Differential Effect of Newly Isolated Phages Belonging to PB1-Like, phiKZ-Like and LUZ24-Like Viruses against Multi-Drug Resistant Pseudomonas aeruginosa under Varying Growth Conditions

In vitro and in vivo evaluation of the biofilm-degrading Pseudomonas phage Motto, as a candidate for phage therapy

Infections caused by Pseudomonas aeruginosa are becoming increasingly difficult to treat due to the emergence of strains that have acquired multidrug resistance. Therefore, phage therapy has gained attention as an alternative to the treatment of pseudomonal infections. Phages are not only bactericidal but occasionally show activity against biofilm as well. In this study, we describe the Pseudomonas phage Motto, a T1-like phage that can clear P. aeruginosa infections in an animal model and also exhibits biofilm-degrading properties. The phage has a substantial anti-biofilm activity against strong biofilm-producing isolates (n = 10), with at least a twofold reduction within 24 h. To demonstrate the safety of using phage Motto, cytotoxicity studies were conducted with human cell lines (HEK 293 and RAW 264.7 macrophages). Using a previously established in vivo model, we demonstrated the efficacy of Motto in Caenorhabditis elegans, with a 90% survival rate when treated with the phage at a multiplicity of infection of 10.

Efficacy and clinical potential of phage therapy in treating methicillin-resistant Staphylococcus aureus (MRSA) infections: A review

Staphylococcus aureus infections have already presented a substantial public health challenge, encompassing different clinical manifestations, ranging from bacteremia to sepsis and multi-organ failures. Among these infections, methicillin-resistant S. aureus (MRSA) is particularly alarming due to its well-documented resistance to multiple classes of antibiotics, contributing significantly to global mortality rates. Consequently, the urgent need for effective treatment options has prompted a growing interest in exploring phage therapy as a potential non-antibiotic treatment against MRSA infections. Phages represent a class of highly specific bacterial viruses known for their ability to infect certain bacterial strains. This review paper explores the clinical potential of phages as a treatment for MRSA infections due to their low toxicity and auto-dosing capabilities. The paper also discusses the synergistic effect of phage-antibiotic combination (PAC) and the promising results from in vitro and animal model studies, which could lead to extensive human clinical trials. However, clinicians need to establish and adhere to standard protocols governing phage administration and implementation. Prominent clinical trials are needed to develop and advance phage therapy as a non-antibiotic therapy intervention, meeting regulatory guidelines, logistical requirements, and ethical considerations, potentially revolutionizing the treatment of MRSA infections.

Jumbo phages are active against extensively drug-resistant eyedrop-associated Pseudomonas aeruginosa infections

Antibiotic-resistant bacteria present an emerging challenge to human health. Their prevalence has been increasing across the globe due in part to the liberal use of antibiotics that has pressured them to develop resistance. Those bacteria that acquire mobile genetic elements are especially concerning because those plasmids may be shared readily with other microbes that can then also become antibiotic resistant. Serious infections have recently been related to the contamination of preservative-free eyedrops with extensively drug-resistant (XDR) isolates of Pseudomonas aeruginosa, already resulting in three deaths. These drug-resistant isolates cannot be managed with most conventional antibiotics. We sought to identify alternatives to conventional antibiotics for the lysis of these XDR isolates and identified multiple bacteriophages (viruses that attack bacteria) that killed them efficiently. We found both jumbo phages (>200 kb in genome size) and non-jumbo phages that were active against these isolates, the former killing more efficiently. Jumbo phages effectively killed the three separate XDR P. aeruginosa isolates both on solid and liquid medium. Given the ongoing nature of the XDR P. aeruginosa eyedrop outbreak, the identification of phages active against them provides physicians with several novel potential alternatives for treatment.

Comparison of Antibiofilm Activity of Pseudomonas aeruginosa Phages on Isolates from Wounds of Diabetic and Non-Diabetic Patients

The persistence of organisms as biofilms and the increase in antimicrobial resistance has raised the need for alternative strategies. The study objective was to compare the ability of isolated bacteriophages to remove in vitro biofilms formed by Pseudomonas aeruginosa isolated from the environment with those isolated from diabetic and non-diabetic wounds. P. aeruginosa were isolated from clinical and environmental sites, and antimicrobial susceptibility was tested. Bacteriophages were isolated and characterized based on plaque morphology and host range. A reduction in the viable count assayed the lytic ability of candidate phages. The crystal violet method was used to determine the residual biofilm after 24 h of phage treatment on 72-h-old biofilms. The statistical significance of phage treatment was tested by one-way ANOVA. Of 35 clinical isolates, 17 showed resistance to 1 antibiotic at least, and 7 were multidrug resistant. Nineteen environmental isolates and 11 clinical isolates were drug-sensitive. Nine phages showed 91.2% host coverage, including multidrug-resistant isolates. Phages eradicated 85% of biofilms formed by environmental isolates compared to 58% of biofilms of diabetic isolates and 56% of biofilms of non-diabetic isolates. Clinical isolates are susceptible to phage infection in planktonic form. Biofilms of P. aeruginosa isolated from diabetic wounds and non-diabetic wounds resist removal by phages compared to biofilms formed by environmental isolates. All phages were efficient in dispersing PAO1 biofilms. However, there was a significant difference in their ability to disperse PAO1 biofilms across the different surfaces tested. Partial eradication of biofilm by phages can aid in complementing antibiotics that are unable to penetrate biofilms in a clinical set-up.

