Interspecies Competition of Mono or Dual Species Biofilms of MDR Staphylococcus aureus and Pseudomonas aeruginosa Promotes the Killing Efficacy of Phage or Phage Cocktail

Staphylococcus aureus and Pseudomonas aeruginosa are opportunistic pathogens commonly associated with burn wound infections. These bacteria can form biofilm and contribute a high-level drug resistance to available antibiotics. This study focused on the bacteriolytic activity of phages vB_SAnS_SADP1 and vB_PAnP_PADP4 on 24 h old single or dual-species biofilms of Staphylococcus aureus and Pseudomonas aeruginosa in alone and in combination. Scanning and confocal laser scanning microscopic studies confirmed the structural organization of biofilms in single or dual-species combinations in in-vitro conditions. Single species biofilms are more robust and densely packed at 24 h of incubation. In contrast, dual-species biofilms (0.67± 0.02) are weakly associated due to their inter-species competition and are easily affected by phage cocktails (0.16 ± 0.02). In Invitro conditions, dual-species biofilms were more easily affected by phage cocktail than single phage. Scanning electron microscopic studies revealed the complete diminishment of biofilm formation by four h treatment with single phage or phage cocktails on single species or dual-species biofilms. Confocal laser scanning microscopic images with stains Syto®9 and propidium iodide revealed that phage treatment showed significant uptake of propidium iodide, indicating massive cell death mediated by respective phage or phage cocktail.