Health Stream Literature Summary - Issue 56 - December 2009

Transmission of Helicobacter pylori and the role of water and biofilms.
Percival, S.L. and Thomas, J.G. (2009) Journal of Water and Health, 7(3); 469-477.

Helicobacter pylori are spiral-shaped bacteria that efficiently colonise the human gastric mucosa. Asymptomatic carriage of H. pylori is common and it is estimated that about half the world's population is colonised with H. pylori with prevalence varying widely by age as well as country, ethnic background and socio-economic conditions. In the developing world, over 70% of children are infected with H. pylori by age 15. In contrast, the developed world has experienced a decrease in prevalence of H. pylori since the 1950s and presently approximately 20% to 30% of individuals harbour H. pylori. In the absence of treatment to eliminate the bacterium, colonisation is believed to persist for life. In a small percentage of people, colonisation causes clinical disease including chronic active gastritis and peptic ulcer disease.

More rarely chronic H. pylori infection has been linked to more serious gastrointestinal disorders including gastric adenocarcinoma and gastric mucosa-associated lymphoid tissue (MALT) lymphoma. The World Health Organization International Agency for Research on Cancer has classified H. pylori as a class I carcinogen in humans. This review was undertaken to critically evaluate published data and determine whether water and biofilms may constitute possible transmission and environmental niches for H. pylori.

Many routes of transmission have been proposed for H. pylori including gastric-oral, oral-oral, faecal-oral, zoonotic and water/food-borne routes. There is growing yet still controversial evidence that suggests a faecal-oral transmission route. If H. pylori is excreted in faeces then these bacteria may well go on to colonise surfaces present in water sources. Such surfaces could then subsequently become transmittable sources of H. pylori. Municipal water is a potential risk factor in the transmission and acquisition of H. pylori. It is possible that breaks in municipal pipes allow for infiltration of contaminated surface water. In developing countries, water from streams, rivers and wells has been considered as a common source of transmission H. pylori.

The first successful isolation of H. pylori by culturable methods, occurred in a heavily contaminated municipal wastewater canal on the US-Mexico border (published in 2002). Apart from this study, positive culture of H. pylori from drinking water has not been successful. H. pylori can transform rapidly into a viable but non-culturable state (VBNC). This state is induced by low nutrient and hyperosmotic conditions which are commonly found in water and the environment. Within the VBNC state, H. pylori cells are still alive, however there is little or no evidence regarding the resuscitation of VBNC cells of H. pylori or on the ability of the VBNC cells to cause infection. There have been a number of PCR assays utilised for the detection of H. pylori in water. Fluorescent in situ hybridization (FISH) has also been validated as a quick and sensitive method for detection of H. pylori in environmental samples. Many studies have shown that H. pylori may survive for prolonged periods in water over a range of physical variables. H. pylori strains have been found to survive for long periods under physiological saline concentrations, low temperatures and a pH range of 5.8 to 6.9. One study showed that H. pylori was able to remain viable for periods ranging from 48 hours to between 20 and 30 days when exposed to different temperatures. H. pylori are able to survive for short periods in water when present in their coccoid morphology. When H. pylori is in this coccoid form it may be able to survive the extremes of conditions associated with drinking water and water distribution systems. It is possible that H. pylori coccoid cells may be able to tolerate levels of disinfection normally used in distribution systems and therefore remain viable. The survival of H. pylori in the aquatic environment is not well understood and it is not know how this environment affects its viability.

There are a limited number of published articles on the effectiveness of standard drinking water disinfection processes on H. pylori survival. It is possible under conditions of inadequate disinfection for H. pylori to enter and persist in drinking water systems. This may particularly be the case if the bacterium grows within a biofilm state. A number of drinking water studies have found H. pylori in water pre- and post-chlorination.

H. pylori can readily form biofilms and in the process produce a novel antibacterial peptide, which may give them increased persistence in a heterogenous biofilm environment. For H. pylori to survive the extremes of water it is possible that it would have to reside within a biofilm. There is evidence from various studies that biofilms in water distribution systems may harbour H. pylori. It has been shown that H. pylori may be present as biofilms on pipe work in drinking water systems and H. pylori have been shown to have the ability to adhere to different plumbing materials, specifically copper and stainless steel. Copper surfaces have been found to be particularly suitable for the maintenance of the bacteria in the spiral form.

H. pylori is still a significant problem in the developing world and will continue to be of concern due to poor levels of sanitation and hygiene that exist in these regions. Therefore it is important to gain a better understanding of the risk factors involved in the acquisition of H. pylori infection and also to not overlook the increasing potential that H. pylori can be transmitted via a waterborne pathway. Further investigation is required of biofilms in which H. pylori may reside, resuscitate, proliferate, interact with other sessile microorganisms and then disseminate as a source of infection.

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