Mycobacteria

Question 1

BCG vaccine

Answer 1

Bacille Calmette Guerin
Isolated from mycobacterium bovis
attenuated 231 times over a period of 13 years in potato broth with added beef broth
gradual loss of virulence in mice
first given as a vax to kids in 1921. now over 3 billion doses given.
NB: immunocompromised humans shouldn’t get BCG d/t risk of disseminated disease.

Question 2

Mycobacteria

Answer 2

many species consisting of major pathogens, opportunist pathogens, harmless saprophytes- pathogens are fairly rare
Cause granulomatous lesions (tubercles) in tissues of a wider range of domestic and wild animals and humans
Specialized granulomas- an attempt to wall off infection from uninfected tissue.
Development of mycobacterial disease in a host depends on the ability of the bacteria to survive and multiply WITHIN the host macrophages.

Question 3

General characteristics of mycobacteria

Answer 3

Aerobic, non-spore-forming, non-motile
Acid fast (gram positive but don’t stain well with Gram stain)- bind phenol based dyes (carbol fuschin) and resist acid alcogol decolation (Z-N stain)
Very unique because of hardy cell wall.
Catalse positive
Many produce pigments on culture
relatively simple growth reqs (except m. leprae can’t grow in lab on solid media)
Fairly slow growing compared to other bacteria- esp. pathogenic forms
Unique cell walls- lipid rich- acid fastness related to presence of peptidoglycan, but particularly glycolipids
Lipids in cell wall related to pathogenicity, particularly survival in phagolysosome of macrophages, resists drying, extreme pH and other stresses.

Question 4

Mycobacterium tuberculosis

Answer 4

TB in humans, but also cats, dogs, pigs, chickens, parrots, canaries, guinea pigs and mice (rare in cattle)- humans can transmit via aerosol to domestic animals

Question 5

Mycobacterium bovis

Answer 5

Bovine TB, also TB in man (badgers, deer), other ruminants, pigs and more rarely in horses, dogs, cats and sheep

Question 6

Mycobacterium avium subspecies paratuberculosis

Answer 6

Johne’s disease in cattle, sheep, goats and deer- chronic wasting disease causing diarrhea

Question 7

Mycobacterium avium complex (incl. subspecies avium)

Answer 7

TB in birds, poultry very susceptible, Pigs susceptible but not cattle. Sporadic cases in horses, dogs and cats. Opportunist in man (AIDS- M. avium intracellulare).

Question 8

M. leprae

Answer 8

Leprosy in man, mice and armadillos

Question 9

M. lepraemurium, M. ulcerans, M. kanasii, M. fortuitum and M. chelonae

Answer 9

skin ulceration and LN involvement in many different species. Chronic RTI

Question 10

Acid-fast staining of Mycobacteria

Answer 10

Red rods are m. tuberculosis, intracellular location via active phagocytosis in macrophage

Question 11

Mycobacterial acid-fast cell wall

Answer 11

Acid-fast cell wall is unique to mycobacteria- glycolipids, wax molecules, arabinan molecules- basiclaly like being covered by a bar of soap

Question 12

Virulence factors of mycobacteria

Answer 12

largely cell wall-related.
Cell wall components: survives in a hostile environment
Mycolic acids: resist phagocytic digestion
Sulfatides: prevent pahgocytic activation and phagosome-lysosome fusion
Trehalose di-mycolate (cord factor): inhibit phagocytic chemotaxis, activation, phagolysosome fusion and digestion– form serpentine cords on staining
Lipoarabinomannan (LAM): prevents phagocyte activation and digestion within the phagocytes
Mycoside: prevent intracellular killing and digestion
Other factors include superoxide dismutase and heat shock protein.

Question 13

Cell wall antigens

Answer 13

In general, they induce delayed type hypersensitivity (DTH). TB exists in macrophages. after several weeks, immune system ramps up and on stimulation with IF-gamma, marcophages can kill TB by forming phagolysosomes and NO radicals. However, hyper-activated macs secrete TNF which recruits multiple monocytes which differentiate into epitheliod histiocytes (activated macs). These wall of the infected cells, but at the cost of significant inflammation and local damage.

Question 14

Epithelioid cells

Answer 14

activated macrophages- essential characteristic of granulomas, which means by definition, TB lesions are granulomatous.

Question 15

Outcomes of infection of M.bovis

Answer 15

ability to mount an effective activated macrophage response determines the outcome of an encounter with pathogenic mycobacteria. Less than 10% of those infeced develop disease.

1) infects, killed by IR, no disease
2) infects, lies dormant for years, no disease (most common)
3) infects, lies dormant for years, reactivates and causes acute disease
4) infectes causes rapid acute disease, may disseminate (young, immunocompromised, HIV)

Question 16

Pulmonary TB lesions in man

Answer 16

most prominent when environment is most oxygenated (cranial portions of the lung). Lymph nodes-caseating material, break down of tissue. lesions can liquefy into bronchi, aerosols disseminate disease.

Question 17

Immune response to mycobacterial infections

Answer 17

1) antibody response irrelevant to protection: Th1 (CMI) required to limit the disease and provide protection
2) immune status of host: active response results in lymphocyte infiltration, central necrosis of the lesion, tubercle may be limited by fibrin capsule. granuloma walls of lesion become fibrosed and most often contains it and it stops growing but mycobacteria are still alive. response may kill it, but often only able to restrict disease. reactivation occurs with stress/immunosuppression.
3) IF-gamma from CD4 lymphocytes activate macs to kill intracellular mycobacteria. CD8 lymphocytes become cytotoxic, killing myobacterial infected cells. CD1 restricted T-cells recognized glycolipids (of cell wall)

Question 18

TB lesion- what does it look like histologically?