Engineered Superinfective Pf Phage Prevents Dissemination of Pseudomonas aeruginosa in a Mouse Burn Model

Pf is a filamentous bacteriophage integrated in the chromosome of most clinical isolates of Pseudomonas aeruginosa. Under stress conditions, mutations occurring in the Pf genome result in the emergence of superinfective variants of Pf (SI-Pf) that are capable of circumventing phage immunity; therefore, SI-Pf can even infect Pf-lysogenized P. aeruginosa. Here, we identified specific mutations located between the repressor and the excisionase genes of Pf4 phage in the P. aeruginosa PAO1 strain that resulted in the emergence of SI-Pf. Based on these findings, we genetically engineered an SI-Pf (eSI-Pf) and tested it as a phage therapy tool for the treatment of life-threatening burn wound infections caused by PAO1. In validation experiments, eSI-Pf was able to infect PAO1 grown in a lawn as well as biofilms formed in vitro on polystyrene. eSI-Pf also infected PAO1 present in burned skin wounds on mice but was not capable of maintaining a sustained reduction in bacterial burden beyond 24 h. Despite not lowering bacterial burden in burned skin tissue, eSI-Pf treatment completely abolished the capability of P. aeruginosa to disseminate from the burn site to internal organs. Over the course of 10 days, this resulted in bacterial clearance and survival of all treated mice. We subsequently determined that eSI-Pf induced a small-colony variant of P. aeruginosa that was unable to disseminate systemically. This attenuated phenotype was due to profound changes in virulence determinant production and altered physiology. Our results suggest that eSI-Pf has potential as a phage therapy against highly recalcitrant antimicrobial-resistant P. aeruginosa infections of burn wounds. IMPORTANCE Pseudomonas aeruginosa is a major cause of burn-related infections. It is also the most likely bacterial infection to advance to sepsis and result in burn-linked death. Frequently, P. aeruginosa strains isolated from burn patients display a multidrug-resistant phenotype necessitating the development of new therapeutic strategies and prophylactic treatments. In this context, phage therapy using lytic phages has demonstrated exciting potential in the control P. aeruginosa infection. However, lytic phages can present a set of drawbacks during phage therapy, including the induction of bacterial resistance and limited bacteria-phage interactions in vivo. Here, we propose an alternative approach to interfere with P. aeruginosa pathogenesis in a burn infection model, i.e., by using an engineered superinfective filamentous phage. Our study demonstrates that treatment with the engineered Pf phage can prevent sepsis and death in a burn mouse model.

Identifying the core genome of the nucleus-forming bacteriophage family and characterization of Erwinia phage RAY

We recently discovered that some bacteriophages establish a nucleus-like replication compartment (phage nucleus), but the core genes that define nucleus-based phage replication and their phylogenetic distribution were still to be determined. Here, we show that phages encoding the major phage nucleus protein chimallin share 72 conserved genes encoded within seven gene blocks. Of these, 21 core genes are unique to nucleus-forming phage, and all but one of these genes encode proteins of unknown function. We propose that these phages comprise a novel viral family we term Chimalliviridae. Fluorescence microscopy and cryoelectron tomography studies of Erwinia phage vB_EamM_RAY confirm that many of the key steps of nucleus-based replication are conserved among diverse chimalliviruses and reveal variations on this replication mechanism. This work expands our understanding of phage nucleus and PhuZ spindle diversity and function, providing a roadmap for identifying key mechanisms underlying nucleus-based phage replication.

Isolation and Characterization of a Novel Lytic Phage, vB_PseuP-SA22, and Its Efficacy against Carbapenem-Resistant Pseudomonas aeruginosa

Carbapenem-resistant Pseudomonas aeruginosa (CRPA) poses a serious public health threat in multiple clinical settings. In this study, we detail the isolation of a lytic bacteriophage, vB_PseuP-SA22, from wastewater using a clinical strain of CRPA. Transmission electron microscopy (TEM) analysis identified that the phage had a podovirus morphology, which agreed with the results of whole genome sequencing. BLASTn search allowed us to classify vB_PseuP-SA22 into the genus Bruynoghevirus. The genome of vB_PseuP-SA22 consisted of 45,458 bp of double-stranded DNA, with a GC content of 52.5%. Of all the open reading frames (ORFs), only 26 (44.8%) were predicted to encode certain functional proteins, whereas the remaining 32 (55.2%) ORFs were annotated as sequences coding functionally uncharacterized hypothetical proteins. The genome lacked genes coding for toxins or markers of lysogenic phages, including integrases, repressors, recombinases, or excisionases. The phage produced round, halo plaques with a diameter of 1.5 ± 2.5 mm on the bacterial lawn. The TEM revealed that vB_PseuP-SA22 has an icosahedral head of 57.5 ± 4.5 nm in length and a short, non-contractile tail (19.5 ± 1.4 nm). The phage showed a latent period of 30 min, a burst size of 300 PFU/infected cells, and a broad host range. vB_PseuP-SA22 was found to be stable between 4–60 °C for 1 h, while the viability of the virus was reduced at temperatures above 60 °C. The phage showed stability at pH levels between 5 and 11. vB_PauP-SA22 reduced the number of live bacteria in P. aeruginosa biofilm by almost five logs. The overall results indicated that the isolated phage could be a candidate to control CRPA infections. However, experimental in vivo studies are essential to ensure the safety and efficacy of vB_PauP-SA22 before its use in humans.

