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

Background: Transfer of Clostridium difficile by Musca domestica has been demonstrated, revealing their potential for disseminating infection in the hospital environment.
Aim: To determine the ability of M. domestica larvae to acquire and retain C. difficile throughout their metamorphosis into adult flies.
Methods: Larvae were exposed to spores of C. difficile in a faecal emulsion and examined externally and internally to determine carriage and internalisation of spores through their development to adults.
Findings: Larvae harboured C. difficile externally, with means of 21.56 +/- 5.76 CFUs at day zero, 22.44 +/- 9.90 after two days, decreasing to 0.56 +/- 0.34 at day four, with no C. difficile isolated thereafter. The same larvae harboured C. difficile internally, with means of 587.33 +/- 238.29 CFUs at day zero, decreasing to 297.44 +/- 155.21 after two days, decreasing further to 73.67 +/- 46.74 after four days, with no C. difficile isolated thereafter. The zero recovery of C. difficile coincided with the development of M. domestica larvae into pupae. From day six 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 twelve), or empty puparia.
Conclusion: Although C. difficile spores are readily acquired and internalised 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.