Cornmeal-induced resistance to ciprofloxacin and erythromycin in enterococci.
OBJECTIVE
To establish a model ecosystem to study the impact of cornmeal on the appearance and persistence of the erythromycin (ERY)- and ciprofloxacin (CIP)-resistant phenotypes in waterborne enterococci.


METHODS
After the model ecosystem was established, the system was divided into six dose groups, with the addition of 8, 4, 1, 0.25, 0.05, and 0 g L(-1) sterilized cornmeal. System mud samples were collected at 0, 1, 3, 7, 14, 30, 40, 61, and 130 d, and enterococci present in the mud samples were evaluated for their sensitivities to CIP and ERY. PCR was employed to detect genes such as gyrA and ermB. The gyrA gene was sequenced, and codons 83 and 87 were analyzed for mutations.


RESULTS
(1) The addition of 0.05-8 g L(-1) cornmeal had an impact on CIP resistance. The higher the dose of cornmeal added, the larger the impact it generated. Furthermore, the earlier the emergence of CIP-resistant strains, the greater the incidence of drug resistance. The impact of cornmeal on resistance to ERY was less consistent, and the degree of the impact was not in proportion to the dose of cornmeal added. (2) There were no mutations at codons 83 and 87 in the gyrA genes from 102 strains isolated from the model ecosystem. The incidence of ermB-positive strains of ERY-resistant enterococci (28 strains) was 78.6%, and the incidence of ermB-positive strains of ERY-sensitive enterococci (16 strains) was 0%.


CONCLUSIONS
(1) Adding different doses of cornmeal can facilitate resistance to CIP and ERY in waterborne enterococci. In this study, the degree of resistance was related to the cornmeal dose. (2) In the model ecosystem, enterococcal CIP resistance was not caused by a gyrA gene mutation; however, in the vast majority of cases, resistance to ERY was related to the ermB resistance gene.
College of Animal Science, Fujian Agriculture and Forestry University, Fu Zhou, Fujian Province 350002, China.
Dao-Jin
DJ
Yu
Bao-Se
BS
Lai
Jian
J
Li
Yu-Fang
YF
Ma
Fan
F
Yang
Zhou
Z
Li
Xiao-Qing
XQ
Luo
Xia
X
Chen
Yi-Fan
YF
Huang
D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D002939:Ciprofloxacin / Q000494:pharmacology*; D027081:DNA Gyrase / Q000235:genetics / Q000378:metabolism; D024881:Drug Resistance, Bacterial / Q000187:drug effects; D017753:Ecosystem; D016983:Enterococcus / Q000187:drug effects*; D004917:Erythromycin / Q000494:pharmacology*; D008954:Models, Biological; D008969:Molecular Sequence Data; D009154:Mutation; D003313:Zea mays / Q000737:chemistry* / Q000378:metabolism
D001426:Bacterial Proteins; D002939:Ciprofloxacin; D004917:Erythromycin; D027081:DNA Gyrase