A "retrocidal" plasmid in Enterococcus faecalis: passage and protection

Antimicrobial resistance in patients with endodontic infections: A systematic scoping review of observational studies

The aim of this study was to assess the prevalence and proportions of antimicrobial-resistant species in patients with endodontic infections. A systematic scoping review of scientific evidence was accomplished involving different databases. Nine investigations were selected including 651 patients. Enterococcus faecalis was resistant to tetracycline (30%-70%), clindamycin (100%), erythromycin (10%-20%), ampicillin (9%) and azithromycin (60%). On the contrary, Prevotella spp., Fusobacterium spp., Peptostreptococcus spp. and Streptococcus spp. were resistant to penicillin, tetracycline, doxycycline, ciprofloxacin, amoxicillin, erythromycin, metronidazole and clindamycin in different proportions. Fusobacterium nucleatum showed high resistance to amoxicillin, amoxicillin plus clavulanate and erythromycin. Prevotella oralis presented a predisposition to augment its resistance to clindamycin over time. Tanerella forsythia exhibited resistance to ciprofloxacin and rifampicin. Lactococcus lactis presented robust resistance to cephalosporins, metronidazole, penicillin, amoxicillin and amoxicillin-clavulanic acid. It was observed high levels of resistance to antimicrobials that have been utilised in the local and systemic treatment of oral cavity infections.

Let Me Upgrade You: Impact of Mobile Genetic Elements on Enterococcal Adaptation and Evolution

Enterococci are Gram-positive bacteria that have evolved to thrive as both commensals and pathogens, largely due to their accumulation of mobile genetic elements via horizontal gene transfer (HGT). Common agents of HGT include plasmids, transposable elements, and temperate bacteriophages. These vehicles of HGT have facilitated the evolution of the enterococci, specifically Enterococcus faecalis and Enterococcus faecium, into multidrug-resistant hospital-acquired pathogens. On the other hand, commensal strains of Enterococcus harbor CRISPR-Cas systems that prevent the acquisition of foreign DNA, restricting the accumulation of mobile genetic elements. In this review, we discuss enterococcal mobile genetic elements by highlighting their contributions to bacterial fitness, examine the impact of CRISPR-Cas on their acquisition, and identify key areas of research that can improve our understanding of enterococcal evolution and ecology.

Characterization of Partially Purified Bacteriocins Produced by Enterococcus faecium Strains Isolated from Soybean Paste Active Against Listeria spp. and Vancomycin-Resistant Enterococci

Three out of one hundred eighty putative LAB isolates from Korean traditional fermented soybean paste were identified to be unique and bacteriocinogenic strains. Based on phenotypic and 16S rRNA sequencing analysis, selected strains were identified as Enterococcus faecium ST651ea, E. faecium ST7119ea and E. faecium ST7319ea. The bacteriocinogenic properties of the studied strains were evaluated against Listeria monocytogenes ATCC15313, Listeria innocua ATCC33090 and vancomycin-resistant E. faecium VRE19 of clinical origin. The strains E. faecium ST651ea, ST7119ea and ST7319ea expressed bacteriocins with an activity of 12,800 AU/mL, 25,600 AU/mL and 25,600 AU/mL, respectively, recorded against L. monocytogenes ATCC15131. According to the PCR-based screening of bacteriocin-related genes, which was further confirmed through amplicon sequencing, showed that strain E. faecium ST651ea carries entB and entP genes, whereas both E. faecium ST7119ea and ST7319ea strains harbor entA and entB genes. The molecular size of expressed bacteriocins was estimated by tricine-SDS-PAGE showing an approximative protein size of 4.5 kDa. The assessment of the spectrum of activity of bacteriocins ST651ea, ST7119ea and ST7319ea showed strong activity against most of clinical VRE isolates, majority of other Enterococcus spp. and Listeria spp. Bacteriocins ST651ea, ST7119ea and ST7319ea were partially purified by combination of 60% ammonium sulfate precipitation and hydrophobic chromatography on the SepPakC₁₈ column. Challenge test with semi-purified (60% 2-propanol fraction) bacteriocins resulted in a significant reduction of viable cells for all test organisms. Thus, indicating that all the bacteriocins evaluated can be used as potential biocontrol in food and feed industries as well as an alternative treatment for VRE-related infections in both veterinary and clinical settings.

