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K. S. Ambrus, M. Nikolic, P. Juarez, A. Lam, N. Brady, S. Kilvington; Microbiology of Contact Lens Cases: Contamination Rates, Prevalent Organisms, Resistancy to MPS Products and Growth of Acanthamoeba. Invest. Ophthalmol. Vis. Sci. 2009;50(13):5661.
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Even in compliant users, contact lens storage cases can harbor large numbers of microbes. Here, the bacteriology of storage cases from asymptomatic lens wearers was investigated. Significant levels of case contamination were found. Several species of bacteria were uniquely associated with the use of a multipurpose solution (MPS-A) and these were found to support the growth of Acanthamoeba sp.
Lens cases from subjects using three MPS were collected after 1 month’s use. The contents were cultured to quantify bacteria and isolates identified using Biolog system. Selected isolates were tested for resistance to the MPS used by the wearer. In addition, the ability of the bacterial isolates to support Acanthamoeba excystment and trophozoite replication was studied
Of 460 items examined (case solutions and lenses) 43% showed bacterial contamination (> 104 cfu/mL), with Stenotrophomonas maltophilia being most frequently isolated (23.9%). MPS-B showed overall contamination of 41% and MPS-C of 34%. The highest contamination rate, 55%, was found with users of MPS-A of which Chryseobacterium sp. (19.4%), Acidovorax sp. (10.5%), Raoutella sp. (9%), and Flavobacterium sp. (4.5%) were uniquely associated. Biocidal challenge testing of these isolates against MPS-A gave only 0-1.8 log kill after 6 hours. Inoculation of the organisms into storage cases with MPS-A resulted in an increase by 0.1-1.2 log after 7 days. The bacteria were able to support Acanthamoeba sp. excystment and trophozoite replication.
This study shows that contact lens storage cases can become colonized with bacteria after a short period of use. The bacterial biodiversity would appear to be selected for by the type of antimicrobial disinfectant in the MPS used. The bacteria were resistant to the respective MPS and can grow in its presence over time. These bacteria were found to support the growth of Acanthamoeba sp. and could provide a food source for the organism if introduced into a storage case.
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