Corynebacterium

Question 1

Which bacterium causes diphtheria, and who first described it?

Answer 1

Corynebacterium diphtheriae causes diphtheria, first described by Klebs in 1883.

Question 2

Describe the appearance of Corynebacterium diphtheriae under a microscope.

Answer 2

It appears as gram-positive, non-motile, club-shaped bacilli with metachromatic granules.

Question 3

What are the five pathogenic species of Corynebacterium?

Answer 3

C. diphtheriae causes diphteria, C. haemolyticum causes pharyngitis, C. xerosis causes Endocarditis C. pseudotuberculosis causes TB like illness, and C. ulcerans causes pharyngitis .

Question 4

What is the shape and staining characteristic of C. diphtheriae?

Answer 4

C. diphtheriae is pleomorphic and shows a ‘V’ or ‘L’ Chinese letter arrangement.

Question 5

Which staining method highlights C. diphtheriae’s granules, and what colors do they appear?

Answer 5

Albert’s method stains the granules bluish-black and cytoplasm green.

Question 6

What is the main pathogenic factor of C. diphtheriae?

Answer 6

The major pathogenic factor is the diphtheria toxin.

Question 7

On what medium does C. diphtheriae show luxurious growth?

Answer 7

Loeffler’s inspissated serum medium.

Question 8

What selective medium is preferred for studying C. diphtheriae colonies?

Answer 8

Blood tellurite agar medium (Mcleod’s medium) is preferred.

Question 9

How does C. diphtheriae appear on cystine-tellurite blood agar?

Answer 9

C. diphtheriae forms black or brownish colonies with a brown halo.

Question 10

What is the optimal growth temperature for C. diphtheriae?

Answer 10

The optimal growth temperature is 37°C.

Question 11

What type of immunity protects newborns from diphtheria?

Answer 11

Passive immunity received transplacentally protects newborns.

Question 12

What is the primary transmission route of diphtheria?

Answer 12

Diphtheria is primarily spread by droplet infection.

Question 13

What are the two main forms of diphtheria infection?

Answer 13

Respiratory and cutaneous diphtheria.

Question 14

Which organs can the diphtheria toxin affect?

Answer 14

It can affect kidneys, heart, and nervous system.

Question 15

What characterizes respiratory diphtheria?

Answer 15

Characterized by low-grade fever, malaise, and sore throat.

Question 16

What is the most common infection site in respiratory diphtheria?

Answer 16

The tonsils or pharynx are the most common infection sites.

Question 17

What forms the pseudomembrane in diphtheria infection?

Answer 17

The pseudomembrane forms from necrotic tissue and exudate.

Question 18

What risk is associated with the diphtheria pseudomembrane?

Answer 18

The pseudomembrane can obstruct airways, risking suffocation.

Question 19

What does fragment A of diphtheria toxin do at the cellular level?

Answer 19

Fragment A inhibits protein synthesis in eukaryotic cells.

Question 20

Which molecule does diphtheria toxin inactivate to halt protein synthesis?

Answer 20

Elongation factor 2 (EF-2) is inactivated by the toxin.

Question 21

What environmental factor limits toxin production by C. diphtheriae?

Answer 21

Low iron levels trigger significant toxin production.

Question 22

Which lab test is used to confirm diphtheria toxin production?

Answer 22

The Elek test confirms toxin production.

Question 23

What immunological component does the Elek test use to detect diphtheria toxin?

Answer 23

A filter paper strip impregnated with diphtheria antitoxin.

Question 24

What medium is required for the in vitro diphtheria toxin detection?

Answer 24

Low iron medium is required in the Elek test.

Question 25

How are control organisms used in the Elek test?

Answer 25

Control organisms are used to verify test accuracy.

Question 26

What are the two animal models used for in vivo diphtheria toxin testing?

Answer 26

Guinea pigs and mice are used in vivo toxin tests.

Question 27

What type of immunity is given by diphtheria toxoid vaccination?

Answer 27

It provides active immunity.

Question 28

What antibiotic is preferred for diphtheria carriers?

Answer 28

Erythromycin is the preferred antibiotic.

Question 29

How is the antitoxin dose determined in clinical diphtheria cases?

Answer 29

Dosage depends on disease severity, typically 20,000–100,000 units.

Question 30

What vaccine combines diphtheria toxoid for children?

Answer 30

DPT (Diphtheria, Pertussis, Tetanus) vaccine.

Question 31

What effect does iron have on diphtheria toxin synthesis?

Answer 31

Low iron concentration limits toxin production.

Question 32

What are the possible systemic effects of diphtheria toxin?

Answer 32

Systemic effects may include kidney, heart, and nerve damage.

Question 33

Why is erythromycin preferred over penicillin in some cases?

Answer 33

Erythromycin is used in penicillin-sensitive patients.

Question 34

What complication may arise from using horse serum antitoxin?

Answer 34

Hypersensitivity reactions may occur due to horse serum.

Question 35

How often should adults revaccinate for diphtheria immunity?

Answer 35

Adults should be revaccinated every 10 years.

Question 36

What can disrupt respiratory diphtheria's pseudomembrane?

Answer 36

Sampling or physical manipulation can dislodge it.

Question 37

Why is C. diphtheriae non-acid fast?

Answer 37

C. diphtheriae lacks mycolic acids, making it non-acid fast.

Question 38

What is the function of metachromatic granules in C. diphtheriae?

Answer 38

Granules serve as phosphate reserves.

Question 39

What is the incubation period for diphtheria?

Answer 39

The incubation period is 2 to 5 days.

Question 40

Which staining gives a beaded appearance to C. diphtheriae?

Answer 40

Albert staining gives a beaded appearance.

Question 41

What is Babes-Ernst granules, and how do they stain?

Answer 41

Babes-Ernst granules stain more intensely, appearing as blue beads.

Question 42

Why is passive immunity crucial in early diphtheria cases?

Answer 42

Antitoxin provides immediate passive immunity support.

Question 43

What alternative test is used to detect the tox gene in C. diphtheriae?

Answer 43

PCR is an alternative method for detecting the tox gene.

Question 44

How does the diphtheria toxin interact with eukaryotic cells?

Answer 44

The toxin binds to eukaryotic cell receptors and enters cells.

Question 45

What precaution should travelers take regarding diphtheria?

Answer 45

CDC recommends diphtheria vaccinations be up-to-date.

Question 46

Which gene carries the diphtheria toxin in bacteriophages?

Answer 46

The tox gene is carried by lysogenic β-phages.

Question 47

What differentiates C. diphtheriae from other corynebacteria on tellurite agar?

Answer 47

Tellurite agar results in brown halos around colonies.

Question 48

What symptoms typically present in early respiratory diphtheria?

Answer 48

Early symptoms include fever, sore throat, and malaise.

Question 49

What lab procedure differentiates toxigenic from non-toxigenic C. diphtheriae?

Answer 49

Elek test differentiates toxigenic strains.

Question 50

How does protein synthesis disruption lead to cellular damage in diphtheria?

Answer 50

EF-2 inactivation by ADP-ribosylation disrupts protein synthesis.