33 terms

Mycobacteria + Actinomycosis


Terms in this set (...)

Name order and family of actinomyces, as well as clinically important anaerobes and facultative anaerobes.
Order: Actinomycetales.
Family: Actinomycetacea.

Anaerobes: A.israelii, A.bovis, A.odontolyticus.

Facultative anaerobes: A.viscosus, A.naeslundii.
How are classical infections caused by actinomyces characterized? How does prevalence vary?
Infection caused by actinomyces = actinomycosis.

Characterized by = development of chronic granulomatous lesions that become suppurative and form abcesses connected by the sinus tracts.

SEX = for unknown reason, it's more common in men than women (3:1) with exception of pelvic actinomycosis.

AGE = It may affect people of all ages but most cases are reported in young to middle aged adults (20-50 y/o).
Describe pathogenesis of actinomyces.
Actinomyces colonize the upper respiratory, GI and female genital tract. They have low virulence potential and are opportunists. Infections are endogenous, with no evidence of person-to-person spread or disease originating from exogenous source.
Describe cervicofacial actinomycosis
Cervicofacial actinomycosis is the most common type of infection (50-70%), developing in persons with poor oral hygiene, have undergone oral surgery or oral trauma. Actinomyces present in the mouth invade diseased tissue and initiate infectious process, producing either an acute pyogenic infection or a slowly, evolving, relatively painless process.

A.israelii grows in oral microflora -> infected patient has tooth abscess following dental surgery -> endogenous m/o become established in traumatized tissue and causes suppurative infection.
Describe thoracic actinomycosis
15-20%. Usually, mechanism of infection is aspiration of oropharyngeal secretions containing m/o. Non-specific symptoms include early, abscess forming in the lung tissues and later spread to adjoining tissues.
Describe abdominal and pelvic actinomycosis
10-20%. Typically, patients have had a recent or remote bowel surgery or ingestion of foreign bodies (chicken or fish bones), during which m/o are introduced into the deep tissues. Infection can spread throughout the abdomen, potentially involving every system.
Classification of Mycobacteria is based on ...
a) pathogenic for humans (M.tuberculosis, M.bovis, M.leprae, M.africanum)
b) atypical mycobacteria, potentially pathogenic (M.avium complex, MAC or MAI)

a) rapid growers, 4-7 days (M.smegmatis, M.fortuitum)
b) slow growers, 10 days
c) very slow growers, 8 weeks (M.tuberculosis)
d) non growing on artificial media (M.leprae)

a) photochromogens have little or no pigments when grown in dark, but becomes highly pigmented when grown in light (M.kansasii, M.marinum)
b) scotochromogens develop pigments in light and dark (M.szulgai)
c) nonchromogens do not produce pigments (M.avium complex)
M. tuberculosis, morphology.
Non-spore forming
Gram positive?
Straight rods (0.4-3 um).
Polymorphic on artificial media (coccoid, filamentous).
Acid-fast (resist decolorization)
Use Ziehl-Neelsen staining technique.
What are characteristic properties of Mycobacteria? What structure is responsible for these properties?
Mycobacteria possess a complex, lipid-rich CW, responsible for characteristic properties of the m/o.

Acid-fastness (lipids are responsible!)
Slow growth.
Resistant to detergents.
Resistant to common antibacterial a/b.
Clumping, or cord formation.
Elicit delayed hypersensitivity reactions in previous sensitized organisms.
Structure of the CW?
1. peptidoglycan layer - NAG, N-glicomuramic acid -> covalently linked with ...
2. polysaccharides: arabinogalactan whose terminal ends are esterified to high-molecular weight mycolic acids, forming s.c arabinogalactan-mycolate layer -> which is overlayed with ...
3. polypeptides (e.g PPD) and a hydrophobic layer of highly antigenic mycolic acids consisting of:

long chain fatty acids,
(constitutes of 60% of the dry weight).

15% of the CW weight are peptide chains in the outer layer - are biologically important antigens, stimulating patients cellular immune response to infection.
Cultivation of Mycobacteria?
We use Löwenstein-Jensen medium (inspissated egg medium) - containing defined salts, glycerol, complex organic substances (egg yolk, potato flour) and malachite green and penicillin for inhibiting growth of other m/o.

