Escherichia coli strains isolated from surface waters. Distribution by resistance to antibiotics and R-plasmid transfer.

Samples were taken from surface waters in Csongrád county in the months March through December, 1980. Escherichia coli isolates selected at random were tested for resistance to 5 antibiotics and for R-plasmid carriership. Of the strains isolated from Tisza river at each of 8 sampling sites, 50-60% were sensitive to all the 5 antibiotics. The percentage of sensitivity was much lower if only the strains isolated during the summer months, when the water level was high, or those isolated from affluents and backwaters were taken into account. The frequency of resistance was the highest for tetracycline, followed in order by ampicillin, streptomycin, kanamycin and chloramphenicol. R-plasmid was carried by 43% of the resistant isolates tested, mainly by multiresistant ones.