Lytic bacteriophages facilitate antibiotic sensitization of Enterococcus faecium

A novel thermostable lytic phage vB_EF_Enf3_CCASU-2024-3 against clinical Enterococcus faecium and Enterococcus faecalis

Enterococci, Gram-positive bacteria, have become a major concern in healthcare settings due to their significant virulence and antibiotic resistance. This research focuses on isolating, phenotypic, and genotypic analysis of enterococci-specific lytic phages to be used as potential candidates in combating multidrug-resistant (MDR) Enterococcus clinical isolates. The virulence of Enterococcus isolates was analyzed by testing for gelatinase and biofilm formation. The phage(s) was isolated from a sewage sample, then purified, propagated, and physiochemically analyzed. The phage was examined using transmission electron microscopy, and the whole genome sequence (WGS) was performed. Sixety-five clinical enterococci including, 27 (41.5%), 33 (50.7%) 3 (4.6%), and 2 (3%) E. faecalis, E. faecium, E. avium, and E. durans, respectively were isolated. Linezolid, teicoplanin, chloramphenicol, and vancomycin exhibited the lowest resistance. Twenty-five (38.5%) isolates were both gelatinase- and biofilm-producers. A novel lytic vB_EF_Enf3 phage belonging to Caudoviricetes class, characterized by an icosahedral head with a diameter of 100 ± 5 nm and a tail measuring 70 ± 5 nm in length was isolated. The phage demonstrated good thermal stability, and viability across various pH levels and exhibited a broad- spectrum of activity against E. faecium and E. faecalis. The vB_EF_Enf3 phage (36,202 bp length) harbored 36 open reading frames (ORFs) with a GC content of 34.4% (GenBank accession, PP747318). In conclusion, a novel thermostable lytic bacteriophage vB_EF_Enf3, belonging to class Caudoviricetes, was isolated from sewage showing broad-spectrum potent lytic activity against E. faecium and E. faecalis and maintained stability under various extreme conditions, including temperature, and pH fluctuations.

Bacteria- and Phage-Derived Proteins in Phage Infection

Phages have exerted severe evolutionary pressure on prokaryotes over billions of years, resulting in major rearrangements. Without every enzyme involved in the phage-bacterium interaction being examined; bacteriophages cannot be used in practical applications. Numerous studies conducted in the past few years have uncovered a huge variety of bacterial antiphage defense systems; nevertheless, the mechanisms of most of these systems are not fully understood. Understanding the interactions between bacteriophage and bacterial proteins is important for efficient host cell infection. Phage proteins involved in these bacteriophage-host interactions often arise immediately after infection. Here, we review the main groups of phage enzymes involved in the first stage of viral infection and responsible for the degradation of the bacterial membrane. These include polysaccharide depolymerases (endosialidases, endorhamnosidases, alginate lyases, and hyaluronate lyases), and peptidoglycan hydrolases (ectolysins and endolysins). Host target proteins are inhibited, activated, or functionally redirected by the phage protein. These interactions determine the phage infection of bacteria. Proteins of interest are holins, endolysins, and spanins, which are responsible for the release of progeny during the phage lytic cycle. This review describes the main bacterial and phage enzymes involved in phage infection and analyzes the therapeutic potential of bacteriophage-derived proteins.

Bacteriophage Therapy as a Promising Alternative for Antibiotic-Resistant Enterococcus faecium: Advances and Challenges

Enterococcus faecium is a Gram-positive bacterium increasingly identified as a critical nosocomial pathogen that poses significant treatment challenges due to its resistance to multiple antibiotics, particularly vancomycin-resistant E. faecium (VRE) strains. The urgent need for alternative therapeutic strategies has renewed interest in bacteriophage (phage) therapy, given phages specificity and bactericidal potential. This review explores the advancements in phage therapy against antibiotic-resistant E. faecium, including phage morphological diversity, genomic characteristics, and infection mechanisms. The efficacy of phage therapy in in vitro, ex vivo, and in vivo models and the compassionate use in clinical settings are evaluated, highlighting the promising outcomes of phage-antibiotic synergies and biofilm disruption. Key challenges and future research directions are discussed, with a focus on improving therapeutic efficacy and overcoming bacterial resistance. This review emphasizes the potential of phage therapy as a viable solution for managing multidrug-resistant E. faecium infections and underscores the importance of future investigations to enhance clinical applications.

Enterococcus faecium: evolution, adaptation, pathogenesis and emerging therapeutics

The opportunistic pathogen Enterococcus faecium colonizes humans and a wide range of animals, endures numerous stresses, resists antibiotic treatment and stubbornly persists in clinical environments. The widespread application of antibiotics in hospitals and agriculture has contributed to the emergence of vancomycin-resistant E. faecium, which causes many hospital-acquired infections. In this Review, we explore recent discoveries about the evolutionary history, the environmental adaptation and the colonization and dissemination mechanisms of E. faecium and vancomycin-resistant E. faecium. These studies provide critical insights necessary for developing novel preventive and therapeutic approaches against vancomycin-resistant E. faecium and also reveal the intricate interrelationships between the environment, the microorganism and the host, providing knowledge that is broadly relevant to how antibiotic-resistant pathogens emerge and endure.

Complete genome sequences of four lytic bacteriophages against multidrug-resistant Enterococcus faecium

We report the genome sequences of four Enterococcus faecium phages isolated from environmental wastewater in Kenya. They are double-stranded DNA phages with genomes varying in length from 42,231 to 43,348 bp, with G+C contents ranging from 34.96% to 35.2%. The genomes contain 78-82 coding sequences.

An enterococcal phage protein inhibits type IV restriction enzymes involved in antiphage defense

The prevalence of multidrug resistant (MDR) bacterial infections continues to rise as the development of antibiotics needed to combat these infections remains stagnant. MDR enterococci are a major contributor to this crisis. A potential therapeutic approach for combating MDR enterococci is bacteriophage (phage) therapy, which uses lytic viruses to infect and kill pathogenic bacteria. While phages that lyse some strains of MDR enterococci have been identified, other strains display high levels of resistance and the mechanisms underlying this resistance are poorly defined. Here, we use a CRISPR interference (CRISPRi) screen to identify a genetic locus found on a mobilizable plasmid from Enterococcus faecalis involved in phage resistance. This locus encodes a putative serine recombinase followed by a Type IV restriction enzyme (TIV-RE) that we show restricts the replication of phage phi47 in vancomycin-resistant E. faecalis. We further find that phi47 evolves to overcome restriction by acquiring a missense mutation in a TIV-RE inhibitor protein. We show that this inhibitor, termed type IV restriction inhibiting factor A (tifA), binds and inactivates diverse TIV-REs. Overall, our findings advance our understanding of phage defense in drug-resistant E. faecalis and provide mechanistic insight into how phages evolve to overcome antiphage defense systems.

