Bacteriology Practice Questions

Q: A 12-year-old girl begins to limp while playing soccer. She has pain in her right leg and upper right thigh. Her temperature is 102°F. X-ray of the femur reveals that the periosteum is eroded. Assuming that this case is managed as an infectious disease, which of the following is the most likely etiologic agent?

Staphylococcus aureus. ***Staphylococcus aureus*** - *S. aureus* is the most common cause of **osteomyelitis** in children, accounting for the symptoms of bone pain, limp, fever, and periosteal erosion. - The organism frequently gains access to bone via **hematogenous spread** from a superficial infection or direct inoculation through trauma. *Salmonella enteritidis* - While *Salmonella* can cause osteomyelitis, especially in patients with **sickle cell disease**, there is no indication of this predisposing factor in the girl's history. - *Salmonella* osteomyelitis is less common than that caused by *S. aureus* in the general pediatric population. *Staphylococcus saprophyticus* - *S. saprophyticus* is primarily associated with **urinary tract infections (UTIs)**, particularly in young, sexually active females. - It is an uncommon cause of osteomyelitis and typically not the primary pathogen in bone infections. *Listeria monocytogenes* - *Listeria monocytogenes* is known to cause severe infections in **immunocompromised individuals**, neonates, and pregnant women. - While it can cause osteomyelitis, it is a rare cause in an otherwise healthy 12-year-old and would usually be associated with specific risk factors.

Q: Griffith classification is based on

M, T, R antigens. ***M, T, R antigens*** - **Griffith classification** (also known as Griffith serotyping) is based on the surface protein antigens: **M, T, and R antigens**. - This system is used for **typing within Group A Streptococcus** (*Streptococcus pyogenes*) to further subdivide strains. - **M protein** is the most important virulence factor and provides the basis for typing into over 100 different M types. - **T and R antigens** are additional surface proteins used for supplementary typing when M typing is not definitive. *'C'-carbohydrate* - The **C-carbohydrate** (also called C-substance) is the basis for **Lancefield grouping**, not Griffith classification. - Lancefield grouping divides streptococci into serogroups (A, B, C, etc.) based on cell wall polysaccharide antigens. - This is a **different classification system** from Griffith typing - broader and more general. *Type of hemolysis* - **Hemolysis pattern** (alpha, beta, gamma) is a phenotypic characteristic observed on blood agar. - While useful for preliminary identification, it is not the basis for Griffith classification. - *Streptococcus pyogenes* shows beta-hemolysis but this doesn't subdivide strains further. *O requirement* - **Oxygen requirement** refers to metabolic characteristics (aerobic, anaerobic, facultative). - This is unrelated to any serological classification system including Griffith typing. - *Streptococcus pyogenes* is a facultative anaerobe.

Q: NOT a cause of bacterial community acquired pneumonia:

Blastomyces. ***Blastomyces*** - *Blastomyces*, a **dimorphic fungus**, causes **blastomycosis**, which is a **fungal infection**, not a bacterial infection. - While it can cause community-acquired pneumonia with pulmonary symptoms, it is **NOT a bacterial pathogen** and therefore not a cause of **bacterial community-acquired pneumonia**. - The question asks specifically about bacterial causes, making this the correct answer. *Streptococcus pneumoniae* - **_Streptococcus pneumoniae_** is the **most common bacterial cause** of **community-acquired pneumonia (CAP)**. - Infection typically presents with **acute onset** of fever, chills, productive cough, and lobar consolidation on chest X-ray. *Mycoplasma pneumoniae* - **_Mycoplasma pneumoniae_** is a common cause of **atypical bacterial community-acquired pneumonia**, often referred to as "**walking pneumonia**". - It typically causes milder symptoms, including a **persistent dry cough** and malaise, and is prevalent in younger adults and children. *Moraxella catarrhalis* - **_Moraxella catarrhalis_** is a **bacterial pathogen** that causes **community-acquired pneumonia**, especially in patients with **chronic obstructive pulmonary disease (COPD)**. - It can also cause **bronchitis**, otitis media, and sinusitis.

Q: All are important causes of UTI except-

Streptococcus viridans. ***Streptococcus viridans*** - *Streptococcus viridans* is a common inhabitant of the **oral flora** and is a frequent cause of **bacterial endocarditis**, especially in individuals with damaged heart valves. - It is **rarely associated with urinary tract infections** because it lacks specific virulence factors to colonize the urinary tract effectively. *Proteus* - *Proteus* species, particularly *Proteus mirabilis*, are well-known causes of UTIs, often associated with **struvite stones** due to their production of **urease**, an enzyme that increases urine pH. - Their motility, mediated by **flagella**, also aids in ascending the urinary tract. *Klebsiella* - *Klebsiella pneumoniae* is a significant Gram-negative bacterium that commonly causes UTIs, particularly in **hospital-acquired infections** and in patients with catheters or underlying medical conditions. - It is known for its **capsule**, which provides resistance against phagocytosis, contributing to its pathogenicity. *E. coli* - **Uropathogenic *E. coli*** (UPEC) is the **most common cause of UTIs**, accounting for 80-90% of community-acquired cases. - Its virulence factors, such as **P fimbriae (pili)**, enable it to adhere to uroepithelial cells and colonize the bladder and kidneys effectively.

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.

Question 1

A 12-year-old girl begins to limp while playing soccer. She has pain in her right leg and upper right thigh. Her temperature is 102°F. X-ray of the femur reveals that the periosteum is eroded. Assuming that this case is managed as an infectious disease, which of the following is the most likely etiologic agent?

Accepted Answer

Staphylococcus aureus

Answer

Salmonella enteritidis

Answer

Staphylococcus saprophyticus

Answer

Listeria monocytogenes

Question 2

Griffith classification is based on

Accepted Answer

M, T, R antigens

Answer

Type of hemolysis

Answer

O requirement

Answer

'C'-carbohydrate

Question 3

NOT a cause of bacterial community acquired pneumonia:

Accepted Answer

Blastomyces

Answer

Streptococcus pneumoniae

Answer

Mycoplasma pneumoniae

Answer

Moraxella catarrhalis

Question 4

All are important causes of UTI except-

Accepted Answer

Streptococcus viridans

Answer

Proteus

Answer

Klebsiella

Answer

E coli

Question 5

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 6

Fatal gastroenteritis is caused by -

Accepted Answer

Typhoid

Answer

Amoebiasis

Answer

Anthrax

Answer

Giardiasis

Question 7

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 8

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 9

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 10

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

Bacteriology — MCQs

Bacteriology — MCQs

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