vibrio cholera*** - *Vibrio cholerae* causes **cholera**, characterized by severe watery diarrhea, dehydration, and electrolyte imbalance, but does not typically produce **Shiga toxin** or cause microangiopathic hemolytic anemia, thrombocytopenia, and acute kidney injury characteristic of HUS. - While it can lead to acute kidney injury due to severe dehydration, it does not directly cause the **microangiopathic hemolytic anemia** and thrombocytopenia seen in HUS. *EHEC* - **Enterohemorrhagic *E. coli* (EHEC)**, particularly serotype O157:H7, is the most common cause of **Shiga toxin-producing E. coli (STEC)-HUS** [2]. - The **Shiga toxin** produced by EHEC damages endothelial cells, leading to platelet aggregation, hemolysis, and renal damage [2]. *Campylobacter* - **Campylobacter jejuni** infections can sometimes precede the development of **HUS**, particularly in children. - While less common than EHEC, *Campylobacter* can produce a **cytolethal distending toxin** which has been implicated in endothelial damage and HUS. *Shigella* - Certain species of **Shigella**, especially *Shigella dysenteriae type 1*, produce **Shiga toxin** and are a known cause of **HUS**. - Similar to EHEC, the Shiga toxin from *Shigella* leads to widespread endothelial damage, resulting in microangiopathic hemolytic anemia, thrombocytopenia, and acute kidney injury [1].

Q: Chlamydia causes all except:

Typical pneumonia. ***Typical pneumonia*** - While *Chlamydia pneumoniae* can cause **atypical pneumonia** (walking pneumonia), it does not cause **typical bacterial pneumonia** characterized by lobar consolidation and acute onset, as would be seen with *Streptococcus pneumoniae*. - **Atypical pneumonia** is distinguished by less severe symptoms, gradual onset, and diffuse interstitial infiltrates rather than lobar consolidation. *LGV* - **Lymphogranuloma venereum (LGV)** is a severe form of chlamydial infection caused by specific serovars of *Chlamydia trachomatis* (L1, L2, L3). - It presents with genital ulcers and painful **inguinal lymphadenopathy** (buboes). *Urethritis* - *Chlamydia trachomatis* is a very common cause of **nongonococcal urethritis** in men, often presenting with dysuria, urethral discharge, and itching. - It can also lead to **cervicitis** in women, often asymptomatic. *Trachoma* - **Trachoma** is a chronic conjunctivitis caused by specific serovars of *Chlamydia trachomatis* (A, B, Ba, C) that primarily affects the eyes. - It is a leading preventable cause of **blindness worldwide**, particularly in impoverished regions.

Q: What is the generation time for *M. tuberculosis*?

20-24 hours. ***20-24 hours*** - *Mycobacterium tuberculosis* is characterized by a **slow growth rate**, with a generation time of approximately **20-24 hours**. - This slow growth contributes to the **prolonged incubation period** and the chronic nature of tuberculosis infections. *10-15 hours* - A generation time of 10-15 hours is still relatively slow but faster than that of *Mycobacterium tuberculosis*. - This range is more typical for some other **fastidious bacteria** or those growing in suboptimal conditions. *6-8 hours* - A generation time of 6-8 hours is too rapid for *Mycobacterium tuberculosis*. - This rate is more characteristic of **moderately fast-growing bacteria** under favorable conditions. *30-36 hours* - While *Mycobacterium tuberculosis* is a slow-growing organism, a generation time of 30-36 hours would be even slower than its typical rate. - This extremely slow growth might be seen in highly **stressed or dormant bacterial populations**.

