Bacteriology Practice Questions

Q: What is the causative organism for the condition depicted in the image?

Staphylococci. ***Staphylococci*** - The image shows **impetigo** with **crusted lesions**, consistent with **_Staphylococcus aureus_** infection. - **Staphylococcus aureus** is a major causative organism of impetigo, particularly **bullous impetigo**, and commonly produces the characteristic **honey-colored crusts** seen in non-bullous forms as well. - This superficial bacterial skin infection is highly contagious and responds well to topical or systemic antibiotics. *Candidal infection* - **Candidal infections** (e.g., candidiasis) typically present as **erythematous patches** with satellite lesions, or white plaques in mucosal areas, which is not consistent with the image. - This fungal infection is often seen in immunocompromised individuals or in warm, moist skin folds, not as crusted superficial lesions. *Streptococcus* - While **_Streptococcus pyogenes_** can also cause impetigo (especially non-bullous impetigo), the clinical presentation in the image is most consistent with **staphylococcal infection**. - Streptococcal infections may present similarly but can also cause other conditions like cellulitis or erysipelas with distinct features. *Actinomycetes* - **Actinomycosis** is a rare, chronic bacterial infection that forms **abscesses and sinus tracts**, often with "sulfur granules," which is distinct from the superficial skin lesions shown. - This infection usually involves deeper tissues and presents as a chronic, indolent infection, unlike the acute superficial presentation of impetigo.

Q: Which organism is responsible for causing Lymphogranuloma venereum (LGV)?

Chlamydia trachomatis. ***Chlamydia trachomatis*** - Specific **serovars L1, L2, and L3** of *Chlamydia trachomatis* are responsible for causing **Lymphogranuloma venereum (LGV)**. - These serovars infect macrophages and proliferate in regional lymph nodes, leading to characteristic **buboes** and **genital ulcers**. *Neisseria gonorrhoeae* - This bacterium causes **gonorrhea**, an STI characterized by **urethritis**, cervicitis, and pharyngitis. - It does not cause the invasive lymphatic infection associated with LGV. *Treponema pallidum* - This spirochete is the causative agent of **syphilis**, which presents with **chancres**, rashes, and systemic symptoms in different stages. - Syphilis is distinct from LGV in its clinical presentation and pathology. *Haemophilus ducreyi* - This bacterium causes **chancroid**, a sexually transmitted infection resulting in painful **genital ulcers** with a ragged border and often accompanied by tender inguinal lymphadenopathy. - While it causes genital lesions and lymphadenopathy, these are distinct from the characteristic buboes and progressive lymphatic destruction of LGV.

Q: Burkholderia cepacia is resistant to which of the following antibiotics?

Cefotetan. ***Cefotetan*** - *Burkholderia cepacia* shows **consistent resistance** to second-generation cephalosporins and cephamycins like **cefotetan**. - This organism is intrinsically resistant to **aminoglycosides** (gentamicin, tobramycin) and **polymyxins** (colistin), and shows variable resistance to many beta-lactams. - Among the options provided, cefotetan represents the most consistently ineffective agent. *Ceftazidime* - **Ceftazidime** (third-generation cephalosporin) shows **variable susceptibility** with *B. cepacia*. - While resistance is common, it is **not uniform**, and ceftazidime is sometimes used in **combination therapy** for B. cepacia infections. - Not considered a classic example of intrinsic resistance. *Trimethoprim-sulfamethoxazole* - **TMP-SMX** is the **first-line treatment** for *Burkholderia cepacia* infections. - It demonstrates good activity and is the preferred antimicrobial agent for this organism. - Resistance can develop but is not intrinsic. *Temocillin* - **Temocillin** (carboxypenicillin) has demonstrated activity against *B. cepacia*. - Used particularly in Europe for treating infections caused by this organism. - Not an antibiotic to which *B. cepacia* shows consistent resistance.

