Identification and characterization of multidrug-resistant ESBL-producing Salmonella enterica serovars Kentucky and Typhimurium isolated in Tunisia CTX-M-61/TEM-34, a novel cefotaxime-hydrolysing β-lactamase of Salmonella

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 (bla_TEM , bla_SHV , bla_OXA-1 and bla_CTX-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 (bla_TEM , bla_SHV , bla_OXA-1 or bla_CTX-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.

Quinolone resistance among Salmonella Kentucky and Typhimurium isolates in Tunisia: first report of Salmonella Typhimurium ST34 in Africa and qnrB19 in Tunisia

AIMS

Characterization of quinolone-resistant Salmonella Kentucky and Typhimurium isolates in Tunisia from various sources, detection of some plasmid-mediated quinolone resistance genes and the genetic relatedness.

METHODS

A total of 1404 isolates of S. Kentucky (n = 1059)/S. Typhimurium (n = 345) from various sources from all over Tunisia were tested for quinolone resistance by disk diffusion method. Minimum inhibitory concentrations of nalidixic acid, ciprofloxacin and ofloxacin were determined. Quinolone-resistant isolates were screened for plasmid-mediated quinolone-resistance genes (qnrA,qnrB,qnrS, aac(6')-Ib-cr and qepA) by polymerase chain reaction (PCR). Mutations in the quinolone-resistance-determining regions of the gyrA and parC genes were detected by PCR and DNA sequencing. Pulsed-field gel electrophoresis and multilocus sequence typing were accomplished for isolates harbouring plasmid-mediated quinolone-resistance genes.

RESULTS

According to our selection criteria (NAL = resistance phenotype; CIP = resistant with diameter 0, or intermediate), only 63 S. Kentucky/41 S. Typhimurium isolates were investigated: 49% (5/104) were multidrug resistant. Two S. Typhimurium isolates harboured qnrB19 with different PFGE profiles. A mutation was detected in the gyrA gene for each of these two isolates. MLST revealed the presence of ST313 and ST34, an endemic sequence type.

CONCLUSION

Our study highlights the presence of quinolone multidrug-resistant Salmonella in humans and animals in Tunisia. This is the first report of S. Typhimurium ST34 in Africa and qnrB19 in Tunisia.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is the first report that describes not only the current epidemiological situation of the quinolone resistance in S. Kentucky and Typhimurium isolated from various sources and regions in Tunisia, but also, the genetic resistance determinants associated with phenotypic antibiotic resistance and the molecular mechanisms of their quinolone-resistance. Also, we provide the first report of S. Typhimurium ST34 in Africa, and the first report of qnrB19 in Salmonella in Tunisia.