Q: All of the following organisms cause gastroenteritis within 6 hours, EXCEPT:

E. coli. ***E. coli*** - **E. coli** gastroenteritis typically has a longer incubation period of **1-3 days (24-72 hours)**, as it involves bacterial colonization and toxin production or invasion of the intestinal lining. - The disease mechanism for most pathogenic *E. coli* strains (ETEC, EPEC, EHEC) involves adhesion and proliferation, which takes significantly more time than preformed toxin ingestion. *Clostridium* - **Clostridium perfringens** is NOT typically associated with onset within 6 hours. Its incubation period is **8-12 hours** (range 6-24 hours). - However, since the question asks about organisms causing gastroenteritis "within 6 hours," and C. perfringens can rarely manifest at 6 hours (lower end of range), it is considered a possible cause within this timeframe, unlike E. coli which requires days. - Symptoms result from **enterotoxin** produced in the gut after spore germination. *Staphylococcus* - **Staphylococcus aureus** food poisoning is caused by ingestion of preformed **enterotoxins** in contaminated food. - This leads to **rapid onset** of symptoms, typically within **1-6 hours** (most commonly 2-4 hours). - Classic presentation: sudden onset of severe vomiting and nausea. *Bacillus cereus* - **Bacillus cereus** emetic type is caused by preformed cereulide toxin, manifesting in **0.5-6 hours** (typically 1-5 hours). - Presents with prominent vomiting, similar to staph food poisoning. - The diarrheal type has a longer incubation of 6-15 hours.

Q: A 9-year-old child presented to OPD with complaints of high-grade fever, vomiting, and one episode of seizure. CSF examination was done and Gram staining of the culture showed lanceolate-shaped gram-positive diplococci. What is the probable causative agent?

Streptococcus pneumoniae. ***Streptococcus pneumoniae*** - The description of **lanceolate-shaped gram-positive diplococci** in CSF is characteristic of *S. pneumoniae*. - This bacterium is a common cause of **bacterial meningitis** in children and can present with high fever, vomiting, and seizures. *Haemophilus influenzae* - This is a **gram-negative coccobacillus**, which would appear as small, pleomorphic rods rather than lanceolate-shaped diplococci on Gram stain. - While it causes meningitis, its Gram stain morphology is distinct from *S. pneumoniae*. *Streptococcus agalactiae* - *S. agalactiae* (Group B Streptococcus) is a **gram-positive coccus**, but it typically appears in **chains** and is a major cause of neonatal meningitis, not usually in a 9-year-old child. - Its morphology on Gram stain would not be described as lanceolate diplococci. *Neisseria meningitidis* - *N. meningitidis* is a **gram-negative diplococcus** and would appear as kidney-bean shaped or flattened paired cocci, not gram-positive. - Though a common cause of meningitis, the Gram stain morphology described rules it out.

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.

Question 1

All of the following cause hemolytic uremic syndrome except

Accepted Answer

Vibrio cholera

Answer

EHEC

Answer

Campylobacter

Answer

Shigella

Question 2

Chlamydia causes all except:

Accepted Answer

Typical pneumonia

Answer

LGV

Answer

Urethritis

Answer

Trachoma

Question 3

Which of the following statements are true regarding Legionella, EXCEPT?

Accepted Answer

L. pneumophila lipopolysaccharide is more toxic than other gram-negative species

Answer

Infections are associated with aerosols

Answer

Amoebas in fresh water habitat act as reservoir

Answer

Carriers are unknown

Question 4

What is the generation time for *M. tuberculosis*?

Accepted Answer

20-24 hours

Answer

10-15 hours

Answer

6-8 hours

Answer

30-36 hours

Question 5

All of the following organisms cause gastroenteritis within 6 hours, EXCEPT:

Accepted Answer

E. coli

Answer

Clostridium

Answer

Staphylococcus

Answer

Bacillus cereus

Question 6

A 9-year-old child presented to OPD with complaints of high-grade fever, vomiting, and one episode of seizure. CSF examination was done and Gram staining of the culture showed lanceolate-shaped gram-positive diplococci. What is the probable causative agent?

Accepted Answer

Streptococcus pneumoniae

Answer

Haemophilus influenzae

Answer

Streptococcus agalactiae

Answer

Neisseria meningitidis

Question 7

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

Accepted Answer

H. Ducreyi

Answer

Trichomonas vaginalis

Answer

Chlamydia trachomatis

Answer

N. gonorrhoeae

Question 8

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 9

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 10

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)

Bacteriology — MCQs

Bacteriology — MCQs

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