Bacterial resistances to antibiotics and high frequency of resistance genes in effluent of shrimp farming facility (Long An, Viet Nam)

The emergence and the spreading of antibiotic resistant (AR) bacteria and antibiotic resistance genes (ARGs) are considered currently as a growing issue for human health. Shrimp farmers in Viet Nam have access to and make use of a wide variety of antibiotics and other chemicals to treat animals or prevent disease outbreak in their farms, but very little data are now available about the effects of these substances on bacterial communities. In this study, molecular analysis and microbiological cultures carried out in the effluent of an industrial shrimp farming facilities (Long An Province, Vietnam) showed the presence of very high numbers of ARGs among the bacterial communities, as well as a high ARGs diversity. PCR analysis showed the presence of nine ARGs (sul1, sul2, qnrA, ermB, tetA, aac (6)lb, dfrA1, dfr12, dfrA5) in bacterial isolates. Most of the strains possessed 4 to 7 different ARGs, conferring multidrug resistance capacity. Real time PCR analysis revealed the presence of high copy numbers of the sul2 gene in the effluent of the shrimp farm, ranging from 1,000 to 7,000 copies/ml, as well as up to 200,000 to 700,000 copies/g in the water and in the sludge respectively. These data indicated that antibiotic usage strongly promoted the emergence of multi-resistant bacteria that subsequently spread into the adjacent natural aquatic environment. These multidrug resistant bacteria could directly cause harmful effects, or serve as antibiotic genes reservoir, spreading the resistance genes to human and farming animal pathogens. This study is considered as a starting point for further projects aiming at monitoring antibiotic resistance issues and finding practical solutions, so as to propose long-term efficiency and sustainability to the aquaculture industry.