Are Bacterial Persisters Dormant Cells Only?

Non-Canonical Aspects of Antibiotics and Antibiotic Resistance

The understanding of antibiotic resistance, one of the major health threats of our time, is mostly based on dated and incomplete notions, especially in clinical contexts. The "canonical" mechanisms of action and pharmacodynamics of antibiotics, as well as the methods used to assess their activity upon bacteria, have not changed in decades; the same applies to the definition, acquisition, selective pressures, and drivers of resistance. As a consequence, the strategies to improve antibiotic usage and overcome resistance have ultimately failed. This review gathers most of the "non-canonical" notions on antibiotics and resistance: from the alternative mechanisms of action of antibiotics and the limitations of susceptibility testing to the wide variety of selective pressures, lateral gene transfer mechanisms, ubiquity, and societal factors maintaining resistance. Only by having a "big picture" view of the problem can adequate strategies to harness resistance be devised. These strategies must be global, addressing the many aspects that drive the increasing prevalence of resistant bacteria aside from the clinical use of antibiotics.

Persisting cancer cells are different from bacterial persisters

The persistence of drug-sensitive tumors poses a significant challenge in cancer treatment. The concept of bacterial persisters, which are a subpopulation of bacteria that survive lethal antibiotic doses, is frequently used to compare to residual disease in cancer. Here, we explore drug tolerance of cancer cells and bacteria. We highlight the fact that bacteria, in contrast to cancer cells, have been selected for survival at the population level and may therefore possess contingency mechanisms that cancer cells lack. The precise mechanisms of drug-tolerant cancer cells and bacterial persisters are still being investigated. Undoubtedly, by understanding common features as well as differences, we, in the cancer field, can learn from microbiology to find strategies to eradicate persisting cancer cells.

Role of Staphylococcus aureus's Buoyant Density in the Development of Biofilm Associated Antibiotic Susceptibility

Biofilms are clusters of microorganisms that form at various interfaces, including those between air and liquid or liquid and solid. Due to their roles in enhancing wastewater treatment processes, and their unfortunate propensity to cause persistent human infections through lowering antibiotic susceptibility, understanding and managing bacterial biofilms is of paramount importance. A pivotal stage in biofilm development is the initial bacterial attachment to these interfaces. However, the determinants of bacterial cell choice in colonizing an interface first and heterogeneity in bacterial adhesion remain elusive. Our research has unveiled variations in the buoyant density of free-swimming Staphylococcus aureus cells, irrespective of their growth phase. Cells with a low cell buoyant density, characterized by fewer cell contents, exhibited lower susceptibility to antibiotic treatments (100 μg/mL vancomycin) and favored biofilm formation at air-liquid interfaces. In contrast, cells with higher cell buoyant density, which have richer cell contents, were more vulnerable to antibiotics and predominantly formed biofilms on liquid-solid interfaces when contained upright. Cells with low cell buoyant density were not able to revert to a more antibiotic sensitive and high cell buoyant density phenotype. In essence, S. aureus cells with higher cell buoyant density may be more inclined to adhere to upright substrates.

Polymyxin B nonapeptide potentiates the eradication of Gram-negative bacterial persisters

Antibiotic-resistant Gram-negative bacteria remain a globally leading cause of bacterial infection-associated mortality, and it is imperative to identify novel therapeutic strategies. Recently, the advantage of using antibacterials selective against Gram-negative bacteria has been demonstrated with polymyxins that specifically target the lipopolysaccharides of Gram-negative bacteria. However, the severe cytotoxicity of polymyxins limits their clinical use. Here, we demonstrate that polymyxin B nonapeptide (PMBN), a polymyxin B derivative without the terminal amino acyl residue, can significantly enhance the effectiveness of commonly used antibiotics against only Gram-negative bacteria and their persister cells. We show that although PMBN itself does not exhibit antibacterial activity or cytotoxicity well above the 100-fold minimum inhibitory concentration of polymyxin B, PMBN can increase the potency of co-treated antibiotics. We also demonstrate that using PMBN in combination with other antibiotics significantly reduces the frequency of resistant mutant formation. Together, this work provides evidence of the utilities of PMBN as a novel potentiator for antibiotics against Gram-negative bacteria and insights for the eradication of bacterial persister cells during antibiotic treatment.

