Abstract
PurposeTo compare the antimicrobial effect of topical anesthetics, antivirals, antibiotics, and biocides on the viability of Acanthamoeba cysts and trophozoites in vitro.MethodsAmoebicidal and cysticidal assays were performed against both trophozoites and cysts of Acanthamoeba castellanii (ATCC 50370) and Acanthamoeba polyphaga (ATCC 30461). Test agents included topical ophthalmic preparations of common anesthetics, antivirals, antibiotics, and biocides. Organisms were exposed to serial two-fold dilutions of the test compounds in the wells of a microtiter plate to examine the effect on Acanthamoeba spp. In addition, the toxicity of each of the test compounds was determined against a mammalian cell line.ResultsProxymetacaine, oxybuprocaine, and especially tetracaine were all toxic to the trophozoites and cysts of Acanthamoeba spp., but lidocaine was well tolerated. The presence of the benzalkonium chloride (BAC) preservative in levofloxacin caused a high level of toxicity to trophozoites and cysts. With the diamidines, the presence of BAC in the propamidine drops was responsible for the activity against Acanthamoeba spp. Hexamidine drops without BAC showed good activity against trophozoites, and the biguanides polyhexamethylene biguanide, chlorhexidine, alexidine, and octenidine all showed excellent activity against trophozoites and cysts of both species.ConclusionsThe antiamoebic effects of BAC, povidone iodine, and tetracaine are superior to the current diamidines and slightly inferior to the biguanides used in the treatment for Acanthamoeba keratitis.Translational RelevanceOphthalmologists should be aware that certain topical anesthetics and ophthalmic preparations containing BAC prior to specimen sampling may affect the viability of Acanthamoeba spp. in vivo, resulting in false-negative results in diagnostic tests.
Highlights
Acanthamoeba is a genus of small, free-living amoebae common to most soil and freshwater habitats.[1]
The inhibitory range against Acanthamoeba trophozoites for the anesthetics proxymetacaine, tetracaine, and oxybuprocaine were 9.75 to 39 lg/ml, whereas lidocaine produced no inhibition of growth until the 312- to 625-lg/ml range for both species
These results suggest that the use of topical anesthetics, especially with tetracaine, can have a potent antiamoebic effect and it may be an important contributory factor in the reported low sensitivity for culture from corneal scrape
Summary
Acanthamoeba is a genus of small, free-living amoebae common to most soil and freshwater habitats.[1]. There are approximately 4.1 million CL wearers in the United Kingdom,[2] and established independent risk factors for developing acanthamoeba keratitis (AK) in CL wearers include exposure to tap water in the home,[3,4] swimming or bathing when wearing CL,[4,5] poor lens hygiene,[4,5,6] and the use of rigid CLs in orthokeratology.[6] previous outbreaks of AK in both the United Kingdom and TVST j 2019 j Vol 8 j No 5 j Article 17. United States and have been attributed to efficacy issue with certain CL disinfections system.[7,8]
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