Study shows commonly used mouthwash could make saliva significantly more acidic

March 24, 2020

The first study looking at the effect of chlorhexidine mouthwash on the entire oral microbiome has found its use significantly increases the abundance of lactate-producing bacteria that lower saliva pH, and may increase the risk of tooth damage.

A team led by Dr Raul Bescos from the University of Plymouth's Faculty of Health gave a placebo mouthwash to subjects for seven days, followed by seven days of a chlorhexidine mouthwash.

At the end of each period, the researchers carried out an analysis of the abundance and diversity of the bacteria in the mouth - the oral microbiome - as well as measuring pH, saliva buffering capacity (the ability to neutralise acids in the mouth), lactate, glucose, nitrate and nitrite concentrations.

The research, published in Scientific Reports today, found using chlorhexidine mouthwash over the seven days led to a greater abundance of species within the families of Firmicutes and Proteobacteria, and fewer Bacteroidetes, TM7 and Fusobacteria. This change was associated with an increase in acidity, seen in lower salivary pH and buffering capacity.

Overall, chlorhexidine was found to reduce microbial diversity in the mouth, although the authors cautioned more research was needed to determine if this reduction in diversity itself increased the risk of oral disease.

One of the primary roles of saliva is to maintain a neutral pH in the mouth, as acidity levels fluctuate as a result of eating and drinking. If saliva pH gets too low, damage can occur to the teeth and mucosa - tissue surrounding the teeth and on the inside of the mouth.

The research also confirmed findings from previous studies indicating that chlorhexidine disrupted the ability of oral bacteria to turn nitrate into nitrite, a key molecule for reducing blood pressure. Lower saliva and blood plasma nitrite concentrations were found after using chlorhexidine mouthwash, followed by a trend of increased systolic blood pressure. The findings supported earlier research led by the University that showed the blood pressure-lowering effect of exercise is significantly reduced when people rinse their mouths with antibacterial mouthwash rather than water.

Dr Bescos said: "There is a surprising lack of knowledge and literature behind the use of these products. Chlorhexidine mouthwash is widely used but research has been limited to its effect on a small number of bacteria linked to particular oral diseases, and most has been carried out in vitro.

"We believe this is the first study to look at the impact of 7-day use on the whole oral microbiome in human subjects."

Dr Zoe Brookes and Dr Louise Belfield, Lecturers in the Peninsula Dental School at the University of Plymouth, are co-authors of the study.

Dr Belfield said: "We have significantly underestimated the complexity of the oral microbiome and the importance of oral bacteria in the past. Traditionally the view has been that bacteria are bad and cause diseases. But we now know that the majority of bacteria - whether in the mouth or the gut - are essential for sustaining human health."

Dr Brookes added: "As dental clinicians, we need more information on how mouthwashes alter the balance of oral bacteria, so we can prescribe them correctly. This paper is an important first step in achieving this.

"In the face of the recent COVID-19 outbreak many dentists are now using chlorhexidine as a pre-rinse before doing dental procedures. We urgently need more information on how it works on viruses"
-end-
The study was carried out by a team from the University of Plymouth's Institute of Health and Community, Peninsula Dental School, Peninsula Medical School and School of Biological and Marine Sciences, along with colleagues from Bishop Grosseteste University and University of the West of Scotland.

University of Plymouth

Related Bacteria Articles from Brightsurf:

Siblings can also differ from one another in bacteria
A research team from the University of Tübingen and the German Center for Infection Research (DZIF) is investigating how pathogens influence the immune response of their host with genetic variation.

How bacteria fertilize soya
Soya and clover have their very own fertiliser factories in their roots, where bacteria manufacture ammonium, which is crucial for plant growth.

Bacteria might help other bacteria to tolerate antibiotics better
A new paper by the Dynamical Systems Biology lab at UPF shows that the response by bacteria to antibiotics may depend on other species of bacteria they live with, in such a way that some bacteria may make others more tolerant to antibiotics.

Two-faced bacteria
The gut microbiome, which is a collection of numerous beneficial bacteria species, is key to our overall well-being and good health.

Microcensus in bacteria
Bacillus subtilis can determine proportions of different groups within a mixed population.

Right beneath the skin we all have the same bacteria
In the dermis skin layer, the same bacteria are found across age and gender.

Bacteria must be 'stressed out' to divide
Bacterial cell division is controlled by both enzymatic activity and mechanical forces, which work together to control its timing and location, a new study from EPFL finds.

How bees live with bacteria
More than 90 percent of all bee species are not organized in colonies, but fight their way through life alone.

The bacteria building your baby
Australian researchers have laid to rest a longstanding controversy: is the womb sterile?

Hopping bacteria
Scientists have long known that key models of bacterial movement in real-world conditions are flawed.

Read More: Bacteria News and Bacteria Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.