Amoebicidal efficiencies of various diamidines against two strains of Acanthamoeba polyphaga

Abstract

The first medical cure of Acanthamoeba keratitis was obtained by use of propamidine isethionate. Since then, it has been the basic drug recommended for use in treatment. Because some Acanthamoeba strains have been reported to be resistant to propamidine and propamidine was found to be only weakly cysticidal, superior homologs such as butamidine, pentamidine, hexamidine, heptamidine, octamidine, and nonamidine were tested for their amoebicidal effects on two Acanthamoeba strains isolated from patients with keratitis. Trophozoicidal and cysticidal efficiencies were found to be increased from propamidine to nonamidine; i.e., when the alkyl chain connecting the two benzene rings in their molecular structures was elongated, in comparison with propamidine, hexamidine and octamidine were the most amoebicidal molecules. As a result of these data, a kinetic study carried out on propamidine, hexamidine, and octamidine demonstrated that the amoebicidal effects resulted from two events: the diffusion of molecules through the plasma membrane or the double wall of trophozoites or cysts, respectively, and the lethal effects of molecules on amoebic protoplasm. The diffusion kinetics were increased when the alkyl chain was elongated, i.e., with an increase in the lipophilic properties of molecules. In contrast, the lethal effect kinetics were found to be unchanged by this elongation, indicating that they originated from the cationic surface-active properties induced by the protonated amidine groups attached to each benzene ring, which themselves remained unchanged from one molecule to the other. These results strongly advocate the immediate replacement of propamidine by hexamidine in the medical treatment of Acanthamoeba keratitis; in France, 0.1% hexamidine eyedrops are available (Desomedine). The results also advocate clinical investigations on the efficiency and toxicity of octamidine, which appears to be the most amoebicidal diamidine in vitro.Acanthamoeba keratitis is a serious and potentially devastating corneal infection generally seen in soft contact lens wearers. The responsible amoeba has been detected in the human cornea in two forms: as fragile trophozoites and as resistant dormant cysts. The medical treatment of this ocular infection remains very difficult because of the lack of antiamoebic drugs effective against cysts, which are responsible for frequent and serious recurrences.Since the first medical cure reported in 1985 (16), propamidine isethionate, an antimicrobial agent belonging to the diamidine family, has been the basic drug recommended for use in treatment, which includes the use of topical neomycin sulfate and various imidazoles (2,5,7,8,15). Unfortunately, propamidine is poorly cysticidal and the resistance of some Acanthamoeba strains has been reported (6, 10). In the present study, superior homologs of propamidine were tested for their amoebicidal effects both on trophozoites and cysts with the intent of finding whether some of them are more amoebicidal and, especially, cysticidal than propamidine. At...

Acanthamoeba keratitis update—incidence, molecular epidemiology and new drugs for treatment

“…The results given in this paper for the MTAC and MCC tests, using the commercial preparation of hexamidine (Desmodine), disagree with those of Perrine et al 61 and Brasseur et al 62 and find it to be less effective than propamidine. These and other results are given in Table 2.…”

Pathogenesis of microbial keratitis

“…The former drugs are membrane-acting cationic biocides that interact with negatively charged surface proteins of Acanthamoeba resulting in leakage of the cellular components [146]. The latter however exert their amoebicidal effects via cationic surface-active properties inducing structural changes resulting in cell permeability and are effective DNA synthesis inhibitors [39].…”

Determination of Amoebicidal Activities of Multipurpose Contact Lens Solutions by Using a Most Probable Number Enumeration Technique

“…The MPN method has been used extensively for the microbiological examination of water, but more recently, it has been adapted to suit the enumeration of a variety of organisms other than bacteria, for example, the enumeration of viable planktonic diatoms from sediment samples (13) and a variety of protozoa from soils and infiltration systems (11,50). In 1995, Perrine et al (38) used the MPN technique to enumerate Acanthamoeba in studies determining the amoebicidal efficiencies of various diamidines against two strains of Acanthamoeba polyphaga; MPNs were read off tables published by the American Public Health Association (1) without modification. However, the investigators gave no detailed comment on the actual usefulness of this method when it was applied to the enumeration of Acanthamoeba.…”

“…With the exception of one study (38), a technique of organism enumeration that has been largely overlooked is the most probable number (MPN) technique, which is a means for estimating, without any direct counting, the density of organisms present in a liquid. The MPN technique was first introduced by McCrady (30,31) and consists of the incubation of aliquots of sample dilutions with appropriate media at an ideal temperature for the desired organism.…”