Bacteriology Practice Questions

Q: Food poisoning with incubation period of 1-6 hours is most probably caused by

Staphylococcus aureus. ***Staphylococcus aureus*** - *Staphylococcus aureus* produces **toxins** that cause rapid-onset food poisoning, typically within **1-6 hours**, due to preformed toxin ingestion. - Symptoms include **nausea, vomiting, abdominal cramps**, and sometimes diarrhea, as the toxin directly irritates the gastrointestinal lining. *H. pylori* - *Helicobacter pylori* is associated with chronic conditions like **gastritis** and **peptic ulcers**, not acute food poisoning with a short incubation period. - Its effects develop over weeks to months, involving colonization of the stomach lining. *Salmonella typhi* - *Salmonella typhi* causes **typhoid fever**, which has a much longer incubation period, ranging from **6 to 30 days**. - It leads to systemic illness with fever, headache, and abdominal pain, rather than acute emetic symptoms. *Streptococcus viridans* - **Viridans streptococci** are normal inhabitants of the oral cavity and are primarily associated with conditions like **infective endocarditis** following dental procedures. - They are not typically a cause of food poisoning with a rapid incubation period.

Q: Saccharolytic reaction in cooked meat broth is produced by

Clostridium perfringens. ***Clostridium perfringens*** - This bacterium is known for its **saccharolytic** and proteolytic activities, thriving in environments rich in carbohydrates, such as cooked meat broth. - It rapidly ferments sugars, producing gas and causing a characteristic **turbidity** in the medium. *Clostridium tetani* - While also a member of the *Clostridium* genus, *C. tetani* is primarily **proteolytic** and shows minimal or no saccharolytic activity. - Its metabolism is focused on breaking down proteins rather than fermenting carbohydrates. *Corynebacterium diphtheriae* - This bacterium is **aerobic** or facultatively anaerobic, and its metabolic capabilities do not typically include robust saccharolytic fermentation in harsh anaerobic conditions like cooked meat broth. - It is more known for its ability to produce **diphtheria toxin** and has specific growth requirements. *Pseudomonas* - *Pseudomonas* species are typically **aerobic** and often found in soil and water. They are generally oxidative and do not exhibit significant saccharolytic fermentation under anaerobic conditions. - They are known for their metabolic versatility but are not typically associated with saccharolytic reactions in anaerobic cooked meat broth cultures.

Q: A baby born at 32 weeks gestation with Apgar scores of 2 and 7 was placed in the neonatal intensive care unit. She developed a fever and leukocytosis; lumbar puncture revealed pleocytosis with increased protein, decreased glucose, and gram-positive rods. Which one of the following organisms was most likely isolated from the CSF?

Listeria monocytogenes. ***Listeria monocytogenes*** - This organism is a common cause of **meningitis in neonates**, often acquired transplacentally or during birth, and presents with gram-positive rods. - The patient's **prematurity**, low Apgar scores, fever, and CSF findings of **pleocytosis, increased protein, and decreased glucose** are highly characteristic of bacterial meningitis, and *Listeria* specifically. *Escherichia coli* - While *E. coli* is a frequent cause of **neonatal meningitis**, it typically presents as **gram-negative rods**, not gram-positive. - The clinical presentation is consistent with bacterial meningitis, but the Gram stain result rules out *E. coli* as the most likely pathogen. *Neisseria meningitidis* - *N. meningitidis* causes bacterial meningitis, but it is characterized by **gram-negative cocci**, not gram-positive rods. - This organism is more commonly associated with meningitis in older infants, children, and young adults, rather than premature neonates. *Streptococcus agalactiae* - *Streptococcus agalactiae* (Group B Strep) is a major cause of **early-onset neonatal sepsis and meningitis**, characterized by **gram-positive cocci in chains**, not rods. - While clinically plausible given the neonatal presentation, the Gram stain finding of "gram-positive rods" makes it less likely than *Listeria monocytogenes*.

Q: Most common causative organism of community-acquired acute pneumonia is:

Streptococcus pneumoniae. ***Streptococcus pneumoniae*** - *Streptococcus pneumoniae* is the **most common bacterial cause** of community-acquired pneumonia (CAP) across all age groups. - It often presents with a **sudden onset**, high fever, chills, and productive cough. *Streptococcus pyogenes* - *Streptococcus pyogenes* is primarily known for causing **strep throat**, **scarlet fever**, and skin infections like erysipelas and cellulitis. - While it can rarely cause pneumonia, it is not a common causative agent for CAP. *Haemophilus influenzae* - *Haemophilus influenzae* is a significant cause of CAP, especially in **smokers**, patients with **COPD**, and children, but it is less common than *S. pneumoniae*. - It can also cause **otitis media**, sinusitis, and meningitis. *Staphylococcus aureus* - *Staphylococcus aureus* is a common cause of **hospital-acquired pneumonia** and pneumonia following viral infections (e.g., influenza), or in patients with intravenous drug use. - It is **less common** as a primary cause of community-acquired pneumonia in otherwise healthy individuals.

