What Role Do Amoeba Play?
Amoeba are important hosts for water bacteria. Legionella pneumophila, Mycobacteria spp. and other “amoeba resistant bacteria” can be carried by these protozoa1-6. Legionellae are taken up into amoeba without being digested and replicate there within vacuoles.
When the Legionellae have reached a certain density, the vacuoles release them into the water system. Amoeba not only function as environmental reservoirs for Legionella, but have been also shown to be involved in selecting for, protecting and maintaining potentially pathogenic Legionella spp. in the environment7,8. They have also been shown to enhance the virulence of Legionella spp.
Amoeba can incorporate Legionella, which then proliferate inside vacuoles and are later released, either in the form of planktonic, free living bacteria, or packed within vacuoles.
Legionellae are well-known water-borne pathogens which may cause respiratory infections including severe pneumonia known as Legionnaire's disease. Legionellae are present in most natural water environments, although the predominant risk of infection is higher within in premise water systems, particularly large plumbing networks. Within drinking water system networks in buildings, conditions are favourable for Legionella spp. proliferation (e.g. temperature, nutrient availability, stagnancy, dead legs and dead ends, biofilm formation) and aerosol generation is common from water outlets such as showers, taps, spa pools, decorative water features etc.
Few countries actively monitor their public building water supply for Legionella, and therefore most buildings are operated without the recognition and/or management of Legionella risk. International guidelines have defined 1000 colony forming units (CFU)/L as a value for public health concern in non-healthcare buildings, although other guidance, including that from the World Health Organization, recognise that for health care facilities the target level should be “not detectable”, because of high risk patient groups being vulnerable to exposure already at low concentration levels.
The number of Legionella bacteria / Litre is only one parameter important when risk assessing the water quality in a building; the subtype, virulence of the Legionella strain, potential exposure routes and the immune status of the users in the building are also significant to include.
Pall Disposable Point-of-Use Water Filters contain double layer, 0.2 micron sterilizing grade membranes which act as a barrier to, and are validated for, removal of waterborne bacteria – including Legionella spp., protozoa, fungi and particles from the drinking water supply. The filters are suitable for various uses including the provision of water for drinking, food production, personal hygiene, showering and bathing. Pall Point-of-Use Water Filters can support the management and control of Legionella risk within buildings.
1. Cateau et al., “Free-living amoebae. What part do they play in healthcare associated infection?” J Hosp Inf, 87:131-40, 2014
2. Drancourt et al., “Interactions between Mycobacterium xenopi, amoeba and human cells”, J Hosp Infect, 65:138-42, 2007
3. Pagnier et al., “Isolation of Vermamoeba vermiformis and associated bacteria in hospital water”, Microb Pathog, 80:14-20, 2015
4. Zeybek & Binay, “Growth ability of gram negative bacteria in free-living amoeba”, Exp Parasitol, 145:121-6, 2014
5. Cervero-Aragó et al., “Effect of common drinking water disinfectants , chlorine and heat, in free Legionella and Amoeba-associated Legionella”, PLOS one, 10(8):e0134726. Doi: 10.1371/journal.pone.0134726, 2015
6. Drancourt, “Looking in amoeba as source of mycobacteria”, Microb Pathog, 77:119-24, 2014
7. Lau & Ashbolt, “The role of biofilms and protozoa in Legionella pathogenesis: implications for drinking water”, J Appl Microbiol, 107(2):368-78, 2009
8. Ashbolt, ”Environmental (Saprozoic) pathogens of engineered water systems: Understanding their ecology for risk assessment and management”, Pathogens, 4:390-405, 2015
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