Biocidal efficacy of multipurpose solutions against Gram‐negative organisms associated with corneal infiltrative events

BACKGROUND: Because corneal infiltrative events (CIEs) may result from bacterial components on contact lenses, which can come from contaminated lens cases, we evaluated the biocidal efficacy of five multipurpose solutions against Gram‐negative commonly isolated and CIE‐associated organisms. METHODS: Of the multipurpose solutions tested, one contained polyhexamethylene biguanide (PHMB)/polyquaternium‐1 (PQ‐1; Bausch & Lomb Incorporated: Biotrue), one contained alexidine dihydrochloride (alexidine)/PQ‐1 (AMO: RevitaLens OcuTec) and three contained PQ‐1/myristamidopropyl dimethylamine (MAPD; Alcon: Opti‐Free PureMoist, PQ‐1/MAPD‐1; Opti‐Free RepleniSH, PQ‐1/MAPD‐2; Opti‐Free Express, PQ‐1/MAPD‐3). Challenge organisms were CIE‐associated Achromobacter xylosoxidans, Delftia acidovorans and Stenotrophomonas maltophilia at manufacturer‐recommended durations (stand‐alone), in lens cases without lenses (up to seven days) and in lens cases with etafilcon A lenses (up to 30 days). RESULTS: In stand‐alone testing against CIE‐associated organisms, PHMB/PQ‐1 and alexidine/PQ‐1 were significantly superior versus MAPD‐based multipurpose solutions against A. xylosoxidans (all p ≤ 0.01), D. acidovorans (all p ≤ 0.001) and S. maltophilia (all p ≤ 0.05). In lens cases, PHMB/PQ‐1 and alexidine/PQ‐1 achieved greater than 3‐log reductions against all challenge organisms at all times evaluated. PQ‐1/MAPD‐1 achieved a greater than 3‐log reduction against D. acidovorans at 24 hours; PQ‐1/MAPD‐1 and PQ‐1/MAPD‐3 achieved greater than 3‐log reductions at seven days against all organisms. In lens cases with lenses, PHMB/PQ‐1 and alexidine/PQ‐1 achieved greater than 3‐log reductions against all organisms at all times. PQ‐1/MAPD‐1 and PQ‐1/MAPD‐3 achieved greater than 3‐log reductions at seven or more days against all organisms. PQ‐1/MAPD‐2 did not achieve a greater than 3‐log reduction at any time; some regrowth was observed. CONCLUSIONS: PHMB‐ and alexidine‐based multipurpose solutions demonstrated significantly greater biocidal activity compared with PQ‐1/MAPD‐based agents against Gram‐negative organisms commonly isolated and CIE‐associated pathogens.