Effet potentiel de quelques facteurs environnementaux sur l'élimination des phages au cours du traitement des eaux usées. Étude in vitro

Potential effect of some environmental factors on the phage removal during wastewater treatment. Study in vitro

¹ Département de Biologie, Faculté des Sciences Dhar Mehrez. BP 1796 Atlas. FES (Maroc)
² Laboratoire de Biologie Comparée des Protistes. URA CNRS 6023. 63177 AUBIERE (France)
³ Hygiène Hospitalière, Faculté de Médecine. 63001 CLERMONT FERRAND (France)
⁴ Laboratoire de Biologie Cellulaire, Faculté de Pharmarcie - 63001 CLERMONT FERRAND (France)

Résumé

Deux bactériophages différents (øX-174 et MS2) ont été utilisés comme virus modèles dans une série d'expériences in vitro pour évaluer l'adsorption virale sur des particules minérales argileuses en suspension dans de l'eau distillée stérile. L'effet potentiel des matières dissoutes dans un effluent pollué, des rayons solaires et du protozoaire cilié Tetrahymena pyriformis sur l'élimination phagique ont été également étudiés. L'adsorption des phages sur les particules de la montmorillonite et de la kaolinite est instantanée et sans dépendance de la durée de contact. La concentration de ces minéraux n'a pas d'influence sur ce processus. Le phage MS2 est plus affecté par l'action des matières dissoutes que le øX-174. Après une exposition solaire de 12 heures, des taux similaires d'inactivation phagique ont été notés pour les deux virus bactériens bien que le øX-174 semble être plus sensible au début de l'exposition. Enfin, en présence de T. pyriformis le phénomène de la prédation n'est pas enregistré.

Abstract

Great quantities of enteric viruses and bacteriophages are included in wastewaters. They represent a contamination risk of natural water systems. But this viral burden is greatly reduced in the sewage treatment plants by the combined action of numerous environmental factors.

To study water quality, some groups of bacteriophages as E. coli phages and Bacteroides fragilis phages have been proposed as model viruses. On an other hand, somatic and, in particular, F-specific coliphages have several morphological, structural and chemical composition ressemblances with the enteric viruses. Two different bacteriophages (øX-174 and MS2) were used as virus models in this in vitro study to evaluate the viral adsorption on suspended clay particles. Distilled sterile water was used as reactional medium to avoid the possible interactions with the considered substrates, the kaolinite (K) and the montmorillonite (M). Phage behaviour in the water and in the recommended diluent for phages, the saline peptone, was first compared.

K and M suspensions were used at 300 mg/l for a contact time of 5, 30 and 60 min. In other series K and M suspensions were prepared at 600, 300 and 100 mg/l then used to determine the phage adsorption capacity in a fixed time 30 min.

Results show that the phage titers for all samples were constant in the organic diluent. They were lower in the distilled sterile water and decrease with the time. Distilled water favours most likely the grouping of virions and leads aggregates formation. The adsorption of øX-174 and MS2 onto K or M particles was instantaneous and independent of the duration contact. The clay concentration had a slight significant influence on the phage adsorption rate.

Using the same phages we have studied, in a second stage, the potential effect of the dissolved matters in a filtered polluted effluent, that of sunlight radiations and that of the protozoan Tetrahymena pyriformis on the phage removal.

No soon significant phage inactivation was caused by the dissolved matters. But the process was progressively more marked (24 hours later, it was 98.8% and 38% respectively for MS2 and øX-174). With solar radiations, an important inactivation of the somatic coliphage was obtained at the earlier exposition times to the sunlight. Later, the effect was amplified. øX-174 phage titer decreased almost 2 log units after exposition of 1.5 hour and more than 5 log units after 12 hours. In the case of MS2, decrease titer was less important at the first exposition times but tended to 5 log units at the last one (12 hours).

The infection of the protozoan culture medium by any of the phages was followed by microscopic observations. The morphology and the mobility of the ciliate were no affected by the presence of phages. The biological cycle was also comparable to the control. The ciliate culture medium seems to have an inactivation effect mainly in the case of øX-174. Predation by Tetrahymena pyriformis cannot be considered as an important factor of phage removal from the medium.