[Evaluation of antibiotics resistance and transmission risk of <i>Escherichia coli</i> in rice-frog coculture system].

In order to assess the antibiotic resistance of <i>Escherichia coli</i> and its transmission risk in a rice-frog coculture system in Zhejiang Province, this study collected <i>E</i>. <i>coli</i> from isolated soil, field water, and frog feces from the rice-frog coculture systems in four different areas of Zhejiang Province. The collected isolates were identified by 16S rRNA sequencing, while their antibiotic-resistant phenotypes were determined by Kirby-Bauer (K-B) method. PCR was used to identify the antibiotic-resistant genotypes and integrons, while conjugative transfer experiments were used to assess resistance transmission characteristics. The results showed a high prevalence of antibiotic resistance in the 82 strains of <i>E</i>. <i>coli</i> tested, primarily against tetracycline, sulfisoxazole, amoxicillin, and erythromycin. Most of these strains exhibited multidrug resistance, with the Fuyang area demonstrating the highest resistance rate compared to the other three areas. Further PCR analysis identified the <i>sul1</i> gene as the most frequently detected resistance gene (63.41%), followed by <i>bla</i>_TEM, <i>tetA</i>, and <i>tetB</i>. Among the 16 antibiotic resistance genes (ARGs) detected, the Fuyang isolates consistencly exhibited higher detection rate of 9 ARGs in comparison to the other regions. Additionally, the integrase gene <i>intI1</i> displayed the highest detection rate, with 14 strains (34.15%) of integrase-positive bacteria carrying gene cassettes. Four different gene cassette compositions were observed, with <i>dfrA1-aadA1</i> and <i>dfrA17-aadA5</i> being the most common combinations. Conjugative transfer experiments demonstrated successful transfer of gene cassettes in 4 out of 14 donor bacteria, with conjugation transfer frequencies ranging from 4.32×10^-5 to 7.13×10^-4. These findings revealed the severity of resistance in the Fuyang area among the four regions. Integrons play a significant role in mediating the resistance to multiple antibiotics in <i>E</i>. <i>coli</i>, facilitating the potential spread of resistance gene cassettes between different bacteria. Overall, this study provides valuable insights into the resistance status and transmission characteristics of <i>E</i>. <i>coli</i> in the rice-frog coculture system in Zhejiang Province, providing a theoretical basis for ensuring the food safety of rice crops.