Bacteriophage therapy: a possible alternative therapy against antibiotic-resistant strains of Klebsiella pneumoniae

Klebsiella pneumoniae is a notorious, Gram-negative pathogen and is a leading cause of healthcare settings and community-acquired infections. This is the commensal of human microbiota and can invade and cause infections in different body parts. The global emergence of antibiotic resistance in K. pneumoniae has become a major challenge in the whole medical community. Alternative paths to treat the infections caused by these MDR pathogens are needed as these bacteria become resistant to last-resort antibiotics like colistin. The lytic bacteriophages (phages) are the bacteria's natural predators and can rapidly eliminate the bacterial cells. Phages are abundant in nature and have recently been found to be effective tools in modern biotechnology. They can be used to control the bacterial infectious diseases. They can be manipulated easily and potentially used in therapeutics, biotechnology, and research. Several studies, both in vitro and in vivo, have demonstrated the possible applications of the lytic phages in treating K. pneumoniae superbug strains. Phage endolysins have drawn the scientific world's attention because of their involvement in phage adsorption and bacterial capsules digestion. These phage-encoded enzymes digest the polysaccharide components of bacterial cell walls by recognizing and binding them. Phage lysins, being strong biological agents, are capable of effectively and swiftly eliminating bacteria. This review summarizes the information on phages of K. pneumoniae and phage-based therapies to target their bacterial hosts.

Phage-antibiotic combinations against Klebsiella pneumoniae: impact of methodological approaches on effect evaluation

Background

The combined use of bacteriophages and antibiotics represents a promising strategy for combating multidrug-resistant bacterial pathogens. However, the lack of uniformity in methods for assessing combination effects and experimental protocols has resulted in inconsistent findings across studies. This study aimed to evaluate the effects of interactions between phages and antibiotics on Klebsiella pneumoniae strains using various statistical approaches to formalize combination effects.

Methods

Effects were assessed for four antibiotics from distinct classes (gentamicin, levofloxacin, meropenem, chloramphenicol), three phages from different genera (Dlv622, Seu621, FRZ284), and a depolymerase (Dep622) on three K. pneumoniae strains of the KL23 capsule type. Antibiotics were used at Cmax concentrations, and phages at sublethal levels. A modified t-test, Bliss independence model, two-way ANOVA, and checkerboard assay were employed to evaluate the results.

Results

Among 48 combinations, 33 effects were statistically significant, including 26 cases of synergy and 7 of antagonism. All statistical methods showed consistency in identifying effects; however, the t-test and Bliss method detected a greater number of effects. The strongest synergy was observed with levofloxacin in combination with Seu621 or Dep622 across all bacterial strains. Checkerboard assays confirmed synergy in selected cases but indicated that combined effects could vary with antimicrobial concentrations.

Conclusion

The choice of analytical method substantially impacts the detection of phage-antibiotic effects. The t-test and Bliss method, due to their simplicity and sensitivity, may be optimal for clinical application, while two-way ANOVA for confirming strong interactions. These results emphasize the need to consider interaction characteristics when designing therapeutic strategies.

Klebsiella pneumoniae Phage M198 and Its Therapeutic Potential

The rapid worldwide spread of antibiotic resistance is quickly becoming an increasingly concerning problem for human healthcare. Non-antibiotic antibacterial agents are in high demand for many Gram-negative bacterial pathogens, including Klebsiella pneumoniae. Klebsiella-targeting phages are among the most promising alternative therapy options. They have already been successfully applied in a number of cases, and it is expected that the need for anti-Klebsiella phages will only increase in the future. This prospect highlights the need for well-characterized therapeutic phages. In this work, we describe a K. pneumoniae phage, which also infects strains of Klebsiella oxytoca. Here, we characterize phage M198 in terms of its biological and genetic properties. Since in some phage therapy cases, phages are administered in combination with antibiotics, here, we also screen for possible synergistic effects of combining phage M198 with six different antibiotics. We found that phage M198 has good lytic activity against clinical isolates; it does not have any indications of a temperate lifestyle, and it has synergistic potential when combined with some therapeutically relevant antibiotics.

Use of adjuvants to improve antibiotic efficacy and reduce the burden of antimicrobial resistance

INTRODUCTION

The increase in antibiotic resistance, together with the absence of novel antibiotics, makes mandatory the introduction of novel strategies to optimize the use of existing antibiotics. Among these strategies, the use of molecules that increase their activity looks promising.

AREAS COVERED

Different categories of adjuvants have been reviewed. Anti-resistance adjuvants increase the activity of antibiotics by inhibiting antibiotic resistance determinants. Anti-virulence approaches focus on the infection process itself; reducing virulence in combination with an antibiotic can improve therapeutic efficacy. Combination of phages with antibiotics can also be useful, since they present different mechanisms of action and targets. Finally, combining antibiotics with adjuvants in the same molecule may serve to improve antibiotics' efficacy and to overcome potential problems of differential pharmacokinetics/pharmacodynamics.

EXPERT OPINION

The successful combination of inhibitors of β-lactamases with β-lactams has shown that adjuvants can improve the efficacy of current antibiotics. In this sense, novel anti-resistance adjuvants able to inhibit efflux pumps are still needed, as well as anti-virulence compounds that improve the efficacy of antibiotics by interfering with the infection process. Although adjuvants may present different pharmacodynamics/pharmacokinetics than antibiotics, conjugates containing both compounds can solve this problem. Finally, already approved drugs can be a promising source of antibiotic adjuvants.

Disruption of the Enterococcus faecalis-Induced Biofilm on the Intraocular Lens Using Bacteriophages

Purpose

To compare the effects of bacteriophages (phages) and vancomycin on Enterococcus faecalis-induced biofilms on the intraocular lens.

Methods

E. faecalis strains EF24, GU02, GU03, and phiEF14H1 were used. The expression of the enterococcus surface protein (esp) gene was analyzed using polymerase chain reaction. Phages or vancomycin was added to the biofilms formed on culture plates or acrylic intraocular lenses. The biofilms were quantified after staining with crystal violet. The structure of the biofilms was analyzed using scanning electron microscopy.

Results

E. faecalis strains EF24, GU02, and GU03 formed biofilms on cell culture plates; however, the esp-negative GU03 strain had a significantly lower biofilm-forming ability than the esp-positive strains EF24 and GU02. The addition of phiEF14H1 resulted in a significant reduction in biofilm mass produced by both EF24 and GU02 compared with the untreated control. However, the addition of vancomycin did not degrade the biofilms. Phages significantly degraded biofilms and reduced the viable EF24 and GU02 bacteria on the intraocular lens.

Conclusions

Phages can degrade biofilms formed on the intraocular lens and destroy the bacteria within it. Thus, phage therapy may be a new treatment option for refractory and recurrent endophthalmitis caused by biofilm-forming bacteria.

Translational Relevance

Phage therapy, a novel treatment option for refractory and recurrent endophthalmitis caused by biofilm-forming bacteria, effectively lyses E. faecalis-induced biofilms.