An enterococcal phage protein broadly inhibits type IV restriction enzymes involved in antiphage defense

The prevalence of multidrug resistant (MDR) bacterial infections continues to rise as the development of antibiotics needed to combat these infections remains stagnant. MDR enterococci are a major contributor to this crisis. A potential therapeutic approach for combating MDR enterococci is bacteriophage (phage) therapy, which uses lytic viruses to infect and kill pathogenic bacteria. While phages that lyse some strains of MDR enterococci have been identified, other strains display high levels of resistance and the mechanisms underlying this resistance are poorly defined. Here, we use a CRISPR interference (CRISPRi) screen to identify a genetic locus found on a mobilizable plasmid from Enterococcus faecalis involved in phage resistance. This locus encodes a putative serine recombinase followed by a Type IV restriction enzyme (TIV-RE) that we show restricts the replication of phage phi47 in E. faecalis. We further find that phi47 evolves to overcome restriction by acquiring a missense mutation in a TIV-RE inhibitor protein. We show that this inhibitor, termed type IV restriction inhibiting factor A (tifA), binds and inactivates diverse TIV-REs. Overall, our findings advance our understanding of phage defense in drug-resistant E. faecalis and provide mechanistic insight into how phages evolve to overcome antiphage defense systems.

Pheromone cCF10 inhibits the antibiotic persistence of Enterococcus faecalis by modulating energy metabolism

Introduction

Bacterial resistance presents a major challenge to both the ecological environment and human well-being, with persistence playing a key role. Multiple studies were recently undertaken to examine the factors influencing the formation of persisters and the underlying process, with a primary focus on Gram-negative bacteria and Staphylococcus aureus (Gram-positive bacteria). Enterococcus faecalis (E. faecalis) is capable of causing a variety of infectious diseases, but there have been few studies of E. faecalis persisters. Previous studies have shown that the sex pheromone cCF10 secreted by E. faecalis induces conjugative plasmid transfer. However, whether the pheromone cCF10 regulates the persistence of E. faecalis has not been investigated.

Methods

As a result, we investigated the effect and potential molecular mechanism of pheromone cCF10 in regulating the formation of persisters in E. faecalis OG1RF using a persistent bacteria model.

Results and discussion

The metabolically active E. faecalis OG1RF reached a persistence state and temporarily tolerated lethal antibiotic concentrations after 8  h of levofloxacin hydrochloride (20 mg/mL) exposure, exhibiting a persistence rate of 0.109 %. During the growth of E. faecalis OG1RF, biofilm formation was a critical factor contributing to antibiotic persistence, whereas 10 ng/mL cCF10 blocked persister cell formation. Notably, cCF10 mediated the antibiotic persistence of E. faecalis OG1RF via regulating metabolic activity rather than suppressing biofilm formation. The addition of cCF10 stimulated the Opp system and entered bacterial cells, inhibiting (p)ppGpp accumulation, thus maintaining the metabolically active state of bacteria and reducing persister cell generation. These findings offer valuable insights into the formation, as well as the control mechanism of E. faecalis persisters.

Secreted antigen A peptidoglycan hydrolase is essential for Enterococcus faecium cell separation and priming of immune checkpoint inhibitor therapy

Enterococcus faecium is a microbiota species in humans that can modulate host immunity (Griffin and Hang, 2022), but has also acquired antibiotic resistance and is a major cause of hospital-associated infections (Van Tyne and Gilmore, 2014). Notably, diverse strains of E. faecium produce SagA, a highly conserved peptidoglycan hydrolase that is sufficient to promote intestinal immunity (Rangan et al., 2016; Pedicord et al., 2016; Kim et al., 2019) and immune checkpoint inhibitor antitumor activity (Griffin et al., 2021). However, the functions of SagA in E. faecium were unknown. Here, we report that deletion of sagA impaired E. faecium growth and resulted in bulged and clustered enterococci due to defective peptidoglycan cleavage and cell separation. Moreover, ΔsagA showed increased antibiotic sensitivity, yielded lower levels of active muropeptides, displayed reduced activation of the peptidoglycan pattern-recognition receptor NOD2, and failed to promote cancer immunotherapy. Importantly, the plasmid-based expression of SagA, but not its catalytically inactive mutant, restored ΔsagA growth, production of active muropeptides, and NOD2 activation. SagA is, therefore, essential for E. faecium growth, stress resistance, and activation of host immunity.

A simple solid media assay for detection of synergy between bacteriophages and antibiotics

The emergence of antibiotic-resistant bacteria (ARB) has necessitated the development of alternative therapies to deal with this global threat. Bacteriophages (viruses that target bacteria) that kill ARB are one such alternative. Although phages have been used clinically for decades with inconsistent results, a number of recent advances in phage selection, propagation, and purification have enabled a reevaluation of their utility in contemporary clinical medicine. In most phage therapy cases, phages are administered in combination with antibiotics to ensure that patients receive the standard-of-care treatment. Some phages may work cooperatively with antibiotics to eradicate ARB, as often determined using non-standardized broth assays. We sought to develop a solid media-based assay to assess cooperativity between antibiotics and phages to offer a standardized platform for such testing. We modeled the interactions that occur between antibiotics and phages on solid medium to measure additive, antagonistic, and synergistic interactions. We then tested the method using different bacterial isolates and identified a number of isolates where synergistic interactions were identified. These interactions were not dependent on the specific organism, phage family, or antibiotic used. A priori susceptibility to the antibiotic or the specific phage were not requirements to observe synergistic interactions. Our data also confirm the potential for the restoration of vancomycin to treat vancomycin-resistant Enterococcus (VRE) when used in combination with phages. Solid media assays for the detection of cooperative interactions between antibiotics and phages can be an accessible technique adopted by clinical laboratories to evaluate antibiotic and phage choices in phage therapy.IMPORTANCEBacteriophages have become an important alternative treatment for individuals with life-threatening antibiotic-resistant bacteria (ARB) infections. Because antibiotics represent the standard-of-care for treatment of ARB, antibiotics and phages often are delivered together without evidence that they work cooperatively. Testing for cooperativity can be difficult due to the equipment necessary and a lack of standardized means for performing the testing in liquid medium. We developed an assay using solid medium to identify interactions between antibiotics and phages for gram-positive and gram-negative bacteria. We modeled the interactions between antibiotics and phages on solid medium, and then tested multiple replicates of vancomycin-resistant Enterococcus (VRE) and Stenotrophomonas in the assay. For each organism, we identified synergy between different phage and antibiotic combinations. The development of this solid media assay for assessing synergy between phages and antibiotics will better inform the use of these combinations in the treatment of ARB infections.

