Growth of starved Escherichia coli O157 cells in selective and non-selective media

Escherichia coli O157 strains starved in sterile deionized water (SDW) and filter-sterilized natural river water (SRW) were investigated with specific reference to their culturability in selective and non-selective media. Gro wth of the strains starved in both SDW and SRW were markedly suppressed wit h time in selective liquid media such as modified trypticase soy broth supp lemented with novobiocin (mTSB+n) and modified E, coli broth supplemented w ith novobiocin (mEC+n), This suppression was more pronounced when incubated at 42 C than at 37 C, especially with mEC+n, By contrast, such growth supp ression was seldom observed when cultured at 37 C in non-selective liquid m edia such as trypticase soy broth (TSB) and buffered peptone water. In mECn at 42 C, the non-starved cells from overnight cultures with an initial de nsity of less than 10(3) colony-forming units (CFU)/ml grew to the density of over 10(7) CFU/ml after 24 hr incubation, whereas those starved for 6 we eks in SRW were only to maintain their initial density or died off after 24 hr incubation under the same culturing conditions. These results indicated that the isolation of starved cells off. coli O157 from water samples woul d be most difficult with selective enrichment or direct plating on the sele ctive plate media. It is thus highly recommended that a "resuscitation" of the cells with non-selective enrichment should be performed as a routine pr actice for maximum recovery of E, coli O157 from water systems.