Antimicrobial activity of argon fluoride (ArF) excimer laser on gram-negative bacteria

Abstract

The objective of this study was to evaluate the antibacterial activity of argon fluoride (ArF) excimer laser radiation on clinically important strains of gram-negative bacteria. The antibacterial activity of ArF excimer laser radiation was evaluated on two Acinetobacter baumannii, one Enterobacter cloacae, three Escherichia coli, two Helicobacter pylori, one Klebsiella pneumoniae and two Pseudomonas aeruginosa strains. The strains were isolated from clinical specimens and typed by the usual biochemical procedures. Square agar plates of 12 x 12 cm were divided into rectangular (2 x 3 cm) regions and spread with 0.5x 10(4) colony forming units (CFU)/ml of bacterial suspension. The excess liquid was removed and the plates were allowed to dry for 30 min. A total of 96 rectangular (2x3 cm) regions were used for each strain, in order to test an equal number of laser parameters. Each rectangular region was irradiated with different laser parameters, using a 193 nm ArF excimer laser, linked with a simple Galilean afocal system and a rectangular diaphragm of the same dimensions as the original laser beam cross-section, at a distance of 10 cm from the irradiated surface. This system was used in order to keep the laser pulse energy under 80 mJ and to cut-out the non-transverse electromagnetic mode branches of the laser beam. We then studied the bacterial survival ratio versus the number of laser pulses, the repetition frequency and the total laser beam fluence. Our results showed that the total laser beam fluence was the most important parameter to consider in evaluating the bactericidal effect of ArF excimer laser radiation. A critical value of the total fluence was determined for each strain, such that, for laser beam fluences greater than this critical value, no colonies appeared to survive while, for laser fluences less than this critical value, the survival ratio did not exceed 2 x 10(7) CFU (2 x 10(-5)%). These critical values were found to vary between 8 J/cm2 and 16 J/cm2 for the bacterial species studied. Under these conditions, ArF laser irradiation is promising for the sterilisation of hard surfaces and for in situ application.

In vitro laser ablation of laboratory developed biofilms using an Nd:YAG laser of 532 nm wavelength

“…Between the two types of coupons, the removal was more evident on titanium coupons. In an earlier study where bacteria on plates were irradiated using an ArF laser at 93 nm, a significant percentage of bacterial mortality was reported (Charvalos and Karoutis, 2001).…”

Laser impact assessment in a biofilm‐forming bacterium Pseudoalteromonas carrageenovora using a flow cytometric system

“…This is considered as an extremely useful technique to test the toxicity of biocides and bioavailability of contaminants in the laboratory (Stauber et al, 2002). Studies of the laser impact on bacteria so far have largely depended on irradiation of static samples or bacterial colonies laid over agar plates (Charvalos and Karoutis, 2001;Dobson and Wilson, 1992). Thus, these studies might not actually represent the effects that occur during irradiation in a flowing water system.…”

“…So far, the laser impact assessment studies on bacteria and biofouling organisms focused on static samples, i.e., irradiation on samples in static condition (Charvalos and Karoutis, 2001;Dobson and Wilson, 1992). This, however, may not represent the actual situation.…”

Impact of pulsed Nd:YAG laser on the marine biofilm-forming bacteria Pseudoalteromonas carrageenovora: significance of physiological status

“…The majority of these studies used very high fluences (Schultz et al 1986;Ward et al 2000). On the other hand, there are few studies measuring the impact of low power laser irradiation (Charvalos and Karoutis 2001;Nandakumar et al 2002). Also, there are few studies addressing details pertaining to the bacterial physiological state such as cell density (Ward et al 2000), growth phases, nutritional status, and (or) stressful situations, such as reduced or increased growth temperature.…”