D. J. G. Davies

ACTION SPECTRA FOR INACTIVATION OF NORMAL and XERODERMA PIGMENTOSUM HUMAN SKIN FIBROBLASTS BY ULTRAVIOLET RADIATIONS

—Action spectra for UV‐induced lethality as measured by colony forming ability were determined both for a normal human skin fibroblast strain (lBR) and for an excision deficient xeroderma pigmentosum strain (XP4LO) assigned to complementation group A using 7 monochromatic wavelengths in the range 254‐365 nm. The relative sensitivity of the XP strain compared to the normal skin fibroblasts shows a marked decrease at wavelengths longer than 313 nm. changing from a ratio of about 20 at the shorter wavelengths to just greater than 1.0 at the longer wavelengths. The action spectra thus indicate that the influence on cell inactivation of the DNA repair defect associated with XP cells is decreased and almost reaches zero at longer UV wavelengths. This would occur, for example, if the importance of pyrimidine dimers as the lethal lesion decreased with increasing wavelength. In common with other studies both in bacterial and mammalian cells, our results are consistent with pyrimidine dimers induced in DNA being the major lethal lesion in both cell strains over the wavelength range 254‐313 nm. However, it is indicated that different mechanisms of inactivation operate at wavelengths longer than 313 nm.

Loss of antibacterial preservatives from contact lens solutions during storage

The preservative content of 34 commercially available contact lens solutions has been determined. Over half of the solutions contained less than 90% of the stated preservative content. Storage tests conducted at 40°, using both simulated and commercially available contact lens solutions in plastics containers of the type used to present these products showed that thiomersal and chlorbutol appeared to be sorbed by these containers in contrast to benzalkonium chloride and chlorhexidine gluconate which interacted mainly by a surface adsorption process. The extent of any interactions was dependent upon the type of plastics material used to fabricate the container.

THE SENSITISING EFFECT OF A SUNSCREENING AGENT, p-AMINOBENZOIC ACID, ON NEAR UV INDUCED DAMAGE IN A REPAIR DEFICIENT STRAIN OF ESCHERICHIA COLI†

Abstract. The use of repair deficient strains of bacteria for detecting mutagenic properties of chemical species is now an established technique. In this paper we present inactivation results obtained with Escherichia coli K12 AB2480 (uvr A rec A) which indicate that p‐aminobenzoic acid, a common component of sunscreening formulations, may increase the frequency of lethal damage induced in DNA when cell populations are exposed to near ultraviolet radiation.

The antimicrobial efficiencies of contact lens solutions

The antimicrobial efficiencies of 34 commercially available contact lens solutions has been tested against Pseudomonas aeruginosa, Staphylococcus aureus, Micrococcus luteus and Candida albicans. A standard inoculum of 106 organisms ml−1 was placed in a sample of a contact lens solution and samples taken at various times up to 48 h. These were placed in a recovery medium and the presence or absence of growth noted after 48 h incubation at 37°. Of 14 solutions used to soak and disinfect lenses only 4 inactivated all four test strains within 1 h, 7 within 4 h, while 6 solutions allowed growth of one or more test organisms even after 24 h contact. Of the remaining 20 solutions, with their various functions such as cleaning and wetting of lenses, 13 failed to inhibit one or more test strains after 24 h contact. Some form of control of the manufacture and presentation together with minimum standards of antimicrobial efficiency would seem to be desirable.

The interaction of preservatives with polyhydroxyethylmethacrylate (polyHEMA)

The interaction of the four most commonly used preservatives in contact lens solutions (chlorbutol, thiomersal, chlorhexidine gluconate and benzalkonium chloride) with polyhydroxyethylmethacrylate (polyHEMA), has been examined. Benzalkonium chloride and chlorhexidine gluconate show typical high affinity type isotherms. The interaction of benzalkonium chloride with polyHEMA from aqueous solution was reversible whereas that of chlorhexidine was only reversible in the presence of electrolyte or surfactant. Chlorbutol showed a typical reversible linear isotherm. Thiomersal does not interact with polyHEMA above pH 5·0. The extent of chlorhexidine—polyHEMA interactions is increased by the presence of formulatory adjuvants such as electrolyte and hydrophilic polymers. PolyHEMA lenses that apparently have been equilibrated with chlorhexidine gluconate will, on the addition of fresh preservative solution, bind further quantities of chlorhexidine above that which would be predicted from the sorption isotherm.

LEAKAGE OF 86Rb+ AFTER ULTRAVIOLET IRRADIATION OF Escherichia coli K-12

Abstract— Stationary phase cultures of a DNA repair proficient Escherichia coli K‐12 strain showed a release of intracellular material as assessed by three different methods (260 nm absorption; [methyl‐3H]thymidine leakage and 86Rb+ leakage) after broad‐band (Black‐Light Blue) near‐UV radiation but not after far‐UV (254 nm) radiation. As a control response for membrane damage to cells, this leakage of intracellular material was also determined by each method after mild‐heat (52°C) treatment of E. coli K‐12. An action spectrum for the release of 86Rb+ from E. coli K‐12 after irradiation with monochromatic wavelengths, from 254 to 405 nm, is also presented. The action spectrum for lethality (F37 values) obtained for this strain, shows that leakage of 86Rb+ occurs at fluences equivalent to or slightly less than fluences causing inactivation at wavelengths above 305 nm. In contrast, at wavelengths below 305 nm, leakage of 86Rb+ from irradiated cells can be induced but only at fluences significantly greater than was required to cause cell inactivation. These results indicate, therefore, that near‐UV radiation can induce a damaging effect on the cells permeability barrier which may be significant in causing the death of the cell, whereas the effect is not significant in causing the death of cells by far‐UV radiation where DNA damage is known to be the main cause of lethality.

