Bacteriology Practice Questions

Q: Legionnaires' disease is caused by?

Motile gram negative. ***Motile gram negative*** - **Legionella pneumophila**, the causative agent of Legionnaire's disease, is a **motile gram-negative** rod. - Its **motility** is due to the presence of flagella, allowing it to move in aqueous environments. *Motile gram positive* - This option is incorrect because Legionella pneumophila is a **gram-negative** bacterium, not gram-positive. - Gram-positive bacteria have a thick peptidoglycan layer that stains purple with gram stain, which is not characteristic of Legionella. *Non-motile gram negative* - While Legionella pneumophila is gram-negative, it is in fact **motile**, making this option incorrect. - The organism uses flagella for movement, which is a key characteristic. *Non-motile gram positive* - This option is incorrect as Legionella pneumophila is both **motile** and **gram-negative**. - Combining these two incorrect characteristics makes this choice definitively false.

Q: Beta phage is seen in:

Corynebacterium diphtheriae. ***Corynebacterium diphtheriae*** - The **toxigenic strains** of *Corynebacterium diphtheriae* carry the diphtheria toxin gene (*tox*) on a **beta phage**. - This phage is a **lysogenic bacteriophage** that infects the bacterium and integrates its genetic material into the bacterial chromosome, leading to toxin production. *Peptostreptococci* - These are **anaerobic gram-positive cocci** that are not typically associated with carrying a beta phage or producing a phage-encoded toxin relevant to human disease in the same manner as diphtheria. - Their pathogenicity is usually due to their ability to cause **abscesses and opportunistic infections**, not phage-mediated toxins. *Bacillus anthracis* - *Bacillus anthracis* produces **anthrax toxin**, which is encoded on **plasmids (pXO1 and pXO2)**, not a bacteriophage. - These plasmids encode for edema factor, lethal factor, and protective antigen, which are essential for its virulence. *Clostridium botulinum* - The neurotoxins (botulinum toxins) produced by *Clostridium botulinum* are encoded by genes located on **plasmids or within the bacterial chromosome**, not specifically a beta phage. - Different strains produce different serotypes of the toxin, and the genetic elements encoding these toxins can vary.

Q: Post operative parotitis is caused by -

Staph aureus. ***Staph aureus*** - **Staphylococcus aureus** is the most common cause of **acute suppurative (post-operative) parotitis** - Post-surgical conditions including **dehydration**, **poor oral hygiene**, **reduced salivary flow**, and **immunosuppression** facilitate **bacterial ascension** through Stensen's duct from the oral cavity - The bacterium proliferates in stagnant saliva, causing acute infection of the parotid gland *E.coli* - **Escherichia coli** is primarily associated with **gastrointestinal and urinary tract infections** - Rarely implicated in salivary gland infections and not a typical cause of post-operative parotitis *Streptococcus* - While **Streptococcal species** can cause various infections, they are less commonly associated with **acute bacterial parotitis** compared to **Staphylococcus aureus** - May occasionally cause parotitis but not the predominant organism in post-operative settings *Pneumococcus* - **Streptococcus pneumoniae** commonly causes **pneumonia, meningitis, and otitis media** - Rarely causes **acute suppurative parotitis** and is not typically associated with post-operative parotitis - When sialadenitis occurs, it usually affects different patient populations

Q: Anaerobic infections can cause:

Both. ***Both*** - Anaerobic bacteria can produce various **toxins** that lead to systemic effects, causing **toxemia** and contributing to the severity of infections like gas gangrene (Clostridium perfringens). - Anaerobic infections can spread beyond localized sites, leading to **systemic infections** such as bacteremia, sepsis, and abscess formation in distant organs. *Causes toxemia* - While anaerobic bacteria can indeed produce toxins that lead to **toxemia**, this option alone does not encompass the full scope of potential complications from anaerobic infections. - Toxemia is a significant aspect, especially in infections like botulism or tetanus, but it's not the only serious outcome. *Cause systemic infection* - Anaerobic bacteria are capable of causing **systemic infections** (e.g., bacteremia, sepsis), but this option alone also does not fully describe the complex pathology that can include toxin-mediated effects. - Systemic infection emphasizes the spread of bacteria through the bloodstream or lymphatics to distant sites, but does not explicitly mention the role of bacterial toxins. *None of the options* - This option is incorrect because anaerobic infections are well-known to cause both **toxemia** (due to toxin production) and **systemic infections** (due to bacterial dissemination). - Many severe anaerobic infections, like those caused by Clostridium species, combine both systemic spread and significant toxin-mediated damage.