The virtue of training: extending phage host spectra against vancomycin-resistant Enterococcus faecium strains using the Appelmans method

Phage therapy has (re)emerged as a serious possibility for combating multidrug-resistant bacterial infections, including those caused by vancomycin-resistant Enterococcus faecium strains. These opportunistic pathogens belong to a specific clonal complex 17, against which relatively few phages have been screened. We isolated a collection of 21 virulent phages growing on these vancomycin-resistant isolates. Each of these phages harbored a typical narrow plaquing host range, lysing at most 5 strains and covering together 10 strains of our panel of 14 clinical isolates. To enlarge the host spectrum of our phages, the Appelmans protocol was used. We mixed four out of our most complementary phages in a cocktail that we iteratively grew on eight naive strains from our panel, of which six were initially refractory to at least three of the combined phages. Fifteen successive passages permitted to significantly improve the lytic activity of the cocktail, from which phages with extended host ranges within the E. faecium species could be isolated. A single evolved phage able to kill up to 10 of the 14 initial E. faecium strains was obtained, and it barely infected nearby species. All evolved phages had acquired point mutations or a recombination event in the tail fiber genetic region, suggesting these genes might have driven phage evolution by contributing to their extended host spectra.

Antimicrobial sensitisers: Gatekeepers to avoid the development of multidrug-resistant bacteria

The resistance of multidrug-resistant bacteria to existing antibiotics forces the continued development of new antibiotics and antibacterial agents, but the high costs and long timeframe involved in the development of new agents renders the hope that existing antibiotics may again play a part. The "antibiotic adjuvant" is an indirect antibacterial strategy, but its vague concept has, in the past, limited the development speed of related drugs. In this review article, we put forward an accurate concept of a "non-self-antimicrobial sensitisers (NSAS)", to distinguish it from an "antibiotic adjuvant", and then discuss several scientific methods to restore bacterial sensitivity to antibiotics, and the sources and action mechanism of existing NSAS, in order to guide the development and further research of NSAS.

A review and new perspective on oral bacteriophages: manifestations in the ecology of oral diseases

Objective

To explore the manifestations of bacteriophages in different oral disease ecologies, including periodontal diseases, dental caries, endodontic infections, and oral cancer, as well as to propel phage therapy for safer and more effective clinical application in the field of dentistry.

Methods

In this literature review, we outlined interactions between bacteriophages, bacteria and even oral cells in the oral ecosystem, especially in disease states. We also analyzed the current status and future prospects of phage therapy in the perspective of different oral diseases.

Results

Various oral bacteriophages targeting at periodontal pathogens as Porphyromonas gingivalis, Fusobacterium nucleatum, Treponema denticola and Aggregatibacter actinomycetemcomitans, cariogenic pathogen Streptococcus mutans, endodontic pathogen Enterococcus faecalis were predicted or isolated, providing promising options for phage therapy. In the realm of oral cancer, aside from displaying tumor antigens or participating in tumor-targeted therapies, phage-like particle vaccines demonstrated the potential to prevent oral infections caused by human papillomaviruses (HPVs) associated with head-and-neck cancers.

Conclusion

Due to their intricate interactions with bacteria and oral cells, bacteriophages are closely linked to the progression and regression of diverse oral diseases. And there is an urgent need for research to explore additional possibilities of bacteriophages in the management of oral diseases.

Secreted antigen A peptidoglycan hydrolase is essential for Enterococcus faecium cell separation and priming of immune checkpoint inhibitor therapy

Enterococcus faecium is a microbiota species in humans that can modulate host immunity1, but has also acquired antibiotic resistance and is a major cause of hospital-associated infections2. Notably, diverse strains of E. faecium produce SagA, a highly conserved peptidoglycan hydrolase that is sufficient to promote intestinal immunity3-5 and immune checkpoint inhibitor antitumor activity6. However, the functions of SagA in E. faecium were unknown. Here we report that deletion of sagA impaired E. faecium growth and resulted in bulged and clustered enterococci due to defective peptidoglycan cleavage and cell separation. Moreover, ΔsagA showed increased antibiotic sensitivity, yielded lower levels of active muropeptides, displayed reduced activation of the peptidoglycan pattern-recognition receptor NOD2, and failed to promote cancer immunotherapy. Importantly, plasmid-based expression of SagA, but not its catalytically-inactive mutant, restored ΔsagA growth, production of active muropeptides and NOD2 activation. SagA is therefore essential for E. faecium growth, stress resistance and activation of host immunity.

Phage-specific immunity impairs efficacy of bacteriophage targeting Vancomycin Resistant Enterococcus in a murine model

Bacteriophage therapy is a promising approach to address antimicrobial infections though questions remain regarding the impact of the immune response on clinical effectiveness. Here, we develop a mouse model to assess phage treatment using a cocktail of five phages from the Myoviridae and Siphoviridae families that target Vancomycin-Resistant Enterococcus gut colonization. Phage treatment significantly reduces fecal bacterial loads of Vancomycin-Resistant Enterococcus. We also characterize immune responses elicited following administration of the phage cocktail. While minimal innate responses are observed after phage administration, two rounds of treatment induces phage-specific neutralizing antibodies and accelerate phage clearance from tissues. Interestingly, the myophages in our cocktail induce a more robust neutralizing antibody response than the siphophages. This anti-phage immunity reduces the effectiveness of the phage cocktail in our murine model. Collectively, this study shows phage-specific immune responses may be an important consideration in the development of phage cocktails for therapeutic use.

Synergistic bactericidal effects of phage-enhanced antibiotic therapy against MRSA biofilms

Methicillin-resistant Staphylococcus aureus (MRSA) causes biofilm-related medical device infections. Phage-antibiotic combinations offer potential therapy due to proven in vitro antibiofilm efficacy. We evaluated phage-antibiotic synergy against biofilms using modified checkerboard and 24-h time-kill assays. Humanized-simulated daptomycin (DAP) (10, 8, and 6 mg/kg q24h) and ceftaroline (CPT) (600 mg q12h) were combined with Intesti13, Sb-1, and Romulus phages (tMOI 1, q12h). Assays were conducted in 168-h biofilm reactor models against DAP non-susceptible (DNS) vancomycin intermediate S. aureus (VISA) MRSA D712 and DAP-susceptible MRSA 8014. Synergistic activity and bactericidal activity were defined as ≥2log10 CFU/mL reduction from antibiotic-only regimens and ≥3log10 CFU/mL decrease from baseline at 24 h. Differences were analyzed by one-way analysis of variance with Tukey's post hoc test (P ≤ 0.05 is considered significant). Surviving bacteria were examined for antibiotic minimum biofilm inhibitory concentration (MBIC) changes and phage susceptibility. In 168-h biofilm models, humanized DAP 10 mg/kg + CPT, combined with a 2-phage cocktail (Intesti13 + Sb-1) against D712, and a 3-phage cocktail (Intesti13 + Sb-1 + Romulus) against 8014, demonstrated synergistic bactericidal activity. At 168 h, bacteria were minimally detectable [2log10 CFU/cm2 (-Δ4.23 and -Δ4.42 log10 CFU/cm2; both P < 0.001)]. Antibiotic MBIC remained unchanged compared to baseline across various time points. None of the tested bacteria at 168 h exhibited complete phage resistance. This study reveals bactericidal efficacy of DAP + CPT with 2-phage and 3-phage cocktails against DNS VISA and MRSA isolates (D712 and 8014) in biofilm models, maintaining susceptibility. Further research is needed for diverse strains and durations, aligning with infection care.

