Bacteriology Practice Questions

Q: All of the following toxins are produced by the organisms shown below except:

Serum opacity factor. ***Serum opacity factor*** - The image shows Gram-positive cocci in clusters, characteristic of **Staphylococcus aureus**. - **Serum opacity factor** is a virulence factor produced by **Streptococcus pyogenes**, not Staphylococcus aureus. *Leukocidin* - **Leukocidin** is a cytotoxic protein produced by **Staphylococcus aureus** that targets and destroys phagocytic cells (leukocytes), contributing to pus formation. - The image depicts numerous **pus cells** along with Gram-positive cocci, consistent with a _S. aureus_ infection. *TSST-1* - **Toxic Shock Syndrome Toxin-1 (TSST-1)** is a superantigen produced by certain strains of **Staphylococcus aureus**. - It causes **toxic shock syndrome**, a severe systemic inflammatory response. *ETA and ETB* - **Exfoliative toxins A (ETA)** and **B (ETB)** are proteases produced by **Staphylococcus aureus**. - These toxins are responsible for **Staphylococcal scalded skin syndrome (SSSS)**, causing epidermal sloughing.

Q: Identify the organism shown below. (AIIMS May 2017)

Nocardia. ***Nocardia*** - The image displays **branching, filamentous, gram-positive rods** that exhibit a **beaded appearance**, which is characteristic of *Nocardia* species. - *Nocardia* are **partially acid-fast** and can cause opportunistic infections, particularly in immunocompromised individuals. *Mycobacterium tuberculosis* - *Mycobacterium tuberculosis* appears as **rod-shaped bacilli** that are **strongly acid-fast** due to their high mycolic acid content, but they do not typically form the long, branching filaments seen in the image. - While they can form cords, these are not the extensive mycelial-like structures shown. *Mycobacterium leprae* - *Mycobacterium leprae* are **acid-fast bacilli** that typically appear in compact bundles ("globi") within host cells, not as branching filamentous structures. - This organism primarily causes leprosy and is difficult to culture in vitro. *Actinomyces* - *Actinomyces* species are also **branching, filamentous gram-positive bacteria**, but they are **not acid-fast**. - While they form characteristic "sulfur granules" in tissue, the image is a stain showing individual organisms, and the acid-fast appearance rules out *Actinomyces*.

Q: All are true about bacteria shown in the smear of pus below, except:

Most strains are inhibited in presence of 5 % NaCl. The image shows **Gram-positive cocci** arranged in clusters, which is characteristic of *Staphylococcus aureus*. Many pus cells (neutrophils) are also seen, indicating an inflammatory response, consistent with a bacterial infection. ***Most strains are inhibited in presence of 5 % NaCl*** - *Staphylococcus aureus* is known to be **halophilic**, meaning it **grows well** in the presence of high salt concentrations (e.g., 7.5% NaCl), which distinguishes it from many other bacteria. - Therefore, the statement that it is 'inhibited in the presence of 5% NaCl' is **incorrect**. *Produce black colonies on potassium tellurite blood agar* - *Staphylococcus aureus* **reduces tellurite** to metallic tellurium, resulting in the production of **black colonies** on potassium tellurite blood agar. - This is a characteristic feature used in the identification of *Staphylococcus aureus*, particularly on media like Baird-Parker agar. *Liquefy gelatin* - *Staphylococcus aureus* produces the enzyme **gelatinase**, which **hydrolyzes gelatin**, causing it to liquefy. - This is a biochemical characteristic used to differentiate *Staphylococcus aureus* from certain other staphylococcal species. *Seen in Job syndrome* - **Job syndrome** (Hyper-IgE syndrome) is characterized by recurrent severe **Staphylococcal infections** of the skin and lungs. - Patients with Job syndrome have impaired neutrophil chemotaxis and elevated IgE levels, making them highly susceptible to *Staphylococcus aureus* infections.

Q: Which of the following bacteria has the flagellar characteristic shown in the image?

Leptospira icterohaemorrhagicae. ***Leptospira icterohaemorrhagicae*** - The image displays **endoflagella** (axial filaments) located beneath the **outer membrane**, which is characteristic of **spirochetes**. - *Leptospira icterohaemorrhagicae* is a spirochete and possesses these internal flagella, allowing for its distinctive corkscrew motility. *Helicobacter pylori* - *Helicobacter pylori* is a gram-negative bacterium that typically has **lophotrichous flagella** (multiple flagella at one pole), which are external, not internal. - Its motility is crucial for penetrating the gastric mucus, but it does not utilize endoflagella. *Mycobacterium tuberculosis* - *Mycobacterium tuberculosis* is a non-motile bacterium and **lacks flagella** altogether. - Its cell wall structure, rich in mycolic acid, contributes to its pathogenicity and resistance but not to motility via flagella. *Vibrio cholerae* - *Vibrio cholerae* is a gram-negative bacterium that possesses a **single polar flagellum** (monotrichous), which is external. - This external flagellum is essential for its motility in aquatic environments and in the human intestine.

