Journal of Antimicrobial Chemotherapy, Vol 40, 817-822, Copyright © 1997 by The British Society for Antimicrobial Chemotherapy
LJ Chalkley, MN Janse van Rensburg, PC Matthee, CA Ison and PL Botha
One group (145 isolates) of Neisseria gonorrhoeae was collected from
municipal clinics in Bloemfontein in 1994 and a second group (65 isolates)
in 1995. Penicillin and tetracycline MICs were determined and plasmid
analysis performed to monitor antimicrobial susceptibilities in conjunction
with the occurrence of plasmids in these isolates. The prevalence of
penicillin resistance caused by beta-lactamase plasmids remained constant
at 9% during the study period. Three high-level tetracycline-resistant
strains (MICs 16 mg/L), the first to be detected in South 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 increase in TetM-encoding
conjugative plasmids (25.2 MDa) from 2% to 18.5%. The tetM genes of 13
isolates shown to exhibit high-level tetracycline 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 plasmids that differed
from the American- and Dutch-type plasmids described previously: one
isolate contained a plasmid that produced two fragments of different sizes
from those of the American- type plasmid and the second isolate possessed
an American/Dutch hybrid plasmid. Auxotyping/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 infections in southern Africa
requiring tetracycline therapy, selective pressures exist in the
environment for the maintenance and rapid spread of high-level
tetracycline-resistant N. gonorrhoeae. It is possible that tetM genes may
have emanated from Botswana and/or Namibia to Bloemfontein. The
establishment of high- level tetracycline-resistant N. gonorrhoeae in
Bloemfontein was seen to be complex as a related group of strains was
identified, plasmid dissemination was evident and two new TetM-encoding
plasmids were demonstrated. The appearance of these TetM-encoding plasmids
indicates either that the American- and Dutch-type plasmids are continuing
to evolve or that tetM genes are being introduced into different families
of 24.5 MDa conjugative plasmids.
ORIGINAL ARTICLES
Plasmid analysis of Neisseria gonorrhoeae isolates and dissemination of tetM genes in southern Africa 1993-1995
Medical Microbiology (G4), Faculty of Medicine University of the Orange Free State, Bloemfontein, South Africa.
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