Characterization and Testing the Efficiency of Acinetobacter baumannii Phage vB-GEC_Ab-M-G7 as an Antibacterial Agent

Bacteriophages as a potential substitute for antibiotics: A comprehensive review

Over the years, the administration of antibiotics for the purpose of addressing bacterial infections has become increasingly challenging due to the increased prevalence of antimicrobial resistance exhibited by various strains of bacteria. Multidrug-resistant (MDR) bacterial species are rising due to the unavailability of novel antibiotics, leading to higher mortality rates. With these conditions, there is a need for alternatives in which phage therapy has made promising results. Phage-derived endolysins, phage cocktails, and bioengineered phages are effective and have antimicrobial properties against MDR and extensively drug-resistant strains. Despite these, it has been observed that phages can give antimicrobial activity to more than one bacterial species. Thus, phage cocktail against resistant strains provides broad spectrum treatment and magnitude of effectivity, which is many folds higher than antibiotics. Many commercially available endolysins such as Staphefekt SA.100, Exebacase (CF-301), and N-Rephasin®SAL200 are used in biofilm penetration and treating plant diseases. The role of CMP1 phage endolysin in transgenic tomato plants in preventing Clavibacter michiganensis infection and the effectiveness of phage in protecting Atlantic salmon from vibriosis have been reported. Furthermore, phage-derived endolysin therapy, such as TSPphg phage exogenous treatment, can aid in disrupting cell walls, leading to bacterial cell lysis. As animals in aquaculture and slaughterhouses are highly susceptible to bacterial infections, effective phage therapy instead of antibiotics can help treat poultry animals, preserve them, and facilitate disease-free trade. Using bioengineered phages and phage cocktails enhances the effectiveness by providing a broad spectrum of phages and target specificity. Research is currently being conducted on clinical trials to confirm the efficacy of engineered phages and phage cocktails in humans. Although obtaining commercial approval may be time-consuming, it will be beneficial in the postantibiotic era. This review provides an overview of the significance of phage therapy as a potential alternative to antibiotics in combating resistant bacterial strains and its application to various fields and emphasizes the importance of safeguarding and ensuring treatment efficacy.

Characterization of a Straboviridae phage vB_AbaM-SHI and its inhibition effect on biofilms of Acinetobacter baumannii

Acinetobacter baumannii (A. baumannii) is a popular clinical pathogen worldwide. Biofilm-associated antibiotic-resistant A. baumannii infection poses a great threat to human health. Bacteria in biofilms are highly resistant to antibiotics and disinfectants. Furthermore, inhibition or eradication of biofilms in husbandry, the food industry and clinics are almost impossible. Phages can move across the biofilm matrix and promote antibiotic penetration. In the present study, a lytic A. baumannii phage vB_AbaM-SHI, belonging to family Straboviridae, was isolated from sauce chop factory drain outlet in Wuxi, China. The DNA genome consists of 44,180 bp which contain 93 open reading frames, and genes encoding products morphogenesis are located at the end of the genome. The amino acid sequence of vB_AbaM-SHI endolysin is different from those of previously reported A. baumannii phages in NCBI. Phage vB_AbaM-SHI endolysin has two additional β strands due to the replacement of a lysine (K) (in KU510289.1, NC_041857.1, JX976549.1 and MH853786.1) with an arginine (R) (SHI) at position 21 of A. baumannii phage endolysin. Spot test showed that phage vB_AbaM-SHI is able to lyse some antibiotic-resistant bacteria, such as A. baumannii (SL, SL1, and SG strains) and E. coli BL21 strain. Additionally, phage vB_AbaM-SHI independently killed bacteria and inhibited bacterial biofilm formation, and synergistically exerted strong antibacterial effects with antibiotics. This study provided a new perspective into the potential application value of phage vB_AbaM-SHI as an antimicrobial agent.

