Emergence of bla_CTX-M-15, bla_TEM-169 and bla_PER-1 extended-spectrum β-lactamase genes among different Salmonella enterica serovars from human faecal samples

Abstract

Background: Broad-spectrum β-lactams are used for empirical therapy of severe infections with non-typhoid Salmonella serotypes; however, activities of these drugs against the strains producing different β-lactamase is not so clear. This study investigated the prevalence of β-lactamase genes among isolates of S. enterica serovars from human faecal samples and determined their diversity in activity against different β-lactams.

Methods: Antimicrobial resistance of faecal isolates of S. enterica to extended-spectrum cephalosporins was analysed and MIC values were determined for the strains presenting extended-spectrum β-lactamases (ESBLs) phenotypes. The β-lactamase genes were identified by PCR and sequencing. β-lactamase activity of the Salmonella strains exhibiting ESBL phenotype was detected by biological, iodometric, spectrophotometry and nitrocefin assays.

Results: Out of 202 S. enterica isolates, ESBLs phenotype was detected among 3.4% (7/202) of the strains. bla_TEM-1 and bla_CTX-M-15 were among the frequent β-lactamase genes. Detection of bla_TEM-169 in S. enterica serovar Typhimurium and S. enterica serovar Bredeney and bla_PER-1 in S. enterica serovar Infantis was a new finding in this experiment. Location of bla_CTX-M-15/bla_TEM-169/bla_PER-1 genes on plasmid was confirmed in a transformation experiment. While crude extracts of the enzymes from each strain showed higher activity against cephalothin and cefotaxime, the lowest activity was detected against ceftazidime. The greatest synergistic activity was seen in a strain of S. enterica that carried bla_CTX-M-15 and bla_PER-1 genes compared with those presenting bla_CTX-M-15/bla_TEM-169 or bla_CTX-M-15/bla_TEM-1 genotypes.

Conclusions: The results show dissemination of ESBLs encoding genes and their combined activity among different serovars of S. enterica that are a threat for future treatment options.

Keywords:

• Antimicrobial resistance
• non-typhoidal Salmonella
• β-lactamase activity

Disclosure statement

The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.

Funding information

The experimental work was supported by research grants from Research Institute for Gastroenterology and Liver Diseases, Shahid Beheshti University of Medical Sciences, Tehran, Iran (grant number of RIGLD 545).