Characterization of Salmonella enterica isolates causing bacteremia in Lima, Peru, using multiple typing methods

Abstract

In this study, different molecular typing tools were applied to characterize 95 Salmonella enterica blood isolates collected between 2008 and 2013 from patients at nine public hospitals in Lima, Peru. Combined results of multiplex PCR serotyping, two- and seven-loci multilocus sequence typing (MLST) schemes, serotyping, IS200 amplification and RAPD fingerprints, showed that these infections were caused by eight different serovars: Enteritidis, Typhimurium, Typhi, Choleraesuis, Dublin, Paratyphi A, Paratyphi B and Infantis. Among these, Enteritidis, Typhimurium and Typhi were the most prevalent, representing 45, 36 and 11% of the isolates, respectively. Most isolates (74%) were not resistant to ten primarily used antimicrobial drugs; however, 37% of the strains showed intermediate susceptibility to ciprofloxacin (ISC). Antimicrobial resistance integrons were carried by one Dublin (dfra1 and aadA1) and two Infantis (aadA1) isolates. The two Infantis isolates were multidrug resistant and harbored a large megaplasmid. Amplification of spvC and spvRA regions showed that all Enteritidis (n = 42), Typhimurium (n = 34), Choleraesuis (n = 3) and Dublin (n = 1) isolates carried the Salmonella virulence plasmid (pSV). We conclude that the classic serotyping method can be substituted by the multiplex PCR and, when necessary, sequencing of only one or two loci of the MLST scheme is a valuable tool to confirm the results. The effectiveness and feasibility of different typing tools is discussed.

Fig 1. PCR typing of representative blood isolates from Lima hospitals using different gene markers.

A) The gyrA-IS200-rcsC amplification distinguishes serovar Typhi from other serovars. B) and C) The spvC and spvRA markers detect the virulence plasmid (pSV). D) traC is a marker for the megaplasmid of Infantis (pESI). E) Plasmid profiles of the same strains. The asterisks below the bands in the plasmid profiles indicate the plasmid suspected to be the pSV. Tm, Typhimurium; E, Enteritidis; Ch, Choleraesuis; Ty, Typhi; PA, Paratyphi A; PB, Paratyphi B; and I, Infantis.