CRISPR Typing and Antibiotic Resistance Correlates with Polyphyletic Distribution in Human Isolates of <i>Salmonella</i> Kentucky

Abstract

Although infrequently associated with reported salmonellosis in humans, Salmonella enterica, subsp. enterica serovar Kentucky (ser. Kentucky) is the most common nonclinical, nonhuman serovar reported in the United States. The goal of this study was to use Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)-multi-virulence-locus sequence typing (MVLST) to subtype a collection of human clinical isolates of ser. Kentucky submitted to the Pennsylvania Department of Health and to determine the extent of antibiotic resistance in these strains. This analysis highlighted the polyphyletic nature of ser. Kentucky, and separated our isolates into two groups, Group I and Group II, which were equally represented in our collection. Furthermore, antimicrobial susceptibility testing on all isolates using a National Antimicrobial Resistance Monitoring System (NARMS) panel of antibiotics demonstrated that resistance profiles could be divided into two groups. Group I isolates were resistant to cephems and penicillins, whereas Group II isolates were resistant to quinolones, gentamicin, and sulfisoxazole. Collectively, 50% of isolates were resistant to three or more classes of antibiotics and 30% were resistant to five or more classes. The correlation of antibiotic resistance with the two different lineages may reflect adaptation within two distinct reservoirs of ser. Kentucky, with differential exposure to antimicrobials.