Role of multidrug resistance and co-resistance on a high percentage of streptomycin resistance in Escherichia coli isolated from chicken meats in Japan

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We focused on streptomycin resistance because of the high percentage of streptomycin-resistant Escherichia coli concerning the amount used of streptomycin. Antimicrobial resistance and horizontal transfer were identified in 117 isolates of coliform bacteria from chicken meat to identify the factors that increase streptomycin resistance. Escherichia (45 isolates) was the predominant genus. Most streptomycin-resistant Escherichia isolates were resistant to other antimicrobials (17/18), suggesting that using various antimicrobials could select streptomycin-resistant Escherichia isolates. Resistance was transferred from 7 out of the 18 streptomycin-resistant isolates. The transconjugants acquired strA/strB (7/7), bla_TEM (5/7), aphA1 (5/7), tetB (3/7), dfrA14 (1/7) and/or dfrA17 (1/7). The co-resistance of streptomycin resistance with other resistances would also increase streptomycin resistance.