Bacteriology Practice Questions

Q: Most commonly associated organism in bacterial vaginosis?

Gardnerella vaginalis. ***Gardnerella vaginalis*** - **Gardnerella vaginalis** is the predominant bacterium associated with the polymicrobial condition known as **bacterial vaginosis (BV)**. - While BV involves a shift in the vaginal microbiome with an increase in various anaerobic bacteria, **Gardnerella vaginalis** is consistently implicated in its pathogenesis and is often present in high concentrations. *Candida albicans* - **Candida albicans** is the most common cause of **vulvovaginal candidiasis** (yeast infection), not bacterial vaginosis. - Symptoms of candidiasis typically include intense itching, burning, and thick, white, "cottage cheese-like" discharge, distinct from BV. *E. coli* - **E. coli** is a common bacterium found in the gastrointestinal tract and is a frequent cause of **urinary tract infections (UTIs)**. - It is not a primary cause of bacterial vaginosis in the vagina. *Trichomonas vaginalis* - **Trichomonas vaginalis** is a **protozoan parasite** that causes **trichomoniasis**, a sexually transmitted infection. - While it causes vaginitis, its presentation often includes frothy, greenish-yellow discharge and a "strawberry cervix," differentiating it from BV.

Q: A neonate develops sepsis with organism showing CAMP test positive. Likely organism?

Group B Streptococcus. ***Group B Streptococcus*** - **Group B Streptococcus (GBS)**, or *Streptococcus agalactiae*, is the **most common cause of neonatal sepsis** and is the **classic organism** associated with a **positive CAMP test**. - The **CAMP test** (Christie-Atkins-Munch-Petersen) detects synergistic hemolysis between the CAMP factor produced by GBS and *Staphylococcus aureus* beta-lysin, resulting in an **arrowhead-shaped zone of enhanced hemolysis**. - GBS is strongly associated with **early-onset neonatal sepsis** (within first 7 days), transmitted vertically during delivery. - When the CAMP test is mentioned in the context of neonatal sepsis, **GBS is the intended answer** due to its classical association and epidemiological importance. *S. aureus* - *Staphylococcus aureus* can cause **sepsis** in neonates but is **CAMP test negative**. - It provides the beta-lysin used in the CAMP test to detect other organisms but does not produce the CAMP factor itself. *E. coli* - *Escherichia coli* is a **Gram-negative rod** and a frequent cause of **neonatal sepsis** and meningitis. - As a Gram-negative bacterium, *E. coli* is **CAMP test negative**. The CAMP test is specific for certain Gram-positive bacteria. *Listeria* - *Listeria monocytogenes* is **also CAMP test positive**, which can cause diagnostic confusion. - However, it causes a distinct clinical pattern: **granulomatosis infantiseptica**, meningoencephalitis, and is associated with **maternal ingestion of contaminated food**. - Listeria is **less common** than GBS as a cause of neonatal sepsis and is not the classic teaching association for CAMP positivity. - The CAMP positivity of Listeria is **weaker** and shows a different pattern (reverse CAMP) compared to the strong, characteristic arrowhead pattern of GBS.

Q: A sex worker presents with purulent urethral discharge and gram-negative diplococci. Diagnosis?

N. gonorrhoeae. ***N. gonorrhoeae*** - The presence of **purulent urethral discharge** and **Gram-negative diplococci** on microscopy is highly characteristic of **gonorrhea**. - **Neisseria gonorrhoeae** is a common cause of sexually transmitted infections, particularly in individuals with a higher risk profile like sex workers. *T. pallidum* - **Treponema pallidum** causes syphilis, which typically presents with a **chancre** (primary stage) or a rash (secondary stage), not purulent urethral discharge. - It is a **spirochete** and cannot be visualized as Gram-negative diplococci. *C. trachomatis* - **Chlamydia trachomatis** causes **nongonococcal urethritis**, which often presents with a less purulent or mucoid discharge, and may be asymptomatic. - It is an **obligate intracellular bacterium** and does not appear as Gram-negative diplococci on Gram stain. *H. ducreyi* - **Haemophilus ducreyi** causes **chancroid**, characterized by painful genital ulcers with regional lymphadenopathy. - It would not typically present with purulent urethral discharge and is a **Gram-negative rod**, not diplococci.