Q: Mycoplasma is inherently resistant to which of the following antibiotic classes due to its lack of a peptidoglycan cell wall?

Ceftriaxone (a cephalosporin). ***Ceftriaxone (a cephalosporin)*** - Cephalosporins are **beta-lactam antibiotics** that inhibit **peptidoglycan cell wall synthesis** by binding to penicillin-binding proteins (PBPs) - *Mycoplasma* species **completely lack a peptidoglycan cell wall**, which is the primary target of all beta-lactam antibiotics - Therefore, cephalosporins (and all beta-lactams) are **inherently ineffective** against *Mycoplasma* infections - This is a classic example of **intrinsic resistance** due to absence of the drug target *Penicillins (e.g., Amoxicillin)* - While penicillins are also beta-lactam antibiotics that target cell wall synthesis, the question specifically asks about ceftriaxone - Penicillins are similarly ineffective against *Mycoplasma* for the same reason (lack of cell wall) - However, when given a specific drug example (ceftriaxone), it is the most precise answer *Aminoglycosides (e.g., Gentamicin)* - Aminoglycosides target the **30S ribosomal subunit** to inhibit **protein synthesis** - While they have **poor penetration** into *Mycoplasma* cells and limited clinical efficacy, the resistance is not due to lack of cell wall - The mechanism of reduced susceptibility is different from the intrinsic resistance seen with beta-lactams *Fluoroquinolones (e.g., Ciprofloxacin)* - Fluoroquinolones inhibit **DNA gyrase** and **topoisomerase IV**, enzymes essential for DNA replication - These antibiotics are **effective** against *Mycoplasma* species and are commonly used to treat *Mycoplasma* infections - They represent appropriate treatment options along with macrolides and tetracyclines

Q: Which organism is the most common cause of acute bacterial prostatitis?

E.coli. ***E.coli*** - **E.coli** is the most common cause of **acute bacterial prostatitis**, accounting for a significant majority of cases. - It is a **gram-negative rod** commonly found in the gastrointestinal tract and can ascend into the urinary tract and prostate. *Enterococcus* - While **Enterococcus species** can cause urinary tract infections and, less commonly, prostatitis, they are a distant second to E.coli in frequency. - They are **gram-positive cocci** and are often associated with catheter-associated infections or healthcare-acquired infections. *Streptococcus viridans* - **Streptococcus viridans** group bacteria are typically commensals of the oral cavity and are more known for causing **endocarditis** or dental infections. - They are not a common cause of acute bacterial prostatitis. *Peptostreptococcus* - **Peptostreptococcus** is a genus of **anaerobic gram-positive cocci** commonly found in the normal flora of the mouth, gastrointestinal tract, and vagina. - They are typically involved in **polymicrobial anaerobic infections** but are not a primary or common cause of acute bacterial prostatitis.

Q: Which anaerobic organism is known to cause multiple abscesses with discharging sinuses and demonstrates sulfur granules in pus?

Actinomyces. ***Actinomyces*** - *Actinomyces* species are classic causes of **actinomycosis**, characterized by chronic, suppurative infections with **multiple abscesses**, draining sinuses, and the presence of **sulfur granules** in pus. - They are **anaerobic or microaerophilic gram-positive bacteria** that are part of the normal flora of the mouth and gastrointestinal tract, causing infection when mucosal barriers are disrupted. *Nocardia asteroides* - *Nocardia asteroides* causes **nocardiosis**, which can also present with abscesses, but it is an **aerobic bacterium** and typically does not produce sulfur granules. - Nocardial infections often involve the lungs, skin, or central nervous system, particularly in **immunocompromised individuals**. *Salmonella enterica* - *Salmonella enterica* is a facultative anaerobic Gram-negative bacterium known for causing **gastroenteritis**, typhoid fever, and bacteremia. - It is not associated with the formation of multiple abscesses with draining sinuses or sulfur granules. *Francisella tularensis* - *Francisella tularensis* causes **tularemia**, a zoonotic disease characterized by ulceroglandular lesions, fever, and lymphadenopathy. - It does not typically cause multiple abscesses with draining sinuses or produce sulfur granules.

