Bacteriology Practice Questions

Q: Identify the following bacterium from the image.

Neisseria meningitidis. ***Neisseria meningitidis*** - The image displays **Gram-negative diplococci** (pink/red, paired cocci) predominantly located **intracellularly within neutrophils**, which is characteristic of *Neisseria meningitidis* in cerebrospinal fluid or blood smears. - The morphology and intracellular presence in phagocytes, combined with the **clinical context suggesting systemic/CNS infection**, strongly indicate **meningococcal infection**. *Neisseria cinerea* - While also a **Gram-negative coccus**, *Neisseria cinerea* is a **commensal organism** of the upper respiratory tract. - It rarely causes invasive disease and is **not pathogenic**, making it incompatible with the clinical presentation suggested by this image. *Neisseria gonorrhoeae* - *Neisseria gonorrhoeae* also appears as **Gram-negative diplococci within neutrophils**, with nearly identical microscopic morphology to *N. meningitidis*. - However, *N. gonorrhoeae* causes **genitourinary infections** (urethritis, cervicitis) and occasionally disseminated gonococcal infection, but **not meningitis**. - The clinical context (CSF or blood smear suggesting systemic/meningeal infection) distinguishes this as *N. meningitidis*. *Neisseria polysaccharea* - *Neisseria polysaccharea* is a **commensal species** of the upper respiratory tract. - It is **non-pathogenic** and does not cause invasive infections or present with the clinical picture suggested by this image.

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

Staphylococcus. ***Staphylococcus*** - ***Staphylococcus aureus* is the MOST COMMON causative organism of impetigo** in current epidemiology, accounting for the majority of cases - Causes both **non-bullous impetigo** (can be sole pathogen or co-infection) and **bullous impetigo** (exclusively S. aureus due to exfoliative toxin production) - Appears as **gram-positive cocci in clusters** and produces characteristic **honey-crusted lesions** with purulent discharge - Often associated with **methicillin-resistant strains (MRSA)** in community settings *Candida* - This is a **fungal pathogen**, not a bacterial cause of impetigo - Causes **cutaneous candidiasis** with satellite lesions, or **mucosal infections** like thrush and vulvovaginal candidiasis - Presents differently from the bacterial skin infection shown in the image *Streptococcus pyogenes* - This is the **second most common cause** of impetigo and can cause non-bullous impetigo either alone or as co-infection with S. aureus - Historically was the primary cause, but **S. aureus now predominates** in most regions - Also causes **pharyngitis, erysipelas, and necrotizing fasciitis** - Characterized by **beta-hemolytic** colonies and gram-positive cocci in chains *Actinomyces* - This **anaerobic bacterium** causes **chronic granulomatous infections** (actinomycosis), typically in cervicofacial, thoracic, or abdominal regions - Presents with **draining sinuses** and **sulfur granules**, not the acute superficial skin infection shown - Not associated with impetigo

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

Cefotetan. ***Cefotetan*** - *Burkholderia cepacia* complex is **intrinsically resistant to second-generation cephalosporins** like cefotetan. - This resistance is mediated by **chromosomally encoded AmpC beta-lactamases** and reduced outer membrane permeability. - Second-generation cephalosporins have **no role** in treating *B. cepacia* infections. *Cefepime* - **Cefepime** (fourth-generation cephalosporin) shows **variable activity** against *B. cepacia* complex. - While it has enhanced stability against some beta-lactamases, resistance is common and susceptibility testing is required. - It may be used in some cases but is **not consistently effective**. *Piperacillin-tazobactam* - **Piperacillin-tazobactam** demonstrates **variable and often limited activity** against *B. cepacia* complex. - Susceptibility is strain-dependent and must be confirmed by testing before use. - The tazobactam component does not adequately inhibit the chromosomal beta-lactamases of *B. cepacia*. *Meropenem* - **Meropenem** and other carbapenems show **better but still variable activity** against *B. cepacia* complex. - While historically considered a treatment option, **carbapenem resistance is increasingly common**. - Treatment should be guided by susceptibility testing; ceftazidime, meropenem, and minocycline are among the agents with better (though inconsistent) activity.

Q: What is the cause of Ritter disease?

