Persistence of crAssBcn phages in conditions of natural inactivation and disinfection process and their potential role as human source tracking markers Journal: Science of the Total Environment

Abstract

Due to their abundance in the human gut, human specificity, and global distribution, some crAss-like phages, including the original p-crAssphage, have been proposed as indicators of human fecal pollution suitable for microbial source tracking (MST). The prevalence of crAss-like phages in water, and consequently their usefulness as MST indicators, is determined by their ability to survive various inactivation and disinfection processes. Recently, we isolated new crAss-like phages (named crAssBcn phages) capable of infecting <em>Bacteroides intestinalis</em> and exhibiting a wide geographical distribution. Here, we assessed the infectivity and DNA integrity of three crAssBcn phages (ΦCrAssBcn6, 10, and 15) and ΦCrAss001, the first crAss-like phage isolated, at different pHs and temperatures, after UV and chlorine treatments, and under natural conditions. Their bacterial host, <em>B. intestinalis</em> and a siphovirus <em>Bacteroides-</em>infecting phage GA17-A were used as controls. Infectious crAssBcn phages remained stable for a month at 4, 22, and 37 °C, and at pH 7, but inactivated when exposed to pH 3. Infective crAssBcn phages decreased by 5 log₁₀ after treatment with 10 ppm of chlorine for 1 min and after UV treatment at a fluence of 5.94 mJ/cm². However, heat treatment at 60 and 70 ºC resulted in only a moderate decrease (less than 1 log₁₀ and almost 3 log₁₀ units of reduction, respectively). Experiments under natural conditions in outdoor mesocosms revealed that inactivation rates for crAssBcn phages, as for the other microorganisms, were higher in summer (up to 6 log₁₀) than in winter (less than 4 log₁₀), suggesting a higher incidence of inactivation factors, such as sunlight and temperature, in the warmer months. <em>B. intestinalis</em> was significantly more prone to inactivation than phages in most conditions except for the irradiation treatment. In contrast, crAssBcn phage DNA remained stable, with minimal reduction under most of the tested conditions, except in the summer mesocosm and UV assays.