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.
Highlights
Salmonella is one of the most prevalent foodborne pathogens worldwide
Using specific primers this region renders a band of about 1.5 kb for Typhi strains, and a band of 0.8 kb for strains belonging to other Salmonella serovars, allowing the rapid differentiation of Typhi from other serovars (Fig 1A)
Despite the low variability within serovars, the random amplified polymorphic DNA (RAPD) fingerprints clearly distinguished isolates from different serovars (S4 Fig). It provided additional evidence for the assignment of the undetermined SPE45 isolate to Choleraesuis since it displayed the G pattern (Table 1). This is the first report analyzing isolates causing bacteremia in Lima, which provides relevant results to understand the epidemiology of invasive Salmonella in Peru and to highlight the importance of establishing molecular typing methods in the region for a timely assessment of the strains causing invasive salmonellosis
Summary
Salmonella is one of the most prevalent foodborne pathogens worldwide. Salmonella classification is based on the characterization of O (somatic) and H (flagellar) antigens by agglutination with hyperimmune antisera according to the Kauffmann-WhiteLeMinor scheme [3]. Classic serotyping has been used for decades in foodborne disease surveillance and outbreak investigations; serotyping requires more than 250 different typing antisera and 350 different antigens for preparation and quality control. Serotyping is laborious, time consuming and, due to production variability, it can lead to imprecise results. Molecular methods have been developed to complement or replace traditional serotyping to classify Salmonella isolates [4,5,6]. Molecular typing methods are highly sensitive, very specific, fast and show better standardization and reproducibility than traditional methods [7]
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