Mycoplasma fermentans, M. hominis, and M. hyorhinis inhibit infectivity and growth of Chlamydia trachomatis and C. pneumoniae in HEp-2 cells.

We read with great interest the data reported by Castilla and Wadowsky about the elimination of a Mycoplasma hominis-like mycoplasma from the TW-183 strain of Chlamydia pneumoniae and its lack of effect on chlamydial infection of HEp-2 cells (1). We recently described detection of Mycoplasma fermentans, M. hominis, and M. hyorhinis in several strains of C. trachomatis and C. pneumoniae, the successful elimination of Mycoplasma from chlamydial culture by the antibiotic mupirocin, and the profound effect of mycoplasmal contamination on chlamydial infectivity and growth in HEp-2 cells (2). We would like to bring to the attention of your readership several important different or additional points. First, in contrast to the detergent Igepal CA-630 suggested by Castilla and Wadowsky for elimination of Mycoplasma, the antibiotic mupirocin enabled the effective elimination of Mycoplasma without affecting the growth of C. trachomatis or C. pneumoniae (2). Second, we would strongly recommend the use of PCR instead of culture for analysis of Mycoplasma contaminations, since we repeatedly observed mycoplasmal contamination as determined by specific PCR in mycoplasmal culture-negative chlamydial preparations (B.K.-O., unpublished observation). In addition, sequencing of the PCR product allows species identification, information which may be important to track down the potential contaminating source (2, 4). Third, the point that we find most intriguing in the paper by Castilla and Wadowsky is the lack of effect of mycoplasmal contamination on chlamydial infectivity. In contrast to their observation, we found a profound inhibitory effect of mycoplasmal contamination on chlamydial infectivity and growth (2). Similar results showing M. hyorhinis contamination of C. psittaci were recently published (3). Of course the differing mycoplasmal species present or differences in the culture media in those chlamydial cultures may explain this lack of effect. However, when we cocultivated M. hominis with chlamydiae, we also observed a strong inhibition of chlamydial growth (B.K.-O., unpublished observation). Another explanation for the observation of Castilla and Wadowsky may be that although the chlamydiae used in their studies were Mycoplasma culture negative, those chlamydiae might have still contained Mycoplasma that was detectable only by PCR. When we determined the ratio of chlamydial organisms, i.e., the number of elementary bodies per inclusion-forming unit for both mycoplasma-free and mycoplasma-contaminated chlamydiae, this ratio was 10 times higher for the mycoplasma-contaminated chlamydiae; that is, although the numbers of inclusion-forming units were identical, the infectivity determined per chlamydial organism was much lower for the mycoplasma-contaminated chlamydiae (2). By using chlamydiae standardized for their infectivity, i.e., the same number of inclusion-forming units, an additional inhibitory effect of the mycoplasma added to the already latently infected chlamydiae might have been missed in their experiments, especially since Castilla and Wadowsky analyzed chlamydial growth already after 3 days of culture. In our experience, the inhibitory effect of Mycoplasma on chlamydial growth became most evident after 7 days of cocultivation (B.K.-O., unpublished observation). REFERENCES 1. Castilla, E. A., and R. M. Wadowsky. 2000. Effect of a Mycoplasma hominislike mycoplasma on the infection of HEp-2 cells by the TW-183 strain of Chlamydia pneumoniae. J. Clin. Microbiol. 38:861–862. 2. Krauße-Opatz, B., P. Dollmann, H. Zeidler, J. G. Kuipers, and L. Köhler. Frequent contamination of Chlamydia trachomatis and Chlamydia pneumoniae strains with mycoplasma. Biological relevance and selective eradication of mycoplasma from chlamydial cultures with mupirocin. Med. Microbiol. Immun., in press. 3. Van Nerom, A., R. Ducatelle, G. Charlier, F. Haesebrouck. 2000. Interaction between turkey monocytes and avian Chlamydia psittaci in the presence of Mycoplasma sp.: the importance of nitric oxide. Dev. Comp. Immunol. 24: 417–432. 4. Wirth, M., E. Berthold, M. Grashoff, H. Pfützner, U. Schubert, and H. Hauser. 1994. Detection of mycoplasma contaminations by polymerase chain reaction. Cytotechnology 16:67–77.