Phenotypic and genotypic studies of extended spectrum beta-lactamase (ESBL) resistance among Salmonella isolates from poultry sources in Iran

Poultry and poultry products are among the major sources of Salmonella infections for humans. Increasing occurrence of antimicrobial resistance among Salmonellae has become a serious public health concern. The detection of extended spectrum b-lactamase (ESBL) producers among Salmonella spp. has increased in recent years. The purpose of this study was to investigate the antibiotic resistance pattern of Salmonella, and to understand whether ESBLs were present in Salmonella isolated from poultry farms and slaughterhouses from various parts of Iran. A total of 314 isolates of Salmonella spp., 272 of poultry and 42 from human origin, collected during winter 2005-2011 were characterized for antimicrobial resistance and the presence of ESBL genes in this study. Phenotypic Disk diffusion method was performed for detection of anti-microbial susceptibility against 16 antimicrobial agents according to the Clinical and Laboratory Standards Institute's recom-mendations (CLSI, 2005). To detect the presence of ESBL genes in 30 isolates out of 61 phenotypical resistant isolates, PCR amplific-ation was used by employing specific primers for screening of the CTX-M and CMY groups, respectively. The highest resistance to ceforoxime in poultry and cefixime in human isolates was observed, and multidrug resistance (MDR) was seen with a maximum seven antimicrobial agents. The PCR detection of CTX-M and CMY genes in all isolates including five phenotypically ESBL positive isolates was negative. This study revealed the incidence of resistance to cephalosporins and the frequency of MDR among Salmonella isolates from poultry farms in Iran. The prevalence of MDR Salmonella isolates from poultry are of particular concern as these strains can transmit to humans through the food chain