Évaluation des cartouches en polyéthersulfone "Envirochek" pour la concentration d'oocystes de Cryptosporidium parvum à partir d'échantillons de 100 litres d'eau de distribution

Evaluation of polyethersulfone filter efficiency (Envirochek cartridge) for Cryptosporidium parvum oocysts concentration in 100 liters tap water samples

¹ Centre de Recherche et de Contrôle des Eaux de Paris 144, avenue Paul-Vaillant-Couturier - 75014 Paris
² École Nationale de la Santé Publique de Rennes avenue du Professeur Léon-Bernard - 36043 Rennes
³ Laboratoire Santé-Environnement-Hygiène de Lyon 321, avenue Jean-Jaurès - 69362 Lyon cedex 07

Résumé

Les cartouches filtrantes en polyéthersulfone "Envirochek" (porosité de 1 µm) ont été examinées pour leur capacité à concentrer des oocystes de Cryptosporidium parvum introduits dans 100 litres d'eau de distribution. Dans un premier temps, nous avons évalué le protocole proposé par le fabricant, puis dans un deuxième temps nous avons été amené à l'optimiser. L'étude présentée ici a engagé trois laboratoires afin de déterminer le rendement de récupération des oocystes de Cryptosporidium parvum et la reproductibilité des expériences, en appliquant un protocole modifié à l'analyse d'échantillons de 100 litres d'eau de distribution artificiellement contaminés par des oocystes de Cryptosporidium parvum (1.10⁶ oocystes/100 litres).

Abstract

Cryptosporidium parvum is a significant waterborne pathogen responsible for several outbreacks worldwide, inducing gastroenteritis which can be fatal to immunocompromised individuals. Thus, sensitive methods for their detection are needed to ensure safe drinking water supply. Filtration through polypropylene cartridge is the concentration technique most widely used. Yet, it is recognised that its efficiency as well as its consistency are highly variables. Therefore, a study involving three laboratories was undertaken to evaluate the efficiency of "Envirochek" capsule commercialized by Gelman in concentrating parasites from drinkingwater samples. The experimental protocol consisted in filtering 100 liters spicked water samples (1.10⁶ Cryptosporidium oocysts/100 liters) through the 1 µm polyethersulfone filter at a 80 L/h flow rate. Oocysts were furtherly recovered by vigourous shaking of the filter soaked in twice 120 ml of eluant. The second concentration step necessary for the detection of low parasites concentrations was performed by centrifugation (1 100g; 10mn; 4°C).

Preliminary tests were run to optimize Cryptosporidium oocysts recovery from the filter during the first concentration step, considering the poor results (17%) we had when strictly following the manufacturer recommendations by using a wrist shaker device, 600 oscillations/mn, twice Wmn. Higher results (# 80%) were obtained when shaking vigourously the filter manually during 2mn 30s, this being repeated twice.

These experimental conditions were applied in the 5 trials each laboratory performed in the same facilities in order to eliminate differences in supply quality. Cryptosporidium oocysts recovery efficiencies averaged 79 % after the first concentration step and 49 % after the second one, with a good reproducibility. Statistical analysis (Student test) showed no significative differences between the three laboratories data (α= 5%).

These first results indicate that "Envirochek" capsules are promising tools for Cryptosporidium recovery from tap water samples. No clogging problems were met when 100 liters samples were processed. Besides, these capsules are easy to handle for field applications and particularly suitable for postal transportation if needed. Nevertheless, more investigations are needed to evaluate their efficiency in the analysis of other waters quality.