IMPORTANCE

The significance of our study lies in addressing the problem of antibiotic-resistant Gram-negative bacteria, which continue to be a global cause of mortality associated with bacterial infections. Therefore, identifying innovative therapeutic approaches is an urgent need. Recent research has highlighted the potential of selective antibacterials like polymyxins, which specifically target the lipopolysaccharides of Gram-negative bacteria. However, the clinical use of polymyxins is limited by their severe cytotoxicity. This study unveils the effectiveness of polymyxin B nonapeptide (PMBN) in significantly enhancing the eradication of persister cells in Gram-negative bacteria. Although PMBN itself does not exhibit antibacterial activity or cytotoxicity, it remarkably reduces persister cells during the treatment of antibiotics. Moreover, combining PMBN with other antibiotics reduces the emergence of resistant mutants. Our research emphasizes the utility of PMBN as a novel potentiator to decrease persister cells during antibiotic treatments for Gram-negative bacteria.

Induced Burkholderia prophages detected from the hemoculture: a biomarker for Burkholderia pseudomallei infection

Bacteriophages (phages), viruses that infect bacteria, are found in abundance not only in the environment but also in the human body. The use of phages for the diagnosis of melioidosis, a tropical infectious disease caused by Burkholderia pseudomallei, is emerging as a promising novel approach, but our understanding of conditions under which Burkholderia prophages can be induced remains limited. Here, we first demonstrated the isolation of Burkholderia phages from the hemocultures of melioidosis patients. The B. pseudomallei-positive hemoculture bottles were filtered to remove bacteria, and then phages were isolated and purified by spot and double agar overlay plaque assays. Forty blood samples (hemoculture-confirmed melioidosis) were tested, and phages were found in 30% of the samples. Transmission electron microscopy and genome analysis of the isolated phages, vB_HM387 and vB_HM795, showed that both phages are Myoviruses. These two phages were stable at a pH of 5-7 and temperatures of 25-37°C, suggesting their ability to survive in human blood. The genome sizes of vB_HM387 and vB_HM795 are 36.3 and 44.0 kb, respectively. A phylogenetic analysis indicated that vB_HM387 has homologs, but vB_HM795 is a novel Myovirus, suggesting the heterogeneity of Burkholderia phages in melioidosis patients. The key finding that Burkholderia phages could be isolated from the blood of melioidosis patients highlights the potential application of phage-based assays by detecting phages in blood as a pathogen-derived biomarker of infection.

Dynamic Adaptation in Extant Porins Facilitates Antibiotic Tolerance in Energetic Escherichia coli

Bacteria can tolerate antibiotics despite lacking the genetic components for resistance. The prevailing notion is that tolerance results from depleted cellular energy or cell dormancy. In contrast to this view, many cells in the tolerant population of Escherichia coli can exhibit motility - a phenomenon that requires cellular energy, specifically, the proton-motive force (PMF). As these motile-tolerant cells are challenging to isolate from the heterogeneous tolerant population, their survival mechanism is unknown. Here, we discovered that motile bacteria segregate themselves from the tolerant population under micro-confinement, owing to their unique ability to penetrate micron-sized channels. Single-cell measurements on the motile-tolerant population showed that the cells retained a high PMF, but they did not survive through active efflux alone. By utilizing growth assays, single-cell fluorescence studies, and chemotaxis assays, we showed that the cells survived by dynamically inhibiting the function of existing porins in the outer membrane. A drug transport model for porin-mediated intake and efflux pump-mediated expulsion suggested that energetic tolerant cells withstand antibiotics by constricting their porins. The novel porin adaptation we have uncovered is independent of gene expression changes and may involve electrostatic modifications within individual porins to prevent extracellular ligand entry.