Potential Usefulness of Bacteriophages for the Treatment of Multidrug-Resistant Acinetobacter Infection

Bacteriophages were discovered in early 20th century. However, the interest in bacteriophage research was reduced with the discovery of antibiotics. With the increasing number of infections due to multidrug-resistant (MDR) organisms, the potential usefulness of bacteriophages as therapeutic agents has been re-evaluated. In this review, we found that more than 30 lytic bacteriophages that infect Acinetobacter species have been characterised. These are mainly members of Caudovirales, with genome sizes ranging from 31 kb to 234 kb and G+C contents ranging from 33.5% to 45.5%. The host range can be as low as < 10% of all tested Acinetobacter strains. Fourteen published murine trials indicated positive outcomes in bacteriophage-treated groups. Only two case reports were pertaining to the use of bacteriophages in the treatment of Acinetobacter infections in humans; in both cases, the infections were resolved with bacteriophage therapy. The use of bacteriophages has been associated with reduced Acinetobacter burden in the environment, as shown in two studies. The major limitation of bacteriophage therapy is its highly selective host strain. In conclusion, the potential usefulness of bacteriophage therapy for the treatment of MDR Acinetobacter species has been documented only in limited studies and more research is needed prior to its extensive use in clinical practice.

Biological and genomic characterization of a polyvalent bacteriophage (S19cd) strongly inhibiting Salmonella enterica serovar Choleraesuis

Bacteriophages are a promising alternative for the control of pathogenic bacteria. In this study, we isolated a virulent bacteriophage, S19cd, from pig gut that could infect both a non-pathogenic bacteria Escherichia coli 44 (EC44) and two pathogenic bacterial strains (ATCC 13312 (SC13312) and CICC 21493 (SC21493)) of Salmonella enterica serovar Choleraesuis (SC). S19cd exhibited strong lytic ability in both SC13312 and SC21493 with an optimal multiplicity of infection (MOI) of 10-6 and 10-5, respectively, and inhibited their growth at an MOI of 10-7 within 24 h. Mice pre-treated with S19cd exhibited protection against the SC13312 challenge. Moreover, S19cd has good heat resistance (80 ℃) and pH tolerance (pH 3-12). Genome analysis revealed that S19cd belongs to the Felixounavirus genus and does not contain any virulence or drug-resistance-related genes. Additionally, S19cd encodes an adenine-specific methyltransferase that has no similarity to methyltransferases from other Felixounavirus phages and shares limited similarity with other methyltransferases in the NCBI protein database. Metagenomic analysis of S19cd genomes from 500 pigs revealed that S19cd-like phages may be widespread in Chinese pig gut. In conclusion, S19cd can be a potential phage therapy targeting SC infections.

Acinetobacter baumannii Bacteriophage: Progress in Isolation, Genome Sequencing, Preclinical Research, and Clinical Application

Acinetobacter baumannii (A. baumannii) is a common nosocomial pathogen associated with serious clinical challenges owing to its rapidly increasing resistance to antibiotics. Due to their high host specificity and easy access to the natural environment, bacteriophages (phages) may serve as good antibacterial agents. Phage therapy has been successfully used to treat antibiotic-resistant A. baumannii infections. As a fundamental step before phage therapy, the characterization and sequencing of A. baumannii phages have been well studied. Until October 2022, 132 A. baumannii phages have been sequenced and studied, with their genomes ranging from 4 to 234 kb, and we summarize the characterized and sequenced A. baumannii phages. This review is a current and short overview that does not go into detail on the A. baumannii phages. In addition, preclinical studies and clinical applications of A. baumannii phages are also included.

Phenotypic and Molecular Characteristics of Carbapenem-Resistant Acinetobacter baumannii Isolates from Bulgarian Intensive Care Unit Patients