Alternatives Therapeutic Approaches to Conventional Antibiotics: Advantages, Limitations and Potential Application in Medicine

Resistance to antimicrobials and particularly multidrug resistance is one of the greatest challenges in the health system nowadays. The continual increase in the rates of antimicrobial resistance worldwide boosted by the ongoing COVID-19 pandemic poses a major public health threat. Different approaches have been employed to minimize the effect of resistance and control this threat, but the question still lingers as to their safety and efficiency. In this context, new anti-infectious approaches against multidrug resistance are being examined. Use of new antibiotics and their combination with new β-lactamase inhibitors, phage therapy, antimicrobial peptides, nanoparticles, and antisense antimicrobial therapeutics are considered as one such promising approach for overcoming bacterial resistance. In this review, we provide insights into these emerging alternative therapies that are currently being evaluated and which may be developed in the future to break the progression of antimicrobial resistance. We focus on their advantages and limitations and potential application in medicine. We further highlight the importance of the combination therapy approach, wherein two or more therapies are used in combination in order to more effectively combat infectious disease and increasing access to quality healthcare. These advances could give an alternate solution to overcome antimicrobial drug resistance. We eventually hope to provide useful information for clinicians who are seeking solutions to the problems caused by antimicrobial resistance.

A novel virulent Litunavirus phage possesses therapeutic value against multidrug resistant Pseudomonas aeruginosa

Pseudomonas aeruginosa is a notable nosocomial pathogen that can cause severe infections in humans and animals. The emergence of multidrug resistant (MDR) P. aeruginosa has motivated the development of phages to treat the infections. In this study, a novel Pseudomonas phage, vB_PaeS_VL1 (VL1), was isolated from urban sewage. Phylogenetic analyses revealed that VL1 is a novel species in the genus Litunavirus of subfamily Migulavirinae. The VL1 is a virulent phage as no genes encoding lysogeny, toxins or antibiotic resistance were identified. The therapeutic potential of phage VL1 was investigated and revealed that approximately 56% (34/60 strains) of MDR P. aeruginosa strains, isolated from companion animal diseases, could be lysed by VL1. In contrast, VL1 did not lyse other Gram-negative and Gram-positive bacteria suggesting its specificity of infection. Phage VL1 demonstrated high efficiency to reduce bacterial load (~ 6 log cell number reduction) and ~ 75% reduction of biofilm in pre-formed biofilms of MDR P. aeruginosa. The result of two of the three MDR P. aeruginosa infected Galleria mellonella larvae showed that VL1 could significantly increase the survival rate of infected larvae. Taken together, phage VL1 has genetic and biological properties that make it a potential candidate for phage therapy against P. aeruginosa infections.

Characterisation of broad-spectrum phiKZ like jumbo phage and its utilisation in controlling multidrug-resistant Pseudomonas aeruginosa isolates

The emergence of highly virulent multidrug-resistant P. aeruginosa has become increasingly evident among hospital-acquired infections and has raised the need for alternative therapies. Phage therapy can be one such alternative to antibiotic therapy to combat multidrug-resistant pathogenic bacteria, but this requires the availability of phages with a broad host range. In this study, isolation and molecular characterisation of P. aeruginosa specific phages were carried out. A total of 17 phages isolated showed different spectra of activity and efficiency of lysis against 82 isolates of P. aeruginosa obtained from clinical samples (n = 13), hospital effluent (n = 46) and fish processing plant effluent (n = 23). Antibiotic susceptibility test results revealed multi-drug resistance in 61 of the total 82 isolates. Three new jumbo lytic P. aeruginosa specific broad host range phages were isolated and characterised in this present study belonged to the family Myoviridae (order Caudovirales). The genetic analysis of ɸU5 revealed that phage has a genome size of 282.6 kbp with 373 putative open reading frames (ORFs), and its genetic architecture is similar to phiKZ like jumbo phages infecting P. aeruginosa. The bacteriophages isolated in this study had lytic ability against biofilm-forming and multidrug-resistant P. aeruginosa and could be candidates for further studies towards phage therapy.

Prophylactic Delivery of a Bacteriophage Cocktail in Feed Significantly Reduces Salmonella Colonization in Pigs

Nontyphoidal Salmonella spp. are a leading cause of human food poisoning and can be transmitted to humans via consuming contaminated pork. To reduce Salmonella spread to the human food chain, bacteriophage (phage) therapy could be used to reduce bacteria from animals' preslaughter. We aimed to determine if adding a two-phage cocktail to feed reduces Salmonella colonization in piglets. This first required spray drying phages to allow them to be added as a powder to feed, and phages were spray dried in different excipients to establish maximum recovery. Although laboratory phage yields were not maintained during scale up in a commercial spray dryer (titers fell from 3 × 108 to 2.4 × 106 PFU/g respectively), the phage titers were high enough to progress. Spray dried phages survived mixing and pelleting in a commercial feed mill, and sustained no further loss in titer when stored at 4°C or barn conditions over 6 months. Salmonella-challenged piglets that were prophylactically fed the phage-feed diet had significantly reduced Salmonella colonization in different gut compartments (P < 0.01). 16S rRNA gene sequencing of fecal and gut samples showed phages did not negatively impact microbial communities as they were similar between healthy control piglets and those treated with phage. Our study shows delivering dried phages via feed effectively reduces Salmonella colonization in pigs. IMPORTANCE Infections caused by Salmonella spp. cause 93.8 million cases of human food poisoning worldwide, each year of which 11.7% are due to consumption of contaminated pork products. An increasing number of swine infections are caused by multidrug-resistant (MDR) Salmonella strains, many of which have entered, and continue to enter the human food chain. Antibiotics are losing their efficacy against these MDR strains, and thus antimicrobial alternatives are needed. Phages could be developed as an alternative approach, but research is required to determine the optimal method to deliver phages to pigs and to determine if phage treatment is effective at reducing Salmonella colonization in pigs. The results presented in this study address these two aspects of phage development and show that phages delivered via feed prophylactically to pigs reduces Salmonella colonization in challenged pigs.

