Acquisition and retention of Clostridium difficile by Musca domestica larvae and pupae during metamorphosis

SummaryBackgroundTransfer of Clostridium difficile by Musca domestica has been demonstrated, revealing their potential for disseminating infection in the hospital environment.AimTo determine the ability of M. domestica larvae to acquire and retain C. difficile throughout their metamorphosis into adult flies.MethodsLarvae were exposed to spores of C. difficile in a faecal emulsion, and examined externally and internally to determine carriage and internalization of spores through their development to adults.FindingsLarvae harboured C. difficile externally, with means of 21.56 +/− 5.76 colony-forming units (cfu) at Day 0, 22.44 +/− 9.90 cfu at Day 2, decreasing to 0.56 +/− 0.34 cfu at Day 4, with no C. difficile isolated thereafter. The same larvae harboured C. difficile internally, with means of 587.33 +/− 238.29 cfu at Day 0, decreasing to 297.44 +/− 155.21 cfu at Day 2, decreasing further to 73.67 +/− 46.74 cfu at Day 4, with no C. difficile isolated thereafter. The zero recovery of C. difficile coincided with the development of M. domestica larvae into pupae. From Day 6 onwards, all larvae had developed into the pupal stage and no C. difficile was recoverable from any pupae. No C. difficile was recovered from adult flies (emerged on Day 12) or empty puparia.ConclusionAlthough C. difficile spores are readily acquired and internalized by larvae during feeding, they are not retained through development to adults. Adult flies therefore acquire C. difficile contamination as adults. The potential antimicrobial action of M. domestica larvae and their extracts against C. difficile spores warrants further investigation.