WATER HYGIENE AND SAFETY 700,000 600,000
n Antibacterial hose n Control hose #1 n Control hose #2
500,000
400,000
300,000
200,000
100,000
0 Week 0 Week 1 Week 2 Week 3 Week 5 Figure 2: Mean aerobic colony count vs. sampling week for all three hose samples measured.
nanoparticles are a popular bacteriostatic additive which can be incorporated into metals, plastics, glass, and industrial membrane surfaces, to reduce fouling. The large surface to volume ratio of these AgNPs enables a high reaction activity. AgNPs have antibacterial effects against a wide range of multidrug-resistant isolates of P. aeruginosa, Escherichia coli (E. coli), and Streptococcus pyogenes (S. pyogenes), all of which have exhibited multidrug- resistance to ampicillin and erythromycin. Their antimicrobial mechanism is primarily based on silver ions interacting with essential molecules in biological macromolecules such as sulphur, oxygen, and nitrogen. Silver ions inhibit the electron transport chain in microbial cytochrome, thus inhibiting energy transfer. They also damage microbial DNA and RNA, thus inhibiting reproduction. Finally, they destroy the 30S sub-unit of ribosomes, inhibiting bacterial growth. AgNPs integrated in plastic material had been shown to reduce P. aeruginosa by >99.99%, L. pneumophila by >99.99%, E. coli by >99.99%, Methicillin resistant Staphylococcus aureus (MRSA) by >99.99%, and Klebsiella pneumoniae (K. pneumoniae) by >99.9% in water after 24 hours.3
(Plastic-integrated AgNPs have negligible leaching rates of 1-8 µg/L, far below the migration limit defined in the EU Regulation 10/2011 of 50 µg/L).
Aston University study
In a laboratory study led by Professor of Microbiology, Anthony Hilton, at Aston University, T-Safe antibacterial shower hoses, manufactured by Johs. Tandrup A/S, were compared with standard shower hoses to investigate their biofilm- reducing potential with particular regard to P. aeruginosa, which is especially critical in terms of the last 1 metre of the
55 Health Estate Journal July 2020
plumbing system and retrograde contamination. The antibacterial shower hoses used in the study incorporated silver nanoparticles (AgNPs) integrated in the hose material.
The shower hose testing was conducted by Water Environmental Treatment UK, with test showers attached to a custom-made copper pipe manifold (Fig. 1) to enable simultaneous, controlled water flushing. In turn, the manifold was connected to the building’s mains hot and cold water supply via a mixer temperature control valve set to c. 40˚C. Every seven days, water was allowed to flow freely through the hoses for 7 minutes at 40˚C, after which the water was kept standing inside the hoses. The hoses’ internal lumen was cut aseptically and sampled microbiologically every seven days for nine weeks to determine the
70,000 60,000
n Antibacterial hose n Control hose #1 n Control hose #2
50,000
aerobic colony count and presence of P. aeruginosa. The sample water was also subjected to microbiological analysis to establish the aerobic colony count and presence of P. aeruginosa, with this work undertaken by Mercian Science, an ISO 17025-accredited UKAS laboratory.
The study results – 90% aerobic bacterial and 50-95% reduction in P. aeruginosa
The mean aerobic colony count rose to over 300,000 cfu/mL throughout the 12 sampling weeks (Fig. 2). While in the antibacterial hoses the increase was almost linear, the mean aerobic colony count in the control hose increased to a maximum, thereafter falling and rising again. This could be a result of an influx of organic material into the control hoses until week 3. With sizeable variations
Week 8 Week 12
40,000
30,000
20,000
10,000
0 Week 8
Figure 3: Mean P. aeruginosa count vs. sampling week for all three hose samples measured.
July 2020 Health Estate Journal 55 Week 12
TVC@22˚C (cfu/mL)
P. aeruginosa (cfu/mL)
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