Genomic characterization of lytic bacteriophages targeting genetically diverse Pseudomonas aeruginosa clinical isolates

Pseudomonas aeruginosa infections can be difficult to treat and new therapeutics are needed. Bacteriophage therapy is a promising alternative to traditional antibiotics, but large numbers of isolated and characterized phages are lacking. We collected 23 diverse P. aeruginosa isolates from people with cystic fibrosis (CF) and clinical infections, and used them to screen and isolate over a dozen P. aeruginosa-targeting phages from hospital wastewater. Phages were characterized with genome sequencing, comparative genomics, and lytic activity screening against all 23 bacterial host isolates. We evolved bacterial mutants that were resistant to phage infection for four different phages, and used genome sequencing and functional analysis to study them further. We also tested phages for their ability to kill P. aeruginosa grown in biofilms in vitro and ex vivo on CF airway epithelial cells. Overall, this study demonstrates how systematic genomic and phenotypic characterization can be deployed to develop bacteriophages as precision antibiotics.

NEW BACTERIOPHAGE OF MULTIDRUG RESISTANT STRAIN OF PSEUDOMONAS AERUGINOSA

Aim: Antimicrobial resistance in bacteria is one of the most discussed and important theme in healthcare field now. Bacteriophages are known as the most promising alternative to antibiotics and a method of fighting the multi-resistant pathogens. In this study, our main aim was to isolate lytic specific phages of multidrug resistant Pseudomonas aeruginosa, one of the most dangerous bacterial human pathogens. Methods: Disk-diffusion method, spot-test, agar overlay method, electron microscopy. Results: Antimicrobial resistance range of P. aeruginosa 458 strain was tested and it appeared to be resistant to all available antibiotics. Phages were isolated from waste waters in Kyiv. They appeared to have a typical morphology of Myoviridae family. Isolated viruses successfully lysed all the bacteria in vitro. Conclusions: Considering high effectiveness of isolated phage in vitro, we propose it as a candidate for phage therapy, though further studies on physical and genetic characteristics are required.

Characterization of a novel bullet-shaped lytic bacteriophage against extensively drug-resistant Pseudomonas aeruginosa isolated from human and domestic sources

Global spread and emergence of the extensively drug-resistant (XDR) strains of P. aeruginosa have become a concern, thus, searching for new alternative treatment approaches are required. This study was aimed to isolate and characterize a novel lytic phage against P. aeruginosa. Seventy XDR isolates of P. aeruginosa were collected from May to September 2018. Wastewater samples were used for isolation of lytic phage against XDR P. aeruginosa isolates. Host range, thermal and pH stability, adsorption rate, latent period, burst size and morphology of phage were determined following the standard protocols. Morphological characteristics of the phage revealed that it belonged to Podoviridae family and it was named vB-PaeP-007. Although the phage had a narrow host range, 47 out of 70 XDR isolates were susceptible to it. The adsorption rate, latent period and burst size of vB-PaeP-007 were approximately 89.80% in 8 min, 10 min and 93 phages per cell, respectively. Its lysis activity remained at a wide range of pH (4 up to 12) and temperature (- 20.00 up to 70.00 ˚C). Regarding the physiological features and host range of the vB-PaeP-007 phage, it could be a promising candidate for phage therapy and bio-controlling of infections from XDR isolates of P. aeruginosa in human and livestock storage centers.

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.

Phages from Genus Bruynoghevirus and Phage Therapy: Pseudomonas Phage Delta Case

The applicability and safety of bacteriophage Delta as a potential anti-Pseudomonas aeruginosa agent belonging to genus Bruynoghevirus (family Podoviridae) was characterised. Phage Delta belongs to the species Pseudomonas virus PaP3, which has been described as a temperate, with cos sites at the end of the genome. The phage Delta possesses a genome of 45,970 bp that encodes tRNA for proline (Pro), aspartic acid (Asp) and asparagine (Asn) and does not encode any known protein involved in lysogeny formation or persistence. Analysis showed that phage Delta has 182 bp direct terminal repeats at the end of genome and lysogeny was confirmed, neither upon infection at low nor at high multiplicity of infection (MOI). The turbid plaques that appear on certain host lawns can result from bacteriophage insensitive mutants that occur with higher frequency (10-4). In silico analysis showed that the genome of Delta phage does not encode any known bacterial toxin or virulence factor, determinants of antibiotic resistance and known human allergens. Based on the broad host range and high lytic activity against planktonic and biofilm cells, phage Delta represents a promising candidate for phage therapy.

