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Author Topic: Stainless steel (and aluminum) as a breeding ground for bacteria
LetterRip
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Interesting,

quote:
Hospitals love stainless steel, because it looks so “clean”. Unfortunately it is a fantastic media for growing pretty much any pathogen, so it’s a major vector for hospital illnesses. Despite appearances, stainless steel is a filthy metal. Should medical care facilities have prioritized an appearance of cleanliness before testing the reality? Most people outside of the profession would say no, especially given how simple the testing is.
quote:
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 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
http://www.typinganimal.net/wp/2013/12/13/stainless-steel-the-metal-bacteria-love/

That is so effed up. So, stainless steel water bottles, stainless steel cooking ware, stainless steel counter tops, stainless steel hospitalware and tools. All based on the 'it looks clean and shiny therefore it is clean'.

[ April 28, 2014, 11:40 AM: Message edited by: LetterRip ]

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Grant
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Is the reasoning behind so much stainless steel the look, or is it the cost? Stainless steel is alot cheaper then brass, copper, or silver. If the cost of healthcare is already a problem, I can't wait until all the doorknobs and surfaces and surgical tools are made of brass.

Great for everybody invested in copper and silver and aluminum, though.

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D.W.
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My knowledge of metallurgy is... well bordering on nonexistent. However as someone who frequently perpetuates the specifying of stainless steel all over the damn place I figured I’d chime in with my speculation.

Stainless steel is easy to clean and maintain. It does not scratch easy either so durability is a serious factor. Epoxy risen counter tops are also a good choice but then cost becomes an issue. So it’s not just the “clean look” but the continued “clean look” throughout the lifespan of the product.

Now as to the self cleaning of brass and copper… Isn’t this a direct result of the same properties that make them tarnish/oxidize? Isn’t it this very process which is proving inhospitable to the bacteria?

So you have to address cost and maintenance. So while brass and copper may have the up side of being more anti-microbial it’s not as if stainless steel is a food source for microbes. It is a neutral environment. There is absolutely a niche in healthcare to be exploited by someone who can produce a cost efficient anti-microbial surface with maintenance and lifespan comparable to stainless steel. So if you want to eat off the same cookware without washing it first, by all means, invest in copper pots. [Smile]

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Pyrtolin
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Resistance to corrosion plays in (brass, copper, and silver lose out to steel there). Overall hardness as well.

In general, I think the test above somewhat misses the overall point- the question is not how long you can leave a somewhat dirty tool or surface alone before it becomes pathological, but how easy it is to sterilize and remove corrosion from before any given use. A soft, scratched surface will protect many more undesirable elements from being cleaned away than a hard smooth one.

EVen more, you have to consider what it means for various metals to be showing the kind of surface toxicity- it may be that the process by which they're killing off the bacterial cells may also be one that we don't want happening as larger amounts of softer metals end up being absorbed by our foods or from medical instruments etc...

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Grant
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quote:
Originally posted by D.W.:

Now as to the self cleaning of brass and copper… Isn’t this a direct result of the same properties that make them tarnish/oxidize? Isn’t it this very process which is proving inhospitable to the bacteria?

I think so, but I am not certain. The self cleaning properties of those heavy metals is apparently not completely understood. I guess it has to do with the ionization properties, which is related to the tarnishing.

I think the actual maintenance cost my be neutral. As it stands, you need to clean stainless steel often with disinfectant. With brass or copper you will have to clean, maybe less often, with polish.

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scifibum
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"Breeding ground" appears to be an exaggeration. The claim in that article is that stainless steel is not as effective at killing off bacteria as those other metals are. The breeding happened in the agar.

quote:
So, stainless steel water bottles, stainless steel cooking ware, stainless steel counter tops, stainless steel hospitalware and tools. All based on the 'it looks clean and shiny therefore it is clean'.
In a lot of cases, it is clean because it was cleaned.
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Grant
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quote:
Originally posted by scifibum:
In a lot of cases, it is clean because it was cleaned.

I think the point is that it looks cleaner then brass or copper or silver. Is stainless steel being given preference over brass or copper because it "looks cleaner" rather then "is cleaner"?
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D.W.
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No the other properties, cost, lack of need to polish, scratch / dent resistance are the leading factors. Or I should say, percieved leading factors.

Maybe there are good alternatives out there just lacking in good marketing representatives. [Wink]

[ April 28, 2014, 01:58 PM: Message edited by: D.W. ]

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scifibum
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Sure, and I think it might make sense in certain applications to take the anti-microbial properties of copper and brass into account. To the extent that they are ruled out because of appearance, maybe there's a problem.

