Influence ofprgHon the Persistence of Ingested Salmonella enterica in the Leafhopper Macrosteles quadrilineatus
ABSTRACTPhytophagous insects can encounterSalmonella entericaon contaminated plant surfaces and transmit externally adhered and internalized bacteria on and among leaves. Excretion of ingestedS. entericaby the leafhopperMacrosteles quadrilineatushas been previously reported; however, the sites of persistence of ingested bacteria remain undetermined. Fluorescence microscopy revealed the presence and persistence ofS. entericain various organs ofM. quadrilineatusfed an inoculated diet for 12 h and then moved to two consecutive noninoculated diets for a total of 48 h. IngestedS. entericawas predominantly observed in the filter chamber, midgut, and Malpighian tubules ofM. quadrilineatusdissected immediately after acquisition and at 24- and 48-h post-acquisition access periods (post-AAPs). Additionally, we examined the potential roles of theSalmonellapathogenicity island 1 (SPI-1) and SPI-2 type III secretion systems (T3SSs) in the persistence and excretion of ingestedS. enterica. In competition assays, aprgHmutant lacking a functional SPI-1 T3SS was recovered at significantly lower levels than the WT in insect homogenates at 24 h post-AAP, and complementation withprgHrestoredS. entericapersistence inM. quadrilineatus. Moreover, expression ofprgHinsideM. quadrilineatuswas observed up to 48 post-AAP. No differences were observed between the WT and anssaKmutant lacking a functional SPI-2 T3SS in insect homogenates or between the WT and either mutant in insect excretions. This study provides novel insight into the presence and persistence ofS. entericainsideM. quadrilineatusand demonstrates that the SPI-1 T3SS influences the persistence of the pathogen in the gut of a potential vector.