Bacteria Associated With Skin Infections 3 Flashcards by asdfg hjkl

Causative agent of Leprosy/Hansen’s disease

Mycobaterium leprae

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Diagnostic feature of M. leprae

Obligate intracellular parasite

Acid-fast bacilli

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

Macrophage (Langerhan cells)
Endothelial cells (blood vessels)
Schwann cells (peripheral nerves)

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Morphology of M. leprae

Red or pink colored bacilli

Singly, in parallel bundles or in globular masses

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

Leonine-like fascies

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General characteristics of M. leprae

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

Develop local granulomatous lesions with limited multiplication of bacilli

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Inoculation of bacilli from ground tissue nasal scrapings in armadillos will

Develop extensive lepromatous leprosy

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Natural hosts of M. leprae

Humans and nine-banded armadillos

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Diagnostic tests for M. leprae

Nine-banded armadillo and mice foot pads

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

True

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

Phenoluc glycolipid-1 (PGL-1)

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

PGL-1

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

PGL-1

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Epidemiology of M. leprae

Endemic in Asia, Africa, Latin America and Pacific

Associated with poverty, rural residence and rarely armadillo contact)

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Continent with the greatest number of cases of lepromatous leprosy

Asia

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Continent with the highest prevalence rate of lepromatous leprosy

Africa

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Mode of transmission of M. leprae

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

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True or False.

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

True

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Shedding of organism in nasal secretions or ulcer exudates

Contact with lepromatous leprosy patients

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Insect vectors that transmit M. leprae

Bed bugs and mosquitos in areas of leprosaria

Outer lipid capsule of M. leprae found in soil

PGL-1

Incubation period of M. leprae

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

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.

True

Clinical manifestation of M. leprae

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)

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

small nerve fibers are functionally impaired

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

Lepromin test

True or False. | Lepromin test is not diagnostic because it lacks specificity.

True

Reactions in Lepromin test

(-) Lepromatous | (+) Tuberculoid

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

True

Laboratory diagnosis of M. leprae

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)

Result of AF stain in smears of tissue juices

Lepra cells characterized by palisafe/parallel cigar pakcets morphology

Treatment for M. leprae

Multi-Drug Treatment: Sulfones, Rifampicin, Clofazimine | Recommended by WHO (2 year treatment)

Prevention and control of M. leprae

Identification and treatment of cases | Chemoprophylaxis until treatment of contagious parents has rendered their children non-infectious

General characteristics of M. marinum

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

M. marinum infection arises when

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

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

Swimming pool granuloma

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

Fish tank granuloma

Habitat of M. marinum

Salt water marine organisms and amphibians

Incubation period of M. marinum

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

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

True

Progression of ulceration in M. marinum infection

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

Diagnosis of M. marinum

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

Treatment of M. marinum

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

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

True

Third most common mycobacterial infection worldwide

M. ulcerans

General characteristics of M. ulcerans

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)

Most common location of ulcerative lesions caused by M. ulcerans

Extensor surfaces of the extremities | Dorsal aspect of the hands

Transmission of M. ulcerans

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

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

True.

Diagnosis of M. ulcerans

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

Treatment of M. ulcerans

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