Diversity of class I, II, and III integrons associated with transmission elements of antibiotic resistance genes of Escherichia coli from aquatic food

Abstract:

[Background] Integrons, as key mobile genetic elements associated with the transmission of antibiotic resistance genes (ARGs), can capture and express ARGs through site-specific recombination, playing a role in the transmission of bacterial antimicrobial resistance (AMR). Therefore, it is of great significance to analyze the integron-carrying status of Escherichia coli from aquatic food and clarify the status of integron-mediated multi-drug resistance (MDR) of E. coli for AMR monitoring and antibiotic use guidance in aquaculture. [Objective] To analyze the diversity of class I, II, and III integrons of E. coli in aquatic food. [Methods] One hundred and sixty samples of Pacific white shrimp (Penaeus vannamei), 160 samples of Pacific oyster (Crassostrea gigas), and 160 samples of Pacific mackerel (Pneumatophorus japonicas) were collected from a farmer's market in Zhejiang province. E. coli was isolated and identified by Eosin Methylene Bule Agar and PCR method. The AMR characteristics of E. coli to 9 categories of 19 antibiotics were analyzed by the Kirby-Bauer disc diffusion method. The integrons and diversity of gene cassettes (GCs) carried by E. coli from aquatic products were analyzed by PCR. [Results] Fifteen, 59, and 26 strains of E. coli were isolated from the samples of Pacific white shrimp, Pacific oyster, and Pacific mackerel, respectively, with a total of 100 strains. The MDR rates of E. coli isolates from Pacific white shrimp, Pacific oyster, and Pacific mackerel were 93.3% (14/15), 76.3% (45/59), and 80.8% (21/26), respectively. The class I, II, and III integron-carrying rates of E. coli isolates was 71.0% (71/100), 5.0% (5/100), and 0.0%, respectively. A total of 10 different class I integron GC arrays and three different class II integron GC arrays were detected. The class II integron GC array dfrA1-catB2-sat2-aadA1 was identified in E. coli for the first time. The Pearson correlation analysis showed that there was a positive correlation between the integron-carrying rate and MDR of E. coli from aquatic food (r=0.99, p<0.05). [Conclusion] This study has significance for revealing the integron-mediated transmission mechanism of ARGs of aquatic food-derived pathogenic microorganisms and promoting the healthy development of aquaculture.