Effect of laser and environmental parameters on reducing microbial contamination of stainless steel surfaces with Nd:YAG laser irradiation.

AIMS: The effect of laser (pulse repetition frequency, pulse energy and exposure time) and environmental parameters (pH, NaCl concentration and wet or dry samples) of Nd:YAG laser decontamination of stainless steel inoculated with Escherichia coli, Staphylococcus aureus and Listeria monocytogenes was investigated. METHODS AND RESULTS: Stainless steel discs were inoculated with the bacterial samples and exposed to laser energy densities to about 900 J cm(-2). These inactivation curves allowed selection of laser parameters for two-level multifactorial designed experiments, the results of which allowed comparisons to be made between effects of individual and combined parameters on the laser inactivation efficiency. Escherichia coli was inactivated most effectively as a wet film with L. monocytogenes and S. aureus showing similar response. For the multifactorial experiments all laser parameters were significant and were smallest for S. aureus as a wet film. CONCLUSIONS: pH and NaCl concentration had little effect on the efficacy of laser inactivation but dry or wet states and all laser parameters were significant. SIGNIFICANCE AND IMPACT OF THE STUDY: Such systems may prove to be applicable in industrial processes where stainless steel may be contaminated with acidic solutions or salt, e.g. in the food industry with laser inactivation seeming to be independent of these parameters. Parameters have been identified that allow optimization of the treatment process.

Bactericidal action of high-power Nd:YAG laser light on Escherichia coli in saline suspension.

Infra-red light (1064 nm) from a high-power Nd:YAG laser caused more than 90% loss of viability of Escherichia coli during exposures that raised the temperature of PBS suspensions of the bacteria to 50 C in a thermocouple-equipped cuvette. In contrast, there was minimal loss of viability after heating the same suspensions to 50 degrees C in a water-bath, or in a PCR thermal cycler. The mechanism of laser killing at 50 degrees C was explored by differential scanning calorimetry, by laser treatment of transparent and turbid bacterial suspensions, and by optical absorbency studies of E. coli suspensions at 1064 nm. Taken together, the data suggested that the bactericidal action of Nd:YAG laser light at 50 degrees C was due partly to thermal heating and partly to an additional, as yet undefined, mechanism. Scanning electron microscopy revealed localized areas of surface damage on laser-exposed E. coli cells.

Inactivation of bacteria and yeasts on agar surfaces with high power Nd:YAG laser light.

Near infrared light from a high-powered, 1064 nm, Neodymium:Yttrium Aluminium Garnet (Nd:YAG) laser killed a variety of Gram-positive and Gram-negative bacteria and two yeasts, lawned on nutrient agar plates. A beam (cross-sectional area, 1.65 cm2) of laser light was delivered in 10 J, 8 ms pulses at 10 Hz, in a series of exposure times. For each microbial species, a dose/response curve was obtained of area of inactivation vs energy density (J cm-2). The energy density that gave an inactivation area (IA) equal to 50% of the beam area was designated the IA50-value and was plotted together with its 95% confidence limits. Average IA50-values were all within a threefold range and varied from 1768 J cm-2 for Serratia marcescens to 4489 J cm-2 for vegetative cells of Bacillus stearothermophilus. There were no systematic differences in sensitivity attributable to cell shape, size, pigmentation or Gram reaction. At the lowest energy densities where inactivation was achieved for the majority of organisms (around 2000 J cm-2), no effect was observed on the nutrient agar surface, but as the energy density was increased, a depression in the agar surface was formed, followed by localized melting of the agar.

Cavitation damage of pyrolytic carbon in mechanical heart valves.

A summary of the observations of cavitation-related damage is presented for over a hundred mechanical heart valves (MHV) containing pyrolytic carbon components. Valves were obtained from several types of simulators, animal studies and clinical explantations, and were primarily of the bileaflet type. Damage on these valves was documented as to location, type, and severity. This report focuses on the damage location where cavitation bubbles have been observed in vitro. Pitting and microcracking are the forms of damage observed that can be associated with cavitation. The pitting is primarily of a focal nature and is thought to be due to cavitation bubble collapse or, possibly, initiation. Certain features of the deposited material appear to be important relative to cavitation damage resistance and the so-called cavitation threshold of a MHV. A highly polished surface with few micropores provides few nucleation sites for cavitation bubbles and will better withstand cavitation forces. Attributing certain observations of in vivo damage to cavitation is done by inference from; 1. the similarity of the damage features observed on explants to those produced by cavitation in vitro, and 2. the identity of the location of this damage with the location of cavitation as observed by high speed video (HSV). In addition, confirmation was obtained in a number of instances by in vitro observation of cavitation coinciding with a specific damage location on the same explanted MHV. In most of the fractures, a focal pit was usually present on the fracture line at or near the fracture origin, indicating pitting as a primary damage mechanism.(ABSTRACT TRUNCATED AT 250 WORDS)

Dosage aspects of danazol therapy in the treatment of endometriosis.

Danazol is effective in the treatment of endometriosis. Individual patient response is very variable as is dosage requirement. The appropriate dose for maintenance therapy for any particular patient is best determined by a trial and error method, starting with a recommended initial dosage. Side effects are slight.

Puritus vulvae: treatment by multiple intradermal alcohol injections.

A Preliminary report is presented on the use of multiple intradermal injections of absolute alcohol in the treatment of intractable pruritus vulvae. Twenty-five patients were followed up for over I year, and of these six (24%) were cured, and thirteen (52%) showed marked symptomatic improvement.