Interactions between Arcobacter butzleri and free-living protozoa in the context of sewage & wastewater treatment

  • Author / Creator
    Oloroso, Mariem Joan W
  • Water reuse is increasingly becoming implemented as a sustainable water management strategy in areas around the world facing freshwater shortages and nutrient discharge limits. However, there are a host of biological hazards that must be assessed prior to and following the introduction of water reuse schemes. Members of the genus Arcobacter are close relatives to the well-known foodborne campylobacter pathogens and are increasingly being recognized as emerging human pathogens of concern. Arcobacters are prevalent in numerous water environments due to their ability to survive in a wide range of conditions. They are particularly abundant in raw sewage and are able to survive wastewater treatment and disinfection processes, which marks this genus as a potential pathogen of concern for water quality. Because the low levels of Arcobacter excreted by humans do not correlate with the high levels of Arcobacter spp. present in raw sewage, it was hypothesised that other microorganisms in sewage may amplify the growth of Arcobacter species. There is evidence that Arcobacter spp. survive both within and on the surface of free-living protozoa (FLP). As such, this thesis investigated the idea that Arcobacter spp. may be growing within free-living protozoa also prevalent in raw sewage and providing them with protection during treatment and disinfection processes. As Arcobacter spp. have been detected in discharged wastewater effluents disinfected by ultraviolet (UV) irradiation, this thesis investigated the potential for free-living protozoa to enhance growth or protect Arcobacter spp. from UV disinfection, a process considered highly effective for wastewater treatment and increasingly implemented worldwide. While wastewater-derived A. butzleri showed no change in CFUs when grown with or without free-living amoebae (FLA), there was a significant decrease when in the presence of the ciliate Tetrahymena pyriformis. Hence, A. butzleri does not appear to use FLP as a vessel for replication. Herein the first UV dose-response work for A. butzleri in water is reported and at the usual wastewater dosages, up to 40 mJ/cm2, a 6-log10 reduction occurred. The uncorrected UV doses required to achieve certain log10 reductions of A. butzleri were greater than the uncorrected UV doses required to achieve the same log10 reductions of E. coli, a traditional water quality indicator, and C. jejuni, a commonly used bacterial reference pathogen in quantitative microbial risk assessments for water reuse schemes. There was no significant difference in log10 reductions when A. butzleri was associated with FLA. However, there was a significant decrease in log10 reduction when A. butzleri was associated with T. pyriformis, which suggests that free-swimming ciliates provide Arcobacter spp. with protection from UV disinfection. These findings point to the importance of considering the ecology of bacterial pathogens during wastewater treatment rather than strictly focusing on CFU counts as an indicator of water quality. Campylobacter is the current surrogate for Arcobacter treatment efficacy. As Arcobacter spp. are much less fastidious and much more abundant in raw sewage than species of Campylobacter, this reference pathogen may need to be reconsidered.

  • Subjects / Keywords
  • Graduation date
    Spring 2021
  • Type of Item
  • Degree
    Master of Science
  • DOI
  • License
    This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.