Increasing multi-resistances because of antibiotics – and toothbrushes

Multiresistant germs are one of the worst-case scenarios in medicine. The term refers to pathogens (bacteria and viruses) that are resistant to one or even all known antibiotics and virostatics. They evolve from “normal” germs and develop so-called antibiotic-resistant genes (ARGs). In doing so, they turn into super-germs, resisting every pressure that environment is imposing on them. A treatment with regular antibiotics is then useless (1).

Does that sound like science-fiction? Unfortunately, scientists from all over the world see the predominance of multiresistant germs in the nearer future. The tv channel Arte published a haunting documentary on that scenario (2). The WHO is holding back a number of “last resort antibiotics” that usually are not in use and because of that, no resistances have evolved against them – yet. Today, this last resort is more and more in use. And not only in human medicine, as investigative inquiries show, but especially in the less-regulated field of food industry (3).

What can we do?

From a medial viewpoint, the discovery of antibiotics counts as one of the most important in the history of humanity. Many severe illness courses could have been shortened and alleviated. So, this is mainly about saving this powerful weapon for the really severe cases.

Using antibiotics sensibly means limiting them strictly to medical prescription and does also include responsible consumer behavior. This also contributes to avoiding multiresistances. And we find one more astonishing example of what we can do in our bathrooms. A recently published interview by the news magazine “der SPIEGEL” with Prof. Dr. Markus Egert (Professor for Microbiology, Furtwangen University), is debunking toothbrushes as potential hotbeds for multiresistant germs (4).

What is living on our toothbrushes?

What the average person might refuse to believe, is long evident among scientists: Toothbrushes are among the most unhygienic places in our bathrooms. We tend to find our toilet seat a bit icky. At the same time, it is relatively poor in germs with its even surface and prevailing dryness. We also clean that obviously contaminated object more frequently, out of intuition. With our toothbrush, the situation is quite different. We tend to treat it a bit neglecting, change it not often enough, and foster the growth of bacteria with that habit.

Egert explains the ecosystem of the toothbrush as follows: “Antimicrobial ingredients from toothpaste and mouthwash and the frequent change between moist and dry imposes a lot of pressure on most microbes”. The microbes that dwell here, can be found also in our oral microbiome, which was to be expected. But apart from traces from within our mouth, we can find gut bacteria and also germs from the environment on the toothbrush. The warm and moist setting between the bristles is attracting practically everything that the bathroom is home to.

A detailed study from Blaustein et.al, published in the Microbiome Journal (5), conducted detailed examinations on the microbial composition of toothbrushes. The authors scrutinized 34 toothbrushes and sequenced the collected samples. It turned out that apart from microbes of the human microbiome (apparently mainly mouth, but also skin, gut, vaginal microbiome etc.), the toothbrushes contained microbes from the environment. The scientists listed the prevalence of the following: Streptococcus, Staphylococcus, Pseudomonas, Poryphromonas, Parvimonas, Lactobacillus, Klebsiella, Fusobacterium, Escherichia, and Enterococcus.

The differentiated analysis showed that the colonization of the toothbrush is linked to diverse factors. Age and health condition of the associated human, to start with the most obvious, environmental factors like the presence or absence of a window in the bathroom, chemical composition of used detergents, and the list can be continued. Even the distance of the toothbrush to the toilet (and if flushing is done with open or closed lid) can be assumed.

Why we should change our toothbrush frequently

Another interesting outcome of the study was that the 34 examined toothbrushes contained 158 antibiotic-resistant genes that could be traced back to buccal mucosa, tongue, supragingival plaque etc.). If we scale that down to one toothbrush, it means that statistically speaking we breed around 22 of those potential resistances in every toothbrush. And this is clearly above the 14 ARGs that the average oral microbiome holds.

The increase of resistances is explained by the microbiologist Prof. Egert in the above-mentioned interview: The ecosystem of a toothbrush is subject to extreme conditions: twice a day, the microbes that dwell here, have to resist moist, mechanical pressure, and the use of anthropogenetic, antimicrobial chemicals, such as chlorhexidine or triclosan. After that stress test, a 10-to-12-hour extreme drought follows. Only the most resistant germs survive this.

And of course, only those survive who turn out to be resistant to antimicrobial ingredients of toothbrush, mouthwash and dental floss. The Blaustein et.al. study could prove resistances especially to triclosan and various antibiotics. And this is exactly what experts like Prof. Egert want to emphasize. Triclosan is a non-clinical antimicrobial that is frequently used in oral care products (especially in the US). And therefore, it could turn out to achieve the exact opposite from what it was meant to. Instead of a cleansing, slight antimicrobial effect in toothpastes, it fosters the development of resistances on toothbrushes.

Apart from toothpastes, Triclosan is mainly used clinical and dental disinfection. The outcome of the study indicates that broad resistance might turn into a loss of effect in that area. In order to prevent that from happening (plus other resistances), we should keep an eye on frequently renewing our toothbrush, rinsing it thoroughly after use and above all, keeping it dry. And of course, it makes sense to check the list of ingredients of a toothpaste before purchasing it.

Links to sources:

1. Wikipedia free enzyklopedia, Multiple drug resistance (2021), 
2. Resistant fighters: die globale Antibiotika-Krise, arte (2019) (GERMAN ONLY)
3. IQ Magazin, Bayerischer Rundfunk (2018), (GERMAN ONLY)
4. Thadeusz F, Zahnbürsten sind ein extremer Ort, Der SPIEGEL, Nr. 7 (2021), (GERMAN ONLY)
5. Blaustein R, Michelitsch L et al., Toothbrush microbiomes feature a meeting ground for human oral and environmental microbiota, Microbiome journal, BMC (2021)