PURPOSE:

Acanthamoeba keratitis (AK) is a devastating ocular infection that can lead to corneal damage and blindness. A. castellanii (A.c) and A. polyphaga (A.p) are keratitis-causing strains utilized in disinfection efficacy tests and understanding amoebicidal activity of contact lens multi-purpose solutions (MPS) against broader Acanthamoeba strains can provide added value. The purpose of this study was to evaluate the efficacy of a unique (Biotrue® Hydration Plus) and two comparator MPS against ocular strains of Acanthamoeba.

METHODS:

A.c (ATCC 50370, PRA-105, and 50498) or A.p (ATCC 30461, 50371, and 50495) trophozoites were prepared to challenge three MPSs: MPS-1 (0.00015% polyquarternium-1 [PQ-1], 0.0005% polyaminopropyl biguanide [PAPB], and 0.00025% alexidine dihydrochloride); MPS-2 (0.0006% myristamidopropyl dimethylamine and 0.001% PQ-1); MPS-3 (0.00016% alexidine dihydrochloride and 0.0003% PQ-1). Disinfection by MPS-1 was determined at 4 hours and MPS-2 and -3 at 6 hours after inoculation. Recovery of Acanthamoeba was performed by serially diluting in a 96-well microtitre plate, adding E. coli and incubating for 14 days at 26-30°C. Acanthamoeba recovery values were determined using the Spearman-Karber method and Mean Log₁₀ Reduction (MLR) values were calculated.

RESULTS:

All three MPS solutions showed strong disinfection efficacy against A.c ATCC 50370 trophozoites with MLR of MPS-1 3.9, MPS-2 3.9, and MPS-3 3.9 (p>0.05) and A.c ATCC 50498 trophozoites with a MLR of MPS-1 3.3, MPS-2 3.4, and MPS-3 3.4 (p>0.05). MPS-1 and -2 (MLR=3.6 for both) showed increased efficacy of A.c ATCC PRA-105 trophozoites when compared to MPS-3 (MLR=2.6, P<0.001). all three mps solutions showed strong disinfection efficacy against a.p atcc 30461 trophozoites with mlr of mps-1 3.8 mps-2 3.8 and mps-3 3.7 p>0.05), MLR of MPS-1 3.7, MPS-2 3.7, and MPS-3, 3.7 (p>0.05) for A.p ATCC 50371 trophozoites, and MLR of MPS-1 4.1, MPS-2 4.1, and MPS-3 4.1 (p>0.05) for A.p ATCC 50495 trophozoites.

CONCLUSION:

MPS-1 (Biotrue® Hydration Plus) showed significantly greater effectiveness against one ocular strain of Acanthamoeba trophozoites when compared to one marketed MPS and similar effectiveness compared to another marketed MPS for multiple additional strains. Overall, the robust amoebicidal efficacy of this MPS supports its use in the protection of contact lens-wearing patients from the risk of AK.