Inactivation of Staphylococcal Virulence Factors Using a Diode Laser light-Activated Antimicrobial Agent

Abstract

Total of 120 samples were collected from different body sites and lesions for patients from both
sexes. There were 78 isolates (65%) Staphylococcus aureus from them 37 isolates were Methicillinresistant Staphylococcus aureus (MRSA). Each isolate was exposed to diode laser 632nm
wavelength with 300µM of methylene blue (MB) at 458.6 watt/cm2
for 15 minutes, both
phenotypic and genotypic changes in virulence factors and the antibiotic-resistance were
evaluated before and after irradiation with laser light. It was observed that the effect of sub-lethal
dose on the antibiotic sensitivity was isolate-dependent. In general, results showed large variations
in the susceptibility of antibiotic. Exposure to diode laser increased resistance to Vancomycin, in
contrast increased sensitivity to Methicillin, Ciprofloxacin, and Norfloxacin. Also Results showed
decreases the activity of β-haemolysin, with 33 (90.3%) isolates of S. aureus in comparison to the
control as shown in blood agar method and haemolytic titration assay, but there was no effect on
thermonuclease enzyme after irradiation. Detection of three genes represented in MRSA isolates
by a confirmatory test was carried out using PCR technique. The results of the PCR amplification
of mecA gene noted that it was present in 27(72.2%) S.aureus isolates and 14(83.3%) isolates
showed reduction in β-toxin production after exposure to laser light, with no altered or deficiency
in thermonuclease gene (nuc).