Flow cytometric analyses of cellular staining with fluorescent viability dyes and direct microscopic observations of methylene blue exclusion were compared for evaluation of the effects of a chlorhexidine gluconatebased contact lens disinfectant solution and a polyhexamethylene biguanide solution against cysts and trophozoites of Acanthamoeba castellanii and Acanthamoeba polyphaga. The flow cytometric procedure with propidium iodide (used to stain dead cells) indicated that more than 90% of trophozoites of both species (inocula of 10 5 to 10 6 /ml) at 22°C lost their viability after 4 h of exposure to chlorhexidine. When propidium iodide was used in combination with fluorescein diacetate (for live cells), the apparent number of propidium iodide-stained cells was reduced, but the relative efficacies of the two biguanide solutions appeared unchanged from those evident with the single dyes; the chlorhexidine solution was more effective than the polyhexamethylene biguanide solution. Similar data were obtained with the more cumbersome methylene blue exclusion procedure. Flow cytometric analyses provided a statistically reproducible and rapid procedure for determining the relative antiamoebal efficacies of the disinfecting solutions.An average of 50% of contact lens wearers have contaminating microorganisms in their contact lens cases at some time during their use of lenses (16,17). Gram-negative bacteria in lens cases, particularly Pseudomonas aeruginosa, present a risk for serious keratitis. Contamination of lens care systems, in particular with gram-negative bacteria, seems to be a prerequisite for the establishment of potentially infectious populations of Acanthamoeba spp. (1, 15). Compared to the incidence of contact lens-related bacterial keratitis, amoebic keratitis is a rare infection, but its recalcitrance to treatment and potential to cause blindness are a serious concern (8, 10, 12). The incidence of amoebic keratitis has been particularly centered among users of home-prepared saline solutions or tap water (particularly if the water supply was from a roof storage facility deficient in disinfectant) as a means of rinsing lenses (9, 13). In the United States, the discontinuation of salt tablets for homeprepared saline from the market in the mid-1980s resulted in a decrease in the incidence of Acanthamoeba keratitis.Acanthamoeba spp. are widespread in fresh and marine aqueous environments, and they are common in moisture reservoirs in buildings. The genus is characterized by typically uninucleate trophozoites with fine protoplasmic acanthopodia. This active motile stage feeds by phagocytosis and pinocytosis and divides by binary fission. Trophozoites can undergo a transition to a double-walled cyst stage within a few hours (1). Early cyst stages often are less resistant than mature cysts to adverse environmental conditions, and mature cysts of a given strain may have varied resistance (1, 7). The relative susceptibilities of Acanthamoeba spp. to biguanide-type and other contact lens disinfectant solutions have...

Bacteria commonly associated with nosocomial urinary tract infections were examined in vitro for their relative adherence to latex, 100% silicone-, hydrogel-coated latex-, and hydrogel/silver-coated latex urinary catheters. Degrees of adherence within 2 h were determined with cells radiolabeled with leucine. Adherence was greatest and equivalent on silicone and latex catheters. Adherence of four strains of Escherichia coli to the hydrogel/silver-coated catheter was decreased by 50% to 99% in comparison with the other catheters. Repeat testing with strains of E. coli and Pseudomonas aeruginosa with over 50 catheters demonstrated a consistency in the inhibition. The hydrophilic coating of the catheter appeared to be primary in the decreased adherence phenomenon followed by a secondary biocidal effect of the silver ion.

Pure silver-, silver oxide- and silver chloride-treated surfaces in comparison to polypropylene inhibited both growth and adherence from saline of Serratia marcescens, Staphylococcus epidermidis, Pseudomonas aeruginosa and Candida albicans. These same organisms demonstrated enhanced adherence to an Ion-Beam-Assisted-Deposited silver surface followed by loss of viability. This type of surface in contrast to the other silver surfaces did not produce zones of inhibition in agar diffusion tests.

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