MLVA as a Tool for Public Health Surveillance of Human Salmonella Typhimurium: Prospective Study in Belgium and Evaluation of MLVA Loci Stability

Abstract

Surveillance of Salmonella enterica subsp. enterica serovar Typhimurium (S. Typhimurium) is generally considered to benefit from molecular techniques like multiple-locus variable-number of tandem repeats analysis (MLVA), which allow earlier detection and confinement of outbreaks. Here, a surveillance study, including phage typing, antimicrobial susceptibility testing and the in Europe most commonly used 5-loci MLVA on 1,420 S. Typhimurium isolates collected between 2010 and 2012 in Belgium, was used to evaluate the added value of MLVA for public health surveillance. Phage types DT193, DT195, DT120, DT104, DT12 and U302 dominate the Belgian S. Typhimurium population. A combined resistance to ampicillin, streptomycin, sulphonamides and tetracycline (ASSuT) with or without additional resistances was observed for 42.5% of the isolates. 414 different MLVA profiles were detected, of which 14 frequent profiles included 44.4% of the S. Typhimurium population. During a serial passage experiment on selected isolates to investigate the in vitro stability of the 5 MLVA loci, variations over time were observed for loci STTR6, STTR10, STTR5 and STTR9. This study demonstrates that MLVA improves public health surveillance of S. Typhimurium. However, the 5-loci MLVA should be complemented with other subtyping methods for investigation of possible outbreaks with frequent MLVA profiles. Also, variability in these MLVA loci should be taken into account when investigating extended outbreaks and studying dynamics over longer periods.

Antimicrobial susceptibility and MLVA analysis of S. Typhimurium strains isolated from human and poultry samples in Tunisia

“…In our study, 50% of the S. Typhimurium isolates showed a multiresistant phenotype, with a greater incidence during 2013-2015 as previously described [31][32][33] suggesting an increase in the use of antibiotics during this period. Hence, a better control to prevent S. Typhimurium food contamination is needed, but severe control is also needed to ensure a better usage of antimicrobials in animals and humans [34].…”

“…It is reported that MLVA typing of serovar Typhimurium may perform better for subtyping than PFGE with enhanced resolution and good reproducibility. Epidemiological concordance has been also observed [8,15,33]. In this study, we have demonstrated the use of MLVA in characterizing S. Typhimurium to establish the genetic diversity among isolates from human and poultry origin in Tunisia.…”

“…However, the resistance to nalidixic acid was higher among poultry isolates, this can be explained by the wide utility of quinolones in veterinary practice [33,37]. It is known that the increase of nalidixic acid resistance, in some way, may reflect the emergence of fluoroquinolone resistance [38].…”

“…The nomenclature of the loci is different in the MLVA protocols, but they are overlaping VNTR loci [24]. Moreover, it has been proved that the discrimination power obtained by a 4-loci or 5-loci MLVA scheme is realy close, and that adding more loci to the scheme does not increase the resolution power of the technique [25,33].…”

Genotypic diversity, pathogenic potential and the resistance profile of Salmonella Typhimurium strains isolated from humans and food from 1983 to 2013 in Brazil

“…Many studies have demonstrated that MLVA is an assay with high discriminatory power (Best et al, 2007;Prendergast et al, 2011;Wuyts et al, 2013 Using ERIC-PCR, the 92 S. Typhimurium strains were differentiated into 63 ERIC types (Table 4) and grouped into two clusters: ERIC-A and ERIC-B (Fig. 3).…”