Staphylococcus aureus infection. ***Staphylococcus aureus infection*** - **Ritter disease**, also known as **Staphylococcal Scalded Skin Syndrome (SSSS)**, is caused by specific strains of **Staphylococcus aureus** that produce exfoliative toxins (ETA and ETB). - These toxins target **desmoglein 1**, a protein responsible for cell-to-cell adhesion in the stratum granulosum of the epidermis, leading to widespread blistering and skin shedding. *Autoimmune disease* - Autoimmune diseases involve the immune system mistakenly attacking the body's own tissues, as seen in conditions like **pemphigus vulgaris** or **bullous pemphigoid**. - Ritter disease is caused by an **exotoxin produced by bacteria**, not an immune response against self-antigens. *Genetic disorder* - Genetic disorders result from mutations or abnormalities in an individual's **DNA**, leading to functional or structural defects. - While susceptibility to infections can have genetic components, Ritter disease itself is directly caused by an **external bacterial infection**, not an inherited genetic defect. *Metabolic disorder* - Metabolic disorders occur when the body's normal chemical reactions are disrupted, often due to enzyme deficiencies or abnormal accumulation of substances, such as in **phenylketonuria** or **Tay-Sachs disease**. - Ritter disease is an **infectious condition** with a distinct bacterial etiology, not a problem with metabolism.

Q: What is the most common cause of acute salpingitis?

Chlamydia trachomatis. ***Chlamydia trachomatis*** - **_Chlamydia trachomatis_** is the most common bacterial cause of **sexually transmitted infections (STIs)** globally and a leading cause of **pelvic inflammatory disease (PID)**, which includes salpingitis. - Its infections are often **asymptomatic**, leading to delayed diagnosis and treatment, increasing the risk of upper genital tract involvement and complications like **infertility** and **ectopic pregnancies**. *N. gonorrhoeae* - **_Neisseria gonorrhoeae_** is another common cause of salpingitis, often presenting with **more acute and severe symptoms** compared to chlamydial infections. - While significant, studies consistently show a **higher prevalence of _Chlamydia_** in confirmed cases of salpingitis/PID. *Mycoplasma* - **_Mycoplasma genitalium_** and **_Ureaplasma urealyticum_** are increasingly recognized as causes of PID and salpingitis. - However, their overall contribution to acute salpingitis is **less frequent** than that of _Chlamydia trachomatis_ and _N. gonorrhoeae_. *Staphylococcus* - **_Staphylococcus_ species** are typically associated with skin and soft tissue infections or bacterial vaginosis, but are **uncommon causes of acute salpingitis**. - While they can be found in the genital tract, they are **not primary pathogens** for acute inflammation of the fallopian tubes.

Q: Most common organism grown in urine culture of a pregnant woman with asymptomatic bacteriuria?

E. coli. ***E. coli*** - **_E. coli_** is the most prevalent uropathogen due to its ability to adhere to uroepithelial cells and its common presence in the perianal flora. - It accounts for approximately **80% of all community-acquired urinary tract infections (UTIs)**, including asymptomatic bacteriuria in pregnant women. *Staph aureus* - **_Staphylococcus aureus_** is an uncommon cause of UTIs and is typically associated with **hematogenous spread** in cases of bacteremia. - It is rarely isolated in asymptomatic bacteriuria and would raise suspicion for a systemic infection if found in urine. *Pseudomonas* - **_Pseudomonas aeruginosa_** is generally associated with **nosocomial infections**, catheter-associated UTIs, or patients with structural urinary tract abnormalities or prolonged antibiotic use. - It is not a common cause of asymptomatic bacteriuria in otherwise healthy pregnant women. *Proteus* - **_Proteus_ species**, particularly **_Proteus mirabilis_**, are known for their ability to produce **urease**, which can lead to alkaline urine and the formation of struvite stones. - While they can cause UTIs, they are less common than _E. coli_ in asymptomatic bacteriuria in pregnant women.

Q: Stalactite growth in ghee broth is due to which of the following organisms?

C. diphtheriae. ***C. diphtheriae*** - **Corynebacterium diphtheriae** exhibits characteristic **stalactite (or stalagmite) growth** when cultured in **ghee broth** or on **Loeffler's serum slope** (which contains ghee). - This distinctive growth pattern appears as **pendant drop-like projections** hanging from the surface, resembling stalactites in caves. - This is a classic microbiological feature used for presumptive identification of C. diphtheriae. *Y. pestis* - *Yersinia pestis*, the causative agent of plague, does not show stalactite growth. - In liquid media, Y. pestis may form a **pellicle** or show floccular growth. - On solid media, it may show **"inverted fir tree" appearance** in stab cultures, not stalactite growth. *C. perfringens* - *Clostridium perfringens* is an anaerobic bacterium causing **gas gangrene** and food poisoning. - Growth in broth is typically **turbid with gas production**, without stalactite formation. *H. influenzae* - *Haemophilus influenzae* requires **X (hemin) and V (NAD) factors** for growth. - Typically grows as **small colonies on chocolate agar**, not in ghee broth. - Does not exhibit stalactite growth patterns.

