The effect of in vitro growth conditions on the resistance of Acanthamoeba cysts

Interactions between free-living amoebae and Cryptosporidium parvum: an experimental study

Free-Living Amebae (FLA) and Cryptosporidium oocysts occasionally share the same environment. From 2004 to 2016, Cryptosporidium was responsible for 60% of 905 worldwide waterborne outbreaks caused by protozoan parasites. The aim of this study was to evaluate interactions between C. parvum oocysts and two common FLAs (Acanthamoeba castellanii and Vermamoeba vermiformis) in a water environment. Encystment and survival of FLAs were evaluated by microscopy using trypan blue vital coloration. Oocysts were numerated on microscopy. Interactions were studied over time in conditions both unfavorable and favorable to phagocytosis. Potential phagocytosis was directly evaluated by several microscopic approaches and indirectly by numeration of microorganisms and oocyst infectivity evaluation. Occasional phagocytosis of C. parvum by FLAs was documented. However, oocyst concentrations did not decrease significantly, suggesting resistance of oocysts to phagocytosis. A temporary decrease of oocyst infectivity was observed in the presence of A. castellanii. The effect of these interactions on C. parvum infectivity is particularly interesting. The biofilm condition could favor the persistence or even the proliferation of oocysts over time. This study demonstrated interactions between C. parvum and FLAs. Further knowledge of the mechanisms involved in the decrease of oocyst infectivity in the presence of A. castellanii could facilitate the development of new therapeutic approaches.

Acanthamoeba spp. aggregate and encyst on contact lens material increasing resistance to disinfection

Introduction

Acanthamoeba keratitis is often caused when Acanthamoeba contaminate contact lenses and infect the cornea. Acanthamoeba is pervasive in the environment as a motile, foraging trophozoite or biocide-resistant and persistent cyst. As contact lens contamination is a potential first step in infection, we studied Acanthamoeba's behavior and interactions on different contact lens materials. We hypothesized that contact lenses may induce aggregation, which is a precursor to encystment, and that aggregated encystment would be more difficult to disinfect than motile trophozoites.

Methods

Six clinically and/or scientifically relevant strains of Acanthamoeba (ATCC 30010, ATCC 30461, ATCC 50370, ATCC 50702, ATCC 50703, and ATCC PRA-115) were investigated on seven different common silicone hydrogel contact lenses, and a no-lens control, for aggregation and encystment for 72 h. Cell count and size were used to determine aggregation, and fluorescent staining was used to understand encystment. RNA seq was performed to describe the genome of Acanthamoeba which was individually motile or aggregated on different lens materials. Disinfection efficacy using three common multi-purpose solutions was calculated to describe the potential disinfection resistance of trophozoites, individual cysts, or spheroids.

Results

Acanthamoeba trophozoites of all strains examined demonstrated significantly more aggregation on specific contact lens materials than others, or the no-lens control. Fluorescent staining demonstrated encystment in as little as 4 hours on contact lens materials, which is substantially faster than previously reported in natural or laboratory settings. Gene expression profiles corroborated encystment, with significantly differentially expressed pathways involving actin arrangement and membrane complexes. High disinfection resistance of cysts and spheroids with multi-purpose solutions was observed.

Discussion

Aggregation/encystment is a protective mechanism which may enable Acanthamoeba to be more disinfection resistant than individual trophozoites. This study demonstrates that some contact lens materials promote Acanthamoeba aggregation and encystment, and Acanthamoeba spheroids obstruct multi-purpose solutions from disinfecting Acanthamoeba.

Variables Affecting the Recovery of Acanthamoeba Trophozoites

While the results of Acanthamoeba testing have been extensively published, laboratories conducting such testing are left to develop their own methods in the absence of a standardized methodology. The wide disparity of methods has resulted in equally inconsistent reported results for contact lens care (CLC) products. This study's objective was to determine the source of these discrepancies by evaluating basic Acanthamoeba biology and their impact on antimicrobial efficacy testing, including the ability of a recovery method to stimulate a single trophozoite to proliferate. Antimicrobial efficacy testing was conducted using well-published Acanthamoeba strains, storage conditions, and growth-based recovery methods. To identify variables that influence results, test solutions with low Acanthamoeba disinfection rates were utilized to prevent differences from being masked by high log reductions. In addition, single-cell proliferation assays were executed to understand the growth requirements to stimulate trophozoite propagation in two recovery methods. These studies indicated that both nutrient density (>106 CFU) and the length of plate incubation (at least 14 days) could significantly influence the accurate recovery of trophozoites. Together, this study emphasizes the need to understand how Acanthamoeba trophozoites biology can impact test methods to create divergent results.

Identification and biochemical characterisation of Acanthamoeba castellanii cysteine protease 3

BACKGROUND

Acanthamoeba spp. are free-living amoeba that are ubiquitously distributed in the environment. This study examines pathogenic Acanthamoeba cysteine proteases (AcCPs) belonging to the cathepsin L-family and explores the mechanism of AcCP3 interaction with host cells.

