Abstract
Members of the Mycobacterium avium complex (MAC) are waterborne, opportunistic pathogens whose characteristics make urban water distribution systems and household plumbing ideal habitats for their survival, persistence and growth. Rather than contaminants, MAC are colonists of drinking water systems. MAC are normal inhabitants of natural soils and water, and enter drinking water treatment systems through surface sources. A proportion of MAC survive transmission through the treatment plant, and regrow in the distribution system and household plumbing. Once within household plumbing, MAC adhere to surfaces and form biofilms, thus preventing their washout. The thermal tolerance of MAC leads to growth in water heating systems. Stagnation does not reduce MAC numbers, as MAC can grow at low oxygen levels. MAC present challenges to current water monitoring approaches as their numbers do not correlate with E. coli, fecal coliforms or heterotrophic plate count bacteria.
Highlights
The Mycobacterium avium complex (MAC) are waterborne, opportunistic pathogens that cause pulmonary, blood stream and skin infections in susceptible individuals [1]
As water leaving the treatment plant is relatively free of Gram-negative waterborne contaminants like E. coli, a proportion of the assimilable organic carbon (AOC) can be utilized by the MAC cells for growth
Unlike E. coli or fecal coliform numbers, which fall as the distance between the source of contamination and collection point increases due to flow or time, MAC numbers increase as witness to their two-fold increase in distribution systems between treatment plant and residence [24]
Summary
The Mycobacterium avium complex (MAC) are waterborne, opportunistic pathogens that cause pulmonary, blood stream and skin infections in susceptible individuals [1]. It is estimated that there are over 180,000 individuals with pulmonary MAC infections [2]. The MAC currently includes four M. avium subspecies (i.e., avium, silvaticum, hominissuis and paratuberculosis) and seven additional species, with M. intracellulare, M. chimaera. As this review will document, distribution systems and premise plumbing are ideal habitats for MAC. Selection for the growth and survival of MAC occurs in water treatment plants, the distribution system and household plumbing. MAC are readily aerosolized [10], and pulmonary infections have been traced to showerheads [11,12,13,14,15].
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