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Acanthamoeba-Mediated Cytopathic Effect Correlates with MBP And Ng et al. Parasites & Vectors (2017) 10:625 DOI 10.1186/s13071-017-2547-0 RESEARCH Open Access Acanthamoeba-mediated cytopathic effect correlates with MBP and AhLBP mRNA expression Sook-Luan Ng1, Anisah Nordin2, Norzana Abd Ghafar3, Yusof Suboh2, Noraina Ab Rahim2 and Kien-Hui Chua1* Abstract Background: In recent years, the concern of Acanthamoeba keratitis has increased since the infection is often associated with contact lens use. Partial 18S rRNA genotypic identification of Acanthamoeba isolates is important to correlate with pathophysiological properties in order to evaluate the degree of virulence. This is the first report of genotypic identification for clinical isolates of Acanthamoeba from corneal scrapings of keratitis in Malaysia. This study is also the first to correlate the mRNA expression of MBP and AhLBP as virulent markers for axenic strains of Acanthamoeba. Results: In this study, ten clinical isolates were obtained from corneal scrapings. Rns genotype and intra-genotypic variation at the DF3 region of the isolates were identified. Results revealed that all clinical isolates belonged to the T4 genotype, with T4/6 (4 isolates), T4/2 (3 isolates), T4/16 (2 isolates) and one new genotype T4 sequence (T4/36), being determined. The axenic clinical isolates were cytopathogenic to rabbit corneal fibroblasts. MBP and AhLBP mRNA expression are directly correlated to Acanthamoeba cytopathic effect. Conclusions: All ten Malaysian clinical isolates were identified as genotype T4 which is predominantly associated with AK. Measuring the mRNA expression of Acanthamoeba virulent markers could be useful in the understanding of the pathogenesis of Acanthamoeba keratitis. Keywords: Keratitis, Acanthamoeba, Genotype, Cytopathic, MBP, AhLBP Background infections [5, 6]. The first reported AK case in Malaysia was Photophobia, severe pain, redness and tearing are the com- also related with a contaminated contact lens [7]. mon symptoms of Acanthamoeba keratitis (AK). AK is a Morphological classification of Acanthamoeba,as rare but sight-threatening corneal infection which is caused described by Pussard & Pons [8] is less reliable due to by the free-living amoebae of the genus Acanthamoeba [1]. the possible alteration of cyst shape by the ionic strength These organisms are widely distributed in the air, soil, water of the growth medium [9]. Genotyping is a useful tool in and domestic water tap, etc. [2, 3]. AK is characterized by the taxonomic and epidemiological study of AK and severe pain due to radial neuritis, and a ring-like stromal in- provides a correlation between genotype and phenotypes filtrate appears in the advanced stage of AK [4]. Poor vision of Acanthamoeba isolates [10]. Recently, the most prom- or even visual loss occurs due to corneal scarring if proper ising method to identify the Acanthamoeba genotype is treatment is delayed. In recent years, the concern of AK has the sequencing of the complete nuclear 18S rRNA (Rns) increased since this infection is often associated with contact gene [11]. Following this, the previous studies found that lens contamination, especially in urban areas. The increasing the partial 18S rRNA gene sequences which contain the use of contact lenses for visual and cosmetic purposes, Acanthamoeba genus-specific amplicon (ASA.S1) were combined with improper cleaning and storage practices sufficient to identify the Acanthamoeba Rns genotypes. could be the reason for the increase in the number of AK ASA.S1 includes a region called diagnostic fragment 3 (DF3) which encodes a highly variable stem 29-1used for * Correspondence: [email protected] genotype discrimination [11, 12]. There were 20 geno- 1Department of Physiology, Faculty of Medicine, Universiti Kebangsaan Malaysia, Jalan Yaacob Latif, 56000 Kuala Lumpur, Bandar Tun Razak, Malaysia types identified and designated as T1-T4 [13], T5-T12 Full list of author information is available at the end of the article [14], T13 [15], T14 [16], T15 [17], T16 [18], T17 [19], © The Author(s). 2017 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. Ng et al. Parasites & Vectors (2017) 10:625 Page 2 of 14 T18 [20] and T19-T20 [21]. The T4 genotype is the 150 μl of heat-killed Escherichia coli at 30 °C. A small piece predominant sequence type associated with AK [14]. of agar containing cysts was removed from the primary cul- Other Rns genotypes have also been reported as a causa- ture and transferred to another new NNA plate, which was tive agent for AK, such as T2 [22], T3 [14], T5 [10], T6 continued until it was totally free from co-contaminant, [23], T10 [19], T11 [13] and T15 [24]. and the culture is known as a xenic culture. Two week-old Physiological properties and genotyping of Acanth- cystswereharvestedfromtheNNAplateandwashedwith