LAUSR

Many studies have examined the survival of Escherichia coli and foodborne pathogens in agricultural soils. The results of these studies can be influenced by various growth conditions and growth media used when preparing cultures for an experiment. The objective of this study was to (i) determine the growth curves of rifampicin-resistant E. coli in three types of growth media containing rifampicin; tryptic soy agar (TSA-R), tryptic soy broth (TSB-R), and heat-treated poultry pellet extract (PPE-R), and (ii) evaluate the influence of growth media on the survival of E. coli in agricultural soil. Poultry pellet extract (PPE) was prepared by filter-sterilizing a 1:10 suspension of heat-treated poultry pellets in sterile water. Generic E. coli (TVS 353) acclimated to 80 µg/ml of rifampicin (R) was grown in TSA-R, TSB-R, and PPE-R at 3.0-3.5 log CFU/ml and at 37 °C. Growth curves were determined by quantifying E. coli populations at 0, 4, 8, 16, 24 and 32 h. Soil microcosms were inoculated with E. coli (6.0 log CFU/g) previously cultured in one of the three media types, stored at 25 °C, and soil samples were quantified for E. coli on days 0, 1, 3, 7, 14, 28 and 42. Growth curves and survival models were generated using DMFit and GInaFiT, respectively. E. coli growth rates were 0.88, 0.77, and 0.69 log CFU/ml/h in TSA-R, TSB-R, and PPE-R, respectively. E. coli populations in stationary phase were greater for cultures grown in TSA-R (9.4 log CFU/ml) and TSB-R (9.1 log CFU/ml) compared to PPE-R (7.9 log CFU/ml). The E. coli in the soil remained stable up to 3 d before declining. An approximate 2 log CFU/g decline of E. coli in soil was observed for each culture type between days 3 and 7, after which E. coli declined more slowly from day 7 to 42. A biphasic shoulder model was used to evaluate E. coli survival in soils based on growth media. Utilizing standardized culture growth preparation may aid in determining the complex interactions of enteric pathogen survival in soils.