Inducing resistant phenotypes of chicken Escherichia coli under sub-inhibitory by Cephalosporins

To investigate the drug resistant of Escherichia coli,the E.coli LG30 strain and O78 standard strain were incubated in Mueller-Hinton broth with sub-inhibitory ceftriaxone or cefotaxime for 30 passages successively.The resistant phenotypes of bacteria were examined using the CLSI broth micro-dilution method.The results demonstrated that the susceptibilities of the bacterias to antimicrobial agents were decreased contiguously with increasing passages.The two bacteria strains were converted to multi-resistance bacteria when they were passaged to the 20th passage.Although the resistance enhanced following the sub-MIC cephalosporins inductions,their progress rates were reduced.In conclusion,bacteria would be liable to be converted to multi-resistance phenotypes with subinhibitory ceftriaxone or cefotaxime.