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Reducing bacterial contamination using silver antimicrobial technology

This study explores whether silver antimicrobial technology improved infection control in a healthcare setting

  • Figures and tables can be seen in the attached print-friendly PDF file of the complete article in the ‘Files’ section of this page

Authors

Lesley Taylor, BSc, is microbiologist; Paul Phillips,BSc, is analytical chemist; Richard Hastings, PhD, is microbiologist; all at BioCote, Wolverhampton.

Abstract

Taylor, L. et al (2009) Reducing bacterial contamination using silver antimicrobial technology. Nursing Times; 105: 7, 24-27.

Background: Silver antimicrobial technology has been developed to reduce contamination in healthcare settings.

Aim: To provide an evidence base on the efficacy of antimicrobial technology (BioCote) in real-life settings.

Method: The study assessed the impact of various BioCote-treated products on counts of viable bacteria cultured from a treated setting compared with a control setting. Untreated products were also placed in the treated setting.

Results: There was a mean reduction in bacterial counts of 96% on treated surfaces in the experimental unit compared with the control unit, and a mean reduction of 44% on untreated surfaces in the experimental compared with the control unit.

Discussion: This suggests that antimicrobial materials can extend decontamination to the wider environment.

Conclusion: Silver-treated materials can reduce levels of bacteria contaminating healthcare settings.

Background

As long as healthcare-associated infections (HCAIs) remain a major clinical and financial problem within the health service, infection prevention and control will remain a priority for healthcare providers (Department of Health, 2008).

Companies continue to develop products to help healthcare professionals meet infection control targets. The number of healthcare-equipment manufacturers incorporating antimicrobial properties in their products has increased dramatically in recent years.

Silver lends itself as an antimicrobial agent owing to its efficacy against a range of micro-organisms and lack of toxicity to non-target cells. Paddock et al (2007) and Rupp et al (2004) described its effectiveness in wound dressings and catheters.
Since technological advances now allow silver ions to be incorporated into a wide range of materials, there is an extensive
and growing range of silver-based antimicrobial products.

Aim

This article describes a pilot study in an acute trust that investigated reducing bacterial contamination using silver antimicrobial (BioCote) technology. Laboratory-validation testing of BioCote-treated products shows up to a 99.9% reduction of bacterial contamination over 24 hours, suggesting that similar efficacy can be achieved in real-life healthcare settings. The study aims to offer evidence to suggest that the efficacy of antimicrobial technology in real-life settings is comparable with that shown in laboratory validation testing.

Literature review

An increasing number of studies suggest that the healthcare environment can contribute to HCAIs (Dancer, 2008; Boyce, 2007; von Baum et al, 2007; Gastmeier et al, 2006; Rusin et al, 2002). Sexton et al (2006) reported that contaminated surfaces may serve as a reservoir of MRSA in hospitals. While the extent of the environment’s contribution to HCAIs is unclear, it is generally accepted that the healthcare setting can play a part in the transfer of infectious agents from inanimate sources, such as fixtures or fittings, to patients.

Pathogens are able to survive in the environment for considerable lengths of time (Kramer et al, 2006; Dietze et al, 2001) and there is evidence to suggest that conventional cleaning practices may not be sufficient to ensure decontamination (Denton et al, 2004; Rampling et al, 2001). Any additional measures that can be shown to reduce contamination levels in healthcare settings are therefore worthy of investigation.

This pilot study investigated the effect of silver ion-treated (BioCote) products on counts of viable bacteria in a healthcare setting compared with a non-treated control environment.

Method

Pilot study settings

Two outpatient units (A and B) of an acute NHS trust provided antimicrobial-treated and control settings respectively. The units were similar in terms of volume of people, layout and floor-surface area. General clinical practice was carried out in each unit throughout the study. Both units were refurbished before the study began, unit A in 2006 and unit B in 2003 and both were cleaned on a regular basis. This included wet-mopping of floors with detergent, high- and low-level dusting, damp-dusting with detergent and the cleaning of sanitary areas with detergent.

BioCote-treated products were placed in unit A in May 2006. Both facilities worked normally for 12 months before environmental swabbing started; this lasted for four months. A number of untreated products were swabbed in unit A to observe any effect that BioCote-treated products had on their contamination.