The potential use of bacteriophages as antibacterial agents against Klebsiella pneumoniae

One of the most common bacteria that cause nosocomial infections is Klebsiella pneumonia (K. pneumoniae), especially in patients who are very sick and admitted to the intensive care unit (ICU). The frequency of multi-drug-resistant Klebsiella pneumoniae (MDRKP) has dramatically increased worldwide in recent decades, posing an urgent threat to public health. The Western world's bacteriophage (phage) studies have been revitalized due to the increasing reports of antimicrobial resistance and the restricted development and discovery of new antibiotics. These factors have also spurred innovation in other scientific domains. The primary agent in phage treatment is an obligately lytic organism (called bacteriophage) that kills the corresponding bacterial host while sparing human cells and lessening the broader effects of antibiotic usage on commensal bacteria. Phage treatment is developing quickly, leading to many clinical studies and instances of life-saving medicinal use. In addition, phage treatment has a few immunological adverse effects and consequences in addition to its usefulness. Since K. pneumoniae antibiotic resistance has made treating multidrug-resistant (MDR) infections challenging, phage therapy (PT) has emerged as a novel therapeutic strategy. The effectiveness of phages has also been investigated in K. pneumoniae biofilms and animal infection models. Compared with antibiotics, PT exhibits numerous advantages, including a particular lysis spectrum, co-evolution with bacteria to avoid the emergence of phage resistance, and a higher abundance and diversity of phage resources than found in antibiotics. Moreover, phages are eliminated in the absence of a host bacterium, which makes them the only therapeutic agent that self-regulates at the sites of infection. Therefore, it is essential to pay attention to the role of PT in treating these infections. This study summarizes the state of knowledge on Klebsiella spp. phages and provides an outlook on the development of phage-based treatments that target K. pneumoniae in clinical trials.

Quenching and quorum sensing in bacterial bio-films

Quorum sensing (QS) is the ability of bacteria to monitor their population density and adjust gene expression accordingly. QS-regulated processes include host-microbe interactions, horizontal gene transfer, and multicellular behaviours (such as the growth and development of biofilm). The creation, transfer, and perception of bacterial chemicals known as autoinducers or QS signals are necessary for QS signalling (e.g. N-acylhomoserine lactones). Quorum quenching (QQ), another name for the disruption of QS signalling, comprises a wide range of events and mechanisms that are described and analysed in this study. In order to better comprehend the targets of the QQ phenomena that organisms have naturally developed and are currently being actively researched from practical perspectives, we first surveyed the diversity of QS-signals and QS-associated responses. Next, the mechanisms, molecular players, and targets related to QS interference are discussed, with a focus on natural QQ enzymes and compounds that function as QS inhibitors. To illustrate the processes and biological functions of QS inhibition in microbe-microbe and host-microbe interactions, a few QQ paradigms are described in detail. Finally, certain QQ techniques are offered as potential instruments in a variety of industries, including agriculture, medical, aquaculture, crop production, and anti-biofouling areas.

Plant-Origin Components: New Players to Combat Antibiotic Resistance in Klebsiella pneumoniae

Klebsiella pneumoniae (Kpn) is an opportunistic pathogen that causes intrahospital complications such as pneumonia, liver abscesses, soft tissue infections, urinary infections, bacteraemia, and, in some cases, death. Since this bacterium has a higher frequency than other Gram-negative pathogens, it has become an important pathogen to the health sector. The adaptative genome of Kpn likely facilitates increased survival of the pathogen in diverse situations. Therefore, several studies have been focused on developing new molecules, synergistic formulations, and biomaterials that make it possible to combat and control infections with and dispersion of this pathogen. Note that the uncontrolled antibiotic administration that occurred during the pandemic led to the emergence of new multidrug-resistant strains, and scientists were challenged to overcome them. This review aims to compile the latest information on Kpn that generates intrahospital infections, specifically their pathogenicity-associated factors. Furthermore, it explains the natural-product-based treatments (extracts and essential oils) developed for Kpn infection and dispersion control.

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.

Use of Bacteriophages to Target Intracellular Pathogens

Bacteriophages (phages) have shown great potential as natural antimicrobials against extracellular pathogens (eg, Escherichia coli or Klebsiella pneumoniae), but little is known about how they interact with intracellular targets (eg, Shigella spp., Salmonella spp., Mycobacterium spp.) in the mammalian host. Recent research has demonstrated that phages can enter human cells. However, for the design of successful clinical applications, further investigation is required to define their subcellular behavior and to understand the complex biological processes that underlie the interaction with their bacterial targets. In this review, we summarize the molecular evidence of phage internalization in eucaryotic cells, with specific focus on proof of phage activity against their bacterial targets within the eucaryotic host, and the current proposed strategies to overcome poor penetrance issues that may impact therapeutic use against the most clinically relevant intracellular pathogens.

Study of Combined Effect of Bacteriophage vB3530 and Chlorhexidine on the Inactivation of Pseudomonas aeruginosa

BACKGROUND

Chlorhexidine (CHG) is a disinfectant commonly used in hospitals. However, it has been reported that the excessive use of CHG can cause resistance in bacteria to this agent and even to other clinical antibiotics. Therefore, new methods are needed to alleviate the development of CHG tolerance and reduce its dosage. This study aimed to explore the synergistic effects of CHG in combination with bacteriophage against CHG-tolerant Pseudomonas aeruginosa (P. aeruginosa) and provide ideas for optimizing disinfection strategies in clinical environments as well as for the efficient use of disinfectants.

METHODS

The CHG-tolerant P. aeruginosa strains were isolated from the First Affiliated Hospital of Wenzhou Medical University in China. The bacteriophage vB3530 was isolated from the sewage inlet of the hospital, and its genome was sequenced. Time-killing curve was used to determine the antibacterial effects of vB3530 and chlorohexidine gluconate (CHG). The phage sensitivity to 16 CHG-tolerant P. aeruginosa strains and PAO1 strain was detected using plaque assay. The emergence rate of resistant bacterial strains was detected to determine the development of phage-resistant and CHG-tolerant strains. Finally, the disinfection effects of the disinfectant and phage combination on the surface of the medical devices were preliminarily evaluated.

RESULTS

The results showed that (1) CHG combined with bacteriophage vB3530 significantly inhibited the growth of CHG-resistant P. aeruginosa and reduced the bacterial colony forming units (CFUs) after 24 h. (2) The combination of CHG and bacteriophage inhibited the emergence of phage-resistant and CHG-tolerant strains. (3) The combination of CHG and bacteriophage significantly reduced the bacterial load on the surface of medical devices.

CONCLUSIONS

In this study, the combination of bacteriophage vB3530 and CHG presented a combined inactivation effect to CHG-tolerant P. aeruginosa and reduced the emergence of strains resistant to CHG and phage. This study demonstrated the potential of bacteriophage as adjuvants to traditional disinfectants. The use of bacteriophage in combination with commercial disinfectants might be a promising method for controlling the spread of bacteria in hospitals.

A systematic review of the use of bacteriophages for in vitro biofilm control

Bacteriophages (phages) are very promising biological agents for the prevention and control of bacterial biofilms. However, little is known about the parameters that can influence the efficacy of phages on biofilms. This systematic review provides a summary and analysis of the published data about the use of phages to control pre-formed biofilms in vitro, suggesting recommendations for future experiments in this area. A total of 68 articles, containing data on 605 experiments addressing the efficacy of phages to control biofilms in vitro were included, after a search conducted in Web of Science, Embase, and Medline (PubMed). The data collected from each experiment included information about biofilm growth conditions, phage characteristics, treatment conditions and biofilm reduction. In most cases, biofilms were formed in the surface of microtiter plates (82.5%); the median time for biofilm formation was 24 h, as is the median treatment duration. Quantification of biofilm biomass (52.6%), viable cells (25.5%) and metabolic activity (17.9%) were the most common biofilm assessment methods. Correlation analysis revealed that some phage parameters can influence the treatment outcome: higher phage concentrations were strongly associated with improved biofilm control, leading to higher levels of biofilm reduction, and phages with higher burst sizes and shorter latent periods seem to be the best candidates to control biofilms in vitro. However, the great variability of the methodologies used prompts the need for the development of standardized in vitro methodologies to characterize phage/biofilm interactions and to assess the efficacy of phages to control biofilms.

