Twenty-Third Annual Meeting and Symposium of the
Desert Tortoise Council, April 3-5, 1998
Abstracts

Mycoplasmas (members of the class Mollicutes) are unique bacteria, being the smallest, self-replicating organisms currently known. They lack the usual cell wall outer structure of most other bacteria, have very small amounts of genetic material (DNA), usually require cholesterol for growth and membrane function, are filterable through the usual bacteriological filters (450 nanometers), and are very dependent upon the host for nutritional support. The important mollicutes include helical wall-less prokaryotes (genus Spiroplasma) found in some plants and many different insect hosts, the non-culturable phytoplasmas that are plant pathogens in a variety of hosts, and members of two genera (Mycoplasma and Ureaplasma) that most often colonize and induce disease in vertebrate hosts. Most Mycoplasma species are quite host specific, but exceptions occur. The oral cavity and urogenital tract of man and animals are the most common sites of mycoplasma colonization, with a considerable number of species in both locations considered as normal flora.

Mycoplasma pneumoniae is an important agent in human acute respiratory disease in children and adults, with recent evidence that Mycoplasma fermentans might also be a respiratory pathogen in man. Ureaplasma urealyticum and Mycoplasma hominis can be important respiratory pathogens in human neonates. Other Mycoplasma and Ureaplasma species are pathogenic for the respiratory tract of an ever expanding number of domestic and wild animal hosts, including avian, bovine, caprine, canine, equine, feline, murine, ovine, porcine, and reptilian hosts.

Mollicutes involved in respiratory disease are inhabitants of mucous membranes and host acquisition occurs through direct oral to oral contact with other infected hosts. Respiratory infections are also transferred via contact with respiratory aerosols, fomites from infected persons or convalescent carriers. Colonization of the respiratory tract by mycoplasmas is mediated through attachment to host target cells, frequently involving specialized attachment proteins (adhesins) on the organisms. This is followed by an induction of a broad range of host immuno-regulatory events (cytokine production and direct effects on host lymphocytes/macrophages), which may either minimize disease through host defense mechanisms or lead to lesion development. Host responses may vary from secondary complications to a variety of extrapulmonary sites, to chronic respiratory disease, or to infections with no obvious signs and symptoms. Exacerbation of infection in a host frequently occurs through intercurrent infections, environmental stress, or in immune deficiencies.

Acquisition of certain pathogenic mycoplasmas into the urogenital tract, or an increase in numbers of mycoplasmas considered as normal flora, can have important consequences in both male and female human or animal hosts. Infections vary from acute localized infections (urethritis, vaginitis, pelvic inflammatory disease) to major effects on reproductive functions (infertility) and to intrauterine or neonatal infections.

Effective control of mycoplasma infections involves chemotherapy with broad spectrum antibiotics (tetracyclines or macrolides) in conjunction with a competent host immune response. Antibiotics that inhibit bacterial cell wall synthesis (penicillin, etc.) are not effective. Widespread chemotherapeutic approaches do not appear to be practical in controlling mycoplasma infections in most wild animals, and possibly in some domesticated animals. Detection of infected hosts, through proper and effective diagnostic procedures (cultural and serological techniques), and removal of such hosts to confinement areas for possible treatment regimens might be effective in some animal populations. There is little evidence at present that such infections can be controlled through immunization procedures.

References

Baseman, J. B., and Tully, J. G. Mycoplasmas: sophisticated, reemerging, and burdened by their notoriety. Emerg. Infect. Diseases, 3:21-32, 1997

Tully, J. G. Mollicute-host interrelationships: current concepts and diagnostic implications. p. 1-21. In: Molecular and Diagnostic Procedures in Mycoplasmology, vol. 2, (ed. J. G. Tully and S. Razin), Academic Press, San Diego, 1996.