Q: A boy presented with multiple non suppurative osteomyelitis with sickle cell anaemia. What will be the causative organism?

Salmonella. ***Salmonella*** - **Salmonella species** are a well-known cause of **osteomyelitis** in patients with **sickle cell anemia**, due to factors like gut mucosal damage and functional asplenia. [1] - The unique pathophysiology of sickle cell disease, including areas of bone infarction and compromised reticulendothelial system function, predisposes these patients to **Salmonella infections**. [1] *Staphylococcus aureus* - While **Staphylococcus aureus** is the most common cause of osteomyelitis in the general population, it is less likely to be the causative organism in patients with **sickle cell anemia** compared to Salmonella. - Its presence usually indicates other predisposing factors like trauma or prosthetic devices. *H. influenzae* - **Haemophilus influenzae** was a common cause of osteomyelitis in children before widespread vaccination but is now rare, especially with routine immunizations. - It is not specifically associated with a higher risk in patients with **sickle cell disease** for osteomyelitis compared to other pathogens. *Enterobacter species* - **Enterobacter species** can cause osteomyelitis, particularly in immunocompromised individuals or following surgery, but they are not uniquely associated with **sickle cell anemia** as a primary cause compared to Salmonella. - Their involvement in non-suppurative osteomyelitis in this specific patient population is less common.

Q: Which microorganism is the most common cause of pyogenic osteomyelitis?

S. aureus. ***Staph aureus*** - **_Staphylococcus aureus_** is the most frequent cause of **pyogenic osteomyelitis** across all age groups and routes of infection. - Its ability to adhere to bone, form biofilms, and produce toxins contributes to its prevalence in bone infections. *Streptococcus spp.* - While various **_Streptococcus_** species can cause infections, they are less common causes of pyogenic osteomyelitis compared to **_Staphylococcus aureus_**. - **Group A _Streptococcus_** can cause severe invasive infections but rarely involves primary bone infection. *Corynebacterium spp.* - **_Corynebacterium_** species, particularly **_Corynebacterium striatum_**, are increasingly recognized as opportunistic pathogens, especially in immunocompromised individuals or those with foreign bodies. - However, they are not the most common cause of osteomyelitis in the general population. *Neisseria gonorrhoeae (gonococcus)* - **_Neisseria gonorrhoeae_** can cause **disseminated gonococcal infection (DGI)**, which may include joint involvement (**septic arthritis**). - While it can lead to bone pain and swelling, it primarily affects joints and is a less common cause of direct **pyogenic osteomyelitis** than **_S. aureus_**.

Q: Which condition is associated with Streptococcus bovis infection?

Colorectal cancer. ***Colorectal cancer*** - *Streptococcus gallolyticus* (formerly known as *Streptococcus bovis* biotype I) infection, particularly **bacteremia** or **endocarditis**, has a strong association with underlying **colorectal cancer**. - It is hypothesized that the bacteria may play a role in **tumorigenesis** or that the cancerous lesions provide an entry point for the bacteria into the bloodstream. *Chronic lymphocytic leukemia (CLL)* - While patients with CLL are **immunocompromised** and prone to infections, there is no specific association between *Streptococcus bovis* and CLL. - Infections in CLL patients are typically due to encapsulated bacteria, such as *Streptococcus pneumoniae* or *Haemophilus influenzae*. *Hairy cell leukemia (HCL)* - Patients with HCL often experience **immunosuppression** due to neutropenia and monocytopenia, leading to increased susceptibility to infections. - However, there is no direct or specific link between *Streptococcus bovis* infection and HCL itself. *Multiple myeloma (MM)* - Patients with multiple myeloma have **impaired humoral immunity** and are at risk for infections, especially from encapsulated bacteria. - There is no established specific association between *Streptococcus bovis* infection and multiple myeloma.

