Photosensitized inactivation of Acanthamoeba palestinensis in the cystic stage

Abstract

Aims: To develop alternative approaches for medical and environmental control of pathogenic Acanthamoeba spp. by means of photodynamic treatment with a tetracationic Zn(II)‐phthalocyanine (RLP068). Methods and Results: Incubation of cyst cultures with RLP068 for 1 h caused an accumulation of readily detectable concentrations of the phthalocyanine, even at doses as low as 0·5 μmol l−1. RLP068 exhibited no dark toxicity towards cysts up to 5 μmol l−1 concentration. A decrease of c. 50% in cyst survival in comparison with controls was measured upon incubation of the cysts with 0·5 μmol l−1 RLP068, followed by exposure to light (600–700 nm) for 20 min at a fluence rate of 50 mW cm−2 (60 J cm−2). After incubation with 3 and 5 μmol l−1 RLP068 and irradiation, the cysts lost their excystment ability as early as day 5 and up to day 10, and were clearly damaged when observed under an interference contrast microscope. Conclusions: These data indicate the promising use of RLP068 in phototreatment of diseases caused by pathogenic amoebae and in initial disinfection of wastewaters. Significance and Impact of the Study: Rapid and extensive photodamage may be induced in the highly resistant cystic stages by means of 600‐ to 700‐nm light sources.

Photodynamic therapy in the treatment of microbial infections: Basic principles and perspective applications

“…In all cases, the driving force for binding of the cationic photosensitizer to the negatively charged functional groups on the cell surface is of electrostatic nature, hence the binding process is completed within a very short time period: several independent reports indicate that extending the preirradiation incubation from 5 minutes to 1-2 hours has no effect on the amount of photosensitizer bound to the microbial cells [17,42,68]. One exception is represented by cysts of protozoa or yeasts where incubation times as long as 30 minutes are necessary in order to achieve sufficiently large endocellular concentrations of the photosensitizer [66,69]. In any case, the critical target for photosensitized killing of microbial cells appears to be represented by the -Fluorescence microscopy studies carried out on both bacteria and protozoa show that the photosensitizer is located at the level of the plasma membrane prior to irradiation and diffuses into the cell only after exposure to light for several minutes, corresponding with an extensive decrease in survival.…”

“…[78]). As a consequence, a variety of targets, including DNA, undergo photooxidative modification at later stages of the overall photoprocess, even though such damage is not directly correlated with cell death [24,69,75,78,80]. Thus, any major influence of DNA modification seems unlikely since (a) Deinococcus radiodurans, which possesses a very efficient DNA repair mechanism, is readily killed by photodynamic processes [81]; and (b) wild E. coli strains, as well as E. coli strains which are defective for DNA repair mechanisms, display a closely similar sensitivity to photoinactivation by a tetracationic porphyrin [72].…”

Photodynamic antimicrobial therapy

“…Photoinactivation of promastigotes and amastigotes of Leishmania amazonensis was described in laboratory conditions [35]. Photoinactivation of Plasmodium falciparum and Acanthamoeba palestinensis was investigated, too [36,37].…”

Inactivation of Bacterial Pathogens following Exposure to Light from a 405-Nanometer Light-Emitting Diode Array

“…The rapidly increasing problem of microbial antibiotic resistance has ignited research interest into the use of PDI as an alternative antimicrobial treatment. Numerous in vitro PDI studies have been made involving microbial inactivation, with successful results for bacteria, fungi, yeasts, viruses, and parasites (29,7,12,2,5). Furthermore, recent work has shown that photosensitization of bacterial cells is independent of the antibiotic resistance spectrum (17).…”