Q: A microbiologist wants to develop a vaccine for prevention of attachment of diarrhoeagenic E.coli to the specific receptors in the gastro-intestinal tract. All of the following fimbrial adhesions would be appropriate vaccine candidates except -

P1-Pili. ***P1-Pili*** - **P1-pili** (also known as P-fimbriae or Pap-pili) are primarily associated with **uropathogenic *E. coli*** causing **urinary tract infections**, not diarrhoeagenic *E. coli* in the gastrointestinal tract. - A vaccine targeting P1-pili would therefore not be relevant for preventing gastrointestinal attachment. *K 88* - **K88 fimbriae** are well-known **adhesins** found in certain strains of **enterotoxigenic *E. coli*** (ETEC) that colonize the gut and cause diarrhoea, especially in piglets. - Targeting K88 would be an appropriate strategy for a vaccine against diarrhoeagenic *E. coli*. *CFA-1* - **Colonization Factor Antigen I (CFA/I)** is a major **fimbrial adhesin** expressed by human **enterotoxigenic *E. coli*** (ETEC) strains. - CFA/I mediates bacterial attachment to intestinal epithelial cells and is a critical virulence factor, making it a suitable vaccine candidate. *CS-2* - **Colonization Factor Antigen II (CFA/II)**, which includes subunits like **CS-2** (CS for "coli surface"), is another important **fimbrial adhesin** found in human **enterotoxigenic *E. coli*** (ETEC). - CS-2 contributes significantly to ETEC's ability to colonize the small intestine and cause diarrhoea, making it a strong vaccine candidate.

Q: Hemorrhagic meningitis is caused by

Bacillus anthracis. ***Bacillus anthracis*** - *Bacillus anthracis* causes **anthrax meningitis**, which is characteristically **hemorrhagic** and rapidly fatal - Characterized by extensive **meningeal and brain parenchymal bleeding** with hemorrhagic CSF - This form of meningitis is specifically known for its **hemorrhagic nature** due to the toxins produced by the bacteria, leading to vascular damage and edema - Often presents as "cardinal's cap" appearance due to severe hemorrhagic involvement *Streptococcus pneumoniae* - *Streptococcus pneumoniae* is the most common cause of **bacterial meningitis** in adults - Typically causes **purulent meningitis** with neutrophilic infiltration, not hemorrhagic meningitis - While severe cases can have complications with vascular involvement, it is not characterized by hemorrhagic meningitis *Neisseria meningitidis* - *Neisseria meningitidis* is a common cause of **bacterial meningitis**, often presenting with petechial rash due to **vasculitis** - Can lead to **disseminated intravascular coagulation (DIC)** and purpura fulminans with hemorrhagic skin lesions - However, the meningitis itself is typically **purulent**, not grossly hemorrhagic *Haemophilus influenzae* - *Haemophilus influenzae* type b (Hib) was a major cause of **bacterial meningitis** before vaccination - Causes **purulent meningitis** with inflammation and pus formation, rather than significant hemorrhage within the meninges - Now rare due to effective vaccination programs

Q: Causative organism for ANUG is:

Fusospirochetal complex. ***Fusospirochetal complex*** - **Acute Necrotizing Ulcerative Gingivitis (ANUG)**, also known as Vincent's angina or trench mouth, is caused by a synergistic polymicrobial infection involving **Fusobacterium species** (particularly F. nucleatum) and **oral spirochetes** (Borrelia vincentii and Treponema species). - This fusospirochetal complex creates a destructive, ulcerative inflammation of the gingiva, presenting with **painful, bleeding gums, punched-out papillae, pseudomembrane formation**, and characteristic **fetid breath**. - The condition typically occurs in patients with **poor oral hygiene, stress, immunosuppression**, or **malnutrition**. *Streptococcus sanguis* - This bacterium is a common commensal of the oral cavity and plays a role in **dental plaque formation** and initial colonization of tooth surfaces. - While present in the mouth, it is **not the causative agent** for the necrotizing lesions characteristic of ANUG. *Treponema pallidum and spirochetes* - **Treponema pallidum** specifically causes **syphilis**, a sexually transmitted infection, not ANUG. - While **oral spirochetes** (other Treponema and Borrelia species) are indeed critical components of ANUG, they work synergistically with **Fusobacterium**, hence the term "fusospirochetal complex." - This option is partially correct but incomplete and includes T. pallidum which is incorrect. *Staphylococcus epidermidis* - **Staphylococcus epidermidis** is a skin commensal organism implicated in **nosocomial infections** and biofilm formation on medical devices. - It has **no role** in the pathogenesis of ANUG.

Q: A 24-year-old man had been treated for gonorrhea 2 months previously. He developed an ulcerative lesion in the glands of the penis that is noted to be condylomata lata. The etiology of condylomata lata is which of the following?

