South Africa has an arid climate
and a rapidly rising Human population, which can place a strain on the
country’s attempts to provide clean water for its entire population. Like many countries
it has begun to recycle wastewater for Human consumption, which adds to the
water available to supply the needs of the nation’s citizens, but also
increases the risk of pathogenic and opportunistic microorganisms entering the
water supply system. Moreover, like many developing countries, South African
water-treatment plants occasionally suffer from maintenance problems, and a
lack of suitably qualified personnel.
In a paper published in the South African Journal of Science on 26 November 2014, Suma George Mulamattathil of
the School of Environmental Science and Development at North-West University
and the Department of Water and Sanitation at the University of Limpopo, Carlos
Bezuidenhout also of the School of Environmental Science and Development at
North-West University and Moses Mbewe, also of the Department of Water and
Sanitation at the University of Limpopo, describe the results of a series of
experiments on which Bacteria were allowed to form biofilms (polysaccharide
matrixes formed by Bacterial colonies as a way of resisting environmental
stresses, which are also known to offer protection against antibiotics,
detergents etc.) on galvanized steel and copper coupons placed within pipes
carrying water from a variety of sources in the Mafikeng area.
Biofilm developing device attached to a main water pipe of a building at
the North-West University in Mafikeng. Mulamattathil et al. (2014).
Pipes carrying domestic water
supplies in South Africa are typically made of cast iron, galvanised steel,
stainless steel, copper or polyethylene. Previous experiments have shown that
biofilms form more rapidly and more extensively in pipes made from polythene or
other plastics than metal pipes, though little work has been done on the merits
of different metals. Anecdotal evidence has it that biofilms form less readily
on copper, but such films are also known to frequently harbour Bacteria that
can attack the copper, raising the rate at which it leaches into the water
supply, potentially causing health problems.
The water used in the tests came
from four sources, untreated water from the Modimola Dam, which receives some
of its water from a water treatment plant, domestic tap water derived entirely
from the Modimola Dam treatment plant, treated spring water from Molopo Eye,
and mixed water from a supply that combined treated water from the Modimola Dam
treatment plant with chlorinated spring water from Molopo Eye.
Filters containing galvanized
steel or copper filters were exposed to each water source for four months. At
the end of this period they were removed and any biofilms present tested for
Coliform Bacteria in general, faecally derived Coliform Bacteria (i.e. Bacteria
that may have derived from Human waste), and Bacteria belonging to the genera Aeromonas and Pseudomonas, both of which are water and soil Bacteria that can be
opportunistic pathogens (i.e. Bacteria which can live their entire life-cycles
in the soil, but which will infect in Humans if the opportunity arises), Aeromonas causing gastroenteritis and Pseudomonas a variety of nosocomial
infections (expand). Aeromonas is
known to form biofilms in water supply systems and is resilient to water
chlorination. Pseudomonas is
naturally resilient to a variety of antibiotics, including β-lactams,
aminoglycosides and fluroquinolones. Bacteria recovered were also tested for
antibiotic resistance and the expression of pathogenic genes (genes likely to
cause harm to humans, typically by the production of toxins).
Mini tap filter (a point-of-use water-treatment device), which was used
to collect biofilms. Mulamattathil et al.
(2014).
The galvanized steel coupons did
have more extensive biofilm communities than the copper coupons, however the
copper coupons, after only four months of exposure (compared to domestic water
pipes which will typically be exposed for decades) were already showing signs
of corrosion, suggesting Bacterial corrosion could indeed lead to the metal
being leached into the water.
Electron micrograph of biofilm from mixed water collected using a
copper coupon. Mulamattathil et al. (2014).
All of the coupons produced
biofilms, with those on the galvanized steel being thick and spongy. Theses
biofilms were dominated by rod-shaped Bacteria, which formed dense colonies
within the polysaccharide layer.
Untreated water from the Modimola
Dam was found to contain Coliform Bacteria, including faecally derived Coliform
Bacteria, as well as the soil Bacteria Pseudomonas,
but not the water-born Aeromonas.
Coupons placed in treated water from the Modimola Dam treatment plant, however,
developed colonies of both Aeromonas
and Pseudomonas. The mixed water
supply was not found to contain any pathogenic Bacteria, however coupons placed
in this water again developed colonies of Aeromonas
and Pseudomonas, suggesting that
these Bacteria were present at low levels, and given an opportunity to form
biofilms, they would increase in numbers rapidly. Only the spring water from
Molopo Eye failed to produce any of the bacteria tested for.
Electron micrograph of biofilm from Modimola Dam collected using a
galvanised coupon. Mulamattathil et al.
(2014).
All of the bacteria tested were
found to be resistant to ampicillin, amoxicillin, cephalothin, erythromycin,
chloramphenicol and trimethoprim, though none showed resistance to ciprofloxacin
and most were susceptible to streptomycin. Four different patterns of gene
expression for antibiotic resistance were found, including KF-AP-C-E-OT-K-TM-A,
which indicates resistance to eight different antibiotics. This strongly
suggests that biofilms in water supplies can act as a reservoir for antibiotic
resistant micro-organisms, and is of particular concern, particularly for
infants and people with compromised immune systems living in Mafikeng. In
addition a variety of pathogenic genes were found to be being expressed in Aeromonas and Pseudomonas Bacteria.
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