Multiple-antibiotic resistance in Salmonella enterica serotype Paratyphi B isolates collected in France between 2000 and 2003 is due mainly to strains harboring Salmonella genomic islands 1, 1-B, and 1-C

Abstract

This study was conducted to investigate the occurrence of multiple-antibiotic resistance among 261 clinical isolates of Salmonella enterica serotype Paratyphi B strains collected between 2000 and 2003 through the network of the French National Reference Center for Salmonella. The 47 multidrug-resistant (MDR) isolates identified (18%), were characterized on the basis of the presence of several resistance genes (bla(TEM), bla(PSE-1), bla(CTX-M), floR, aadA2, qacEdelta1, and sul1), the presence of Salmonella genomic island 1 (SGI1) by PCR mapping and hybridization, and the clonality of these isolates by several molecular (ribotyping, IS200 profiling, and pulsed-field gel electrophoresis [PFGE]) and phage typing methods. The results of PCR and Southern blot experiments indicated that 39 (83%) of the 47 S. enterica serotype Paratyphi B biotype Java MDR isolates possessed the SGI1 cluster (MDR/SGI1). Among these 39 MDR/SGI1 isolates, only 3 contained variations in SGI1, SGI1-B (n = 1) and SGI1-C (n = 2). The 39 MDR/SGI1 isolates showed the same specific PstI-IS200 profile 1, which contained seven copies from 2.6 to 18 kb. Two PstI ribotypes were found in MDR/SGI1 isolates, RP1 (n = 38) and RP6 (n = 1). Ribotype RP1 was also found in two susceptible strains. Analysis by PFGE using XbaI revealed that all the MDR/SGI1 isolates were grouped in two related clusters, with a similarity percentage of 82%. Isolation of MDR/SGI1 isolates in France was observed mainly between the second quarter of 2001 and the end of 2002. The source of the contamination has not been identified to date. A single isolate possessing the extended-spectrum beta-lactamase bla(CTX-M-15) gene was also identified during the study.

FIG. 1.

Southern blot hybridization with the QS probe of XbaI-digested genomic DNA of S. enterica serotype Typhimurium DT104 strain 02-5494 (lane 1) and MDR/SGI1 serotype Paratyphi B isolates 02-5269 (lane 2), 02-3610 (lane 3), 02-616 (lane 4), and 02-3609 (lane 5).

FIG. 2.

A. IS200 profiles of representative multidrug-resistant S. enterica serotype Paratyphi B isolates and comparison strains. B. Dendrogram generated by BioNumerics showing the results of cluster analysis of the 14 XbaI-PFGE patterns observed among 49 S. enterica serotype Paratyphi B isolates typed. Similarity analysis was performed using the Dice coefficient, and clustering was by the unweighted pair group method with arithmetic averages. The different PFGE types and corresponding numbers of isolates are indicated.

FIG. 3.

Total number of S. enterica serotype Paratyphi B isolates (white bars) and the number of multidrug-resistant S. enterica serotype Paratyphi B isolates (black bars) identified at the NRC-Salm between 2000 and 2003, by quarter.