Bacteriophages: The promising therapeutic approach for enhancing ciprofloxacin efficacy against bacterial infection

BACKGROUND

The emergence of ciprofloxacin-resistant bacteria is a serious challenge worldwide, bringing the need to find new approaches to manage this bacterium. Bacteriophages (phages) have been shown inhibitory effects against ciprofloxacin-resistance bacteria; thus, ciprofloxacin resistance or tolerance may not affect the phage's infection ability. Additionally, researchers used phage-ciprofloxacin combination therapy for the inhibition of multidrug-resistant bacteria.

RESULTS

The sublethal concentrations of ciprofloxacin could lead to an increase in progeny production. Antibiotic treatments could enhance the release of progeny phages by shortening the lytic cycle and latent period. Thus, sublethal concentrations of antibiotics combined with phages can be used for the management of bacterial infections with high antibiotic resistance. In addition, combination therapy exerts various selection pressures that can mutually decrease phage and antibiotic resistance. Moreover, phage ciprofloxacin could significantly reduce bacterial counts in the biofilm community. Immediate usage of phages after the attachment of bacteria to the surface of the flow cells, before the development of micro-colonies, could lead to the best effect of phage therapy against bacterial biofilm. Noteworthy, phage should be used before antibiotics usage because this condition may have allowed phage replication to occur first before ciprofloxacin interrupted the bacterial DNA replication process, thereby interfering with the activity of the phages. Furthermore, the phage-ciprofloxacin combination showed a promising result for the management of Pseudomonas aeruginosa infections in mouse models. Nevertheless, low data are existing about the interaction between phages and ciprofloxacin in combination therapies, especially regarding the emergence of phage-resistant mutants. Additionally, there is a challenging and important question of how the combined ciprofloxacin with phages can increase antibacterial functions. Therefore, more examinations are required to support the clinical usage of phage-ciprofloxacin combination therapy.

What’s old is new again: Insights into diabetic foot microbiome

Diabetes is a chronic disease that is considered one of the most stubborn global health problems that continues to defy the efforts of scientists and physicians. The prevalence of diabetes in the global population continues to grow to alarming levels year after year, causing an increase in the incidence of diabetes complications and health care costs all over the world. One major complication of diabetes is the high susceptibility to infections especially in the lower limbs due to the immunocompromised state of diabetic patients, which is considered a definitive factor in all cases. Diabetic foot infections continue to be one of the most common infections in diabetic patients that are associated with a high risk of serious complications such as bone infection, limb amputations, and life-threatening systemic infections. In this review, we discussed the circumstances associated with the high risk of infection in diabetic patients as well as some of the most commonly isolated pathogens from diabetic foot infections and the related virulence behavior. In addition, we shed light on the different treatment strategies that aim at eradicating the infection.

Isolation, Characterization, Genome Analysis and Host Resistance Development of Two Novel Lastavirus Phages Active against Pandrug-Resistant Klebsiella pneumoniae

Klebsiella pneumoniae is a global health threat and bacteriophages are a potential solution in combating pandrug-resistant K. pneumoniae infections. Two lytic phages, LASTA and SJM3, active against several pandrug-resistant, nosocomial strains of K. pneumoniae were isolated and characterized. Their host range is narrow and latent period is particularly long; however, their lysogenic nature was refuted using both bioinformatic and experimental approaches. Genome sequence analysis clustered them with only two other phages into the new genus Lastavirus. Genomes of LASTA and SJM3 differ in only 13 base pairs, mainly located in tail fiber genes. Individual phages, as well as their cocktail, demonstrated significant bacterial reduction capacity in a time-dependent manner, yielding up to 4 log reduction against planktonic, and up to 2.59 log on biofilm-embedded, cells. Bacteria emerging from the contact with the phages developed resistance and achieved numbers comparable to the growth control after 24 h. The resistance to the phage seems to be of a transient nature and varies significantly between the two phages, as resistance to LASTA remained constant while resensitization to SJM3 was more prominent. Albeit with very few differences, SJM3 performed better than LASTA overall; however, more investigation is needed in order to consider them for therapeutic application.

Biofilm Lifestyle in Recurrent Urinary Tract Infections

Urinary tract infections (UTIs) represent one of the most common infections that are frequently encountered in health care facilities. One of the main mechanisms used by bacteria that allows them to survive hostile environments is biofilm formation. Biofilms are closed bacterial communities that offer protection and safe hiding, allowing bacteria to evade host defenses and hide from the reach of antibiotics. Inside biofilm communities, bacteria show an increased rate of horizontal gene transfer and exchange of resistance and virulence genes. Additionally, bacterial communication within the biofilm allows them to orchestrate the expression of virulence genes, which further cements the infestation and increases the invasiveness of the infection. These facts stress the necessity of continuously updating our information and understanding of the etiology, pathogenesis, and eradication methods of this growing public health concern. This review seeks to understand the role of biofilm formation in recurrent urinary tact infections by outlining the mechanisms underlying biofilm formation in different uropathogens, in addition to shedding light on some biofilm eradication strategies.

Biological foundations of successful bacteriophage therapy

Bacteriophages (phages) are selective viral predators of bacteria. Abundant and ubiquitous in nature, phages can be used to treat bacterial infections (phage therapy), including refractory infections and those resistant to antibiotics. However, despite an abundance of anecdotal evidence of efficacy, significant hurdles remain before routine implementation of phage therapy into medical practice, including a dearth of robust clinical trial data. Phage-bacterium interactions are complex and diverse, characterized by co-evolution trajectories that are significantly influenced by the environments in which they occur (mammalian body sites, water, soil, etc.). An understanding of the molecular mechanisms underpinning these dynamics is essential for successful clinical translation. This review aims to cover key aspects of bacterium-phage interactions that affect bacterial killing by describing the most relevant published literature and detailing the current knowledge gaps most likely to influence therapeutic success.

Development of Phage Cocktails to Treat E. coli Catheter-Associated Urinary Tract Infection and Associated Biofilms

High rates of antimicrobial resistance and formation of biofilms makes treatment of Escherichia coli catheter-associated urinary tract infections (CAUTI) particularly challenging. CAUTI affect 1 million patients per year in the United States and are associated with morbidity and mortality, particularly as an etiology for sepsis. Phage have been proposed as a potential therapeutic option. Here, we report the development of phage cocktails that lyse contemporary E. coli strains isolated from the urine of patients with spinal cord injury (SCI) and display strong biofilm-forming properties. We characterized E. coli phage against biofilms in two in vitro CAUTI models. Biofilm viability was measured by an MTT assay that determines cell metabolic activity and by quantification of colony forming units. Nine phage decreased cell viability by >80% when added individually to biofilms of two E. coli strains in human urine. A phage cocktail comprising six phage lyses 82% of the strains in our E. coli library and is highly effective against young and old biofilms and against biofilms on silicon catheter materials. Using antibiotics together with our phage cocktail prevented or decreased emergence of E. coli resistant to phage in human urine. We created an anti-biofilm phage cocktail with broad host range against E. coli strains isolated from urine. These phage cocktails may have therapeutic potential against CAUTI.

Bacteriophages and antibiotic interactions in clinical practice: what we have learned so far

Bacteriophages (phages) may be used as an alternative to antibiotic therapy for combating infections caused by multidrug-resistant bacteria. In the last decades, there have been studies concerning the use of phages and antibiotics separately or in combination both in animal models as well as in humans. The phenomenon of phage–antibiotic synergy, in which antibiotics may induce the production of phages by bacterial hosts has been observed. The potential mechanisms of phage and antibiotic synergy was presented in this paper. Studies of a biofilm model showed that a combination of phages with antibiotics may increase removal of bacteria and sequential treatment, consisting of phage administration followed by an antibiotic, was most effective in eliminating biofilms. In vivo studies predominantly show the phenomenon of phage and antibiotic synergy. A few studies also describe antagonism or indifference between phages and antibiotics. Recent papers regarding the application of phages and antibiotics in patients with severe bacterial infections show the effectiveness of simultaneous treatment with both antimicrobials on the clinical outcome.

