PLASMID ANALYSIS OF NEISSERIA-GONORRHOEAE ISOLATES AND DISSEMINATION OF TETM GENES IN SOUTHERN AFRICA 1993-1995

One group (145 isolates) of Neisseria gonorrhoeae was collected from m unicipal clinics in Bloemfontein in 1994 and a second group (65 isolat es) in 1995. Penicillin and tetracycline MICs were determined and plas mid analysis performed to monitor antimicrobial susceptibilities in co njunction with the occurrence of plasmids in these isolates. The preva lence of penicillin resistance caused by beta-lactamase plasmids remai ned constant at 9% during the study period. Three high-level tetracycl ine-resistant strains (MICs 16 mg/L), the first to be detected in Sout h Africa, were isolated in 1994. Although there was a reduction in the percentage of isolates harbouring 24.5 MDa conjugative plasmids (from 79% in 1994 to 46% in 1995), this was partially counteracted by an in crease in TetM-encoding conjugative plasmids (25.2 MDa) from 2% to 18. 5%. The tetM genes of 13 isolates shown to exhibit high-level tetracyc line resistance were characterized as the American type. The American- type tetracycline resistance plasmid was demonstrated in 11 isolates. Digestion with Bg/l showed that two isolates harboured tetM-encoding p lasmids that differed from the American- and Dutch-type plasmids descr ibed previously: one isolate contained a plasmid that produced two fra gments of different sizes from those of the American-type plasmid and the second isolate possessed an American/Dutch hybrid plasmid. Auxotyp ing/serotyping and random amplified polymorphic DNA analysis revealed a predominant tetracycline-resistant family (NR/IA-6, genomic group I) in Bloemfontein. As there is a high incidence of chlamydial infection s in southern Africa requiring tetracycline therapy, selective pressur es exist in the environment for the maintenance and rapid spread of hi gh-level tetracycline-resistant N. gonorrhoeae. It is possible that te tM genes may have emanated from Botswana and/or Namibia to Bloemfontei n. The establishment of high-level tetracycline-resistant N. gonorrhoe ae in Bloemfontein was seen to be complex as a related group of strain s was identified, plasmid dissemination was evident and two new TetM-e ncoding plasmids were demonstrated. The appearance of these TetM-encod ing plasmids indicates either that the American-and Dutch-type plasmid s are continuing to evolve or that tetM genes are being introduced int o different families of 24.5 MDa conjugative plasmids.