In-Situ Investigation on Nanoscopic Biomechanics of Streptococcus mutans at Low pH Citric Acid Environments Using an AFM Fluid Cell.

Linh Thi Phuong Nguyen,Bernard Haochih Liu

doi:10.3390/ijms21249481

Linh Thi Phuong Nguyen, Bernard Haochih Liu

Open Access

https://doi.org/10.3390/ijms21249481

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Abstract

Streptococcus mutans (S. mutans) is widely regarded as the main cause of human dental caries via three main virulence factors: adhesion, acidogenicity, and aciduricity. Citric acid is one of the antibiotic agents that can inhibit the virulence capabilities of S. mutans. A full understanding of the acidic resistance mechanisms (ARMs) causing bacteria to thrive in citrate transport is still elusive. We propose atomic force microscopy (AFM) equipped with a fluid cell to study the S. mutans ARMs via surface nanomechanical properties at citric acid pH 3.3, 2.3, and 1.8. Among these treatments, at pH 1.8, the effect of the citric acid shock in cells is demonstrated through a significantly low number of high adhesion zones, and a noticeable reduction in adhesion forces. Consequently, this study paves the way to understand that S. mutans ARMs are associated with the variation of the number of adhesion zones on the cell surface, which is influenced by citrate and proton transport. The results are expected to be useful in developing antibiotics or drugs involving citric acid for dental plaque treatment.

Highlights

Streptococcus mutans (S. mutans) is a Gram-positive bacterium that is widely regarded as the main cause of human dental caries
The 3D-printed atomic force microscopy (AFM) fluid cell consisted of three components. (1) A glass substrate was placed on top of a sample substrate holder
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Summary

Introduction

Streptococcus mutans (S. mutans) is a Gram-positive bacterium that is widely regarded as the main cause of human dental caries. These anaerobic bacteria produce acid, which is a part of the bacterial biofilm that mostly causes dental plaque or discharges virulence factors, hemolysin [1,2,3,4,5,6]. Acidogenic S. mutans can produce extracellular polysaccharides (EPSs) in the presence of sucrose, fructose, and glucose [6]. The presence of EPSs in biofilm is a weapon to maintain the persistence of bacterial infection through the reduction of bacterial sensitivity to the signaling system of the host, antibiotics, and even drugs [10]

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