NON SPORE GRAM POSITICE RODS. PART 1

Question 1

What is the genus of bacteria that includes many species of aerobic and facultative Gram-positive rods

Answer 1

Corynebacterium

Question 2

What is the characteristic shape of Corynebacterium cells after division?

Answer 2

Corynebacterium cells tend to have clubbed ends and often remain attached after division, forming “Chinese letter” or palisade arrangements or V- or L-shaped formations.

Question 3

What gives Corynebacterium rods their beaded appearance?

Answer 3

The beads in Corynebacterium rods consist of granules of highly polymerized polyphosphate, which serve as a storage mechanism for high-energy phosphate bonds.

Question 3

How do these granules stain when using metachromatic dyes?

Answer 3

The granules stain metachromatically, meaning that a dye that stains the rest of the cell blue will stain the granules red.

Question 4

Under what conditions does Corynebacterium generally grow best?

Answer 4

Growth of Corynebacterium is generally best under aerobic conditions on media enriched with blood or other animal products, although many strains can also grow anaerobically.

Question 5

What is the typical size of colonies formed by Corynebacterium on blood agar?

Answer 5

Colonies on blood agar are typically small (1-2 mm), and most are nonhemolytic.

Question 6

What is the primary pathogenic feature of Corynebacterium diphtheriae?

Answer 6

Corynebacterium diphtheriae produces a powerful exotoxin that is responsible for diphtheria.

Question 6

What are diphtheroids, and where are they commonly found?

Answer 6

Diphtheroids are other corynebacteria that are nonpathogenic commensal inhabitants of various body sites:
Pharynx
Nasopharynx
Distal urethra
Skin

Question 7

What type of infections are diphtheroids implicated in?

Answer 7

Diphtheroids are implicated in opportunistic infections.

Question 8

what is the transmission of corynebacterum diphtheriae

Answer 8

Humans are the only natural host of C. diphtheriae.
* Both toxigenic and nontoxigenic organisms reside in the upper
respiratory tract and are transmitted by droplet spread, by direct
contact with cutaneous infections, and, to a lesser extent, by fomites
* The organism can also infect the skin at the site of a preexisting skin
lesion.

Question 9

What is essential for pathogenesis in diphtheria

Answer 9

Exotoxin production is essential for pathogenesis.
Invasiveness is also necessary because the organism must first establish and maintain itself in the throat.

Question 10

What type of toxin is expressed in diphtheria?

Answer 10

Diphtheria toxin is an A-B toxin

Question 11

How is diphtheria toxin produced?

Answer 11

Diphtheria toxin is expressed from a temperate phage in the presence of low iron.

Question 12

What does diphtheria toxin do?

Answer 12

The toxin binds to receptors on the surface of many eukaryotic cells, particularly heart and nerve cells.
It inhibits protein synthesis by ADP-ribosylation of elongation factor-2 (EF-2).

Question 13

What is the role of the active (A) domain of diphtheria toxin?

Answer 13

The active (A) domain possesses enzymatic activity that cleaves nicotinamide from nicotinamide adenine dinucleotide (NAD) and transfers the remaining ADP-ribose to EF-2, thereby inactivating it.

Question 14

What are the components of the host response to Corynebacterium diphtheriae?

Answer 14

Local inflammation in the throat: This results in the formation of a fibrinous exudate.

The exudate forms a tough, adherent, gray pseudomembrane characteristic of the disease.

Question 15

How does the antibody counteract diphtheria exotoxin activity?

Answer 15

The antibody can neutralize exotoxin activity by blocking the interaction of the binding domain with the receptors. This prevents the toxin from entering the cell.

Question 16

explain the clinical manifestation of corynebacterium diphtheriae

Answer 16

.After an incubation period of 2 to 4 days, diphtheria usually manifests
as pharyngitis or tonsillitis.
* Malaise, sore throat, and fever occur, and a patch of exudate or
membrane develops on the tonsils, uvula, soft palate, or pharyngeal
wall.
* Thick, gray, adherent pseudomembrane over the tonsils and
throat

Question 17

What are the three prominent complications of diphtheria

Answer 17

1. Extension of the membrane into the larynx and trachea, causing airway obstruction.
2. Myocarditis accompanied by arrhythmias and circulatory collapse.
3. Nerve weakness or paralysis, especially of the cranial nerves.
   ~Paralysis of the muscles of the soft palate and pharynx can lead to regurgitation of fluids through the nose.

Question 18

What does laboratory diagnosis for diphtheria involve?

Answer 18

1. Isolating the organism.
2. Demonstrating toxin production.
3. The decision to treat with antitoxin is a clinical one and cannot wait for the laboratory results.

Question 19

What culture media should be used for throat swab testing in diphtheria diagnosis?

Answer 19

A throat swab should be cultured on:
~Loeffler’s medium.
~A tellurite plate.
~A blood agar plate.
~The typical gray-black color of tellurium in the colony is a telltale diagnostic criterion.

Question 20

How can toxin production be documented in C. diphtheriae cultures

Answer 20

Either animal inoculation or an antibody-based gel diffusion precipitin test is performed to document toxin production.

A PCR assay for the presence of the toxin gene in the organism isolated from the patient can also be used.

Question 21

Treatment of Corynebacterium diphtheriae

Answer 21

Erythromycin