TRIMETHOPRIM RESISTANCE IN SOUTH-AFRICAN ISOLATES OF AEROBIC GRAM-NEGATIVE FECAL FLORA

Aerobic gram-negative commensal faecal flora from 362 healthy volunteers was examined for resistance to trimethoprim. Three hundred fifty-seven trimethoprim-resistant organisms were isolated from 272 of the volunteers (297 Escherichia coli, 46 Klebsiella spp., 9 Enterobacter spp. and 7 other species). Trimethoprim resistance was associated with resistance to other antibiotics at the following frequencies: ampicillin 71.4 %, tetracycline 88 %, cephalosporins 14 % and aminoglycosides 4 %. High-level resistance to trimethoprim (MIC greater than or equal to 1024 mg/l) occurred in 98.6 % of the isolates. Trimethoprim resistance was transferable in 51.2 % of the isolates. An X(+) factor was required to mobilize resistance in a further 3.4 %. Resistance to other antibiotics cotransferred with trimethoprim at the following frequencies: ampicillin 55.4 %, tetracycline 30 %, cephalosporins 1.5 % and aminoglycosides 2.6 %. Restriction enzyme analysis of 148 plasmids revealed 79 different profiles. Two restriction profiles represented 10.1 and 8.8 % of these plasmids, respectively. The large number of different antibiograms and restriction profiles indicates that there is a large gene pool of trimethoprim-resistant organisms in the faecal flora.