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

Figures & data

Table 1 Summary of test solutions in this study

Test solution	Key components	Experiment
PBS-PAPB-PG+	PBS, 0.25 ppm PAPB, 0.5% PG	Figure 1
PBS-PAPB-PG−	PBS, 0.25 ppm PAPB	Figure 1
BBS-PAPB-PG+	BBS, 0.25 ppm PAPB, 0.5% PG	Figure 1
BBS-PAPB-PG−	BBS, 0.25 ppm PAPB	Figure 1
H2O2 range	PBS, 1% PG, H2O2 range	Figure 2
PeroxiClear (PER-1), Bausch & Lomb	PBS/citrate, 1% PG, 3% H2O2	Figure 3
PER-1a	PER-1, minus PG	Figure 3
PER-1b	PER-1, minus H2O2	Figure 3
PER-1c	PER-1, minus PG and H2O2	Figure 3
PG range in PAPB	PBS, 0.25 ppm PAPB, 0%–1% PG	Figure 4
POV range in PAPB	PBS, 0.25 ppm PAPB, 0%–2% POV	Figure 4
PG range in H2O2	PBS, 0.25 ppm 3% H2O2, 0%–1% PG	Figure 4
POV range in H2O2	PBS, 0.25 ppm 3% H2O2, 0%–2% POV	Figure 4
PER-1	PBS/citrate, 1% PG, 3% H2O2	Figure 5
Clear Care (PER-2), Alcon Laboratories	PBS, 3% H2O2	Figure 5

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; PER-1a, PeroxiClear solution lacking propylene glycol; PER-1b, PeroxiClear solution lacking H₂O₂; PER-1c, PeroxiClear solution lacking propylene glycol and H₂O₂; PG, propylene glycol; POV, povidone.

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 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 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 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 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.