occurrence of escherichia coli and pasteurella multocida in layer chickens in bangladesh with special reference to colistin and quinolone resistance

Pasteurella multocida and escherichia coli are two important gram-negative bacterial pathogens causing septicemia and are responsible for high morbidity and mortality in poultry with economic losses. to investigate the occurrence of these two pathogens in layer chickens, a cross-sectional study was conducted with liver samples of affected layers (n=100) from july 2018 to november 2018. p. multocida and e. coli were isolated using conventional bacteriological methods and the isolates were confirmed by polymerase chain reaction using species-specific primers. the e. coli isolates obtained were subsequently investigated to determine their susceptibility to different antimicrobials by disc diffusion method.  the minimum inhibitory concentration (mic) of colistin in e. coli isolates showing phenotypical resistance to colistin was detected using the broth microdilution method. pcr further characterized isolates displaying resistance to colistin and ciprofloxacin.  the occurrence of e. coli in layers was 35% (95% confidence interval 26.4 – 44.8%). no p. multocida was confirmed in the samples collected. all e. coli isolates showed phenotypical resistance to ampicillin, ciprofloxacin, sulfamethoxazole-trimethoprim, and tetracycline while 22.9% and 62.9% isolates displayed resistance to colistin and ciprofloxacin, respectively. all isolates were found to be multi-drug resistant. the minimum inhibitory concentration of colistin in e. coli isolates ranged from 8 to 128µg/ml, and 3 out of 8 colistin-resistant e. coli isolates harbored the mcr-1 gene. all ciprofloxacin-resistant isolates contained the gyra gene. about 94% and 14% of isolates harbored gyrb and parc genes, respectively. the study highlights the circulation of colistin and ciprofloxacin-resistant e. coli in layers in chattogram, bangladesh.