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Medical Microbiology > Corynebacterium > Flashcards

Corynebacterium Flashcards

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USMLE® Step 1 flashcards Biology 101 flashcards
1
Q

Which bacterium causes diphtheria, and who first described it?

A

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

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2
Q

Describe the appearance of Corynebacterium diphtheriae under a microscope.

A

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

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3
Q

What are the five pathogenic species of Corynebacterium?

A

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

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4
Q

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

A

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

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5
Q

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

A

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

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6
Q

What is the main pathogenic factor of C. diphtheriae?

A

The major pathogenic factor is the diphtheria toxin.

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7
Q

On what medium does C. diphtheriae show luxurious growth?

A

Loeffler’s inspissated serum medium.

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8
Q

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

A

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

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9
Q

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

A

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

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10
Q

What is the optimal growth temperature for C. diphtheriae?

A

The optimal growth temperature is 37°C.

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11
Q

What type of immunity protects newborns from diphtheria?

A

Passive immunity received transplacentally protects newborns.

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12
Q

What is the primary transmission route of diphtheria?

A

Diphtheria is primarily spread by droplet infection.

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13
Q

What are the two main forms of diphtheria infection?

A

Respiratory and cutaneous diphtheria.

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14
Q

Which organs can the diphtheria toxin affect?

A

It can affect kidneys, heart, and nervous system.

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15
Q

What characterizes respiratory diphtheria?

A

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

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16
Q

What is the most common infection site in respiratory diphtheria?

A

The tonsils or pharynx are the most common infection sites.

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17
Q

What forms the pseudomembrane in diphtheria infection?

A

The pseudomembrane forms from necrotic tissue and exudate.

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18
Q

What risk is associated with the diphtheria pseudomembrane?

A

The pseudomembrane can obstruct airways, risking suffocation.

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19
Q

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

A

Fragment A inhibits protein synthesis in eukaryotic cells.

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20
Q

Which molecule does diphtheria toxin inactivate to halt protein synthesis?

A

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

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21
Q

What environmental factor limits toxin production by C. diphtheriae?

A

Low iron levels trigger significant toxin production.

22
Q

Which lab test is used to confirm diphtheria toxin production?

A

The Elek test confirms toxin production.

23
Q

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

A

A filter paper strip impregnated with diphtheria antitoxin.

24
Q

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

A

Low iron medium is required in the Elek test.

25
Q

How are control organisms used in the Elek test?

A

Control organisms are used to verify test accuracy.

26
Q

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

A

Guinea pigs and mice are used in vivo toxin tests.

27
Q

What type of immunity is given by diphtheria toxoid vaccination?

A

It provides active immunity.

28
Q

What antibiotic is preferred for diphtheria carriers?

A

Erythromycin is the preferred antibiotic.

29
Q

How is the antitoxin dose determined in clinical diphtheria cases?

A

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

30
Q

What vaccine combines diphtheria toxoid for children?

A

DPT (Diphtheria, Pertussis, Tetanus) vaccine.

31
Q

What effect does iron have on diphtheria toxin synthesis?

A

Low iron concentration limits toxin production.

32
Q

What are the possible systemic effects of diphtheria toxin?

A

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

33
Q

Why is erythromycin preferred over penicillin in some cases?

A

Erythromycin is used in penicillin-sensitive patients.

34
Q

What complication may arise from using horse serum antitoxin?

A

Hypersensitivity reactions may occur due to horse serum.

35
Q

How often should adults revaccinate for diphtheria immunity?

A

Adults should be revaccinated every 10 years.

36
Q

What can disrupt respiratory diphtheria’s pseudomembrane?

A

Sampling or physical manipulation can dislodge it.

37
Q

Why is C. diphtheriae non-acid fast?

A

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

38
Q

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

A

Granules serve as phosphate reserves.

39
Q

What is the incubation period for diphtheria?

A

The incubation period is 2 to 5 days.

40
Q

Which staining gives a beaded appearance to C. diphtheriae?

A

Albert staining gives a beaded appearance.

41
Q

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

A

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

42
Q

Why is passive immunity crucial in early diphtheria cases?

A

Antitoxin provides immediate passive immunity support.

43
Q

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

A

PCR is an alternative method for detecting the tox gene.

44
Q

How does the diphtheria toxin interact with eukaryotic cells?

A

The toxin binds to eukaryotic cell receptors and enters cells.

45
Q

What precaution should travelers take regarding diphtheria?

A

CDC recommends diphtheria vaccinations be up-to-date.

46
Q

Which gene carries the diphtheria toxin in bacteriophages?

A

The tox gene is carried by lysogenic β-phages.

47
Q

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

A

Tellurite agar results in brown halos around colonies.

48
Q

What symptoms typically present in early respiratory diphtheria?

A

Early symptoms include fever, sore throat, and malaise.

49
Q

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

A

Elek test differentiates toxigenic strains.

50
Q

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

A

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

Medical Microbiology (4 decks)

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