Persistence and viable but non-culturable state induced by streptomycin in Erwinia amylovora

Persister cell and viable but non-culturable (VBNC) state of bacteria are survival strategies against antibiotics and various environmental stresses, respectively, but they tend to be ignored in agriculture fields, even though bacteria can regain their abilities to survive and produce disease once those stresses disappear. This study was carried out to determine whether persister cell and VBNC state in Erwinia amylovora are present after exposures to streptomycin, the length of their persistence, and the steps needed to decrease the inoculum. Persister cells were observed using biphasic killed growth curve for 4-8 h when the late stationary phase cells of E. amylovora were cultured in liquid medium containing streptomycin. This state was maintained for up to 12 h based on the colony forming units (CFUs) of the colonies that grew on the mannitol glutamate yeast extract (MGY) medium after streptomycin was removed. The CFUs on the MGY medium were lower than the total count determined using the LIVE/DEAD Kit, suggesting that persister cells and VBNC state might co-exist for up to 12 h after exposure to streptomycin. However, after 12 h, E. amylovora cells did not continue to grow on the medium for 9 days, suggesting that they entered a VBNC state at that time and remained in a persistent state. In addition, based on the Redox Sensor Green staining method, the presence of both states was confirmed for up to 12 h, and only then did the VBNC state became apparent. Furthermore, persister cells were observed for up to 24 h, and damaged cells reduced when E. amylovora cells were culture in distilled water with streptomycin, indicating that the uptake of lower nutrients in E. amylovora led to prolonged persister cells and VBNC state, which are more likely to survive after streptomycin treatments. The addition of sucrose and oxytetracycline to distilled water containing streptomycin reduced persister cells than other sources did. Thus, to inhibit the spread of fire blight, management techniques must consider the hazards of using streptomycin treatments that induce dormancy, such as persister cells and VBNC state, beyond the development of resistant strain.

Metabolic dormancy in Chlamydia trachomatis treated with different antibiotics

Diseases caused by Chlamydia spp. are often associated with persistent infections. Chlamydial persistence is commonly associated with a unique non-infectious intracellular developmental form, termed an aberrant form. Although infectious chlamydiae can be cultured consistently in cells stressed to aberrancy, their role in persistence is not clear. Recovery from antibiotic stress was explored as a model to determine how survival of non-aberrant chlamydiae, in the presence of fully inhibitory drug concentrations, may participate in persistence. Assays included incubation in quinolones, tetracyclines, or chloramphenicol for differing lengths of time, followed by an extended recovery period in antibiotic-free media. Culturable elementary bodies were not detected during treatment with each antibiotic, but viable and culturable Chlamydia trachomatis emerged after the drug was removed. Time-lapse imaging of live, antibiotic-treated infected cells identified metabolically dormant developmental forms within cells that emerged to form typical productive inclusions. The effects of the increasing concentration of most tested antibiotics led to predictable inhibitory activity, in which the survival rate decreased with increasing drug concentration. In contrast, in fluoroquinolone-treated cells, there was a paradoxical increase in productive development that was directly correlated with drug concentration and inversely associated with aberrant form production. This model system uncovers a unique chlamydial persistence pathway that does not involve the chlamydial aberrant form. The association between productive latency and metabolic dormancy is consistent with models for many bacterial species and may lead to a different interpretation of mechanisms of chlamydial persistence in patients.IMPORTANCEThe life history of most pathogens within the genus Chlamydia relies on lengthy persistence in the host. The most generally accepted model for Chlamydia spp. persistence involves an unusual developmental stage, termed the aberrant form, which arises during conditions that mimic a stressful host environment. In this work, we provide an alternate model for chlamydial persistence in the face of antibiotic stress. This model may be relevant to antibiotic treatment failures in patients infected with C. trachomatis.

