The Impact of Human Activities on the Ecology of

Nontuberculous Mycobacteria

Joseph O. Falkinham, III

Department of Biological Sciences

Virginia Tech

Blacksburg, Virginia, USA

Correspondence:

J.O. Falkinham, III

Department of Biological Sciences

Virginia Tech

Blacksburg, VA 24061-0406

USA

Phone 1-540-231-5931

FAX 1-540-231-9307

E-mail jofiii@vt.edu

Summary

Nontuberculous mycobacteria (NTM) are environmental opportunistic pathogens of

humans and animals. They are found in a wide variety of habitats that are also occupied by humans;

including drinking water distribution systems and household water and plumbing. In that regard,

they are distinct from their obligate pathogenic relatives, the members of the Mycobacterium tuberculosis

complex. Because of the presence of NTM in the human environment, human activities have had

direct impacts on their ecology and hence their epidemiology.

NTM are oligotrophic, able to grow at low organic matter concentrations and over a wide

range of temperatures and even at low oxygen concentrations. Thus, NTM are normal inhabitants of

natural waters and drinking waters. Discovery of the presence of NTM polluted soils is not

surprising in light of the ability of NTM to degrade a variety of hydrocarbon pollutants.

A major human activity selecting for the growth and predominance of mycobacteria is

habitats is disinfection. Compared to other bacteria, NTM are relatively disinfectant-, heavy metal-,

and antibiotic-resistant. Thus, the use of any anti-microbial agent selects for mycobacteria.

Employment of disinfectants for drinking water treatment, leads to selection for mycobacteria that

can grow and come to dominate in drinking water distribution systems in the absence of

disinfectant-sensitive competing microorganisms. NTM selection may also occur as consequence of

the presence of antibiotics in drinking water and drinking water sources.

Keywords: Mycobacteria, Drinking Water Distribution Systems, Disinfectant, Antibiotic,

Selection, Oligotrophic, Household Plumbing

Introduction

It is the objective of this review to cite instances illustrating how human activities may have

impacts on the ecology of the nontuberculous mycobacteria (NTM). NTM are soil- and water-

borne human and animal opportunistic pathogens whose environmental distribution includes

habitats to which humans are regularly and routinely exposed (e.g., drinking water). Consequently,

human activities such as water disinfection, water transmission, and pollution have direct and

positive effects on NTM populations.

The Nontuberculous Mycobacteria (NTM)

The nontuberculous mycobacteria (NTM) are environmental opportunistic pathogenic

members of the genus Mycobacterium. There are over 120 species, most of which have described in

the past 20 years [1]. Some NTM species, namely the Mycobacterium avium complex (MAC, which

includes Mycobacterium intracellulare), Mycobacterium kansasii, Mycobacterium malmoense, Mycobacterium

xenopi, Mycobacterium ulcerans, Mycobacterium fortuitum, Mycobacterium abscessus, and Mycobacterium chelonae

(Table 1) are responsible for a disproportionate number of infections [2, 3, 4, 5]. NTM cause

diseases in humans [5] and wild and domesticated animals (e.g., cattle, deer, sheep, and goats), wild

and domesticated birds, fish, reptiles, and amphibians [6].

NTM are opportunistic pathogens. In humans, an individual with one or more of a particular

set of genetic or physiologic conditions is at risk for NTM disease. Historically, the risk factors for

pulmonary NTM disease include prior Mycobacterium tuberculosis infection, alcoholism, occupational

exposure to dusts (e.g., farmers, coal miners), and silicosis [5, 7]. Surgery is also a risk factor for

NTM disease, particularly for members of rapidly growing species [4]. M. avium is associated with

cervical lymphadenitis in young children [8]. NTM bacteremia is found in immunosuppressed

individuals as a consequence of HIV-infection, chemotherapy, cancer, or transplant-associated

immunosuppression [5]. In addition to those two groups, there is a population of individuals at

increased risk for NTM pulmonary disease, yet who lack the classic risk factors and are not

immunosuppressed [9, 10, 11]. The patients share the characteristic of being slender and elderly.

Most are women (50 % more women than men). Amongst that group of NTM patients are found

those with cystic fibrosis or those heterozygous for one of the mutations in the cystic fibrosis

transport regulator (CFTR) gene or with α-1-antitrypsin deficiencies [12]. Gastroesophageal reflux

disease (GERD) has also been suggested to place individuals at increased risk for NTM pulmonary

disease [13, 14].