Q: The commonest organism causing cellulitis is -

Streptococcus pyogenes. ***Streptococcus pyogenes*** - This organism, also known as **Group A Streptococcus (GAS)**, is the most common bacterial cause of uncomplicated **cellulitis**. - **Cellulitis** is an acute, spreading bacterial infection of the **dermis** and **subcutaneous tissues**, often presenting as a red, swollen, and painful area. ***Streptococcus viridans*** - Primarily found in the **oral cavity** and are common causes of **subacute bacterial endocarditis**, not typically cellulitis. - While they can cause infections, they are not the primary pathogen for uncomplicated skin and soft tissue infections like cellulitis. ***Microaerophilic streptococci*** - These bacteria require a **reduced oxygen environment** for growth and are more often associated with **abscesses** or deep-seated infections. - They are not the most common cause of superficial spreading infections such as typical cellulitis. ***Streptococcus faecalis*** - Now known as **Enterococcus faecalis**, this organism is a common cause of **urinary tract infections** and nosocomial infections. - While it can cause skin and soft tissue infections, particularly in hospitalized or immunocompromised patients, it is not the most common cause of community-acquired cellulitis.

Q: A 2 weeks old infant has conjunctivitis, which later developed into respiratory distress and pneumonia. Chest X-ray showed bilateral lung infiltrates. WBC count was 14,300/dL. Which of the following is the most likely organism?

Chlamydia trachomatis. ***Chlamydia trachomatis*** - **Chlamydia trachomatis** is a common cause of **neonatal conjunctivitis** (ophthalmia neonatorum) and can subsequently lead to **pneumonia** in infants, typically presenting at 2-3 weeks of age. - The characteristic presentation includes **conjunctivitis** followed by **respiratory distress** and **cough** (often staccato), with **bilateral interstitial infiltrates** on chest X-ray and normal to slightly elevated white blood cell count. *Haemophilus influenzae* - While *Haemophilus influenzae* can cause **neonatal infections**, it typically presents as **sepsis**, **meningitis**, or **epiglottitis** rather than a combination of conjunctivitis and pneumonia in a 2-week-old. - It is a less common cause of **neonatal conjunctivitis** and **pneumonia** in this specific sequence compared to *Chlamydia trachomatis*. *Streptococcus agalactiae* - *Streptococcus agalactiae* (**Group B Strep**) is a major cause of **early-onset neonatal sepsis** and **pneumonia** but does not commonly cause **conjunctivitis**. - Infections usually present within the first week of life (early-onset) with **sepsis**, **pneumonia**, or **meningitis**, rather than initial conjunctivitis. *Gonococcus* - **Gonococcal conjunctivitis** (*Neisseria gonorrhoeae*) in neonates is typically severe, purulent, and appears within the **first few days of life** (hyperacute onset), much earlier than two weeks. - While it can be associated with **disseminated infection**, **pneumonia** secondary to **gonococcal conjunctivitis** is rare, and it's not the primary cause of the combined presentation described.

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.

Question 1

Legionnaires' disease is caused by?

Accepted Answer

Motile gram negative

Answer

Motile gram positive

Answer

Non-motile gram negative

Answer

Non-motile gram positive

Question 2

Beta phage is seen in:

Accepted Answer

Corynebacterium diphtheriae

Answer

Peptostreptococci

Answer

Bacillus anthracis

Answer

Clostridium botulinum

Question 3

Post operative parotitis is caused by -

Accepted Answer

Staph aureus

Answer

E.coli

Answer

Streptococcus

Answer

Pneumococcus

Question 4

Anaerobic infections can cause:

Accepted Answer

Both

Answer

Cause toxemia

Answer

Cause systemic infection

Answer

None of the options

Question 5

The commonest organism causing cellulitis is -

Accepted Answer

Streptococcus pyogenes

Answer

Streptococcus viridans

Answer

Microaerophilic streptococci

Answer

Streptococcus faecalis

Question 6

A 2 weeks old infant has conjunctivitis, which later developed into respiratory distress and pneumonia. Chest X-ray showed bilateral lung infiltrates. WBC count was 14,300/dL. Which of the following is the most likely organism?

Accepted Answer

Chlamydia trachomatis

Answer

Haemophilus influenzae

Answer

Streptococcus agalactiae

Answer

Gonococcus

Question 7

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 8

Saccharolytic reaction in cooked meat broth is produced by

Accepted Answer

Clostridium perfringens

Answer

Clostridium tetani

Answer

Corynebacterium diphtheriae

Answer

Pseudomonas

Question 9

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 10

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

Accepted Answer

Streptococcus pneumoniae

Answer

Streptococcus pyogenes

Answer

Haemophilus influenzae

Answer

Staphylococcus aureus

Bacteriology — MCQs

Bacteriology — MCQs

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