Maggot excretions/secretions are differentially effective against biofilms of Staphylococcus aureus and Pseudomonas aeruginosa

OBJECTIVES: Lucilia sericata maggots are successfully used for treating chronic wounds. As the healing process in these wounds is complicated by bacteria, particularly when residing in biofilms that protect them from antibiotics and the immune system, we assessed the effects of maggot excretions/secretions (ES) on Staphylococcus aureus and Pseudomonas aeruginosa biofilms, the clinically most relevant species. METHODS: We assessed the effects of ES on biofilms using microtitre plate assays, on bacterial viability using in vitro killing and radial diffusion assays, and on quorum sensing systems using specific reporter bacteria. RESULTS: As little as 0.2 microg of ES prevented S. aureus biofilm formation and 2 microg of ES rapidly degraded biofilms. In contrast, ES initially promoted P. aeruginosa biofilm formation, but after 10 h the biofilms collapsed. Degradation of P. aeruginosa biofilms started after 10 h and required 10-fold more ES than S. aureus biofilms. Boiling of ES abrogated their effects on S. aureus, but not on P. aeruginosa, biofilms, indicating that different molecules within ES are responsible for the observed effects. Modulation of biofilms by ES did not involve bacterial killing or effects on quorum sensing systems. CONCLUSIONS: Maggot ES are differentially effective against biofilms of S. aureus and P. aeruginosa.