Salmonella enterica serotype Kentucky associated with human infections in Switzerland: genotype and resistance trends 2004-2009

Salmonella serotype Kentucky emerged since 2002 and now ranks among the top ten serovars isolated from humans in Europe, and 8th to 10th in Switzerland. A total of 106 strains isolated from different patients from 2004 through 2009 in Switzerland were further characterized by (i) assessing phenotypic antibiotic resistance profiles using the disk diffusion method and (ii) by genotyping using pulsed-field gel electrophoresis (PFGE) after macrorestriction with XbaI in order to evaluate strain relationships and trends. In Switzerland, there is evidence for an outbreak in 2006 as the annual incidence almost doubled. A total of 30 strains (28%) were resistant or showed intermediate resistance to one to three antimicrobials and 48 strains (45%) displayed resistance to more than three antibiotics. We found a high prevalence (67%) of nalidixic acid resistance, and 58% were resistant to ciprofloxacin. One strain was a producer of extended-spectrum β-lactamase (ESBL). PFGE discriminated four clusters (similarity coefficient cut off at 80%). The resistance situation among the strains isolated from 2004 to 2009 in Switzerland is discussed and shown to coincide with findings in other European countries. Based on genetic subtyping, a so far undetected outbreak is likely to have occurred in Switzerland in 2006. Finally, our data identified travelling to Northern Africa as a risk factor for S. Kentucky infections