ARS | Publication request: Control of foodborne pathogens and soft rot bacteria on bell pepper as a model system by three strains of bacterial antagonists

Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 31, 2008
Publication Date: N/A

Interpretive Summary: Eating tainted produce has emerged as the leading cause of food-borne illness during the last two decades. Conventional washing and sanitization treatments can reduce but do not eliminate the pathogens (i.e. disease-causing microbes) from produce. A biological-based intervention method may be added to suppress the re-growth of pathogens that survive the initial chemical or physical treatment. In this study, three strains of antagonistic bacteria which can be used to inhibit the growth of pathogens on bell pepper have been identified. One of them known as Pf 2-79 was particularly effective. Dipping peppers in a Pf 2-79 solution for about 2 minutes halted pathogen multiplication almost entirely. On bell pepper not treated with Pf 2-79, pathogen populations multiplied about 100,000 when stored at 20 deg C for two days. Pf 2-79 also inhibited the growth of two common spoilage bacteria and reduced the development of soft rot. Since Pf 2-79 was capable of growing at refrigeration temperature, it could be used to control the cold-tolerant pathogens. All of the data presented show that treatment of produce with Pf 2-79 is an effective method to suppress the growth of pathogens on bell pepper. Efforts are currently underway to reproduce the research on a larger scale and to identify more bacterial strains that could be used with Pf 2-79 to further improve produce safety and quality.

Technical Abstract: Forty-two representative strains of native bacteria associated with fresh peeled baby carrots were isolated and characterized. Two of them identified as Pseudomonas fluorescens AG3A (Pf AG3A) and Bacillus YD1 were evaluated in conjunction with another known antagonist, P. fluorescens 2-79 (Pf 2-79), for their potential as biocontrol agents of foodborne pathogens (Listeria monocytogenes, Yersinia enterocolitica, Salmonella enterica, and Escherichia coli O157:H7) and soft-rot bacteria (Erwinia carotovora subsp. carotovora, P. marginalis, and P. viridiflava). When grown on iron-deficient agar media, all three antagonists produced inhibition zones up to 25 mm in diameter against the growth of human pathogens and soft rot bacteria. However when grown on iron-rich agar media, only Pf 2-79 and Bacillus YD1 exhibited antimicrobial activity. All three antagonists also inhibited the growth of pathogens on bell pepper disks, but the degree of inhibition was dependent upon the ratio of the number of antagonist to pathogen tested. The greatest inhibition was observed when 100-fold higher number of the antagonist than pathogen was applied. Pf AG3A and Bacillus YD1 also inhibited the growth of foodborne pathogens on pepper disks at 20 C but not at 10 C. However, Pf 2-79 inhibited the growth of L. monocytogenes and Y. enterocolitica by up to 4 log units at either 20 C or 10 C. Treatment of pepper disks with Pf 2-79 reduced the incidence of soft rot by 40 to 70%. Pf 2-79 is the most effective among the three antagonists tested for control of spoilage bacteria and human pathogens on bell pepper.