Materials and methods

The BioCote-treated products placed in unit A are listed in Table 1. Previous validation testing had shown reductions of more than 95% of viable counts of Escherichia coli and Staphylococcus aureus, compared with untreated materials.

The untreated products used in the pilot were not made by the same companies producing the treated products. However, they were made from the same material and were of similar size and shape.

Environmental swabbing

Environmental swabbing started in April 2007. Samples were collected from BioCote-treated and untreated products in treatment rooms, consultation areas, washrooms and laboratories. Table 2 lists swabs collected and products sampled.

Sterile cotton-tipped Transtube swabs containing a neutralising buffer were used to collect samples. Swabs were inoculated on plate-count agar and incubated aerobically at 30C for 48 hours. Total viable counts were expressed as colony-forming units (CFUs).

Results

CFU counts are shown in Table 3. Counts from individual swabs were used to calculate an average CFU for each product. Those from BioCote-treated products in unit A were 62-98% lower than from comparable, untreated products in unit B.

Average CFU counts varied but tended to conform to a predictable pattern. The highest were found on tiles around sinks, which tend to be damp environments promoting bacteria growth. BioCote-treated tiles had 90% less contamination than untreated tiles in the control unit. The products with the lowest CFU counts were those of relatively dry surfaces (curtains/blinds and signs). These showed relatively lower rates of reduction, at 73% and 75% respectively.

Untreated products that have relatively high hand contact (door handles, electrical switches and chairs) showed relatively high CFU counts. Reductions of contamination on the treated versions were at 84-95%.

A comparison of CFU counts from the various types of coatings used to treat the products is shown in Table 4. These ranged from 70% (fabrics) to 99% (laminates) lower than in untreated equivalent surfaces.

The average CFU counts from treated products in unit A were compared with those from both untreated products in unit A and untreated products in unit B. Also, average CFU counts from untreated samples in unit A were compared with those from untreated products in unit B (see Fig 1). This three-way comparison reveals that the average CFU counts from any BioCote-treated product at any point of the four-month study were 96% lower than those from any untreated product in unit B. The average CFU counts from any BioCote-treated product were 93% lower than the average CFU counts from any untreated product within the same facility (unit A). The average CFU counts from any untreated product in unit A were 44% lower than the average CFU counts from any untreated product in unit B.

Discussion

An increasing number of antimicrobial products are now offered but the evidence base to support the use of specific products is too often lacking. This study aimed to produce evidence to show the environmental effectiveness of silver ion (BioCote) antimicrobial technology.

Laboratory-validation testing suggested that treated products placed in a healthcare setting would result in reduced bacterial contamination of their surfaces. This was confirmed, with reductions of CFU counts of 62-98% compared with untreated products in a control setting. It is, then, possible to decontaminate surfaces in a healthcare setting by using permanently positioned objects with effective antimicrobial properties.

During laboratory trials, BioCote-treated materials consistently demonstrate high antimicrobial efficacy. This study has shown and quantified the extent to which this can be reproduced in a real-life setting. When BioCote-treated products are validated in
a laboratory, the levels of reductions are relatively constant, regardless of the product tested. In comparison, this study showed variations in levels of bacterial reduction between product types in a real-life setting. This is likely to be attributable to environmental variables in real-life healthcare, which are notoriously difficult to monitor and control during environmental studies and produce results that give limited insights.

Since this study did not identify environmental isolates such as specific bacteria, it was not possible to determine the proportion of pathogens present on surfaces in both units. However, specific pathogens have been repeatedly isolated from healthcare settings, so it is reasonable to expect a proportion of this study’s isolates to be capable of nosocomial infection.

This study aimed to establish the ability of antimicrobial products to reduce levels of bacterial contamination in addition to effects of cleaning. Observations have shown sustained reductions in bacterial levels, in addition to cleaning. Therefore, the study supports the case for including silver-treated products in infection-control strategies.

Organic disinfectants will reduce levels of contamination but tend not to maintain their effect (Brady et al, 2003). Furthermore, the suspicion that conventional cleaning may not sufficiently decontaminate a healthcare setting supports the view that cleaning would benefit from adding antimicrobial products (Denton et al, 2004). In a practical sense, continuous decontamination of healthcare settings can be achieved by integrating products with antimicrobial properties. The antimicrobial activity of the treated surfaces in this study was seen to last for the study period, that is, over 12 months.