Deinococcus radiodurans Exopolysaccharide Inhibits Staphylococcus aureus Biofilm Formation

Deinococcus radiodurans is an extremely resistant bacterium against extracellular stress owing to on its unique physiological functions and the structure of its cellular constituents. Interestingly, it has been reported that the pattern of alteration in Deinococcus proportion on the skin is negatively correlated with skin inflammatory diseases, whereas the proportion of Staphylococcus aureus was increased in patients with chronic skin inflammatory diseases. However, the biological mechanisms of deinococcal interactions with other skin commensal bacteria have not been studied. In this study, we hypothesized that deinococcal cellular constituents play a pivotal role in preventing S. aureus colonization by inhibiting biofilm formation. To prove this, we first isolated cellular constituents, such as exopolysaccharide (DeinoPol), cell wall (DeinoWall), and cell membrane (DeinoMem), from D. radiodurans and investigated their inhibitory effects on S. aureus colonization and biofilm formation in vitro and in vivo. Among them, only DeinoPol exhibited an anti-biofilm effect without affecting bacterial growth and inhibiting staphylococcal colonization and inflammation in a mouse skin infection model. Moreover, the inhibitory effect was impaired in the Δdra0033 strain, a mutant that cannot produce DeinoPol. Remarkably, DeinoPol not only interfered with S. aureus biofilm formation at early and late stages but also disrupted a preexisting biofilm by inhibiting the production of poly-N-acetylglucosamine (PNAG), a key molecule required for S. aureus biofilm formation. Taken together, the present study suggests that DeinoPol is a key molecule in the negative regulation of S. aureus biofilm formation by D. radiodurans. Therefore, DeinoPol could be applied to prevent and/or treat infections or inflammatory diseases associated with S. aureus biofilms.

Friends or Foes? Rapid Determination of Dissimilar Colistin and Ciprofloxacin Antagonism of Pseudomonas aeruginosa Phages

Phage therapy is a century-old technique employing viruses (phages) to treat bacterial infections, and in the clinic it is often used in combination with antibiotics. Antibiotics, however, interfere with critical bacterial metabolic activities that can be required by phages. Explicit testing of antibiotic antagonism of phage infection activities, though, is not a common feature of phage therapy studies. Here we use optical density-based 'lysis-profile' assays to assess the impact of two antibiotics, colistin and ciprofloxacin, on the bactericidal, bacteriolytic, and new-virion-production activities of three Pseudomonas aeruginosa phages. Though phages and antibiotics in combination are more potent in killing P. aeruginosa than either acting alone, colistin nevertheless substantially interferes with phage bacteriolytic and virion-production activities even at its minimum inhibitory concentration (1× MIC). Ciprofloxacin, by contrast, has little anti-phage impact at 1× or 3× MIC. We corroborate these results with more traditional measures, particularly colony-forming units, plaque-forming units, and one-step growth experiments. Our results suggest that ciprofloxacin could be useful as a concurrent phage therapy co-treatment especially when phage replication is required for treatment success. Lysis-profile assays also appear to be useful, fast, and high-throughput means of assessing antibiotic antagonism of phage infection activities.

Isolation, Genomic Analysis, and Preliminary Application of a Bovine Klebsiella pneumoniae Bacteriophage vB_Kpn_B01

Klebsiella pneumoniae is an important pathogen that can infect both humans and cattle. The widespread K. pneumoniae and its high drug resistance make it difficult to treat Klebsiella infections/diseases. In this study, a lytic K. pneumoniae bacteriophage vB_Kpn_B01 was isolated from a dairy farm trough in Sichuan Province, and its biological properties were studied, and the entire genome of vB_Kpn_B01 was sequenced. The therapeutic effects of the phage on disease-causing mice were preliminarily tested. Phages found in this study are double-stranded DNA bacterial viruses belonging to the family Siphoviridae, Sugarlandvirus. The results suggest that vB_Kpn_B01 has strong specificity and low adaptability to different adverse conditions. Meanwhile, the predicted gene products of phage vB_Kpn_B01 comprised 149 coding sequences (CDS) and 25 tRNAs, of which 34 CDS had known functions. Of course, vB_Kpn_B01 did not contain any known antibiotic-resistant or virulent genes. The pathological sections of the liver and lungs of mice showed that the inflammatory scores of the treatment group were lower than in the bacterial group. Phage vB_Kpn_B01 alleviated the inflammatory response in the organs of the infected mice, and the organ tissue bacterial load of the treatment group was significantly lower than that of the bacterial group. Therefore, vB_Kpn_B01 can inhibit the proliferation of K. pneumoniae 18 in vivo and can alleviate the inflammation of target organs caused by infectious bacteria, which preliminarily indicates that vB_Kpn_B01 has a certain therapeutic effect on laboratory-infected mice.

A combination therapy of Phages and Antibiotics: Two is better than one

Emergence of antibiotic resistance presents a major setback to global health, and shortage of antibiotic pipelines has created an urgent need for development of alternative therapeutic strategies. Bacteriophage (phage) therapy is considered as a potential approach for treatment of the increasing number of antibiotic-resistant pathogens. Phage-antibiotic synergy (PAS) refers to sublethal concentrations of certain antibiotics that enhance release of progeny phages from bacterial cells. A combination of phages and antibiotics is a promising strategy to reduce the dose of antibiotics and the development of antibiotic resistance during treatment. In this review, we highlight the state-of-the-art advancements of PAS studies, including the analysis of bacterial-killing enhancement, bacterial resistance reduction, and anti-biofilm effect, at both in vitro and in vivo levels. A comprehensive review of the genetic and molecular mechanisms of phage antibiotic synergy is provided, and synthetic biology approaches used to engineer phages, and design novel therapies and diagnostic tools are discussed. In addition, the role of engineered phages in reducing pathogenicity of bacteria is explored.

Functional hydrogels for diabetic wound management

Diabetic wounds often have a slow healing process and become easily infected owing to hyperglycemia in wound beds. Once planktonic bacterial cells develop into biofilms, the diabetic wound becomes more resistant to treatment. Although it remains challenging to accelerate healing in a diabetic wound due to complex pathology, including bacterial infection, high reactive oxygen species, chronic inflammation, and impaired angiogenesis, the development of multifunctional hydrogels is a promising strategy. Multiple functions, including antibacterial, pro-angiogenesis, and overall pro-healing, are high priorities. Here, design strategies, mechanisms of action, performance, and application of functional hydrogels are systematically discussed. The unique properties of hydrogels, including bactericidal and wound healing promotive effects, are reviewed. Considering the clinical need, stimuli-responsive and multifunctional hydrogels that can accelerate diabetic wound healing are likely to form an important part of future diabetic wound management.

