Comparsion of selected growth media for culturing Serratia marcescens, Aeromonas sp., and Pseudomonas aeruginosa as pathogens of adult Stomoxys calcitrans (Diptera: Muscidae)

Stable flies, Stomoxys calcitrans (L.), were orally infected with Aeromonas sp., Pseudomonas aeruginosa (Schroeter), and Serratia marcescens Bizio that were cultured on egg-yolk media, nutrient broth, and fly egg media. Aeromonas and Serratia caused mortality when the bacteria were originally grown on egg-yolk medium. Pseudomonas was equally lethal regardless of the media on which it was cultured. A wild isolate of Aeromonas caused greater death than an isolate that had been passed through host flies and had been reisolated from killed flies. Mortality increased with bacterial dose for all species. Aeromonas and Serratia caused mortality within several days after ingestion, whereas Pseudomonas caused a gradual increase in mortality 3-7 d after ingestion. The pathologic activity of Aeromonas and Serratia required extracellular products produced when cells were grown in egg yolk medium. Aeromonas required both supernatant and cells from egg yolk medium, wereas Serratia required supernatant from egg yolk medium and cells from either nutrient broth or egg yolk medium. Mortality due to ingestion of Aeromonas was correlated with the presence of enzymes that cause alpha- and beta-hemolysis, while mortality following ingestion of Serratia was associated with alpha-hemolysins, elastases, and chitinases.