Q: Which of the following statements is NOT true about the El Tor biotype of Vibrio cholerae?

Reduced environmental persistence. ***Reduced environmental persistence*** - The **El Tor biotype** of *Vibrio cholerae* is known for its **increased environmental persistence** compared to the classical biotype, making this statement NOT true. - El Tor survives longer in water sources due to its hardiness and ability to form biofilms, which contributes to its pandemic potential and makes outbreaks harder to control. *VP (+)* - The El Tor biotype is **Voges-Proskauer (VP) positive**, which is a key biochemical characteristic used to differentiate it from the classical biotype (VP negative). - This is a TRUE statement about El Tor. *Lower mortality* - The El Tor biotype causes **milder disease with lower mortality rates** compared to the classical biotype. - While individual cases may be less severe, the higher infectivity and asymptomatic carriage of El Tor contribute to its widespread transmission - this is a TRUE statement. *Hemolysis negative* - The El Tor biotype is **hemolysis positive** (produces beta-hemolysis on sheep blood agar), which is another key differentiating feature from the classical biotype (hemolysis negative). - This makes the statement "hemolysis negative" NOT true about El Tor.

Question 1

What is the causative organism for the condition depicted in the image?

Accepted Answer

Staphylococci

Answer

Candidal infection

Answer

Streptococcus

Answer

Actinomycetes

Question 2

Which organism is responsible for causing Lymphogranuloma venereum (LGV)?

Accepted Answer

Chlamydia trachomatis

Answer

Neisseria gonorrhoeae

Answer

Treponema pallidum

Answer

Haemophilus ducreyi

Question 3

Burkholderia cepacia is resistant to which of the following antibiotics?

Accepted Answer

Cefotetan

Answer

Trimethoprim-sulfamethoxazole

Answer

Ceftazidime

Answer

Temocillin

Question 4

Mycoplasma is inherently resistant to which of the following antibiotic classes due to its lack of a peptidoglycan cell wall?

Accepted Answer

Ceftriaxone (a cephalosporin)

Answer

Penicillins (e.g., Amoxicillin)

Answer

Aminoglycosides (e.g., Gentamicin)

Answer

Fluoroquinolones (e.g., Ciprofloxacin)

Question 5

Which organism is the most common cause of acute bacterial prostatitis?

Accepted Answer

E.coli

Answer

Enterococcus

Answer

Streptococcus viridans

Answer

Peptostreptococcus

Question 6

Which anaerobic organism is known to cause multiple abscesses with discharging sinuses and demonstrates sulfur granules in pus?

Accepted Answer

Actinomyces

Answer

Nocardia asteroides

Answer

Salmonella enterica

Answer

Francisella tularensis

Question 7

A boy presented with multiple non suppurative osteomyelitis with sickle cell anaemia. What will be the causative organism?

Accepted Answer

Salmonella

Answer

H. influenzae

Answer

Enterobacter species

Answer

Staphylococcus aureus

Question 8

Which microorganism is the most common cause of pyogenic osteomyelitis?

Accepted Answer

S. aureus

Answer

Streptococcus spp.

Answer

Corynebacterium spp.

Answer

Neisseria gonorrhoeae (gonococcus)

Question 9

Which condition is associated with Streptococcus bovis infection?

Accepted Answer

Colorectal cancer

Answer

Chronic lymphocytic leukemia (CLL)

Answer

Hairy cell leukemia (HCL)

Answer

Multiple myeloma (MM)

Question 10

Which of the following statements is NOT true about the El Tor biotype of Vibrio cholerae?

Accepted Answer

Reduced environmental persistence

Answer

VP (+)

Answer

Lower mortality

Answer

Hemolysis negative

Bacteriology — MCQs

Bacteriology — MCQs

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