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Doorknobs: A Source of Nosocomial Infection?

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DISCLAIMER: The following article is based upon independent scientific research and is provided for informational purposes only. The conclusions reached in this article are the opinions of the researchers and authors. U.S. EPA-approved testing demonstrates antimicrobial effectiveness for copper alloys against only the following organisms: Staphylococcus aureus, Enterobacter aerogenes, Escherichia coli O157:H7, Pseudomonas aeruginosa and Methicillin resistant Staphylococcus aureus (MRSA). References to effectiveness against Streptococcus have not been proven by U.S. EPA-approved testing and are only the product of initial exploratory testing. No claim of antimicrobial effectiveness is made, either express of implied, with regard to these organisms. Additionally, copper alloy surfaces are not approved for use in direct food-contact applications. Sleek and shining stainless steel doorknobs and push plates look reassuringly clean on a hospital door. By contrast, doorknobs and push plates of tarnished brass look dirty and contaminating. But even when tarnished, brass – an alloy typically of 67% copper and 33% zinc – is bactericidal, while stainless steel – about 88% iron and 12% chromium – does little to impede bacterial growth. My interest in comparing hardware on hospital doors arose from in-service training conducted for housekeeping and maintenance personnel at Hamot Medical center. To heighten their awareness of modes of infection, the students were given blood agar plates and instructions on their use, and they returned with cultures from such diverse sources as toilet bowl water (remarkably clean), salad from the employees' cafeteria (heavily colonized), and doorknobs. Brass doorknob cultures showed sparse streptococcal and staphylococcal growth; stainless steel doorknob cultures showed heavy growth of Gram-positive organisms and an array of Gram-negative organisms, including Proteus species. In a later pursuit of the investigation of bacterial growth on metal, small strips of stainless steel, brass, aluminum, and copper were inoculated with broths of Escherichia coli, Staphylococcus aureus, Streptococcus group D, and Pseudomonas species. The broths contained approximately 10,000,000 bacteria/ml, a very heavy inoculum. Then the strips were air-dried for 24 hours at room temperature, inoculated onto blood agar plates, and incubated for 24 hours at 37°C.
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Home > Applications > Antimicrobial Copper Surfaces > Additional Research Information > Doorknobs: A Source of
Nosocomial Infection?
Doorknobs: A Source of Nosocomial Infection?
by Phyllis J. Kuhn, Ph.D.
DISCLAIMER: The following article is based upon independent scientific research and is provided for
informational purposes only. The conclusions reached in this article are the opinions of the researchers and
authors. U.S. EPA-approved testing demonstrates antimicrobial effectiveness for copper alloys against
only the following organisms: Staphylococcus aureus, Enterobacter aerogenes, Escherichia coli O157:H7,
Pseudomonas aeruginosa and Methicillin resistant Staphylococcus aureus (MRSA). References to
effectiveness against Streptococcus have not been proven by U.S. EPA-approved testing and are only the product
of initial exploratory testing. No claim of antimicrobial effectiveness is made, either express of implied, with
regard to these organisms. Additionally, copper alloy surfaces are not approved for use in direct food-contact
applications.
Sleek and shining stainless steel doorknobs and push plates look reassuringly clean on a hospital door. By
contrast, doorknobs and push plates of tarnished brass look dirty and contaminating. But even when tarnished,
brass – an alloy typically of 67% copper and 33% zinc – is bactericidal, while stainless steel – about 88% iron and
12% chromium – does little to impede bacterial growth. My interest in comparing hardware on hospital doors arose
from in-service training conducted for housekeeping and maintenance personnel at Hamot Medical center. To
heighten their awareness of modes of infection, the students were given blood agar plates and instructions on their
use, and they returned with cultures from such diverse sources as toilet bowl water (remarkably clean), salad from
the employees’ cafeteria (heavily colonized), and doorknobs. Brass doorknob cultures showed sparse
streptococcal and staphylococcal growth; stainless steel doorknob cultures showed heavy growth of Gram-positive
organisms and an array of Gram-negative organisms, including Proteus species.
In a later pursuit of the investigation of bacterial growth on metal, small strips of stainless steel, brass, aluminum,
and copper were inoculated with broths of Escherichia coli, Staphylococcus aureus, Streptococcus group D, and
Pseudomonas species. The broths contained approximately 10,000,000 bacteria/ml, a very heavy inoculum. Then
the strips were air-dried for 24 hours at room temperature, inoculated onto blood agar plates, and incubated for 24
hours at 37°C.