Interplay between the cell envelope and mobile genetic elements shapes gene flow in populations of the nosocomial pathogen Klebsiella pneumoniae

Mobile genetic elements (MGEs) drive genetic transfers between bacteria using mechanisms that require a physical interaction with the cellular envelope. In the high-priority multidrug-resistant nosocomial pathogens (ESKAPE), the first point of contact between the cell and virions or conjugative pili is the capsule. While the capsule can be a barrier to MGEs, it also evolves rapidly by horizontal gene transfer (HGT). Here, we aim at understanding this apparent contradiction by studying the covariation between the repertoire of capsule genes and MGEs in approximately 4,000 genomes of Klebsiella pneumoniae (Kpn). We show that capsules drive phage-mediated gene flow between closely related serotypes. Such serotype-specific phage predation also explains the frequent inactivation of capsule genes, observed in more than 3% of the genomes. Inactivation is strongly epistatic, recapitulating the capsule biosynthetic pathway. We show that conjugative plasmids are acquired at higher rates in natural isolates lacking a functional capsular locus and confirmed experimentally this result in capsule mutants. This suggests that capsule inactivation by phage pressure facilitates its subsequent reacquisition by conjugation. Accordingly, capsule reacquisition leaves long recombination tracts around the capsular locus. The loss and regain process rewires gene flow toward other lineages whenever it leads to serotype swaps. Such changes happen preferentially between chemically related serotypes, hinting that the fitness of serotype-swapped strains depends on the host genetic background. These results enlighten the bases of trade-offs between the evolution of virulence and multidrug resistance and caution that some alternatives to antibiotics by selecting for capsule inactivation may facilitate the acquisition of antibiotic resistance genes (ARGs).

A study of how the complex interaction between capsules and mobile genetic elements shapes gene flow in populations of Klebsiella pneumoniae reveals that capsule inactivation by phage pressure facilitates its subsequent re-acquisition by conjugation, and this loss and re-gain process influences the gene flow towards other lineages whenever it leads to serotype changes.

Understanding the Complex Phage-Host Interactions in Biofilm Communities

Bacteriophages and bacterial biofilms are widely present in natural environments, a fact that has accelerated the evolution of phages and their bacterial hosts in these particular niches. Phage-host interactions in biofilm communities are rather complex, where phages are not always merely predators but also can establish symbiotic relationships that induce and strengthen biofilms. In this review we provide an overview of the main features affecting phage-biofilm interactions as well as the currently available methods of studying these interactions. In addition, we address the applications of phages for biofilm control in different contexts.

Improving Phage-Biofilm In Vitro Experimentation

Bacteriophages or phages, the viruses of bacteria, are abundant components of most ecosystems, including those where bacteria predominantly occupy biofilm niches. Understanding the phage impact on bacterial biofilms therefore can be crucial toward understanding both phage and bacterial ecology. Here, we take a critical look at the study of bacteriophage interactions with bacterial biofilms as carried out in vitro, since these studies serve as bases of our ecological and therapeutic understanding of phage impacts on biofilms. We suggest that phage-biofilm in vitro experiments often may be improved in terms of both design and interpretation. Specific issues discussed include (a) not distinguishing control of new biofilm growth from removal of existing biofilm, (b) inadequate descriptions of phage titers, (c) artificially small overlying fluid volumes, (d) limited explorations of treatment dosing and duration, (e) only end-point rather than kinetic analyses, (f) importance of distinguishing phage enzymatic from phage bacteriolytic anti-biofilm activities, (g) limitations of biofilm biomass determinations, (h) free-phage interference with viable-count determinations, and (i) importance of experimental conditions. Toward bettering understanding of the ecology of bacteriophage-biofilm interactions, and of phage-mediated biofilm disruption, we discuss here these various issues as well as provide tips toward improving experiments and their reporting.

Efficacy of Phage-Antibiotic Combinations Against Multidrug-Resistant Klebsiella pneumoniae Clinical Isolates

Background: Increasing antibiotic resistance warrants therapeutic alternatives to eradicate resistant bacteria. Combined phage-antibiotic therapy is a promising approach for eliminating bacterial infections and limiting the evolution of therapy-resistant diseases. Objectives: In the present study, we evaluated the effects of combinations of bacteriophages and antibiotics against multidrug-resistant (MDR) Klebsiella pneumoniae. Methods: Two MDR strains (GenBank no. MF953600 & MF953599) of K. pneumoniae were used. Bacteriophages were isolated from hospital sewage samples by employing a double agar overlay assay and identified by transmission electron microscopy. For further characterization of bacteriophages, the killing assay and host range test were performed. To assess therapeutic efficacy, phages (7.5 × 104 PFU/mL) were used in combination with various antibiotics. Results: The phage-cefepime and tetracycline combinations displayed promising therapeutic effects, restricting the growth of K. pneumoniae isolates, as evidenced by recording OD650nm values. Conclusions: The results of the current study showed that phage-antibiotic combination was a potential therapeutic approach to treat the infections caused by MDR K. pneumoniae.

Efficacy of Phage-Antibiotic Combinations Against Multidrug-Resistant Klebsiella pneumoniae Clinical Isolates

Background: Increasing antibiotic resistance warrants therapeutic alternatives to eradicate resistant bacteria. Combined phage-antibiotic therapy is a promising approach for eliminating bacterial infections and limiting the evolution of therapy-resistant diseases. Objectives: In the present study, we evaluated the effects of combinations of bacteriophages and antibiotics against multidrug-resistant (MDR) Klebsiella pneumoniae. Methods: Two MDR strains (GenBank no. MF953600 & MF953599) of K. pneumoniae were used. Bacteriophages were isolated from hospital sewage samples by employing a double agar overlay assay and identified by transmission electron microscopy. For further characterization of bacteriophages, the killing assay and host range test were performed. To assess therapeutic efficacy, phages (7.5 × 104 PFU/mL) were used in combination with various antibiotics. Results: The phage-cefepime and tetracycline combinations displayed promising therapeutic effects, restricting the growth of K. pneumoniae isolates, as evidenced by recording OD650nm values. Conclusions: The results of the current study showed that phage-antibiotic combination was a potential therapeutic approach to treat the infections caused by MDR K. pneumoniae.

Bacteriophage-Derived Depolymerases against Bacterial Biofilm

In addition to specific antibiotic resistance, the formation of bacterial biofilm causes another level of complications in attempts to eradicate pathogenic or harmful bacteria, including difficult penetration of drugs through biofilm structures to bacterial cells, impairment of immunological response of the host, and accumulation of various bioactive compounds (enzymes and others) affecting host physiology and changing local pH values, which further influence various biological functions. In this review article, we provide an overview on the formation of bacterial biofilm and its properties, and then we focus on the possible use of phage-derived depolymerases to combat bacterial cells included in this complex structure. On the basis of the literature review, we conclude that, although these bacteriophage-encoded enzymes may be effective in destroying specific compounds involved in the formation of biofilm, they are rarely sufficient to eradicate all bacterial cells. Nevertheless, a combined therapy, employing depolymerases together with antibiotics and/or other antibacterial agents or factors, may provide an effective approach to treat infections caused by bacteria able to form biofilms.

Amikacin and bacteriophage treatment modulates outer membrane proteins composition in Proteus mirabilis biofilm

Modification of outer membrane proteins (OMPs) is the first line of Gram-negative bacteria defence against antimicrobials. Here we point to Proteus mirabilis OMPs and their role in antibiotic and phage resistance. Protein profiles of amikacin (AMKrsv), phage (Brsv) and amikacin/phage (AMK/Brsv) resistant variants of P. mirabilis were compared to that obtained for a wild strain. In resistant variants there were identified 14, 1, 5 overexpressed and 13, 5, 1 downregulated proteins for AMKrsv, Brsv and AMK/Brsv, respectively. Application of phages with amikacin led to reducing the number of up- and downregulated proteins compared to single antibiotic treatment. Proteins isolated in AMKrsv are involved in protein biosynthesis, transcription and signal transduction, which correspond to well-known mechanisms of bacteria resistance to aminoglycosides. In isolated OMPs several cytoplasmic proteins, important in antibiotic resistance, were identified, probably as a result of environmental stress, e.g. elongation factor Tu, asparaginyl-tRNA and aspartyl-tRNA synthetases. In Brsv there were identified: NusA and dynamin superfamily protein which could play a role in bacteriophage resistance. In the resistant variants proteins associated with resistance mechanisms occurring in biofilm, e.g. polyphosphate kinase, flagella basal body rod protein were detected. These results indicate proteins important in the development of P. mirabilis antibiofilm therapies.

