Bacteriology — MCQs
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A patient in ICU and on ventilator develops cough with fever. The gram-staining on microscopy will show:
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?
Griffith classification is based on
Historically, mesosomes in bacteria were thought to be functional units for -
All are important causes of UTI except-
A cystic fibrosis patient presented with an episode of pneumonia. On sputum culture, mucoid colonies of Pseudomonas were seen. What does this indicate?
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?
Pinta disease is caused by
Trismus is due to infection by
Which is NOT transmitted by arthropods:
Bacteriology Indian Medical PG Practice Questions and MCQs
Question 2171: A patient in ICU and on ventilator develops cough with fever. The gram-staining on microscopy will show:
- A. Gram negative cocci
- B. Gram negative bacilli (Correct Answer)
- C. Gram variable organism
- D. Gram positive bacilli
Explanation: ***Gram negative bacilli*** - **Ventilator-associated pneumonia (VAP)** is most commonly caused by **Gram-negative bacilli**, particularly in late-onset VAP (>5 days of mechanical ventilation). - Common pathogens include *Pseudomonas aeruginosa*, *Klebsiella pneumoniae*, *Escherichia coli*, and *Acinetobacter baumannii*, which are prevalent in the ICU environment. - These organisms commonly colonize the oropharynx of critically ill, intubated patients and can be aspirated into the lower respiratory tract, leading to pneumonia. - Gram-negative bacilli account for the **majority of VAP cases**, making this the most likely microscopic finding. *Gram negative cocci* - **Gram-negative cocci** like *Neisseria meningitidis* and *Neisseria gonorrhoeae* are primary causes of meningitis and sexually transmitted infections, respectively, and are not typical pathogens for VAP. - While *Moraxella catarrhalis* is a Gram-negative coccobacillus that can cause respiratory infections, it is uncommon in severe VAP cases compared to Gram-negative bacilli. *Gram variable organism* - The term **"Gram variable"** is rarely used in clinical microbiology to describe a consistent bacterial morphology; it usually refers to mixed staining results where some cells stain Gram-positive and others Gram-negative. - This description does not fit the typical profile of bacteria causing VAP and is not a standard morphological category for common VAP pathogens. *Gram positive bacilli* - **Gram-positive bacilli**, such as *Bacillus* species or *Corynebacterium* species, are generally not recognized as common causes of VAP. - Note: While **Gram-positive cocci** like *Staphylococcus aureus* (including MRSA) and *Streptococcus pneumoniae* are important VAP pathogens, they would appear as **cocci**, not bacilli, on microscopy. - The question specifically asks about morphology on Gram staining, and Gram-positive **bacilli** are not the predominant morphological pattern in VAP.
Question 2172: 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?
- A. Salmonella enteritidis
- B. Staphylococcus saprophyticus
- C. Listeria monocytogenes
- D. Staphylococcus aureus (Correct Answer)
Explanation: ***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.
Question 2173: Griffith classification is based on
- A. Type of hemolysis
- B. O requirement
- C. M, T, R antigens (Correct Answer)
- D. 'C'-carbohydrate
Explanation: ***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.
Question 2174: Historically, mesosomes in bacteria were thought to be functional units for -
- A. Protein synthesis
- B. Respiratory enzymes (Correct Answer)
- C. Carbohydrate breakdown
- D. Lipid storage
Explanation: ***Respiratory enzymes*** - **Mesosomes** were initially hypothesized to be invaginations of the plasma membrane that housed **respiratory enzymes** in a manner analogous to eukaryotic mitochondria. - This theory arose from observations of their close association with the bacterial chromosome and their perceived role in **oxidative phosphorylation**. *Protein synthesis* - **Protein synthesis** in bacteria primarily occurs on **ribosomes**, which are small organelles found in the cytoplasm. - While mesosomes were thought to have various roles, protein synthesis was not their main proposed function. *Carbohydrate breakdown* - **Carbohydrate breakdown** (glycolysis and fermentation) largely occurs in the **cytoplasm** of bacterial cells. - Mesosomes were not implicated as the primary site for these metabolic pathways. *Lipid storage* - **Lipid storage** in bacteria typically occurs in specialized structures like **lipid droplets** or inclusions within the cytoplasm. - Mesosomes were not considered storage organelles for lipids.