Q: A sex worker presents with purulent urethral discharge and gram-negative diplococci in culture. What is the most likely diagnosis?

Neisseria gonorrhoeae. ***Neisseria gonorrhoeae*** - **Purulent urethral discharge** and identification of **Gram-negative diplococci** on microscopy are classic diagnostic features of gonococcal urethritis [1]. - This sexually transmitted infection is common among sexually active individuals, including **sex workers** [1]. *Treponema pallidum* - This bacterium causes **syphilis**, which is characterized by **chancres** in the primary stage, and widespread rashes or lesions in later stages [2]. - It would not typically present with Gram-negative diplococci or purulent urethral discharge [2]. *Haemophilus ducreyi* - This organism is responsible for **chancroid**, a sexually transmitted infection that causes painful **genital ulcers** with ragged borders and often associated with lymphadenopathy [3]. - It would not lead to purulent urethral discharge, and while Gram-negative, it is typically seen as pleomorphic rods in chains. *Chlamydia trachomatis* - **Chlamydia** infection often presents with mucopurulent urethral discharge, but it is typically less purulent than gonorrhea and may be **asymptomatic** [1]. - **Chlamydia** is an **obligate intracellular bacterium** and would not be visualized as Gram-negative diplococci on a Gram stain [1].

Q: Which venereal disease is associated with the 'school of fish' appearance in gram stain?

Chancroid. ***Chancroid*** - **Chancroid**, caused by *Haemophilus ducreyi*, is classically associated with the **"school of fish" appearance** on Gram stain due to the characteristic arrangement of short, plump, gram-negative rods. - This venereal disease presents with **painful genital ulcers** and often **inguinal lymphadenopathy**. *Donovanosis* - Donovanosis, caused by *Klebsiella granulomatis*, is characterized by **Donovan bodies** (large macrophages packed with bacteria) on microscopy, not a "school of fish" pattern. - It presents with **painless, progressive ulcerative lesions** that can be highly vascular. *Gonorrhea* - Gonorrhea, caused by *Neisseria gonorrhoeae*, typically shows **intracellular gram-negative diplococci within neutrophils** on Gram stain. - It commonly causes urethritis, cervicitis, and other mucosal infections, but not the "school of fish" pattern. *Syphilis* - Syphilis is caused by the spirochete *Treponema pallidum*, which is **not visible on Gram stain** and requires darkfield microscopy for visualization. - It presents in stages, with primary syphilis characterized by a **painless chancre**.

Q: A 50-year-old diabetic presents with a foot ulcer. Which pathogen is most likely?

Staphylococcus aureus. ***Staphylococcus aureus*** - **_Staphylococcus aureus_** is the most common pathogen isolated from **diabetic foot ulcers** due to its prevalence on the skin and ability to infect compromised tissues. - Diabetic patients are particularly susceptible to **_S. aureus_** infections due to **impaired immune function** and **poor circulation**. *Pseudomonas aeruginosa* - While _Pseudomonas aeruginosa_ can cause foot infections, it is typically associated with **chronic, wet wounds** or those exposed to water, and is less common as a primary pathogen than _S. aureus_. - Infections by _Pseudomonas_ often result in a **greenish discharge** and a characteristic fruity odor, which are not mentioned here. *Escherichia coli* - **_Escherichia coli_** is primarily a cause of **urinary tract infections** and **gastrointestinal infections**. - While it can be found in polymicrobial wound infections, it is not the most likely single pathogen to initiate a diabetic foot ulcer infection. *Candida albicans* - **_Candida albicans_** is a **fungus** that can cause infections, particularly in immunocompromised individuals and in moist areas. - While **fungal infections** can complicate diabetic foot ulcers, it is not the primary bacterial pathogen typically responsible for the initial presentation of such ulcers.

