Bacteriology Practice Questions

Q: Chlamydia causes:

Trachoma and Lymphogranuloma venereum. **Trachoma and Lymphogranuloma venereum** - This is the **most comprehensive correct answer** as it lists two major diseases caused by different serovars of *Chlamydia trachomatis* - **Trachoma** (serovars A, B, Ba, C) - chronic keratoconjunctivitis and the leading infectious cause of blindness worldwide - **Lymphogranuloma venereum (LGV)** (serovars L1, L2, L3) - systemic sexually transmitted infection with inguinal lymphadenopathy - This answer captures both the **ocular** and **genital** manifestations of *C. trachomatis*, making it the best option *Trachoma* - While medically accurate, this is **incomplete** as it only mentions one disease - *C. trachomatis* causes multiple clinically significant diseases beyond trachoma - This option ignores LGV and other important chlamydial syndromes *Trachoma and Conjunctivitis* - This option is **redundant and misleading** - trachoma IS a specific type of chronic bacterial conjunctivitis - Listing both together suggests they are separate entities when trachoma is actually a subset of conjunctivitis - Misses other major non-ocular diseases like LGV, making it inferior to the correct answer *Conjunctivitis* - While *C. trachomatis* does cause conjunctivitis (trachoma, inclusion conjunctivitis), this is **too broad and non-specific** - Conjunctivitis has numerous causes (viral, bacterial, allergic) and this answer lacks specificity - Completely omits systemic/genital manifestations like LGV, urethritis, and PID

Q: Acute infectious diarrhea can be caused by all EXCEPT:

Enterococcus faecalis. ***Enterococcus faecalis*** - While *Enterococcus faecalis* is a significant hospital-acquired pathogen, it is **not a common cause of acute infectious diarrhea**. - It primarily causes infections like **urinary tract infections**, **endocarditis**, and **bacteremia**, especially in immunocompromised individuals. *Staphylococcus* - *Staphylococcus aureus* can cause **food poisoning** due to preformed toxins, leading to acute onset vomiting and diarrhea. - This is an example of an **acute infectious diarrheal illness**, though often toxin-mediated rather than direct infection. *Clostridium* - *Clostridium difficile* is a well-known cause of **antibiotic-associated diarrhea** and pseudomembranous colitis, which is an acute infectious diarrhea. - Other *Clostridium* species, like *Clostridium perfringens*, can cause **food poisoning** with diarrheal symptoms. *Vibrio* - *Vibrio cholerae* is the classic cause of **cholera**, an acute, severe watery diarrhea that can lead to rapid dehydration. - Other *Vibrio* species, such as *Vibrio parahaemolyticus*, frequently cause **foodborne illness** from contaminated seafood, presenting with acute diarrhea.

Q: A man had Egg omelet 1-4 hours back and developed diarrhea, vomiting and abdominal cramps. Most likely cause of poisoning is

Staphylococcus. ***Staphylococcus*** - **Staphylococcal food poisoning** is characterized by a rapid onset (1-6 hours, most commonly 2-4 hours) of symptoms like **nausea**, **vomiting**, **abdominal cramps**, and **diarrhea** after consuming contaminated food. - Omelets prepared with eggs can be a source if handled improperly, allowing pre-formed **heat-stable enterotoxins** produced by *Staphylococcus aureus* to cause illness, even if the bacteria themselves are killed by cooking. *Bacillus cereus* - This organism can cause two types of food poisoning: diarrheal and emetic. The **emetic type**, characterized by prominent vomiting, has a rapid onset (0.5-6 hours, usually 1-5 hours) often associated with *rice products* contaminated with **heat-stable toxin**. - While vomiting is present, the consumption of an omelet and the typical 1-4 hour timeframe match Staphylococcal more closely, and *Bacillus cereus* diarrheal type usually has a longer incubation (6-15 hours). *Clostridium* - **Clostridium perfringens** food poisoning typically causes primarily **diarrhea** and **abdominal cramps** with less prominent vomiting, and has a longer incubation period of 6-24 hours. - **Clostridium botulinum** causes a neuroparalytic illness, not primarily gastroenteritis, and is associated with improperly canned foods. *Salmonella* - **Salmonella food poisoning** usually has a longer incubation period, typically 12-72 hours (average 12-36 hours), with symptoms including diarrhea, fever, and abdominal cramps. - The **rapid onset** (1-4 hours) in this case makes Salmonella less likely, as it primarily causes infection rather than pre-formed toxin ingestion.