Competent but complex communication: The phenomena of pheromone-responsive plasmids

Enterococci are robust gram-positive bacteria that are found in a variety of surroundings and that cause a significant number of healthcare-associated infections. The genus possesses a high-efficiency pheromone-responsive plasmid (PRP) transfer system for genetic exchange that allows antimicrobial-resistance determinants to spread within bacterial populations. The pCF10 plasmid system is the best characterised, and although other PRP systems are structurally similar, they lack exact functional homologues of pCF10-encoded genes. In this review, we provide an overview of the enterococcal PRP systems, incorporating functional details for the less-well-defined systems. We catalogue the virulence-associated elements of the PRPs that have been identified to date, and we argue that this reinforces the requirement for elucidation of the less studied systems.

Harnessing the Potential of Killers and Altruists within the Microbial Community: A Possible Alternative to Antibiotic Therapy?

In the context of a post-antibiotic era, the phenomenon of microbial allolysis, which is defined as the partial killing of bacterial population induced by other cells of the same species, may take on greater significance. This phenomenon was revealed in some bacterial species such as Streptococcus pneumoniae and Bacillus subtilis, and has been suspected to occur in some other species or genera, such as enterococci. The mechanisms of this phenomenon, as well as its role in the life of microbial populations still form part of ongoing research. Herein, we describe recent developments in allolysis in the context of its practical benefits as a form of cell death that may give rise to developing new strategies for manipulating the life and death of bacterial communities. We highlight how such findings may be viewed with importance and potential within the fields of medicine, biotechnology, and pharmacology.

Codon-optimized fluorescent mTFP and mCherry for microscopic visualization and genetic counterselection of streptococci and enterococci

Despite the powerful potential of fluorescent proteins for labeling bacteria, their use has been limited in multi-species oral biofilm models. Fermentative metabolism by streptococcal species that initiate biofilm colonization results in an acidic, reduced microenvironment that may limit the activities of some fluorescent proteins which are influenced by pH and oxygen availability. The need to reliably distinguish morphologically similar strains within biofilms was the impetus for this work. Teal fluorescent protein (mTFP1) and red fluorescent protein (mCherry) were chosen because their fluorescent properties made them promising candidates. Since tRNA availability has been implicated in efficient translation of sufficient quantities of protein for maximum fluorescence, a streptococcal codon optimization approach was used. DNA was synthesized to encode either protein using codons most frequently used in streptococci; each coding region was preceded by an engineered ribosomal binding site and restriction sites for cloning a promoter. Plasmids carrying this synthesized DNA under control of the Streptococcus mutans lactate dehydrogenase promoter conferred fluorescence to nine representative streptococcal and two Enterococcus faecalis strains. Further characterization in Streptococcus gordonii showed that mTFP1 and mCherry expressions could be detected in cells grown planktonically, in biofilms, or in colonies on agar when expressed on an extrachromosomal plasmid or in single copy integrated into the chromosome. This latter property facilitated counterselection of chromosomal mutations demonstrating value for bacterial strain construction. Fluorescent and non-fluorescent bacteria were distinguishable at acidic pH. These codon-optimized versions of mTFP1 and mCherry have promising potential for use in multiple experimental applications.

Antimicrobial resistance and virulence traits of Enterococcus faecalis from primary endodontic infections

OBJECTIVES

To determine the phenotypic and molecular characteristics of Enterococcus faecalis recovered from primary endodontic infections in Brazilian patients.

METHODS

Twenty isolates of E. faecalis recovered from 43 Brazilian patients with primary endodontic infections were identified by biochemical profiling (API20Strep) and 16S rDNA sequencing. Antimicrobial susceptibility was ascertained by agar dilution, using the recommended protocol of the Clinical and Laboratory Standards Institute (CLSI). PCR with validated primers was used to detect genes associated with antibiotic resistance and specific virulence factors.

RESULTS

All isolates were deemed susceptible to penicillin G, erythromycin and vancomycin. However, nine isolates had a minimum inhibitory concentration of 4μg/mL to vancomycin (the resistance breakpoint). Fourteen isolates (70% of isolates) were also resistant to tetracycline with MICs of >64μg/mL. PCR products for tetracycline resistance genes were detected in test isolates, while erythromycin and vancomycin resistance genes were not evident. Gelatinase, aggregation substance and enteroccocal surface protein genes were detected in 20, 18 and 12 isolates, respectively.

