Tryptic Soy Case Study

Abstract: Escherichia coli (E. coli) is currently one of the most predominant human food-borne pathogens. In the dairy industry, recently, attention has been drawn to the potential use of bacteriophages

(phages) to control bacteria in dairy products. In this study, a cocktail of three Escherichia coli bacteriophages (EcoM-AG2, EcoM-AG3 and

EcoM-AG10) was tested to evaluate its ability to control Escherichia coli O126:H7 in experimentally contaminated skim milk. In Tryptic Soy

Broth (TSB), there was an E. coli growth suppression of 1.8, 5.7 and 8.9 logs in phage treatments compared to controls over 8 days, at 4, 10 and

25°C, respectively. While in skim milk, the phage cocktail reduced E. coli populations by 1.2, 1.0 and 8.3 log compared to control samples over 15

Using bacteriophages for bioconontrol of Salmonella on fresh cut fruits, was also reported (Leverentz et al.,

2001). A cocktail of four lytic phages was used and there was a remarkable reduction of Salmonella populations on melons; however, similar results were not obtained from apples, in which inactivation of phages was found and the authors attributed this to the pH difference between melons (pH 5.8) and apples (pH 4.2).

O’Flynn et al. (2004) evaluated a cocktail of three phages for control of E. coli O157:H7 on beef. Small amounts of E. coli O157:H7 were inoculated with the phage cocktail on beef surfaces at 37°C for 1 h, resulting in disappearance of E. coli in 7 out of 9 samples, while the other two samples had low bacteria counts of <10 CFU/mL. However, it has been argued that, the temperature (37°C) used in the study, which gave a good result, was much higher than normal storage temperate (I5°C) in real life.

In this study, we tested the ability and efficiency of some lytic phages against pathogenic E. coli in skim milk stored at 4, 10 and 25°C. To avoid the potential development of phage-resistant mutants, we used