Q: A 40-year old woman presented to the surgical OPD with features suggestive of colitis. She was on prolonged treatment with clindamycin. Fecal sample was positive for toxin produced by this agent. Her condition improved on treatment with metronidazole. The clinical condition is associated with -

Clostridium difficile. ***Clostridium difficile*** - The history of **clindamycin use**, followed by **colitis symptoms**, a **positive fecal toxin test**, and improvement with **metronidazole**, are classic indicators of *Clostridium difficile* infection (CDI) [1]. - *C. difficile* produces toxins (Toxin A and Toxin B) that cause **pseudomembranous colitis**, often after antibiotic disruption of normal gut flora [1]. *Listeria monocytogenes* - This bacterium is primarily a cause of **foodborne illness**, leading to febrile gastroenteritis, meningitis, or sepsis, particularly in immunocompromised individuals, pregnant women, and neonates. - It is not typically associated with **antibiotic-associated colitis** or treated with metronidazole as a primary agent for bowel infection. *Bacillus anthracis* - This is the causative agent of **anthrax**, which can manifest as cutaneous, inhalational, or gastrointestinal forms. - **Gastrointestinal anthrax** causes severe abdominal pain, vomiting, bloody diarrhea, and fever, but it is rare and not linked to antibiotic use or toxin detection in stool in the context described. *Acinetobacter baumannii* - *Acinetobacter baumannii* is an important **opportunistic pathogen** often associated with hospital-acquired infections, such as pneumonia, urinary tract infections, and bloodstream infections, particularly in critically ill patients. - It is not a known cause of **antibiotic-associated colitis** due to toxin production, nor is metronidazole the primary treatment.

Q: A 45 year-old HIV-positive male presented with multiple red hemangioma-like lesions. Biopsy specimens show clusters of bacilli that stain positively with the Warthin-Starry stain. Which of the following could be the causative organism?

Bartonella henselae. ***Bartonella henselae*** - This clinical presentation of **red hemangioma-like lesions** (bacillary angiomatosis) in an **HIV-positive** individual, coupled with **Warthin-Starry stain positive bacilli** on biopsy, is highly characteristic of infection with *Bartonella henselae*. - *Bartonella henselae* is associated with **cat scratch disease** and bacillary angiomatosis, particularly in immunocompromised patients. *Bartonella quintana* - While *Bartonella quintana* can also cause **bacillary angiomatosis**, it is classically associated with **trench fever** and **endocarditis** more frequently than *Bartonella henselae*. - The clinical picture of typical "cat-scratch-like" lesions (hemangioma-like) more strongly points to *B. henselae*. *HHV8* - **Human Herpesvirus 8 (HHV8)** is the causative agent of **Kaposi's sarcoma**, which can also present with purple-red skin lesions in HIV-positive patients. - However, Kaposi's sarcoma lesions are typically **spindle cell proliferations** and would not show **clusters of bacilli** on Warthin-Starry stain. *EBV* - **Epstein-Barr Virus (EBV)** is associated with various lymphoproliferative disorders and **oral hairy leukoplakia** in HIV-positive individuals. - It does not cause **bacillary angiomatosis** or present with Warthin-Starry positive bacilli.