METHODS

Six AcCP genes were amplified by polymerase chain reaction (PCR). Quantitative real-time PCR was used to analyse the relative mRNA expression of AcCPs during the encystation process and between pre- and post-reactivated trophozoites. To further verify the role of AcCP3 in these processes, AcCP3 recombinant proteins were expressed in Escherichia coli, and the hydrolytic activity of AcCP3 was determined. The influence of the AcCP3 on the hydrolytic activity of trophozoites and the toxicity of trophozoites to human corneal epithelial cells (HCECs) was examined by inhibiting AcCP3 expression using siRNA. Furthermore, the levels of p-Raf and p-Erk were examined in HCECs following coculture with AcCP3 gene knockdown trophozoites by Western blotting.

RESULTS

During encystation, five out of six AcCPs exhibited decreased expression, and only AcCP6 was substantially up-regulated at the mRNA level, indicating that most AcCPs were not directly correlated to encystation. Furthermore, six AcCPs exhibited increased expression level following trophozoite reactivation with HEp-2 cells, particularly AcCP3, indicating that these AcCPs might be virulent factors. After refolding of recombinant AcCP3 protein, the 27 kDa mature protein from the 34 kDa pro-protein hydrolysed host haemoglobin, collagen and albumin and showed high activity in an acidic environment. After AcCP3 knockdown, the hydrolytic activity of trophozoite crude protein against gelatin was decreased, suggesting that these trophozoites had decreased toxicity. Compared with untreated trophozoites or negative control siRNA-treated trophozoites, AcCP3-knockdown trophozoites were less able to penetrate and damage monolayers of HCECs. Western blot analysis showed that the activation levels of the Ras/Raf/Erk/p53 signalling pathways in HCECs decreased after inhibiting the expression of trophozoite AcCP3.

CONCLUSIONS

AcCP6 was correlated to encystation. Furthermore, AcCP3 was a virulent factor in trophozoites and participated in the activation of the Ras/Raf/Erk/p53 signalling pathways of host cells.

Heat and chlorine resistance of a soil Acanthamoeba sp. cysts in water

AIMS

The study established the inactivation kinetic parameters of an Acanthamoeba cyst isolate subjected to heating and chlorination.

METHODS AND RESULTS

A strain of Acanthamoeba was isolated and purified from an area surrounding a pilot food plant. Mature cysts (14 days) were subjected to heat inactivation studies at 71, 76, 81, 86 and 91°C; and chlorination at 100, 200, 300, 400 and 500 ppm. The decimal reduction times (D-values) at 71, 76, 81, 86 and 91°C were 18·31, 9·26, 7·35, 4·52 and 1·81 min respectively. The calculated thermal resistance constant (z-value) was 21·32°C (R²  = 0·96-0·97). The D-value in 100, 200, 300, 400 and 500 ppm chlorine-treated water were 47·17, 25·06, 24·51, 23·70 and 18·55 min respectively. The chlorine resistance constant (z-value) was 1179 ppm chlorine (R²  = 0·65-0·74).

CONCLUSIONS

Results demonstrated high resistance of the isolated Acanthamoeba cysts towards the common methods applied in ensuring food and food processing environment sanitation.

SIGNIFICANCE AND IMPACT OF THE STUDY

The resistance parameters of the test organisms established in this study may be used in the establishment of Sanitation Standard Operating Procedures (SSOPs), which are often based on inactivation of bacteria. These SSOPs could render better protection to food and food processing environments.

Dual 0.02% chlorhexidine digluconate - 0.1% disodium EDTA loaded thermosensitive ocular gel for Acanthamoeba keratitis treatment

Poor bioavailability and low residence time limit the efficiency of conventional biguanide-based eye drops against Acanthamoeba keratitis. The aim of this work was to formulate an original anti-amoebic thermoreversible ocular gel combining biguanide and metalloproteases inhibitor - chelating agent. Chlorhexidine digluconate (CHX)-ethylenediaminetetraacetic acid disodium salt (Na₂EDTA) were compounded in poloxamer 407 saline solution. 0.02% CHX - 0.1% Na₂EDTA loaded thermosensitive ocular gel exhibited appropriate pH (5.73 ± 0.06), iso-osmolality (314 ± 5 mOsm/kg), viscosity (ranged between 15 and 25 mPa.s) and thermal gelation (26.5 °C and 33 °C) properties. Bioadhesion of gel was successfully tested onto isolated bovine eyes as well as the assessment of CHX penetration into the cornea. Intracorneal CHX concentration was found greater than trophozoite minimum amoebicidal concentration and minimal cysticidal concentration after 15-min and 2-h ocular exposure, respectively, while any CHX permeation through the cornea was detected (<51 ng/cm²/h). Improvement of CHX ocular bioavailability was attributed to probable solubilization of tear film lipid layer by poloxamer. In vitro efficiency of CHX-Na₂EDTA ocular gel was confirmed from the drastic reduction of trophozoite and cyst survival (to 25% and 2%, respectively), confirming the potential of the multicomponent pharmaceutical material strategy for the treatment of Acanthamoeba keratitis.