Growth rate = 2 months.
Colonies appear as buff colored, R forms.
Biochemical activities are not characteristic.
Increased CO2 tension enhances growth.
Resistance of Mycobacteria?
Quite high.
To chemical agents, e.g phenol 5% - 5-6 hours.
To malachite green and penicillin.
It can survive temperatures of 60 degrees for 15-20' and in 100 degrees for 5'.
Resistant to drying and can survive for long periods in dried sputum (~1 year).
Name virulence factors of Mycobacteria!
No exotoxin, only CW structures!

- cord factor (trehalose-6,6-dimycolate) inhibits migration of Leu, causes formation of chronic granulomas, serves as an immunologic adjuvant.

- fatty acids (muramyl dipeptide from peptidoglycan layer complexed with mycolic acids can cause granuloma formation).

- phospholipids induce caseation necrosis.

- waxes

polysaccharides role in pathogenesis is uncertain.
proteins are type specific and elicit the tuberculin reaction.
Explain "epidemiology" of Mycobacteria!
Different mycobacteria spp. have different ability to cause lesions in various host species.
Humans and guniea pigs are highly susceptible (85-95%) to M. tuberculosis infection, but fowl and cattle are resistant. M. tuberculosis and M. bovis are equally pathogenic for humans.

Route of infection (respiratory vs. intestinal) determines the patterns of lesions. In developed countries, M. bovis is very rare.
It's highly pathogenic for animals (60%) - beef, cats, dogs, rodents, etc.
They can survive in butter (240 days= and cheese (200 days). Humans are the only natural reservoir.
Pathology of lesions is determined by...?
1. M/o - virulence, number and their multiplication.

2. Host - cellular immune system.

3. Route of infection.
Explain pathogenesis steps of M. tuberculosis
1. Emitted by patients when they cough, talk or sneeze in form of DROPLETS (<25 um). They evaporate, leaving organisms (10 m/o, 1-5 um) small enough to be inhaled.

2. M/o are deposited in the alveoli and immune system responds by releasing cytokines and lymphokines to stimulate monocytes and macrophages.

3. Phagocytosis is mediated by CR 1-4 (unspecific immunity). However, it is uncomplete because cord-factor inhibits phagolysosome fusion and PLMN migration. Mycobacteria also have waxy coats and produce catalse that inhibits oxidative burst (specific T cells secrete interferon gamma which activates macrophages enough to contain the infection).

4. Mycobacteria multiply within macrophages. 1-2 months after exposure, pathogenic lesions associated with infection appear in the lung.
Name the two principal types of lesions!
1. Exudative type,
2. Productive type.
Describe exudative type of lesions!
Exudative type consists of an acute inflammatory reaction with edema fluid, PMLN, and later, monocytes around the tubercle bacilli.

- particularly seen in lung tissue, where it resembles bacterial pneumonia.
- may heal by resolution so that entire exudate becomes absorbed.
- may lead to massive tissue necrosis.
- may develop into the second lesion type.
Explain productive type of lesions!
It's a chronic granuloma with three zones.

1. Central area of m/ph with i/c m/o.
2. Midzone of pale, epitheloid cells arranged radially.
3. Peripheral zone of fibroblast, Ly and monocytes.
What happens later in the productive type of lesion?
peripheral fibrous tissue develops -> central part undergoes caseation necrosis (such a lesion is called a tubercle) -> caseous tubercle may break into bronchus -> empty its content -> form a cavity.

It may subsequently heal by fibrosis or calcification.
Explain spread of organism through the host!
Tubercle bacilli spread in the host by direct extension, through the lymphatic channels and bloodstream, and via the bronchi and GI tract.

In first infection, tubercle bacilli always spread from the initial site via lymphatics -> regional lymph nodes -> bloodstream -> distributed to all organs.

Multiple host factors are involved in this process, including cytokine toxicity and local activation of C' cascade.