IMPORTANCE

The prevalence of biofilm-associated medical device infections caused by methicillin-resistant Staphylococcus aureus (MRSA) presents a pressing medical challenge. The latest research demonstrates the potential of phage-antibiotic combinations (PACs) as a promising solution, notably in vitro antibiofilm efficacy. By adopting modified checkerboard and 24-h time-kill assays, the study investigated the synergistic action of phages combined with humanized-simulated doses of daptomycin (DAP) and ceftaroline (CPT). The results were promising: a combination of DAP, CPT, and either a 2-phage or 3-phage cocktail effectively exhibited bactericidal activity against both DAP non-susceptible vancomycin intermediate S. aureus MRSA and DAP-susceptible MRSA strains within 168-h biofilm models. Moreover, post-treatment evaluations revealed no discernible rise in antibiotic resistance or complete phage resistance. This pioneering work suggests the potential of PACs in addressing MRSA biofilm infections, setting the stage for further expansive research tailored to diverse bacterial strains and treatment durations.

Promiscuous, persistent and problematic: insights into current enterococcal genomics to guide therapeutic strategy

Vancomycin-resistant enterococci (VRE) are major opportunistic pathogens and the causative agents of serious diseases, such as urinary tract infections and endocarditis. VRE strains mainly include species of Enterococcus faecium and E. faecalis which can colonise the gastrointestinal tract (GIT) of patients and, following growth and persistence in the gut, can transfer to blood resulting in systemic dissemination in the body. Advancements in genomics have revealed that hospital-associated VRE strains are characterised by increased numbers of mobile genetic elements, higher numbers of antibiotic resistance genes and often lack active CRISPR-Cas systems. Additionally, comparative genomics have increased our understanding of dissemination routes among patients and healthcare workers. Since the efficiency of currently available antibiotics is rapidly declining, new measures to control infection and dissemination of these persistent pathogens are urgently needed. These approaches include combinatory administration of antibiotics, strengthening colonisation resistance of the gut microbiota to reduce VRE proliferation through commensals or probiotic bacteria, or switching to non-antibiotic bacterial killers, such as bacteriophages or bacteriocins. In this review, we discuss the current knowledge of the genomics of VRE isolates and state-of-the-art therapeutic advances against VRE infections.

Bacteriophage and antibiotic combination therapy for recurrent Enterococcus faecium bacteremia

Enterococcus faecium is a member of the human gastrointestinal (GI) microbiota but can also cause invasive infections, especially in immunocompromised hosts. Enterococci display intrinsic resistance to many antibiotics, and most clinical E. faecium isolates have acquired vancomycin resistance, leaving clinicians with a limited repertoire of effective antibiotics. As such, vancomycin-resistant E. faecium (VREfm) has become an increasingly difficult to treat nosocomial pathogen that is often associated with treatment failure and recurrent infections. We followed a patient with recurrent E. faecium bloodstream infections (BSIs) of increasing severity, which ultimately became unresponsive to antibiotic combination therapy over the course of 7 years. Whole-genome sequencing (WGS) showed that the patient was colonized with closely related E. faecium strains for at least 2 years and that invasive isolates likely emerged from a large E. faecium population in the patient's gastrointestinal (GI) tract. The addition of bacteriophage (phage) therapy to the patient's antimicrobial regimen was associated with several months of clinical improvement and reduced intestinal burden of VRE and E. faecium. In vitro analysis showed that antibiotic and phage combination therapy improved bacterial growth suppression compared to therapy with either alone. Eventual E. faecium BSI recurrence was not associated with the development of antibiotic or phage resistance in post-treatment isolates. However, an anti-phage-neutralizing antibody response occurred that coincided with an increased relative abundance of VRE in the GI tract, both of which may have contributed to clinical failure. Taken together, these findings highlight the potential utility and limitations of phage therapy to treat antibiotic-resistant enterococcal infections.

IMPORTANCE

Phage therapy is an emerging therapeutic approach for treating bacterial infections that do not respond to traditional antibiotics. The addition of phage therapy to systemic antibiotics to treat a patient with recurrent E. faecium infections that were non-responsive to antibiotics alone resulted in fewer hospitalizations and improved the patient's quality of life. Combination phage and antibiotic therapy reduced E. faecium and VRE abundance in the patient's stool. Eventually, an anti-phage antibody response emerged that was able to neutralize phage activity, which may have limited clinical efficacy. This study demonstrates the potential of phages as an additional option in the antimicrobial toolbox for treating invasive enterococcal infections and highlights the need for further investigation to ensure phage therapy can be deployed for maximum clinical benefit.

Bacteriophage therapy against ESKAPE bacterial pathogens: Current status, strategies, challenges, and future scope

The ESKAPE pathogens are the primary threat due to their constant spread of drug resistance worldwide. These pathogens are also regarded as opportunistic pathogens and could potentially cause nosocomial infections. Most of the ESKAPE pathogens have developed resistance to almost all the antibiotics that are used against them. Therefore, to deal with antimicrobial resistance, there is an urgent requirement for alternative non-antibiotic strategies to combat this rising issue of drug-resistant organisms. One of the promising alternatives to this scenario is implementing bacteriophage therapy. This under-explored mode of treatment in modern medicine has posed several concerns, such as preferable phages for the treatment, impact on the microbiome (or gut microflora), dose optimisation, safety, etc. The review will cover a rationale for phage therapy, clinical challenges, and propose phage therapy as an effective therapeutic against bacterial coinfections during pandemics. This review also addresses the expected uncertainties for administering the phage as a treatment against the ESKAPE pathogens and the advantages of using lytic phage over temperate, the immune response to phages, and phages in combinational therapies. The interaction between bacteria and bacteriophages in humans and countless animal models can also be used to design novel and futuristic therapeutics like personalised medicine or bacteriophages as anti-biofilm agents. Hence, this review explores different aspects of phage therapy and its potential to emerge as a frontline therapy against the ESKAPE bacterial pathogen.

