An investigation was conducted to determine the occurrence, resistant efficiency of bacteria collected from four shrimp farming zones, Vunh Tau (VT), Nha Trang (NT), Da Nang (DN) and Hue (HU) of Viet Nam against five commonly applied antibiotics [sulphamethoxazole (SMX), trimethoprim (TMP), norfloxacin (NFC), amoxillin (AXC) and streptomycin (SMC)] and bacterial degradation of antibiotic. Mud samples were employed to examine the resistant population and antibiotic resistant assay of bacteria using spread plate technique and disc diffusion method, respectively. Significantly high resistant bacterial populations were found in SMX (76–296 X 103 cfu/g), TMP (39–309 X 103 cfu/g), AXC (135–154 X 103 cfu/g) and SMC (93–239 X 103 cfu/g), whereas NFC showed a lowest count (0–17 X 103 cfu/g) in all sampling stations. Antibiotic resistant of bacteria was also strong as no clear zones were found in SMX and TMP up to 6 μg/ml and in AXC upto 4 μg/ml concentrations among five antibiotics. Bacterial degradation of the antibiotic (TMP, 0.098 μg/ml/day) clearly pronounced that rate of antibiotic degradation governed by the bacterial resistant ability against the antibiotic. It may also be indicated that unutilized excessive antibiotic residues in mud of shrimp ponds lead to immeasurable loss in the microbial profile by acquiring high degree of resistant efficiency against SMX, TMP and AXC antibiotics in aquaculture environment. Therefore, avoidance of antibiotics application in aquaculture system would be the priority step to minimize and control the severe effects of antibiotic residues and resistant microbial population for the conservation of environment.
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