An ideal subtyping method has a high discriminatory power (i.e. can separate all unrelated strains) but is not so discriminatory that it inadvertently separates isolates that are part of the same outbreak (i.e. possesses high epidemiologic concordance). There are several molecular-based subtyping approaches that CHIR98014 in vitro have been developed, including pulsed-field gel electrophoresis (PFGE) [7], amplified fragment length polymorphism (AFLP) [8–10], Selleck Lenvatinib multiple-locus variable-number tandem-repeat analysis (MLVA) [11–17], multiple amplification of prophage locus typing (MAPLT) [13, 18] and, most recently, a
multiplex DNA suspension array [19]. PFGE was adapted to Salmonella in
the 1990s and generally provides a high discriminatory power for subtyping most Salmonella serovars, though it certainly does not provide equal sensitivity across all serovars [20]. Despite being labor-intensive and time-consuming, conventional serotyping and concurrent PFGE fingerprinting is still considered the gold standard for Salmonella subtyping and is widely used by public health surveillance laboratories [21–23]. Although PFGE data are uploaded to PulseNet USA (http://www.cdc.gov/pulsenet), the national electronic network for food disease surveillance that is coordinated by the CDC, inter-laboratory comparisons of PFGE fingerprints can be ambiguous. There are several different PFGE patterns, or pulsotypes, though most often a limited number of
common patterns are associated with the majority of isolates within a given serovar. Ruxolitinib cost Two recent S. ZD1839 Typhimurium and S. Heidelberg foodborne outbreaks in the United States involved contaminated cantaloupe melons (S. Typhimurium, 2012; 228 reported illnesses) [24] and broiled chicken livers (S. Heidelberg, 2011; 190 reported illnesses) [25]. In both cases, the individual XbaI PFGE patterns associated with each strain were fairly common: for S. Typhimurium, the associated PFGE pattern is typically seen in 10–15 cases per month [24] and for S. Heidelberg, the pattern occurs even more frequently, 30–40 cases per month [25]. Consequently, identification of the outbreak strains was particularly difficult and to more accurately identify isolates that were part of the S. Typhimurium cantaloupe outbreak, these isolates were also analyzed by MVLA to define the outbreak strain. Additionally, another S. Heidelberg outbreak in 2011, linked to ground turkey, involved isolates with two similar but distinctly different PFGE patterns, thus showing reduced epidemiologic concordance by this subtyping method [26]. This last example may indicate evolutionary relatedness between the two sets of isolates which, unlike some methods, PFGE cannot really provide.