Fitness Trade-Offs between Phage and Antibiotic Sensitivity in Phage-Resistant Variants: Molecular Action and Insights into Clinical Applications for Phage Therapy

In recent decades, phage therapy has been overshadowed by the widespread use of antibiotics in Western countries. However, it has been revitalized as a powerful approach due to the increasing prevalence of antimicrobial-resistant bacteria. Although bacterial resistance to phages has been reported in clinical cases, recent studies on the fitness trade-offs between phage and antibiotic resistance have revealed new avenues in the field of phage therapy. This strategy aims to restore the antibiotic susceptibility of antimicrobial-resistant bacteria, even if phage-resistant variants develop. Here, we summarize the basic virological properties of phages and their applications within the context of antimicrobial resistance. In addition, we review the occurrence of phage resistance in clinical cases, and examine fitness trade-offs between phage and antibiotic sensitivity, exploring the potential of an evolutionary fitness cost as a countermeasure against phage resistance in therapy. Finally, we discuss future strategies and directions for phage-based therapy from the aspect of fitness trade-offs. This approach is expected to provide robust options when combined with antibiotics in this era of phage 're'-discovery.

A simple solid media assay for detection of synergy between bacteriophages and antibiotics

The emergence of antibiotic resistant bacteria (ARB) has necessitated the development of alternative therapies to deal with this global threat. Bacteriophages (viruses that target bacteria) that kill ARB are one such alternative. While phages have been used clinically for decades with inconsistent results, a number of recent advances in phage selection, propagation and purification have enabled a reevaluation of their utility in contemporary clinical medicine. In most phage therapy cases, phages are administered in combination with antibiotics to ensure that patients receive the standard-of-care treatment. Some phages may work cooperatively with antibiotics to eradicate ARB, as often determined using non-standardized broth assays. We sought to develop a solid media-based assay to assess cooperativity between antibiotics and phages to offer a standardized platform for such testing. We modeled the interactions that occur between antibiotics and phages on solid medium to measure additive, antagonistic, and synergistic interactions. We then tested the method using different bacterial isolates, and identified a number of isolates where synergistic interactions were identified. These interactions were not dependent on the specific organism, phage family, or antibiotic used. A priori susceptibility to the antibiotic or the specific phage were not requirements to observe synergistic interactions. Our data also confirm the potential for the restoration of vancomycin to treat Vancomycin Resistant Enterococcus (VRE) when used in combination with phages. Solid media assays for the detection of cooperative interactions between antibiotics and phages can be an accessible technique adopted by clinical laboratories to evaluate antibiotic and phage choices in phage therapy.

Top-Down Genomic Surveillance Approach To Investigate the Genomic Epidemiology and Antibiotic Resistance Patterns of Enterococcus faecium Detected in Cancer Patients in Arkansas

Control of hospital-associated Enterococcus faecium infection is a strenuous task due to the difficulty of identifying transmission routes and the persistence of this nosocomial pathogen despite the implementation of infection control measures that have been successful with other important nosocomial pathogens. This study provides a comprehensive analysis of over 100 E. faecium isolates collected from 66 cancer patients at the University of Arkansas for Medical Sciences (UAMS) between June 2018 and May 2019. In the top-down approach used in this study, we employed, in addition to the 106 E. faecium UAMS isolates, a filtered set of 2,167 E. faecium strains from the GenBank database to assess the current population structure of E. faecium species and, consequently, to identify the lineages associated with our clinical isolates. We then evaluated the antibiotic resistance and virulence profiles of hospital-associated strains from the species pool, focusing on antibiotics of last resort, to establish an updated classification of high-risk and multidrug-resistant nosocomial clones. Further investigation of the clinical isolates collected from UAMS patients using whole-genome sequencing analytical methodologies (core genome multilocus sequence typing [cgMLST], core single nucleotide polymorphism [coreSNP] analysis, and phylogenomics), with the addition of patient epidemiological data, revealed a polyclonal outbreak of three sequence types occurring simultaneously in different patient wards. The integration of genomic and epidemiological data collected from the patients increased our understanding of the relationships and transmission dynamics of the E. faecium isolates. Our study provides new insights into genomic surveillance of E. faecium to assist in monitoring and further limiting the spread of multidrug-resistant E. faecium. IMPORTANCE Enterococcus faecium is a member of the gastrointestinal microbiota. Although its virulence is low in healthy, immunocompetent individuals, E. faecium has become the third leading cause of health care-associated infections in the United States. This study provides a comprehensive analysis of over 100 E. faecium isolates collected from cancer patients at the University of Arkansas for Medical Sciences (UAMS). We employed a top-down analytical approach (from population genomics to molecular biology) to classify our clinical isolates into their genetic lineages and thoroughly evaluate their antibiotic resistance and virulence profiles. The addition of patient epidemiological data to the whole-genome sequencing analytical methodologies performed in the study allowed us to increase our understanding of the relationships and transmission dynamics of the E. faecium isolates. This study provides new insights into genomic surveillance of E. faecium to help monitor and further limit the spread of multidrug-resistant E. faecium.

"Two Is Better Than One": The Multifactorial Nature of Phage-Antibiotic Combinatorial Treatments Against ESKAPE-Induced Infections

Phage-antibiotic synergy (PAS) has been extensively explored over the past decade, with the aim of developing more effective treatments against multidrug-resistant organisms. However, it remains unclear how to effectively combine these two approaches. To address this uncertainty, we assessed four main aspects of PAS interactions in this review, seeking to identify commonalities of combining treatments within and between bacterial species. We examined all literature on PAS efficacy toward ESKAPE pathogens and present an analysis of the data in papers focusing on: (1) order of treatment, (2) dose of both phage and antibiotics, (3) mechanism of action, and (4) viability of transfer from in vivo or animal model trials to clinical applications. Our analysis indicates that there is little consistency within phage-antibiotic therapy regimens, suggesting that highly individualized treatment regimens should be used. We propose a set of experimental studies to address these research gaps. We end our review with suggestions on how to improve studies on phage-antibiotic combination therapy to advance this field.

Enterococcus faecium Bacteriophage vB_EfaH_163, a New Member of the Herelleviridae Family, Reduces the Mortality Associated with an E. faecium vanR Clinical Isolate in a Galleria mellonella Animal Model

The rise of antimicrobial resistant (AMR) bacteria is a major health concern, especially with regard to members of the ESKAPE group, to which vancomycin-resistant (VRE) Enterococcus faecium belongs. Phage therapy has emerged as a novel alternative for the treatment of AMR infections. This, however, relies on the isolation and characterisation of a large collection of phages. This work describes the exploration of human faeces as a source of new E. faecium-infecting phages. Phage vB_EfaH_163 was isolated and characterised at the microbiological, genomic, and functional levels. vB_EfaH_163 phage, a new member of Herelleviridae, subfamily Brockvirinae, has a dsDNA genome of 150,836 bp that does not harbour any virulence factors or antibiotic resistance genes. It infects a wide range of E. faecium strains of different origins, including VRE strains. Interestingly, it can also infect Enterococcus faecalis strains, even some that are linezolid-resistant. Its capacity to control the growth of a clinical VRE isolate was shown in broth culture and in a Galleria mellonella animal model. The discovery and characterisation of vB_EfaH_163 increases the number of phages that might be used therapeutically against AMR bacteria.

