Children can suffer an aggressive form of tooth decay from poor dental hygiene and eating lots of fermentable carbohydrates.
Microbes that stoke this decay include the bacterium Streptococcus mutans and the opportunistic yeast Candida albicans.
These two germs work together to form a biofilm, which is reinforced by an enzyme secreted by the bacteria – glucosyltransferase B (GtfB) – when sucrose is present. The insoluble glue that forms binds strongly to a polysaccharide on the cell wall of the yeast: mannan. Researchers at the University of Pennsylvania, Philadelphia, US, now report using a collection of enzymes to degrade the mannan on yeast (mBio, 2021, 12, e00651-21). ‘We thought mannan may be a receptor for glucosyltransferaseB, and we decided to target mannan on C. albicans,’ says lead scientist Geelsu Hwang.
They measured a 15-fold reduction in the strength of binding between the bacterial enzyme to yeast, as a result of their enzyme cocktail – plus significantly reduced biofilm formation. Five minutes of incubation was enough to meaningfully disrupt the bonds between the bacterial protein and yeast cells in a lab. Hwang says they will now work on improving retention of the enzymes in the mouth surface using a carrier. The enzyme cocktail could be an ingredient in toothpaste or mouthwash, so long as the product does not impact the activity of the enzymes.
The treatment also reduced damaging acidity on teeth. Once microbes begin their metabolic activity, they produce acid and reduce the pH of the biofilm as low as 4.2. However, enzyme treatment raised the pH to above 5.5, a critical threshold below which tooth enamel suffers demineralisation.
Most oral healthcare applications use mechanical disruption, ‘so in essence a blasting of the oral biofilm,’ says dental microbiologist Gordon Ramage at the University of Glasgow, UK, which he describes as a ‘blunderbuss approach of complete destruction’. In contrast this research, ‘which specifically targets a key interaction,’ is a potentially more subtle way of controlling oral health, he says.
Ramage notes, however, that displacing one or several microorganisms could just mean something else comes and takes its place. One area he is interested in is prebiotics, ‘where you modulate the microbiome by feeding particular bacteria or fungi, which displaces the bad ones with good ones’. Formulating existing products with enzymes might be a step too far for some companies involved in dental hygiene products, he warns, because of stability challenges by including fragile proteins. Also, introducing a metabolically active enzyme into the human mouth might require more stringent safety studies.
The treatment interrupts formation of the biofilm, rather than killing microbes, says Hwang. ‘There are a couple of therapies that can kill Streptococcus mutans and Candida albicans, but there are a bunch of potential side effects because most of the antimicrobials are broad spectrum, so kill everything in the mouth,’ he explains. ‘These often induce antimicrobial resistance if administered in the long term.’
The best enzyme was beta-mannanase, which was 2.5-fold more effective than beta-mannosidase and alpha-mannosidase. ‘In terms of clinical application, we didn’t test it in vivoyet, but we are about to start the test,’ says Hwang. ‘We tested its cytotoxicity using human tissue and found that even concentrations five times greater than optimum didn’t cause any significant tissue damage.’
Image credit: Kateryna Kon / Science Photo Library