Effect Of Soil And Irrigation Water On Microbial Quality Of Fresh Produce Grown In North Carolina

Tracie Davis, North Carolina Agricultural and Technical State University


Foodborne outbreaks involving Listeria monocytogenes, Salmonella enteritidis, and E. coli O157:H7 from contaminated fresh produce have been increasingly recognized all over the world. The purpose of this research was to determine the effect of irrigation water and soil on microbial quality of leafy greens and tomatoes grown in different parts of North Carolina (NC). Soil and water samples were collected from 4 small farms located in NC and inoculated onto selective media (TSA for total aerobic count, XLT4 for Salmonella spp. (SS), and MacConkey for total E. coli species, EC). All plates were incubated for 48 hours at 37°C. Following incubation, colonies were counted and the numbers were expressed as Log CFU/ml. The identification of microorganisms was carried out by multiplex PCR analysis. The results indicated that soil samples collected from the farms located in the eastern part of NC had the highest microbial load (7.46 Log CFU/ml on TSA, 6.68 Log CFU/ml on MAC, 5.61 Log CFU/ml on XLT4) in the summer. Both water and soil samples collected from farms located in the western part of the state had the lowest microbial counts, indicating that humidity and temperature directly affect the microbial content of soil and irrigation water. The PCR analysis confirmed the presence of SS only in soil samples collected from a farm located in the eastern part of the state. These findings indicate that improvements are needed to avoid pathogenic bacterial contamination in fresh produce farming operations in NC and this should be carried out by training farmers on produce safety.