Sreerama Sruti, Sanderson Michael W, Wilkerson Melinda, Nagaraja T G
Department of Clinical Sciences, Kansas State University, 103J Mosier Hall, Manhattan, KS, USA.
Curr Microbiol. 2008 Jun;56(6):651-5. doi: 10.1007/s00284-008-9131-y. Epub 2008 Mar 11.
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.
本研究的目的是确定免疫抑制是否在大肠杆菌O157粪便排出水平和持续时间中起作用。通过给予地塞米松在犊牛中诱导免疫抑制。对6头1周龄的荷斯坦公牛犊进行肌肉注射地塞米松，并口服接种10⁹CFU的三种耐萘啶酸的大肠杆菌O157:H7菌株混合物。另外5头1周龄的荷斯坦公牛犊给予相同的大肠杆菌O157:H7口服接种，但未注射地塞米松，作为对照。每天对所有犊牛进行检查，每周收集三次粪便样本，用于检测和计数耐萘啶酸的大肠杆菌O157。在最后一头犊牛停止排菌后四周，对所有犊牛进行剖检，并采集胃肠道样本检测耐萘啶酸的大肠杆菌O157。注射地塞米松的犊牛在接种后第4天和第7天排菌水平较高（P = 0.04），但之后则不然。剖检时采集的样本中没有一份大肠杆菌O157呈阳性。本研究数据表明，地塞米松免疫抑制与大肠杆菌O157粪便浓度之间可能存在时间依赖性关系，但短暂的免疫抑制似乎并不会延长大肠杆菌O157的排菌时间。
