World Journal of Microbiology and Biotechnology, 8 (Supplement 1), 50-51

Frontiers in mycoplasma pathogenicity I. Kahane

Today, mycoplasmas need little introduction. This class of small, wall-less bacteria (Mollicutes) is, in number, the fastest growing group of bacteria. In the I960s, only five species were known. Today, there are more than. 120 and the number is growing. ~Am0ng the latest discovered is Mycoplasma incognitus, Which is highly pathogenic and is also incriminated in setting the stage for HIV infections and AIDS (Lo i986; Balter 1991). As a group, the mycoplasmas are characterized by their small genomic size, which is in the range of 5 x 108 to 2 x i09 kD, the smallest in bacteria. Mycoplasmas are the smallest self-replicating organisms, but, in order to replicate, they require a complex medium. Most are parasites and many are pathogens of a vast variety of hosts, spanning the entire spectrum of flora and fauna, including man. In addition, they are considered to be the pest of cells in culture. These organisms pose many interesting questions for us to study during this coming decade, including the elucidation of their entire genome, which will allow the understanding of the organization and packaging of the minimal free:living cell; and the elucidation of mycoplasmal parasitism and pathogenicity. The latter areas should draw much attention.

Mechanisms of Adherence and Pathogenicity In most pathogenic mycoplasmas, adherence is a prerequisite for the cytopathic effects. Adhesins and other mycoplasma membrane compounds are involved in the process (Kahane 1984). The characteristics of this process have to be studied for each adhering mycoplasma, since no general rule can be indicated (Kahane 1984; Saada et al. 1991). Some of the adhesins have been studied in great detail, e.g. P1 of M.

I. Kahane is at the Department of Membrane and Ultrastructure Research, The Hebrew University, Hadassah Medical School, Jerusalem, 91010 Israel, 9 1992 Ra•id Communications of Oxford Ltd 50

World Journal of Microbiology and Biotechno[ogy, VoI 8 Supplement 1. 1992

pneumoniae and a 135 kD protein of 2M/.genitalium (Inamine et al. !990; Suet a]. 1990), but much research is still needed. 'In addition, the adherence process is complex and, at least in some mycoplasmas, auxiliary proteins, such as the high molecular weight proteins of M. pneumonia.e, are involved. Those of M. pneumoniae are being studied now (Stevens & Krause i991), but.again, more knowledge is needed. This includes not only their identification, but more importantly the understanding of their pl~ysiological role in the cytoskeleton (Kahane 1984) and organization of the adhesins and the tip area of t h e many flask-shaped, pathogenic species. So far, the data indicate that the adhesin and other surface components which are involved in adherence are not responsible for the cytopathic effects, suggesting that the adhering mycoplasmas, by their proximity tO the host cell membrane, form the microenvironment in which other factors cause the cytopathic process. It has been previously suggested that oxidative stress is the initial stage of cytotoxicity for a variety of pathogenic mycoplasmas. Whether all other pathogenic mycoplasmas employ oxidative stress in their initial stages of pathogenicity has yet to be elucidated.

Involvement in Fertility, Sterility and Genital Tract Infections Several mycoplasmas are found in the genital tract. Ureaplasma urealyticum and M. hominis are the most commonly isolated mycoplasmas from the human urogenital tract (Saada et a]. 1991). The former is associated with various clinical conditions such as infertility and spontaneous abortions. The data are still ambiguous and more detailed and controlled studies are needed. These should also include studies on the physiology of U. urealyticum and efforts should be directed toward improving its cultivation. The latter is the major obstacle in these studies, as the organism grows only to about 106 to 107 ml.

Frontiers in mycopJasma pathogenicity

Aspects of Mycoplasma incognitus and Mycoplasma [ermentans and Possibly other Pathogenic Mycoplasmas in Presetting the Stages for HIV Infection and, Ultimately, AIDS Infections Mvcop]asrna incognitu5 (Lo 1%6) for a while was thought to be a virus-like a g e n t (VLIA). This organism is now recognized as a very close relative, or a strain of, M. fermentans. It was reported to be a very potent pathogen. It seems to infect cells and, contrary to most pathogenic mycoplasmas, it is not a membrane parasite but an intracellular.one. Moreover, the data of the groups of Lo and Montangier indicate that the organisms may, by their infection, set the stage for HIV if present, to infect the specific cells and induces AIDS. The details of the mechanism are not yet k n o w n and need further investigation. Would this be confirmed, then, rapid diagnosis of the mycoplasmas and effective antibiotic treatment, will lead in the foreseeable future to a way to half the onset of AIDS and prevention of the further spread Of this pandemia.

References

Baiter," M. I991 Montagnier pursues the mycoplasma-AIDS link. Science 251, 27I. Inamine, J.M., Ho, K.C., Loechel, S. & Hu, P.-C. 1990 Evidence that Uga is read as a tryptophan codon rather than as a stop codon by My. coplasma pneumoniae. Journal of Bacteriology 172, 504-506. Kahane, 1. 1984 In vitro studies on the mechanism of adherence and pathogenicity of mycoplasmas. Israel Journal of Medical Science 20, 874-877. Lo, S.-C. 1986 Isolation and identification, of a novel virus from patients with AIDS. American Journal of Tropical Medicine and Hygiene 35, 675-676. Saada, A., Terespolsky, Y,, Adoni, A. & Kahane, 1. 199I Adherence of Ureaplasma urealyticum to human erythrocytes. Infection and Immunity 59, 467-470. Stevens, M.K. & Krause, D.C. 1991 Localization of the Mycoplasma pneumon& cytadherence-accessory proteins HMWI and HMW4 in the cytoskeletonlike Triton shell. Journal of Bacteriology 173, 1041-1050. Su, C.]., Charoya, A., Dallo, S.F. & Baseman, J.B. 1990 Sequence divergency of the cytadhesin gene of Mycoplasma pneumoniae. Infection and Immunity 58, 2669~

WorldJournalof Microbiolo,~jand Biotechnology,!7oi8 Supplementt 91992

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Frontiers in mycoplasma pathogenicity.

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