Salmonella suppression by known populations of bacteria in flies.

Survivorship of Salmonella typhimurium, Streptococcus faecalis, Proteus mirabilis, and Pseudomonas aeruginosa was studied in dibiotic and tribiotic interactions in vitro and in various regions of the digestive tract of the blow fly, Calliphora vicina. In dibiotic interactions, Salmonella typhimurium dominated Streptococcus faecalis and was dominated by P. mirabilis, but in neither case was it eliminated from the larval gut. In tribiotic interactions, there was synergic suppression and a definite trend toward elimination of Salmonella typhimurium from the gut. This trend approaches but does not match the total exclusion of S. typhimurium from the gut of maggots with a normal flora. Bacterial survival in the gut of the fly is discussed in relation to doubling time, sweep-out rate of the maggot and prepupal gut, and the midgut bactericide.