Vector Potential of the German Cockroach (Dictyoptera: Blattellidae) in Dissemination of Salmonella Enteritidis Serotype Typhimurium

Abstract

The German cockroach, Blattella germanica, is an effective mechanical transmitter of Salmonella enteritidis serotype Typhimurium via feces. Groups of restrained German cockroaches from a laboratory colony free of Salmonella were fed graded doses of S. enteritidis and their feces were assayed daily. The amount and duration of Salmonella in feces is dose-related, with outputs from 8 × 10¹ to 2 × 10⁷ cells/defecation over a range of 3 to 20 days. The percentage of specimens excreting S. enteritidis is also dose-related and ranges from 8% with a 10² input to 70% with an infective feeding of 10⁷. Salmonella multiplication in the gut or feces is a rare event. The ID₅₀, or infective dose at which 50% of the feces will contain Salmonella during the first 10 days following ingestion, is 1.6 × 10⁷. There were no significant sex differences in excretion of Salmonella at each dose. S. enteritidis is recoverable about 10 days longer in the cockroach gut than in the feces. Persistence is primarily in the hindgut and numbers of Salmonella decline over time in living cockroaches, with no recoveries from gut or feces after a month.