Saturday 17 January 2015

Bacteria from biofilms in the water supply at Mafikeng, South Africa.

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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