Lack of efflux mediated quinolone resistance in Salmonella enterica serovars Typhi and Paratyphi A

Sylvie Baucheron,Simon Le Hello,Isabelle Monchaux,Axel Cloeckaert,François-Xavier Weill

doi:10.3389/fmicb.2014.00012

Abstract

Salmonella enterica serovars Typhi and Paratyphi A isolates from human patients in France displaying different levels of resistance to quinolones or fluoroquinolones were studied for resistance mechanisms to these antimicrobial agents. All resistant isolates carried either single or multiple target gene mutations (i.e., in gyrA, gyrB, or parC) correlating with the resistance levels observed. Active efflux, through upregulation of multipartite efflux systems, has also been previously reported as contributing mechanism for other serovars. Therefore, we investigated also the occurrence of non-target gene mutations in regulatory regions affecting efflux pump expression. However, no mutation was detected in these regions in both Typhi and Paratyphi isolates of this study. Besides, no overexpression of the major efflux systems was observed for these isolates. Nevertheless, a large deletion of 2334 bp was identified in the acrS-acrE region of all S. Typhi strains but which did not affect the resistance phenotype. As being specific to S. Typhi, this deletion could be used for specific molecular detection purposes. In conclusion, the different levels of quinolone or FQ resistance in both S. Typhi and S. Paratyphi A seem to rely only on target modifications.

Highlights

Enteric fever caused by the human-adapted pathogens Salmonella enterica serovars Typhi
We have previously reported the contribution of the AcrAB-TolC efflux system in resistance to FQ in several Multidrug resistance (MDR) epidemic clones of S
Since the plasmid-mediated quinolone resistance-conferring genes qnrA, qnrB, qnrD or qnrS, qepA, and aac(6 )-Ib-cr were not detected, we investigated the role of the AcrAB-TolC efflux system

Summary

Introduction

Enteric fever caused by the human-adapted pathogens Salmonella enterica serovars Typhi Paratyphi A), B, and C, remains a major health problem (Crump and Mintz, 2010). Paratyphi A was responsible for a growing proportion of enteric fever in Asia (Ochiai et al, 2005; Crump and Mintz, 2010). Enteric fever being associated with poor sanitation and unsafe food and water, it affects children and adolescents in developing countries of Asia, Africa and Latin America (Crump et al, 2004; Bhan et al, 2005; Crump and Mintz, 2010). Patients are most often ill-returned travellers or migrant workers (Bhan et al, 2005; Connor and Schwartz, 2005; Hassing et al, 2013)

Methods

Results

Conclusion