Prevalence of the bla(CTX-M-1) group and their transferability in resistant clinical isolates of Salmonella serogroups from several hospitals of Tehran

BACKGROUND AND OBJECTIVES: Salmonella is an important food-borne pathogen in humans. Strains of Salmonella spp. that producing extended-spectrum β-Lactamases have become a concern in medicine regarding both antimicrobial treatment and infection control program. The objective of this study was to describe the antibiotic susceptibility, ESBL production and determining the prevalence of the bla(CTX-M-1) group among clinical isolates of Salmonella spp. MATERIALS AND METHODS: A total of 110 Salmonella isolates collected from four Tehran hospitals during May 2012 and April 2013. The specific monovalan Salmonella antisera were used for serogrouping of Salmonella isolates. Antibacterial susceptibility was determined by disk diffusion and ESBL phenotype was confirmed by combination disk method. The bla(CTX-M-1) group was identified by PCR with specific primers. The transferability of the bla(CTX-1) group was tested by conjugation with broth matting method. RESULTS: The prevalence of Salmonella serogroups consist of 56.4% serogroup D, 13.6 % serogroup C, 10 % serogroup B, and 1.8 % serogroup A and 18.2% other serogroups. Maximal resistance in Salmonella isolates was noticed against trimethoprim–sulfamethoxazole (63.6%) and nalidixic-acid (47/3%). All isolates were susceptible to imipenem and ciprofloxacin. Four isolates (3.6%) showed ESBLs phenotype. All Salmonella spp. that produce ESBls have bla(CTX-1) genes group. A conjugative plasmid containing bla(CTX-1) group was found in one Salmonella isolate. CONCLUSION: This study demonstrates the predominant presence of the gene encoding CTX-M-1 group among ESBLs producing of Salmonella spp. They can transmit to bacteria of this genus or even other genera of enteric bacteria.