Mycobacteria consists of a class of pathogens that come in between bacteria and viruses. They are far more resistant to chemical agents than bacteria, yet are able to hide in cells like viruses. To illustrate how mycobacteria can vary, the two most infamous diseases caused are tuberculosis and leprosy. Despite popular opinion, both are difficult diseases to contract. For the sake of simplicity, these two diseases are often referred to as being caused by a bacterium, but as stated, this is not totally accurate. In addition, AIDS can also be added to the list of well known mycobacteria, even though it is officially being labelled as a disease caused by a virus.
Mycobacteria are rod-shaped and cannot be stained. They are found in soil, water, insects, plant roots, animals, and humans. A relatively large number of people become infected with these microorganisms, yet remain healthy until there is a significant change in their immune status. This is seen in all three of the diseases caused by the mycobacteria where there is a startling increase in secondary infections.
Mycobacterial diseases include:
- M. kansasii (pulmonary tuberculosis) – noncommunicable.
- M. avium and M. avium-intracellulare (pulmonary tuberculosis) – noncommunicable.
- M. chelonei and M. fortuitum (wound infections) – noncommunicable.
- M. tuberculosis, M. bovis, and M. africanum (human tuberculosis) – communicable.
- M. leprae (human leprosy).
Microbes related to the mycobacteria:
Actinomycetes and related microbes are Gram-positive, anaerobic, non-acid-fast, filaments that may or may not branch out. However, they are procaryotes, possessing bacterial-type cellular structure. Actinomyces israelii is the major human pathogen, and is often part of the normal flora of the mouth, but acts as an opportunist, causing infections in damaged tissues. Such infections include the following:
- Head and neck infections, following injury to the mouth or jaw, even in tooth extractions.
- Pulmonary infections, resulting from aspirations of infectious material from the mouth.
- Abdominal infections, resulting from swallowing organisms after abdominal surgery or injury.
- Human bites.
Infections are often characterized by draining abscesses with the actinomyces filaments embedded in yellowish granuales in the exudate. Penicillin is still the antibiotic of choice, but surgical removal of the abscesses is often necessary before successful treatment is even possible.
Norcardia asteroides is the most frequently encountered species. It is generally an opportunistic pathogen, causing diseases in patients whose medical conditions are already compromised. Lung infections are the most common disease it causes, sometimes misdiagnosed as tuberculosis. The infection can spread from the lungs to the blood, and even to the brain. The Nocardia species can also penetrate any lesions, superficial or deep tissue types. These lesions often have sinuses or passages to the surface of the skin through which the infection drains. Characteristic clumps or granules made of compact colonies of nocardia are present in the exudate. Infections are treated with sulfa drugs.
Streptomyces form long branched filaments that segment into beadlike structures called conidia. Each conidium can develop into a new colony. Most streptomyces found in the soil are nonpathogens, but a few species (S. somaliensis, etc.) can cause localized swollen lesions that are distinguishable from the Nocardia species.