Unlocking the enigma of phenotypic drug tolerance: Mechanisms and emerging therapeutic strategies

In the ongoing battle against antimicrobial resistance, phenotypic drug tolerance poses a formidable challenge. This adaptive ability of microorganisms to withstand drug pressure without genetic alterations further complicating global healthcare challenges. Microbial populations employ an array of persistence mechanisms, including dormancy, biofilm formation, adaptation to intracellular environments, and the adoption of L-forms, to develop drug tolerance. Moreover, molecular mechanisms like toxin-antitoxin modules, oxidative stress responses, energy metabolism, and (p)ppGpp signaling contribute to this phenomenon. Understanding these persistence mechanisms is crucial for predicting drug efficacy, developing strategies for chronic bacterial infections, and exploring innovative therapies for refractory infections. In this comprehensive review, we dissect the intricacies of drug tolerance and persister formation, explore their role in acquired drug resistance, and highlight emerging therapeutic approaches to combat phenotypic drug tolerance. Furthermore, we outline the future landscape of interventions for persistent bacterial infections.

Medical Device-Associated Healthcare Infections: Sterilization and the Potential of Novel Biological Approaches to Ensure Patient Safety

Healthcare-associated infections caused by multi-drug-resistant pathogens are increasing globally, and current antimicrobial options have limited efficacy against these robust species. The WHO details the critically important bacterial and fungal species that are often associated with medical device HAIs. The effective sterilization of medical devices plays a key role in preventing infectious disease morbidity and mortality. A lack of adherence to protocol and limitations associated with each sterilization modality, however, allows for the incidence of disease. Furthermore, issues relating to carcinogenic emissions from ethylene oxide gas (EtO) have motivated the EPA to propose limiting EtO use or seeking alternative sterilization methods for medical devices. The Food and Drug Administration supports the sterilization of healthcare products using low-temperature VH2O2 as an alternative to EtO. With advances in biomaterial and medical devices and the increasing use of combination products, current sterilization modalities are becoming limited. Novel approaches to disinfection and sterilization of medical devices, biomaterials, and therapeutics are warranted to safeguard public health. Bacteriophages, endolysins, and antimicrobial peptides are considered promising options for the prophylactic and meta-phylactic control of infectious diseases. This timely review discusses the application of these biologics as antimicrobial agents against critically important WHO pathogens, including ESKAPE bacterial species.

The Benefits of Toxicity: M. smegmatis VapBC TA Module Is Induced by Tetracycline Exposure and Promotes Survival

Toxin-antitoxin (TA) systems are widely present in bacterial genomes. Mycolicibacterium smegmatis, a common model organism for studying Mycobacterium tuberculosis physiology, has eight TA loci, including mazEF and vapBC. This study aims to investigate the physiological significance of these TA systems. Proteomic profiling was conducted on a culture overexpressing the VapC toxin, and the involvement of VapC in M. smegmatis stress responses to heat shock and antibiotic treatment was examined. While deciphering the underlying mechanisms of the altered stress resistance, we assessed the antibiotic susceptibility of vapBC, mazEF, and double vapBC-mazEF deletion mutants. Additionally, the mRNA levels of vapC and mazF were measured following tetracycline supplementation. The results reveal changes in the abundance of metabolic enzymes and stress response proteins associated with VapC overexpression. This activation of the general stress response leads to reduced thermosensitivity in M. smegmatis, but does not affect susceptibility to ciprofloxacin and isoniazid. Under tetracycline treatment, both vapC and mazF expression levels are increased, and the fate of the cell depends on the interaction between the corresponding TA systems.

The Potential Role of Persister Cells in Urinary Tract Infections

PURPOSE OF REVIEW

This review explores the role of persister cells in urinary tract infections (UTIs). UTIs are one of the most common bacterial infections, affecting millions of people worldwide. Persister cells are a subpopulation of bacteria with dormant metabolic activity which allows survival in the presence of antibiotics.

