Efficiency Assessment of Simultaneous Media to Enrich Listeria Monocytogenes, Staphylococcus Aureus and Enterohaemorrhagic Escherichia Coli

Due to low quantity of pathogens in foods, designing a broth medium to enrich simultaneously several pathogens through a suitable time to a detectable level is one of point of interest of many microbiologists. This study aimed to enrich simultaneously three food-borne pathogens (Listeria monocytogenes, Staphylococcus aureus and Enterohaemorrhagic Escherichia coli) transferred by milk products. This experimental study was carried out in Kerman in 2013. First, a mixture of five enrichment media, including TSB, TB, TSBYE, SEB and TSB (NaCl 1.5%) was provided. These mediums were evaluated to enrich of L.monocytogenes, S.aureus and Enterohaemorrhagic E. coli using culture method. Then sterilized and pasteurized milk samples were artificially contaminated with these bacteria, separately and in a mixture. The enrichment ability of these five broth media was evaluated in three times (8, 18 and 24 hours). All five media were able to enrich the pathogens in both single and triple contaminated tubes. The bacteria in the contaminated milk were enriched through 8 hours, probably due to use of the nutrients in the milk. However, growth of Listeria monocytogenes and Staphylococcus aureus were inhibited in the mentioned condition due to the inhibitory components of milk. Based on results of this study, incubation of the bacteria in SEB broth for 18 hours showed the highest simultaneous enriching ability. Furthermore, it is the first report in which Tryptose Broth was able to show a simultaneous enriching ability for these pathogens.