Combinations of maggot excretions/secretions and antibiotics are effective against Staphylococcus aureus biofilms and the bacteria derived therefrom

OBJECTIVES: Maggots of the blowfly Lucilia sericata are used for the treatment of chronic wounds. Previously we reported that maggot excretions/secretions (ES) break down Staphylococcus aureus biofilms but do not kill the bacteria. As many antibiotics are not effective against biofilms we assessed the effect of combinations of ES and antibiotics on S. aureus biofilms and on the survival of the bacteria released from the biofilms. METHODS: Effects of ES, antibiotics (vancomycin, daptomycin or clindamycin) and combinations thereof on S. aureus ATCC 29 213 biofilms and bacterial viability were determined using microtitre plates and in vitro killing assays. RESULTS: Vancomycin and daptomycin dose-dependently enhanced biofilm formation, whereas clindamycin reduced S. aureus biofilm size. Adding ES to antibiotic incubations caused a complete biofilm breakdown. After a lag time the bacteria derived from biofilms became susceptible to vancomycin and clindamycin, provided that the medium was refreshed. Daptomycin dose-dependently eliminated the biofilm-derived bacteria immediately. Furthermore, it was significantly more effective against bacteria derived from ES-exposed biofilms than those from control biofilms. ES did not affect the activity of the antibiotics against log-phase S. aureus. CONCLUSIONS: Combinations of maggot ES and antibiotics eliminate S. aureus biofilms and the bacteria derived therefrom.