Answer 18

central necrosis, surrounded by a region of lymphocytes and macrophages (often Langhan’s cells- multinucleate giant cells formed by fusion of epithelioid cells). also see some fibrosis surrounding.

Question 19

Spread of Mycobacterium bovis

Answer 19

spread promoted by high stocking densities and immune suppresion. generally primary respiratory infection leads to tuberlces in lung and associated LNs (bronchial and retropharyngeal)
Closed lesions are less infectious than animals actively coughing out M. bovis.
Spread to intestine via sputum and serosal surface
Pleural TB lesions= pearl’s disease
Further spread to liver, spleen, kidney and brain (usually hematogenous).
Vertical transmission possible after spread to mammary glands and uterus.

Question 20

Presentation of mycobacterium bovis

Answer 20

multifocal to coalescing caseous granulomas.

Question 21

Epidemiology of bovine TB

Answer 21

Cattle transmit infection to cattle via infected resp. droplets. Badgers are wildlife reserve. Badgers transmit via respr route and by biting. mums transmit to cubs, but not by milk, rather via close personal contact. Cattle may get TB from badgers via grazing on contaminated pasture (badger feces, urine, pus etc) or badgers urinate and defecate, or dried badger saliva in cattle feeders.

Question 22

Diagnosis of Mycobacterial infection

Answer 22

immunological detection (tuberculin)
lab diagnosis: Z-N staining
Culture
ID by PCR

Question 23

Comparative intradermal test

Answer 23

Two sites prepared on animal neck (13cm apart). Hair clipped in 2 cm radius and skin fold is measured. Inject purified protein derivative (containing different antigens). Use M. avium at preparation in upper site and M. bovis on lower site. Re-measure fold after 72 hours. If reaction to M. bovis, PPD is 5mm greater than M. avium. If 1-4mm greater, retest within 40-60 days.
This test measures lymphocyte infiltration into site. If previous exposure, increased size.
TB specific lymphocytes in lesion lead to the increased size.

Question 24

Interfron gamma assay

Answer 24

whole blood assay or assay that takes T-cells. whole blood or t-cels exposed and then IFN gamma response is measured. Can get a negative response ot TB skin tests with a massive/severe infection (i.e. T-cells too busy responding to real disease). Increased pathogens, increased bacterial load, decreased TB skin test and decreased IF gamma.

Question 25

Mycobacterium avium

Answer 25

widest host range among mycobacteria.
M. avium ssp. avium serovars 1,2, and 3 isolated from TB lesions in avian species.
other avium serovars produce minimal disease.
Non-human primates, cattle and pigs infection. Avium is confined to LN infection (spoils carcass–> mycobacteriosis in pigs).

Question 26

M. avium ssp. paratuberculosis- Johne’s disease

Answer 26

transmissible chronic and progressive enteritis (diarrhea and ileal inflammation) in cattle, sheep and goats. Infection usually occurs within 1st month, but may take 6 months to 5 years.

Question 27

Clinical course of Johne’s disease

Answer 27

starts with general signs of illness (weight loss, intermittent diarrhea) followed by severe diarrhea, emaciation and death. Impaired intestinal function due to chronic inflammation. Evidence of diffuse granulomatous changes. accumulation of lymphocytes and epithelioid cells in the lamina propria and submucosa.

Question 28

Pathogenesis of Johne’s disease

Answer 28

Organism ingested–> penetration of ileal mucosa –> phagocytosis by local macrophages–> inflammatory response (IR and DTH (granulomatous response)–> granuloma formation (ileum/colon/mesenteric LNs)–>proliferation of sub-epithelial macs –> thickening of intestine, increased permeability (tight junctions are leaky now) –> protein losing enteropathy–> diarrhea.

thickened and corrugated infected ileum.

Question 29

Cutaneous mycobacterial infections

Answer 29

M. leprae: leprosy in man and primates, cutaneous lesions and nerve damage. also in armadillos and mice. peripheal nerves- leprosy likes lower temp of skin
M. lepramurium- skin lesions–> more acute than leprosy- cats and rodents
M. ulcerans- skin nodules (granulomas) which can ulcerate. ulcers undermine tissue, become susceptible to secondary infection (humans)
M. Marinum: fatal infections common in frogs and fish. colonies skin abrasions in man

Question 30

Tuberculoid leprosy

Answer 30

strong IR to organism, few organisms in tissue; IR destroys tissue–> little disfigurement. Few organisms in well-contained granulomatous lesions in tissue

Question 31

Lepromatous leprosy

Answer 31

disfigurement, nodular swellings full of bacteria, anesthesia, shortening of toes and fingers in response to repeated, un-felt trauma. No IR to organisms. No cell-mediated IR, massive number of organisms

Question 32

Transmission of leprosy

Answer 32

via aerosol, but NOT very contagious

Question 33

Ridley-Jopling spectrum of bacterial load/ CMI

Answer 33

Tuberculoid leprosy: high CMI, low bacterial load
Lepromatous leprosy: low CMI, high bacterial load
Can fall anywhere on the spectrum.