Q: Identify the organism seen in the slide shown below.

Nocardia asteroides. ***Nocardia asteroides*** - The image exhibits **branching, beaded, filamentous rods** that stain **acid-fast**, key characteristics of *Nocardia*. - These morphological features, especially the irregular acid-fast staining and branching, differentiate it from other bacteria. *Streptococcus pyogenes* - *Streptococcus pyogenes* are Gram-positive cocci typically arranged in **chains**, showing none of the filamentous or branching forms seen in the image. - They are **not acid-fast** and would not appear as pink/red rods on an acid-fast stain. *M. tuberculosis* - While *M. tuberculosis* is **acid-fast** and appears as red rods, it typically presents as **straight or slightly curved rods**, not the extensively branching, beaded filaments observed. - It does not form the complex filamentous structures characteristic of *Nocardia*. *Corynebacterium diphtheriae* - *Corynebacterium diphtheriae* are Gram-positive, **club-shaped rods** that often assume V or L forms (palisades), and are not acid-fast. - This bacterium does not exhibit the extensive branching or beaded appearance characteristic of the organism in the image.

Q: CSF gram stain of a child suffering with meningitis is shown below. What is the causative agent? (NEET Pattern 2019)

H. influenzae. ***H. Influenzae*** - The image shows **Gram-negative rods or coccobacillary forms**, which are characteristic of *Haemophilus influenzae*. - *H. influenzae* is a common cause of **bacterial meningitis** in children, particularly before the widespread use of vaccines. *Streptococcus pneumoniae* - This bacterium would appear as **Gram-positive cocci** in pairs or short chains, which is not consistent with the image. - *Streptococcus pneumoniae* is also a common cause of meningitis but has a distinct morphological appearance. *Klebsiella pneumonia* - While *Klebsiella pneumoniae* is a Gram-negative rod, it is typically a larger, more plump rod, and less commonly a cause of **pediatric meningitis** compared to *H. influenzae*. - The morphology in the image, particularly the coccobacillary appearance, is more typical of *Haemophilus*. *Staphylococcus aureus* - This bacterium would appear as **Gram-positive cocci** in grape-like clusters, which clearly differs from the Gram-negative rods/coccobacillary forms seen in the image. - *Staphylococcus aureus* can cause meningitis, especially in cases of head trauma or neurosurgery, but its morphology is distinct.

Q: A 21-year-old college student presents with this clinical finding. All are true about the condition except:

Three genome copies per coccal unit. ***Three genome copies per coccal unit*** - The image depicts **urethral discharge**, characteristic of **gonococcal or chlamydial urethritis**. - *Neisseria gonorrhoeae* is a **Gram-negative diplococcus** that contains a **single bacterial genome** per cell, not "three genome copies per coccal unit." - This statement is **false**, making it the correct answer to this "EXCEPT" question. *In case of absence of laboratory facility, initial treatment regimens must incorporate azithromycin or doxycycline* - This statement is **true**. Empirical treatment for suspected urethritis includes **azithromycin (1g single dose)** or **doxycycline (100mg BD for 7 days)** to provide coverage for both *N. gonorrhoeae* and *Chlamydia trachomatis*. - Dual therapy with **ceftriaxone plus azithromycin** is recommended when gonococcal infection is suspected. *Most common complication is prostatitis* - This statement is **true**. In untreated or inadequately treated male urethritis, complications include **prostatitis, epididymitis, and epididymo-orchitis**. - In females, complications include **pelvic inflammatory disease (PID)**, which can lead to infertility and ectopic pregnancy. *Nucleic acid amplification is used with >90% sensitivity* - This statement is **true**. **Nucleic acid amplification tests (NAATs)** are the gold standard for diagnosing both gonorrhea and chlamydia. - NAATs demonstrate **sensitivity >90-95%** and high specificity, and can be performed on first-void urine, urethral swabs, or vaginal swabs.

Q: All are true about Helicobacter pylori on special stain preparation of stomach except:

S shaped non-flagellated bacteria. ***S shaped non-flagellated bacteria*** - *H. pylori* are generally **spiral-shaped** or **curved rods**, not typically S-shaped, and are characterized by their **polar flagella** which are essential for their motility in the viscous gastric mucus. - The presence of flagella is a key feature distinguishing *H. pylori* and enabling its survival in the stomach environment. *Steiner stain preparation* - The **Steiner silver stain** is commonly used to visualize *H. pylori* in gastric biopsies, demonstrating them as dark, helical organisms. - While effective, other stains like Giemsa or Warthin-Starry are also used, but Steiner stain is a valid method for detection. *Dormant stage is coccoid form* - Under stressful conditions, such as antibiotic exposure or prolonged culture, *H. pylori* can transform into a **coccoid form**. - This coccoid form is considered a **viable but non-culturable** dormant stage, potentially contributing to persistence and recurrence of infection. *Attaches but does not invade the cells* - *H. pylori* colonizes the **mucus layer** and attaches to the apical surface of gastric epithelial cells but generally **does not invade** the cells. - Its effects are mediated by toxins and enzymes released into the extracellular space, leading to inflammation and cellular damage without direct intracellular invasion.

