Studies on the pathogenicity of different strains of Bacillus cereus for the cockroach, Leucophaea maderae

Abstract

The pathogenicity of four strains of Bacillus cereus for the cockroach, Leucophaea maderae, was determined by oral and intrahemocoelic challenge. The most pathogenic strain was found to be B. cereus B1, previously isolated from naturally infected cockroaches, Blaberus giganteus, with an LD 50 at 10 days of 3.2 × 10 4 and 7.9 × 10 7 viable bacteria/insect by intrahemocoelic injection and oral challenge, respectively. The least pathogenic strain was B. cereus NCIB 3329, with LD 50 values of >2 × 10 9 and 1 × 10 8 viable bacteria/insect following oral challenge and intrahemocoelic injection, respectively. Studies on the production of phospholipase C-like activity by all four strains of B. cereus showed that there was a correlation with pathogenicity, in that the B1 isolate released the greatest amount of enzyme, while B. cereus NCIB 3329 synthesized lower levels of phospholipase C-like material under the same incubation conditions. Similar results were also found with the hemolytic factor seen in culture supernatants of B. cereus. Initial histological studies of the midgut region of alimentary canals from cockroaches fed LD 50 levels of the B1 isolate showed damage to the columnar secretory cells after 12 hr postchallenge, but with no signs of active invasion of bacteria through this region.