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Salmonella serovar Kentucky is frequently isolated from chickens and dairy cattle, but recovery from humans is comparatively low based on the U.S. National Antimicrobial Resistance Monitoring System (NARMS) reports. We aimed to better describe the genetic diversity, antimicrobial resistance, and virulence determinants of Salmonella Kentucky isolates from humans, food animal ceca, retail meat and poultry products, imported foods and food products, and other samples. We analyzed the genomes of 774 Salmonella Kentucky isolates and found that 63% (54/86) of human isolates were sequence type (ST)198, 33% (29/86) were ST152, and 3.5% (3/86) were ST314. Ninety-one percent (570/629) of cecal isolates and retail meat and poultry isolates were ST152 or ST152-like (one allele difference), and 9.2% (58/629) were ST198. Isolates from imported food were mostly ST198 (60%, 22/37) and ST314 (29.7%, 11/37). ST198 isolates clustered into two main lineages. Clade ST198.2 comprised almost entirely isolates from humans and imported foods, all containing triple mutations in the quinolone resistance-determining region (QRDR) that confer resistance to fluoroquinolones. Clade ST198.1 contained isolates from humans, ceca, retail meat and poultry products, and imported foods that largely lacked QRDR mutations. ST152 isolates from cattle had a lineage (Clade 2) distinct from ST152 isolates from chicken (Clade 4), and half of ST152 human isolates clustered within two other clades (Clades 1 and 3), largely distinct from Clades 2 and 4. Although clinical illness associated with Salmonella Kentucky is low, ST198 appears to account for most human infections in the Unites States but is uncommon among ceca of domestic food animals and retail meat and poultry products. These findings, combined with human exposure data, suggest that fluoroquinolone-resistant ST198 infections may be linked to the consumption of food products that are imported or consumed while traveling. We also found unique differences in the composition of virulence genes and antimicrobial resistance genes among the clades, which may provide clues to the host specificity and pathogenicity of Salmonella Kentucky lineages.

We tested a diverse set of 500 isolates of nontyphoidal Salmonella enterica subsp. enterica from various animal, food, and human clinical sources for susceptibility to antimicrobials currently lacking epidemiological cutoff values (ECOFFs) set by the European Committee on Antimicrobial Susceptibility Testing. A consortium of five different laboratories each tested 100 isolates, using broth microdilution panels containing twofold dilutions of ceftriaxone, cefepime, and colistin to determine the minimum inhibitory concentrations of each drug when tested against the Salmonella isolates. Based on the resulting data, new ECOFFs of 0.25 μg/mL for ceftriaxone, 0.12 μg/mL for cefepime, and 2 μg/mL for colistin have been proposed. These thresholds will aid in the identification of Salmonella that have phenotypically detectable resistance mechanisms to these important antimicrobials.

Pulsed-field gel electrophoresis XbaI patterns of Shiga toxin-producing Escherichia coli O157 (STEC O157) isolates (n = 156) found in ground beef sampled from U.S. processing plants and retail stores during 2001 to 2006 were summarized and compared with XbaI patterns from human STEC O157 isolates (n = 14,591) in the national PulseNet E. coli database. Four ground beef samples contained more than one pulsed-field gel electrophoresis subtype of STEC O157. Of the 117 unique patterns found in ground beef, 100 (85%) appeared only once, and 17 (15%) were found in more than one isolate. The six patterns that appeared most frequently in human isolates were also found among the eight most common ground beef patterns. The yearly proportion of human isolates with the two most common patterns changed inversely, such that these patterns traded dominance over the study period. Human isolates with patterns that were first detected in both ground beef and humans contemporaneously were clustered in a 6-month window around the time of the respective ground beef sample. Of the 156 ground beef isolates, 82 (53%) were indistinguishable from at least one human isolate in this 6-month window. The yearly proportions of human STEC O157 isolates that were indistinguishable from ground beef isolates decreased significantly from 2002 to 2003 (12.3-0.8%), and then increased significantly from 2003 to 2006 (overall 0.8-12.6%). This increase in the numbers of human isolates that matched a ground beef isolate occurred during a period of relatively consistent rates of ground beef contamination with STEC O157. Pattern similarity of STEC O157 isolates derived from ground beef and clinical cases may serve as a good predictor of human incidence trends.