Bacteriology Practice Questions

Q: Which of the following organisms is the most common cause of urinary tract infections in sexually active women?

Escherichia coli. ***Escherichia coli*** - **Uropathogenic *E. coli*** (*UPEC*) is responsible for 75-95% of all **uncomplicated UTIs**, making it the most common pathogen. - Its virulence factors, such as **fimbriae (pili)**, enable it to adhere to and colonize the uroepithelium. *Staphylococcus saprophyticus* - While a common cause of UTIs, especially in **young, sexually active women**, it ranks second to *E. coli*. - It accounts for 5-15% of community-acquired UTIs in this demographic. *Klebsiella pneumoniae* - This organism is a common cause of **complicated UTIs**, particularly in hospitalized patients or those with catheterization. - It is less frequently the causative agent in **uncomplicated UTIs** in healthy, sexually active women. *Proteus mirabilis* - Known for its ability to produce **urease**, which hydrolyzes urea to ammonia, leading to alkaline urine and the formation of **struvite stones**. - More commonly associated with complicated UTIs, recurrent infections, and **kidney stones**, rather than typical uncomplicated UTIs in sexually active women.

Q: Which microorganism is most likely to cause a rapidly progressive, painful infection with gas formation in the tissues?

Clostridium perfringens. **Clostridium perfringens** *(CORRECT)* - This bacterium is the classic cause of **gas gangrene** (clostridial myonecrosis), characterized by rapid progression, severe pain, and **crepitus** (gas in the tissues). - It produces potent **exotoxins**, such as alpha-toxin, which cause extensive tissue destruction and hemolysis. - Key clinical feature: **Gas formation** in tissues is pathognomonic. *Staphylococcus aureus* - While *S. aureus* can cause severe and painful infections (e.g., **cellulitis**, **abscesses**, **necrotizing fasciitis**), it does not typically produce gas in the tissues. - It is a common cause of skin and soft tissue infections, often presenting with **purulent drainage**. *Pseudomonas aeruginosa* - This organism can cause rapidly progressive and severe infections, especially in immunocompromised individuals or burn patients, but **gas production is not a characteristic feature**. - Infections often have a **grape-like odor** and can produce a blue-green pigment (pyocyanin). *Mycobacterium tuberculosis* - *M. tuberculosis* causes **tuberculosis**, a chronic infection primarily affecting the lungs, and sometimes other organs. - It is characterized by slow progression, **granuloma formation**, and does not cause rapid, painful infections with gas formation.

Q: Which pathogen is responsible for causing tuberculosis?

Mycobacterium tuberculosis. ***Mycobacterium tuberculosis*** - This bacterium is the **primary causative agent** of tuberculosis (TB), a serious infectious disease. - It predominantly affects the **lungs** but can also spread to other organs. *Streptococcus pneumoniae* - This pathogen is a common cause of **bacterial pneumonia**, as well as **meningitis** and **otitis media**. - It does not cause tuberculosis; its disease presentation is distinct and usually more acute. *Haemophilus influenzae* - This bacterium is frequently associated with **respiratory tract infections**, including **bronchitis**, **pneumonia**, and **otitis media**, especially in children. - It is not the causative agent of tuberculosis. *Mycobacterium leprae* - This bacterium is the causative agent of **leprosy**, a chronic infectious disease that primarily affects the skin, nerves, and upper respiratory tract. - While it belongs to the *Mycobacterium* genus, it causes a distinct disease from tuberculosis.

Q: Which of the following is the primary cause of infection in post-traumatic osteomyelitis?

Staphylococcus aureus. ***Staphylococcus aureus*** - **Staphylococcus aureus** is the most common pathogen responsible for **post-traumatic osteomyelitis**. - It gains entry to the bone through the **open wound** or **surgical site** after trauma. *Pseudomonas aeruginosa* - **Pseudomonas aeruginosa** is more commonly associated with **puncture wounds** of the foot, especially through footwear, and infections in **immunocompromised** individuals or those with extensive burns. - While it can cause osteomyelitis, it is not the primary cause in general post-traumatic cases. *E. coli* - **E. coli** is typically associated with **urinary tract infections** and **intra-abdominal infections**. - It is a less common cause of osteomyelitis, usually seen in contiguous infections from the gastrointestinal or genitourinary tracts, or in **diabetic foot infections**. *Anaerobes* - **Anaerobic bacteria** can cause osteomyelitis, especially in cases of **deep, contaminated wounds** or **diabetic foot ulcers**. - However, they are generally part of a **polymicrobial infection** and are not as frequently identified as the sole primary cause compared to *Staphylococcus aureus* in typical post-traumatic scenarios.

Q: A patient with chronic sinusitis has nasal discharge that is positive for gram-positive, coagulase-positive cocci. What is the most likely causative organism?

