Bacteriology Practice Questions

Q: MC cause of atypical pneumonia?

Mycoplasma pneumoniae. ***Mycoplasma pneumoniae*** - *M. pneumoniae* is the most common cause of **atypical pneumonia**, often referred to as **"walking pneumonia"** due to milder symptoms compared to typical bacterial pneumonia. - It lacks a **cell wall**, making it resistant to many common antibiotics like penicillin and cephalosporins. *Klebsiella pneumoniae* - *Klebsiella pneumoniae* typically causes **lobar pneumonia**, particularly in individuals with compromised immune systems or alcoholism. - It is associated with **severe symptoms**, such as thick, "currant jelly" sputum, and often forms dense consolidated infiltrates on chest X-rays. [1] *Hemophilus influenzae* - *Haemophilus influenzae* is a common cause of **bacterial pneumonia**, especially in children and adults with underlying lung disease (e.g., COPD). - It usually presents as **typical pneumonia** with more acute and severe symptoms, rather than the milder, atypical presentation. *Chlamydia* - While *Chlamydia pneumoniae* can cause a form of atypical pneumonia, it is **less common** than *Mycoplasma pneumoniae* as the primary cause. [1] - *Chlamydia* infections can also cause other conditions, such as **urethritis** and **cervicitis**, depending on the species involved.

Q: Which of the following is anaerobic non-acid fast bacilli:

Actinomyces. ***Actinomyces*** - *Actinomyces* species are **obligate anaerobes** to **facultative anaerobes** that appear as **Gram-positive, non-acid-fast, filamentous rods** (bacilli). - They are classically described as **anaerobic bacteria** and are the prototypical example of anaerobic non-acid-fast bacilli. - They cause chronic infections (actinomycosis) often involving abscess formation with sulfur granules and sinus tracts. *Mycobacterium tuberculosis* - *Mycobacterium tuberculosis* is an **obligate aerobe**, not anaerobic. - It is characterized by its **acid-fastness** due to high mycolic acid content in its cell wall. - Requires oxygen for growth and is the causative agent of tuberculosis. *Listeria* - *Listeria monocytogenes* is a **facultative anaerobe**, meaning it preferentially grows in **aerobic conditions** but can survive anaerobically. - While it is a non-acid-fast Gram-positive bacillus, it is **not classified as an anaerobic organism** in standard microbiology terminology. - *Actinomyces* is the classic answer for anaerobic non-acid-fast bacilli. *Nocardia* - *Nocardia* species are **strict aerobes**, not anaerobic. - They are **weakly acid-fast** filamentous bacteria, distinguishing them from the non-acid-fast *Actinomyces*. - Require oxygen for growth and are found in soil.

Q: Eaton agent is:

Mycoplasma. ***Correct: Mycoplasma*** - The term **"Eaton agent"** refers to *Mycoplasma pneumoniae*, a common cause of atypical pneumonia. - This organism was initially identified by Monroe D. Eaton in the 1940s while studying respiratory infections. - *M. pneumoniae* is a cell wall-deficient bacterium that causes "walking pneumonia" and is resistant to beta-lactam antibiotics. *Incorrect: Pseudomonas* - **Pseudomonas** species, particularly *Pseudomonas aeruginosa*, are opportunistic pathogens often associated with nosocomial infections and infections in immunocompromised individuals. - They are not related to the "Eaton agent" or atypical pneumonia caused by *Mycoplasma pneumoniae*. *Incorrect: Gonococcus* - **Gonococcus** refers to *Neisseria gonorrhoeae*, a bacterium responsible for the sexually transmitted infection gonorrhea. - It causes distinct symptoms in the genitourinary tract and is unrelated to respiratory infections or the "Eaton agent." *Incorrect: Corynebacterium* - **Corynebacterium** species include *Corynebacterium diphtheriae*, the causative agent of diphtheria, which primarily affects the upper respiratory tract and skin. - While it can cause respiratory issues, it is not the "Eaton agent" and has a different clinical presentation and pathogenicity from *Mycoplasma pneumoniae*.

Q: A 47-year-old man with chronic asthma who has been treated with steroids for many years develops a productive cough, weight loss, and night sweats. Imaging studies reveal the presence of abscesses in the lungs and brain. Cultures show gram-positive filaments that are weakly acid-fast. Which of the following organisms is responsible for this patient's condition?

Nocardia asteroides. ***Nocardia asteroides*** - The presence of **productive cough, weight loss, night sweats**, and **abscesses in the lungs and brain** in an immunocompromised patient (due to chronic steroid use for asthma) is highly suggestive of Nocardiosis. - Identification of **gram-positive, branching filaments** that are **weakly acid-fast** in cultures confirms *Nocardia* as the causative organism. *Actinomyces israelii* - While *Actinomyces* causes chronic abscesses and is a **gram-positive filamentous bacterium**, it is **not acid-fast** and typically causes cervicofacial, thoracic, or abdominal infections often associated with trauma or surgery, not disseminated brain abscesses in this context. - *Actinomyces* infections are characterized by **"sulfur granules"** in pus, which are not mentioned here. *Bacillus anthracis* - *Bacillus anthracis* is a **gram-positive rod** that causes **anthrax**, typically presenting as cutaneous, inhalational, or gastrointestinal forms. - It does **not form filamentous structures** and is not acid-fast, and its clinical presentation of rapid-onset severe pneumonia or skin lesions does not match the described chronic progressive illness with multiple abscesses. *Mycobacterium tuberculosis* - *Mycobacterium tuberculosis* causes **tuberculosis**, characterized by cough, weight loss, and night sweats, and can cause lung and brain abscesses (tuberculomas). - However, *Mycobacterium* species are **strongly acid-fast** due to their mycolic acid cell wall and are not described as gram-positive filamentous organisms.

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.

Question 1

MC cause of atypical pneumonia?

Accepted Answer

Mycoplasma pneumoniae

Answer

Klebsiella pneumoniae

Answer

Hemophilus influenzae

Answer

Chlamydia

Question 2

Which of the following is anaerobic non-acid fast bacilli:

Accepted Answer

Actinomyces

Answer

Mycobacterium tuberculosis

Answer

Listeria

Answer

Nocardia

Question 3

Eaton agent is:

Accepted Answer

Mycoplasma

Answer

Pseudomonas

Answer

Gonococcus

Answer

Corynebacterium

Question 4

A 47-year-old man with chronic asthma who has been treated with steroids for many years develops a productive cough, weight loss, and night sweats. Imaging studies reveal the presence of abscesses in the lungs and brain. Cultures show gram-positive filaments that are weakly acid-fast. Which of the following organisms is responsible for this patient's condition?

Accepted Answer

Nocardia asteroides

Answer

Actinomyces israelii

Answer

Bacillus anthracis

Answer

Mycobacterium tuberculosis

Question 5

Chlamydia causes:

Accepted Answer

Trachoma and Lymphogranuloma venereum

Answer

Trachoma

Answer

Trachoma and Conjunctivitis

Answer

Conjunctivitis

Question 6

Acute infectious diarrhea can be caused by all EXCEPT:

Accepted Answer

Enterococcus faecalis

Answer

Staphylococcus

Answer

Clostridium

Answer

Vibrio

Question 7

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 8

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 9

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 10

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

Bacteriology — MCQs

Bacteriology — MCQs

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