The results were striking. The copper and brass showed little or no growth, while the aluminum and stainless steel
produced a heavy growth of all microbes.
How fast did the microbes die on copper and brass? The test was repeated at drying intervals of 15 minutes, I
hour, 5 hours, 7 hours, 20 hours, and 24 hours. Brass disinfected itself in seven hours or less, depending on the
inoculum size and the condition of the surface of the metal, freshly scoured brass disinfecting itself in one hour.
Copper disinfected itself of some microbes within 15 minutes. Aluminum and stainless steel produced heavy
growths of all isolates after eight days and growths of most isolates (except Pseudomonas) when I ended that part
of my investigation after three weeks.
In the next part of the investigation, brass and copper strips were covered with seeded agar and incubated in
culture for 24 hours. Because the metals are toxic, I expected a zone of inhibition around the strips, but instead,
most of the bacteria piled up by the edges of the strips. Why? According to the Arndt-Shultz law, low levels of
poisons tend to stimulate biological activity rather than depress it¹, making an organism’s membrane more
permeable to entry by nutrients. Streptococcus group D, however, grew equally well around and over the metal.
To determine whether bacteria in the clear areas under the seeded agar were killed or merely inhibited, the areas
were replica-plated. (This consists of tamping a sterile nubby material like velveteen on a culture plate and
inoculating it onto a fresh plate. The technique allows the transferred bacteria to proliferate-if they are still viable.)
Replica plates from the stainless steel and aluminum strips grew, while replica plates from the brass and copper
strips did not. Scanning electron micrographs of the surfaces of the metals showed that E. coli was completely
disrupted on the brass while remaining intact on the stainless steel.1
What are the implications? Culturing a stainless steel knob on a door between a burn unit and an intensive-care
unit, I found a multiply resistant Staphylococcus epidermidis with a susceptibility pattern identical to that found in
the blood of a septic patient in the intensive-care unit. Cultures of wounds of several other patients yielded similar
organisms. None of these observations prove cause, of course, but they ought to impress us with the need to take
precautions, particularly in the presence of multiply resistant microbes.
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Ironically, stainless steel is actually more expensive than steel coated with brass – $117 vs. $108 for the hardware
for one door, according to one price quotation. If your hospital is being renovated, try to retain old brass hardware
or have it repeated; if you have stainless steel hardware, make certain that it is disinfected daily, especially in
critical-care areas.
We have known for years that certain metals are toxic to bacteria. It is the application of this knowledge to better
infection control that warrants further attention.
Reference
1. Lamanna C. and Mallette MF. Chemical disinfection. In: Basic Bacteriology, Its Biological and chemical
Background. Baltimore: Williams & Wilkins, 1965, p 897.
© 1983 and published by Medical Economics Company Inc., at Oradell, N.J. 07649. All rights reserved. None of the content
of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means (electronic,
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... Candida albicans 67 1,5 ...
... En 1983, une étude menée par Kuhn montre que les poignées de portes étaient des réservoirs à bactéries, mais que sur les poignées de porte en laiton, un alliage de cuivre et de zinc, la prolifération des bactéries E. coli et S. aureus restait limitée par rapport aux poignées en acier inoxydable, avec une disparition des bactéries de la surface en environ 7 heures (67) . A partir des années 1990, l'apparition de bactéries multirésistantes aux antibiotiques a entraîné un essor de la recherche sur les propriétés antibactériennes du cuivre métallique. ...
... La faible augmentation du pH (pH de 7,62 au bout de 3 heures) de la suspension de particules de Mg 0,80 Cu 0,2 O micro s'explique par sa stabilité relative vis-à-vis de l'hydrolyse, comme montréprécédemment. Nos valeurs de pH sont proches de celles de la littérature pour des nanoparticules Mg(OH) 2 (pH = 10)(67) et MgO (pH = 10,6)(57) . ...
