Utilization of Plant Growth Promoting Rhizobacteria to Inhibit Growth of Foodborne Pathogens on Plants

Introduction: Plant science and food microbiology fields have connected to enhance produce safety; however, critical knowledge gaps remain.  There is limited use of biocontrol strategies against human pathogens in produce crops.  Beneficial rhizobacterium Bacillus subtilis FB17 has been previously shown to elicit an induced systemic resistance response in plants against plant pathogen Pseudomonas syringae. Use of FB17 in field crops may protect against invasion of human foodborne pathogens.

Purpose: The purpose of this study was to determine if B. subtilis FB17 has the ability to inhibit the growth of foodborne pathogens.

Methods: To obtain cell free lysate (CFL), overnight cultures of FB17 and negative control Pseudomonas chlorophalis EA105 were centrifuged at 2500 rpm for 10 min and filtered using a 0.2 micron filter. To obtain CFL of heat-killed cultures, following centrifugation cell pellets were washed 3 times with sterile water, resuspended in LB broth and incubated at 65°C overnight. Microtiter assays were performed in 96-well plates to determine the level of inhibition of FB17 on bacterial strains. Microtiters were performed in either FB17 CFL, EA105 CFL, or LB broth. Strains in this study included 3 outbreak strains of L. monocytogenes, E. coli O157:H7, E. coli O104:H4 and Salmonella Agona (n = 6).

Results: Growth of all 3 L. monocytogenes isolates was significantly inhibited upon incubation with FB17 CFL compared to controls (P < 0.05). E. coli O104:H4 growth was significantly inhibited by FB17 (P < 0.0001); however E. coli O157:H7 was not (P = 0.13). Growth of S. Agona was not significantly inhibited when incubated with FB17 (P = 0.63). CFL obtained from heat killed cultures did not significantly inhibit growth of L. monocytogenes isolates indicating live cell cultures are essential for growth inhibition to occur.

Significance: B. subtilis FB17 may be used as a biocontrol agent in field crops to inhibit the growth of plant pathogens as well as a variety of L. monocytogenes and E. coli isolates and increase crop yield.