Corynebacterium and Listeria

Question 1

What are the general characteristics of Corynebacterium?

Answer 1

Gram-positive bacilli, non-motile, non-capsulated, aerobic or facultative anaerobes, catalase-positive.

Question 2

What is the distinctive shape of Corynebacterium under the microscope?

Answer 2

Club-shaped rods with metachromatic (volutin) granules at one or both ends, arranged singly or in V or L shapes resembling Chinese letters.

Question 3

How is diphtheria transmitted?

Answer 3

Through carriers who harbor the organism in the oropharynx or skin, respiratory droplets, secretions, or direct contact with infected cutaneous lesions.

Question 4

What are the hallmark symptoms of diphtheria?

Answer 4

Sore throat, cough, loss of appetite, mild fever, formation of a grayish-white pseudomembrane in the throat, and swollen lymph nodes (bull neck).

Question 5

What is the mechanism of action of diphtheria toxin?

Answer 5

The toxin consists of an active (A) subunit and a binding (B) subunit. The A subunit inhibits protein synthesis by ADP-ribosylating elongation factor-2 (EF-2), leading to host cell death.

Question 6

What are the potential complications of diphtheria?

Answer 6

Sepsis, myocarditis, acute kidney failure, liver failure, and pneumonia.

Question 7

How is diphtheria diagnosed in the laboratory?

Answer 7

By isolating the organism and demonstrating toxin production. Swabs from the throat, nose, or skin are examined using Gram stain or Albert stain.

Question 8

What culture media are used for Corynebacterium diphtheriae?

Answer 8

Selective and differential media such as cystine-tellurite blood agar, modified Tinsdale’s medium, and Loeffler’s medium.

Question 9

What is the Schick test?

Answer 9

A test to evaluate immunity to C. diphtheriae and sensitivity to diphtheria toxin. A small amount of toxin is injected under the skin, and a red, swollen rash indicates susceptibility.

Question 10

What is the recommended treatment for diphtheria?

Answer 10

Immediate administration of antitoxin to neutralize unbound toxin, along with antibiotics like penicillin G or erythromycin.

Question 11

How can diphtheria be prevented?

Answer 11

Vaccination with the DTaP vaccine (diphtheria, tetanus, and pertussis) and identifying healthy carriers during outbreaks.

Question 12

What are the clinical types of diphtheria?

Answer 12

Nasopharyngeal (respiratory) diphtheria and cutaneous (skin) diphtheria.

Question 13

What are the risk factors for diphtheria?

Answer 13

Unvaccinated children and adults, people living in crowded or unsanitary conditions, and travelers to endemic areas.

Question 14

What are the characteristic symptoms of cutaneous diphtheria?

Answer 14

Ulcerating skin lesions covered by a gray membrane, usually without systemic symptoms.

Question 15

What are the biotypes of C. diphtheriae?

Answer 15

Gravis, mitis, intermedius, and belfanti. Gravis causes more severe disease than mitis.

Question 16

What is the role of the diphtheria toxin’s A subunit?

Answer 16

The A subunit inhibits protein synthesis by ADP-ribosylating elongation factor-2 (EF-2), leading to cell death.

Question 17

What is the role of the diphtheria toxin’s B subunit?

Answer 17

The B subunit binds the toxin to specific receptors on host cells, allowing the A subunit to enter the cell.

Question 18

What is the appearance of C. diphtheriae under Albert stain?

Answer 18

Green bacilli with bluish-black metachromatic granules.

Question 19

What is the purpose of the Elek immunodiffusion test?

Answer 19

To determine the toxigenicity of C. diphtheriae by detecting the presence of diphtheria toxin.

Question 20

Why is antitoxin given immediately in suspected diphtheria cases?

Answer 20

To neutralize unbound toxin in the blood before it binds irreversibly to cells, as bound toxin cannot be neutralized.

Question 21

What is the significance of the ‘bull neck’ appearance in diphtheria?

Answer 21

It indicates severe cervical lymphadenopathy due to systemic spread of the toxin.

Question 22

What is the primary method for preventing diphtheria outbreaks?

Answer 22

Vaccination with the DTaP vaccine and identifying and treating healthy carriers.

Question 23

What is the difference between nasopharyngeal and cutaneous diphtheria?

Answer 23

Nasopharyngeal diphtheria involves the throat and respiratory system, while cutaneous diphtheria affects the skin and rarely causes systemic symptoms.

Question 24

What is the role of Loeffler’s medium in culturing C. diphtheriae?

Answer 24

It stimulates the growth of C. diphtheriae and enhances the production of metachromatic granules.

Question 25

What is the significance of the tox gene in C. diphtheriae?

Answer 25

The tox gene encodes diphtheria toxin, which is responsible for the pathogenicity of the bacterium.