Purpose: Previously, we developed a new subtyping method, CRISPR-MVLST, which is capable of discriminating between clonal populations of several common Salmonella serovars. Here, we hypothesize that CRISPR-MVLST will identify source associated populations within S. Typhimurium and separate populations within S. Typhimurium with distinct antibiotic resistance profiles.
Methods: A collection of 80 S. Typhimurium isolates from a variety of animal sources throughout central Pennsylvania was assembled and the CRISPR1, CRISPR2, fimH, and sseL alleles of each isolate were sequenced to determine a CRISPR-MVLST subtype. Each isolate was tested for resistance to a panel of 18 antibiotics, and associations between CRISPR-MVLST subtype and resistance to each antibiotic in the panel were tested using a Fisher’s exact test (P < 0.05).
Results: CRISPR-MVLST identified 22 subtypes within the isolate collection, six of which were identified in more than two isolates. Two of these more frequently identified subtypes were identified in only a single animal source, while the other subtypes were all identified in several animal sources. Prevalence of resistance to seven antibiotics tested differed significantly among the six most frequently identified subtypes.
Significance: Therefore, CRISPR-MVLST is a promising subtyping method for monitoring the spread of antibiotic resistance in S. Typhimurium.