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Microbiology and Parasitology > Bacteria Associated With Skin Infections 3 > Flashcards

Bacteria Associated With Skin Infections 3 Flashcards

1
Q

Causative agent of Leprosy/Hansen’s disease

A

Mycobaterium leprae

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2
Q

Diagnostic feature of M. leprae

A

Obligate intracellular parasite

Acid-fast bacilli

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3
Q

M. leprae cannot live on its own. Its preferred cells include:

A 
Macrophage (Langerhan cells)
Endothelial cells (blood vessels)
Schwann cells (peripheral nerves)
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4
Q

Morphology of M. leprae

A

Red or pink colored bacilli

Singly, in parallel bundles or in globular masses

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5
Q

This is the result of the destruction of the nasal septum for patients with lepromatous leprosy

A

Leonine-like fascies

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6
Q

General characteristics of M. leprae

A

Waxy exterior coating (presence of mycolic acid)
Gram variable (mostly Gram +)
Regularly found in skin or mucous membranes, particularly nasal septum
Cannot be grown in cell-free media or tissue culture
Grow best in mice and humans at below 37C

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7
Q

Inoculation of bacilli from ground tissue nasal scrapings in footpads of mice will

A

Develop local granulomatous lesions with limited multiplication of bacilli

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8
Q

Inoculation of bacilli from ground tissue nasal scrapings in armadillos will

A

Develop extensive lepromatous leprosy

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9
Q

Natural hosts of M. leprae

A

Humans and nine-banded armadillos

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10
Q

Diagnostic tests for M. leprae

A

Nine-banded armadillo and mice foot pads

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11
Q

True or False.
M. leprae from armadillo or human tissue contain a unique enzyme characteristic of leprosy bacilli called
o-diphenoxidase.

A

True

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12
Q

M. leprae contains a dense, largely lipid outer capsule outside of the cell wall

A

Phenoluc glycolipid-1 (PGL-1)

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13
Q

Major antigenic glycolipid in bacterium detected in the serologic test for leprosy

A

PGL-1

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14
Q

Associated in determining the bacterial predilection to the peripheral nerve by binding to the basal lamina of Schwann cells

A

PGL-1

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15
Q

Epidemiology of M. leprae

A

Endemic in Asia, Africa, Latin America and Pacific

Associated with poverty, rural residence and rarely armadillo contact)

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16
Q

Continent with the greatest number of cases of lepromatous leprosy

A

Asia

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17
Q

Continent with the highest prevalence rate of lepromatous leprosy

A

Africa

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18
Q

Mode of transmission of M. leprae

A 
Inhalation of nasal droplet secretions
Contact with infected skin
Insect vectors
Transmitter by soil
Direct dermal inoculation (Tattoo)
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19
Q

True or False.

M. leprae infection is directly related to overcrowding and poor hygiene.

A

True

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20
Q

Shedding of organism in nasal secretions or ulcer exudates

A

Contact with lepromatous leprosy patients

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21
Q

Insect vectors that transmit M. leprae

A

Bed bugs and mosquitos in areas of leprosaria

22
Q

Outer lipid capsule of M. leprae found in soil

A

PGL-1

23
Q

Incubation period of M. leprae

A

Minimum of 2-3 years
Can be as long as 40 years or more
Doubling every 14 days
Longer than routine laboratory culture

24
Q

True or False.
The number of bacilli harbored by a lepromatous patient on initial diagnosis is far greater than that of any human bacterial disease, 10^15.

A

True

25
Q

Clinical manifestation of M. leprae

A

Largely confined to the skin, URT, testes and peripheral nerves
Small nerve fibers are functionally impaired (loss of fine touch, pain, hot and cold sensation)

26
Q

Most serious sequelae of M. leprae that is the result of affinity of particular organism for peripheral nerves

A

small nerve fibers are functionally impaired

27
Q

Intradermal skin test that uses heat-killed human or armadillo dervided M. leprae

A

Lepromin test

28
Q

True or False.

Lepromin test is not diagnostic because it lacks specificity.

A

True

29
Q

Reactions in Lepromin test

A

(-) Lepromatous

(+) Tuberculoid

30
Q

True or False.