Thesis
Les bactéries pathogènes responsables des infections associées aux soins posent des problèmes permanents et croissants dans les établissements de santé. En France, les bactéries Escherichia coli et Staphylococcus aureus sont responsables de plus de 40% de ces infections. Face à l'adaptation permanente de ces bactéries aux nouveaux antibiotiques mis sur le marché, des solutions complémentaires doivent être trouvées. Une des solutions proposée dans ce travail de thèse vise à exacerber les performances de composés bactéricides connus (effet de synergie) ou à procurer des propriétés bactéricides à des composés inactifs en substituant partiellement des ions magnésium par les ions cuivriques ou vice versa. De nouvelles solutions solides ont ainsi été découvertes. Des réactions dans l'état solide, la co-précipitation, la voie hydrothermale ou la mécanosynthèse ont été employées pour synthétiser des particules de taille micro- ou nanométrique des composés désirés. Une fois obtenues, la Diffraction des Rayons X, les Microscopies Electroniques, l'adsorption de diazote, les spectroscopies IR/UV-visible, l'Analyse ThermoGravimétrique couplée à la Spectrométrie de Masse et la Spectrométrie d'Emission Atomique ont été utilisées afin de déterminer la nature, la composition et la taille de ces particules ainsi que leur stabilité dans l'eau ou sous une atmosphère riche en CO2. L'évaluation des propriétés bactéricides dans l'eau et à 20°C révèle que la substitution partielle du magnésium par le cuivre accroît l'activité des composés à la fois en termes d'amplitude et de cinétique. Ces performances accrues ne sont pas nécessairement liées à la teneur en cuivre dans le composé actif.
... In healthcare settings, the initial observations on the potential of brass to limit the bacterial contamination of touch surfaces, as compared to stainless steel, were published in the early eighties [14]. These observations paved the way towards a possible mean of reducing indirect transmission of bacteria originating from touch surfaces, especially in healthcare facilities. ...
... The first report of the antibacterial properties of brass in hospital settings was published by Kuhn in 1983 [14]. This paper highlighted that, even though the door hardware made of brass looked dirtier than the stainless steel one, it limited the bacterial bioburden and could be a mean of reducing HAIs. ...
Article
Full-text available
Copper has been used for its antimicrobial properties since Antiquity. Nowadays, touch surfaces made of copper-based alloys such as brasses are used in healthcare settings in an attempt to reduce the bioburden and limit environmental transmission of nosocomial pathogens. After a brief history of brass uses, the various mechanisms that are thought to be at the basis of brass antimicrobial action will be described. Evidence shows that direct contact with the surface as well as cupric and cuprous ions arising from brass surfaces are instrumental in the antimicrobial effectiveness. These copper ions can lead to oxidative stress, membrane alterations, protein malfunctions, and/or DNA damages. Laboratory studies back up a broad spectrum of activity of brass surfaces on bacteria with the possible exception of bacteria in their sporulated form. Various parameters influencing the antimicrobial activity such as relative humidity, temperature, wet/dry inoculation or wear have been identified, making it mandatory to standardize antibacterial testing. Field trials using brass and copper surfaces consistently report reductions in the bacterial bioburden but, evidence is still sparse as to a significant impact on hospital acquired infections. Further work is also needed to assess the long-term effects of chemical/physical wear on their antimicrobial effectiveness.
... Touch surfaces in high-traffic areas 1 can become vectors for disease propagation through indirect contact between infected and vulnerable persons, 2, 3 making it critical to develop self-sanitizing materials which are effective against a broad range of pathogens. Previous works have shown that microorganisms can remain alive or active on surfaces for hours to days, [4][5][6][7] including many human pathogens such as Methicillin susceptible Staphylococcus aureus (MSSA) and resistant Staphylococcus aureus (MRSA), 8 Rhinovirus 9 , Influenza virus A 10 , Rotovirus 11 and corona viruses such as the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), 5 which has caused the global pandemic of 2020-2022. 12 These long lifetimes partly determine the potential for pathogens to spread during subsequent contact with the surface. ...
Preprint
Full-text available
High traffic touch surfaces such as doorknobs, countertops, and handrails can be transmission points for the spread of pathogens, emphasizing the need to develop materials that actively self-sanitize. Metals are frequently used for these surfaces due to their durability, but many metals also possess antimicrobial properties which function through a variety of mechanisms. This work investigates metallic alloys comprised of several bioactive metals with the target of achieving broad-spectrum, rapid bioactivity through synergistic activity. An entropy-motivated stabilization paradigm is proposed to prepare scalable alloys of copper, silver, nickel and cobalt. Using combinatorial sputtering, thin-film alloys were prepared on 100 mm wafers with 50% compositional grading of each element across the wafer. The films were then annealed and investigated for alloy stability. Bioactivity testing was performed on both the as-grown alloys and the annealed films using four microorganisms -- Phi6, MS2, Bacillus subtilis and Escherichia coli -- as surrogates for human viral and bacterial pathogens. Testing showed that after 30 s of contact with some of the test alloys, Phi6, an enveloped, single-stranded RNA bacteriophage that serves as a SARS-CoV 2 surrogate, was reduced up to 6.9 orders of magnitude (>99.9999%). Additionally, the non-enveloped, double-stranded DNA bacteriophage MS2, and the Gram-negative E. coli and Gram-positive B. subtilis bacterial strains showed a 5.0, 6.4, and 5.7 log reduction in activity after 30, 20 and 10 minutes, respectively. Bioactivity in the alloy samples showed a strong dependence on the composition, with the log reduction scaling directly with the Cu content. Concentration of Cu by phase separation after annealing improved activity in some of the samples. The results motivate a variety of themes which can be leveraged to design ideal bioactive surfaces.
