Survival Analysis and Detection of Human Pathogens for Organic Strawberry Production in Tennessee

The consumption of strawberry (Fragaria xananassa) in the U.S has grown favorably in the recent years. This consumption of strawberries has brought a rapid increase in food borne illnesses too. According to food borne and illness outbreak database, strawberries are the second main produce in USA that are associated with the outbreak of many pathogenic diseases. These outbreaks indicate that strawberries are suitable substrates for foodborne pathogens to survive and their consumption may cause infection. Little information is known about the behavior of these human pathogens in the strawberry. So, the main objective of this research is to develop a strategic plan to study the survival analysis and detection of these human pathogens on fresh strawberries. For this study, fully mature fresh strawberries were collected from U-pick farms and spot inoculated with bacterial species including Escherichia coli 0157:H7, Salmonella typhimurium and Listeria monocytogenes. Isolated colonies of bacteria were transferred into tryptic soy broth and incubated overnight at 35 °C. After harvesting and suspending cells in butterfield buffer, fresh strawberries were spot inoculated with these pathogenic bacteria and stored at 4˚C and 25˚C.Ten microliters of inoculum were used to inoculate strawberry surface. After drying for 30 min, strawberries were transferred to blender bags and filled with 50 mL of butterfield buffer and homogenized in a stomacher. Appropriate serial dilutions were made in butterfield buffer and spread plated on selective media (E. coli O157:H7; Sorbitol MacConkey agar, Salmonella; XLT- 4 agar supplemented with Tergitol, Listeria; Selective Agar supplemented with SR0140) and incubated at 35°C for 48 hours. Enumeration studies were done until third and fifth day of inoculation and two experiments were conducted with triplicate samples. At 4°C E.coli 0157:H7, Salmonella and Listeria populations declined by 0.32-0.71log CFU/berry and 0.56-0.97 log CFU/berry over a period of 48hrs and 96hrs respectively. At 25°C these bacterial populations declined by 0.9-1.91 log CFU/berry over a period of 48 hours. A significant decline in pathogen population was found in strawberries at each time point. Strawberry surface didn’t support the growth of these bacteria.