Submitted to: Food Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/2/2013
Publication Date: 5/1/2014
Publication URL: http://handle.nal.usda.gov/10113/59690
Citation: Olanya, O.M., Ukuku, D.O., Niemira, B.A. 2014. Effects of temperature and storage time on resting populations of Escherichia coli 0157:H7 and Pseudomonas flurorescens in vitro. Food Control. 39:128-134. Interpretive Summary: An understanding of how microbes interact in pure and mixed cultures is crucial for determining how harmful pathogens might be controlled by applications of non-pathogens. Escherichia coli O157:H7 is a human pathogen commonly found on meats, fruits and vegetables. We determined how the biocontrol microbe Pseudomonas fluorescens changed the survival and growth of the pathogen. Tests were conducted: 1) with each organism alone or together; 2) on various growth media; 3) at different temperatures; 4) and for various lengths of time in storage. Both bacteria showed a similar response to temperature, with total numbers generally increased at temperatures of 25 deg C and 37 deg C, with little growth observed at 5 deg C or 15 deg C. When both bacteria were grown together, the biocontrol organism suppressed the pathogen. The degree of suppression depended on the specific growth media, the storage temperatures, and the length of time in storage. This research will be useful in designing protocols that rely on biocontrol organisms to suppress pathogens on fresh and fresh-cut produce. Applications of this research may be most significant in addressing transitory temperature abuse conditions, such as during transportation of leafy green produce from fields to processing sheds.
Technical Abstract: Assessment of microbial interactions is crucial for documenting bacterial growth in pure and mixed cultures and their potential for biological applications. Pseudomonas fluorescens (non-plant pathogenic and non-pectinolytic) has been used as a biocontrol microbe for plant pathogens and food-borne bacteria. We determined the growth of E. coli O157:H7 (Ec) and P. fluorescens(Pf) in monocultures and co-cultures in sterile distilled water (SDW), buffered peptone water(BPW) and trypticase soy broth (TSB). The effects of temperatures (5, 10, 15, 20, 25, 35, and 37 deg C) and storage time (0, 2, 4, 6, 24, and 48 hrs) on bacteria populations were assessed. Bacteria counts in monocultures in SDW ranged from 2.14-3.03 and 2.54-3.31 Log CFU/ml for Ec and Pf; respectively. In BPW, mean bacteria counts (monocultures) ranged from 3.15-6.14 and 2.54-6.41 Log CFU/ml for Ec and Pf, respectively. Ec populations in co-culture varied with storage temperatures and time. After 48 hrs, Ec 43894 monocultures in TSB ranged from 2.17-8.75 and 2.31-8.85 Log CFU/ml at 20 and 35 deg C; respectively. In co-cultures with Pf 2-79, Ec 43894 counts ranged from 1.71-5.83 (20 deg C) and 1.90-9.03 Log CFU/ml (35 deg C) in TSB. The suppression of Ec by Pf 2-79 varied among strains and reductions in bacteria numbers ranged from 0.20-1.20 Log CFU/ml in BPW (10 deg C). Substrate availability, storage temperatures, and time significantly (P<0.05) impacted Ec populations in co-culture. The liquid substrate experiments indicated suppressive conditions of Ec by Pf, however; the reduction of produce contamination by E. coli O157:H7 during transitory temperature abuse conditions such as the transportation of produce from fields needs further investigation.