RECENT FINDINGS

This review summarizes recent research on the pathogenesis of persister cell formation in UTIs, the impact of persister cells on the effectiveness of antibiotics, the challenges they pose for treatment, and the need for new strategies to target these cells. Furthermore, this review examines the current state of research on the identification and characterization of persister cells in UTIs, as well as the future directions for investigations in this field. This review highlights the importance of understanding the role of persister cells in UTIs and the potential impact of targeting these cells in the development of new treatments.

Transcriptome Analysis of Streptococcus mutans Quorum Sensing-Mediated Persisters Reveals an Enrichment in Genes Related to Stress Defense Mechanisms

Persisters are a small fraction of growth-arrested phenotypic variants that can survive lethal concentrations of antibiotics but are able to resume growth once antibiotics are stopped. Their formation can be a stochastic process or one triggered by environmental cues. In the human pathogen Streptococcus mutans, the canonical peptide-based quorum-sensing system is an inducible DNA repair system that is pivotal for bacterial survival. Previous work has shown that the CSP-signaling peptide is a stress-signaling alarmone that promotes the formation of stress-induced persisters. In this study, we exposed S. mutans to the CSP pheromone to mimic DNA damage conditions and isolated the antibiotic persisters by treating the cultures with ofloxacin. A transcriptome analysis was then performed to evaluate the differential gene expression between the normal stationary-phase cells and the persisters. RNA sequencing revealed that triggered persistence was associated with the upregulation of genes related to several stress defense mechanisms, notably, multidrug efflux pumps, the arginine deaminase pathway, and the Opu/Opc system. In addition, we showed that inactivation of the VicK kinase of the YycFG essential two-component regulatory system abolished the formation of triggered persisters via the CSP pheromone. These data contribute to the understanding of the triggered persistence phenotype and may suggest new therapeutic strategies for treating persistent streptococcal infections.

New Strategies to Kill Metabolically-Dormant Cells Directly Bypassing the Need for Active Cellular Processes

Antibiotic therapy failure is often caused by the presence of persister cells, which are metabolically-dormant bacteria capable of surviving exposure to antimicrobials. Under favorable conditions, persisters can resume growth leading to recurrent infections. Moreover, several studies have indicated that persisters may promote the evolution of antimicrobial resistance and facilitate the selection of specific resistant mutants; therefore, in light of the increasing numbers of multidrug-resistant infections worldwide, developing efficient strategies against dormant cells is of paramount importance. In this review, we present and discuss the efficacy of various agents whose antimicrobial activity is independent of the metabolic status of the bacteria as they target cell envelope structures. Since the biofilm-environment is favorable for the formation of dormant subpopulations, anti-persister strategies should also include agents that destroy the biofilm matrix or inhibit biofilm development. This article reviews examples of selected cell wall hydrolases, polysaccharide depolymerases and antimicrobial peptides. Their combination with standard antibiotics seems to be the most promising approach in combating persistent infections.

Purine metabolism regulates Vibrio splendidus persistence associated with protein aggresome formation and intracellular tetracycline efflux

A small subpopulation of Vibrio splendidus AJ01 that was exposed to tetracycline at 10 times the minimal inhibitory concentration (MIC) still survived, named tetracycline-induced persister cells in our previous work. However, the formation mechanisms of persister is largely unknown. Here, we investigated tetracycline-induced AJ01 persister cells by transcriptome analysis and found that the purine metabolism pathway was significantly downregulated, which was consistent with lower levels of ATP, purine, and purine derivatives in our metabolome analysis. Inhibition of the purine metabolism pathway by 6-mercaptopurine (6-MP, inhibits ATP production), increased persister cell formation and accompanied with the decreasing intracellular ATP levels and increasing cells with protein aggresome. On the other hand, the persister cells had reduced intracellular tetracycline concentrations and higher membrane potential after 6-MP treatment. Inhibition of the membrane potential by carbonyl cyanide m-chlorophenyl hydrazone reversed 6-MP-induced persistence and resulted in higher levels of intracellular tetracycline accumulation. Meanwhile, cells with 6-MP treatment increased the membrane potential by dissipating the transmembrane proton pH gradient, which activated efflux to decrease the intracellular tetracycline concentration. Together, our findings show that reduction of purine metabolism regulates AJ01 persistence and is associated with protein aggresome formation and intracellular tetracycline efflux.

