Aims: Molecular characterization of extended-spectrum β-lactamases (ESBLs) among Salmonella Kentucky and Typhimurium isolates: partial sequence analysis of the types of β-lactamases found in these isolates, clonality, resistance and supposed emergence of ESBL-producing strains.
Methods and results: A retrospective study surveyed the ESBLs occurring in a total of 1404 Salmonella Kentucky and Typhimurium isolates collected over a 5-year period in Tunisia. Antimicrobial susceptibility tests, ESBL phenotype determination (double-disc synergy) were performed. Polymerase chain reaction assays were used for the detection of β-lactamase genes (blaTEM , blaSHV , blaOXA-1 and blaCTX-M ), class 1 and class 2 integrases (intI1 and intI2) and the 3' conserved segment (3'-CS) of class 1 integron (qacEΔ1+sul1). Sequencing of amplicons of β-lactamase genes was performed. Percentage of 9.8 of the isolates (S. Kentucky = 117, S. Typhimurium = 20) were either resistant to penicillin and had decreased susceptibility to cefotaxime or had a positive double-disc synergy test result. Polymerase chain reaction detected that these isolates harboured one or more β-lactamase genes (blaTEM , blaSHV , blaOXA-1 or blaCTX-M ). TEM-1, TEM-34, CTX-M15, CTX-M9 and CTX-M61 type ESBLs were identified through sequencing. The novel Salmonella cefotaxime-hydrolysing β-lactamase, CTX-M61/TEM-34, detected in this study showed the emergence of new CTX-M-type ESBLs in Tunisia. There were found 33 different multidrug resistance (MDR) patterns.
Conclusion: These findings highlighted the proliferation of ESBLs and MDR in Salmonella Kentucky and Typhimurium isolates from numerous regions and sources in Tunisia, indicating an emerging public health concern.
Significance and impact of the study: For the first time CTX-M-61/TEM-34, a novel cefotaxime-hydrolysing β-lactamase of Salmonella had been detected.
Keywords: Salmonella; DNA sequencing; Tunisia; extended-spectrum β-lactamase.
© 2021 The Society for Applied Microbiology.