This study also showed reduced levels of bacterial contamination on untreated products in unit A, compared with untreated products in unit B - average counts were 44% lower. Our results suggest that a reduction in bacteria on antimicrobial surfaces results in lower numbers of bacteria on other surfaces because there are fewer bacteria to be transferred. Decontamination of the wider setting may be a beneficial consequence of placing a limited number of antimicrobial objects in that environment.

While objects in healthcare settings can be contaminated from a variety of sources, including colonised and infected patients (Boyce et al, 2007; Oie et al, 2007), there is less evidence to suggest that a contaminated environment can lead to patients becoming colonised and infected. However, studies are starting to produce evidence to support the hypothesis that environmental bacteria contribute to HCAIs.

Conclusion

This study highlights the ability of silver-treated materials to reduce levels of bacteria contaminating healthcare settings.

As silver becomes more commonly used in healthcare settings, further studies are needed on how silver-treated products affect bacterial contamination in the environment. BioCote continues to work with the NHS and government organisations to increase the evidence base.

References

Boyce, J.M. (2007) Environmental contamination makes an important contribution to hospital infection. Journal of Hospital Infection; 65: S2, 50-54.

Boyce, J.M. et al (2007) Widespread environmental contamination associated with patients with diarrhoea and methicillin-resistant Staphylococcus aureus colonisation of the gastrointestinal tract. Infection Control and Hospital Epidemiology; 28: 10, 1142-1147.

Brady, M.J. et al (2003) Persistent silver disinfectant for the environmental control of pathogenic bacteria. American Journal of Infection Control; 32: 5, 309.

Dancer, S.J. (2008) Importance of the environment in methicillin-resistant Staphylococ-cus aureus acquisition: the case for hospital cleaning. The Lancet Infectious Diseases; 8: 101-113.

Denton, M. et al (2004) Role of environmental cleaning in controlling an outbreak of Acinetobacter baumannii on a neurosurgical unit. Journal of Hospital Infection; 56: 2, 106-110.

Department of Health (2008) The Health Act 2006: Code of Practice for the Prevention and Control of Health Care Associated Infec-tions . London: DH.

Dietze, B. et al (2001) Survival of MRSA on sterile goods packaging. Journal of Hospital Infection; 49: 4, 255-261.

Gastmeier, P. et al (2006) Correlation between the genetic diversity of nosocomial pathogens and their survival time in intensive care units. Journal of Hospital Infection; 62: 181-186.

Kramer, A. et al (2006) How long do nosocomial pathogens persist on inanimate surfaces? A systematic review. BMC Infectious Diseases; 16: 6, 130-145.

Oie, S. et al (2007) Association between isolation sites of methicillin-resistant Staphylococcus aureus (MRSA) in patients with MRSA-positive body sites and MRSA contamination in their surrounding environmental surfaces. Japanese Journal of Infectious Diseases; 60: 367-369.

Paddock, H. et al (2007) A silver impregnated antimicrobial dressing reduces hospital length of stay for pediatric patients with burns. Journal of Burn Care and Research; 23: 3, 409-411.

Rampling, A. et al (2001) Evidence that hospital hygiene is important in the control of methicillin-resistant Staphylococcus aureus. Journal of Hospital Infection; 49: 2, 109-116.

Rupp, M.E. et al (2004) Effect of silver-coated urinary catheters: efficacy, cost-effectiveness, and antimicrobial resistance. American Journal of Infection Control; 32: 8, 445-450.

Rusin, P. et al (2002) Comparative surface to hand and finger to mouth transfer efficiency of gram-positive, gram-negative bacteria and phage. Journal of Applied Microbiology; 93: 4, 585-592.

Sexton, T. et al (2006) Environmental reservoirs of methicillin-resistant Staphylococcus aureus in isolation rooms: correlation with patient isolates and implications for hospital hygiene. Journal of Hospital Infection; 62: 2, 187-194.

Taylor, L. et al (2009) Reduction of bacterial contamination in a healthcare environment by silver antimicrobial technology. Journal of Infection Prevention; 10: 1, 6-12. DOI: 10.1177/1757177408099083

VonBaum, H. et al (2007) Environmental Contamination in the Rooms of MRSA-Colonised Patients. 17th European Congress of Clinical Microbiology and Infectious Diseases, ICC Munich, Germany.

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