Emerging Phage Resistance in Pseudomonas aeruginosa PAO1 Is Accompanied by an Enhanced Heterogeneity and Reduced Virulence

Bacterial surface structures of a proteinic nature and glycoconjugates contribute to biofilm formation and provide shields to host defense mechanisms (e.g., the complement system and phagocytosis). A loss or alteration of these molecules, leading to phage resistance, could result in fewer virulent bacteria. In this study, we evaluate the biology and phenotype changes in Pseudomonas aeruginosa PAO1 phage-resistant clones, which emerge in phage-treated biofilms. We characterize these clones for phage-typing patterns, antibiotic resistance, biofilm formation, pathogenicity, and interactions with the innate immune system. Another important question that we address is whether phage-resistant mutants are also generated incidentally, despite the phage treatment-selective pressure, as the natural adaptation of the living biofilm population. It is found that the application of different phages targeting a particular receptor selects similar phage resistance patterns. Nevertheless, this results in a dramatic increase in the population heterogeneity, giving over a dozen phage-typing patterns, compared to one of the untreated PAO1 sessile forms. We also confirm the hypothesis that "phage-resistant bacteria are more susceptible to antibiotics and host-clearance mechanisms by the immune system". These findings support phage application in therapy, although the overall statement that phage treatment selects the less virulent bacterial population should be further verified using a bigger collection of clinical strains.

Therapeutic Effect of a Newly Isolated Lytic Bacteriophage against Multi-Drug-Resistant Cutibacterium acnes Infection in Mice

Acne vulgaris, which is mostly associated with the colonization of Cutibacterium acnes (C. acnes), is a common skin inflammatory disease in teenagers. However, over the past few years, the disease has extended beyond childhood to chronically infect approximately 40% of adults. While antibiotics have been used for several decades to treat acne lesions, antibiotic resistance is a growing crisis; thus, finding a new therapeutic target is urgently needed. Studies have shown that phage therapy may be one alternative for treating multi-drug-resistant bacterial infections. In the present study, we successfully isolated a C. acnes phage named TCUCAP1 from the skin of healthy volunteers. Morphological analysis revealed that TCUCAP1 belongs to the family Siphoviridae with an icosahedral head and a non-contractile tail. Genome analysis found that TCUCAP1 is composed of 29,547 bp with a G+C content of 53.83% and 56 predicted open reading frames (ORFs). The ORFs were associated with phage structure, packing, host lysis, DNA metabolism, and additional functions. Phage treatments applied to mice with multi-drug-resistant (MDR) C.-acnes-induced skin inflammation resulted in a significant decrease in inflammatory lesions. In addition, our attempt to formulate the phage into hydroxyethyl cellulose (HEC) cream may provide new antibacterial preparations for human infections. Our results demonstrate that TCUCAP1 displays several features that make it an ideal candidate for the control of C. acnes infections.

Clinical Pharmacology of Bacteriophage Therapy: A Focus on Multidrug-Resistant Pseudomonas aeruginosa Infections

Pseudomonas aeruginosa is one of the most common causes of healthcare-associated diseases and is among the top three priority pathogens listed by the World Health Organization (WHO). This Gram-negative pathogen is especially difficult to eradicate because it displays high intrinsic and acquired resistance to many antibiotics. In addition, growing concerns regarding the scarcity of antibiotics against multidrug-resistant (MDR) and extensively drug-resistant (XDR) P. aeruginosa infections necessitate alternative therapies. Bacteriophages, or phages, are viruses that target and infect bacterial cells, and they represent a promising candidate for combatting MDR infections. The aim of this review was to highlight the clinical pharmacology considerations of phage therapy, such as pharmacokinetics, formulation, and dosing, while addressing several challenges associated with phage therapeutics for MDR P. aeruginosa infections. Further studies assessing phage pharmacokinetics and pharmacodynamics will help to guide interested clinicians and phage researchers towards greater success with phage therapy for MDR P. aeruginosa infections.

Phage phiKZ-The First of Giants

The paper covers the history of the discovery and description of phiKZ, the first known giant bacteriophage active on Pseudomonas aeruginosa. It also describes its unique features, especially the characteristic manner of DNA packing in the head around a cylinder-shaped structure ("inner body"), which probably governs an ordered and tight packaging of the phage genome. Important properties of phiKZ-like phages include a wide range of lytic activity and the blue opalescence of their negative colonies, and provide a background for the search and discovery of new P. aeruginosa giant phages. The importance of the phiKZ species and of other giant phage species in practical phage therapy is noted given their broad use in commercial phage preparations.

Bacteriophage - A Promising Alternative Measure for Bacterial Biofilm Control

Bacterial biofilms can enhance bacteria's viability by providing resistance against antibiotics and conventional disinfectants. The existence of biofilm is a serious threat to human health, causing incalculable loss. Therefore, new strategies to deal with bacterial biofilms are needed. Bacteriophages are unique due to their activity on bacteria and do not pose a threat to humans. Consequently, they are considered safe alternatives to drugs for the treatment of bacterial diseases. They can effectively obliterate bacterial biofilms and have great potential in medical treatment, the food industry, and pollution control. There are intricate mechanisms of interaction between phages and biofilms. Biofilms may prevent the invasion of phages, and phages can kill bacteria for biofilm control purposes or influence the formation of biofilms. At present, there are various measures for the prevention and control of biofilms through phages, including the combined use of drugs and the application of phage cocktails. This article mainly reviews the function and formation process of bacterial biofilms, summarizes the different mechanisms between phages and biofilms, briefly explains the phage usage for the control of bacterial biofilms, and promotes phage application maintenance human health and the protection of the natural environment.

