Bacteriology Practice Questions

Q: A cystic fibrosis patient presented with an episode of pneumonia. On sputum culture, mucoid colonies of Pseudomonas were seen. What does this indicate?

It formed a biofilm on bronchial walls. ***It formed a biofilm on bronchial walls*** - The presence of **mucoid Pseudomonas aeruginosa** in cystic fibrosis (CF) patients indicates a change in bacterial phenotype, allowing it to produce **alginate**, a polysaccharide that forms a **biofilm**. - This **biofilm** protects the bacteria from antibiotics and host immune responses, facilitating chronic infection and persistence in the airways of CF patients. *It is resistant to most of antibiotics* - While **biofilm formation** can contribute to antibiotic resistance, a mucoid colony does not *directly* confirm resistance to **most antibiotics**. - Antibiotic resistance needs to be determined through **susceptibility testing**, even though biofilm-producing bacteria are typically harder to eradicate. *It underwent a mutation* - The mucoid phenotype in *Pseudomonas aeruginosa* is indeed due to a **mutation**, specifically in genes involved in **alginate synthesis (e.g., mucA)**. - However, the *clinical significance* of this mutation is primarily its role in **biofilm formation** and chronic infection in CF, which is the more direct and relevant answer to the prompt. *There is a mistake with the culture technique* - The appearance of **mucoid colonies** of *Pseudomonas* is a well-recognized and specific finding in CF sputum cultures. - This indicates a true characteristic of the bacteria and not a **laboratory error**.

Q: Fatal gastroenteritis is caused by -

Typhoid. ***Typhoid*** - Typhoid fever, caused by **Salmonella Typhi**, can lead to severe gastrointestinal complications, including intestinal perforation and hemorrhage, which can be fatal if untreated [1]. - While other forms of gastroenteritis are usually self-limiting, **typhoid** can progress to systemic illness with multi-organ involvement, significantly increasing mortality risk [1]. *Amoebiasis* - Amoebiasis, caused by **Entamoeba histolytica**, can lead to dysentery and liver abscesses but is generally less acutely fatal as a primary cause of gastroenteritis compared to severe typhoid. - While it can cause severe disease, its progression to a fatal outcome directly from gastroenteritis is often slower and with more specific complications than the rapid systemic deterioration seen in severe typhoid. *Anthrax* - **Gastrointestinal anthrax** is a severe form of infection caused by *Bacillus anthracis* that can be fatal [2], but it is a rare cause of gastroenteritis and is typically associated with ingestion of contaminated animal products, not general gastroenteritis. - Its clinical presentation is distinct, involving severe abdominal pain, vomiting, bloody diarrhea, and often leads to **septic shock**, differentiating it from common gastroenteritis [2]. *Giardiasis* - Giardiasis, caused by **Giardia lamblia**, is a common parasitic infection leading to chronic diarrhea, malabsorption, and weight loss, but it is typically not fatal. - The disease course is usually associated with non-bloody diarrhea and abdominal cramping, without the systemic toxicity or high fatality risk observed in severe typhoid.

Q: Devi, a 28 year female, has diarrhea, confusion, high grade fever with bilateral pneumonitis. The diagnosis is -

Legionella. ***Legionella*** - The constellation of **diarrhea, confusion (neurological symptoms), high-grade fever, and bilateral pneumonitis** is highly characteristic of **Legionnaires' disease**, caused by *Legionella pneumophila* [1]. - This organism commonly causes **extrapulmonary symptoms** such as gastrointestinal and neurological manifestations, in addition to severe pneumonia. *H. influenzae* - While *H. influenzae* can cause pneumonia, it typically presents with **lobar pneumonia** [1] and rarely involves gastrointestinal or significant neurological symptoms beyond general debility. - It is more commonly associated with **epiglottitis** and **meningitis** in unimmunized children. *Streptococcus pneumoniae* - *Streptococcus pneumoniae* is the most common cause of **community-acquired pneumonia**, often presenting with acute onset of fever, chills, and productive cough [1]. - While it can cause bacteremia and sepsis, **gastrointestinal symptoms like prominent diarrhea and significant neurological confusion** are not typical primary features of pneumococcal pneumonia. *Neisseria meningitidis* - *Neisseria meningitidis* is primarily known for causing **meningitis** and **meningococcemia**, involving symptoms like stiff neck, headache, rash, and fever [1]. - While it can sometimes cause pneumonia, the combination with **prominent diarrhea and severe, bilateral pneumonitis** as the primary presentation is not characteristic; the neurological symptoms point more towards Legionella given the other features.