Aztreonam Lysine Increases the Activity of Phages E79 and phiKZ against Pseudomonas aeruginosa PA01

Pseudomonas aeruginosa is a pernicious bacterial pathogen that is difficult to treat because of high levels of antibiotic resistance. A promising alternative treatment option for such bacteria is the application of bacteriophages; the correct combination of phages plus antibiotics can produce synergistic inhibitory effects. In this study, we describe morphological changes induced by sub-MIC levels of the antibiotic aztreonam lysine (AzLys) on P. aeruginosa PA01, which may in part explain the observed phage–antibiotic synergy (PAS). One-step growth curves for phage E79 showed increased adsorption rates, decreased infection latency, accelerated time to lysis and a minor reduction in burst size. Phage E79 plus AzLys PAS was also able to significantly reduce P. aeruginosa biofilm growth over 3-fold as compared to phage treatment alone. Sub-inhibitory AzLys-induced filamentation of P. aeruginosa cells resulted in loss of twitching motility and a reduction in swimming motility, likely due to a reduction in the number of polar Type IV pili and flagella, respectively, on the filamented cell surfaces. Phage phiKZ, which uses Type IV pili as a receptor, did not exhibit increased activity with AzLys at lower sub-inhibitory levels, but still produced phage–antibiotic synergistic killing with sub-inhibitory AzLys. A one-step growth curve indicates that phiKZ in the presence of AzLys also exhibits a decreased infection latency and moderately undergoes accelerated time to lysis. In contrast to prior PAS studies demonstrating that phages undergo delayed time to lysis with cell filamentation, these PAS results show that phages undergo accelerated time to lysis, which therefore suggests that PAS is dependent upon multiple factors, including the type of phages and antibiotics used, and the bacterial host being tested.

Phage Therapy

Phage therapy refers to the use of bacteriophages (phages - bacterial viruses) as therapeutic agents against infectious bacterial diseases. This therapeutic approach emerged in the beginning of the 20th century but was progressively replaced by the use of antibiotics in most parts of the world after the second world war. More recently however, the alarming rise of multidrug-resistant bacteria and the consequent need for antibiotic alternatives has renewed interest in phages as antimicrobial agents. Several scientific, technological and regulatory advances have supported the credibility of a second revolution in phage therapy. Nevertheless, phage therapy still faces many challenges that include: i) the need to increase phage collections from reference phage banks; ii) the development of efficient phage screening methods for the fast identification of the therapeutic phage(s); iii) the establishment of efficient phage therapy strategies to tackle infectious biofilms; iv) the validation of feasible phage production protocols that assure quality and safety of phage preparations; and (v) the guarantee of stability of phage preparations during manufacturing, storage and transport. Moreover, current maladapted regulatory structures represent a significant hurdle for potential commercialization of phage therapeutics. This article describes the past and current status of phage therapy and presents the most recent advances in this domain.

Advantages and limitations of microtiter biofilm assays in the model of antibiofilm activity of Klebsiella phage KP34 and its depolymerase

One of the potential antibiofilm strategies is to use lytic phages and phage-derived polysaccharide depolymerases. The idea is to uncover bacteria embedded in the biofilm matrix making them accessible and vulnerable to antibacterials and the immune system. Here we present the antibiofilm efficiency of lytic phage KP34 equipped with virion-associated capsule degrading enzyme (depolymerase) and its recombinant depolymerase KP34p57, depolymerase-non-bearing phage KP15, and ciprofloxacin, separately and in combination, using a multidrug-resistant K. pneumoniae biofilm model. The most effective antibiofilm agents were (1) phage KP34 alone or in combination with ciprofloxacin/phage KP15, and (2) depolymerase KP34p57 with phage KP15 and ciprofloxacin. Secondly, applying the commonly used biofilm microtiter assays: (1) colony count, (2) LIVE/DEAD BacLight Bacterial Viability Kit, and (3) crystal violet (CV) biofilm staining, we unravelled the main advantages and limitations of the above methods in antibiofilm testing. The diverse mode of action of selected antimicrobials strongly influenced obtained results, including a false positive enlargement of biofilm mass (CV staining) while applying polysaccharide degrading agents. We suggest that to get a proper picture of antimicrobials' effectiveness, multiple examination methods should be used and the results must be read considering the principle of each technique and the antibacterial mechanism.

Bacteriophage Infections of Biofilms of Health Care-Associated Pathogens: Klebsiella pneumoniae

Members of the family Enterobacteriaceae, such as Klebsiella pneumoniae, are considered both serious and urgent public health threats. Biofilms formed by these health care-associated pathogens can lead to negative and costly health outcomes. The global spread of antibiotic resistance, coupled with increased tolerance to antimicrobial treatments in biofilm-associated bacteria, highlights the need for novel strategies to overcome treatment hurdles. Bacteriophages (phages), or viruses that infect bacteria, have reemerged as one such potential strategy. Virulent phages are capable of infecting and killing their bacterial hosts, in some cases producing depolymerases that are able to hydrolyze biofilms. Phage therapy does have its limitations, however, including potential narrow host ranges, development of bacterial resistance to infection, and the potential spread of phage-encoded virulence genes. That being said, advances in phage isolation, screening, and genome sequencing tools provide an upside in overcoming some of these limitations and open up the possibilities of using phages as effective biofilm control agents.

Characterization of extended-spectrum-β-lactamase producing Klebsiella pneumoniae phage KP1801 and evaluation of therapeutic efficacy in vitro and in vivo

Extended spectrum β lactamase-producing Klebsiella pneumoniae (ESBL-KP) is being reported with high morbidity and mortality rates and is considered as the highest priority for new antimicrobial strategies. To develop an alternative antimicrobial agent, phage KP1801 with broad lytic activity was isolated. The genome of phage KP1801 was double stranded DNA of 49,835 base pairs, with a GC content of 50.26%. There were 75 putative open reading frames. Phage KP1801 was classified as being in the order Caudovirales, belonging to the Siphoviridae family. About 323 proteins were detected by shotgun proteome analysis. The phage inhibited biofilm formation and reduced pre-formed biofilm in a dose dependent manner. Scanning electron microscopic studies demonstrated a membrane damage of bacterial cells treated with phage, resulting in cell death. Prophylactic and therapeutic efficacies of the phage were evaluated in Galleria mellonella. Administration of ESBL-KP infection with phage significantly improved the survival of G. mellonella. The number of intracellular bacteria in larvae showed a significant decrease compared with untreated control while the number of phage increased. These studies suggested that phage KP1801 has the potential for development as an alternative for antibiotics and biocontrol agents against ESBL-KP infection.

Phage Therapy as a Novel Strategy in the Treatment of Urinary Tract Infections Caused by E. Coli

Urinary tract infections (UTIs) are regarded as one of the most common bacterial infections affecting millions of people, in all age groups, annually in the world. The major causative agent of complicated and uncomplicated UTIs are uropathogenic E. coli strains (UPECs). Huge problems with infections of this type are their chronicity and periodic recurrences. Other disadvantages that are associated with UTIs are accompanying complications and high costs of health care, systematically increasing resistance of uropathogens to routinely used antibiotics, as well as biofilm formation by them. This creates the need to develop new approaches for the prevention and treatment of UTIs, among which phage therapy has a dominant potential to eliminate uropathogens within urinary tract. Due to the growing interest in such therapy in the last decade, the bacteriophages (natural, genetically modified, engineered, or combined with antibiotics or disinfectants) represent an innovative antimicrobial alternative and a strategy for managing the resistance of uropathogenic microorganisms and controlling UTIs.