Heterogeneous Distribution of Proton Motive Force in Nonheritable Antibiotic Resistance

Bacterial infections that are difficult to eradicate are often treated by sequentially exposing the bacteria to different antibiotics. Although effective, this approach can give rise to epigenetic or other phenomena that may help some cells adapt to and tolerate the antibiotics. Characteristics of such adapted cells are dormancy and low energy levels, which promote survival without lending long-term genetic resistance against antibiotics. In this work, we quantified motility in cells of Escherichia coli that adapted and survived sequential exposure to lethal doses of antibiotics. In populations that adapted to transcriptional inhibition by rifampicin, we observed that ~1 of 3 cells continued swimming for several hours in the presence of lethal concentrations of ampicillin. As motility is powered by proton motive force (PMF), our results suggested that many adapted cells retained a high PMF. Single-cell growth assays revealed that the high-PMF cells resuscitated and divided upon the removal of ampicillin, just as the low-PMF cells did, a behavior reminiscent of persister cells. Our results are consistent with the notion that cells in a clonal population may employ multiple different mechanisms to adapt to antibiotic stresses. Variable PMF is likely a feature of a bet-hedging strategy: a fraction of the adapted cell population lies dormant while the other fraction retains high PMF to be able to swim out of the deleterious environment. IMPORTANCE Bacterial cells with low PMF may survive antibiotic stress due to dormancy, which favors nonheritable resistance without genetic mutations or acquisitions. On the other hand, cells with high PMF are less tolerant, as PMF helps in the uptake of certain antibiotics. Here, we quantified flagellar motility as an indirect measure of the PMF in cells of Escherichia coli that had adapted to ampicillin. Despite the disadvantage of maintaining a high PMF in the presence of antibiotics, we observed high PMF in ~30% of the cells, as evidenced by their ability to swim rapidly for several hours. These and other results were consistent with the idea that antibiotic tolerance can arise via different mechanisms in a clonal population.

Assessment of phenotypic heterogeneity in Salmonella Typhimurium preadapted to ciprofloxacin and tetracycline

Bacterial population exposed to stressful antibiotic conditions consists of various subpopulations such as tolerant, persister, and resistant cells. The aim of this study was to evaluate the phenotypic heterogeneity of Salmonella Typhimurium preadapted to sublethal concentrations of antibiotics. Salmonella Typhimurium cells were treated with 1/2 × MIC of antibiotics for the first 48 h and successively 1 × MIC for the second 24 h at 37°C, including untreated control (CON), no antibiotic and 1 × MIC ciprofloxacin (NON-CIP), 1/2 × MIC ciprofloxacin and 1 × MIC ciprofloxacin (CIP-CIP), 1/2 × MIC tetracycline and 1 × MIC ciprofloxacin (TET-CIP), no antibiotic and 1 × MIC tetracycline (NON-TET), 1/2 × MIC ciprofloxacin and 1 × MIC tetracycline (CIP-TET), and 1/2 × MIC tetracycline and 1 × MIC tetracycline (TET-TET). All treatments were evaluated by antibiotic susceptibility, ATP level, relative fitness, cross-resistance, and persistence. S. Typhimurium cells were more susceptible to non-adapted NON-CIP and NON-TET (>3-log reduction) than pre-adapted CIP-CIP, TET-CIP, CIP-TET, and TET-TET. CON exhibited the highest ATP level, corresponding to the viable cell number. The relative fitness levels were more than 0.95 for all treatments, except for NON-CIP (0.78). The resistance to ciprofloxacin and tetracycline was increased at all treatments with the exception of NON-TET. The persister cells were noticeably induced at CIP-TET treatment, showing more than 5 log CFU mL-1. The results suggest that the antibiotic preadaptation led to heterogeneous populations including persisters that can develop to resistance. This study provides new insight in the bacterial persistence associated with their potential risk and paves the way to design antibiotic therapy targeting dormant bacteria.