Q: A mother brings her 1-month-old infant to the pediatrician. She says the baby is crying more than usual and is vomiting and does not want to eat. Meningitis is suspected, and a lumbar puncture is done, which shows the following results; Opening pressure = 240 mm H2O (normal = 100-200 mm H2O), WBC count: 1200/mm3, Protein: 200 mg/dL, Glucose: 30 mg/dL, Gram stain: gram-positive rods, Which of the following organisms is most likely responsible for this infant's meningitis?

Listeria monocytogenes. ***Listeria monocytogenes*** - The presence of **gram-positive rods** in the CSF of a 1-month-old infant with meningitis, coupled with the classic CSF findings (high WBC, high protein, low glucose), is highly suggestive of *Listeria monocytogenes*. - This organism is a significant cause of **neonatal meningitis** and is known for its rod-shaped morphology. *Neisseria meningitidis* - This organism is a **gram-negative diplococcus**, which is inconsistent with the gram stain result of **gram-positive rods**. - While it causes meningitis, its typical presentation and Gram stain morphology differ significantly. *Streptococcus agalactiae* - Also known as **Group B Streptococcus (GBS)**, this is a common cause of neonatal meningitis but is characterized as **gram-positive cocci in chains**, not rods. - The gram stain finding rules out GBS in this case. *Escherichia coli* - *E. coli* is a **gram-negative rod** and can cause neonatal meningitis. - However, the CSF gram stain in this case indicated **gram-positive rods**, which rules out *E. coli*.

Q: A group of friends had a party together. After 4 hours, a few of them had diarrhoea and vomiting. Organism responsible for food poisoning is:

B. cereus. ***B. cereus*** - The rapid onset of symptoms (within **4 hours**) strongly suggests intoxication by preformed toxins, which is characteristic of *Bacillus cereus* food poisoning, specifically the **emetic toxin**. - *Bacillus cereus* produces two main types of toxins: an **emetic toxin** (causing vomiting, rapid onset 1-6 hours) and diarrheal toxins (causing diarrhea, longer onset 8-16 hours). Among the given options, B. cereus is the only organism capable of causing symptoms within this short timeframe. *S. typhi* - *Salmonella typhi* causes **typhoid fever**, characterized by a more prolonged illness with fever, headache, and abdominal pain, usually with an incubation period of **1-3 weeks**, which is much longer than the described 4 hours. - It typically leads to systemic infection rather than acute, toxin-mediated food poisoning symptoms. *Cl. perfringens* - *Clostridium perfringens* typically causes **diarrhea and abdominal cramps**, with an onset usually between **6 to 24 hours** after ingestion, which is longer than the 4-hour timeframe mentioned. - Vomiting is less common with *Clostridium perfringens* food poisoning compared to *B. cereus* emetic type. *C. jejuni* - *Campylobacter jejuni* causes **bacterial gastroenteritis** with symptoms like watery or bloody diarrhea, fever, and abdominal pain, but its incubation period is typically **2 to 5 days**. - The rapid onset of symptoms in this scenario (4 hours) rules out *Campylobacter jejuni* infection.

