Stability and growth characteristics of GFPuv-labeled Cronobacter sakazakii isolated from foods

Stability of ultraviolet green fluorescent protein (GFPuv)-labeled Cronobacter sakazakii and C. muytjensii isolated from foods and the effects of the plasmid GFPuv (pGFPuv) on growth were analyzed. PCR analysis and microscopic observation showed that C. sakazakii and C. muytjensii isolates took up the plasmid into cells and expressed the GFPuv gene. All Cronobacter transformants maintained this plasmid after frozen storage and 2 consecutive subcultures. The C. sakazakii FWHd16 transformant was the most stable, while the C. muytjensii FWHd11 transformant was the least stable. All transformants showed nearly identical growth curves during lag, log and stationary phases, compared to wild type parental isolates. The maximum bacterial growth rates (μmax) of the transformants and parents were similar, indicating that the presence of pGFPuv in transformants did not affect cell growth. Stable GFPuv-labeled Cronobacter has potential for use in tracking bacterial behavior during food handling and drying.