Habitats Populated by Nontuberculous Mycobacteria

NTM populate a variety of natural and human-engineered habitats (Table 2). Populate was

chosen deliberately as NTM are normal inhabitants of both natural and engineered environments;

not contaminants. In all the habitats where NTM have been recovered, the mycobacteria are part of

the normal flora, existing as stable, resident, and growing populations. An exception may be M.

avium subsp. paratuberculosis whose growth and persistence in the environment has not been reported.

Natural habitats for NTM include soils and rivers, ponds, lakes, and bays [15, 16, 17]. As NTM are

in soils and natural waters, dusts and aerosols (respectively) carry NTM [18, 19]. NTM have also

been isolated from polluted waste dumps [20, 21]. NTM also populate drinking water distribution

systems [22, 23], buildings [24, 25], and household plumbing [26, 27]. Numbers of NTM are highest

in biofilms [23, 28]. In both natural and human-engineered habitats, NTM coexist with phagocytic

protozoa and amoebae [29, 30]. Simply because humans are exposed to drinking water routinely and

regularly, it is likely that the most important source of NTM exposure for humans is drinking water,

compared to natural waters and soils.

Physiologic Traits as Determinants of NTM Distribution

NTM Hydrophobicity and Impermeability

As NTM are slow growing (i.e., generation times of 24 hr and 4 hr for slowly and rapidly

growing NTM at 37° C, respectively), they would not be expected to be successful competitors in

natural and human-engineered environments. However, they are quite good competitors and as

documented above, found in a wide variety of natural and human-engineered habitats. At least two

factors contribute to the relatively slow growth of NTM. First, NTM are surrounded by a lipid-rich

outer membrane that is quite impermeable to hydrophilic compounds [31, 32]. Second, NTM have

either one (slowly growing) or two (rapidly growing) copies of the rRNA operons [33]. Thus, NTM

growth is limited by its reduced protein-synthetic capacity. Although NTM grow slowly, their rate

of metabolism, measured by oxygen consumption, is equal to that of bacteria that grow substantially

faster [34].

The high lipid content of NTM cells (i.e., 60-70 % of cell weight principally in the outer

membrane), results in membrane impermeability [35] and the highest cell surface hydrophobicity

amongst bacteria [36]. NTM hydrophobicity and impermeability are major determinants of their

ecology (Table 3); but act as a two-edged sword. Advantages of NTM hydrophobicity and

impermeability include: resistance to disinfectants [37, 38] and heavy metals [39, 40], preferential

attachment to surfaces and air-water interfaces [18], concentration in bubbles rising in a water

column and concentration in water droplets ejected from waters [41], and ability to degrade

hydrocarbons (see below). Disadvantages of NTM hydrophobicity and impermeability include: slow

growth and reduced rates of transport of hydrophilic compounds [35].

NTM Disinfectant Resistance

NTM, for example Mycobacterium avium and Mycobacterium intracellulare, are resistant to

disinfectants commonly used in the treatment of drinking water (i.e., chlorine, chloramines, chlorine

dioxide, and ozone) [37]. NTM-disinfectant resistance is increased by growth of NTM cells in

biofilms [42]. In addition to resistance provided by layers of cells and extracellular material of NTM

cells in biofilms, biofilm growth induces adaptive resistance. M. avium cells grown in biofilms, yet

isolated from biofilms and washed and exposed to disinfectant in suspension are more disinfectant-

resistant compared to cells grown in suspension [42]. The survival of such cells is intermediate

between that of cells grown in suspension (sensitive) and of cells grown and exposed to disinfectant

in biofilms [42]. The biofilm-growth-induced resistance is adaptive based on the fact that it is lost

by growth of cells in suspension [42]. Other than determine that the adaptive resistance requires 18-

14 hours of cultivation at 37° C in suspension, no further experiments have been undertaken to

date. The slow growth rate of NTM also directly contributes to the relative resistance of NTM to

disinfectants [44]. In slowly growing cells it is more difficult to provoke lethal events by unbalancing

macromolecular synthetic events [45].

