Investigating the Streptococcus sinensis competence regulon through a combination of transcriptome analysis and phenotypic evaluation.

Streptococcus sinensis is a recently identified member of the Mitis group of streptococci. This species has been associated with infective endocarditis; however its mechanisms of pathogenesis and virulence are not fully understood. This study aimed to investigate the influence of the competence-stimulating peptide (CSP) and the competence regulon quorum-sensing circuitry (ComABCDE) on subsequent gene transcription and expression, as well as resultant phenotypes. In this study we confirmed the native CSP identity, ascertained when endogenous CSP was produced and completed a transcriptome-wide analysis of all genes following CSP exposure. RNA sequencing analysis revealed the upregulation of genes known to be associated with competence, biofilm formation and virulence. As such, a variety of phenotypic assays were utilized to assess the correlation between increased mRNA expression and potential phenotype response, ultimately gaining insight into the effects of CSP on both gene expression and developed phenotypes. The results indicated that the addition of exogenous CSP aided in competence development and successful transformation, yielding an average transformation efficiency comparable to that of other Mitis group streptococci. Additional studies are needed to further delineate the effects of CSP exposure on biofilm formation and virulence. Overall, this study provides novel information regarding S. sinensis and provides a substantial foundation on which this species and its role in disease pathogenesis can be further investigated.

Modulating streptococcal phenotypes using signal peptide analogues.

Understanding bacterial communication mechanisms is imperative to improve our current understanding of bacterial infectivity and find alternatives to current modes of antibacterial therapeutics. Both Gram-positive and Gram-negative bacteria use quorum sensing (QS) to regulate group behaviours and associated phenotypes in a cell-density-dependent manner. Group behaviours, phenotypic expression and resultant infection and disease can largely be attributed to efficient bacterial communication. Of particular interest are the communication mechanisms of Gram-positive bacteria known as streptococci. This group has demonstrated marked resistance to traditional antibiotic treatment, resulting in increased morbidity and mortality of infected hosts and an ever-increasing burden on the healthcare system. Modulating circuits and mechanisms involved in streptococcal communication has proven to be a promising anti-virulence therapeutic approach that allows managing bacterial phenotypic response but does not affect bacterial viability. Targeting the chemical signals bacteria use for communication is a promising starting point, as manipulation of these signals can dramatically affect resultant bacterial phenotypes, minimizing associated morbidity and mortality. This review will focus on the use of modified peptide signals in modulating the development of proliferative phenotypes in different streptococcal species, specifically regarding how such modification can attenuate bacterial infectivity and aid in developing future alternative therapeutic agents.

Attenuating the Selection of Vancomycin Resistance Among Enterococci through the Development of Peptide-Based Vancomycin Antagonists.

The emergence and spread of multidrug resistant (MDR) pathogens with acquired resistance to almost all available antimicrobial agents has severely threatened the international healthcare community over the last two decades. The last resort antibiotic vancomycin is critical for treatment of several of these pathogens; howeverc vancomycin resistance is spreading due to the undesired accumulation of IV vancomycin in the colon post-treatment. This accumulation exerts selective pressure upon members of the colonic microflora, including Enterococci, which possess vancomycin resistance genes. To ensure the continual effectiveness of vancomycin in the clinical setting by preventing the spread of antibiotic resistance, it is crucial to develop strategies that reduce selective pressure on the colonic microflora while allowing vancomycin to maintain its desired activity at the site of infection. Herein we report that modification of the native l-Lys-d-Ala-d-Ala vancomycin binding site can be used to produce peptides with the ability to competitively bind vancomycin, reducing its activity against susceptible Enterococci. Moreover, several modifications to the N-termini of the native tripeptide have produced compounds with enhanced vancomycin binding activity, including several analogs that were designed to covalently bind vancomycin, thereby acting as suicide inhibitors. Finally, in a mixed culture of susceptible and resistant bacteria, a single lead compound was found to protect high ratios of susceptible bacteria from vancomycin over the course of a week-long period, preventing the selection for vancomycin-resistant Enterococci. These findings demonstrate the ability of these peptides as potential therapeutic adjuvants for counteracting the undesired accumulation of colonic vancomycin, allowing for protection of the colonic microflora.