Survival rate and detection of human pathogenic bacteria on fresh strawberry

In recent years, the consumption and production of fresh strawberries (Fragaria ananassa) in the U.S has been increasing at a very fast rate. At the same time, food safety relevant to pathogenic contamination that cause food borne illnesses on these fruits has become a major issue from field production through supply chain to consumers.. The main objective of this research was to develop a strategic plan to identify microbial human pathogens (E. coli O157:H7, Salmonella typhimurium and Listeria monocytogenes) on fresh strawberries after stored in refrigerators at 4 °C. For this study, fully mature strawberries were collected from eight U-pick farms and inoculated with three bacterial species (Escherichia coli O157:H7, Salmonella typhimurium and Listeria monocytogenes) and stored at 4°C for 6-7 weeks. Extracts from these stored strawberries were collected and analyzed for the presence of microbial populations using direct spreading and enrichment methods. Antigens from individual inoculated bacterial species, isolated from strawberry extracts were tested against commercially available polyclonal and monoclonal antibodies. These experiments confirmed the presence of bacterial antigens even after long term storage at 4°C. These pathogenic bacterial strains were also inoculated on fresh organic and non-organic strawberries to determine the survival of these pathogenic bacterial strains over time after incubation in refrigerators at (4°C) and at room temperature (25°C). Suspended cultures (7logCFU/mL) of each individual bacterial strains were spot inoculated on the intact surfaces of strawberries and incubated at 4°C and 25°C for one (24 hours), three and five days respectively. Highly significant differences (p\u3c0.05) in bacterial populations were observed in non-organic strawberries inoculated with individual bacterial strains. Overall, initial bacterial populations of all three pathogens on organic strawberries were found to be less. A novel, fast and highly sensitive analysis method, “Dip stick analysis” was developed for the detection of lower inoculum levels of bacterial population on fresh produce. This method was successful in identifying the single bacterial pathogen cells of Salmonella and Listeria is fast, highly sensitive and reliable and can be done by non-scientists for the determination of the status of a strawberry crop for the presence of human pathogen contamination. Taste test surveys were also done to evaluate the consumer’s preference for organic and non-organic strawberries, and also to identify direct-market fresh strawberry customers and their buying behaviors