Q: A 17 year old adolescent, presented with fever since one week which is step-ladder in pattern. He also has loose stools which are "pea-soup" in consistency. Rose spots are seen on his body. He is most probably infected with:

Salmonella typhi. ***Salmonella typhi*** - The combination of **step-ladder fever**, **"pea-soup" diarrhea**, and **rose spots** is a classic presentation of **typhoid fever**, caused by *Salmonella typhi* [1]. - This bacterial infection predominantly affects the gastrointestinal tract and can lead to systemic symptoms [1]. *Adenovirus* - **Adenovirus** typically causes **respiratory tract infections**, **conjunctivitis**, or **gastroenteritis**, but not with the specific symptom profile of step-ladder fever or rose spots. - While it can cause diarrhea, it's usually not described as "pea-soup" and lacks the other systemic features. *Rotavirus* - **Rotavirus** is a common cause of **severe gastroenteritis** in infants and young children, characterized by **watery diarrhea** and vomiting. - It does not present with step-ladder fever or rose spots, which are pathognomonic for typhoid. *Vibrio cholerae* - **Vibrio cholerae** causes **cholera**, an acute diarrheal illness characterized by **profuse watery diarrhea** (often described as "rice-water stools") and rapid dehydration. - It does not typically cause step-ladder fever or skin manifestations like rose spots.

Q: Tetanus affects primarily -

Presynaptic terminal of spinal cord. **Presynaptic terminal of spinal cord** - The **tetanus toxin (tetanospasmin)**, produced by *Clostridium tetani*, acts on the **presynaptic terminals** of inhibitory interneurons in the spinal cord. - It **blocks the release of inhibitory neurotransmitters** like glycine and GABA, leading to uncontrolled muscle spasms and rigidity. *Neuromuscular junction* - While muscles are the target of tetanus symptoms, the primary action of the toxin is not directly at the neuromuscular junction to affect acetylcholine release or receptor function. - Diseases like **myasthenia gravis** or **Lambert-Eaton myasthenic syndrome** primarily affect the neuromuscular junction. *Muscle fibres* - The tetanus toxin does not directly damage or alter the contractile properties of **muscle fibers** themselves. - Muscle pathology in tetanus is secondary to continuous, uncontrolled contraction due to nerve dysfunction. *Postsynaptic terminal of spinal cord* - The toxin's primary effect is on the **presynaptic release** of neurotransmitters, not on the postsynaptic receptors of spinal cord neurons. - Conditions affecting postsynaptic terminals in the spinal cord would involve issues with neurotransmitter reception or integration.

Q: Most common cause of bacterial diarrhea in children of developing countries is:

ETEC. ***ETEC*** - **Enterotoxigenic E. coli (ETEC)** is the most common cause of **bacterial diarrhea** in children in developing countries and a frequent cause of **traveler's diarrhea**. - It produces **heat-labile (LT)** and/or **heat-stable (ST)** toxins that stimulate fluid secretion in the small intestine, leading to watery diarrhea. *EHEC* - **Enterohemorrhagic E. coli (EHEC)**, particularly O157:H7, is primarily known for causing **hemorrhagic colitis** and **hemolytic-uremic syndrome (HUS)**, not the most common diarrhea in developing countries. - While it can cause bloody diarrhea, it is not the predominant pathogen responsible for the overall burden of diarrhea in these regions. *EIEC* - **Enteroinvasive E. coli (EIEC)** causes **dysentery-like illness** by invading and destroying the intestinal epithelial cells, similar to *Shigella*. - While it causes significant disease, it is relatively rare compared to ETEC as a cause of widespread diarrhea in developing countries. *EAEC* - **Enteroaggregative E. coli (EAEC)** is recognized as an important cause of **persistent diarrhea**, especially in children and immunocompromised individuals. - Although implicated in a significant portion of diarrheal episodes, particularly chronic ones, ETEC is still considered the leading single cause of acute sporadic diarrhea in developing countries.