Staphylococcus aureus. ***Staphylococcus aureus*** - **Gram-positive, coagulase-positive cocci** are classic microbiological findings for **Staphylococcus aureus**. - This organism is a common cause of **chronic sinusitis**, particularly in cases that are refractory to initial treatment. *Streptococcus pneumoniae* - While a common cause of **acute bacterial sinusitis**, it is typically identified as **Gram-positive cocci in pairs or short chains**, not primarily as coagulase-positive. - It is often **alpha-hemolytic** on blood agar, but coagulase testing is not a primary identifier. *Haemophilus influenzae* - This bacterium is a **Gram-negative coccobacillus**, which distinctly differentiates it from the Gram-positive cocci described in the question. - It is a common cause of both acute and chronic sinusitis. *Moraxella catarrhalis* - This organism is a **Gram-negative diplococcus**, which also differentiates it from the Gram-positive cocci described. - It is a frequent cause of acute otitis media and sinusitis, especially in children.

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: 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: On what basis are E. coli subtypes classified?

Somatic O antigen. ***Somatic O antigen*** - *E. coli* subtypes are commonly classified based on the **somatic O antigen**, which is part of the **lipopolysaccharide (LPS)** layer on the bacterial surface. - This antigenic classification system, along with H (flagellar) and K (capsular) antigens, helps in **epidemiological tracking** and identifying pathogenic strains. *Virulence properties* - While *E. coli* subtypes do possess different **virulence properties** (e.g., toxins, adhesins), these are characteristics of specific strains rather than the primary basis for their initial laboratory classification. - Virulence factors determine disease manifestation but are not the standard phenotypic markers used for general subtyping. *Lactose fermentation* - **Lactose fermentation** is a general characteristic of *E. coli* as a species, used to distinguish it from **non-lactose fermenting enterics** like *Salmonella* and *Shigella*. - It does not differentiate between different pathogenic or non-pathogenic *E. coli* subtypes. *Maltose fermentation* - **Maltose fermentation** is a biochemical test that can be used to differentiate certain bacteria but is not a primary or standard method for classifying *E. coli* into subtypes. - *E. coli* generally ferments maltose, but this characteristic does not provide the specificity needed for subtyping.

Q: Which of the following diseases is caused by Borrelia?

Lyme disease. ***Lyme disease*** - **Lyme disease** is caused by the spirochete bacterium **_Borrelia burgdorferi_**, transmitted primarily by ticks. - Its classic early symptom is an **erythema migrans** rash, often described as a "bull's-eye" appearance. *Weil's disease* - **Weil's disease** is a severe form of **leptospirosis**, caused by the bacterium **_Leptospira interrogans_**, not _Borrelia_. - It presents with **jaundice**, **renal failure**, and **hemorrhage**. *Bejel* - **Bejel** (also known as endemic syphilis) is caused by **_Treponema pallidum subspecies endemicum_**, a bacterium closely related to the one causing syphilis, but not _Borrelia_. - It primarily affects the **skin**, **mucous membranes**, and **bones**, particularly in children in arid regions. *Vincent angina* - **Vincent angina** (also known as necrotizing ulcerative gingivitis or "trench mouth") is caused by a polymicrobial infection involving **anaerobic bacteria**, particularly **_Fusobacterium nucleatum_** and **_Treponema vincentii_**, not _Borrelia_. - It is characterized by **painful**, bleeding gums, and **halitosis**.

Question 1

Which of the following organisms is the most common cause of urinary tract infections in sexually active women?

Accepted Answer

Escherichia coli

Answer

Staphylococcus saprophyticus

Answer

Klebsiella pneumoniae

Answer

Proteus mirabilis

Question 2

Which microorganism is most likely to cause a rapidly progressive, painful infection with gas formation in the tissues?

Accepted Answer

Clostridium perfringens

Answer

Staphylococcus aureus

Answer

Pseudomonas aeruginosa

Answer

Mycobacterium tuberculosis

Question 3

Which pathogen is responsible for causing tuberculosis?

Accepted Answer

Mycobacterium tuberculosis

Answer

Streptococcus pneumoniae

Answer

Haemophilus influenzae

Answer

Mycobacterium leprae

Question 4

Which of the following is the primary cause of infection in post-traumatic osteomyelitis?

Accepted Answer

Staphylococcus aureus

Answer

E. coli

Answer

Anaerobes

Answer

Pseudomonas aeruginosa

Question 5

A patient with chronic sinusitis has nasal discharge that is positive for gram-positive, coagulase-positive cocci. What is the most likely causative organism?

Accepted Answer

Staphylococcus aureus

Answer

Streptococcus pneumoniae

Answer

Haemophilus influenzae

Answer

Moraxella catarrhalis

Question 6

Gonococci have affinity for :

Accepted Answer

Columnar epithelium

Answer

Glandular epithelium

Answer

Squamous epithelium

Answer

Stratified squamous epithelium

Question 7

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 8

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 9

On what basis are E. coli subtypes classified?

Accepted Answer

Somatic O antigen

Answer

Virulence properties

Answer

Lactose fermentation

Answer

Maltose fermentation

Question 10

Which of the following diseases is caused by Borrelia?

Accepted Answer

Lyme disease

Answer

Vincent angina

Answer

Weil's disease

Answer

Bejel

Bacteriology — MCQs

Bacteriology — MCQs

On this page

Practice by Chapter

Want unlimited practice?