Q: Which of the following are the primary organisms involved in PID ? I. N. gonorrhoeae II. Chlamydia III. Mycoplasma hominis IV. Candida albicans Select the correct answer using the code given below :

I, II and III. ***I, II and III*** - **Neisseria gonorrhoeae** and **Chlamydia trachomatis** are the two most common and well-established primary bacterial causes of PID, responsible for the majority of sexually transmitted cases that ascend from the cervix to the upper genital tract. - **Mycoplasma hominis** is frequently isolated in PID cases and is recognized as a significant pathogen contributing to the polymicrobial nature of PID, particularly in cases not solely due to gonorrhea or chlamydia. - These three organisms together represent the primary causative pathogens in acute PID. *II, III and IV* - This option incorrectly omits **Neisseria gonorrhoeae**, which is one of the two most important primary causes of PID. - **Candida albicans** causes vulvovaginal candidiasis but is **not a primary causative agent of PID**, which involves ascending bacterial infection of the upper reproductive tract (endometrium, fallopian tubes, ovaries, and pelvic peritoneum). *I, II and IV* - While **Neisseria gonorrhoeae** and **Chlamydia trachomatis** are correctly identified as major primary causes, **Candida albicans** is not typically involved in PID pathogenesis. - This option incorrectly excludes **Mycoplasma hominis**, which is a recognized pathogen in PID. *I, III and IV* - This option correctly identifies **Neisseria gonorrhoeae** and **Mycoplasma hominis** but incorrectly includes **Candida albicans**, which is not a PID pathogen. - Critically, this omits **Chlamydia trachomatis**, the single most common cause of PID and a leading cause of tubal factor infertility.

Question 1

All of the following toxins are produced by the organisms shown below except:

Accepted Answer

Serum opacity factor

Answer

Leukocidin

Answer

TSST-1

Answer

ETA and ETB

Question 2

Identify the organism shown below. (AIIMS May 2017)

Accepted Answer

Nocardia

Answer

Mycobacterium tuberculosis

Answer

Mycobacterium leprae

Answer

Actinomyces

Question 3

All are true about bacteria shown in the smear of pus below, except:

Accepted Answer

Most strains are inhibited in presence of 5 % NaCl

Answer

Produce black colonies on potassium tellurite blood agar

Answer

Liquefy gelatin

Answer

Seen in Job syndrome

Question 4

Which of the following bacteria has the flagellar characteristic shown in the image?

Accepted Answer

Leptospira icterohaemorrhagicae

Answer

Helicobacter pylori

Answer

Mycobacterium tuberculosis

Answer

Vibrio cholerae

Question 5

Identify the organism seen in the slide shown below.

Accepted Answer

Nocardia asteroides

Answer

Streptococcus pyogenes

Answer

M. tuberculosis

Answer

Corynebacterium diphtheriae

Question 6

CSF gram stain of a child suffering with meningitis is shown below. What is the causative agent? (NEET Pattern 2019)

Accepted Answer

H. influenzae

Answer

Streptococcus pneumoniae

Answer

Klebsiella pneumoniae

Answer

Staphylococcus aureus

Question 7

A 21-year-old college student presents with this clinical finding. All are true about the condition except:

Accepted Answer

Three genome copies per coccal unit

Answer

In case of absence of laboratory facility, initial treatment regimens must incorporate azithromycin or doxycycline

Answer

Most common complication is prostatitis

Answer

Nucleic acid amplification is used with >90% sensitivity

Question 8

A 13-year-old girl with cystic fibrosis has been having recurrent severe respiratory infections and transtracheal aspirate was sent for culture. The growth of pink colonies in the image shows presence of:

Accepted Answer

Burkholderia cepacia

Answer

Pseudomonas aeruginosa

Answer

Haemophilus influenzae

Answer

Pseudomonas fluorescens

Question 9

All are true about Helicobacter pylori on special stain preparation of stomach except:

Accepted Answer

S shaped non-flagellated bacteria

Answer

Steiner stain preparation

Answer

Dormant stage is coccoid form

Answer

Attaches but does not invade the cells

Question 10

Which of the following are the primary organisms involved in PID ?
I. N. gonorrhoeae
II. Chlamydia
III. Mycoplasma hominis
IV. Candida albicans

Select the correct answer using the code given below :

Accepted Answer

I, II and III

Answer

II, III and IV

Answer

I, II and IV

Answer

I, III and IV

Bacteriology — MCQs

Bacteriology — MCQs

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