Bacteria boost antifungal drug resistance in severe childhood tooth decay

April 25, 2018 by Katherine Unger Baillie, University of Pennsylvania
Credit: University of Pennsylvania

Early childhood caries, a form of severe tooth decay affecting toddlers and preschoolers, can set children up for a lifetime of dental and health problems. The problem can be significant enough that surgery is the only effective way to treat it.

Recently researchers from the University of Pennsylvania School of Dental Medicine discovered that, in many cases, early childhood caries result from that contains both bacteria and fungus working together to make the on the teeth more pathogenic and difficult to remove. Now they have shown that these two types of microorganisms synergize to enhance drug resistance, enabling the to avoid being killed by antifungal therapies. Yet simultaneously targeting the matrix produced by the bacteria along with the fungus offers a way around this protection.

"The current antimicrobial modalities for treating early childhood caries have limited efficacy," says Hyun (Michel) Koo, a professor in the Department of Orthodontics and divisions of Pediatric Dentistry & Community Oral Health in Penn's School of Dental Medicine. "Available evidence shows that biofilm-associated diseases are polymicrobial in nature, including a mix of bacterial and fungal species; therefore a treatment aimed at just one type of microorganism may not be effective. I think this work gives us a glimpse into alternative ways to disrupt cross-kingdom biofilm, a combinatorial approach that considers the fungal and bacterial components."

Koo was the senior author on the work and Dongyeop Kim, a postdoctoral research fellow, was first author. They collaborated with teams from Tel Aviv University and the University of Wisconsin-Madison on the work, which was published in the ISME Journal.

During the last several years, researchers have observed that the dental plaque in children with early childhood caries often contained Candida albicans, a that normally colonizes mucosal surfaces, in addition to Streptococcus mutans, the bacteria generally associated with tooth decay. Work in Koo's lab demonstrated that an enzyme produced by the bacteria, termed GtfB, can bind to Candida and when sugar is present (a dietary hallmark in childhood caries) a sticky polymeric matrix forms on its cell surface, enabling the fungus to bind to teeth and associate with bacterial counterparts. Once together, these organisms work in concert to increase severity of in a rodent model.

Realizing this, Koo, Kim, and colleagues wanted to see whether a two-pronged approach might break apart the synergistic association and effectively treat the biofilm. "Initially, we decided to look into therapies that are clinically used in dentistry to attack or prevent either fungal or bacterial infections," Koo says.

They came up with , which is used as an antifungal, and povidone iodide, which is an antiseptic agent with antibacterial properties. Used alone to treat biofilms grown on a tooth-like material in the lab, the drugs had only moderate effects, confirming that monotherapy doesn't work very well against polymicrobial biofilms. But in combination, the results were much more impressive.

"We completely eradicated the fungal infection, both in the lab-grown biofilms but also those formed in vivo using an animal model," Koo notes, yet this achievement came without enhancing antibacterial activity.

To understand why the combination approach was so effective against C. albicans even without killing many more bacteria, the researchers looked closely at high-resolution microscopic images of the biofilms with the various treatment combinations. They observed that, in untreated biofilms and those treated with solely fluconazole, the fungus was coated with abundant sticky matrix, which seemed to serve as a protective shield against the antifungal compound. But in biofilms treated with povidone iodide as well, the matrix was substantially reduced, leaving the fungus exposed to the fluconazole.

"We thought, that's interesting," Koo says, and turned to the scientific literature to find out more. They discovered that iodide-containing drugs can inhibit the activity of GtfB. In a series of experiments, they found that povidone iodide acted as a powerful inhibitor of the sticky-matrix production. The agent was almost 100-fold more potent as an inhibitor of the matrix than it was as an antibacterial agent.

That led them to the hypothesis that the matrix was serving as a "drug-trapping shield," preventing the fluconazole from accessing and killing the fungal cells. To see whether disrupting the matrix could allow the fluconazole to penetrate and reach the fungus, they collaborated with Tel Aviv University scientists to track, in real time, fluorescently-labeled fluconazole as it moved through a biofilm.