Structural variations and roles of rhamnose-rich cell wall polysaccharides in Gram-positive bacteria

Rhamnose-rich cell wall polysaccharides (Rha-CWPSs) have emerged as crucial cell wall components of numerous Gram-positive, ovoid-shaped bacteria—including streptococci, enterococci, and lactococci—of which many are of clinical or biotechnological importance. Rha-CWPS are composed of a conserved polyrhamnose backbone with side-chain substituents of variable size and structure. Because these substituents contain phosphate groups, Rha-CWPS can also be classified as polyanionic glycopolymers, similar to wall teichoic acids, of which they appear to be functional homologs. Recent advances have highlighted the critical role of these side-chain substituents in bacterial cell growth and division, as well as in specific interactions between bacteria and infecting bacteriophages or eukaryotic hosts. Here, we review the current state of knowledge on the structure and biosynthesis of Rha-CWPS in several ovoid-shaped bacterial species. We emphasize the role played by multicomponent transmembrane glycosylation systems in the addition of side-chain substituents of various sizes as extracytoplasmic modifications of the polyrhamnose backbone. We provide an overview of the contribution of Rha-CWPS to cell wall architecture and biogenesis and discuss current hypotheses regarding their importance in the cell division process. Finally, we sum up the critical roles that Rha-CWPS can play as bacteriophage receptors or in escaping host defenses, roles that are mediated mainly through their side-chain substituents. From an applied perspective, increased knowledge of Rha-CWPS can lead to advancements in strategies for preventing phage infection of lactococci and streptococci in food fermentation and for combating pathogenic streptococci and enterococci.

The Mechanism of Bacterial Resistance and Potential Bacteriostatic Strategies

Bacterial drug resistance is rapidly developing as one of the greatest threats to human health. Bacteria will adopt corresponding strategies to crack the inhibitory effect of antibiotics according to the antibacterial mechanism of antibiotics, involving the mutation of drug target, secreting hydrolase, and discharging antibiotics out of cells through an efflux pump, etc. In recent years, bacteria are found to constantly evolve new resistance mechanisms to antibiotics, including target protective protein, changes in cell morphology, and so on, endowing them with multiple defense systems against antibiotics, leading to the emergence of multi-drug resistant (MDR) bacteria and the unavailability of drugs in clinics. Correspondingly, researchers attempt to uncover the mystery of bacterial resistance to develop more convenient and effective antibacterial strategies. Although traditional antibiotics still play a significant role in the treatment of diseases caused by sensitive pathogenic bacteria, they gradually lose efficacy in the MDR bacteria. Therefore, highly effective antibacterial compounds, such as phage therapy and CRISPER-Cas precision therapy, are gaining an increasing amount of attention, and are considered to be the treatments with the moist potential with regard to resistance against MDR in the future. In this review, nine identified drug resistance mechanisms are summarized, which enhance the retention rate of bacteria under the action of antibiotics and promote the distribution of drug-resistant bacteria (DRB) in the population. Afterwards, three kinds of potential antibacterial methods are introduced, in which new antibacterial compounds exhibit broad application prospects with different action mechanisms, the phage therapy has been successfully applied to infectious diseases caused by super bacteria, and the CRISPER-Cas precision therapy as a new technology can edit drug-resistant genes in pathogenic bacteria at the gene level, with high accuracy and flexibility. These antibacterial methods will provide more options for clinical treatment, and will greatly alleviate the current drug-resistant crisis.

Phage Cocktails with Daptomycin and Ampicillin Eradicates Biofilm-Embedded Multidrug-Resistant Enterococcus faecium with Preserved Phage Susceptibility

Multidrug-resistant (MDR) Enterococcus faecium is a challenging nosocomial pathogen known to colonize medical device surfaces and form biofilms. Bacterio (phages) may constitute an emerging anti-infective option for refractory, biofilm-mediated infections. This study evaluates eight MDR E. faecium strains for biofilm production and phage susceptibility against nine phages. Two E. faecium strains isolated from patients with bacteremia and identified to be biofilm producers, R497 (daptomycin (DAP)-resistant) and HOU503 (DAP-susceptible dose-dependent (SDD), in addition to four phages with the broadest host ranges (ATCC 113, NV-497, NV-503-01, NV-503-02) were selected for further experiments. Preliminary phage-antibiotic screening was performed with modified checkerboard minimum biofilm inhibitory concentration (MBIC) assays to efficiently screen for bacterial killing and phage-antibiotic synergy (PAS). Data were compared by one-way ANOVA and Tukey (HSD) tests. Time kill analyses (TKA) were performed against R497 and HOU503 with DAP at 0.5× MBIC, ampicillin (AMP) at free peak = 72 µg/mL, and phage at a multiplicity of infection (MOI) of 0.01. In 24 h TKA against R497, phage-antibiotic combinations (PAC) with DAP, AMP, or DAP + AMP combined with 3- or 4-phage cocktails demonstrated significant killing compared to the most effective double combination (ANOVA range of mean differences 2.998 to 3.102 log10 colony forming units (CFU)/mL; p = 0.011, 2.548 to 2.868 log10 colony forming units (CFU)/mL; p = 0.023, and 2.006 to 2.329 log10 colony forming units (CFU)/mL; p = 0.039, respectively), with preserved phage susceptibility identified in regimens with 3-phage cocktails containing NV-497 and the 4-phage cocktail. Against HOU503, AMP combined with any 3- or 4-phage cocktail and DAP + AMP combined with the 3-phage cocktail ATCC 113 + NV-497 + NV-503-01 demonstrated significant PAS and bactericidal activity (ANOVA range of mean differences 2.251 to 2.466 log10 colony forming units (CFU)/mL; p = 0.044 and 2.119 to 2.350 log10 colony forming units (CFU)/mL; p = 0.028, respectively), however, only PAC with DAP + AMP maintained phage susceptibility at the end of 24 h TKA. R497 and HOU503 exposure to DAP, AMP, or DAP + AMP in the presence of single phage or phage cocktail resulted in antibiotic resistance stabilization (i.e., no antibiotic MBIC elevation compared to baseline) without identified antibiotic MBIC reversion (i.e., lowering of antibiotic MBIC compared to baseline in DAP-resistant and DAP-SDD isolates) at the end of 24 h TKA. In conclusion, against DAP-resistant R497 and DAP-SDD HOU503 E. faecium clinical blood isolates, the use of DAP + AMP combined with 3- and 4-phage cocktails effectively eradicated biofilm-embedded MDR E. faecium without altering antibiotic MBIC or phage susceptibility compared to baseline.

