Potential of sequential treatment with minocycline and S. aureus specific phage lysin in eradication of MRSA biofilms: an in vitro study.

Lysins are novel class of anti-infectives which are derived from bacteriophage. In the present study, the potential of previously characterised phage borne endolysin MR-10 in eradicating methicillin-resistant Staphylococcus aureus (MRSA) biofilm was evaluated. Scanning electron microscopic examination showed that both ica-positive and ica-negative MRSA formed equally potent mature biofilm. Different approaches were employed to eradicate the young as well as older biofilm formed by both types of MRSA strains. Our results showed a significant decrease (p < 0.01) in biofilm count on sequentially treating the MRSA biofilm with minocycline (4 μg/ml) for 3 h followed by treatment with endolysin MR-10. Since endolysin can act effectively irrespective of the metabolic status of the cells hence, they are capable of killing the rapidly growing cells (log phase cells) as well as non-dividing (stationary phase) cells. As a result they are effective in eradicating the younger and older biofilm. On staining the ica-positive MRSA biofilm with wheat germ agglutinin (WGA)-Alexa Flour 350, reduction in poly-intercellular adhesion (PIA) content was observed in comparison to control biofilm. In addition, a significant decrease (p < 0.01) in extracellular DNA (eDNA) content of ica-negative MRSA biofilm was also observed. Further, Live/Dead Baclight™ staining also showed presence of higher population of dead cells after treatment with minocycline and endolysin MR-10. Hence, our results showed that using minocycline sequentially with endolysin, MR-10 can effectively eradicate both young as well as older biofilm formed by ica-positive and ica-negative MRSA.