Mouthwash: A case of disrupting the balance of the human-hosted bacterial ecosystem

It is well known the our bodies are inhabited by billions of microorganisms, mostly bacteria. The majority of those are benign and don't pose any threat to us, provided that we are reasonably healthy. Having said that, current thinking suggests that maintaining one 's health is tightly connected to the maintenance of properly functioning bacterial communities in our bodies.

'Vintage 80's Scope Mouthwash'
by twitchery under a CC license

Most of the things we do in our normal life affect the microorganisms living within us. Whatever we eat, for instance, affects our gut flora. Eating food with lots of fibre equals giving more food to the microrganisms of the gut - it may be even possible to fine tune gut flora this way. Showering and bathing alter the composition of our skin microbiota (there are times when clean skin becomes too clean, in a risky kind of way). Brushing our teeth changes the bacterial demographics of the oral cavity, etc.

Some - and, hopefully, most - of those changes have negligible effect of human health. Major disruptions, however, may lead to more pronounced outcomes. For instance, courses of antibiotics strongly reduce the gut flora populations, leaving ground for more resistant species to settle in and, if the are pathogens, to cause trouble to their host.

A common practice with potentially detrimental effects, which seems to go unnoticed, is the use of mouthwashs. Some of those, strongly impact the baterial populations within the mouth. That is a good thing if we are talking about bacteria that cause cavities or gingivitis but probably not so good if we are talking about the bacteria that can reduce dietary nitrate to nitrite.

What?

OK, let's have a quick close look at that.

The topic of dietary nitrite (which originates from the nitrate that exists in foods, mostly leafy vegetables, which is converted to nitrite by the mouth bacteria) is still a bit controversial. The reason for that is that nitrites, which are further converted to nitrous oxide in the acidic environment of the stomach, can have good properties but also, possibly, some bad ones.

The good ones have to do with the function of the immune system, especially the organism 's defence in the gastrointestinal track against pathogens, the function of the cardiovascular system (improving blood flow, lowering blood pressure) and also the improvement of performance in moderate aerobic exercise. The bad ones are associated with cases where nitrosamine is formed, which is a carcinogen. The latter is, of course, of great concern. Nitrosamine can be formed by nitrites in the presence of secondary amines under the effect of high temperature or strongly acidic environment. Adding antioxidants (such as ascorbic acid) or keeping food processing temperature at lower level can help reduce considerably foodborne nitrosamine. Practically, nitrosamine levels from food intake are very low, though (e.g., considerably lower than the nitrosamine smokers receive from tobacco products).

So what is the bottom line?

As usual, it is a question of the right balance (as in the case of nutrition). Some mouthwashes can have an effect on nitrate-reducing bacteria and that may be not-so-good. But there may be very good reason to use them. Dental or gum problems pose considerable risks both in the long and in the short term. Really, a dentist should be the one to advise. Under normal circumstances, however, I thing that not overdoing it is quite important!

Superbugs

A few days ago, just before the entry of 2010, I came across an article on the BBC News website on the undesirable effect that disinfectants may have on bacteria. The article was supporting the the incorrect use of disinfectants (e.g., incorrect dilution) could allow bacteria to develop resistance to antibiotics.

I am by no means an expert in microbiology, or even plain-vanilla biology, however, I was aware that overuse or misuse of antibiotics could lead to increased resistance to those antibiotics; a trait which, once acquired by a group of bacteria, can be passed onto others, under certain conditions. In the hospital world, where people (patients) often have a weakened immune system, MRSA is a considerable threat, while an increasing number of other pathogens (or potential pathogens) begin to exhibit threatening tolerance to the available antibiotics, turning from simple "bugs" to "superbugs".

To my understanding, the antibiotics-induced antibiotic resistance can be mitigated by a tight antibiotic-use regime. Sweden has had considerable success in tackling the MRSA problem by forcing the health care system to resort to antibiotics only when absolutely necessary. The transition period might have taken considerable time but the gain sounds considerable: they can still make good use of antibiotics that on many place of this world are now considered to be ineffective.

The article of the BBC I spoke of earlier, however, is alarming in the sense that not only antibiotics but also disinfectants (and possibly other bacteria control means???) can somehow lead to antibiotic resistance. Clearly, improper use of disinfectants, which allows for a select portion of the microbial population to survive, favours that surviving population in the sense that it eliminates the competition. I would assume that this process effectively ensures that the descending bacteria will have those gene combinations that allowed their ancestors to survive the disinfectant. It seems, if my understanding of the article is correct, that those "disinfectant-survival" gene combinations can also be effective against antibiotics.

The alarming bit is that the use of disinfectants is much, much wider than the use of antibiotics. There not only used by hospitals but by a very high number of businesses, including the food industry, and they are also at hand in the typical household. I admit it would be inconsiderate to extrapolate that all disinfectants, if misused, could lead to superbugs. The fact that the number of known supebugs is still rather a small one, while the use of disinfectants has been more-or-less systematic over the last decades would rather support that the risk is minor.

I mentioned the food industry before. Interestingly, the agro-food industry was alarmed, in the past, by the antibiotic resistance problem but managed to sort it out by adopting good livestock practices and by considerably limiting the use of antibiotics. In Europe, there is legislation in place to ensure that things stay this way. But what about the use of disinfectants? The manufacturers of such products do include instructions for use, which normally are followed. I wonder though, with the modern foodstuffs enjoying increasingly longer shelf-lives, are there any significant chances that microorganisms which find their way into foods can turn into threatening superbugs?

In "live" foodstuffs (i.e., foods that contain a flora consisting of living microorganisms, such as yogurt, fermented sausages, various cheeses, tea, etc.), which contain a small eco-system, it is likely to be much easier to keep things under control. An undesirable contamination would be worse in the case of previously sterilised (or poorly sterilised) products under packaging conditions that lack bacteria growth barriers.

In any case, and for any of the existing reasons (ranging from health and safety concerns to competitiveness and sustainability issues), it may be worth revisiting some of the practices in our every day "war" with bacteria.

The use of good practices when it comes to cleaning surfaces or when actually using antibiotics has been proven to be an effective one. The use of phages to fight off antibiotic resistant bacteria has also been tested - successfully I believe; although, I'm not sure if it can find wide scale application beyond the health sector. The manipulation of the microbial ecology could be another promising sector, which has recently re-attracted research interest; after all, it may be time to remember that microorganisms are our valuable friends far more often than otherwise (not only when it comes to the function of the human body).

(Photo "big bug", CC by G J Hutton)