Evaluation of Cronobacter Growth and Phenotypic Variation Under Modified Culture Conditions.

Cronobacter sakazakii is an opportunistic pathogen known to cause acute meningitis and necrotizing enterocolitis in neonates and immunocompromised individuals. It has been isolated from a wide range of food and environmental samples, and has been linked to outbreaks associated with powdered infant formula. This study was carried out to assess variations in growth conditions (temperature, pH, and sugar supplement) and to establish how these changes impact phenotypic characteristics for successful recovery and identification of Cronobacter, particularly for routine surveillance purposes. A total of six Cronobacter isolates were tested to evaluate the above growth conditions, including three ATCC Cronobacter reference and three environmental isolates obtained from regulatory sample screening. Although only slight changes in colony-forming units were observed across the pH range and the sugars tested, the morphology was significantly impacted by changes in these growth factors. Incubation between 30 and 50 °C resulted in growth after 24 h, and the growth was slower at ambient temperature and colony formation was most robust at 30 °C. Results of this study suggest that 30 °C may be suitable for recovery of some Cronobacter strains, and minor variations in growth conditions can alter colony morphology and appearance. Expression of unique biological characteristics based on phenotypic observations may be beneficial for differentiating various Cronobacter strains.