Model ecosystems were established to study the effect of glucose on the resistant phenotype of water source enterococcus to erythromycin (ERY) and ciprofloxacin (CIP). The mechanism of ERY and CIP-resistant were studied as well. After the model ecosystem was established, the system were divided into six groups, with the addition of 0.02 g/L, 0.1 g/L, 0.4 g/L, 1.6 g/L, 3.2 g/L and 0 g/L sterilized glucose. Isolation time at 0 d, 1 d, 8 d, 16 d, 28 d, 40 d, 84 d and 140 d, enterococci present in the mud samples were evaluated for their sensitivities to CIP and ERY. The ermB, mefA, gyrA and Esp genes were detected, gyrA gene was sequenced and codons 83 and 87 were analyzed for mutations. Isolation rates were highest in 0.02 g/L kegs. CIP-resistant phenotype was correlated to the dosages of glucose. The incidence of ermB-positive strains of ERY-resistant enterococci (28 strains) was 63.6%, while 0% from ERY-sensitive enterococcus (16 strains). The incidence of gyA-positive strains of ERY-resistant enterococci (28 strains) was 63.6%. There were no mutations at codons 83 and 87 in the gyrA gene from 72 strains. Our study indicated that adding different doses of glucose caused enterococci resistance to CIP and ERY in different degrees. The more glucose added the greater CIP-resistance and resistant strains appeared relatively earlier. CIP-resistant strains were not caused by Esp, mefA and gyrA genes mutation. However, in the vast majority of cases, ERY-resistance was related to the ermB resistance gene.
Author(s): Zhengrun Xiao, Daojin Yu, Liaqat Ali, Jing Lin, Yanqiu Wang, and Jie Zhang