Submitted to: BARC Poster Day
Publication Type: Abstract Only
Publication Acceptance Date: 4/6/2006
Publication Date: 4/26/2006
Citation: Sharma, M., Bhagwat, A.A., Patel, J.R., Mudd, C.L. 2006. The role of RPOS in alkali tolerance of enterohemorrhagic E. coli [abstract]. BARC Poster Day. Paper No. 34.
Technical Abstract: The alkali tolerance of foodborne pathogens contributes to the survival of cells when encountering the alternating acidic and alkali conditions of gastrointestinal environments. The rpoS gene may play a role in the alkali tolerance of enterohemorrhagic Escherichia coli (EHEC). The objective was to determine if rpoS contributes to alkali tolerance of EHEC strains grown under alkaline or acidic conditions. E. coli O157:H7 (strains 52, 258, and 251), E. coli O111:H11 (strain 229), E. coli O26:H11 (strain 205), rpoS-deficient strain 52 (55), and strain 52 containing a plasmid with the rpoS allele (55-1) were evaluated. All strains other than 55 expressed RpoS. Stationary phase cells of each strain were grown under alkaline pH (8.0) or under acidic pH (5.5) conditions in LB or LB-MES broth, respectively, before being treated in 100 mM CAPS buffer (pH 10.2) for 4 h. When grown under alkaline conditions, strains 52 and 229 survived alkali treatment at significantly (P<0.05) greater percentages than all other strains. Strains 55 (rpoS-deficient) and 205 survived at significantly lower percentages than all others. When grown under acidic conditions, strains 52 and 229 survived alkali treatment at significantly greater percentages than all other strains. Strains 55 and 205 survived at percentages 10,000- and 100-fold lower than strain 52, respectively. The 10,000-fold difference in survival percentage between strains 52 and 55 indicates that rpoS may play a role in cross protecting cells from alkali stress after growth under acidic conditions. However, the presence of rpoS does not ensure that EHEC strains will be alkali tolerant, as evidenced by the similar responses of strains 205 (wild-type rpoS) and 55 (rpoS-deficient) to alkali treatment after growth under acidic or alkaline conditions. Differences in survival of EHEC strains exposed to alkali stress indicate that rpoS may not mediate the sole mechanism of alkali tolerance.