Lepromin test can be induced in normal healthy individuals by vaccination with Bacillus Calmette-Guerin (BCG).

A

True

31
Q

Laboratory diagnosis of M. leprae

A

Biopsy of skin or thickened nerve
Culture in footpads of mice
Smears of tissue juice subjected to AF stain (Wade-Fite)
AFB smear on NEST (nasal scrapings, ear lobes, skin lesion, tissue sections)

32
Q

Result of AF stain in smears of tissue juices

A

Lepra cells characterized by palisafe/parallel cigar pakcets morphology

33
Q

Treatment for M. leprae

A

Multi-Drug Treatment: Sulfones, Rifampicin, Clofazimine

Recommended by WHO (2 year treatment)

34
Q

Prevention and control of M. leprae

A

Identification and treatment of cases

Chemoprophylaxis until treatment of contagious parents has rendered their children non-infectious

35
Q

General characteristics of M. marinum

A 
Non-tuberculous
Free living
Water-borne
Leisure time pathogen or hobby hazard
Slow growing at low temperature (32C)
Shares antigens with other Mycobacteria
36
Q

M. marinum infection arises when

A

Traumatized skin comes into contact with infected water in swimming pools, aquariums, oceans or lakes

37
Q

Type of M. marinum granuloma that affects feet and hands of swimmers (particularly in non-chlorinated pools)

A

Swimming pool granuloma

38
Q

Type of M. marinum granuloma that causes lesions on hands of fish handlers/keepers

A

Fish tank granuloma

39
Q

Habitat of M. marinum

A

Salt water marine organisms and amphibians

40
Q

Incubation period of M. marinum

A

2-3 weeks after entry from traumatized skin from pools, aquarium, natural bodies of water, fish spines or nips by crustaceans

41
Q

True or False.

M. marinum almost always confined to superficial cooler body tissues, most often on the extremities

A

True

42
Q

Progression of ulceration in M. marinum infection

A

Begins as small papules ➡️ enlarges ➡️ acquire blue purple hue ➡️ suppuration ➡️ ulceration

43
Q

Diagnosis of M. marinum

A 
Culture of skin lesions (do not  grow  in  incubators usually  set at  37°C)
Histologic exam (granuloma + clinical history)
44
Q

Treatment of M. marinum

A

Good results with rifampicin and EMB
Tetracyclines
TMP-SMX (Trimethoprim/Sulfamethoxazole)

45
Q

True or False.

Most strains of M. marinum are resistant to Isoniazid (INH), Para-aminosalicylic acid (PAS) and Streptomycin (SM).

A

True

46
Q

Third most common mycobacterial infection worldwide

A

M. ulcerans

47
Q

General characteristics of M. ulcerans

A

Slow growing
Inhabits water and colonize aquatic plants, herbivores, and aquatic insects
Endemic in countries with tropical rain forests
Prevalent in Australia and Africa
Causes chronic, painless, cutaneous ulcers (Buruli or Bairnsdale ulcers)

48
Q

Most common location of ulcerative lesions caused by M. ulcerans

A

Extensor surfaces of the extremities

Dorsal aspect of the hands

49
Q

Transmission of M. ulcerans

A

Not fully understood but linked to contaminated water, soil and vegetation
Abraded skin
Insects play an important role
Begins as a nodule then ulcerates over 4-6 weeks

50
Q

True or False.
In M. ulcerans, centers of ulcers are necrotic, without caseation while organisms are located at the periphery, adjacent to normal tissue.

A

True.

51
Q

Diagnosis of M. ulcerans

A

Smears from necrotic base of ulcers stained by Ziehl-Neelsen method for Acid Fast Bacilli
Biopsy specimens from necrotic base of lesions
Culture of lesions (from exudates or tissue fragments): 6-8 weeks incubation at 33°C

52
Q

Treatment of M. ulcerans

A

Local heat, excision and grafting
Combination of either INH-SM or diaminodiphenylsulfone + oxytetracycline
Combination of SMX, RMP and minocycline

Microbiology and Parasitology (8 decks)

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