Q: A child with pyoderma becomes toxic and presents with respiratory distress. His chest radiograph shows patchy areas of consolidation and multiple bilateral thin-walled air containing cysts. The most likely etiological agent in this case is –

Staphylococcus aureus. ***Staphylococcus aureus*** - *S. aureus* is a common cause of **severe pyoderma** and can lead to **systemic toxicity** and **hematogenous spread** to the lungs. - The characteristic lung findings of **patchy consolidation** and **multiple thin-walled air-containing cysts** (pneumatoceles) are highly suggestive of *S. aureus* pneumonia, particularly in children. *Mycobacterium tuberculosis* - While *M. tuberculosis* can cause lung consolidation, it typically presents with **granulomatous inflammation** and is less likely to produce **multiple thin-walled cysts** rapidly in an acute, toxic presentation. - Pulmonary tuberculosis often has a more **insidious onset** and may be associated with risk factors like immunocompromise or exposure. *Pneumocystis jirovecii* - This pathogen primarily causes pneumonia in **immunocompromised individuals**, such as those with HIV, and is less common in an otherwise healthy child with pyoderma. - Chest radiographs typically show **diffuse interstitial infiltrates**, not distinct patchy consolidation or thin-walled cysts. *Mycobacterium avium intracellulare* - Like *P. jirovecii*, *M. avium intracellulare* (MAC) usually affects **immunocompromised individuals** or those with pre-existing lung disease. - MAC lung disease typically presents as **nodular or cavitary lesions** or diffuse infiltrates, not the characteristic acute cyst formation seen in this case.

Q: A 35 year old man presents to an emergency department with an exquisitely tender prostate gland. An acute bacterial infection is suspected. Which of the following organisms is the most common pathogen in this setting?

Escherichia. ***Escherichia*** - **_Escherichia coli_** is the most common Gram-negative bacillus responsible for both acute and chronic bacterial prostatitis due to its prevalence in the normal gut flora and its ability to ascend the urinary tract. - It accounts for approximately **80% of all acute bacterial prostatitis cases** because of its uropathogenic factors like fimbriae that allow adherence to urinary epithelial cells. *Enterobacter* - While **_Enterobacter_ species** can cause urinary tract infections and prostatitis, they are significantly less common than _E. coli_. - Prostatitis due to _Enterobacter_ often occurs in **hospitalized patients** or those with complicated UTIs, not typically in a healthy 35-year-old in the community. *Klebsiella* - **_Klebsiella pneumoniae_** is another Gram-negative rod that can cause prostatitis, frequently in patients with **urinary tract abnormalities** or catheterization. - It is less common than _E. coli_ in community-acquired acute bacterial prostatitis and is often associated with more severe disease or resistance patterns. *Proteus* - **_Proteus mirabilis_** is known for its ability to produce **urease**, which can lead to struvite stone formation in the urinary tract, and can cause UTIs. - While it can cause prostatitis, it is much **less frequent than _E. coli_** and often associated with urinary calculi or long-term catheter use.

Q: BPF (Brazilian purpuric fever) is caused by:

H.influenzae biotype aegyptius. ***H.influenzae biotype aegyptius*** - **Brazilian purpuric fever (BPF)** is a severe, acute pediatric disease characterized by **fever, purpura, vascular collapse, and high mortality**, specifically caused by this distinct strain of *Haemophilus influenzae biotype aegyptius*. - The infection typically starts as a **conjunctivitis** caused by the same organism, which then disseminates, leading to the systemic symptoms of BPF. *Salmonella* - *Salmonella* species are typically associated with **gastroenteritis**, **typhoid fever**, or other systemic infections, but not Brazilian purpuric fever. - While *Salmonella* can cause severe infections in children, its clinical presentation and typical symptoms (e.g., diarrhea, enteric fever) differ significantly from BPF. *V. cholerae* - *Vibrio cholerae* is the causative agent of **cholera**, an acute diarrheal illness characterized by severe watery diarrhea and dehydration. - It does not cause the purpuric rash, vasculitis, or the specific sudden onset and high mortality seen in Brazilian purpuric fever. *None of the options* - This option is incorrect because *H.influenzae biotype aegyptius* is the established and specific cause of Brazilian purpuric fever. - The disease is well-defined with a particular etiology, making "none of the options" an invalid choice.