Barriers to genetic manipulation of Enterococci: Current Approaches and Future Directions

Enterococcus faecalis and Enterococcus faecium are Gram-positive commensal gut bacteria that can also cause fatal infections. To study clinically relevant multi-drug resistant E. faecalis and E. faecium strains, methods are needed to overcome physical (thick cell wall) and enzymatic barriers that limit the transfer of foreign DNA and thus prevent facile genetic manipulation. Enzymatic barriers to DNA uptake identified in E. faecalis and E. faecium include type I, II and IV restriction modification systems and CRISPR-Cas. This review examines E. faecalis and E. faecium DNA defence systems and the methods with potential to overcome these barriers. DNA defence system bypass will allow the application of innovative genetic techniques to expedite molecular-level understanding of these important, but somewhat neglected, pathogens.

Bacteriophage and Bacterial Susceptibility, Resistance, and Tolerance to Antibiotics

Bacteriophages, viruses that infect and replicate within bacteria, impact bacterial responses to antibiotics in complex ways. Recent studies using lytic bacteriophages to treat bacterial infections (phage therapy) demonstrate that phages can promote susceptibility to chemical antibiotics and that phage/antibiotic synergy is possible. However, both lytic and lysogenic bacteriophages can contribute to antimicrobial resistance. In particular, some phages mediate the horizontal transfer of antibiotic resistance genes between bacteria via transduction and other mechanisms. In addition, chronic infection filamentous phages can promote antimicrobial tolerance, the ability of bacteria to persist in the face of antibiotics. In particular, filamentous phages serve as structural elements in bacterial biofilms and prevent the penetration of antibiotics. Over time, these contributions to antibiotic tolerance favor the selection of resistance clones. Here, we review recent insights into bacteriophage contributions to antibiotic susceptibility, resistance, and tolerance. We discuss the mechanisms involved in these effects and address their impact on bacterial fitness.

Phage Cocktails Constrain the Growth of Enterococcus

Phages that infect pathogenic bacteria present a valuable resource for treating antibiotic-resistant infections. We isolated and developed a collection of 19 Enterococcus phages, including myoviruses, siphoviruses, and a podovirus, that can infect both Enterococcus faecalis and Enterococcus faecium. Several of the Myoviridae phages that we found in southern California wastewater were from the Brockvirinae subfamily (formerly Spounavirinae) and had a broad host range across both E. faecium and E. faecalis. By searching the NCBI Sequence Read Archive, we showed that these phages are prevalent globally in human and animal microbiomes. Enterococcus is a regular member of healthy human gut microbial communities; however, it is also an opportunistic pathogen responsible for an increasing number of antibiotic-resistant infections. We tested the ability of each phage to clear Enterococcus host cultures and delay the emergence of phage-resistant Enterococcus. We found that some phages were ineffective at clearing Enterococcus cultures individually but were effective when combined into cocktails. Quantitative PCR was used to track phage abundance in cocultures and revealed dynamics ranging from one dominant phage to an even distribution of phage growth. Genomic characterization showed that mutations in Enterococcus exopolysaccharide synthesis genes were consistently found in the presence of phage infection. This work will help to inform cocktail design for Enterococcus, which is an important target for phage therapy applications.

IMPORTANCE Due to the rise in antibiotic resistance, Enterococcus infections are a major health crisis that requires the development of alternative therapies. Phage therapy offers an alternative to antibiotics and has shown promise in both in vitro and early clinical studies. Here, we established a collection of 19 Enterococcus phages and tested whether combining phages into cocktails could delay growth and the emergence of resistant mutants in comparison with individual phages. We showed that cocktails of two or three phages often prevented the growth of phage-resistant mutants, and we identified which phages were replicating the most in each cocktail. When resistant mutants emerged to single phages, they showed consistent accumulation of mutations in exopolysaccharide synthesis genes. These data serve to demonstrate that a cocktail approach can inform efforts to improve efficacy against Enterococcus isolates and reduce the emergence of resistance.

Acquisition of Daptomycin Resistance by Enterococcus faecium Confers Collateral Sensitivity to Glycopeptides

Daptomycin is a last-line antibiotic used in the treatment of multidrug-resistant Enterococcus faecium infections. Alarmingly, daptomycin-resistant E. faecium isolates have emerged. In this study, we investigated the evolution and mechanisms of daptomycin resistance in clinical E. faecium isolates and the corresponding acquisition of collateral sensitivity (CS) as an evolutionary trade-off. We evolved daptomycin resistance in six daptomycin-susceptible E. faecium isolates to obtain daptomycin-resistant mutants. The six E. faecium strains successfully acquired high-level resistance to daptomycin in vitro, but this led to fitness costs in terms of growth, in vitro competition, and virulence. Mutations in liaFSR, yycFG, and cls; increased surface positive charge; thicker cell walls; and elevated expression of dltABCD and tagGH were observed in daptomycin-resistant mutants. Surprisingly, we observed the emergence of CS in SC1762 isolates after the induction of daptomycin resistance. Compared with parental strains, the SC1174-D strain (i.e., daptomycin-resistant mutant of SC1174; non-CS) showed significantly upregulated expression of the vanA gene cluster. However, in SC1762-D (i.e., daptomycin-resistant mutant of SC1762), all vanA cluster genes except the vanX gene were obviously downregulated. Further in silico analyses revealed that an IS1216E-based composite transposon was generated in SC1762-D, and it disrupted the vanH gene, likely affecting the structure and expression of the vanA gene cluster and resulting in resensitization to glycopeptides. Overall, this study reports a novel form of CS between daptomycin and glycopeptides in E. faecium. Further, it provides a valuable foundation for developing effective regimens and sequential combinations of daptomycin and glycopeptides against E. faecium.

A Phage Foundry Framework to Systematically Develop Viral Countermeasures to Combat Antibiotic-Resistant Bacterial Pathogens

At its current rate, the rise of antimicrobial-resistant (AMR) infections is predicted to paralyze our industries and healthcare facilities while becoming the leading global cause of loss of human life. With limited new antibiotics on the horizon, we need to invest in alternative solutions. Bacteriophages (phages)-viruses targeting bacteria-offer a powerful alternative approach to tackle bacterial infections. Despite recent advances in using phages to treat recalcitrant AMR infections, the field lacks systematic development of phage therapies scalable to different applications. We propose a Phage Foundry framework to establish metrics for phage characterization and to fill the knowledge and technological gaps in phage therapeutics. Coordinated investment in AMR surveillance, sampling, characterization, and data sharing procedures will enable rational exploitation of phages for treatments. A fully realized Phage Foundry will enhance the sharing of knowledge, technology, and viral reagents in an equitable manner and will accelerate the biobased economy.

