The housefly Musca domestica as a mechanical vector of Clostridium difficile

Background: Clostridium difficile is a bacterial healthcare-associated infection that may be transferred by houseflies (Musca domestica) due to their close ecological association with humans and cosmopolitan nature. Aim: To determine the ability of M. domestica to transfer C. difficile both mechanically and following ingestion. Methods: M. domestica were exposed to independent suspensions of vegetative cells and spores of C. difficile, then sampled on to selective agar plates immediately postexposure and at 1-h intervals to assess the mechanical transfer of C. difficile. Fly excreta was cultured and alimentary canals were dissected to determine internalization of cells and spores. Findings: M. domestica exposed to vegetative cell suspensions and spore suspensions of C. difficile were able to transfer the bacteria mechanically for up to 4 h upon subsequent contact with surfaces. The greatest numbers of colony-forming units (CFUs) per fly were transferred immediately following exposure (mean CFUs 123.8 +/- 66.9 for vegetative cell suspension and 288.2 +/- 83.2 for spore suspension). After 1 h, this had reduced (21.2 +/- 11.4 for vegetative cell suspension and 19.9 +/- 9 for spores). Mean C. difficile CFUs isolated from the M. domestica alimentary canal was 35 +/- 6.5, and mean C. difficile CFUs per faecal spot was 1.04 +/- 0.58. C. difficile could be recovered from fly excreta for up to 96 h. Conclusion: This study describes the potential for M. domestica to contribute to environmental persistence and spread of C. difficile in hospitals, highlighting flies as realistic vectors of this micro-organism in clinical areas. Crown Copyright (C) 2016 Published by Elsevier Ltd on behalf of The Healthcare Infection Society. All rights reserved.