Enteritidis [34] as well as among a broad set of Salmonella enterica ABT-888 in vivo serovars [33]. Though the number of isolates for each serovar was similar, the number of STs within each serovar is surprisingly disparate: among 89 S. Heidelberg isolates we identified 21 HSTs and in 86 S. Typhimurium isolates, we identified 37 TSTs. This presumably reflects varied levels of clonality in different serovars. Independently of the number of STs defined for either serovar, the CRISPR loci are responsible for the vast majority of alleles: (S. Heidelberg – 83.3% and S. Typhimurium

– 80%) (Figure 2). In S. Heidelberg, 50% of the different alleles identified were CRISPR1 alleles. Given that CRISPRs are of one of the more dynamic loci in bacteria [30, 31], this finding is not unexpected. Although PFGE was more discriminatory than CRISPR-MVLST among 89 S. Heidelberg isolates (D = 0.81 versus 0.69, respectively), a combination of both techniques provided an improved value of 0.92. find more This represents a 92% probability that two unrelated strains can be separated. JF6X01.0022 is the most common PFGE pattern in PulseNet for S. Heidelberg [49] and is seen 30–40 times a month by

the CDC. In our data set, 42% of the isolates have the JF6X01.0022 pattern and using CRISPR-MVLST, we were able to further separate these into seven distinct CRISPR-MVLST types (Figure 3b and d). Given the frequency at which this PFGE pattern occurs nationally, not all isolates that have this pattern may be associated with a specific outbreak, further enhancing the utility of CRISPR-MVLST as a complement to PFGE analysis. Collectively, these findings in S. Heidelberg show that the JF6X01.0022 pattern is analogous to the JEGX01.0004 pattern Tenoxicam in S. Enteritidis, where the latter was observed in 51% of isolates analyzed and was separated into 12 distinct STs [34]. A proposed improvement for discrimination

in S. Heidelberg and S. Enteritidis by PFGE is to increase the number of enzymes used for PFGE analysis [50, 51], though the concurrent use of PFGE and CRISPR-MVLST would be much more efficient than this approach. Regarding S. Heidelberg, our data are similar to that observed in a broad set of S. Enteritidis isolates [34]: both serovars exhibit fewer number of STs identified and both require combining CRISPR-MVLST and PFGE to obtain a sufficient discriminatory power. This presumably reflects similar levels of clonality in S. Heidelberg and S. Enteritidis as compared to more heterogenous serovars such as S. Typhimurium where we observed many more STs present within a similar number of isolates examined. Our data show that in S. Typhimurium, the discrimination provided by either PFGE or CRISPR-MVLST is similar (0.9486 versus 0.9415, respectively). When CRISPR-MVLST was applied to outbreak isolates, we were able to correctly identify the 20 isolates representing the two outbreaks, showing an extremely good epidemiologic concordance with this typing method.