AN ACTION SPECTRUM FOR ULTRAVIOLET RADIATION‐INDUCED MEMBRANE DAMAGE IN Escherichia coli K‐12

A wild‐type Escherichia coli K‐12 strain was irradiated using monochromatic radiation in the range 254 to 405 nm. A measure of the cell membrane damage induced at each wavelength was investigated by comparing cell viability after irradiation on nutrient agar and on minimal medium containing either a low or high inorganic salt concentration. An action spectrum for lethality and for cell membrane damage was then determined. From 254 to 310 nm lethality closely corresponded to the absorption spectrum of DNA, and there was no indication of membrane damage. However, above a wavelength of 310 nm, the direct absorption of radiation by DNA could not account for the sensitivity observed. Moreover, at wavelengths longer than 310 nm, cell membrane damage was induced and by an increasing factor up to a peak at 334 nm. At the longer wavelengths of 365 and 405 nm, there was a gradual decrease from the peak of damage to cell membranes induced by 334 nm radiation. These results indicate that cell membrane damage may contribute significantly to near‐UV radiation‐induced cell lethality in wild‐type E. coli K‐12.

Evaluation of the anti-acanthamoebal activity of five contact lens disinfectants☆

Abstract We investigated the ability of five commercially available contact lens disinfectants to kill Acanthamoeba cysts. Two methods were employed: a microtiter plate method (using Acanthamoeba polyphaga SHI and A. castellanii CLAP 150112 g), which determines the presence or absence of growth after a challenge and measures efficacy by total kill only, and a bacterial lawn plaque method (A. polyphaga only), which quantitates the number of cysts surviving different periods of exposure. With the microtiter method, there was no growth of excysted Acanthamoeba after exposure to LENS PLUS ® Oxysepto ® 1 Disinfecting Solution ∗ for 4 hours or to Allergan ® HYDROCARE ® Cleaning and Disinfecting Solution ∗ for 6 hours. Excysted Acanthamoeba were recovered in all trials after exposure to ReNu ®, † Opti-Soft ®, † or AOSept ®† for up to 24 hours. With the bacterial lawn plaque method, HYDROCARE and Oxysept 1 (with or without Ultrazyme TM Enzymatic Cleaner) reduced the challenge cysts to zero recovery by the 8- and 24-hour time points, respectively; ReNu, Opti-Soft, and AOSept disinfectants showed poor anti-Acanthamoebal activity, reducing the cyst challenge by only 66, 66, and 79%, respectively, at 24 hours. The difference in the efficacies of Oxysept 1 and AOSept (both nominally 3% hydrogen peroxide) is probably due to the initial rapid neutralization of hydrogen peroxide in the AOSept system during the disinfection soaking cycle.

The Response of Normal and Ataxia-telangiectasia Human Fibroblasts to the Lethal Effects of Far, Mid and Near Ultraviolet Radiations

The responses of two ataxia-telangiectasia (A-T) cell strains to the lethal effects of monochromatic far, mid and near ultraviolet radiations have been determined and compared with the responses of three normal human cell strains. Our results confirm a previous observation that the A-T cell strain AT4BI is abnormally sensitive to the lethal effects of mid u.v. (313 nm) radiation. After far u.v. (254 nm) radiation the strain AT4BI exhibits a small but statistically significant increase in sensitivity compared to the normal strains. Of most interest, in terms of a mechanistic interpretation of the sensitivity of A-T strains, the survival responses of neither A-T strain tested to near u.v. (365 nm) radiation differed significantly from the mean response of the normal strains, although it is of interest that one normal strain (48BR) was found to be significantly more resistant to near u.v. radiation than any of the other strains tested. The results are discussed in terms of the possible induction of radiogenic lesions in DNA by ultraviolet radiations and the possible mechanisms of radiation sensitivity in ataxia-telangiectasia.

The influence of various counter ions on the interaction of chlorhexidine with the hydrophilic contact lens polymer, poly(2-hydroxyethyl methacrylate)†

The commercially available salts of chlorhexidine were found to interact with the hydrogel poly (2‐hydroxyethyl methacrylate) to different extents, the affinity for the polymer decreasing in the order acetate, gluconate, chloride. The uptakes of the acetate and gluconate salts were almost entirely irreversible over the concentration range studied. The influence of some alternative counter ions, namely amino acids and dicarboxylic acid salts, was examined and found to generate a three‐fold variation in the extent of the chlorhexidine interaction. Uptakes were greatest for counter ions that were either hydrophobic in character or bore a net negative charge. Only two compounds, glycine and monosodium oxalate, were successful in reducing the extent of sorption below that observed for chlorhexidine hydrochloride.