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Fecal samples of 310 healthy persons, from two populations from different areas in the Netherlands, were examined for the presence of Escherichia coli resistant to ampicillin, tetracycline, sulfamethoxazole, trimethoprim and nitrofurantoin. High prevalences of resistance were found in both populations, ranging from 28% for trimethoprim to 89% for ampicillin. The percentages of the fecal samples with a dominantly resistant E. coli flora (> 50% resistance) were distinctly lower, ranging from 1% for nitrofurantoin to 21% for tetracycline. No significant differences in the level of resistance were observed between these two comparable populations in two different areas. The susceptibilities to 11 antimicrobial agents of 456 at random isolated E. coli were determined. The percentages of resistance varied widely: from 80% for chloramphenicol to 9% for nitrofurantoin. Only 19% of the isolates were susceptible to all antibiotics tested and 14% were resistant to more than four of the agents tested. Great differences in resistance rates between the two populations examined were seen for chloramphenicol (80% to 41%) and trimethoprim (16% to 36%). The results of this study underscore the presence of a human reservoir of antibiotic resistant microorganisms.

From December 1988 to March 1989 172 faecal samples from first and second year students at the University of Limburg, Maastricht, The Netherlands, were collected and analysed for the presence of Escherichia coli strains resistant to ampicillin, sulphamethoxazole, tetracycline, trimethoprim and nitrofurantoin. In addition, the antibiotic susceptibility (MIC) to these agents and six other compounds (i.e. aminoglycosides, nitrofurantoin, nalidixic acid and cephalothin) was determined. The prevalence of resistance of the samples analysed ranged from 86% (i.e. 148 out of 172) for sulphamethoxazole to 25% for trimethoprim. The prevalence figures for ampicillin, tetracycline and nitrofurantoin resistance were 76%, 47% and 29%, respectively. The percentages of the faecal samples with a high proportion of E. coli (greater than 50% of the total number of E. coli) resistant to ampicillin, tetracycline and sulphamethoxazole were 8%, 11% and 37%, respectively. For nitrofurantoin and trimethoprim the figures were 3% and 1%, respectively. Of the isolated E. coli (n = 797), 84% was resistant to ampicillin, 82% resistant to sulphamethoxazole. The lowest percentages (9%) were observed for both nalidixic acid and nitrofurantoin.

From 1980 to 1986 a regional survey was performed to investigate the susceptibility of beta-lactam antibiotics in clinical isolates of Escherichia coli, Proteus mirabilis, Klebsiella pneumoniae, Enterobacter cloacae and Pseudomonas aeruginosa in 6 hospitals located in the southern part of the Netherlands. Each year 300 to 400 strains were tested. The susceptibility to representatives of the older and the newer beta-lactam antibiotics was determined by a microbroth dilution assay using an inoculum size of 10(5) colony forming units (CFU)/ml in ISO-Sensitest broth (Oxoid). No significant differences in antibiotic sensitivity of the micro-organisms from the different hospitals were found. There was no evidence for an increase in antibiotic resistance of the strains during the sampling period. In contrast, there was a general tendency to an increase in antibiotic sensitivity.