Q: Most common causative organism for bacterial meningitis beyond 3 years of age is -

Pneumococcus. ***Pneumococcus*** - *Streptococcus pneumoniae* (Pneumococcus) is currently the most common cause of **bacterial meningitis** in individuals older than 3 years, particularly after the widespread use of the HiB vaccine. - It frequently causes severe disease with **high mortality and morbidity** due to its ability to colonize the nasopharynx and invade the bloodstream and meninges. *H. influenzae Type b* - Before the introduction of the **HiB vaccine**, *Haemophilus influenzae* type b was the leading cause of bacterial meningitis in children under 5 years of age. - Due to **routine vaccination**, its incidence has dramatically decreased, making it less common now in children beyond 3 years. *Meningococcus* - *Neisseria meningitidis* (Meningococcus) is a significant cause of bacterial meningitis, particularly in **epidemics** and in young adults and adolescents. - While it causes outbreaks and serious disease, it is generally less common than pneumococcal meningitis beyond childhood in areas with high vaccination coverage. *Staphylococcus aureus* - *Staphylococcus aureus* can cause bacterial meningitis but is more often associated with **neurosurgical procedures**, head trauma, or indwelling medical devices, rather than being a primary community-acquired pathogen for meningitis in immunocompetent individuals. - It is not the most common causative organism for community-acquired bacterial meningitis in the general population beyond 3 years of age.

Question 1

Chlamydia causes:

Accepted Answer

Trachoma and Lymphogranuloma venereum

Answer

Trachoma

Answer

Trachoma and Conjunctivitis

Answer

Conjunctivitis

Question 2

Acute infectious diarrhea can be caused by all EXCEPT:

Accepted Answer

Enterococcus faecalis

Answer

Staphylococcus

Answer

Clostridium

Answer

Vibrio

Question 3

A man had Egg omelet 1-4 hours back and developed diarrhea, vomiting and abdominal cramps. Most likely cause of poisoning is

Accepted Answer

Staphylococcus

Answer

Bacillus cereus

Answer

Clostridium

Answer

Salmonella

Question 4

A 40-year old woman presented to the surgical OPD with features suggestive of colitis. She was on prolonged treatment with clindamycin. Fecal sample was positive for toxin produced by this agent. Her condition improved on treatment with metronidazole. The clinical condition is associated with -

Accepted Answer

Clostridium difficile

Answer

Listeria monocytogenes

Answer

Bacillus anthracis

Answer

Acinetobacter baumannii

Question 5

A 45 year-old HIV-positive male presented with multiple red hemangioma-like lesions. Biopsy specimens show clusters of bacilli that stain positively with the Warthin-Starry stain. Which of the following could be the causative organism?

Accepted Answer

Bartonella henselae

Answer

Bartonella quintana

Answer

HHV8

Answer

EBV

Question 6

A child with pyoderma becomes toxic and presents with respiratory distress. His chest radiograph shows patchy areas of consolidation and multiple bilateral thin-walled air containing cysts. The most likely etiological agent in this case is –

Accepted Answer

Staphylococcus aureus

Answer

Mycobacterium tuberculosis

Answer

Pneumocystis jirovecii

Answer

Mycobacterium avium intracellulare

Question 7

A 35 year old man presents to an emergency department with an exquisitely tender prostate gland. An acute bacterial infection is suspected. Which of the following organisms is the most common pathogen in this setting?

Accepted Answer

Escherichia

Answer

Enterobacter

Answer

Klebsiella

Answer

Proteus

Question 8

BPF (Brazilian purpuric fever) is caused by:

Accepted Answer

H.influenzae biotype aegyptius

Answer

Salmonella

Answer

V. cholerae

Answer

None of the options

Question 9

Most common causative organism for bacterial meningitis beyond 3 years of age is -

Accepted Answer

Pneumococcus

Answer

H. influenzae Type b

Answer

Meningococcus

Answer

Staphylococcus aureus

Question 10

A major step in the pathogenesis of listeriosis is?

Accepted Answer

The survival and multiplication of L. monocytogenes within mononuclear phagocytes and host epithelial cells

Answer

The antiphagocytic activity of the L. monocytogenes capsule

Answer

The release of hyaluronidase by L. monocytogenes, which contributes to its dissemination from local sites

Answer

The formation of antigen-antibody complexes with resultant complement activation and tissue damage

Bacteriology — MCQs

Bacteriology — MCQs

On this page

Practice by Chapter

Want unlimited practice?