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Original Research

Acanthamoeba encystment: multifactorial effects of buffers, biocides, and demulcents present in contact lens care solutions

, , , &
Pages 1905-1913 | Published online: 13 Oct 2015

Figures & data

Table 1 Summary of test solutions in this study

Figure 1 Impact of buffer agents on Acanthamoeba castellanii encystment rates.

Note: Red bar represents percentage of trophozoites that encysted after 24 hours’ incubation, while blue bars represent percentage of population that did not (*P<0.05).
Abbreviations: BBS, borate-buffered saline; BBS-PAPB-PG+, solution containing BBS, PAPB and PG; BBS-PAPB-PG−, solution containing BBS and PAPB, without PG; PAPB, polyaminopropyl biguanide; PBS, phosphate-buffered saline; PBS-PAPB-PG+, solution containing PBS, PAPB and PG; PBS-PAPB-PG−, solution containing PBS and PAPB, without PG; PG, propylene glycol; POS, positive.
Figure 1 Impact of buffer agents on Acanthamoeba castellanii encystment rates.

Figure 2 Encystment rates of Acanthamoeba castellanii exposed to PBS-PAPB-PG+ control and to 1% PG with varying concentrations of H2O2.

Note: Red bar represents percentage of trophozoites that encysted after 24 hours’ incubation, while blue bars represent percentage of population that did not (*P<0.05).
Abbreviations: PAPB, polyaminopropyl biguanide; PBS, phosphate-buffered saline; PBS-PAPB-PG+, solution containing PBS, PAPB and PG; PG, propylene glycol.
Figure 2 Encystment rates of Acanthamoeba castellanii exposed to PBS-PAPB-PG+ control and to 1% PG with varying concentrations of H2O2.

Figure 3 Encystment rates of Acanthamoeba castellanii exposed to phosphate-buffered solutions that contained either 0.25 ppm polyaminopropyl biguanide (PAPB) or 3% H2O2 with increasing concentrations of povidone (POV) and propylene glycol (PG).

Notes: Red bars represent percentage of trophozoites that encysted after 24 hours’ incubation, while blue bars represent percentage of population that did not (P<0.05 for PAPB-2.0% POV vs PAPB-0.0% POV; *P<0.05 for all PAPB-PG containing solutions vs PAPB-0.0% PG).
Figure 3 Encystment rates of Acanthamoeba castellanii exposed to phosphate-buffered solutions that contained either 0.25 ppm polyaminopropyl biguanide (PAPB) or 3% H2O2 with increasing concentrations of povidone (POV) and propylene glycol (PG).

Figure 4 Encystment rates of Acanthamoeba castellanii trophozoites exposed to PeroxiClear (PER-1), PeroxiClear solution lacking propylene glycol (PER-1a), PeroxiClear solution lacking H2O2 (PER-1b), and PeroxiClear solution lacking propylene glycol and H2O2 (PER-1c) for 24 hours, 7 days, and 14 days. No significant differences were observed across any of the solutions tested regardless of the time point (P>0.05).

Notes: Red bars represent percentage of trophozoites that encysted, while blue bars represent percentage of population that did not. The + and − symbols indicate whether or not the 3% H2O2 and/or the 1% PG were included within the solution.
Abbreviation: PG, propylene glycol.
Figure 4 Encystment rates of Acanthamoeba castellanii trophozoites exposed to PeroxiClear (PER-1), PeroxiClear solution lacking propylene glycol (PER-1a), PeroxiClear solution lacking H2O2 (PER-1b), and PeroxiClear solution lacking propylene glycol and H2O2 (PER-1c) for 24 hours, 7 days, and 14 days. No significant differences were observed across any of the solutions tested regardless of the time point (P>0.05).

Figure 5 (A) Encystment rates of Acanthamoeba castellanii exposed to PBS-PAPB-PG+ control, PeroxiClear (PER-1), and Clear Care® (PER-2) solutions. Encystment rates for both PER-1 and PER-2 were <1% after 24 hours’ incubation, significantly (*P<0.05) lower than the positive control solution. (B) For stand-alone biocidal efficacy testing, log10 reduction values of A. castellanii exposed to PER-1, and PER-2 solutions reached complete kill at 6 and 24 hours, while PBS control did not.

Note: Red bar represents percentage of trophozoites that encysted after 24 hours’ incubation, while blue bars represent percentage of population that did not.
Abbreviations: PAPB, polyaminopropyl biguanide; PBS, phosphate-buffered saline; PBS-PAPB-PG+, solution containing PBS, PAPB and PG.
Figure 5 (A) Encystment rates of Acanthamoeba castellanii exposed to PBS-PAPB-PG+ control, PeroxiClear (PER-1), and Clear Care® (PER-2) solutions. Encystment rates for both PER-1 and PER-2 were <1% after 24 hours’ incubation, significantly (*P<0.05) lower than the positive control solution. (B) For stand-alone biocidal efficacy testing, log10 reduction values of A. castellanii exposed to PER-1, and PER-2 solutions reached complete kill at 6 and 24 hours, while PBS control did not.