Bacteriophage therapy against Pseudomonas aeruginosa biofilms: a review

Multi-Drug Resistant (MDR) Pseudomonas aeruginosa is one of the most important bacterial pathogens that causes infection with a high mortality rate due to resistance to different antibiotics. This bacterium prompts extensive tissue damage with varying factors of virulence, and its biofilm production causes chronic and antibiotic-resistant infections. Therefore, due to the non-applicability of antibiotics for the destruction of P. aeruginosa biofilm, alternative approaches have been considered by researchers, and phage therapy is one of these new therapeutic solutions. Bacteriophages can be used to eradicate P. aeruginosa biofilm by destroying the extracellular matrix, increasing the permeability of antibiotics into the inner layer of biofilm, and inhibiting its formation by stopping the quorum-sensing activity. Furthermore, the combined use of bacteriophages and other compounds with anti-biofilm properties such as nanoparticles, enzymes, and natural products can be of more interest because they invade the biofilm by various mechanisms and can be more effective than the one used alone. On the other hand, the use of bacteriophages for biofilm destruction has some limitations such as limited host range, high-density biofilm, sub-populate phage resistance in biofilm, and inhibition of phage infection via quorum sensing in biofilm. Therefore, in this review, we specifically discuss the use of phage therapy for inhibition of P. aeruginosa biofilm in clinical and in vitro studies to identify different aspects of this treatment for broader use.

Multisubunit RNA Polymerases of Jumbo Bacteriophages

Prokaryotic viruses with DNA genome longer than 200 kb are collectively referred to as “jumbo phages”. Some representatives of this phylogenetically diverse group encode two DNA-dependent RNA polymerases (RNAPs)—a virion RNAP and a non-virion RNAP. In contrast to most other phage-encoded RNAPs, the jumbo phage RNAPs are multisubunit enzymes related to RNAPs of cellular organisms. Unlike all previously characterized multisubunit enzymes, jumbo phage RNAPs lack the universally conserved alpha subunits required for enzyme assembly. The mechanism of promoter recognition is also different from those used by cellular enzymes. For example, the AR9 phage non-virion RNAP requires uracils in its promoter and is able to initiate promoter-specific transcription from single-stranded DNA. Jumbo phages encoding multisubunit RNAPs likely have a common ancestor allowing making them a separate subgroup within the very diverse group of jumbo phages. In this review, we describe transcriptional strategies used by RNAP-encoding jumbo phages and describe the properties of characterized jumbo phage RNAPs.

Tackling Intrinsic Antibiotic Resistance in Serratia Marcescens with A Combination of Ampicillin/Sulbactam and Phage SALSA

During the antibiotic crisis, bacteriophages (briefly phages) are increasingly considered as potential antimicrobial pillars for the treatment of infectious diseases. Apart from acquired drug resistance, treatment options are additionally hampered by intrinsic, chromosomal-encoded resistance. For instance, the chromosomal ampC gene encoding for the AmpC-type β-lactamases is typically present in a number of nosocomial pathogens, including S. marcescens. In this study, phage SALSA (vB_SmaP-SALSA), with lytic activity against clinical isolates of S. marcescens, was isolated from effluent. Besides phage characterization, the aim of this study was to evaluate whether a synergistic effect between the antibiotic ampicillin/sulbactam (SAM) and phage can be achieved despite intrinsic drug resistance. Phage SALSA belongs to the Podoviridae family and genome-wide treeing analysis groups this phage within the phylogenetic radiation of T7-like viruses. The genome of Phage SALSA consists of 39,933 bp, which encode for 49 open reading frames. Phage SALSA was able to productively lyse 5 out of 20 clinical isolates (25%). A bacterial challenge with phage alone in liquid medium revealed that an initial strong bacterial decline was followed by bacterial re-growth, indicating the emergence of phage resistance. In contrast, the combination of SAM and phage, together at various concentrations, caused a complete bacterial eradication, confirmed by absorbance measurements and the absence of colony forming units after plating. The data show that it is principally possible to tackle the axiomatic condition of intrinsic drug resistance with a dual antimicrobial approach, which could be extended to other clinically relevant bacteria.

