RESUMO
The distribution of the O-groups of E. coli isolated in rivers (Arno, Serchio) and other surface waters is compared with the distribution of those isolated in urinary tract infections. The "chi square" test indicates a good correlation between the observed and expected frequencies in these two distributions, for all the O-groups, but six. Two of these (08 and 019) are significantly more frequent in the waters than in urinary isolates and four (02, 01, 018 and 075) viceversa. The O-group 6 its the most frequent in both, however the observed frequency in urine is greater than the expected one as regards the frequency in water isolates. These results would confirm, with the mentioned exceptions, the prevalence theory. The different patterns of resistance to the antibiotics suggest us to research a possible correlation between the antibotic resistance and the most frequent isolated O-groups. But no evidence of such correlation is demonstrated.