On the Influence of the Metamorphosis of Musca domestica upon Bacteria administered in the Larval Stage

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Abstract
(1) Pathogenic organisms such as B. dysenteriae (type “Y”) cannot be recovered from pupae or imagines reared from larvae to which these organisms have been administered.(2) When the larvae have been bred from disinfected ova and are subsequently fed on B. dysenteriae (type “Y”), this organism may be successfully recovered from the pupae and imagines in a small proportion of cases.(3) Under similar conditions B. typhosus was not recovered in a single case from pupae or imagines.(4) In those cases in which B. dysenteriae (Y) was successfully recovered from pupae, the colonies on the plate were invariably fewer than those obtained from pupae and imagines after administration to the larvae of more adaptable organisms such as “Bac. A”(Ledingham).(5) When organisms such as “Bac. A” were administered to larvae bred from disinfected ova, or non-disinfected ova contaminated with this organism, it was in many cases possible to recover the organism from pupae and imagines.(6) In no series of pupae examined after administration to the larvae of either B. dysenteriae or “Bac. A” was it possible to recover the organisms in every instance. A certain proportion of pupae in both cases proved sterile, so that the process of metamorphosis is undoubtedly accompanied by a considerable destruction of the bacteria present in the larval stage.(7) The temperature at which the larvae develop (19°–25°C.) has probably an important bearing on the survival of pathogenic organisms such as “Bac. Y” of dysentery, administered in association with organisms such as “Bac. A,” in view of the fact that the latter grows far more luxuriantly at this temperature. Even when grown in broth at 37°C. (the optimum temperature for Bac. Y) together with “Bac. A,” the “Bac. Y” was found to form after two days only one quarter of the total number of bacteria present in the mixed growth.(8) There was no evidence that the larval juices contained substances bactericidal for Bac. Y. The bacilli died more rapidly in normal saline solution.(9) The possibility of flies becoming infected from the presence of pathogenic organisms in the breeding ground of the larvae may be considered as very remote.