Manal M. Gabriel

In vitro evaluation of the efficacy of a silver-coated catheter.

Abstract. 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.

Adherence of organisms to silver-coated surfaces

Pure silver-, silver oxide- and silver chloride-treated surfaces in comparison to polypropylene inhibited both growth and adherence from saline ofSerratia marcescens, Staphylococcus epidermidis, Pseudomonas aeruginosa andCandida 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.

Effects of silver on adherence of bacteria to urinary catheters: In vitro studies

Strains of Escherichia coli, Proteus mirabilis, Pseudomonas aeruginosa, Enterococcus faecalis, and Klebsiella pneumoniae, mostly from complicated urinary tract infections, showed reduced adherence to silver-treated silicone or latex catheters as compared with latex or silicone catheters. The relative degrees of cell adherence to catheters at 2 h or 18 h, as indicated by radiolabeled cell assays, were in general agreement with growth rate-reduction assays and scanning-electron-microscopy data. For strains of E. coli, the correlation between cell hydrophobicity and degree of adherence to catheters was not significant. Antibiotic resistance (tetracycline, sulfathiazine, neomycin, kanamycin) and silver resistance were not associated. The radiolabel adherence procedure provided a quantitative method for evaluating the relative antimicrobial efficacy of silver-treated catheters.

In vitro adherence of Pseudomonas aeruginosa to four intraocular lenses

Purpose: To compare the relative degrees of adherence of a clinical strain of Pseudomonas aeruginosa to the optic material of four intraocular lenses (IOLs). Setting: Center for Applied and Environmental Microbiology, Georgia State University, Atlanta, Georgia, USA. Methods: Intraocular lens optics made of poly(methyl methacrylate) (PMMA), AcrySof®‐acrylic, and silicone were included in this study. The IOLs were incubated in a minimal medium with cells of P. aeruginosa for 2 hours and 18 hours. Cells in the 2 hour experiment were prelabeled with 3H‐leucine; those in the 18 hour experiments were postlabeled. After rinsing the IOLs to remove loosely adherent cells, we determined the number of cells adhered to coded lenses from calibration curves of disintegrations per minute versus cells per square millimeter. Additional lenses were incubated with P. aeruginosa and examined with scanning electron microscopy. Results: The adherence of P. aeruginosa in order of increasing magnitude was AcrySof‐acrylic < PMMA < silicone 1 < silicone 2. The differences between all groups were statistically significant. The scanning electron microscopy observations were in general agreement with the radiolabel studies. Conclusions: The AcrySof‐acrylic IOL was less susceptible to primary adherence and 18 hour biofilm formation by P. aeruginosa than the PMMA and silicone IOLs, indicating that this material reduced pseudomonad adherence and the risk of endophthalmitis following cataract surgery.

Contact Lenses, Disinfectants, and Acanthamoeba Keratitis

Publisher Summary The chapter introduces Acanthamoeba Keratitis as a small filose, free-living amoeba with a cyst stage with ostioles. Acanthamoeba species are voracious predators of various Gram-negative bacteria, cyanobacteria, and fungi. Species are cannibalistic or pathogenic and grows in axenic enrichment culture and on defined media. The chapter discusses its taxonomy and various strains and culture conditions. The chapter also discusses the infectious nature of the amoeba. Acanthamoeba species cause the disease of the central nervous system which occurs primarily among the immunosuppressed or chronically ill, particularly AIDS patients. Acanthamoeba keratitis occurs most commonly among healthy normal individuals and seems associated with the minor trauma to the eye that accompanies contact lens wear. Failure to comply with proper hygienic procedures for cleaning and disinfecting lenses appears to be the major factor in most contact-lens-related eye infections. Species of Acanthamoeba dwell in damp soils and upper zones of mud in rivers and lakes and in anthropogenic water reservoirs. Cysts and trophozoites are carried by humans and distributed by wind, water, and animals. Species of Acanthamoeba readily colonize surface biofilms in swimming pools, hot tubs, heating-, ventilation-, and air-conditioning systems, and domestic water taps and eye-wash stations. The chapter also discusses disinfecting methods such as isopropyl alcohol cleaning system an “O 2 conditioner” which can kill both cysts and trophozoites within 30 minutes of exposure. Various reports indicate that trophozoites adhere preferentially over cysts to contact lenses and that various species and strains differentially adhere to the four Food and Drug administration (FDA) hydrogel lens groups. Both cysts and trophozoites show greater adherence to the higher-water-content lenses. Fastidious cleaning and disinfection of contact lenses, with particular care in lens storage, are necessary in the control of Acanthamoeba keratitis .

Creating antimicrobial surfaces and materials for contact lenses and lens cases.

