Fate of bacteria, Aeromonas caviae, in the midgut of the housefly, Musca domestica

Abstract. The role of houseflies as agents in the spread of bacterial diseases has been thoroughly investigated, yet the fate of bacteria ingested by flies has not. We examined the physical location of the bacterial enteropathogen Aeromonas caviae in the midgut of laboratory‐reared adult houseflies. Food ingested by houseflies was separated from the midgut epithelium by a double‐layered peritrophic matrix (PM). The inner PM intimately enveloped the food as fecal pellets (food boluses), while the outer PM appeared as a long continuous tube. In flies fed a suspension of A. caviae, live bacteria were not observed within the inner PM, but were compartmentalized between folds of the PM in the inter‐PM space. Similar observations were made for flies fed a suspension of Serratia liquefaciens and for highly contaminated feral flies. Isolates of both A. caviae and S. liquefaciens were chitinolytic (as demonstrated by clearing zones on chitin agar), but the potential role of bacterial enzymes in the alteration of PM morphology or formation needs further investigation.