NTM Antibiotic-Resistance

NTM are resistant to a wide variety of commonly employed antibiotics; for example, the

penicillins [31, 46, 47]. That has necessitated the search for anti-mycobacterial antibiotics, many of

which have utility only against the mycobacteria; for example isoniazid (isonicotinic acid hydrazide,

INH) and ethambutol. However, most NTM are resistant to isoniazid unlike Mycobacterium

tuberculosis, which is sensitive (M. kansasii is one exception). It is likely that, as is the case for

disinfectant-resistance, that the architecture of the NTM envelope contributes to antibiotic-

resistance as well [46]. Hydrophobicity reduces the ability of antibiotics, many of which are polar, to

interact with the mycobacterial surface and envelope. The reduced permeability of antibiotics

through the outer membrane [35] also contributes to antibiotic resistance of mycobacteria. As was

the case for increased disinfectant-resistance of M. avium grown in biofilms, M. avium grown in

catheter biofilms is more resistant to antibiotics compared to suspension-grown cells [48]. It has

been suggested that as the majority of NTM cells in drinking water distribution systems [23] and

infected patients [49] are on surfaces, in vitro antibiotic susceptibility measurements ought to be

performed on biofilm-grown cells.

NTM Heavy Metal Resistance

NTM, including M. avium, M. intracellulare, and M. scrofulaceum can tolerate heavy metals such

as mercury (Hg+2), cadmium (Cd+2), and copper (Cu+2) at concentrations that are approximately 10-

fold higher than those tolerated by other bacteria [39, 40]. It is likely that one factor leading to

relative heavy metal resistant is the impermeability of the NTM envelope [46]. In addition, the

heavy metals Cu+2 and Cd+2 were found to be precipitated as sulfides and sequestered in the

envelope by a strain of M. scrofulaceum [34, 50, resp.]. Mercury (Hg+2) resistance of an M. avium strain

isolated from a mercury-polluted sediment collected from the Chester River near the Chesapeake

Bay was shown to be due to the plasmid-encoded production of mercuric reductase [51]. As the

cells containing the mercuric reductase would volatize mercury (Hg0), their presence in a habitat

would lead to reduction in Hg+2 concentrations [51]. Thus, not only would the M. avium cells survive,

but other members of the microbial community would survive.

NTM Temperature-Resistance

Nontuberculous mycobacteria are relatively resistant to temperatures that can be attained in

hot water heaters [i.e., 50° C (122° F) and 55° C (131° F)] (Table 4) [from 52]. Temperature-

resistance of M. avium, M. intracellulare, M. scrofulaceum, and M. xenopi is considerably higher than that

of Legionella pneumophila. M. xenopi, whose infections are epidemiologically linked to hot water

distribution systems [3], is the most heat-resistant among the mycobacteria. If water in a water heater

at was 50° C (122° F) had 1,000 M. avium cells/mL, it would take 50 hours to reduce the number to

1 M. avium cell/mL. At 55° C (131° F) it would take 2.7 hr and at 60° C (140° F) it would take 12

min. In contrast, if water in a water heater was at 50° C (122° F) had 1,000 L. pneumophila cells/mL,

it would take 8.25 hours to reduce the number to 1 L. pneumophila cell/mL. At 55° C (131° F) it

would take 1 hour and at 60° C (140° F) it would take approximately 5 min. Therefore, raising the

temperature of a water heater to temperatures able to inhibit the growth or kill L. pneumophila would

be insufficient to kill M. avium, M. intracellulare and M. xenopi.

Growth of NTM at Low Nutrient Concentrations

Available evidence suggests that NTM are oligotrophic; capable of growth at low nutrient

concentrations [53, 54, 55]. There are several experimental studies supporting this observation.

First, a variety of NTM species, most notably M. avium, M. intracellulare, M. chelonae, M. abscessus and

M. fortuitum have been shown to grow in drinking water [53, 54, 55]. In one study, a pilot drinking

water distribution system, it was shown that a strain of M. avium was able to grow at assimilable

organic carbon (AOC) levels as low as 50 µg/L [55]. In that study the carbon source was ozonated

humic acid. Consistent with that growth pattern is the fact that numbers of NTM correlate with

humic and fulvic acid concentrations [17] and humic and fulvic acids stimulate the growth of M.

