Abstract
Efflux transporters have been implicated in regulating bacterial virulence properties such as resistance to antibiotics, biofilm formation and colonization. The pathogenicity of Streptococcus mutans, the primary etiologic agent of human dental caries, relies on the bacterium’s ability to form biofilms on tooth surface. However, the studies on efflux transporters in S. mutans are scare and the function of these transporters remained to be clarified. In this study, we identified an efflux transporter (LmrB) in S. mutans through cloning the lmrB gene into Escherichia coli. Introducing lmrB into E. coli conferred a multidrug-resistant phenotype and resulted in higher EtBr efflux activity which could be suppressed by efflux inhibitor. To explore whether LmrB was involved in S. mutans virulence properties regulation, we constructed the lmrB inactivation mutant and examined the phenotypes of the mutant. It was found that LmrB deficiency resulted in increased IPS storage and prolonged acid production. Enhanced biofilm formation characterized by increased extracellular polysaccharides (EPS) production and elevated resistance to hydrogen peroxide and antimicrobials were also observed in lmrB mutant. To gain a better understanding of the global role of LmrB, a transcriptome analysis was performed using lmrB mutant strain. The expression of 107 genes was up- or down-regulated in the lmrB mutant compared with the wild type. Notably, expression of genes in several genomic islands was differentially modulated, such as stress-related GroELS and scnRK, sugar metabolism associated glg operons and msmREFGK transporter. The results presented here indicate that LmrB plays a vital global role in the regulation of several important virulence properties in S. mutans.
Highlights
As the primary etiologic agent of human dental caries, Streptococcus mutans has evolved to be the normal member of oral flora (Smith and Spatafora, 2012)
Streptococcus mutans UA159 cells were cultured in BHI broth (Difco, Sparks, MD, United States) at 37◦C under anaerobic conditions (90% N2, 5% CO2, and 5% H2) and 1% sucrose was included in the medium for biofilm formation
For biofilm formation abilities of S. mutans strains under antimicrobial pressure, S. mutans cells (OD600 = 0.6) were diluted 1:100 in fresh BHI-1% sucrose with sub-inhibitory concentrations (0.25xMIC) of chlorhexidine for biofilm formation in flat-bottom 96-well microtiter plates (Corning Inc.) After 12 and 24 h of incubation, the biofilms were quantified using crystal violet staining
Summary
As the primary etiologic agent of human dental caries, Streptococcus mutans has evolved to be the normal member of oral flora (Smith and Spatafora, 2012). The primary virulence characteristics that allow S. mutans to survive and thrive in oral cavity are their ability to form tenacious biofilms and respond to environmental challenges presented by oxidative stress and changes in carbohydrate availability (Cheng et al, 2016). In Listeria monocytogenes, an ABC transporter was involved in negative regulation of biofilm formation, which exported signaling molecules to activate a pattern of genome expression characteristic of planktonic growth of L. monocytogenes (Zhu et al, 2008). It has been reported that possible efflux pump encoding genes were elevated when S. mutans was exposed to heat shock, osmotic stress, and oxidative conditions, suggesting a potential role of efflux system in regulating S. mutans virulence (Nagayama et al, 2014). The global gene expression upon lmrB deletion was profiled to uncover the role of LmrB
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
