Bacteriology — MCQs

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?

Q2240

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

Bacteriology Indian Medical PG Practice Questions and MCQs

Question 2231: Beta phage is seen in:

A. Peptostreptococci
B. Bacillus anthracis
C. Corynebacterium diphtheriae (Correct Answer)
D. Clostridium botulinum

Explanation: ***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.

Question 2232: Post operative parotitis is caused by -

A. E.coli
B. Streptococcus
C. Pneumococcus
D. Staph aureus (Correct Answer)

Explanation: ***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

Question 2233: Anaerobic infections can cause:

A. Cause toxemia
B. Cause systemic infection
C. Both (Correct Answer)
D. None of the options

Explanation: ***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.

Question 2234: Jail fever is related to

A. Rickettsia conorii
B. Rickettsia typhi
C. Rickettsia prowazekii (Correct Answer)
D. Rickettsia akari

Explanation: ***Rickettsia prowazekii*** - **Jail fever** is another name for **epidemic typhus**, which is caused by *Rickettsia prowazekii*. - This disease is historically associated with crowded, unsanitary conditions like those found in jails or during wartime. *Rickettsia conorii* - This bacterium causes **Mediterranean spotted fever** (boutonneuse fever), which is characterized by a distinctive skin rash and eschar. - It is transmitted by dog ticks, and is not associated with the term "jail fever." *Rickettsia typhi* - *Rickettsia typhi* is responsible for **murine typhus** (endemic typhus), which is typically transmitted by fleas, mainly from rats. - While it is a rickettsial disease, it is not referred to as jail fever. *Rickettsia akari* - This species causes **rickettsialpox**, a mild rickettsial infection characterized by an initial papule that develops into an eschar, followed by a generalized papulovesicular rash. - It is transmitted by mites found on house mice and is distinct from jail fever.

Question 2235: The commonest organism causing cellulitis is -

A. Streptococcus viridans
B. Microaerophilic streptococci
C. Streptococcus pyogenes (Correct Answer)
D. Streptococcus faecalis

Explanation: ***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.

Question 2236: 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?

A. Chlamydia trachomatis (Correct Answer)
B. Haemophilus influenzae
C. Streptococcus agalactiae
D. Gonococcus

Explanation: ***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.

Question 2237: Rickettsia rickettsii is responsible for which disease -

A. Endemic typhus
B. Scrub typhus
C. Rocky mountain spotted fever (Correct Answer)
D. Epidemic typhus

Explanation: ***Rocky mountain spotted fever*** - **Rickettsia rickettsii** is the specific etiologic agent responsible for **Rocky Mountain Spotted Fever (RMSF)**, a severe tick-borne illness. - RMSF is characterized by a distinctive **rash** that typically begins on the ankles and wrists and spreads inwards, affecting the palms and soles. *Endemic typhus* - Endemic typhus, also known as **murine typhus**, is caused by **Rickettsia typhi**, not Rickettsia rickettsii. - It is typically transmitted by fleas, particularly those found on rodents, and is less severe than RMSF. *Scrub typhus* - Scrub typhus is caused by **Orientia tsutsugamushi**, a different rickettsial species. - This disease is transmitted by the bite of infected chiggers (larval mites) and is prevalent in rural Asia and the Pacific. *Epidemic typhus* - Epidemic typhus is caused by **Rickettsia prowazekii** and is transmitted by the human body louse. - It is historically associated with crowded, unsanitary conditions and can cause severe systemic illness.

Question 2238: Saccharolytic reaction in cooked meat broth is produced by

A. Clostridium tetani
B. Corynebacterium diphtheriae
C. Pseudomonas
D. Clostridium perfringens (Correct Answer)

Explanation: ***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.

Question 2239: 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?

A. Escherichia coli
B. Neisseria meningitidis
C. Streptococcus agalactiae
D. Listeria monocytogenes (Correct Answer)

Explanation: ***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*.

Question 2240: Most common causative organism of community-acquired acute pneumonia is:

A. Streptococcus pyogenes
B. Streptococcus pneumoniae (Correct Answer)
C. Haemophilus influenzae
D. Staphylococcus aureus

Explanation: ***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.

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

Practice Questions

Bordetella and Brucella

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Mycobacteria

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Spirochetes

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