avium in a minimal defined medium [56]. Second, numerical taxonomic studies of the NTM that

identified the carbon and nitrogen sources utilized by different NTM species grew the strains in

minimal, defined media that lacked organic carbon and nitrogen sources [57]. Notably, the strains

grew in the absence of oleic acid; a constituent of Middlebrook 7H9 broth and 7H10 agar, originally

developed for the cultivation of Mycobacterium tuberculosis [58]. However, I am aware of one exception

to the rule that NTM are not auxotrophs. Strains of M. avium and M. intracellulare form

interconvertible colonial variants, transparent and opaque [59] and only the transparent variants

require oleic acid for growth (Falkinham, unpublished observation). That oleic acid auxotrophy may

be of significance, as the transparent variants are more virulent and drug-resistant and the form most

commonly recovered from patients [60].

Metabolism of Hydrocarbons by NTM

One under-appreciated area of NTM metabolism is that NTM are capable of degrading

hydrocarbons, including chlorinated hydrocarbons. Recent reports document the presence of

hydrocarbon pollutants and other chemical contaminants in rivers used as drinking water sources

[61, 62]. A number of Mycobacterium species, including Mycobacterium tuberculosis, have been shown

capable of dehalogenation of holoalkanes [63]. This is critical as it has been shown that NTM can be

isolated from polluted dumps [20, 21]. It is likely that the participation of NTM in consortia

involved in the mineralization of pollutants has been missed in many studies because of the necessity

of incubating cultures for periods as long as 4-6 weeks. The list of hydrocarbons, chlorinated

hydrocarbons, and pollutants subject to degradation and metabolism by NTM is quite long (Table

5). Further, a number of mycobacterial strains are used to prepare cholesterol metabolites [64, 65].

As human activities lead to pollution and a number of pollutants are substrates for NTM growth

(Table 5), it follows that pollution would be expected to both stimulate the growth and select for

NTM.

Summary: Habitats Where Human Activities Influence NTM

Based on the background on the habitats and physiology of the nontuberculous

mycobacteria, I propose the hypothesis that human activities have a direct effect on NTM

populations. To support that hypothesis I provide a number of scenarios, namely habitats

influenced by humans and occupied by both humans and NTM. They are listed in Table 6. Note

that one common feature of many of these habitats is that anti-microbial agents are routinely

employed.

Scenario 1. Does Disinfection Select for NTM in Drinking Water?

Passage of the Clean Water Acts, starting in 1970 and continuing, there has been a marked

improvement in water quality across the United States [66]. Those Acts provided funds for water

treatment, including disinfection (e.g., chlorination) and have substantially contributed to reducing

numbers of water-borne diseases. Disinfection reduces the number of microorganisms and viruses

causing gastro-intestinal disease, but has little effect on mycobacterial numbers [37]. In fact,

disinfection leads to selection for mycobacteria in drinking water distribution systems [55]. In the

absence of competitors, mycobacteria have all the available carbon. Additional support for the

hypothesis that disinfection leads to NTM selection comes from a study of individuals with NTM

disease [67]. Patients whose source water was from bore holes were less likely to be infected with

NTM than individuals whose water was from piped systems [67]. A direct test for the hypothesis

could be performed by measuring NTM numbers in systems with and without disinfection. The

systems would not use groundwater: NTM are infrequently detected in groundwater [68] and NTM

are less likely to be found in household plumbing whose source of water is from wells (Falkinham,

in preparation). Quite possibly, a correlation between levels of disinfectant (e.g., chlorine) and

numbers of NTM or NTM disease in various locations might yield useful information.

Scenario 2. Do Antibiotics Select for NTM in Drinking Water?

It is well established that streams and rivers in the United States contain antibiotics [61, 62].

Further, the presence of antibiotics has been correlated with the presence of antibiotic-resistant

microorganisms [68, 69] and antibiotic-resistance genes [68, 70, 71]. The more antibiotics in the

stream water or drinking water, the more likely antibiotic-resistant bacteria and antibiotic-resistance

genes are detected [68, 69, 70, 71, 72]. As exposure of bacteria to vanadium-induced multidrug

resistance [73], it is possible that the presence of metals, particularly heavy metals, in drinking water

may induce antibiotic resistance.

