Nayduch Dana, Zurek Klara, Thomson Jessica L, Yeater Kathleen M
USDA-ARS, Arthropod-Borne Animal Diseases Research Unit, Center for Grain and Animal Health Research, Manhattan, KS.
Department of Entomology, Kansas State University, Manhattan, KS.
J Med Entomol. 2018 Aug 29;55(5):1264-1270. doi: 10.1093/jme/tjy055.
Salmonella Typhimurium (Le Minor and Popoff 1987; Enterobacteriales: Enterobacteriaceae) is a pathogen that causes gastroenteritis in humans and can be harbored by house flies. Factors influencing excretion of S. Typhimurium from infected flies have not been elucidated but are essential for assessing transmission potential. We determined the persistence and excretion of a green fluorescent protein (GFP) expressing strain of S. Typhimurium from house flies. Individual male and female flies were fed either sterile Luria-Bertani (LB) broth (controls) or cultures of "high" (105 colony forming units [CFU]) or "low" (104 CFU) doses of bacteria (treatments). Bacterial persistence was determined over 16 h by culturing whole-fly homogenate. Both sex and dose affected persistence between 6 and 12 h postingestion. In a separate experiment, fly excretion events were monitored during this time interval and excreta droplets were individually cultured for bacteria. Female flies had more excretion events than males across treatments. We observed interactions of fly sex and bacterial abundance (dose), both on the proportion of Salmonella-positive droplets and the CFU shed per droplet (CFU/droplet). In the low-dose treatment, males excreted a greater proportion of positive droplets than females. In the high-dose treatment, males excreted more CFU/droplet than females. High-dose male flies excreted more CFU/droplet than low-dose males, but low-dose females excreted more CFU/droplet than high-dose females. Irrespective of sex, low-dose flies excreted a greater dose-adjusted CFU (CFU droplet/CFU fed) than high-dose flies. This study demonstrates that both bacterial abundance and fly sex may influence excretion of bacteria from flies, and should be considered when assessing the risk of house fly transmission of pathogens.
鼠伤寒沙门氏菌（勒米诺尔和波普夫，1987年；肠杆菌目：肠杆菌科）是一种可导致人类肠胃炎的病原体，家蝇可携带该病菌。影响被感染苍蝇排出鼠伤寒沙门氏菌的因素尚未阐明，但对于评估传播潜力至关重要。我们测定了家蝇体内表达绿色荧光蛋白（GFP）的鼠伤寒沙门氏菌菌株的持续存在情况和排泄物情况。分别给雄性和雌性家蝇喂食无菌的Luria-Bertani（LB）肉汤（对照组）或“高”剂量（约105个菌落形成单位[CFU]）或“低”剂量（约104 CFU）的细菌培养物（处理组）。通过培养全蝇匀浆来测定16小时内细菌的持续存在情况。摄食后6至12小时内，性别和剂量均会影响细菌的持续存在情况。在另一个实验中，在此时间间隔内监测苍蝇的排泄情况，并对排泄物液滴分别进行细菌培养。在所有处理组中，雌性苍蝇的排泄次数均多于雄性。我们观察到家蝇性别与细菌丰度（剂量）之间在沙门氏菌阳性液滴比例和每液滴排出的CFU（CFU/液滴）方面存在相互作用。在低剂量处理组中，雄性排出的阳性液滴比例高于雌性。在高剂量处理组中，雄性每液滴排出的CFU多于雌性。高剂量雄性苍蝇每液滴排出的CFU多于低剂量雄性，但低剂量雌性每液滴排出的CFU多于高剂量雌性。无论性别如何，低剂量苍蝇排出的剂量调整后CFU（CFU/液滴/CFU摄入）均高于高剂量苍蝇。本研究表明，细菌丰度和苍蝇性别均可能影响苍蝇排出细菌的情况，在评估家蝇传播病原体的风险时应予以考虑。