Q: Gonococci have affinity for :

Columnar epithelium. ***Columnar epithelium*** - **Gonococci** (Neisseria gonorrhoeae) have a particular tropism for **columnar epithelial cells**, which are found in areas such as the endocervix, urethra, rectum, and conjunctiva. - This affinity is due to the presence of specific surface structures on the bacteria, like **pili** and **Opa proteins**, that bind to receptors on these host cells. *Glandular epithelium* - While some glands contain columnar epithelium and can be affected (e.g., endocervical glands), **gonococci** do not exclusively target glandular tissue per se, but rather the type of epithelial cells lining them. - The primary clinical impact is on the **columnar epithelial lining** of various ducts and surfaces, not specifically the secretory cells of glands. *Stratified squamous epithelium* - **Stratified squamous epithelium**, found in areas like the vagina and ectocervix, is generally more resistant to gonococcal infection. - The multiple layers and mature surface cells of this epithelium do not offer the same binding sites for **gonococci** as columnar cells. *Squamous epithelium* - Similar to stratified squamous epithelium, typical **squamous epithelium** (which can be stratified or simple) is not the preferred target for Neisseria gonorrhoeae. - The bacterium's pathogenesis is largely dependent on its ability to adhere to and invade **columnar epithelial cells**.

Q: A 60-year-old farmer presents with swelling on the sole of the foot accompanied by discharging yellow granules. What is the most likely diagnosis?

Actinomycosis. ***Actinomycosis*** - The presentation of a **slowly progressive swelling** with **draining sinuses** that exude **"sulfur granules" (yellow granules)** is highly characteristic of actinomycosis. - While often associated with the cervicofacial region, actinomycosis can affect other sites such as the foot, especially after **trauma** or through direct inoculation from soil, consistent with a farmer's occupation. *Fungal mycetoma* - While fungal mycetoma also presents with **swelling, draining sinuses**, and **granules**, these granules are typically **black or white** from fungal elements, not yellow [1]. - The causative agents are true fungi, and the clinical course might differ subtly, but the **color of the granules** is a key differentiator [1]. *Actinomycetoma* - Actinomycetoma is caused by **filamentous bacteria** (like *Nocardia* or *Actinomadura*), which are a type of bacterial mycetoma. It presents similarly to fungal mycetoma with **granules**, but these are usually **white, red, or yellow-brown**, and less commonly the bright yellow "sulfur granules" seen in classical actinomycosis. - It’s important to distinguish actinomycetoma (bacterial mycetoma) from actinomycosis, which is caused by *Actinomyces* species and is characterized specifically by the classic sulfur granules. *Candidiasis* - **Candidiasis** (yeast infection) typically presents as **mucocutaneous lesions, thrush, or invasive systemic infections**, not localized swelling with discharging yellow granules on the sole of the foot. - It does not involve the formation of granules or sinuses in this manner.

Question 1

Identify the following bacterium from the image.

Accepted Answer

Neisseria meningitidis

Answer

Neisseria cinerea

Answer

Neisseria gonorrhoeae

Answer

Neisseria polysaccharea

Question 2

What is the MOST COMMON causative organism for the condition depicted in the provided image?

Accepted Answer

Staphylococcus

Answer

Candida

Answer

Streptococcus pyogenes

Answer

Actinomyces

Question 3

Burkholderia cepacia is resistant to which of the following antibiotics?

Accepted Answer

Cefotetan

Answer

Cefepime

Answer

Piperacillin-tazobactam

Answer

Meropenem

Question 4

What is the cause of Ritter disease?

Accepted Answer

Staphylococcus aureus infection

Answer

Autoimmune disease

Answer

Genetic disorder

Answer

Metabolic disorder

Question 5

What is the most common cause of acute salpingitis?

Accepted Answer

Chlamydia trachomatis

Answer

N. gonorrhoeae

Answer

Mycoplasma

Answer

Staphylococcus

Question 6

Most common organism grown in urine culture of a pregnant woman with asymptomatic bacteriuria?

Accepted Answer

E. coli

Answer

Staph aureus

Answer

Pseudomonas

Answer

Proteus

Question 7

Stalactite growth in ghee broth is due to which of the following organisms?

Accepted Answer

C. diphtheriae

Answer

C. perfringens

Answer

Y. pestis

Answer

H. influenzae

Question 8

Gonococci have affinity for :

Accepted Answer

Columnar epithelium

Answer

Glandular epithelium

Answer

Squamous epithelium

Answer

Stratified squamous epithelium

Question 9

Which of the following statements about Vibrio cholerae is correct?

Accepted Answer

El Tor strain has more asymptomatic carriers than the classical strain.

Answer

Cholera is more common in women than men.

Answer

All statements are correct.

Answer

The classical strain of Vibrio cholerae provides immunity against El Tor strain.

Question 10

A 60-year-old farmer presents with swelling on the sole of the foot accompanied by discharging yellow granules. What is the most likely diagnosis?

Accepted Answer

Actinomycosis

Answer

Fungal mycetoma

Answer

Candidiasis

Answer

Actinomycetoma

Bacteriology — MCQs

Bacteriology — MCQs

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