Ultrastructural changes in the midgut epithelium of an elaterid larva (Coleoptera) infected enterically with Pseudomonas aeruginosa

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Abstract
Soil bacteria enter the digestive tract of wireworms at ecdysis through the dorsal exuvial split and ecdysial space. Pseudomonas aeruginosa, a potential pathogen of insects, multiplies in the enteron, but many are killed within it. The mucopeptide layer of the bacterial cell wall is affected early in the degenerative process.A surface epithelial mucoid layer provides a temporary protective barrier for the midgut epithelium against the bacteria. The bacteria affect the fine structure of the host midgut epithelium in three primary ways. (1) The cells take up and retain fluids in the cytoplasm and membrane-bound vacuoles to the point of apical rupture; the selective permeability of the membranes of the cell and vacuoles appears to be affected. (2) The surface mucoid covering is degraded, the exposed plasma membrane is disrupted, and a lytic erosion of the exposed cytoplasm occurs opposite bacterial colonies. Lesions thus form in the midgut epithelium, and could lead to perforation of the wall at these points. (3) Pathological changes occur in various cell organelles, the most striking of which are an increase in abundance of rough endoplasmic reticulum (RER) and cytoplasmic ribosomes, and a transposition of membrane material from mitochondria and Golgi complexes to RER. The functional implications of these pathological changes in fine structure are discussed.

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