McGaughey Joseph, Nayduch Dana
Department of Biology, Georgia Southern University, 202 Georgia Ave., Statesboro, GA 30460, USA.
J Med Entomol. 2009 Jan;46(1):123-30. doi: 10.1603/033.046.0116.
To gain insight into the transmissibility of bacteria by house flies, the temporal and spatial fate of green fluorescent protein (GFP)-expressing motile and nonmotile strains of Aeromonas hydrophila was examined within the alimentary canal. Liquid food consumed by house flies is first stored in the crop and then is regurgitated and/or passed into the midgut. Once within the midgut, food is contained inside a double-layered peritrophic matrix (PM), with the inner layer enveloping digested material and forming fecal pellets for excretion. Between 1 and 12 h after ingestion, and irrespective of motility, live GFP+ A. hydrophila adhered to the luminal surfaces of the crop and inner PM of bacteria-fed flies. However, some nonadherent, motile bacteria moved freely within the PM lumen in the anteromedial midgut, whereas fecal pellets (lysed bacteria) continued passing posteriorly. At 12-24 h, adhered bacteria of both strains were lysed in the distal midgut, compressed into fecal pellets, and excreted. Viable bacteria in the crop visually exceeded numbers within these fecal pellets. Culture recovery at the same time points showed a 1,000-fold increase of viable bacteria at 2 h, presumably in the crop, with a temporal decline thereafter. Further, viable bacteria were recovered from vomit specks and orally contaminated substrates up to 2 h after feeding but never from feces. These results suggest that A. hydrophila is a transient resident of the house fly alimentary canal and is only orally transmissible for a short time after ingestion. Thus, regurgitation may be more significant than fecal transmission in the spread of some house fly transmitted bacterial diseases.
为深入了解家蝇传播细菌的能力，我们研究了表达绿色荧光蛋白（GFP）的运动型和非运动型嗜水气单胞菌菌株在消化道内的时空归宿。家蝇摄取的液体食物首先储存在嗉囊中，然后被反刍和/或进入中肠。一旦进入中肠，食物就被包裹在双层围食膜（PM）内，内层包裹着消化后的物质并形成粪便颗粒以便排出。在摄入后1至12小时内，无论运动性如何，活的GFP +嗜水气单胞菌都附着在喂食细菌的家蝇嗉囊腔表面和围食膜内层。然而，一些未附着的运动细菌在前内侧中肠的围食膜腔内自由移动，而粪便颗粒（裂解的细菌）继续向后移动。在12 - 24小时时，两种菌株附着的细菌在中肠远端被裂解，压缩成粪便颗粒并排出。嗉囊中活细菌的数量在视觉上超过了这些粪便颗粒中的数量。在相同时间点的培养物回收显示，在2小时时活细菌数量增加了1000倍，推测是在嗉囊中，此后数量随时间下降。此外，在喂食后2小时内从呕吐斑点和经口污染的底物中回收了活细菌，但从未从粪便中回收。这些结果表明，嗜水气单胞菌是家蝇消化道的短暂寄居者，仅在摄入后短时间内通过口传播。因此，在某些家蝇传播的细菌疾病传播中，反刍可能比粪便传播更重要。
