• Mycobacteria are slender rod bacteria that are
stained with special differential stains (Ziehl-
Neelsen). Once the staining has taken, they
cannot be destained with dilute acids, hence
the designation acid-fast.
2. • In terms of human disease, the most important
mycobacteria are the tuberculosis bacteria
(TB) M. tuberculosis and M. bovis and the
leprosy pathogen (LB) M. leprae.
3. Mycobacterium tuberculosis
• Morphology and culturing. TB are slender,
acid-fast rods, nonsporing and nonmotile.
They can be stained with special agents (Ziehl-
Neelsen or auramine fluorescent staining).
6. • M. tuberculosis are obligate aerobes. Their
reproduction is enhanced by the presence of 5–
10% CO2 in the atmosphere.
• They are grown on culture mediums with a high
lipid content, e.g., egg-enriched glycerol
mediums (Lo¨wenstein- Jensen).
• The generation time of TB is approximately 12–
18 hours, so that cultures must be incubated for
four to eight weeks at 37 8C.
7. Cell wall.
• The cell wall of mycobacteria contain several complex
a) Mycolic acids, which contribute to the organism acid-
fastness, resistance to phagocytosis and intracellular
destruction and resistance to acids, alkalis and antibiotics.
b)Phosphatides, which play a role in caseation necrosis.
c) Wax D, the active components in Freund's adjuvant.
d)Cord factor is correlated with virulence.
8. Pathogenesis and clinical picture.
• It is necessary to differentiate between
primary and secondary tuberculosis
(reactivation or postprimary tuberculosis).
• The clinical symptoms are based on
reactions of the cellular immune system
with TB bacilli.
9. • Primary tuberculosis.
• In the majority of cases, the pathogens
enter the lung in droplets, where they are
phagocytosed by alveolar macrophages.
• TB bacteria are able to reproduce in these
macrophages due to their ability to inhibit
formation of the phagolysosome.
10. • Within 10–14 days a reactive inflammatory focus
develops, the so-called primary focus from which the TB
bacteria move into the regional hilar lymph nodes, where
they reproduce and stimulate a cellular immune
response, which in turn results in clonal expansion of
specific T lymphocytes and lymph node swelling.
• The Ghon’s complex (primary complex, PC) develops
between six and 14 weeks after infection. At the same
time, granulomas form at the primary infection site and
in the affected lymph nodes.
11. • The further course of the disease depends on the
outcome of the battle between the TB bacilli and the
specific cellular immune defenses, development of
local tissue defect foci at other localizations, typically
the apices of the lungs may occur.
• Mycobacteria may also be transported to other organs
via the lymph vessels or bloodstream and produce
dissemination foci there. The host eventually prevails in
over 90% of cases: the granulomas and foci fibrose,
scar, and calcify, and the infection remains clinically
12. - Secondary tuberculosis.
• In about 10% of infected persons the primary
tuberculosis reactivates to become an organ
tuberculosis, either within months (5 %) or after a
number of years (5 %).
• Exogenous reinfection is rare but may occur.
Reactivation begins with a caseation necrosis in the
center of the granulomas (also called tubercles) that
may progress to cavitation (formation of caverns).
13. Tuberculin reaction. (Mantoux tuberculin skin test)
• Five tuberculin units (PPD = purified protein derivative) are
applied intracutaneously in the tuberculin test. A positive reaction
appears within 48 to 72 hours as an inflammatory reaction
(induration) at least10mm in diameter at the site of antigen
• A positive reaction means that the person has either been infected
with TB or vaccinated with BCG.
• It is important to understand that a positive test is not an indicator
for an active infection.
14. • Diagnosis requires microscopic and cultural
identification of the pathogen or pathogen-
- Treatment of specimen with N-acetyl-L-
cysteine-NaOH (NALC-NaOH method) to
liquefy viscous mucus and eliminate rapidly
proliferating accompanying flora, followed by
centrifugation to enrich the concentration.
15. - Microscopy. Ziehl-Neelsen and/or auramine
fluorescent staining. This method produces rapid
results but has a low level of sensitivity (>10⁴–
10⁵/ml) and specificity (acid-fast rods only).
- Culture on special solid and in special liquid
mediums. Time requirement: four to eight weeks.
• DNA probes. Used to identify M. tuberculosis
complex and other mycobacteria
17. MYCOBACTERIUM LEPRAE
(Leprosy Bacteria )
• Morphology and culture. Mycobacterium
leprae (Hansen, 1873) is the causative pathogen
of leprosy. In morphological terms, these acid-
fast rods are identical to tuberculosis bacteria.
They differ, however, in that they cannot be
grown on nutrient mediums or in cell cultures.
18. • Pathogenesis. The patho-mechanisms of LB are
identical to those of TB. The host organism attempts
to localize and isolate infection foci by forming
granulomas. Leprous granulomas are
histopathologically identical to tuberculous
granulomas. High counts of leprosy bacteria are
often found in the macrophages of the granulomas.
19. • Immunity. The immune defenses against a leprosy
infection are strictly of the cellular type. The lepromin
skin test can detect a postinfection allergy (lepromin skin
test). This test is not very specific (i.e., positive reactions
in cases inwhich no leprosy infection is present). The
clinically differentiated infection course forms observed
are probably due to individual immune response variants.
20. • Clinical picture. Leprosy is manifested mainly on the skin,
mucosa, and peripheral nerves. A clinical differentiation is
made between tuberculoid leprosy (TL) and lepromatous
leprosy (LL). There are many intermediate forms. TL is the
benign, non-progressive form characterized by spotty dermal
lesions. The LL form, on the other hand, is characterized by a
malignant, progressive course with nodular skin lesions and
cordlike nerve thickenings that finally lead to neuroparalysis.
The inflammatory foci contain large numbers of leprosy
21. • Diagnosis. Detection of the pathogens in skin or nasal
mucosa scrapings under the microscope using Ziehl-Neelsen
staining. Molecular confirmation of DNA sequences specific
to leprosy bacteria in a polymerase chain reaction is possible.
• Therapy. Paucibacillary forms are treated with dapson plus
rifampicin for six months. Multibacillary forms require
treatment with dapson, rifampicin, and clofazimine over a
period of at least two years.