Variability in Adaptive Resistance of Salmonella Typhimurium to Sublethal Levels of Antibiotics

This study was designed to evaluate the adaptive resistance of Salmonella Typhimurium under continuous sublethal selective pressure. Salmonella Typhimurium ATCC 19585 (STATCC) and S. Typhimurium CCARM 8009 (STCCARM) were sequentially cultured for 3 days at 37 °C in trypticase soy broth containing 1/2 × MICs of cefotaxime (CEF1/2), chloramphenicol (CHL1/2), gentamicin (GEN1/2), and polymyxin B (POL1/2). The STATCC and STCCARM exposed to CEF1/2, CHL1/2, GEN1/2, and POL1/2 were evaluated using antibiotic susceptibility, cross-resistance, and relative fitness. The susceptibilities of STATCC exposed to GEN1/2 and POL1/2 were increased by a 2-fold (gentamicin) and 8-fold (polymyxin B) increase in minimum inhibitory concentration (MIC) values, respectively. The MIC values of STCCARM exposed to CEF1/2, CHL1/2, GEN1/2, and POL1/2 were increased by 4-fold (cefotaxime), 2-fold (chloramphenicol), 2-fold (gentamicin), and 8-fold (polymyxin B). The highest heterogeneous fractions were observed for the STATCC exposed to CEF1/2 (38%) and POL1/2 (82%). The STCCARM exposed to GEN1/2 was cross-resistant to cefotaxime (p < 0.05), chloramphenicol (p < 0.01), and polymyxin B (p < 0.05). The highest relative fitness levels were 0.92 and 0.96, respectively, in STATCC exposed to CEF1/2 and STCCARM exposed to POL1/2. This study provides new insight into the fate of persistent cells and also guidance for antibiotic use.

A DNA-Damage Inducible Gene Promotes the Formation of Antibiotic Persisters in Response to the Quorum Sensing Signaling Peptide in Streptococcus mutans

Bacteria use quorum sensing (QS) to communicate with each other via secreted small autoinducers produced by individuals. QS allows bacteria to display a unified response that benefits the species during adaptation to environment, colonization, and defense against competitors. In oral streptococci, the CSP-ComDE QS is an inducible DNA damage repair system that is pivotal for bacterial survival. In the oral pathogen Streptococcus mutans, the QS system positively influences the formation of antibiotic persisters, cells that can survive antibiotic attack by entering a non-proliferative state. We recently identified a novel gene, pep299, that is activated in the persister cell fraction induced by QS. In this study, we focused our investigation on the role of pep299, a gene encoding a bacteriocin-like peptide, in the formation of antibiotic persisters. Mutant Δ299, unable to produce Pep299, showed a dramatic reduction in the number of stress-induced persisters. Using a co-culture assay, we showed that cells overproducing pep299 induced the formation of persisters in the mutant, suggesting that Pep299 was actively secreted and detected by neighboring cells. Cells exposed to DNA damage conditions activated the gene expression of pep299. Interestingly, our results suggested that the pep299 gene was also involved in the regulation of a QS-inducible toxin−antitoxin system. Our study suggests that the pep299 gene is at the core of the triggered persistence phenotype in S. mutans, allowing cells to transition into a state of reduced metabolic activity and antibiotic tolerance.