Q: Which of the following bacteria produces a toxin that inhibits protein synthesis?

Corynebacterium diphtheriae. ***Corynebacterium diphtheriae*** - This bacterium produces the **diphtheria toxin**, which is an **A-B toxin**. - The **A subunit** of the toxin inhibits **protein synthesis** by inactivating elongation factor-2 (EF-2), leading to cell death. *Bacillus anthracis* - Produces **anthrax toxin**, which consists of three components: protective antigen, edema factor, and lethal factor. - The **lethal factor** cleaves specific protein kinases, while the **edema factor** acts as an adenylate cyclase, disturbing cell water balance, but neither directly inhibits protein synthesis in the same manner as diphtheria toxin. *Staphylococcus aureus* - Produces numerous toxins, including **superantigens** (like toxic shock syndrome toxin-1) and **exfoliative toxins**, which cause scaly skin, and **alpha-toxin**, which forms pores in cell membranes. - These toxins have diverse mechanisms of action, but none primarily inhibit **protein synthesis**. *Vibrio cholerae* - Produces **cholera toxin**, an **A-B toxin**, which acts on intestinal cells. - The **A subunit** irreversibly activates **adenylate cyclase**, leading to increased cyclic AMP (cAMP) levels and massive efflux of water and electrolytes, causing severe diarrhea, but it does not inhibit protein synthesis.

Q: A patient presents with bloody diarrhea after eating undercooked meat. Which bacterial pathogen is most likely?

Escherichia coli O157:H7. ***Escherichia coli O157:H7*** - **Enterohemorrhagic E. coli (EHEC)** is the classic cause of **bloody diarrhea** following consumption of **undercooked ground beef** or hamburgers, producing **Shiga toxins** that cause **hemorrhagic colitis**. - Can lead to serious complications like **hemolytic uremic syndrome (HUS)**, particularly in children and elderly patients. *Salmonella typhi* - **Salmonella typhi** specifically causes **typhoid fever** with sustained fever, headache, and rose spots, not acute bloody diarrhea from undercooked meat. - While non-typhoidal Salmonella can cause gastroenteritis, it typically produces **non-bloody diarrhea** and is more associated with poultry and eggs. *Shigella dysenteriae* - Although it causes **bloody diarrhea** and severe **dysentery**, transmission is primarily **person-to-person** through the fecal-oral route or contaminated water. - Not typically associated with **undercooked meat consumption** but rather with poor sanitation and contaminated produce. *Vibrio cholerae* - Causes **cholera** with characteristic profuse, **watery diarrhea** ("rice-water stools") leading to severe dehydration, not bloody diarrhea. - Transmission occurs through contaminated **water and seafood**, not undercooked meat.

Q: Which of the following organisms causes paroxysmal coughing and is prevented by DPT vaccine?

Bordetella pertussis. ***Bordetella pertussis*** - This bacterium is the causative agent of **pertussis**, commonly known as whooping cough, characterized by severe, **paroxysmal coughing fits** followed by a characteristic \"whooping\" sound. - The **DPT vaccine** (Diphtheria, Pertussis, Tetanus) provides immunity against *Bordetella pertussis*, preventing this highly contagious respiratory infection. *Neisseria meningitidis* - This organism causes **meningitis** and **meningococcemia**, which are characterized by fever, headache, stiff neck, and rash, not paroxysmal coughing. - While there are vaccines for *Neisseria meningitidis*, it is not covered by the DPT vaccine. *Corynebacterium diphtheriae* - This bacterium causes **diphtheria**, a disease marked by a **pseudomembrane** formation in the throat, which can lead to airway obstruction and systemic toxin effects like myocarditis. - Although the 'D' in DPT stands for Diphtheria and this organism is prevented by the DPT vaccine, **diphtheria does not present with paroxysmal coughing** as its characteristic feature. *Haemophilus influenzae* - This bacterium can cause a variety of infections, including **meningitis**, **epiglottitis**, and **otitis media**, but not typically paroxysmal coughing. - The **Hib vaccine** specifically targets *Haemophilus influenzae* type b, not the DPT vaccine.

