Bactericidal effects of high-power Nd:YAG laser radiation on Staphylococcus aureus

The effect of laser radiation on Staphylococcus aureus 6571 (Oxford strain) was studied with high-power Nd:YAG laser radiation between 50 and 300 W. A range of laser pulse repetition frequencies (PRF) from 5 to 30 Hz, with a combination of pulse energies from 2 to 30 J were applied; this covered a range of energy densities from 800 to 2700 J cm(-2). The area of inactivation of S. aureus, lawned on nutrient agar plates, was quantified as a function of energy density and exposure time. The shortest exposure time which produced an area of inactivation equal to 50% of the beam area was achieved at a PRF of 30 Hz, pulse energy of 10 J, and with an exposure time of 10.75 s; this was equivalent to an applied energy density of 1723 J cm(-2). No bacterial inactivation was observed at relatively low-power settings for PRF, pulse energies and exposure time of: 20 Hz, 3 J and 34 s; 25 Hz, 2 J and 45 s and 30 Hz, 2 J and 35 s, respectively. These results shows that pulse energy, PRF and exposure time are important criteria when considering inactivation of micro-organisms by laser radiation.