Significance of bacteria associated with invertebrates in drinking water distribution networks

Abstract

The implication of invertebrates found in drinking water distribution networks to public health is of concern to water utilities. Previous studies have shown that the bacteria associated with the invertebrates could be potentially pathogenic to humans. This study investigated the level and identity of bacteria commonly associated with invertebrates collected from the drinking water treatment systems as well as from the main pipelines leaving the treatment works. On all sampling occasions bacteria were isolated from the invertebrate samples collected. The highest bacterial counts were observed for the samples taken before filtration as was expected. There were, however, indications that optimal removal of invertebrates from water did not always occur. During the investigation, 116 colonies were sampled for further identification. The isolates represent several bacterial genera and species that are pathogenic or opportunistic pathogens of humans. Diarrhoea, meningitis, septicaemia and skin infections are among the diseases associated with these organisms. The estimated number of bacteria that could be associated with a single invertebrate (as based on average invertebrate numbers) could range from 10 to 4000 bacteria per organism. It can, therefore, be concluded that bacteria associated with invertebrates might under the worst case scenario pose a potential health risk to water users. In the light of the above findings it is clear that invertebrates in drinking water should be controlled at levels as low as technically and economically feasible.

Protection of waterborne pathogens by higher organisms in drinking water: a review

“…Invertebrates in distribution systems were found to be colonized by a large variety of bacteria, in numbers ranging from 1 to 10 CFU/copepod and from 10 to 100 CFU/nematode, both inside their digestive system and on their surface where the bacteria could be found individually or in colonies (Levy et al 1986). Average colony counts reaching up to 4000 bacteria per invertebrate were observed in a drinking water system, approaching the infectious dose for certain of the bacterial species identified, possibly associated with a single superior organism (Wolmarans et al 2005). Some of the invertebrateassociated bacteria from that system were identified to be frank or opportunistic human pathogens (including Aeromonas hydrophila, Burkholderia cepacia, Klebsiella pneumonia, Pseudomonas aeruginosa, Enterococcus faecium, and Streptococcus agalactiae, to name only a few).…”

“…It is also important to include, in such studies, a relevant assessment of the ability of the recovered pathogens to infect a human host. Additionally, we deem it important to better investigate the occurrence of viable pathogens located inside invertebrates in water distribution systems, similar to the work of Wolmarans et al (2005), since the abundance of invertebrates in the pipe systems is well known, whereas their sanitary significance remains poorly characterized and addressed.…”

Comparison of the role of attachment, aggregation and internalisation of microorganisms in UVC and UVA (solar) disinfection

“…To predict performances of UV disinfection processes, it would be required to better assess the occurrence of internalised pathogenic (or indicator) bacteria in field conditions, which presents high methodological challenges. Preliminary data on that topic have been obtained by Bichai et al (2010) and Wolmarans et al (2005).…”

The use of chlorine dioxide for the inactivation of copepod zooplankton in drinking water treatment

“…In addition to their negative effect on the aesthetic values of drinking water, the presence of zooplankton -which may carry microbes such as bacteria -increases the threat to human health. [8,9] Zooplankton is present in a waterworks in Shijiazhuang in northern China [10] and has been recorded in the water supply to households in Jilin province. [11] BAC filters provide a suitable living environment for the propagation of zooplankton.…”