Bacteriophage Therapy Increases Complement-Mediated Lysis of Bacteria and Enhances Bacterial Clearance After Acute Lung Infection With Multidrug-Resistant Pseudomonas aeruginosa

Emergence of multidrug-resistant (MDR) bacterial infections is a major problem in clinical medicine. Development of new strategies such as phage therapy may be a novel approach for treatment of life-threatening infections caused by MDR bacteria. A newly isolated phage, MMI-Ps1, with strong lytic activity was used for treatment of acute lung infection with Pseudomonas aeruginosa in a mouse model. Intranasal administration of a single dose of MMI-Ps1 immediately after infection provided a significant level of protection and increased the survival duration. Moreover, treatment of infected mice with phage as late as 12 hours after infection was still protective. Our in vitro results are the first to show the synergistic elimination of serum-resistant Pseudomonas strains by phage and complement. Phage therapy increases the efficacy of complement-mediated lysis of serum-resistant P. aeruginosa strains, indicating the importance of an intact complement system in clearing Pseudomonas infection during phage 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.

vB_PaeM_MIJ3, a Novel Jumbo Phage Infecting Pseudomonas aeruginosa, Possesses Unusual Genomic Features

Phages are the most abundant biological entity on Earth. There are many variants in phage virion sizes, morphology, and genome sizes. Large virion sized phages, with genome sizes greater than 200 kbp have been identified and termed as Jumbo phages. These phages exhibit certain characteristics that have not been reported in phages with smaller genomes. In this work, a jumbo phage named MIJ3 (vB_PaeM_MIJ3) that infects Pseudomonas aeruginosa PAO1 was isolated from an equine livery yard in Leicestershire, United Kingdom. The genome and biological characteristics of this phage have been investigated. MIJ3 is a Myovirus with multiple long tail fibers. Assessment of the host range of MIJ3 revealed that it has the ability to infect many clinical isolates of P. aeruginosa. Bioinformatics analysis of the phage genome indicated that MIJ3 is closely related to the Pseudomonas phage, PA5oct. MIJ3 possesses several unusual features that are either rarely present in other phages or have not yet been reported. In particular, MIJ3 encodes a FtsH-like protein, and a putative lysidine synthase, TilS. These two proteins have not been reported in phages. MIJ3 also possesses a split DNA polymerase B with a novel intein. Of particular interest, unlike other jumbo phages infecting Pseudomonas spp., MIJ3 lacks the genetic elements required for the formation of the phage nucleus, which was believed to be conserved across jumbo Pseudomonas phages.

Natural Occurrence of Escherichia coli-Infecting Bacteriophages in Clinical Samples

The interaction between bacteriophages, bacteria and the human host as a tripartite system has recently captured attention. The taxonomic diversity of bacteriophages, as a natural parasite of bacteria, still remains obscure in human body biomes, representing a so-called “viral dark matter.” Here, we isolated and characterized coliphages from blood, urine and tracheal aspirates samples collected at a tertiary care hospital in Austria. Phages were more often isolated from blood, followed by urine and tracheal aspirates. Phylogenetic analysis and genome comparisons allowed the identification of phages belonging to the Tunavirinae subfamily, and to the Peduovirus and Tequintavirus genera. Tunavirinae phages cluster together and are found in samples from 14 patients, suggesting their prevalence across a variety of human samples. When compared with other phage genomes, the highest similarity level was at 87.69% average nucleotide identity (ANI), which suggests that these are in fact a newly isolated phage species. Tequintavirus phages share a 95.90% with phage 3_29, challenging the ANI threshold currently accepted to differentiate phage species. The isolated phages appear to be virulent, with the exception of the Peduovirus members, which are integrative and seem to reside as prophages in bacterial genomes.

Epidemiology and Treatment of Multidrug-Resistant and Extensively Drug-Resistant Pseudomonas aeruginosa Infections

In recent years, the worldwide spread of the so-called high-risk clones of multidrug-resistant or extensively drug-resistant (MDR/XDR) Pseudomonas aeruginosa has become a public health threat. This article reviews their mechanisms of resistance, epidemiology, and clinical impact and current and upcoming therapeutic options. In vitro and in vivo treatment studies and pharmacokinetic and pharmacodynamic (PK/PD) models are discussed. Polymyxins are reviewed as an important therapeutic option, outlining dosage, pharmacokinetics and pharmacodynamics, and their clinical efficacy against MDR/XDR P. aeruginosa infections. Their narrow therapeutic window and potential for combination therapy are also discussed. Other "old" antimicrobials, such as certain β-lactams, aminoglycosides, and fosfomycin, are reviewed here. New antipseudomonals, as well as those in the pipeline, are also reviewed. Ceftolozane-tazobactam has clinical activity against a significant percentage of MDR/XDR P. aeruginosa strains, and its microbiological and clinical data, as well as recommendations for improving its use against these bacteria, are described, as are those for ceftazidime-avibactam, which has better activity against MDR/XDR P. aeruginosa, especially strains with certain specific mechanisms of resistance. A section is devoted to reviewing upcoming active drugs such as imipenem-relebactam, cefepime-zidebactam, cefiderocol, and murepavadin. Finally, other therapeutic strategies, such as use of vaccines, antibodies, bacteriocins, anti-quorum sensing, and bacteriophages, are described as future options.

Identification and characterization of phage protein and its activity against two strains of multidrug-resistant Pseudomonas aeruginosa

Pseudomonas aeruginosa is an opportunistic pathogen with a capacity to develop antibiotic resistance, which underlies a larger proportion of hospital-acquired infections and higher morbidity and mortality, compared to other bacterial infections. Effective novel approaches for treatment of infections induced by this pathogen are therefore necessary. Phage therapy represents a promising alternative solution to eradicate antibiotic-resistant pathogens. Here, we investigated phage protein efficacy against multi-drug resistant (MDR) P. aeruginosa PAR21 and PAR50 strains isolated from diabetic foot ulcer patients. The results obtained using spot assay, zymography, spectrophotometry and scanning electron microscopy at low voltage (SEM-LV) indicate that the phage protein, PA-PP, exerts activity against P. aeruginosa PAR50 while having no impact on the PAR21 strain. Using LC-MS-MS/MS and comparative analysis of the peptide molecular mass with the protein sequence database, PA-PP was identified as a member of the serine protease family, a result corroborated by its ability to digest casein. We additionally showed a capacity of PA-PP to digest porin protein on the bacterial outer membrane (OM). Moreover, synergistic activity between PA-PP protein and piperacillin led to higher sensitivity of bacterial cells to this antibiotic. Our collective findings suggest that PA-PP targets porin protein on PAR50 OM, thereby increasing its sensitivity to specific antibiotics. The adverse effects observed on bacterial cells using SEM-LV suggest further roles of this protein that remain to be established.

