## 3 Factors Governing Survival and Occurrence of Opportunistic Pathogens in Premise Plumbing Systems
### Mycobacterium Avium  
Non-tuberculosis mycobacteria (NTM) are a group of opportunistic pathogens found in water and soil, including building water systems [2; 72; 98]. The most frequently isolated mycobacteria of the approximately 150 known species are displayed in Table 4.  
Factors that influence _Mycobacterium avium_ growth in pipes include temperature, water flow, nutrients, pipe material and condition, and residual disinfectant. A study by [PERSON] and [PERSON] [99] demonstrated the ability of _Mycobacterium avium_ to survive at 50 \({}^{\circ}\)C for up to 60 min. Similar results are widely replicated and can explain the residence particularly in domestic hot water heaters and pipes [100]. Another study by [PERSON] and [PERSON] [101] observed the tolerance of _Mycobacterium avium_ during periods of stagnancy, which is common in the operation of premise plumbing. This study also showed growth at 6% and 12% oxygen as well as in air (21% oxygen). Another study by [PERSON] et al. [102] revealed a correlation between concentrations of _Mycobacterium avium_ and organic carbon concentrations. _Mycobacterium avium_ is relatively chlorine resistant and can survive concentrations otherwise able to destroy or inactivate indicator bacteria (e.g., _Escherichia coli_) [103]. Additionally, chlorine resistance is higher in water than in culture medium, and most stains appear more tolerant of chloramine than free chlorine disinfection. Although all NTM species are at least 100 times more resistant to chlorine and other disinfectants compared to _Escherichia coli_, not all withstand chlorine disinfection equally [103; 104; 105; 19; 19; 106]. [PERSON] et al. [6] suggest that turbidity may be an important factor during the inactivation of planktonic NTM in drinking water. The mechanism by which disinfection selects for NTM in drinking water distribution (i.e., by reducing numbers of competing organisms) is well documented in several studies [107; 102]. Pilot system studies have been designed to simulate and study the behaviour of NTM in the drinking water distribution system. One such study demonstrated the ability of _Mycobacterium avium_ to form biofilms in pipe under different concentrations of organic matter and disinfectant residuals [107]. Furthermore, _Mycobacterium avium_ is resistant to killing by amoebae and does not undergo phagocytosis but rather multiplies within these hosts [108]. There is mounting evidence that suggests this as another factor contributing to its residence in drinking water systems and premise plumbing. Drinking water contains both rapid and slow-growing mycobacterial species. Although their rate of growth in rich laboratory media can be very low (at 1 generation per day), _Mycobacterium avium_ complex (MAC) and NTM are generally well adapted to life in aqueous, flowing environments, owing to their physiological properties [6; 102]. NTM possess a waxy, hydrophobic cell surface, which is a consequence of long-chain (C40-C80) mycolic acids [109]. Researchers often credit these cell envelopes as the basis for antibiotic and disinfectant resistance [110]. The waxy, hydrophobic surface of NTM cells has also been linked to increased surface adherence and biofilm formation [111; 112]. The enrichment of NTM in biofilms is a particularly important aspect for slow-growing species in flowing systems. Hydrophobicity also makes NTM susceptible to dispersion and transport \begin{table}
\begin{tabular}{c c} \hline
**Slowing Growing Species** & **Rapidly Growing Species** \\ \hline _Mycobacterium avium_ & \\ subspecies avium & \\ subspecies hominisuis & \\ subspecies silvalticum & _Mycobacterium abscess_ \\ subspecies paratuberculosis & \\ subspecies marseillense & \\ subspecies iturinese & \\ \hline _Mycobacterium intracellular_ & _Mycobacterium chelonae_ \\ \hline _Mycobacterium kansasii_ & _Mycobacterium fortuitum_ \\ \hline _Mycobacterium xenopi_ & \\ \hline _Mycobacterium malmone_ & \\ \hline _Mycobacterium marinum_ & \\ \hline \end{tabular}
\end{table}