Bacteriophages of Klebsiella spp., their diversity and potential therapeutic uses

Klebsiella spp. are commensals of the human microbiota, and a leading cause of opportunistic nosocomial infections. The incidence of multidrug resistant (MDR) strains of Klebsiella pneumoniae causing serious infections is increasing, and Klebsiella oxytoca is an emerging pathogen. Alternative strategies to tackle infections caused by these bacteria are required as strains become resistant to last-resort antibiotics such as colistin. Bacteriophages (phages) are viruses that can infect and kill bacteria. They and their gene products are now being considered as alternatives or adjuncts to antimicrobial therapies. Several in vitro and in vivo studies have shown the potential for lytic phages to combat MDR K. pneumoniae infections. Ready access to cheap sequencing technologies has led to a large increase in the number of genomes available for Klebsiella-infecting phages, with these phages being heterogeneous at the whole-genome level. This review summarizes our current knowledge on phages of Klebsiella spp. and highlights technological and biological issues relevant to the development of phage-based therapies targeting these bacteria.

Bacteriophage Therapeutics: A Primer for Clinicians on Phage-Antibiotic Combinations

Multidrug-resistant organisms have caused a marked depletion of effective antimicrobials, and the narrow pipeline of antibiotics has demanded the need to find novel therapeutic alternatives including nonantibiotic agents. Bacteriophages (phages) are viruses that use the bacterial machinery to infect, replicate, and kill bacterial cells. Although a marked decline in their use was driven by the discovery of antibiotics, the era of antibiotic resistance has led to a resurgence of phage therapy into clinical practice. The term phage-antibiotic synergy (PAS) was coined just over a decade ago and described that sublethal concentrations of antibiotics could stimulate phage production by bacterial cells. Recent literature has described PAS and other encouraging interactions with various phage and antibiotic combinations against a variety of bacterial strains. The primary objective of this review is to discuss the positive interactions between phage and antibiotic combinations, with an emphasis on PAS, reductions in bacterial growth or minimum inhibitory concentrations, enhanced biofilm eradication, and alterations in the emergence of bacterial resistance. A peer-reviewed literature search was conducted (1890-2019) using the PubMed, Medline, and Google Scholar databases. Although more investigation is certainly needed, the combination of bacteriophages with antibiotics is a promising strategy to target organisms with limited or no therapeutic options. This approach may also foster the ability to lower the antibiotic dose and may reduce the potential for antibiotic resistance emergence during therapy.

How Phages Overcome the Challenges of Drug Resistant Bacteria in Clinical Infections

Nowadays the most important problem in the treatment of bacterial infections is the appearance of MDR (multidrug-resistant), XDR (extensively drug-resistant) and PDR (pan drug-resistant) bacteria and the scarce prospects of producing new antibiotics. There is renewed interest in revisiting the use of bacteriophage to treat bacterial infections. The practice of phage therapy, the application of phages to treat bacterial infections, has been around for approximately a century. Phage therapy relies on using lytic bacteriophages and purified phage lytic proteins for treatment and lysis of bacteria at the site of infection. Current research indicates that phage therapy has the potential to be used as an alternative to antibiotic treatments. It is noteworthy that, whether phages are used on their own or combined with antibiotics, phages are still a promising agent to replace antibiotics. So, this review focuses on an understanding of challenges of MDR, XDR, and PDR bacteria and phages mechanism for treating bacterial infections and the most recent studies on potential phages, cocktails of phages, and enzymes of lytic phages in fighting these resistant bacteria.

Phage-Antibiotic Combination Treatments: Antagonistic Impacts of Antibiotics on the Pharmacodynamics of Phage Therapy?

Bacteria can evolve resistance to antibiotics. Even without changing genetically, bacteria also can display tolerance to antibiotic treatments. Many antibiotics are also broadly acting, as can result in excessive modifications of body microbiomes. Particularly for antibiotics of last resort or in treating extremely ill patients, antibiotics furthermore can display excessive toxicities. Antibiotics nevertheless remain the standard of care for bacterial infections, and rightly so given their long track records of both antibacterial efficacy and infrequency of severe side effects. Antibiotics do not successfully cure all treated bacterial infections, however, thereby providing a utility to alternative antibacterial approaches. One such approach is the use of bacteriophages, the viruses of bacteria. This nearly 100-year-old bactericidal, anti-infection technology can be effective against antibiotic-resistant or -tolerant bacteria, including bacterial biofilms and persister cells. Ideally phages could be used in combination with standard antibiotics while retaining their anti-bacterial pharmacodynamic activity, this despite antibiotics interfering with aspects of bacterial metabolism that are also required for full phage infection activity. Here I examine the literature of pre-clinical phage-antibiotic combination treatments, with emphasis on antibiotic-susceptible bacterial targets. I review evidence of antibiotic interference with phage infection activity along with its converse: phage antibacterial functioning despite antibiotic presence.

Genetic Engineering of Bacteriophages Against Infectious Diseases

Bacteriophages (phages) are the most abundant and widely distributed organisms on Earth, constituting a virtually unlimited resource to explore the development of biomedical therapies. The therapeutic use of phages to treat bacterial infections (“phage therapy”) was conceived by Felix d’Herelle nearly a century ago. However, its power has been realized only recently, largely due to the emergence of multi-antibiotic resistant bacterial pathogens. Progress in technologies, such as high-throughput sequencing, genome editing, and synthetic biology, further opened doors to explore this vast treasure trove. Here, we review some of the emerging themes on the use of phages against infectious diseases. In addition to phage therapy, phages have also been developed as vaccine platforms to deliver antigens as part of virus-like nanoparticles that can stimulate immune responses and prevent pathogen infections. Phage engineering promises to generate phage variants with unique properties for prophylactic and therapeutic applications. These approaches have created momentum to accelerate basic as well as translational phage research and potential development of therapeutics in the near future.

Fighting Pathogenic Bacteria on Two Fronts: Phages and Antibiotics as Combined Strategy

With the emerging threat of infections caused by multidrug resistant bacteria, phages have been reconsidered as an alternative for treating infections caused by tenacious pathogens. However, instead of replacing antibiotics, the combination of both types of antimicrobials can be superior over the use of single agents. Enhanced bacterial suppression, more efficient penetration into biofilms, and lowered chances for the emergence of phage resistance are the likely advantages of the combined strategy. While a number of studies have provided experimental evidence in support of this concept, negative interference between phages and antibiotics have been reported as well. Neutral effects have also been observed, but in those cases, combined approaches may still be important for at least hampering the development of resistance. In any case, the choice of phage type and antibiotic as well as their mixing ratios must be given careful consideration when deciding for a dual antibacterial approach. The most frequently tested bacterium for a combined antibacterial treatment has been Pseudomonas aeruginosa, but encouraging results have also been reported for Escherichia coli, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Enterococcus faecalis, and Burkholderia cepacia. Given the immense play area of conceivable phage-antibiotic combinations and their potential excess value, it is time to recapitulate of what has been achieved so far. This review therefore gathers and compares the results from most relevant studies in order to help researchers and clinicians in their strategies to combat multidrug resistant bacteria. Special attention is given to the selected bacterial model organisms, the phage families and genera employed, and the experimental design and evaluation (e.g., in vitro vs. in vivo models, biofilm vs. planktonic culture experiments, order and frequency of administration etc.). The presented data may serve as a framework for directed further experimental approaches to ultimately achieve a resolute challenge of multidrug resistant bacteria based on traditional antibiotics and phages.

