Purpose. To compare the susceptibilities of clinical isolates of Serratia marcescens and the standard ISO ATCC 13880 strain to five contact lens multipurpose disinfection solutions (MPDSs).
Methods. Five commercially available MPDSs, containing either a polymeric biguanide or polyquaternium, were tested using ISO/CD 14729 stand-alone test for contact lens care products against four ocular isolates of S. marcescens and the strain ATCC 13880. An average log reduction in bacterial numbers at the manufacturer's minimum recommended disinfection time was determined and compared with the criteria for stand-alone disinfection products for each MPDS against each bacterial strain.
Results. All the MPDSs tested met the stand-alone criteria of 3-log reduction of viable bacteria against the ATCC strain of S. marcescens. However, there was more variability in their ability to meet disinfection criteria when tested against the clinical isolates. Two of the clinical isolates were significantly more resistant to disinfection than was the recommended ISO strain (p ≤ 0.034). Two of the polyquaternium-1-based disinfection solutions (solutions D and E, p ≤ 0.005) were less effective overall than the other MPDSs against S. marcescens.
Conclusions. The importance of strain selection for the testing of MPDSs is indicated, and the use of a single laboratory strain may be insufficient to provide assurance that the disinfection solution will be effective against clinical isolates. Furthermore, clinical isolates of S. marcescens may show increased resistance to disinfection with polyquaternium.