Mixed culture enrichment of Escherichia coli O157:H7, Listeria monocytogenes, Salmonella enterica, and Yersinia enterocolitica

• Published in: Food control 2012-08, Vol.26 (2), p.269-273
• Main Authors: Gehring, Andrew G., Albin, David M., Bhunia, Arun K., Kim, Hyochin, Reed, Sue A., Tu, Shu-I
• Format: Article
• Language: English
• Subjects: Co-enrichment; E. coli O157:H7; Escherichia coli; Listeria monocytogenes; Mixed culture; Salmonella enterica; Yersinia enterocolitica
• ISSN: 0956-7135; 1873-7129
• DOI: 10.1016/j.foodcont.2012.01.047

Rapid methods for testing foods for the presence of pathogenic bacteria typically suffer from poor sensitivity and therefore require large concentrations of the bacteria to be present for detection. Food contaminated with pathogenic bacteria may often contain only a very small number of the microorganisms making their direct detection very challenging even with existing state-of-the-art methods. Therefore prior to detection, it may be of pertinence to increase the number of potentially present pathogenic bacteria through growth in an appropriate culture medium. Furthermore, multiplexed testing for the presence of different bacteria in food samples necessitates the ability to simultaneously increase, through growth/culture, the concentration of each targeted bacterial pathogen to a detectable level. We have evaluated several commercially available and custom media preparations for their ability to support the simultaneous growth of the following bacteria: Escherichia coli O157:H7, Listeria monocytogenes, Salmonella enterica, and Yersinia enterocolitica. Growth conditions (primarily enrichment media formulation and incubation temperature) that resulted in multiplication of all four pathogens to ca. 1×105cells/mL within 24h or less were considered sufficient as a culture enrichment step prior to testing with most rapid methods. Axenic culture enrichment of all the bacteria for 18h readily yielded concentrations significantly greater than 1×105cells/mL for each of 5 different growth media. Mixed culture enrichment of the bacteria in pristine culture media and ground pork slurries indicated that several of the tested conditions appeared to be suitable for the growth of the selected bacteria to the targeted detection level, with the exception of L. monocytogenes in the ground meat (inoculated at 1.1CFU/mL). ► Mixed culture enrichment desired for newer, multiplexed rapid methods. ► Target growth was 10e5CFU/mL, a level greater than detection limit for most rapid methods. ► Compared are commercially available and custom-developed co-enrichment media. ► Except L. monocytogenes in pork, all pathogens grew beyond target concentration.