My point was in response to this list:

quote:
...stainless steel water bottles, stainless steel cooking ware, stainless steel counter tops...
We clean these things. It doesn't really matter if they don't kill bacteria if we clean them appropriately. Formica doesn't kill bacteria either, and it's okay if you clean it after you prep your raw chicken on it.
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D.W.
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As for those other things. I would think that stainless steel is also a neutral color. Copper or brass may clash with your interior decorating. Stainless steel, not so much. Unless you make a conscious decision to incorporate warmer colored metals into that design.

Probably why there are more white, black and stainless steel appliances rather than other color options as well. Though I will confess I do think stainless steel "looks" more sanitary to me. Maybe that is just a factor of association with medical equipment/furnishings...

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LetterRip
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There are multiple reasons for using stainless

1) asthetics
2) durability

scifibum,

quote:
We clean these things. It doesn't really matter if they don't kill bacteria if we clean them appropriately. Formica doesn't kill bacteria either, and it's okay if you clean it after you prep your raw chicken on it.
Actually people don't clean them properly. People tend to reuse a water bottle multiple times before cleaning.

Scifibum, it isn't 'lack of antimicrobrial properties' - I suspect more that it provides nickel atoms (many types of stainless steel contain nickel) that allow biofilm formation. Biofilms can protect bacteria against most of our tools we use to eradicate them.

quote:
The resistance to threats covers a wide range of treatments: Biofilms exposed to chlorine bleach for 60 min are reported to still have live cells (3); biofilms in pipes continuously flushed over 7 d with multiple biocides recolonize the pipes (10), and biofilms have been reported to survive in bottled iodine solution for up to 15 mo (11).
http://www.pnas.org/content/108/3/995.full
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D.W.
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Didn't get through the whole article, just the abstract then did a few word seaches. Where do you get the nickel connection? Interesting stuff though.
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Mynnion
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As LetterRip pointed out durability is a major reason. Many of the places you see stainless use bleach as a primary cleaner to kill bacteria and virus'. Try using bleach on cooper or silver and you will have a tarnished mess. The bleach does a great job of sanitizing a surface.
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scifibum
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quote:
Scifibum, it isn't 'lack of antimicrobrial properties' - I suspect more that it provides nickel atoms (many types of stainless steel contain nickel) that allow biofilm formation. Biofilms can protect bacteria against most of our tools we use to eradicate them.
The link you shared at first was describing an experiment testing whether inoculated metal samples would or would not kill the microbes they were inoculated with.
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OpsanusTau
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quote:
Hospitals love stainless steel, because it looks so “clean”.
I'm sorry, but that's just nonsense.

Hospitals love stainless steel because it is possible to clean it really well. My stainless steel surgical instruments are soaked, scrubbed, dried, and autoclaved between uses; they don't LOOK clean, they ARE clean. In point of fact, they are sterile when I open the pack. The stainless steel surfaces in a well-kept hospital are also clean, because they are cleaned with an appropriate cleaning solution frequently. The material stands up to this treatment.

What, is this person suggesting that it would be better to make hospital surfaces out of brass and then NOT WASH THEM? I can't even.

The article also seems to conflate "effective antimicrobial cleaning agents" and "antibiotic drugs". Which I also can't even.

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Pyrtolin
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quote:
Originally posted by LetterRip:
There are multiple reasons for using stainless

1) asthetics
2) durability

And number 2 is the important one; the more durable a tool is, the less likely that it will accumulate scratches and other damage that will make it harder to sterilize efficiently.
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LetterRip
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Ops,

quote:
I'm sorry, but that's just nonsense.
The authors point was presumably mostly about doors (handles, knobs, push plates), trim, fixtures (bathrooms), etc. These have been replaced in hospitals that had brass to stainless.

The individual is suggesting that we switch back to using metals that have antibiotic properties - for handles, knobs and other frequently touched surfaces.

Autoclaved stainless surgical instruments aren't the concern.

If you have swinging doors anywhere in the hospital with stainless push plates, handles, or latches - what is the cleaning schedule for them? It almost certainly is not frequent enough.

quote:
Even with regular cleaning, bacteria were detected on more than 20% of handles [13].
quote:
Our data indicate that, while cleaning is important, it is not always practical, as in some cases a single touch by a contaminated hand was sufficient to result in a confluent plate. A potentially innovative approach to limiting environmental contamination is the use of spontaneously antimicrobial surfaces. Of these, copper-based microfibre cleaning systems [15] or copper furnishings look particularly promising, although the latter are expensive and still in need of regular cleaning [16]
http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0040171

Did you see my mention earlier of biofilms being able to withstand a bleach solution for 60 minutes? Or bacteria repopulating after long term continuous exposure to biocides?

The author of the initial link didn't do a good job communicating, but as the PLOS piece points out it is a serious problem, and one of the most promising solutions is switching from stainless to copper/brass.

