Laser disruption and killing of methicillin-resistant Staphylococcus aureus biofilms

Objective

The aim of the study was to study the efficacy of 2 different lasers in vitro, in disrupting biofilm and killing planktonic pathogenic bacteria.

Materials and methods

Biofilms of a stable bioluminescent of Staphylococcus aureus Xen 31 were grown in a 96-well microtiter plate for 3 days. The study included 7 arms: (a) control; (b) ciprofloxacin (3 mg/L, the established minimum inhibitory concentration MIC]) alone; (c) shock wave (SW) laser alone; (d) near-infrared (NIR) laser alone; (e) SW laser and ciprofloxacin; (f) SW and NIR lasers; (g) SW, NIR lasers, and ciprofloxacin. The results were evaluated with an in vivo imaging system (IVIS) biophotonic system (for live bacteria) and optical density (OD) for total bacteria.

Results

Without antibiotics, there was a 43% reduction in OD (P < .05) caused by the combination of SW and NIR suggesting that biofilm had been disrupted. There was an 88% reduction (P < .05) in live biofilm. Ciprofloxacin alone resulted in a decrease of 28% of total live cells (biofilm remaining attached) and 58% of biofilm cells (both P > .05). Ciprofloxacin in combination with SW and SW + NIR lasers caused a decrease of more than 60% in total live biomass and more than 80% of biofilm cells, which was significantly greater than ciprofloxacin alone (P < .05).

Conclusions

We have demonstrated an effective nonpharmacologic treatment method for methicillin-resistant Staphylococcus aureus (MRSA) biofilm disruption and killing using 2 different lasers. The preferred treatment sequence is a SW laser disruption of biofilm followed by NIR laser illumination. Treatment optimization of biofilm is possible with the addition of ciprofloxacin in concentrations consistent with planktonic MIC.