Treponema pallidum. ***Treponema pallidum*** - **Condylomata lata** are characteristic lesions of **secondary syphilis**, caused by *Treponema pallidum* [1]. - They are typically broad, flat, moist, wart-like lesions that occur in warm, moist areas such as the anogenital region [1]. *Herpesvirus hominis, type II* - Herpesvirus hominis, type II (HSV-2) causes **genital herpes**, which manifests as painful vesicles that ulcerate [1]. - The lesions caused by HSV-2 are typically clustered, vesicular, and very painful, which is distinct from the hypertrophic, non-painful nature of condylomata lata [1]. *Hemophilus ducreyi* - *Hemophilus ducreyi* is the causative agent of **chancroid**, which presents as painful, soft ulcers with ragged, undermined borders, often accompanied by painful inguinal lymphadenopathy. - Chancroid lesions are typically destructive and highly painful, contrasting with the proliferative and less painful nature of condylomata lata. *Mixture of organisms* - While some sexually transmitted infections can involve coinfection, **condylomata lata** specifically point to a single etiological agent: *Treponema pallidum* [1]. - Attributing condylomata lata to a "mixture of organisms" is too vague and inaccurate given the specific morphology and strong association with syphilis [1].

Q: Epiglottitis is mainly caused by:

Haemophilus. ***Haemophilus*** - **_Haemophilus influenzae_ type b (Hib)** was historically the leading cause of epiglottitis, especially in children, prior to widespread vaccination. - While other bacteria can cause epiglottitis, **_Haemophilus influenzae_** remains one of the most significant causative agents, particularly in unvaccinated populations or in adults. *Streptococcus* - Various species of **_Streptococcus_**, such as **_Streptococcus pneumoniae_** and **Group A _Streptococcus_ (GAS)**, can cause other upper respiratory tract infections like pharyngitis or pneumonia. - While they can occasionally be isolated in epiglottitis, they are **not the main cause** compared to Haemophilus. *Staphylococcus* - **_Staphylococcus aureus_** is a common cause of skin infections, abscesses, and some respiratory infections, such as pneumonia. - It is **rarely the primary pathogen** responsible for acute epiglottitis. *Mycoplasma* - **_Mycoplasma pneumoniae_** is a common cause of atypical pneumonia, often presenting with a more gradual onset and milder symptoms compared to bacterial epiglottitis. - It is a **bacterium lacking a cell wall** and does not typically cause the acute, life-threatening inflammation characteristic of epiglottitis.

Question 1

Food poisoning with incubation period of 1-6 hours is most probably caused by

Accepted Answer

Staphylococcus aureus

Answer

H. pylori

Answer

Salmonella typhi

Answer

Streptococcus viridans

Question 2

Saccharolytic reaction in cooked meat broth is produced by

Accepted Answer

Clostridium perfringens

Answer

Clostridium tetani

Answer

Corynebacterium diphtheriae

Answer

Pseudomonas

Question 3

A baby born at 32 weeks gestation with Apgar scores of 2 and 7 was placed in the neonatal intensive care unit. She developed a fever and leukocytosis; lumbar puncture revealed pleocytosis with increased protein, decreased glucose, and gram-positive rods. Which one of the following organisms was most likely isolated from the CSF?

Accepted Answer

Listeria monocytogenes

Answer

Escherichia coli

Answer

Neisseria meningitidis

Answer

Streptococcus agalactiae

Question 4

Most common causative organism of community-acquired acute pneumonia is:

Accepted Answer

Streptococcus pneumoniae

Answer

Streptococcus pyogenes

Answer

Haemophilus influenzae

Answer

Staphylococcus aureus

Question 5

A microbiologist wants to develop a vaccine for prevention of attachment of diarrhoeagenic E.coli to the specific receptors in the gastro-intestinal tract. All of the following fimbrial adhesions would be appropriate vaccine candidates except -

Accepted Answer

P1-Pili

Answer

K 88

Answer

CFA-1

Answer

CS-2

Question 6

Hemorrhagic meningitis is caused by

Accepted Answer

Bacillus anthracis

Answer

Neisseria meningitidis

Answer

Haemophilus influenzae

Answer

Streptococcus pneumoniae

Question 7

Causative organism for ANUG is:

Accepted Answer

Fusospirochetal complex

Answer

Streptococcus sanguis

Answer

Treponema pallidum and spirochetes

Answer

Staphylococcus epidermidis

Question 8

A 24-year-old man had been treated for gonorrhea 2 months previously. He developed an ulcerative lesion in the glands of the penis that is noted to be condylomata lata. The etiology of condylomata lata is which of the following?

Accepted Answer

Treponema pallidum

Answer

Herpesvirus hominis, type II

Answer

Hemophilus ducreyi

Answer

Mixture of organisms

Question 9

Epiglottitis is mainly caused by:

Accepted Answer

Haemophilus

Answer

Streptococcus

Answer

Staphylococcus

Answer

Mycoplasma

Question 10

Residual auditory defect is a common complication in meningitis caused by

Accepted Answer

Haemophilus influenzae

Answer

Staphylococcus

Answer

Meningococcus

Answer

Escherichia coli

Bacteriology — MCQs

Bacteriology — MCQs

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