Possible reservoir and routes of transmission of Cronobacter (Enterobacter sakazakii) via wheat flour

Contamination of food products is a major route of transmission for opportunistic foodborne pathogen. Cronobacter spp. (formerly Enterobacter sakazakii) are an important group of emerging opportunistic foodborne pathogens that may cause rare but severe systemic infection such as neonatal meningitis, septicemia, and enterocolitis in neonates. Here, we tried to investigate the possible natural reservoir and routes of transmission of this pathogen. Samples of food (N = 141) were screened for the presence of the bacterium, and 34 isolates of Cronobacter spp. were collected in total. Of the initial of 108 samples including infant formulas, dry milk powder, milk and milk related beverages, cereal (products), chocolate and candy, miscellaneous food products, 12% were positive for Cronobacter spp., with the highest percentage (69.3%) coming from cereal products. Further investigation indicated that 100% of 13 wheat flours, 5 of 8 (62.5%) wheat kernel samples, 100% of 5 different brands of dry noodles, and 3 of 7 (42.9%) deep-frozen dumpling samples contained Cronobacter spp. Biochemical analysis (ID32E strips) of the 34 isolates resulted in 11 different biogroups based on the utilization of 8 substrates. In addition, pulsed field gel electrophoresis (PFGE) demonstrated extremely high genetic diversity as 24 unique PFGE profiles were revealed among the 25 isolates acquired mainly from wheat flour or related products. We therefore conclude that wheat flour is one likely reservoir and/or transmission route for Cronobacter spp., and special care should be taken while preparing infant foods or formulas in order to avoid cross-contamination from this source.