Propionibacterium (Cutibacterium) acnes Bacteriophage Therapy in Acne: Current Evidence and Future Perspectives

Acne vulgaris is the most common dermatological disorder worldwide. It is a multifactorial disease that involves increased sebum production, hyperkeratinization of the pilosebaceous unit, Propionibacterium acnes (Cutibacterium acnes) colonization, and inflammation. The human skin microbiome hosts a wide variety of microorganisms, including bacteria, viruses, and fungi. A delicate balance of these microorganisms is essential for the barrier function of the skin. Propionibacterium acnes represents nearly 90% of the human skin microbiome of healthy adults. Acne is a chronic recurrent disease that requires long-lasting treatment, which has led to the emergence of antibiotic resistance. New alternatives to traditional therapy are emerging, including antimicrobial peptides, natural engineered antibodies, and bacteriophages. Bacteriophages have been shown to play a role in human skin health and disease. There is evidence supporting phage therapy in many types of skin infections. P. acnes bacteriophages have been isolated and characterized. However, only a few in vitro studies have tested the ability of bacteriophages to kill P. acnes. Furthermore, there is no evidence on bacteriophage therapy in the treatment of acne in humans. In this review, we summarize the most recent evidence regarding P. acnes bacteriophages and the potential role of these bacteriophages in the treatment of acne. Further research on this field will provide the evidence to use phage therapy to decrease rates of antibiotic resistance and restore antibiotic susceptibility of P. acnes.

Sequential Combined Effect of Phages and Antibiotics on the Inactivation of Escherichia coli

The emergence of antibiotic resistance in bacteria is a global concern. The use of bacteriophages (or phages) alone or combined with antibiotics is consolidating itself as an alternative approach to inactivate antibiotic-resistant bacteria. However, phage-resistant mutants have been considered as a major threat when phage treatment is employed. Escherichia coli is one of the main responsible pathogens for moderate and serious infections in hospital and community environments, being involved in the rapid evolution of fluoroquinolones and third-generation cephalosporin resistance. The aim of this study was to evaluate the effect of combined treatments of phages and antibiotics in the inactivation of E. coli. For this, ciprofloxacin at lethal and sublethal concentrations was added at different times (0, 6, 12 and 18 h) and was tested in combination with the phage ELY-1 to inactivate E. coli. The efficacy of the combined treatment varied with the antibiotic concentration and with the time of antibiotic addition. The combined treatment prevented bacterial regrowth when the antibiotic was used at minimum inhibitory concentration (MIC) and added after 6 h of phage addition, causing less bacterial resistance than phage and antibiotic applied alone (4.0 × 10-7 for the combined treatment, 3.9 × 10-6 and 3.4 × 10-5 for the antibiotics and the phages alone, respectively). Combined treatment with phage and antibiotic can be effective in reducing the bacterial density and it can also prevent the emergence of resistant variants. However, the antibiotic concentration and the time of antibiotic application are essential factors that need to be considered in the combined treatment.

Rapid evolution of generalized resistance mechanisms can constrain the efficacy of phage-antibiotic treatments

Antimicrobial resistance has been estimated to be responsible for over 700,000 deaths per year; therefore, new antimicrobial therapies are urgently needed. One way to increase the efficiency of antibiotics is to use them in combination with bacteria-specific parasitic viruses, phages, which have been shown to exert additive or synergistic effects in controlling bacteria. However, it is still unclear to what extent these combinatory effects are limited by rapid evolution of resistance, especially when the pathogen grows as biofilm on surfaces typical for many persistent and chronic infections. To study this, we used a microcosm system, where genetically isogenic populations of Pseudomonas aeruginosa PAO1 bacterial pathogen were exposed to a phage 14/1, gentamycin or a combination of them both in a spatially structured environment. We found that even though antibiotic and phage-antibiotic treatments were equally effective at controlling bacteria in the beginning of the experiment, combination treatment rapidly lost its efficacy in both planktonic and biofilm populations. In a mechanistic manner, this was due to rapid resistance evolution: While both antibiotic and phage selected for increased resistance on their own, phage selection correlated positively with increase in antibiotic resistance, while biofilm growth, which provided generalized resistance mechanism, was favoured most in the combination treatment. Only relatively small cost of resistance and weak evidence for coevolutionary dynamics were observed. Together, these results suggest that spatial heterogeneity can promote rapid evolution of generalized resistance mechanisms without corresponding increase in phage infectivity, which could potentially limit the effectiveness of phage-antibiotic treatments in the evolutionary timescale.

Enhanced antibacterial effect of the novel T4-like bacteriophage KARL-1 in combination with antibiotics against multi-drug resistant Acinetobacter baumannii

The continuing rise of infections caused by multi-drug resistant bacteria has led to a renewed interest in bacteriophage therapy. Here we characterize phage vB_AbaM-KARL-1 with lytic activity against multi-drug resistant clinical isolates of Acinetobacter baumannii (AB). Besides genomic and phenotypic phage analysis, the objective of our study was to investigate the antibacterial outcome when the phage acts in concert with distinct antibiotics. KARL-1 belongs to the family of Myoviridae and is able to lyse 8 of 20 (40%) tested clinical isolates. Its double-stranded DNA genome consists of 166,560 bp encoding for 253 open reading frames. Genome wide comparison suggests that KARL-1 is a novel species within the subfamily Tevenvirinae, sharing 77% nucleotide identity (coverage 58%) with phage ZZ1. The antibacterial efficacy at various multiplicities of infection (MOI) was monitored either alone or in combination with meropenem, ciprofloxacin, and colistin. A complete clearance of liquid cultures was achieved with KARL-1 at an MOI of 10^-1 and meropenem (>128 mg/l). KARL-1 was still effective at an MOI of 10^-7, but antibacterial activity was significantly augmented with meropenem. While ciprofloxacin did generally not support phage activity, the application of KARL-1 at an MOI of 10^-7 and therapeutic doses of colistin significantly elevated bacterial suppression. Hence, KARL-1 represents a novel candidate for use against multi-drug resistant AB and the therapeutic outcome may be positively influenced by the addition of traditional antibiotics.

Phage therapy for respiratory infections

A respiratory infection caused by antibiotic-resistant bacteria can be life-threatening. In recent years, there has been tremendous effort put towards therapeutic application of bacteriophages (phages) as an alternative or supplementary treatment option over conventional antibiotics. Phages are natural parasitic viruses of bacteria that can kill the bacterial host, including antibiotic-resistant bacteria. Inhaled phage therapy involves the development of stable phage formulations suitable for inhalation delivery followed by preclinical and clinical studies for assessment of efficacy, pharmacokinetics and safety. We presented an overview of recent advances in phage formulation for inhalation delivery and their efficacy in acute and chronic rodent respiratory infection models. We have reviewed and presented on the prospects of inhaled phage therapy as a complementary treatment option with current antibiotics and as a preventative means. Inhaled phage therapy has the potential to transform the prevention and treatment of bacterial respiratory infections, including those caused by antibiotic-resistant bacteria.

Resistance Development to Bacteriophages Occurring during Bacteriophage Therapy

Bacteriophage (phage) therapy, i.e., the use of viruses that infect bacteria as antimicrobial agents, is a promising alternative to conventional antibiotics. Indeed, resistance to antibiotics has become a major public health problem after decades of extensive usage. However, one of the main questions regarding phage therapy is the possible rapid emergence of phage-resistant bacterial variants, which could impede favourable treatment outcomes. Experimental data has shown that phage-resistant variants occurred in up to 80% of studies targeting the intestinal milieu and 50% of studies using sepsis models. Phage-resistant variants have also been observed in human studies, as described in three out of four clinical trials that recorded the emergence of phage resistance. On the other hand, recent animal studies suggest that bacterial mutations that confer phage-resistance may result in fitness costs in the resistant bacterium, which, in turn, could benefit the host. Thus, phage resistance should not be underestimated and efforts should be made to develop methodologies for monitoring and preventing it. Moreover, understanding and taking advantage of the resistance-induced fitness costs in bacterial pathogens is a potentially promising avenue.