Food Protection Trends - September/October 2020 - 318

Mexican health authorities is needed to verify compliance
with standards regarding microbial safety.
In this study, NTM were identified in 25% of water
samples. The results are similar to our previous results
(29.7%) in bottled purified water in Mexico City (7), a large
metropolitan area. All NTM species identified in the present
study belonged to the M. fortuitum complex, composed of
related species that share a close phylogenetic relationship
and can cause pulmonary and extrapulmonary infections
(5, 19). M. fortuitum has been frequently isolated from wild
animals including reptiles, amphibians, and invertebrates,
whereas M. porcinum is primarily recovered from swine with
lymphadenitis (4). Recently, M. conceptionense has been
isolated from aquarium fish (10). Thus, a variety of animals
can be a permanent or transient source of NTM species.
The NTM species identified in this study were detected in
various environments, including natural waters, drinking
water distribution systems, and soils. By contrast, both M.
fortuitum and M. porcinum were isolated from potable water
in a previous study carried out by us (30) in Mexico City.
Control of NTM is challenging because, unlike traditional
pathogens, they are native members of drinking water
microbial communities. In addition, they can be resistant
to disinfectant residuals and other biocides (such as copper
ions) due to a thick, hydrophobic cell wall rich in mycolic
acids that helps them form aggregates in liquid media (31).
Moreover, NTM have the ability to form biofilms on different
surfaces, resist high temperatures, and grow in marginal
environments with low nutrient and oxygen content (11).
It has been reported that Mycobacterium avium can survive
attached to polyethylene terephtalate water bottles and
that the cell adhesiveness to the polyethylene terephtalate
wall increases with time (36). Furthermore, NTM are
also highly resistant to chlorine and UV light radiation. Le
Dantec et al. (21) reported that to obtain an inactivation
level of 99.9% for mycobacteria it is necessary to use chlorine
concentrations that are 100 to 330 times higher, depending

of the species, than the concentrations required to obtain
the same inactivation level for E. coli. Also, Schiavano et al.
(33) found that a dose of 192 mJ/cm2 was needed to obtain
complete inactivation of M. avium subsp. hominissuis, a dose
that is much higher than the limit recommended by the
international standards for UV disinfection of drinking water
(16 to 40 mJ/cm2).
This study has some limitations. Although the number of
water samples represents 43% of purification plants found
in Morelia, the number of samples is still small. Therefore,
a more representative sample across the population would
need to be taken to assess the risk. In addition, the source and
treatment process of bottled water contamination should be
investigated more thoroughly. Further studies of final product
quality in storage conditions are also required.
RECOMMENDATIONS
This pilot study showed that most of the purified bottled
water analyzed had unsatisfactory microbiological quality,
and some harbored NTM associated with illness. Thus,
there is a need for pertinent authorities to intensify efforts
in routine monitoring of the various activities in the purified
bottled water industry, with the view to supplying safe and
wholesome water to the public.
ACKNOWLEDGMENTS
We thank M. T. Horn-Copeland for English language
review of the article. The study was supported by Instituto
Politécnico Nacional Secretaría de Investigación y Posgrado
20200033 (to J. Francisco Cerna-Cortes). We acknowledge
the support of the Consejo Nacional de Ciencia y Tecnología
studentship to R. Jiovanni Soria-Herrera and K. Gabriela
Dominguez-Gonzalez. S. Rivera-Gutierrez, J. Alberto
Gonzalez-Y-Merchand, and J. Francisco Cerna-Cortes
are fellows of Comisión de Operación y Fomento de
Actividades Académicas and Estímulos al Desempeño de los
Investigadores, Instituto Politécnico Nacional.

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