[Frequency of Escherichia coli resistance in Switzerland]

Monitoring the drug resistance of bacteria is necessary at regional, national and international levels. Over a two-week period in October 1978, 2561 strains of Escherichia coli and coliforms were isolated from stool specimens obtained from 19 civilian institutions (1338 strains) and from 9 army training camps (1223 strains) located all over Switzerland. Only a few of the donors had undergone recent antimicrobial therapy. The bacterial strains were rapidly distributed among 7 Swiss army microbiological field laboratories and tested for resistance against ampicillin, gentamycin, tetracycline and cotrimoxazole by standard disc diffusion techniques. Criteria for the interpretation of inhibition zones were adapted from WHO and NCCLS guidelines. E. coli ATCC 25922 served as a control strain. The overall resistance rates of E. coli and coliforms were 18% for ampicillin, 0.3% for gentamycin, 33% for tetracycline and 4% for cotrimoxazole. Multiple drug resistance patterns involving these four drugs plus sulfisoxazole, streptomycin, kanamycin, chloramphenicol, cefalothin and colistin were analyzed. Many combinations of drug resistances occurred in far higher numbers than was expected from individual drug resistance frequencies, a fact which suggested linkage of resistance genes. The resistance frequencies observed were shown by several tests of reproducibility to be subject to a modest overall error of approximately 20%.