Question 2175: All are important causes of UTI except-
- A. Streptococcus viridans (Correct Answer)
- B. Proteus
- C. Klebsiella
- D. E coli
Explanation: ***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.
Question 2176: A cystic fibrosis patient presented with an episode of pneumonia. On sputum culture, mucoid colonies of Pseudomonas were seen. What does this indicate?
- A. It is resistant to most of antibiotics
- B. It formed a biofilm on bronchial walls (Correct Answer)
- C. It underwent a mutation
- D. There is a mistake with the culture technique
Explanation: ***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**.
Question 2177: 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?
- A. Neisseria meningitidis
- B. Streptococcus agalactiae
- C. Escherichia coli
- D. Listeria monocytogenes (Correct Answer)
Explanation: ***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*.
Question 2178: Pinta disease is caused by
- A. Treponema carateum (Correct Answer)
- B. Leptospira interrogans
- C. Treponema pallidum
- D. Treponema pertenue
Explanation: ***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 2179: Trismus is due to infection by
- A. Clostridium Tetani (Correct Answer)
- B. Staphylococci
- C. Streptococci
- D. Corynebacterium diphtheriae
Explanation: ***Clostridium Tetani*** - **Trismus**, or **lockjaw**, is a hallmark symptom of **tetanus**, caused by the neurotoxin **tetanospasmin** produced by **Clostridium tetani**. - The toxin blocks inhibitory neurotransmitters, leading to uncontrolled muscle spasms, particularly in the jaw muscles. *Staphylococci* - **Staphylococci** are common causes of skin infections, abscesses, and some systemic infections, but they **do not produce neurotoxins** that cause trismus. - Infections by *Staphylococci* typically manifest as localized infections or **sepsis**, not muscle spasms like lockjaw. *Streptococci* - **Streptococci** cause a wide range of infections including **strep throat**, **scarlet fever**, and **necrotizing fasciitis**, but they are **not associated with trismus or tetanus-like symptoms**. - Their toxins and virulence factors lead to different pathogenic mechanisms. *Diphtheria* - **Diphtheria** is caused by **Corynebacterium diphtheriae**, which produces a toxin that can lead to **pseudomembrane formation** in the throat and myocarditis or neuritis. - While diphtheria toxin can cause neurological complications (e.g., paralysis of the soft palate), it **does not specifically cause trismus**.
Question 2180: Which is NOT transmitted by arthropods:
- A. Rickettsia rickettsii
- B. Rickettsia prowazekii
- C. Borrelia burgdorferi
- D. Coxiella burnetii (Correct Answer)
Explanation: ***Coxiella burnetii*** - **Coxiella burnetii** is the causative agent of **Q fever**, which is primarily transmitted through **inhalation of contaminated aerosols** from infected animals (e.g., sheep, goats, cattle). - While animals can be infected via ticks, direct human transmission is **not arthropod-borne**. *Rickettsia rickettsii* - **Rickettsia rickettsii** causes **Rocky Mountain spotted fever**, which is transmitted by **ticks**, primarily the American dog tick (*Dermacentor variabilis*) and Rocky Mountain wood tick (*Dermacentor andersoni*). - This is a classic example of an **arthropod-borne disease**. *Rickettsia prowazekii* - **Rickettsia prowazekii** is the causative agent of **epidemic typhus**, which is transmitted by the **human body louse** (*Pediculus humanus corporis*). - This organism is transmitted when infected louse feces are scratched into the skin or inhaled. *Borrelia burgdorferi* - **Borrelia burgdorferi** causes **Lyme disease**, which is transmitted by **Ixodes ticks** (deer ticks), primarily *Ixodes scapularis* in the eastern US and *Ixodes pacificus* in the western US. - These ticks are **true arthropod vectors** for the bacteria.
Practice by Chapter
Staphylococci
Practice Questions
Streptococci and Enterococci
Practice Questions
Neisseria and Moraxella
Practice Questions
Corynebacterium and Listeria
Practice Questions
Bacillus and Clostridium
Practice Questions
Enterobacteriaceae
Practice Questions
Vibrio, Aeromonas, and Plesiomonas
Practice Questions
Pseudomonas and Related Bacteria
Practice Questions
Haemophilus and HACEK Group
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Bordetella and Brucella
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Mycobacteria
Practice Questions
Spirochetes
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