Q: A patient presents with urethral discharge. Gram stain shows intracellular gram-negative diplococci. What is the causative organism?

Neisseria gonorrhoeae. ***Neisseria gonorrhoeae*** - The presence of **intracellular gram-negative diplococci** in urethral discharge is a classic microscopic finding for *Neisseria gonorrhoeae*. - This organism directly invades host cells, and its unique gram staining characteristic makes it readily identifiable in clinical samples. *Mycoplasma genitalium* - This organism does not have a **cell wall** and therefore will not gram stain. It cannot be identified by Gram stain. - Diagnosis typically requires molecular methods like **PCR**. *Treponema pallidum* - This spirochete is too thin to be visualized with standard Gram stain and is typically identified using **dark-field microscopy** or serological tests. - It does not present as gram-negative diplococci. *Chlamydia trachomatis* - *Chlamydia trachomatis* is an **obligate intracellular bacterium** but does not stain well with Gram stain due to its unique cell wall structure (lacks peptidoglycan). - It is often diagnosed using **nucleic acid amplification tests (NAATs)**.

Question 1

Most commonly associated organism in bacterial vaginosis?

Accepted Answer

Gardnerella vaginalis

Answer

Candida albicans

Answer

E. coli

Answer

Trichomonas vaginalis

Question 2

A neonate develops sepsis with organism showing CAMP test positive. Likely organism?

Accepted Answer

Group B Streptococcus

Answer

S. aureus

Answer

E. coli

Answer

Listeria

Question 3

A sex worker presents with purulent urethral discharge and gram-negative diplococci. Diagnosis?

Accepted Answer

N. gonorrhoeae

Answer

T. pallidum

Answer

C. trachomatis

Answer

H. ducreyi

Question 4

A sex worker presents with purulent urethral discharge and gram-negative diplococci in culture. What is the most likely diagnosis?

Accepted Answer

Neisseria gonorrhoeae

Answer

Treponema pallidum

Answer

Haemophilus ducreyi

Answer

Chlamydia trachomatis

Question 5

Which venereal disease is associated with the 'school of fish' appearance in gram stain?

Accepted Answer

Chancroid

Answer

Donovanosis

Answer

Gonorrhea

Answer

Syphilis

Question 6

A 50-year-old diabetic presents with a foot ulcer. Which pathogen is most likely?

Accepted Answer

Staphylococcus aureus

Answer

Pseudomonas aeruginosa

Answer

Escherichia coli

Answer

Candida albicans

Question 7

Which of the following bacteria produces a toxin that inhibits protein synthesis?

Accepted Answer

Corynebacterium diphtheriae

Answer

Bacillus anthracis

Answer

Staphylococcus aureus

Answer

Vibrio cholerae

Question 8

A patient presents with bloody diarrhea after eating undercooked meat. Which bacterial pathogen is most likely?

Accepted Answer

Escherichia coli O157:H7

Answer

Salmonella typhi

Answer

Shigella dysenteriae

Answer

Vibrio cholerae

Question 9

Which of the following organisms causes paroxysmal coughing and is prevented by DPT vaccine?

Accepted Answer

Bordetella pertussis

Answer

Neisseria meningitidis

Answer

Corynebacterium diphtheriae

Answer

Haemophilus influenzae

Question 10

A patient presents with urethral discharge. Gram stain shows intracellular gram-negative diplococci. What is the causative organism?

Accepted Answer

Neisseria gonorrhoeae

Answer

Mycoplasma genitalium

Answer

Treponema pallidum

Answer

Chlamydia trachomatis

Bacteriology — MCQs

Bacteriology — MCQs

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