Impact of dexamethasone-induced immunosuppression on the duration and level of shedding of Escherichia coli O157:H7 in calves.

The goal of this study was to determine whether immunosuppression plays a role in the level and duration of fecal shedding of Escherichia coli O157. Immunosuppression was induced in calves by administering dexamethasone. Six 1-week-old Holstein bull calves were injected intramuscularly with dexamethasone and orally inoculated with 10(9) CFU of a mixture of three nalidixic-acid resistant strains of E. coli O157:H7. Five 1-week-old Holstein bull calves that were given the same oral inoculation of E. coli O157:H7, but not the dexamethasone injections, served as controls. All calves were examined daily and fecal samples were collected three times a week for detection and enumeration of the nalidixic-acid resistant E. coli O157. Four weeks after the last calf stopped shedding, all calves were necropsied and samples from the gastrointestinal tract were taken for the detection of the nalidixic-acid resistant E. coli O157. Dexamethasone-injected calves shed at higher levels (P = 0.04) on days 4 and 7 postinoculation, but not thereafter. None of the samples collected at necropsy were positive for E. coli O157. Data from this study suggest that there may be a time-dependent relationship between dexamethasone immunosuppression and the fecal concentration of E. coli O157 but that transient immunosuppression does not appear to prolong shedding of E. coli O157.