Evaluating the preservative effectiveness of RGP lens care solutions.

We examined the antimicrobial preservative efficacy of nine rigid gas permeable (RGP) contact lens care solutions by challenging them in a laboratory study with both standard test organisms and preservative-resistant strains. Solutions containing polyhexamethylene biguanide (PHMB), such as Boston Advance (15 ppm) and a Boston Advance Enhanced Comfort Formula (5 ppm PHMB + 30 ppm chlorhexidine gluconate [CHG]) were most effective at rapidly killing vegetative cells, killing all bacteria and yeast by 6 hours. Boston Advance only slightly reduced the number of Aspergillus niger spores during the 28 day study, but Boston Advance Enhanced Comfort Formula reduced the spores by almost 3 logs by 14 days and by 4 logs by 21 days. Thimerosal-preserved Soaclens only reduced Staphylococcus aureus by 1 log at 6 hours, but at 1 day all tested organisms including S. aureus and A. niger were killed. Barnes Hind Gas Permeable Wetting and Soaking Solution, containing 50 ppm CHG, had little effect on adapted Serratia marcescens or Pseudomonas cepacia during the 28 day study. Allergan Wet-N-Soak Plus, containing 30 ppm benzalkonium chloride (BAK), was also unable to kill adapted S. marcescens or P. cepacia. CIBA Vision Premus (40 ppm BAK) was unable to kill adapted S. marcescens. Alcon Opti-Free, with 50 ppm polyquaternium-1 (polyquad), did not kill P. cepacia. Sherman Stay-Wet 3, containing 0.1% benzyl alcohol, was not effective against S. marcescens (adapted or unadapted), P. cepacia, or A. niger. Sherman DeStat 3, which contains 0.1% benzyl alcohol plus surfactants and five times the concentration of EDTA as in Stay-Wet 3, was able to kill all the vegetative cells by 7 days but did not significantly reduce A. niger.

Selective medium for Pseudomonas aeruginosa that uses 1,10-phenanthroline as the selective agent.

The MIC of 1,10-phenanthroline for 35 Pseudomonas aeruginosa strains was 128 micrograms/ml, whereas 32 micrograms or less per ml inhibited all other microorganisms tested. On the basis of these results, a selective agar for P. aeruginosa which contained 15 g of Trypticase soy broth (BBL Microbiology Systems), 15 g of agar, and 0.1 g of phenanthroline per liter was formulated. Forty-four P. aeruginosa strains yielded a mean efficiency of plating on this medium of 79% of the counts obtained on Trypticase soy agar, which was significantly higher than that obtained with pseudomonas isolation agar or Pseudosel agar. Pseudomonas cepacia, Pseudomonas fluorescens, Pseudomonas putida, Pseudomonas stutzeri, representatives of 13 other genera (including gram-negative rods, gram-positive rods, and cocci), and a yeast were not recovered within 48 h at 35 degrees C when approximately 10(7) CFU were plated on this medium. Only small colonies from one strain each of P. fluorescens and P. putida could be seen at 3 and 7 days, respectively, and they had an efficiency of plating of only less than 0.001%. When 10(7) CFU of either of these strains was plated with 10(2) CFU of P. aeruginosa, it did not interfere with the quantitative recovery of P. aeruginosa.