Purpose: Assess the effects of storage temperatures and time of incubation on interactions of bacteria under diverse nutrient conditions and evaluate the effect of relative ratios of Pseudomonas fluorescens to E. coli O157:H7 on survival and growth of E. coli O157:H7 population.
Methods: Bacteria populations were assayed in monocultures and co-cultures in sterile distilled water (SDW), buffered peptone water (BPW), and trypticase soy agar (TSA) following incubation at temperatures of 5-37°C and storage times of 0 (control), 24 and 48 hrs.
Results: In co-cultures, E. coli O157:H7 cell counts were 1.71-6.27 (20°C) and 1.90-9.03 log CFU/ml at 35°C. Similarly, populations of P. fluorescens in co-cultures ranged from 3.09-5.91 and 2.88-8.36 log CFU/ml at 20 and 35°C, respectively. As expected, the populations varied with bacterial strains, storage temperatures and time, and growth substrates; and were significantly (P < 0.05) lower on SDW and BPW than on TSB. Populations of both bacteria were significantly (P < 0.05) lower at 5°C than at temperatures of 20 or 35°C. Low suppressive activity of P. fluorescens against E. coli O157:H7 were recorded and varied with pathogen strains.
Significance: The biological control implications of the experiments suggest that P. fluorescens co-cultured with E. coli O157:H7 can be used to assess microbial interactions. This may also be utilized to quantify the biocontrol potential of P. fluorescens on E. coli O157:H7 on produce during transportation of leafy greens or abusive temperature conditions. The potential for suppressive activity should be assessed on produce to optimize biocontrol efficacy.