Impact of Acanthamoeba Cysts on Stress Resistance of Salmonella enterica Serovar Typhimurium, Yersinia enterocolitica 4/O:3, Listeria monocytogenes 1/2a, and Escherichia coli O:26

The formation of robust resting cysts enables Acanthamoeba to resist harsh environmental conditions. This study investigated to what extent these cysts are resistant to physical and chemical stresses as applied in food industry cleaning and disinfection procedures. Moreover, it was assessed whether certain intracystic meat-borne bacterial pathogens are more stress resistant than free-living bacterial monocultures and if intracystic passage and subsequent association with trophozoites induces cross-tolerance toward other stressors. Several physical and chemical stressors (NaCl, H₂O₂, benzalkonium chloride, 55°C, heating until boiling, ethanol, dishwashing detergent, and sodium hypochlorite) frequently used in domestic and industrial food-related environments were tested against (i) Acanthamoeba castellanii cysts, (ii) single strains of bacterial monocultures, (iii) intracystic bacteria, and (iv) bacteria after intracystic passage (cyst-primed bacteria). Only heating until boiling and hypochlorite treatment were cysticidal. After boiling, no viable trophozoites could be recovered from the cysts, and hypochlorite treatment caused a 1.34- to 4.72-log₁₀ cells/ml reduction in cyst viability. All treatments were effective in reducing or even eliminating the tested bacterial monocultures, whereas bacteria residing inside cysts were more tolerant toward these stressors. All cyst-primed bacteria exhibited an increased tolerance toward subsequent H₂O₂ (>92% decrease in median log₁₀ CFU/ml reduction) and 70% ethanol (>99% decrease) treatments. Moreover, intracystic passage significantly increased the survival of Yersinia enterocolitica (74% decrease in median log₁₀ reduction), Escherichia coli (58%), and Salmonella enterica (48%) after NaCl treatment and of E. coli (96%), S. enterica (99%), and Listeria monocytogenes (99%) after sodium hypochlorite treatment compared with that of nonprimed bacteria.IMPORTANCE The results from this study demonstrated that both viable and nonviable amoebal cysts can protect internalized bacteria against stressful conditions. Moreover, cyst passage can induce cross-tolerance in bacteria, increasing their survival when exposed to selected stressors. These findings underscore the potential importance of free-living amoebae in food-related environments and their impact on the persistence of meat-borne bacterial pathogens.

Encystment in Acanthamoeba castellanii: a review

Differentiation of Acanthamoeba castellanii trophozoites involves massive turnover of cellular components and remodelling of organelle structure and function so as to produce a cryptobiotic cell, resistant to desiccation, heat, freezing, and chemical treatments. This review presents a summary of a decade of research on the most studied aspects of the biochemistry of this process, with emphasis on problems of biocide and drug resistances, putative new targets, molecular and cell biology of the process of encystment, and the characteristics of the encysted state. As well as the intrinsic pathogenicity of the organism towards the cornea, and the ability of related species to invade the human brain, its propensity for harbouring and transmitting pathogenic bacteria and viruses is considerable and leads to increasing concerns. The long-term survival and resistance of cysts to drugs and biocides adds another layer of complexity to the problem of their elimination.

Sensitivity of free-living amoeba trophozoites and cysts to water disinfectants

Free-living amoebae are naturally present in water. These protozoa could be pathogenic and could also shelter pathogenic bacteria. Thus, they are described as a potential hazard for health. Also, free-living amoebae have been described to be resistant to biocides, especially under their cyst resistant form. There are several studies on amoeba treatments but none of them compare sensitivity of trophozoites and cysts from different genus to various water disinfectants. In our study, we tested chlorine, monochloramine and chlorine dioxide on both cysts and trophozoites from three strains, belonging to the three main genera of free-living amoebae. The results show that, comparing cysts to trophozoites inactivation, only the Acanthamoeba cysts were highly more resistant to treatment than trophozoites. Comparison of the disinfectant efficiency led to conclude that chlorine dioxide was the most efficient treatment in our conditions and was particularly efficient against cysts. In conclusion, our results would help to adapt water treatments in order to target free-living amoebae in water networks.

Characterization of a bioflocculant MBF-5 by Klebsiella pneumoniae and its application in Acanthamoeba cysts removal

This study evaluated the potential of an extracellular, novel biopolymeric flocculant produced by a strain of Klebsiella pneumoniae isolated from a sputum sample for removal of Acanthamoeba cysts, a potent pathogen prevalent in water, soil, air, and dust. The presence of cations did not enhance flocculating activity. The component of MBF-5 was mainly polysaccharide and protein with proportional of 96.8% and 2.1% respectively. Infrared spectrum analysis showed the presence of carboxyl and hydroxyl groups in MBF-5. MBF-5 is nontoxic and can be used for removal of amoebae cysts from water. Conditions for flocculation of kaolin suspension and Acanthamoeba cysts were optimized by response surface methodology (RSM) and determined to be 54.38 mg/L dosage, 26.14°C and pH 3.32 and 129.73 mg/L dosage, 30.75°C and pH 4.36, respectively. The results of this study indicates a possible use of the K. pneumoniae biopolymer as an alternative to typically used chemical flocculants for removal of amoebae cysts from water.