Contact lenses are a safe and effective mode of vision correction used by more than 100 million people worldwide, yet some adverse responses to microbial contamination of contact lenses still occur. Various medical devices, including contact lens cases, currently use antimicrobial agents to eliminate or reduce microbial contamination at the surface. The application of antimicrobial surface technologies to contact lenses and lens cases is being explored. This article describes agents that hold promise for antimicrobial surfaces for contact lenses or lens cases.

Effects of polyhexamethylene biguanide and chlorhexidine on four species of Acanthamoeba in vitro

We determined the relative minimal inhibitory and minimal amoebicidal concentrations of chlorhexidine digluconate and polyhexamethylene biguanide for four species of Acanthamoeba. The amoebae were grown in peptone-glucose-yeast extract broth for 72 h in tissue culture flasks. Either washed trophozoites (approximately 10(5)) or cysts (approximately 10(5)) were incubated in the enrichment broth in 96 well microtiter trays. Antimicrobial concentrations of the biguanides were determined from microscopic examinations of methylene blue uptake and from subcultures. In general, killing was time dependent. Minimal amoebicidal concentrations at 24 h ranged from 50 to 100 mg/ml and to as low as 25 mg/ml by 72 h. Trophozoites were killed more rapidly than cysts. Both biguanides had similar levels of activity. A synergistic combination of chlorhexidine and polyhexamethylene biguanide (total concentration 25 mg/ml) was most evident for A. castellanii and A. polyphaga. Cysts of A. culbertsoni and A. hatchetti stained more rapidly after exposure to the combination of biguanides than to the single biguanides, but there were no statistically significant differences in the final numbers of dead or stained cysts after exposure to the combination or to the single biguanides.

Radiopacity additives in silicone stent materials reduce in vitro bacterial adherence

In vitro adherence of the nosocomial pathogensPseudomonas aeruginosa, Escherichia coli, Staphylococcus aureus, Staphylococcus epidermidis, Serratia marcescens, andCandida albicans to select radiopaque silicone compounds was lower than that observed for the base silicone (p<0.03). Except forE. coli ATCC 11775 andCandida albicans, all microorganisms showed significantly lower adherence to a silicone compound impregnated with tantalum in comparison with a silicone compound impregnated with barium sulfate (p<0.05). Surface hydrophobicity of the silicone compounds did not show a direct correlation with the concentration of radiopacity additives or with degree of bacterial adherence. Scatchard analyses of data indicated that the number of adherence sites forP. aeruginosa on the base silicone, BaSO4-silicone, and Ta-silicone were 9.2×106 per mm2, 6.1×106 per mm2, and 3.7×106 per mm2 respectively. As determined by the Langmuir adsorption isotherm, the dissociation constants for adheredP. aeruginosa to the base silicone, BaSO4-silicone, and Ta-silicone were 2.50×103 mm4, 1.45×103 mm4, and 6.27×103 mm4 respectively.Pseudomonas aeruginosa demonstrated first order kinetics of adherence to the silicone compounds with a half saturation time of 4.15 h for the base silicone, 1.06 h for the BaSO4-silicone, and 2.14 h for the Ta-silicone. The use of Ta-silicone stents may delay the development of ascending urinary tract infections.

[40] Primary adhesion of Pseudomonas aeruginosa to inanimate surfaces including biomaterials

Publisher Summary The primary adhesion of bacteria to surfaces is governed by cell surface–surface and substrate–surface changes and hydrophobicities. Cells after initial contact may be desorbed from a surface by repulsive or shear forces or they may become irreversibly bound. The degree and strength of the “irreversible” bond appear to be strain-variable properties. This chapter focuses on a strain of Pseudomonas aeruginosa that has been used in examining adhesion to contact lenses, intraocular lenses, and urinary catheters, as well as in assessment of the relative efficacies of various antimicrobials on adhered cells, but any strain with consistent primary adhesion to materials such as Teflon, polyethylene, polyvinyl acetate, or silicone could be employed. The strain, substratum, and other environmental conditions all interact in determining the degree of adhesion, with strain properties being dominant factors.

Adherence of Pseudomonas aeruginosa to inanimate polymers including biomaterials.

Cells of Pseudomonas aeruginosa were adhered to polymethyl methacrylate, polyvinyl acetate, polyvinyl chloride, polyhydroxyethyl methacrylate, mixed-acrylic, silicone, and natural latex materials. Planktonic bacteria and bacteria that adhered to the test materials were compared for their uptake of either L-[3,4,5-3H] leucine or [methyl-3H] thymidine during growth in a minimal medium. Leucine incorporation was reduced and thymidine uptake was negligible in adherent bacteria for up to 8 h following primary attachment by which time cells in the planktonic state showed active uptake of both substrates. These reduced uptake periods correlated with lag phases of growth of adherent cells as determined with a sonication-release plate count procedure and analyses of adenosine triphosphate (ATP). The extent of the lag phase of the adherent populations was dependent on initial densities of adhered cells and the nature of the substratum.