Antibiotic Resistance and Characteristics of Integrons in Escherichia coli Isolated from Penaeus vannamei at a Freshwater Shrimp Farm in Zhejiang Province, China

ABSTRACT Our study was conducted to investigate the antibiotic susceptibility profiles, integrons and their associated gene cassettes (GCs), and insertion sequence common regions of Escherichia coli isolates from Penaeus vannamei collected at a large-scale freshwater shrimp farm in Zhejiang Province, People's Republic of China. A total of 182 E. coli isolates were identified from 200 samples. With the exception of imipenem, isolates were most commonly resistant to β-lactams, followed by tetracylines and sulfonamides. Fifty-two (28.6%) E. coli isolates were classified as multidrug resistant, and the patterns were highly diverse, with 29 types represented. The multiple-antibiotic resistance indices of the isolates were 0.17 to 0.56; 9.3% (17) of the 182 isolates were positive for class 1 integrons, 0.5% (1 isolate) was positive for class 2 integrons, and an insertion sequence common region 1 element was found upstream of the intI1 (integrase) gene in one of the intI1-positive isolates. Four GC arrays were d...