Although the concentrations of antibiotics in drinking water and their sources are low and

below the minimal inhibitory concentrations necessary to inhibit growth or kill microorganisms [61,

62], evidence of the increase in frequency of antibiotic-resistance genes [68, 70, 71, 72] and

antibiotic-resistant microorganisms [68, 69] is consistent with that the low concentrations are

sufficient to selective for antibiotic-resistance [74]. Further, it is possible that selection occurs not

within the streams and rivers, but within the source of the contaminating antibiotics.

It follows that antibiotics in river and drinking waters would serve as selective agents,

promoting an increase in proportion of the antibiotic-resistant NTM at the expense of antibiotic-

sensitive members of the microbial flora. In drinking water, chlorination during water treatment has

been shown to result in an increase in the proportion of antibiotic-resistant bacteria [75]. Although

that would be a factor in selecting for antibiotic-resistant bacteria during water treatment, it would

not influence the increase in the proportion of antibiotic-resistant bacteria in drinking water sources.

Thus, antibiotics in source waters might increase the proportion of the antibiotic-resistant NTM in

drinking water sources.

Scenario 3. Are Humans Exposed to NTM in Showers, Hot Tubs, and Therapy Baths?

As a consequence of the very high cell surface hydrophobicity, particularly documented for

M. avium and M. intracellulare, NTM are readily aerosolized from water [41]. The concentration of

NTM cells in droplets ejected from waters can be as high at 10,000-fold higher than the

concentration of cells in the bulk suspension [41]. There are a number of sites where aerosolization

of NTM cells can occur. In particular, showers and hot tubs (spas) are sites where humans can be

exposed to aerosolized NTM cells. M. avium pulmonary disease was linked to M. avium exposure in a

shower [27]. There are a variety of reports linking hot tub (spa) aerosol NTM exposure to either

NTM pulmonary disease [75] or hypersensitivity penumonitis [77, 78].

In the instances cited above, a common thread is exposure to aerosols generated in closed

spaces from water-borne NTM. In addition, many of the instances of hot tub (spa) NTM aerosol

exposure have followed routine disinfection [76]. Disinfection would be expected to kill off

disinfectant-susceptible microorganisms, but leave the disinfectant-resistant NTM unaffected,

leading to their proliferation in the absence of competition.

Scenario 4. Are Workers Exposed to NTM Aerosols from Metal Recovery Fluids?

Outbreaks of hypersensitivity pneumonitis (HP) among automobile workers have been

associated with exposures to metal recovery fluids [79]. Metal recovery fluids (MRF) are often oil:

water emulsions used to cool metal-cutting or grinding tools and carry off metal particles during the

cutting and grinding of metal castings. Mycobacteria, in particular the newly described species

Mycobacterium immunogenum, have been recovered from metal recovery fluids [80]. NTM are capable

of utilizing the non-aqueous constituents of MRF, including tall oils [81]. It is likely that the MRF

concentrates that are added to water are free of NTM; the NTM sources include the water used for

mixing, as well as due to the recycling of MRF in flowing system with NTM in biofilms. In mostly

all of the outbreaks, HP has appeared after disinfectant (biocide) was added to the MRF to reduce

the growth of Gram-negative bacteria [79]. As M. immunogenum was shown to be relatively resistant

to most biocides used in disinfection of MRFs [38], it follows that biocide use may have led to the

proliferation of M. immunogenum (or other NTM) in the absence of competition.

Scenario 5. Are NTM Agents of Pollutant Degradation and Nutrient Cycling?

A number of NTM, including the rapidly growing species Mycobacterium austroafricanum,

Mycobacterium frederiksbergense, and Mycobacterium tusciae, have been detected in Belgian soils

contaminated with polycyclic aromatic hydrocarbons (PAHs) by amplification of the 16S rRNA

gene for rapidly growing mycobacteria [20]. Polluted sites in Japan yielded isolates of Mycobacterium

austroafricanum, Mycobacterium chubuense, Mycobacterium chlorophenicolicum, Mycobacterium frederiksbergense,

Mycobacterium mageritense, and Mycobacterium vanbaalenii [21]. It is likely that the ubiquitous water-borne

slowly growing Mycobacterium species such as M. avium were also present, but either undetected [20]

or not isolated due to insufficient time for colony development [21].

