Bacteria Associated With Skin Infections 3 Flashcards
Causative agent of Leprosy/Hansen’s disease
Mycobaterium leprae
Diagnostic feature of M. leprae
Obligate intracellular parasite
Acid-fast bacilli
M. leprae cannot live on its own. Its preferred cells include:
Macrophage (Langerhan cells) Endothelial cells (blood vessels) Schwann cells (peripheral nerves)
Morphology of M. leprae
Red or pink colored bacilli
Singly, in parallel bundles or in globular masses
This is the result of the destruction of the nasal septum for patients with lepromatous leprosy
Leonine-like fascies
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
Inoculation of bacilli from ground tissue nasal scrapings in footpads of mice will
Develop local granulomatous lesions with limited multiplication of bacilli
Inoculation of bacilli from ground tissue nasal scrapings in armadillos will
Develop extensive lepromatous leprosy
Natural hosts of M. leprae
Humans and nine-banded armadillos
Diagnostic tests for M. leprae
Nine-banded armadillo and mice foot pads
True or False.
M. leprae from armadillo or human tissue contain a unique enzyme characteristic of leprosy bacilli called
o-diphenoxidase.
True
M. leprae contains a dense, largely lipid outer capsule outside of the cell wall
Phenoluc glycolipid-1 (PGL-1)
Major antigenic glycolipid in bacterium detected in the serologic test for leprosy
PGL-1
Associated in determining the bacterial predilection to the peripheral nerve by binding to the basal lamina of Schwann cells
PGL-1
Epidemiology of M. leprae
Endemic in Asia, Africa, Latin America and Pacific
Associated with poverty, rural residence and rarely armadillo contact)
Continent with the greatest number of cases of lepromatous leprosy
Asia
Continent with the highest prevalence rate of lepromatous leprosy
Africa
Mode of transmission of M. leprae
Inhalation of nasal droplet secretions Contact with infected skin Insect vectors Transmitter by soil Direct dermal inoculation (Tattoo)
True or False.
M. leprae infection is directly related to overcrowding and poor hygiene.
True
Shedding of organism in nasal secretions or ulcer exudates
Contact with lepromatous leprosy patients
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
