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S. Zhang, D. G. Ahearn, R. D. Stulting, R. B. Simmons, S. A. Crow, Jr.; Survival and Distribution of Fusarium and Acanthamoeba in Drying MPS. Invest. Ophthalmol. Vis. Sci. 2008;49(13):5521.
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To examine further the association between the recent outbreaks of microbial keratitis caused by unusual organisms and the contamination of multipurpose contact lens disinfection solutions (MPS) during use.
Conidia of representative isolates of the Fuarium solani-F. oxysporum complexes and trophozoites of Acanthamoeba castelanii were inoculated (~104 ml-1) into 1-2 ml of MPS that contained either polyhexamethylene biguanide (PHMB) or polyquaternium-1 (PQ) as active disinfecting components. Phosphate-buffered saline (PBS) served as a control. These preparations were examined microscopically during drying under a laminar flow hood at ambient temperatures.
The various MPS formed distinct and characteristic concentric bands of precipitates and viscous globules while drying. The distribution of the conidia, trophozoites and amoebic cysts among the distinctive residual- precipitate patterns varied for the different MPS. Cysts were not evident in the initial trophozoite inocula. Fusaria survived the drying process in at least one replicate for all MPS and the PBS. The conidia in the drying MPS were either scattered in bands or agglomerated in viscous globules. Cysts and globose trophozoites, 0-5 in number, were observed among replicates of all MPS except one dried PHMB formulation that contained from about 8-20 mature cysts per dried MPS sample. Determination of definitive numbers was difficult because of occasional clumping of cysts and the density of precipitate patterns.
We hypothesize that drying MPS may stimulate rapid cyst formation within 6-8 h by some isolates of Acanthamoeba and induce rapid formation or selection of dormant resistant cells among some fusaria. The residual patterns of drying MPS over a 24 h period may provide a simple and rapid test for identification of residual solution in contact lens cases and verification of the MPS in used containers. These data may be of aid in epidemiological investigations of MPS-associated microbial keratitis.
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