Role of rpoS in Acid Resistance and Fecal Shedding of Escherichia coli O157:H7

Acid resistance (AR) is important to survival ofEscherichia coli O157:H7 in acidic foods and may play a role during passage through the bovine host. In this study, we examined the role in AR of therpoS -encoded global stress response regulator ςS and its effect on shedding ofE. coli O157:H7 in mice and calves. When assayed for each of the three AR systems identified inE. coli , anrpoS mutant (rpoS ::pRR10) ofE. coli O157:H7 lacked the glucose-repressed system and possessed reduced levels of both the arginine- and glutamate-dependent AR systems. After administration of therpoS mutant and the wild-type strain (ATCC 43895) to ICR mice at doses ranging from 101 to 104 CFU, we found the wild-type strain in feces of mice given lower doses (102 versus 103 CFU) and at a greater frequency (80% versus 13%) than the mutant strain. The reduction in passage of therpoS mutant was due to decreased AR, as administration of the mutant in 0.05 M phosphate buffer facilitated passage and increased the frequency of recovery in feces from 27 to 67% at a dose of 104 CFU. Enumeration ofE. coli O157:H7 in feces from calves inoculated with an equal mixture of the wild-type strain and therpoS mutant demonstrated shedding of the mutant to be 10- to 100-fold lower than wild-type numbers. This difference in shedding between the wild-type strain and therpoS mutant was statistically significant (P ≤ 0.05). Thus, ςS appears to play a role inE. coli O157:H7 passage in mice and shedding from calves, possibly by inducing expression of the glucose-repressed RpoS-dependent AR determinant and thus increasing resistance to gastrointestinal stress. These findings may provide clues for future efforts aimed at reducing or eliminating this pathogen from cattle herds.