Selection of Bacteriophages to Control In Vitro 24 h Old Biofilm of Pseudomonas Aeruginosa Isolated from Drinking and Thermal Water

Pseudomonas aeruginosa is an opportunistic pathogen that causes public healthcare issues. In moist environments, this Gram-negative bacterium persists through biofilm-associated contamination on surfaces. Bacteriophages are seen as a promising alternative strategy to chemical biocides. This study evaluates the potential of nine lytic bacteriophages as biocontrol treatments against nine environmental P. aerginosa isolates. The spot test method is preliminarily used to define the host range of each virus and to identify their minimum infectious titer, depending on the strain. Based on these results, newly isolated bacteriophages 14.1, LUZ7, and B1 are selected and assessed on a planktonic cell culture of the most susceptible isolates (strains MLM, D1, ST395E, and PAO1). All liquid infection assays are achieved in a mineral minimum medium that is much more representative of real moist environments than standard culture medium. Phages 14.1 and LUZ7 eliminate up to 90% of the PAO1 and D1 bacterial strains. Hence, their effectiveness is evaluated on the 24 h old biofilms of these strains, established on a stainless steel coupon that is characteristic of materials found in thermal and industrial environments. The results of quantitative PCR viability show a maximum reduction of 1.7 equivalent Log CFU/cm² in the coupon between treated and untreated surfaces and shed light on the importance of considering the entire virus/host/environment system for optimizing the treatment.

Characterization of Two Pseudomonas aeruginosa Viruses vB_PaeM_SCUT-S1 and vB_PaeM_SCUT-S2

The sophisticated antibiotic resistance mechanism of Pseudomonas aeruginosa has urged the development of alternative antibacterial strategies. Phage therapy has been proven successful for the treatment of multidrug-resistant infections. In this study, we reported two virulent P. aeruginosa phages, vB_PaeM_SCUT-S1 (S1) and vB_PaeM_SCUT-S2 (S2), which were characterized at morphological, genomic, and proteomic levels. Phages S1 and S2 were assigned to the Myoviridae family. The genome sequencing showed that the genome size of Phage S1 was 66,046 bp and that of Phage S2 was 94,434 bp. The phylogenetic tree indicated that the two phages were distantly related to each other and were classified in the genera Pbunavirus and Pakpunavirus respectively. Thirty-one proteins were identified for each phage by mass spectrometry and were used to substantiate the function of the predicted coding genes. The two phages inhibited the growth of P. aeruginosa strain PAO1 at low multiplicity of infection levels and had good performance both on preventing biofilm formation and eradicating preformed biofilms. They were also stable over a wide range of temperature and pH values, supporting their potential use in the treatment of P. aeruginosa infections.

Use of Greater Wax Moth Larvae (Galleria mellonella) as an Alternative Animal Infection Model for Analysis of Bacterial Pathogenesis

Alternative infection models of bacterial pathogenesis are useful because they reproduce some of the disease characteristics observed in higher animals. Insect models are especially useful for modeling bacterial infections, as they are inexpensive, generally less labor-intensive, and more ethically acceptable than experimentation on higher organisms. Similar to animals, insects have been shown to possess innate immune systems that respond to pathogenic bacteria.

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.

Standardization of G. mellonella Larvae to Provide Reliable and Reproducible Results in the Study of Fungal Pathogens

In the past decade, Galleria mellonella (wax moth) larvae have become widely used as a non-mammalian infection model. However, the full potential of this infection model has yet to be realised, limited by the variable quality of larvae used and the lack of standardised procedures. Here, we review larvae suitable for research, protocols for dosing larvae, and methods for scoring illness in larvae infected with fungal pathogens. The development of standardised protocols for carrying out our experimental work will allow high throughput screens to be developed, changing the way in which we evaluate panels of mutants and strains. It will also enable the in vivo screening of potential antimicrobials at an earlier stage in the research and development cycle.

1st German Phage Symposium-Conference Report

In Germany, phage research and application can be traced back to the beginning of the 20th century. However, with the triumphal march of antibiotics around the world, the significance of bacteriophages faded in most countries, and respective research mainly focused on fundamental questions and niche applications. After a century, we pay tribute to the overuse of antibiotics that led to multidrug resistance and calls for new strategies to combat pathogenic microbes. Against this background, bacteriophages came into the spotlight of researchers and practitioners again resulting in a fast growing “phage community”. In October 2017, part of this community met at the 1st German Phage Symposium to share their knowledge and experiences. The participants discussed open questions and challenges related to phage therapy and the application of phages in general. This report summarizes the presentations given, highlights the main points of the round table discussion and concludes with an outlook for the different aspects of phage application.