Bacteriology Practice Questions

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.

Q: Which one of the following is the causative organism of Erythrasma, a mild, localized and superficial skin infection?

Corynebacterium minutissimum. ***Corynebacterium minutissimum*** - This bacterium is the **primary causative agent** of erythrasma, a superficial skin infection. - It produces **porphyrins**, which fluoresce with a characteristic **coral-red color** under a Wood's lamp, aiding in diagnosis. *Corynebacterium matruchotii* - This species is typically found in the **oral cavity** and is associated with dental plaque and periodontal diseases. - It is **not known** to cause erythrasma or superficial skin infections. *Corynebacterium pseudotuberculosis* - This bacterium is a significant pathogen in **animals**, particularly livestock, causing conditions like caseous lymphadenitis. - While it can *rarely* cause infections in humans (e.g., lymphadenitis), it is **not associated** with erythrasma. *Corynebacterium diphtheriae* - This is the causative agent of **diphtheria**, a severe respiratory illness characterized by a pseudomembrane in the throat. - It causes systemic toxemia and is **not responsible** for localized, superficial skin infections like erythrasma.

Q: Gas Gangrene resulting in crepitus in tissues and a sweet smelling brown exudate is caused due to infection by :

Clostridium perfringens. ***Clostridium perfringens*** - **Gas gangrene** is caused by obligate anaerobic, gram-positive rods, notably **Clostridium perfringens**. - This bacterium produces **alpha-toxin (lecithinase)**, which destroys tissues and leads to gas formation (crepitus) and a characteristic **sweet-smelling brown exudate**. *Synergistic bacteria* - While synergistic infections can occur and lead to severe tissue damage, they are not the primary or specific cause of **gas gangrene** with its distinct clinical presentation. - The classic features of gas production and a specific exudate are directly tied to the metabolic activity and toxins of **Clostridial species**. *Anaerobic bacteroides spp.* - **Bacteroides** are common anaerobic bacteria, but they are typically associated with **intra-abdominal abscesses** and **wound infections**, not the specific clinical syndrome of gas gangrene. - They do not produce the potent toxins that lead to extensive gas formation and rapid tissue necrosis characteristic of **Clostridium perfringens**. *Gas-forming Klebsiella spp.* - **Klebsiella spp.** are gram-negative, facultative anaerobic bacteria that can produce gas, especially in deep-seated infections like **emphysematous pyelonephritis** or **liver abscesses**. - However, they do not cause **gas gangrene** with its rapid tissue destruction, crepitus, and sweet-smelling brown exudate, which is pathognomonic for **Clostridial infection**.

Q: Clinical signs and symptoms in tetanus are a result of

Exotoxins fixed to nerve endings. ***Exotoxins fixed to nerve endings*** - Tetanus symptoms are caused by **tetanospasmin**, an exotoxin produced by *Clostridium tetani*, which undergoes **retrograde axonal transport** from peripheral nerve terminals to the CNS. - The toxin **irreversibly binds** to presynaptic terminals of **inhibitory interneurons** (Renshaw cells) in the spinal cord, blocking the release of **glycine and GABA**. - This results in **unopposed excitatory impulses** to motor neurons, causing **spastic paralysis** and characteristic muscle rigidity. *Circulating exotoxins* - While tetanospasmin circulates after production at the wound site, it must **bind to nerve tissue** and reach the CNS to exert its pathogenic effects. - Systemic circulation acts as a transport mechanism; the clinical manifestations result from toxin **fixation at neural synapses**, not from circulating toxin. *Endotoxins* - **Endotoxins** are lipopolysaccharides (LPS) found in the outer membrane of gram-negative bacteria. - *Clostridium tetani* is a **gram-positive, spore-forming anaerobic bacillus** that does not produce endotoxins. - Endotoxins play no role in tetanus pathogenesis. *Both endotoxins and exotoxins* - This option is incorrect because *Clostridium tetani* does **not produce endotoxins**. - The clinical manifestations of tetanus are **exclusively due to tetanospasmin**, an exotoxin that acts by blocking inhibitory neurotransmission in the CNS.

Question 1

Identify the organism seen in the slide shown below.

Accepted Answer

Nocardia asteroides

Answer

Streptococcus pyogenes

Answer

M. tuberculosis

Answer

Corynebacterium diphtheriae

Question 2

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 3

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 4

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 5

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 6

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

Question 7

Which one of the following is the causative organism of Erythrasma, a mild, localized and superficial skin infection?

Accepted Answer

Corynebacterium minutissimum

Answer

Corynebacterium matruchotii

Answer

Corynebacterium pseudotuberculosis

Answer

Corynebacterium diphtheriae

Question 8

Gas Gangrene resulting in crepitus in tissues and a sweet smelling brown exudate is caused due to infection by :

Accepted Answer

Clostridium perfringens

Answer

Synergistic bacteria

Answer

Anaerobic bacteroides spp.

Answer

Gas-forming Klebsiella spp.

Question 9

Which one of the following statements regarding Gas Gangrene Infection is correct?

Accepted Answer

It is caused by C. perfringens, a gram positive anaerobic spore-forming bacilli.

Answer

It is caused by C. perfringens, a gram negative aerobic non-spore-forming bacilli.

Answer

It is caused by C. tetani, a gram negative anaerobic non-spore-forming bacilli.

Answer

It is caused by C. tetani, a gram positive anaerobic spore-forming bacilli.

Question 10

Clinical signs and symptoms in tetanus are a result of

Accepted Answer

Exotoxins fixed to nerve endings

Answer

Circulating exotoxins

Answer

Endotoxins

Answer

Both endotoxins and exotoxins

Bacteriology — MCQs

Bacteriology — MCQs

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