Taking time-lapsed images, they found that the fluconazole were trapped in the matrix, largely failing to reach the fungal cells, which was further confirmed by directly measuring radiolabeled fluconazole absorbed in the matrix. In contrast, fluconazole readily moved inside the fungal cells when they were located in biofilms with the matrix disrupted by povidone iodine.

Using three different assays to disrupt the matrix, either by directly degrading the matrix or using bacteria defective in GtfB, the researchers found that the antifungal-killing ability of fluconazole could be completely restored, confirming the role of the bacteria-produced matrix in promoting antifungal drug resistance.

The fungus itself has its own mechanisms for avoiding being killed by antifungals, but this resistance is exacerbated by the shielding effect of the matrix, the researchers found.

Looking ahead, the Penn-led team hopes their findings lead to new strategies for treating bacterial-fungal infections associated with early childhood caries and possibly other polymicrobial diseases. For the researchers' part, they are making use of nanotechnology to develop targeted approaches that can precisely target the and both the fungal and bacterial components of the oral biofilm.

Explore further: Blocking yeast-bacteria interaction may prevent severe biofilms that cause childhood tooth decay

More information: Dongyeop Kim et al, Bacterial-derived exopolysaccharides enhance antifungal drug tolerance in a cross-kingdom oral biofilm, The ISME Journal (2018). DOI: 10.1038/s41396-018-0113-1

Related Stories

Blocking yeast-bacteria interaction may prevent severe biofilms that cause childhood tooth decay

June 20, 2017
Though most tooth decay can be blamed on bacteria, such as Streptococcus mutans, the fungus Candida albicans may be a joint culprit in an alarmingly common form of severe tooth decay affecting toddlers known as early childhood ...

Bacterium and fungus team up to cause virulent tooth decay in toddlers

March 12, 2014
Early childhood caries, a highly aggressive and painful form of tooth decay that frequently occurs in preschool children, especially from backgrounds of poverty, may result from a nefarious partnership between a bacterium ...

Small molecule inhibitor prevents or impedes tooth cavities in a preclinical model

August 10, 2017
University of Alabama at Birmingham researchers have created a small molecule that prevents or impedes tooth cavities in a preclinical model. The inhibitor blocks the function of a key virulence enzyme in an oral bacterium, ...

Recommended for you

Researchers discover cellular messengers communicate with bacteria in the mouth

May 8, 2018
A new UCLA-led study provides clear evidence that cellular messengers in saliva may be able to regulate the growth of oral bacteria responsible for diseases, such as periodontitis and meningitis.

Drug-filled, 3-D printed dentures could fight off infections

April 25, 2018
Nearly two-thirds of the U.S. denture-wearing population suffer frequent fungal infections that cause inflammation, redness and swelling in the mouth.

Bacteria boost antifungal drug resistance in severe childhood tooth decay

April 25, 2018
Early childhood caries, a form of severe tooth decay affecting toddlers and preschoolers, can set children up for a lifetime of dental and health problems. The problem can be significant enough that surgery is the only effective ...

Absence of a transcription factor halts tooth development in mid-stride

April 11, 2018
Amjad Javed, Ph.D., and University of Alabama at Birmingham colleagues have found a key role in tooth development for the transcription factor Specificity protein 7, or Sp7.

Toothpaste alone does not prevent dental erosion or hypersensitivity

March 14, 2018
The rising prevalence of dental erosion and dentin hypersensitivity has led to the emergence of more toothpastes that claim to treat these problems. While no such toothpaste existed 20 years ago, today, many such brands are ...

Study: Absence of key protein, TTP, rapidly turns young bones old

March 10, 2018
The absence of a protein critical to the control of inflammation may lead to rapid and severe bone loss, according to a new University at Buffalo study.

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.