... Kuhn's research [10], as one of the first in this field, confirmed the positive influence of brass handles in order to reduce some bacterial cultures from different hospital areas. The clinical trial included monitoring the growth of the so-called "hospital" bacteria such as Escherichia coli, Staphylococcus aureus, Streptococcus group D and Pseudomonas on stainless steel, brass, aluminium and copper. ...
Article
Full-text available
Copper has long been known as a metal with outstanding antimicrobial properties. Although ancient healers were not familiar with the mechanisms of its influence on microorganisms, they had empirically established its effectiveness in sterilizing drinking water, disinfecting wounds, treating skin diseases, various infections and other maladies. Recently, there has been renewed interest in investigating copper and its alloys as possible materials that can limit the spread of bacteria and viruses, given that humanity is often facing various local epidemics, and rarely pandemics, as ongoing Corona virus, SARS CoV-2, first detected in March 2020. This paper reviews the recent literature in the research field of antimicrobial properties of metallic copper, its alloys and other copper - based materials, with the aim to promote their future implementation on contact surfaces, primarily in hospitals and institutions with a high frequency of people where the probability of spreading infection is increased.
... The contact-killing ability of copper surfaces was studied with respect to bacteria in the early 1980s due to the emerging of hospital superbugs. In 1983, Kuhn [64] compared the bioburden on doorknobs made of brass and stainless steel and found that brass doorknobs showed reduced pathogenic growth in the healthcare environment compared to the stainless steel variety. Recently, Schmidt et al. [17] replaced the normal plastic rails of hospital patients' beds with copper and then tested for the microbial burden. ...
Article
Full-text available
Pathogen transfer and infection in the built environment are globally significant events, leading to the spread of disease and an increase in subsequent morbidity and mortality rates. There are numerous strategies followed in healthcare facilities to minimize pathogen transfer, but complete infection control has not, as yet, been achieved. However, based on traditional use in many cultures, the introduction of copper products and surfaces to significantly and positively retard pathogen transmission invites further investigation. For example, many microbes are rendered unviable upon contact exposure to copper or copper alloys, either immediately or within a short time. In addition, many disease-causing bacteria such as E. coli O157:H7, hospital superbugs, and several viruses (including SARS-CoV-2) are also susceptible to exposure to copper surfaces. It is thus suggested that replacing common touch surfaces in healthcare facilities, food industries, and public places (including public transport) with copper or alloys of copper may substantially contribute to limiting transmission. Subsequent hospital admissions and mortality rates will consequently be lowered, with a concomitant saving of lives and considerable levels of resources. This consideration is very significant in times of the COVID-19 pandemic and the upcoming epidemics, as it is becoming clear that all forms of possible infection control measures should be practiced in order to protect community well-being and promote healthy outcomes.
... In 1983 an observant medical intern Kuhn, at Hamot Medical Centre in Pennsylvania, USA, noted a surprising lack of bacteria on brass door knobs during an incidental training exercise for their cleaning staff (Kuhn, 1983),. Subsequent and more detailed investigations in the hospital and laboratory confirmed the efficacy: copper disinfected itself in 15 minutes whilst stainless steel and aluminium showed heavy growths even after three weeks. ...
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Chemical disinfection In: Basic Bacteriology, Its Biological and chemical Background
  • C Lamanna
  • Mf Mallette
Lamanna C. and Mallette MF. Chemical disinfection. In: Basic Bacteriology, Its Biological and chemical Background. Baltimore: Williams & Wilkins, 1965, p 897.
Chemical disinfection
  • C Lamanna
  • M F Mallette
Lamanna C. and Mallette MF. Chemical disinfection. In: Basic Bacteriology, Its Biological and chemical Background. Baltimore: Williams & Wilkins, 1965, p 897.