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OpsanusTau
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Door handles (and handrails) can and should be assumed to be contaminated, this is known. Also shared keyboards.

Replacing with brass or copper or whatever might help decrease CFUs picked up from these surfaces. If I were redesigning with an eye to reducing contamination, though, I would redesign with kick plates. Because the problem is not the material. The problem is people who don't know how to wash their hands correctly and don't reliably restrict their hands' contact with inappropriate orifices and surfaces.

I tend to open doors in the hospital with my feet (if a swinging door) or my elbow (if a lever handle).

Other possible solutions include: wearing gloves.

Also, do you seriously think that it is not known that biofilms can withstand immersion in cleaning solutions (and additionally, that different agents are susceptible to different kinds of cleaning solutions)? This is why we have to brush our teeth instead of just rinsing the mouth out - physical disruption of a biofilm is necessary. I grant that there are probably a lot of laypeople who don't really think about the difference between effective and ineffective cleaning methods, but I guarantee you this is not news to the medical field.

Anyways, the article itself is moderately interesting and I think that this is the most important sentence in it:
quote:
Architects may not have the necessary information or knowledge available to inform optimal healthcare design as regards the spread of infection.
Saying that "one of the most promising solutions is switching from stainless to copper/brass" overstates the case substantially, and is also not what the authors claimed. They claimed (correctly, IMO) that the switch to spontaneously antimicrobial surfaces is "a potentially innovative approach" to the problem and that among these surfaces, copper-microfiber and copper are "particularly promising".

This thread and the original linked blog post are great examples of misinterpretation of scientific literature. Because, note, even the article you linked most recently didn't include any experimental investigation of the performance of copper-containing metals in a hospital situation; it was a paper about differential contamination of different shapes of doorhandles with an aside about the potential of copper materials in the discussion section. The discussion section also contains this:
quote:
[...]we cannot dismiss the possibility that door handle design had no influence on contamination and that sole determinants of contamination were ward activity and hand hygiene.
It is great to read scientific literature and think about the implications of the ideas but it is very important to apply restraint in the interpretation of results and attribution of the importance thereof. And also of course to apply Diax's Rake.
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D.W.
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quote:
Architects may not have the necessary information or knowledge available to inform optimal healthcare design as regards the spread of infection.
As someone in the architecture field, the possibility that some metals may have properties that are anti-microbial compared to other metals had never occurred to or been presented to me. I definatly found it interesting. Considering the amount of healthcare work I've done I find it odd that this isn't more widely known, if it is indeed a substantial inhibiter of bacterial transmission.

Though if it were more widely known you may run the risk of housekeeping apathy because "that surface is self cleaning".

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LetterRip
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I wonder how much public savings could be had by engineerinr all public handrails, doors, computers and other frequently touched surfaces so that they reduce risk of transfer of infection.

An ad campaign I'd love to see is how to properly wash ones hands (it is scary how few people know the proper way).

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D.W.
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Handrails I don't think you can manage. You could go more towards the expense of escalators and install a self cleaning device into the unexposed portion of the handrail tracks. You could create some aftermarket device which snaps onto an existing pipe rail and travels down it cleaning the rail periodically as well but that seems quite extravagant and expensive.

Maybe something with transparent handrails and light? I don't know how effective eye-safe U.V. is as a reducer (if at all) to contaminants on surfaces. If you get rich off this idea, I'd appreciate a cash "gift". [Smile]

Doors, would be an interesting cost/benefit analysis between automated doors and just how often we get sick because we touched a door. A hard sell. I can't think of any passive device you could retrofit allowing you to pull a door open without risking the device be more of a hazard or liability than it's worth. Maybe a robust motor which could fit into a typical door closer hardware profile which can pull open a door? These exist already but tend to be more specialized for the door than a retrofit item but it could likely work in many areas. But they wouldn't be cheep and require you power them.

Public computers? https://www.leapmotion.com/ and other camera based inputs may be an avenue to explore. This is probably the most practical of the lot. Biometric cameras instead of PIN keypads and the like.

In particularly high risk areas such as hospitals I think a lot of these measures may be more reasonable. Wide spread adoption however I don't see as going anywhere. You'd get businesses offering mask and glove dispensers at their entry vestibules before you see a lot of owners going to the expense of installing these types of precautions which only improve, not eliminate infection vectors.


Again all of these options would cost a lot of money and as serious as some cases may be I don’t expect enough direct cost of people being sick could be alleviated by reducing the contamination rather through these objects. The hand washing ad campaign would likely do more good. Though I think a lot of it is apathy rather than ignorance. You could try scare tactics informing people just how much they come in contact with every day to see if that changes their habits. Seems easier than having automated systems following and cleaning up after us filthy humans. [Smile]

[ April 29, 2014, 05:57 PM: Message edited by: D.W. ]

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