No known mycobacteria toxin or enzyme has been associated with tissue damage!
What does the intracellular replication of MTb stimulate?
CD4Th cells -> AB production -> immune response is ineffective because mycobacteria are inside the cell.

CD8th cells.
Explain the role of the adaptive immune system.
Initial MTb infection of the macrophage results in production of pro-inflammatory cytokines IL-6, IL-1beta, IL-12 and TNF-alfa.

In latent infection, there is a balance of mycobacterial proliferation and host defense and Mtb is contained in granulomas with no clinical symptoms.

10% of those with latent MTb infection will eventually develop clinically active disease that manifests as localized pulmonary infection (in 80% of individuals) or disseminated disease.

These diverse clinical outcomes may be regulated by variations in the innate IR of macrophages and/or dendritic cells.
Explain how different type of T-cells work against Mtb.
T-cells responses are shaped by interactions with dendritic cells, which depend on the innate IR to MTb.

Th1 T cells produce IFN-g and promote mycobacterial killing of Tb infected m/ph.

Th17 T cells secrete IL-17 and may be important for protective vaccine-induced responses.

The role of Th2 T cells in host defense to MTb infection is less clear.

the combination of innate and adaptive responses influences the macrophage response to TB infection as well as the clinical outcome.
Explain primary infection of tuberculosis.
When a host has first contact with MTb, following features are observed:

1. acute exudative lesion develops;
2. lymph node undergoes massive caseation, which usually calcifies,
3. tuberculin test becomes positive 4-6 weeks after infection.
Explain the tuberculin test.
Old tuberculin (alttuberculin) is a concentrated filtrate of broth in which MTb have grown for 6 weeks. This material consists of reactive tuberculoproteins, growth medium and of other MTb constituents - PPD (purified protein derivative) obtained by chemical fractionation of old tuberculin. PPD is standardized in terms of its biologic reactivity as tuberculin units (TU).

Tuberculin tests in surveys use intracellular injection of 5 TU in 0.1 mL solution. Afterwards, the tuberculin skin test is placed, the area is examinated after 48-72 hours. The vaccinated (BCG) individual or individual who has had a primary infection develops positive test: 1. induration, 2. edema, 3. erythema.
Explain reactivation type of MTb.
Reactivation type is usually caused by Mycobacterium that have survived in the primary lesion. It's characterized by
1. chronic tissue lesions,
2. formation of tubercles,
3. caseation,
4. and fibrosis.
It almost always begins at the apex of the lung, where oxygen tension (PO2) is highest.
Explain the BCG vaccine!
- made in 1919
- attenuated M. bovis organism
- it's used to induce resistance
- vaccination can occur 3-4-7 days after birth and leads to increased resistance for the following 5-7 years
- revaccinate if tuberculin test is negative!
- in sweden, vaccine is given from the age of 1, in UK - 12 years. No revaccination in these countries.
- in USA, revaccination is only for tuberculin-negative persons who are heavily exposed (members of tuberculous families, medical personnel) because vaccines are inadequate from many technical and biologic standpoints.
How come treatment against mycobacteria is difficult?
Difficulties are due to
- mycobacteria are i/c in the cells.
- host resistance to aminoglycosides
- chronic forms
Define the MAC and MAI
M.avium complex / M.avium intracellulare.

- ubiquitous in environment (water, soil, food, animals, birds).
- MAI infection is the most common.
- 40% are opportunistic infections in AIDS patients.
Define M.kansasii
Pulmonary and systemic disease indistinguishable from tuberculosis, especially in patients with impaired IR.

Where can we find M.marinum & ulcerans?
In water. They cause superficial skin lesions - ulcers "swimming pool granulomas".
Explain M.leprae
(Cause leprosy, Hansen's disease).

Morphology: acid fast, nonmotile, obligate i/c.
Cultivation: cannot on bacteriologic media. inoculated into armadillos and footpads of mice.
Source of infection: humans.
Transmission: contact?

IP: 6 months - 8 years.
Leprosy is chronic infection of the skin, mucous membranes and peripheral nerves. There are 2 major forms of the disease: tuberculoid and lepramatous leprosy.