Although underappreciated, NTM are capable of degrading a wide range of pollutants,

including a number of organic wastewater contaminants found in U.S. streams, including:

anthracene, benzo[a]pyrene, fluoranthene, naphthalene, phenanthrene, phenol, pyrene, and

tetrachloroethylene [61, 62]. A list of organic pollutants degraded by NTM are listed in Table 5. In

addition to the degradation of pollutants, a substantial proportion of Mycobacterium species, including

Mycobacterium tuberculosis and the major water-borne pathogens Mycobacterium avium, Mycobacterium

chelonae, Mycobacterium kansasii possess haloalkane dehalogenase activity [63]. Cholesterol, another

organic wastewater contaminant found in U.S. streams [61, 62] is subject to NTM metabolism and

transformation. In fact, NTM are used in industrial production of some cholesterol derivatives [64,

65].

It is likely that NTM hydrophobicity contributes to their ability to metabolize organic

wastewater contaminants; the majority of which are non-polar and partition in the organic phase.

One reason for the lack of appreciation for the role of NTM in nutrient cycling and degradation of

organic wastewater contaminants is their slow growth. Most surveys of microorganisms responsible

or involved in pollutant degradation fail to incubate media for enough time for the appearance of

NTM colonies. Thus, NTM haven’t been detected as members of pollutant-degrading microbial

consortia.

Scenario 6. Have Humans Activities Resulted in the Disappearance of Mycobacterium

scrofulaceum?

Before approximately 1985, M. scrofulaceum was the predominant mycobacterium isolated

from cervical lymph nodes in children suffering from cervical lymphadenitis [8]. However, since

1985, Mycobacterium avium has been isolated almost exclusively from children with cervical

lymphadenitis [8]. M. scrofulaceum has disappeared; it is seldom recovered from pulmonary patients

and not isolated it from drinking water. In surveys of natural waters (e.g., streams, ponds, rivers,

and lakes) performed from 1975-1983, we recovered M. scrofulaceum [15]….but no more [22, 23, 25].

We have only isolated M. avium and Mycobacterium intracellulare, but never M. scrofulaceum and have not

altered the isolation regimen. The only published M. scrofulaceum isolations are from untreated water

and patients exposed to untreated water [67].

Why has M. scrofulaceum disappeared? M. scrofulaceum grows significantly faster than either M.

avium or M. intracellulare. Therefore, in untreated water, M. scrofulaceum is the predominant

mycobacterium. However, M. scrofulaceum is significantly more susceptible to chlorine and other

disinfectants used in water treatment [37]. As M. avium, M. intracellulare, and M. scrofulaceum occupy

many of the same environments, chlorination (brought about by the Clean Water Acts) killed off M.

scrofulaceum , such that its habitats are now occupied solely by M. avium and M. intracellulare.

Future Perspective

The overlap between the habitats shared by nontuberculous mycobacteria (NTM) and

humans, demonstrates that human behaviors (e.g., disinfection and transmission of water, and

generation of aerosols), select for the proliferation and transmission of NTM. Current examples of

human influences on NTM ecology and epidemiology suggest that the incidence of NTM disease

will continue to increase. Although the review focuses on NTM, it is anticipated that human

behaviors may be selecting for proliferation and transmission of other microorganisms.

Executive Summary

Nontuberculous mycobacteria (NTM) are opportunistic pathogens of humans and animals

whose source is the environment. In addition to the natural environment (e.g., soils and waters),

NTM are normal inhabitants of environments where they can come in contact with humans and

animals; namely their habitats overlap. Importantly, a number of human behaviors, such as

disinfection and transmission of drinking water lead to increased numbers of NTM. Others, such as

the generation of aerosols in either households or industry, lead to increased transmission of NTM

to humans. These increases are due to the fact that NTM cells grow at low carbon concentrations

and are hydrophobic. Hydrophobicity leads to disinfectant-resistance and preferential aerosolization

and attachment to pipe surfaces. Attachment leads to formation of biofilms leading to further

increases in disinfectant-resistance. Discovery that human behaviors lead to selection and

proliferation of NTM in habitats occupied by both humans and NTM, creates the dilemma that

human actions taken to reduce pathogen exposure (i.e., water disinfection), lead to possible

increased NTM disease; an unforeseen consequence.

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Financial Disclosure

The author has no conflict of interest.

