Genetic diversity of Cronobacter sakazakii isolates collected from a Swiss infant formula production facility.

In this study, 141 Cronobacter isolates that were collected based on a hygienic monitoring program performed in a powdered infant formula production facility in Switzerland between September 2011 and October 2012 were further characterized. Isolates were identified to the species level by molecular methods, and strains of Cronobacter sakazakii were further subtyped by applying PCR-based O-antigen serotyping, multilocus sequence typing (MLST), and pulsed-field gel electrophoresis (PFGE). C. sakazakii was the most prevalent species identified (93.6%). Among this collection of isolates, representatives of all but one O-antigen serotype (serotype O5) were recognized. MLST analysis of 19 selected isolates revealed that most of the typeable isolates belonged to sequence type (ST) 4. Correlations between ST4 and serotype O2 and between ST83 and serotype O7 were observed. PFGE analysis revealed clusters with multiple isolates, including strains from samples collected at different time points and sampling sources. Generally, the observed heterogeneity among strains collected over the 13 months of the monitoring program was high, suggesting a constant flux among strains rather than a selection for persisting organisms.