Genetically distant bacteriophages select for unique genomic changes in Enterococcus faecalis

The human microbiota harbors diverse bacterial and bacteriophage (phage) communities. Bacteria evolve to overcome phage infection, thereby driving phage evolution to counter bacterial resistance. Understanding how phages select for genetic alterations in medically relevant bacteria is important as phages become established biologics for the treatment of multidrug-resistant (MDR) bacterial infections. Before phages can be widely used as standalone or combination antibacterial therapies, we must obtain a deep understanding of the molecular mechanisms of phage infection and how host bacteria alter their genomes to become resistant. We performed coevolution experiments using a single Enterococcus faecalis strain and two distantly related phages to determine how phage pressure impacts the evolution of the E. faecalis genome. Whole-genome sequencing of E. faecalis following continuous exposure to these two phages revealed mutations previously demonstrated to be essential for phage infection. We also identified mutations in genes previously unreported to be associated with phage infection in E. faecalis. Intriguingly, there was only one shared mutation in the E. faecalis genome that was selected by both phages tested, demonstrating that infection by two genetically distinct phages selects for diverse variants. This knowledge serves as the basis for the continued study of E. faecalis genome evolution during phage infection and can be used to inform the design of future therapeutics, such as phage cocktails, intended to target MDR E. faecalis.

Identification and Characterization of vB_PreP_EPr2, a Lytic Bacteriophage of Pan-Drug Resistant Providencia rettgeri

Providencia rettgeri is an emerging opportunistic Gram-negative pathogen with reports of increasing antibiotic resistance. Pan-drug resistant (PDR) P. rettgeri infections are a growing concern, demonstrating a need for the development of alternative treatment options which is fueling a renewed interest in bacteriophage (phage) therapy. Here, we identify and characterize phage vB_PreP_EPr2 (EPr2) with lytic activity against PDR P. rettgeri MRSN 845308, a clinical isolate that carries multiple antibiotic resistance genes. EPr2 was isolated from an environmental water sample and belongs to the family Autographiviridae, subfamily Studiervirinae and genus Kayfunavirus, with a genome size of 41,261 base pairs. Additional phenotypic characterization showed an optimal MOI of 1 and a burst size of 12.3 ± 3.4 PFU per bacterium. EPr2 was determined to have a narrow host range against a panel of clinical P. rettgeri strains. Despite this fact, EPr2 is a promising lytic phage with potential for use as an alternative therapeutic for treatment of PDR P. rettgeri infections.

Evaluation of Bacteriophage-Antibiotic Combination Therapy for Biofilm-Embedded MDR Enterococcus faecium

Multidrug-resistant (MDR) Enterococcus faecium is a challenging pathogen known to cause biofilm-mediated infections with limited effective therapeutic options. Lytic bacteriophages target, infect, and lyse specific bacterial cells and have anti-biofilm activity, making them a possible treatment option. Here, we examine two biofilm-producing clinical E. faecium strains, daptomycin (DAP)-resistant R497 and DAP-susceptible dose-dependent (SDD) HOU503, with initial susceptibility to E. faecium bacteriophage 113 (ATCC 19950-B1). An initial synergy screening was performed with modified checkerboard MIC assays developed by our laboratory to efficiently screen for antibiotic and phage synergy, including at very low phage multiplicity of infection (MOI). The data were compared by one-way ANOVA and Tukey (HSD) tests. In 24 h time kill analyses (TKA), combinations with phage-DAP-ampicillin (AMP), phage-DAP-ceftaroline (CPT), and phage-DAP-ertapenem (ERT) were synergistic and bactericidal compared to any single agent (ANOVA range of mean differences 3.34 to 3.84 log10 CFU/mL; p < 0.001). Furthermore, phage-DAP-AMP and phage-DAP-CPT prevented the emergence of DAP and phage resistance. With HOU503, the combination of phage-DAP-AMP showed the best killing effect, followed closely by phage-DAP-CPT; both showed bactericidal and synergistic effects compared to any single agent (ANOVA range of mean differences 3.99 to 4.08 log10 CFU/mL; p < 0.001).

Bacteriophage Therapy for Critical and High-Priority Antibiotic-Resistant Bacteria and Phage Cocktail-Antibiotic Formulation Perspective

Phage therapy is revolving to address the issues mainly dealing with antibiotic resistance in the pathogenic bacteria. Among the drug-resistant microbial populations, the bacterial species have been categorized as high-priority or critical-priority bacteria. This review summarizes the efficiency and development in phage therapy used against these drug-resistant bacteria in the past few years mainly belonging to the critical- and high-priority list. Phage therapy is more than just an alternative to antibiotics as it not only kills the target microbial population directly but also leads to the chemical and physical modifications in bacterial cell structures. These phage-mediated modifications in the bacterial cell may make them antibiotic sensitive. Application of phage therapy in antibiotic-resistant foodborne bacteria and possible modulation in gut microbes has also been explored. Further, the phage cocktail antibiotic formulation, containing more than one type of phage with antibiotics, has also been discussed.

Evaluation of Bacteriophage Cocktails Alone and in Combination with Daptomycin Against Daptomycin-Nonsusceptible Enterococcus faecium

Enterococcus faecium(E. fcm) is a significant multidrug-resistant pathogen. Bacteriophage cocktails are being proposed to complement antibiotic therapy. After a screen of 8 E. fcm strains against 4 phages, two phages(113, 9184) with the broadest host ranges were chosen for further experiments. Transmission electron microscopy, whole-genome sequencing, comparative genome analyses, and time-kill analyses were performed. Daptomycin(DAP) plus phage cocktail(113:myophage;9184:siphopage) showed bactericidal activity in most regimens, while DAP addition prevented phage 9184 resistance against daptomycin non-susceptible E. fcm.

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.

The Age of Phage: Friend or Foe in the New Dawn of Therapeutic and Biocontrol Applications?

Extended overuse and misuse of antibiotics and other antibacterial agents has resulted in an antimicrobial resistance crisis. Bacteriophages, viruses that infect bacteria, have emerged as a legitimate alternative antibacterial agent with a wide scope of applications which continue to be discovered and refined. However, the potential of some bacteriophages to aid in the acquisition, maintenance, and dissemination of negatively associated bacterial genes, including resistance and virulence genes, through transduction is of concern and requires deeper understanding in order to be properly addressed. In particular, their ability to interact with mobile genetic elements such as plasmids, genomic islands, and integrative conjugative elements (ICEs) enables bacteriophages to contribute greatly to bacterial evolution. Nonetheless, bacteriophages have the potential to be used as therapeutic and biocontrol agents within medical, agricultural, and food processing settings, against bacteria in both planktonic and biofilm environments. Additionally, bacteriophages have been deployed in developing rapid, sensitive, and specific biosensors for various bacterial targets. Intriguingly, their bioengineering capabilities show great promise in improving their adaptability and effectiveness as biocontrol and detection tools. This review aims to provide a balanced perspective on bacteriophages by outlining advantages, challenges, and future steps needed in order to boost their therapeutic and biocontrol potential, while also providing insight on their potential role in contributing to bacterial evolution and survival.