Acknowledgements

Investigations in the author’s laboratory have been supported by the NonTuberculous Mycobacteria

Information and Research Foundation (NTMir, Inc.), the American Water Works Association

Research Foundation (AWWARF, now the Water Research Foundation, WRF), the National

Institutes of Allergy and Infectious Diseases, and the United States Council for Automotive

Research (USCAR).

Table1. NTM of Medical Importance.

Mycobacterium species

Mycobacterium avium and Mycobacterium intracellulare (M. avium complex, MAC)

Mycobacterium kansasii

Mycobacterium malmoense

Mycobacterium xenopi

Mycobacterium ulcerans

Mycobacterium fortuitum

Mycobacterium abscessus

Mycobacterium chelonae

(Marras and Daley, 2002) [5].

Table 2. Habitats Occupied by NTM

Habitats Reference(s)

Natural Waters [15]

Natural Aerosols [18]

Drinking Water Distribution Systems [22, 23]

Household Plumbing [26, 27]

Spas and Hot Tubs [75]

Aerosols in Showers [27]

Metal-Recovery Fluid [77]

Soils [16, 19]

Potting Soils [19, 81]

Waste Dumps [20, 21]

Table 3. Advantages and disadvantages of NTM Hydrophobicity

Advantages Disadvantages

Disinfactant- Antibiotic- and Low Permeability to Hydrophilic Nutrients

Heavy Metal-Resistance Low Transport Rates of hydrophilic Nutrients

Surface Attachment = Reduced Washout Slow Growth

Slow Growth = Anti-microbial Resistance

Aerosolization

Hydrocarbon Degradation

Table 4. Time (in minutes) necessary to kill 90 % of different species of Mycobacterium and Legionella

pneumophila at temperatures relevant to those attained in hot water heaters in households or boilers in

buildings [52].

Mycobacterium spp. or 50° C (122° F) 55° C (131° F) 60° C (140° F)

Legionella pneumophila

M. avium 1,000 min 54 min 4 min

M. intracellulare 550 min 24 min 1.5 min

M. scrofulaceum 934 min 61 min 5.3 min

M. kansasii 77 min 6.6 min 0.7 min

M. marinum 75 min 13 min 1 min

M. xenopi No Killing in 48 hr 346 min 33 min

M. chelonae 169 min 23 min 4.3 min

M. fortuitum 100 min 25 min 3.7 min

Legionella pneumophila 165 min 17 min 1.8 min

Table 5. Organic Wastewater Contaminants Degraded by NTM

Contaminant a Mycobacterium Strain(s) Reference

Anthracene Mycobacterium sp. strain PYR-1 [82]

Benzo[a]pyrene Mycobacterium sp. strain PYR-1 [82]

Cholesterol Mycobacterium sp. strains DP and

ATCC 29472 [64]

Fluoranthene Mycobacterium sp. strain PYR-1 [82]

Mycobacterium sp. strain CH-1 [83]

Naphthalene Mycobacterium convolutum ATCC 29673 and

Mycobacterium vaccae JOB5 [84]

Phenanthrene Mycobacterium sp. strain PYR-1 [82]

Mycobacterium sp. strain CH-1 [83]

Phenol Mycobacterium vaccae strain JOB5 [85]

Pyrene Mycobacterium sp. strain PYR-1 [82]

Mycobacterium sp. strain CH-1 [83]

Tetrachloroethylene Mycobacterium vaccae strain JOB5 84]

a [61, 62]

Table 6. Habitats where Human Activities Influence NTM

Habitat Human Influence

Drinking Water Distribution Systems (1) Disinfection kills competitors

(2) Nutrient removal favors oligotrophs

(3) Biofilm formation supports growth and persistence

Household Plumbing (1) Heated water favors NTM growth

(2) Hot Water Temperatures favor NTM

(3) Biofilm formation in hot water heater

Household Showers (1) Showerhead collects particulates

(2) Showerhead biofilm formation

(3) Efficient generation of NTM-enriched aerosols

Hot tubs and Spas (1) Organic contamination reduces disinfectant concentration

(2) Efficient generation of NTM-enriched aerosols

Food Baths (1) Organic contamination reduces disinfectant concentration

Metal Removal Fluid (1) MRF constituents support NTM growth

(2) Biocides kill NTM competitors

(3) MRF organics reduce biocide concentration

(4) High velocity spray generates NTM-enriched aerosol