amoeba should be studied simultaneously to evaluate the PAGE amoebic saline (PAS) solution twice and then incu- pathogenic potential of the isolates. Cytopathic tests could bated overnight with 0.5 N sterile HCl during the process be used as a pathogenic marker to determine the degree of of axenization. The cysts were washed with PAS solution virulence of the interested Acanthaoeba isolates; virulent three times and centrifuged at 500× g for 10 min to obtain isolates are able to induce a cytopathic effect but non- the cyst pellet. The cyst pellet was suspended with enriched pathogenic Acanthamoeba cannot [25]. The cytoadherence PYG medium (4% peptone, 4% yeast extract, 2% glucose) of Acanthamoeba to mannosylated glycoproteins on the supplemented with 10% fetal bovine serum (FBS; Gibco, corneal epithelial cells is a critical step to initiate the Grand Island, New York, USA), 1% antibiotic-antimycotic Acanthamoeba keratitis [26, 27]. It has been shown that the (Gibco) and cultured in a T-25 flask (Greiner Bio-One, adhesion of Acanthamoeba tohostcellsismediatedbythe Frickenhausen, Germany) at 37 °C. The PYG medium was mannose binding protein (MBP) on the surface of tropho- adjusted to pH 7.2. The axenic trophozoites were excysted zoites. Through MBP-mediated adhesion to host cells, the in the PYG medium after 1 day of incubation. The axenic amoebae produce a contact-dependent mechanism which cultures were subcultured every 3 days. able to exhibit a cytopathic effect involving direct cytolysis, phagocytosis, apoptosis and proteolytic activity [28]. Identification of Acanthamoeba Acanthamoeba trophozoites are stimulated to produce A wet smear of xenic cultures was observed under a 133 kDa mannose induced protein after exposure to the light microscope for the morphology features of tropho- upregulated mannose-specific lectins in the ulcerated cor- zoites and cysts. The diameter of cysts was measured neal epithelium and lead to the activation and upregula- using the VideoTest Morphology software (VideoTest, tion of matrix metalloproteinases in corneal cells [29, 30]. Saint Petersburg, Russia, version 5). Isolates were classi- Besides that, the ability of Acanthamoeba to adhere on the fied as Acanthamoeba spp. groups I, II or III according laminin of the Bowman’s membrane and extracellular to the keys of Pussard & Pons [8]. matrix via its Acanthamoeba laminin binding protein The 18S rDNA identification of Acanthamoeba spp. (AhLBP), is also important to allow Acanthamoeba to was performed as per the following procedures. Acanth- invade the corneal stroma in AK [31]. Acanthamoeba amoeba isolates with a density of 5 × 105 trophozoites were capable of adhering and invading the extracellular were harvested from NNA plates and DNA was extracted matrix components such as laminin and collagen type I with a commercially available AccuPrep® Genomic DNA [32]. Previous studies provided information on the role of Extraction Kit (Bioneer, Daejeon, Korea). The pelleted MBP and AhLBP as the marker of pathogenicity, mostly trophozoites were resuspended in 200 μl PAS solution, in protein level and a few in DNA works [31, 33–36]. mixed with 20 μl proteinase K and 200 μl binding buffer Genotyping of Acanthamoeba isolates is still under- and incubated at 60 °C for 10 min. The lysate was trans- reported in Malaysia. This study, therefore, aimed to ferred into the upper reservoir of the binding column determine the Rns genotype of Malaysian clinical isolates tube after added 100 μl isopropanol. The tube was centri- from corneal scrapings by analyzing the intra-genotypic fuged at 8000× g for 1 min. The binding column tube variation at the DF3 region. The characterization of mor- was washed with 500 μl ethanol twice and the DNA was phological and cytopathic properties for Acanthamoeba eluted with 200 μl elution buffer. After that, amplicon isolates was studied. This study is the first evaluation of ASA.S1 was amplified by PCR using Platinum® Taq DNA mRNA expression of MBP and AhLBP quantitatively for Polymerase High Fidelity kit (Invitrogen, Carlsbad, CA, Acanthamoeba spp. and correlates both virulent markers USA) following the recommended protocol with genus- and their growth rate with cytopathic effect. specific primers JDP1 and JDP2 (Table 2). The PCR reac- tion was started with incubation at 94 °C for 3 min, Methods followed with 35 cycles of 30 s at 94 °C, 30 s at 61 °C and Sample collection 1 min at 72 °C. Incubation for another 5 min at 72 °C Ten Acanthamoeba isolates are maintained cultures which was done for final extension. Amplification products were were obtained from the Acanthamoeba Culture Laboratory visualized by ethidium bromide staining in 1.5% agarose of Parasitology Department, UKM. The source of the gel electrophoresis and followed by gel extraction using samples is described in Table 1.
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