Competition Status of Salmonella sp., Shigella sp., and Escherichia coli in Tris Egg Yolk Semen Preservation Medium at Different Experimental Conditions

Competition is a very important fact of microorganisms' life, with the major goal to gain an advantage in terms of scarce nutrients and limited space. In this study, bacterial competition of Salmonella sp., Shi¬gella sp., and Escherichia coli were assessed in Tris- egg-yolk (TEY) semen preservation medium at two temperature degrees and three periods of incubation (3 h at 37°C, 1 and 7 days at 4°C). The three pathogen species were incubated with an initial bacterial load of 103 CFU/mL. After three hours of incubation at 37°C, there were significant differences (P < 0.05) between the three species; however, Salmonella sp. had the highest CFU/ml compared to the two other pathogen species in bilateral and triple competition. Also after one day of storage at 4°C, a clear dominance of Salmonella sp. was noted, while in contrast, no signif¬icant difference (P > 0.05) between E.coli and Shigella sp., was observed in the bilateral and triple compe¬tition cases. However, the maximum dominance of Salmonella sp. was observed after 7 days at 4°C, where the bacterial load percentages between all species for the triple competition were 74±5.6/12±5.9/14±6.9 for Salmonella sp., E. coli, and Shigella sp., respectively. In conclusion, regardless of the temperature degrees and the time point of incubation, Salmonella was always able to dominate and compete very effectively compared with the two other bacterial pathogens in the TEY medium. Moreover, 4°C gave clear preference to the survival of salmonella with its clear vitality percentage in this media compared to both E. coli and Shigella sp.