bacteria and hand washing

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steveb | 01:28 Sat 09th Dec 2006 | Science
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In a recent lecture we were shown some slides of bacteria growing on agar dishes. there were 3 conditions. the first was where a person placed unwashed fingertips on the jelly. the second the hand was washed with warm water then the fingertip were placed on the jelly, and the final condition was where the hands underwent a surgical scrub using a disposable nail brush, then the finger tips were placed on the jelly. all samples were incubated at 37 degrees.

The unwashed hands provided the widest variety of bacteria, then followed by the surgical scub and finally the hands washed in warm water.

Can anyone explain these results?


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I'll assume that when you say "the hands underwent a surgical scrub" that an antibacterial agent was used. If this is so, read on.

A few reasons come to mind, but the most likely is that the surgical scrub used contained a quaternary ammonium compound. These substances generally cause lysis of the bacterial cell although in some species, the cells remain intact and may even continue to be metabolically active. As a result, there is a degree of bacterial resistance to these compounds.

In addition, although QAC's are reasonably effective bactericidal agents against staphylococcus and many bacilli, species such as Bacillus subtilis, Klebsiella pneumonia and many Listeria species are immune to their action. In addition, they are deactivated in the presence of hard water and organic matter.

Most importantly though, QAC's are totally ineffective against bacterial spores. Once these spores are transferred to the agar... well, you know the rest.

Was a surfuctant present in the "surgical scrub"? The name of the scrub would be useful.

Warm water rubbed vigorously over the hand would mechanically remove many bacteria and spores.

Question Author
thanks theprof, we werent given much information about he surgical scrub, im not sure of the name or whether it contained a surfactant, but the info you have given me is great thanks.
It's my fault - if I'd have paid more attention to the question, I'd have seen the part about slides. I'd have realised then that you would be unlikely to know the name of the surgical scrub or if it contained surfactant.

Glad to have been of help.
A few questions come to mind (although I realise that you probably don't have the info to answer them.

Were the same fingers used each time?
Were all of the fingers used each time?
Was only one set of plates used?
How did bacteria which were not there after the hand wash appear after the surgical scrub?
Did the nail brush dislodge bacteria from under the nails?
What was your lecturer's expanation of the results?
Was he testing your knowledge of correct microbiological procedures?

Sorry to pose more questions than you did but is questioning not the essence of science? In simple terms, was this a "fair" experiment and were you given all of the facts?

I am not disputing anything that theprof wrote.

Question Author
Cheers Gef, we were told by the lecturer that it was a fair test, and that the difference was something to do with the washing, not experimental procedure, we werent really given much other information to be honest. It was in a lecture about correct microbial procedures.
You've asked some valid questions Gef.

It occurs to me that more than one person could have been involved in this experiment. We don't really know if one person's fingers were used for the experiment or more than one set of fingers. Furthermore, it's feasible that even if one person's fingers were used, each part of the experiment may have been conducted on three consecutive days.

The demonstration was clearly not intended to show the rate of growth of bacteria, so it was not necessary to carry out each part on the same day.

I'm quite surprised that your lecturer has been so vague in explaining the experiment procedures and the conclusions. To my mind, he/she was very wrong to sideline these matters. I don't consider you were given all the facts to work with, and to be honest, if one of my lecturers behaved in this way, I'd soon summon him/her to my office. It's just not good enough.
Was the nail brush sterile prior to use? If not, a variety of different bacterial strains could be introduced that way as well.
As it was a disposable nail brush, I'm assuming it was sterile (hope that doesn't sound like I'm jumping down your throat).

Interesting results. With MRSA and the scares round hospitals we are all being encouraged to use the alco type anti bacterial fluids when we go into or out of hospital wards. Are these less effective then than washing in warm water would be? Even taking into account that after washing your hands you'd then wipe them dry on 'something'?

I often wonder if they're there more for reassurance than practical purposes?
You can never assume anything is sterile.
Disposable things need to be labeled sterile or autoclaved.

As for the soap issue, washing with soap is more effective at removing bacteria than washing with water alone.

There is debate about the antibacterial soaps for a few reasons - one, generally you have to wash with them for more than a few seconds to kill the bacteria. Secondly, many strains of bacteria have been shown to develop resistance to triclosan (the most common antimicrobial used in these soaps). But there is little question that washing with soap or antibacterial soap will remove more bacteria from your hands than just warm water alone.
None of the disinfectants and cleansers used in hospital wards are less effective than washing in warm water. Despite some bacterial flora resistance to these products, rest assured that they continue to kill bacteria in their millions.

Much of the apparent failure of these products is down to the person using them. Medical staff are trained in the correct washing techniques and vigilance allows these products to be the best available for this purpose. However, little time is devoted to showing the public the right washing techniques and some people assume that a quick wash like they do at home with soap and water will suffice. Furthermore, even in this day and age, there are people who seem to have an aversion to soap and water and general hygiene. How many times have you seen someone leaving a public toilet, hospitals included, without washing their hands? On a similar vein, we've all seen someone scratching their skin, head or picking their nose while walking into a ward or being in there.

The truth is that no antiseptic product can protect the patient from bacteria transferred in this manner.

Surveys have shown that the use of hot-air hand driers has eliminated bacteria transfer via towelling etc in washrooms etc. Wiping hands dry on anything is a risky business.

I don't deny that washing with antibacterial disinfectants and cleansers can be burdensome: surgeons spend hours on the job every week. However, right now, they are the best we've got.

I agree that there is a growing resistance to the phenolic compound, triclosan. However, it does depend on the presentation of the product. Aquasept is a 2% solution of triclosan in water. Another version, Manusept, contains 0.5% triclosan and 70% isopropyl alcohol.

Studies have shown that Manusept is far more effective because of the alcohol content. Furthermore, the majority of alcohols continue to be very effective bactericidal agents. One of the best bug-killers is the mouthwash, Listerine. the stuff kills virtually all bacteria it comes into contact with because of the high alcohol content and I've used the stuff on skin in an emergency.

Personally, I prefer to rely on good old chlorhexidine or povidone iodine. The chlorhexidine versions in alcohol such as Hibisol are about the best skin bactericidal agents available in my view. If a sufactant is needed, I use the versions with cetrimide.

Unquestionably, washing with soap or antibacterial soap does remove more bacteria from hands than warm water alone. However, if a soapless solution containing a QAC was used as a handwash, bacterial spores would survive. It would then be down to the warm water to flush these spores off the skin.
So Steveb, did the professor eventually give you the 'correct' explanation for the results he presented?
The lecturer/professor seems to have kept the students very much in the dark with regard to the "correct" explanation drestie.
Let us hope that the lecturer/professor intends discussing this matter at a later date with Steveb and his fellow students.
Question Author
thanks for that everyone,yeh i think ive got all the infomation i needed, and a lot more as well
So are you gonna fill us in, Steve?? We are dying to know what the "right" answer was!!

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