Study On Antibiotics Resistance And Influence Factors Of Water Source Enterococcus Faecalis

With the abuse of antibiotics in animal husbandry and aquaculture, the problem of antibiotic resistance of bacteria has caused wide attention at home and abroad. To study the resistance of bacteria to common antibiotics in aquatic environment and the influence of veterinary drug residues on water source bacteria. Enterococcus faecalis was chosen as indicative bacteria in this study, bacterial resistance in different aquatic environments was monitored. Then, model pond ecosystem was built to research the effect of different medication ways on antibiotics resistance of water source Enterococcus faecalis. This study includes two parts.(1) 539 strains of E. faecalis were isolated from natural water (national forest park in fuzhou city and model pond ecosystem), aquaculture farms (fish farm, eel farm, cattle-fish farm and pig-fish farm), human inhabitation environments (residence district pond, sewage and Minjiang River), and aquatic animals (tadpoles, eel, yellow catfish, mud carp and crucian carp), antibiotic susceptibility test was carried by micro-broth-dilution method according to Clinical and Laboratory Standards Institute (CLSI).The objective was to investigate antibiotic resistance conditions to six kinds of antibiotics of water source E. faecalis. The result indicated that:Different water source E. faecalis had different resistance conditions. Natural water isolated E. faecalis had the lowest resistance rate, resistance level, multi-drug resistance rate and antibacterial resistance index(ARI). Residence district pond and eel farm isolated E. faecalis had high resistance rates to oxytetracycline, which were 69.2% and 100%, respectively; and had low resistance rates to other antibiotics. Aquaculture farms (except for eel farm), human inhabitation environments (sewage and Minjiang River) and aquatic animal isolated E. faecalis showed complex resistance conditions, they had not only high resistance rates, resistance levels and ARI, but also severe multi-drug resistance conditions. At the same time, aquatic animal isolated E. faecalis had more serious resistance than relevant aquatic environments isolated E. faecalis.The results proved that there was a definite relation between bacterial resistance and water pollution conditions by antibiotics. The higher the antibiotics exposure level was, the heavier the resistance rate, resistance level and multi-drug resistance of E. faecalis were; conversely, the resistance conditions of isolates were simple.(2) By building model pond ecosystem, we chosen two antibiotics (oxytetracycline and ciprofloxacin) to study the effect factors of resistance of water source E. faecalis. Three different medication groups including direct medication group, drug-containing feed group and drug-containing feces group were used, samples were collected before medication and after medication in different time points, then antibiotic susceptibility test was carried. The result indicated that:Comparison the three medication ways, drug-containing feed group showed the most influence to antibiotic resistance of water source E. faecalis. On the 3rd day after medication, the resistance rates of isolates reached to the highest, and there were some high level drug-resistant bacteria with MIC≥256μg/mL in oxytetracycline-containing feed group and ciprofloxacin-containing feed group, the rates of them were 63.3% and 20%, respectively; then the resistance rate fell slowly. After 4 months, resistant bacteria still could be isolated; the rate was above 20%. The influence of water source E. faecalis in direct medication group was a little bigger than drug-containing feces group. But resistance rate in drug-containing feces group fell fast; and became few after 2 months. Compared with ciprofloxacin-containing group, E. faecalis isolated in oxytetracycline-containing group showed the severer resistance conditions. After 4 months, we could still isolate E. faecalis resistant to oxytetracycline.The results suggested that different medication ways had different resistance rates and resistance levels. It also provided reliable medication evidences for aquaculture farming.