title: Inactivation of Clostridium difficile in sewage sludge by anaerobic thermophilic digestion.
abstract: There has been an increase in community-associated Clostridium difficile infections with biosolids derived from wastewater treatment being identified as one potential source. The current study evaluated the efficacy of thermophilic digestion in decreasing levels of C. difficile ribotype 078 associated with sewage sludge. Five isolates of C. difficile 078 were introduced (final density of 5 log CFU/g) into digested sludge and subjected to anaerobic digestion at mesophilic (36 or 42 °C) or thermophilic (55 °C) temperatures for up to 60 days. It was found that mesophilic digestion at 36 °C did not result in a significant reduction in C. difficile spore levels. In contrast, thermophilic sludge digestion reduced endospore levels at a rate of 0.19-2.68 log CFU/day, depending on the strain tested. The mechanism of lethality was indirect - by stimulating germination then inactivating the resultant vegetative cells. Acidification of sludge by adding acetic acid (6 g/L) inhibited the germination of spores regardless of the sludge digestion temperature. In conclusion, thermophilic digestion can be applied to reduce C. difficile in biosolids, thereby reducing the environmental burden of the enteric pathogen.
authors.affiliation: a Department of Food Science, University of Guelph, ON N1G 2W1, Canada.
authors.forename: Changyun
authors.initials: C
authors.lastname: Xu
authors.affiliation: b School of Engineering, University of Guelph, ON N1G 2W1, Canada.
authors.forename: Hamidreza
authors.initials: H
authors.lastname: Salsali
authors.affiliation: c Department of Pathobiology, Ontario Veterinary College, University of Guelph, ON N1G 2W1, Canada.
authors.forename: Scott
authors.initials: S
authors.lastname: Weese
authors.affiliation: a Department of Food Science, University of Guelph, ON N1G 2W1, Canada.
authors.forename: Keith
authors.initials: K
authors.lastname: Warriner
mesh_terms: D000693:Anaerobiosis; D016360:Clostridioides difficile / Q000378:metabolism*; D004063:Digestion; D006863:Hydrogen-Ion Concentration; D012722:Sewage / Q000382:microbiology*; D013696:Temperature
chemical_list: D012722:Sewage
keywords: Clostridium difficile; anaerobic digester; community-associated infections; digesteur anaérobie; endospores; infections acquises dans la communauté; sewage; thermophile; thermophilic; traitement des eaux usées; wastewater treatment; égouts