Q: Pinta disease is caused by

Treponema carateum. ***Treponema carateum*** - Pinta is a **non-venereal treponematosis** caused by *Treponema carateum*, primarily affecting the skin. - The disease is characterized by changes in skin pigmentation, including **dyschromic patches**, which can be reddish, bluish, or brownish initially. - Transmitted through **direct skin contact** and endemic in Central and South America. *Leptospira interrogans* - This bacterium is responsible for **leptospirosis**, a zoonotic disease that can cause a wide range of symptoms, from mild flu-like illness to severe conditions like Weil's disease. - It primarily affects the **kidneys** and **liver**, and is not associated with skin lesions characteristic of pinta. *Treponema pallidum* - *Treponema pallidum* subspecies *pallidum* is the causative agent of **syphilis**, a sexually transmitted infection with distinct stages and diverse clinical manifestations. - While related to pinta, it has **different transmission routes** (sexual contact) and presents with chancres and systemic manifestations. *Treponema pertenue* - *Treponema pertenue* causes **yaws**, another non-venereal treponematosis. - Yaws presents with **papillomatous lesions** and bone involvement, distinct from the dyschromic skin changes seen in pinta.

Question 1

A cystic fibrosis patient presented with an episode of pneumonia. On sputum culture, mucoid colonies of Pseudomonas were seen. What does this indicate?

Accepted Answer

It formed a biofilm on bronchial walls

Answer

It is resistant to most of antibiotics

Answer

It underwent a mutation

Answer

There is a mistake with the culture technique

Question 2

Fatal gastroenteritis is caused by -

Accepted Answer

Typhoid

Answer

Amoebiasis

Answer

Anthrax

Answer

Giardiasis

Question 3

Devi, a 28 year female, has diarrhea, confusion, high grade fever with bilateral pneumonitis. The diagnosis is -

Accepted Answer

Legionella

Answer

H. influenzae

Answer

Streptococcus pneumoniae

Answer

Neisseria meningitidis

Question 4

A mother brings her 1-month-old infant to the pediatrician. She says the baby is crying more than usual and is vomiting and does not want to eat. Meningitis is suspected, and a lumbar puncture is done, which shows the following results; Opening pressure = 240 mm H2O (normal = 100-200 mm H2O), WBC count: 1200/mm3, Protein: 200 mg/dL, Glucose: 30 mg/dL, Gram stain: gram-positive rods, Which of the following organisms is most likely responsible for this infant's meningitis?

Accepted Answer

Listeria monocytogenes

Answer

Neisseria meningitidis

Answer

Streptococcus agalactiae

Answer

Escherichia coli

Question 5

A group of friends had a party together. After 4 hours, a few of them had diarrhoea and vomiting. Organism responsible for food poisoning is:

Accepted Answer

B. cereus

Answer

S. typhi

Answer

Cl. perfringens

Answer

C. jejuni

Question 6

A 80-year-old male presented with acute shortness of breath. His SpO2 levels were 80%. He was immediately intubated and shifted to the ICU and put on the ventilator. He was a chronic smoker and a known case of COPD for the past 5 years. He was started on empirical antibiotics. Initial culture tests were negative. After 9 days, he developed certain lesions in the lungs along with high grade fever. A bronchoalveolar lavage was done and sent for Gram staining. The organism isolated was a multi-drug resistant organism. Biochemical reactions revealed oxidase positive and did not ferment any sugars. The organism isolated is resistant to all antibiotics except: -

Accepted Answer

Colistin

Answer

Azithromycin

Answer

Amoxicillin

Answer

Amikacin

Question 7

A 17 year old adolescent, presented with fever since one week which is step-ladder in pattern. He also has loose stools which are "pea-soup" in consistency. Rose spots are seen on his body. He is most probably infected with:

Accepted Answer

Salmonella typhi

Answer

Adenovirus

Answer

Rotavirus

Answer

Vibrio cholerae

Question 8

Tetanus affects primarily -

Accepted Answer

Presynaptic terminal of spinal cord

Answer

Neuromuscular junction

Answer

Muscle fibres

Answer

Postsynaptic terminal of spinal cord

Question 9

Most common cause of bacterial diarrhea in children of developing countries is:

Accepted Answer

ETEC

Answer

EHEC

Answer

EIEC

Answer

EAEC

Question 10

Pinta disease is caused by

Accepted Answer

Treponema carateum

Answer

Leptospira interrogans

Answer

Treponema pallidum

Answer

Treponema pertenue

Bacteriology — MCQs

Bacteriology — MCQs

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