Prevalence Of Antibiotic Resistance?-lactamasamong Escherichia Coliisolated From Pigs And Chickens At Slaughter

As an important indicator bacteria, Escherichia coli?E. coli? was commonly used to indicate bacterial contamination of foods or antibiotic resistance, prompting concerns about the transmission of resistant bacteria through food chain. Live swine market was one of the most important processes of animal food from animal feedlots to consumption. Antibiotic resistance could enter food chain during the unstrict manage of slaughter. Extended-spectrum ?-lactamases?ESBLs? and Amp C ?-lactamases has been documented as the two main resistance mechanisms of gram negative bacteria to cephalosporins. In this study, we assessed the susceptibility of E. coli isolated from swine in live swine market and investigated the prevalence of ?-lactamases. The aim was to facilitate better understanding of the dissemination of antibiotic resistance through food chain.772 and 240 E. coli were isolated from live swineand chicken marketin of Guangzhou province, China, through 2013 to 2015. The bacterial strains were isolated from Mac Con Agar and further identified by classical biochemical methods.Susceptibilities to 18 antibiotics were determined by the antimicrobial disk diffusion test according to the Clinical and Laboratory Standards Institute?CLSI? guidelines. Results showed none of the 1012 isolates was resistant to imipenem, while 1.2%, 1.5%, 5.7% and 6.6%isolates showed resistance to ceftazidime, amikacin?cefquinome and apramycin, respectively. The highest rates of resistance were found insulfamethoxazole /trimethoprim?87.9%?, tetracycline?82.7%?, ampicillin?79.8%?, doxycycline?79.8%?, chloramphenicol?71.4%?,florfenicol?69.5%? and streptomycin?65.3%?. Increase in resistance to most of the 18 antibiotics was observed during 2013 to 2015, except for ampicillin, cefquinome and sulfamethoxazole /trimethoprim. The resistance rate of ciprofloxacin and doxycycline rose from 17.9%?2013? and 73.5%?2014? to 37.4%?2015? and 90.5%?2015?, respectively. Although no significant difference was found in antibiotic susceptibilities between E. coli isolates recovered from the two live swine market, general increase in resistance rate by year was observed. MIC of the isolates collected from chickens market was similar with swine,but with a higher resistance rate of CAZ and CTX, lower resistance rate in CL?The 772 isolates were investigated for the presence of 5 ESBLs-producing genes and Amp C by PCR amplification. Results showed that bla^CTX-M-9Gwas detected in 2.7% of all strains, followed by bla^CTX-M-1G?1.9%? and bla^CMY-2?0.3%?, while bla^SHV?bla^TEM and bla ^DHAwere all negative detected. Sequencing analysis showed that subgroup of bla ^CTX-Mwere found, among which bla ^CTX-M-55 was the most highest positive?1.86%, 16/772?, followed by bla^CTX-M-14?1.7%, 10/772?, bla^CTX-M-65?0.8%,5/772? and bla^CTX-M-24?0.2%, 1/772?.In addition, ?-lactamase genescarrying isolates were found to show more resistance to most of the 18 antibiotics except for doxycycline. Results of isolates collected from chicken showedbla^CTX-M-55 was the most highest positive?13.4%?, followed by bla ^CTX-M-65?5.8%,14/240?, bla ^CTX-M-14?1.5%,4/240?, bla ^CTX-M-15?n=1?,bla ^CTX-M-24?n=2?and bla ^CTX-M-121?n=1?.In conclusion, E. coli isolates recovered from live swine marketshowed higher resistance to the 18 antibiotics and ?-lactamase genes were prevalent. The data about this study indicated thatfurtherstudy on the dissemination of resistant bacteria from thelive swine market was neededto reduce the risks of transmission of antimicrobial resistance to humans via food chain.