A Case Study for the Change in Antibiotic-Resistant Ratios of Escherichia coli Taken from Rivers in the Suburbs

The antibiotic-resistant ratios of Escherichia coli taken from rivers in Kanagawa prefecture were investigated to clarify their changes since the early 2000s. A considerable number of isolates taken from urbanized rivers carried resistance to cefotaxime, indicating human-related sources such as combined sewer overflows and companion animals. On the other hand, some of the isolates from rivers in the suburbs carried simultaneous resistances to tetracycline and to sulfamethoxazole, which were associated with livestock farming. A comparison of resistant ratios in 2019 with those in the early 2000s shows a significant decrease in the resistance associated with livestock farming and an increase in the resistance to levofloxacin and to gentamicin, although this increase was not statistically significant.