CONCLUSIONS

Endodontic E. faecalis isolates exhibit high level of resistance to tetracycline, an antibiotic that has use in local treatment of dental infections. This opens up a much-needed debate on the role and efficacy of this antibiotic for oral infections. Furthermore, these isolates were shown to possess genes that could contribute to pathogenicity in the pulp cavity.

Class IIa bacteriocins: diversity and new developments

Class IIa bacteriocins are heat-stable, unmodified peptides with a conserved amino acids sequence YGNGV on their N-terminal domains, and have received much attention due to their generally recognized as safe (GRAS) status, their high biological activity, and their excellent heat stability. They are promising and attractive agents that could function as biopreservatives in the food industry. This review summarizes the new developments in the area of class IIa bacteriocins and aims to provide uptodate information that can be used in designing future research.

A genetic determinant in Streptococcus gordonii Challis encodes a peptide with activity similar to that of enterococcal sex pheromone cAM373, which facilitates intergeneric DNA transfer

Enterococcus faecalis strains secrete multiple peptides representing different sex pheromones that induce mating responses by bacteria carrying specific conjugative plasmids. The pheromone cAM373, which induces a response by the enterococcal plasmid pAM373, has been of interest because a similar activity is also secreted by Streptococcus gordonii and Staphylococcus aureus. The potential to facilitate intergeneric DNA transfer from E. faecalis is of concern because of extensive multiple antibiotic resistance, including vancomycin resistance, that has emerged among enterococci in recent years. Here, we characterize the related pheromone determinant in S. gordonii and show that the peptide it encodes, gordonii-cAM373, does indeed induce transfer of plasmid DNA from E. faecalis into S. gordonii. The streptococcal determinant camG encodes a lipoprotein with a leader sequence, the last 7 residues of which represent the gordonii-cAM373 heptapeptide SVFILAA. Synthetic forms of the peptide had activity similar to that of the enterococcal cAM373 AIFILAS. The lipoprotein moiety bore no resemblance to the lipoprotein encoded by E. faecalis. We also identified determinants in S. gordonii encoding a signal peptidase and an Eep-like zinc metalloprotease (lspA and eep, respectively) similar to those involved in processing certain pheromone precursors in E. faecalis. Mutations generated in camG, lspA, and eep each resulted in the ablation of gordonii-cAM373 activity in culture supernatants. This is the first genetic analysis of a potential sex pheromone system in a commensal oral streptococcal species, which may have implications for intergeneric gene acquisition in oral biofilms.

Identification and characterization of a family of toxin-antitoxin systems related to the Enterococcus faecalis plasmid pAD1 par addiction module

The par locus of the Enterococcus faecalis plasmid pAD1 is an RNA-regulated addiction module encoding the peptide toxin Fst. Homology searches revealed that Fst belongs to a family of at least nine related peptides encoded on the chromosomes and plasmids of six different Gram-positive bacterial species. Comparison of an alignment of these peptides with the results of a saturation mutagenesis analysis indicated regions of the peptides important for biological function. Examination of the genetic context of the fst genes revealed that all of these peptides are encoded within par-like loci with conserved features similar to pAD1 par. All four Ent. faecalis family members were demonstrated to produce the expected toxin-encoding and regulatory RNA products. The locus from the Ent. faecalis plasmid pAMS1 was demonstrated to function as an addiction module and Fst was shown to be toxic to Staphylococcus aureus, suggesting that a plasmid-encoded module in that species is performing the same function. Thus, the pAD1-encoded par locus appears to be the prototype of a family of related loci found in several Gram-positive species.

Plasmid pAMS1-encoded, bacteriocin-related "Siblicide" in Enterococcus faecalis

The Enterococcus faecalis class IIa bacteriocin MC4-1 encoded by the sex pheromone-responding, multiple-antibiotic resistance plasmid pAMS1 exhibits "siblicidal" (sibling-killing) activity under certain conditions. Stabs of plasmid-containing cells on solid medium containing lawns of bacteria of the same (plasmid-containing) strain give rise to zones of inhibition. If the plasmid-containing host also produces gelatinase, bacteriocin cannot be detected.