Carbapenem-resistant Acinetobacter baumannii (CRAB) is designated as an urgent public health threat, both due to its remarkable multidrug resistance and propensity for clonal spread. This study aimed to explore the phenotypic and molecular characteristics of antimicrobial resistance in CRAB isolates (n = 73) from intensive care unit (ICU) patients in two university hospitals in Bulgaria (2018–2019). The methodology included antimicrobial susceptibility testing, PCR, whole-genome sequencing (WGS), and phylogenomic analysis. The resistance rates were as follows: imipenem, 100%; meropenem, 100%; amikacin, 98.6%; gentamicin, 89%; tobramycin, 86.3%; levofloxacin, 100%; trimethoprim–sulfamethoxazole, 75.3%; tigecycline, 86.3%; colistin, 0%; and ampicillin–sulbactam, 13.7%. All isolates harbored blaOXA-51-like genes. The frequencies of distribution of other antimicrobial resistance genes (ARGs) were: blaOXA-23-like, 98.6%; blaOXA-24/40-like, 2.7%; armA, 86.3%; and sul1, 75.3%. The WGS of selected extensively drug-resistant A. baumannii (XDR-AB) isolates (n = 3) revealed the presence of OXA-23 and OXA-66 carbapenem-hydrolyzing class D β-lactamases in all isolates, and OXA-72 carbapenemase in one of them. Various insertion sequencies, such as ISAba24, ISAba31, ISAba125, ISVsa3, IS17, and IS6100, were also detected, providing increased ability for horizontal transfer of ARGs. The isolates belonged to the widespread high-risk sequence types ST2 (n = 2) and ST636 (n = 1) (Pasteur scheme). Our results show the presence of XDR-AB isolates, carrying a variety of ARGs, in Bulgarian ICU settings, which highlights the crucial need for nationwide surveillance, especially in the conditions of extensive antibiotic usage during COVID-19.

The applications of animal models in phage therapy: An update

The rapid increase in antibiotic resistance presents a dire situation necessitating the need for alternative therapeutic agents. Among the current alternative therapies, phage therapy (PT) is promising. This review extensively summarizes preclinical PT approaches in various in-vivo models. PT has been evaluated in several recent clinical trials. However, there are still several unanswered concerns due to a lack of appropriate regulation and pharmacokinetic data regarding the application of phages in human therapeutic procedures. In this review, we also presented the current state of PT and considered how animal models can be used to adapt these therapies for humans. The development of realistic solutions to circumvent these constraints is critical for advancing this technology.

Efficacy in Galleria mellonella Larvae and Application Potential Assessment of a New Bacteriophage BUCT700 Extensively Lyse Stenotrophomonas maltophilia

In recent years, Stenotrophomonas maltophilia (S. maltophilia) has become an important pathogen of clinically acquired infections accompanied by high pathogenicity and high mortality. Moreover, infections caused by multidrug-resistant S. maltophilia have emerged as a serious challenge in clinical practice. Bacteriophages are considered a promising alternative for the treatment of S. maltophilia infections due to their unique antibacterial mechanism and superior bactericidal ability compared with traditional antibiotic agents. Here, we reported a new phage BUCT700 that has a double-stranded DNA genome of 43,214 bp with 70% GC content. A total of 55 ORFs and no virulence or antimicrobial resistance genes were annotated in the genome of phage BUCT700. Phage BUCT700 has a broad host range (28/43) and can lyse multiple ST types of clinical S. maltophilia (21/33). Furthermore, bacteriophage BUCT700 used the Type IV fimbrial biogenesis protein PilX as an adsorption receptor. In the stability test, phage BUCT700 showed excellent thermal stability (4 to 60°C) and pH tolerance (pH = 4 to 12). Moreover, phage BUCT700 was able to maintain a high titer during long-term storage. The adsorption curve and one-step growth curve showed that phage BUCT700 could rapidly adsorb to the surface of S. maltophilia and produce a significant number of phage virions. In vivo, BUCT700 significantly increased the survival rate of S. maltophilia-infected Galleria mellonella (G. mellonella) larvae from 0% to 100% within 72 h, especially in the prophylactic model. In conclusion, these findings indicate that phage BUCT700 has promising potential for clinical application either as a prophylactic or therapeutic agent. IMPORTANCE The risk of Stenotrophomonas maltophilia infections mediated by the medical devices is exacerbated with an increase in the number of ICU patients during the Corona Virus Disease 2019 (COVID-19) epidemic. Complications caused by S. maltophilia infections could complicate the state of an illness, greatly extending the length of hospitalization and increasing the financial burden. Phage therapy might be a potential and promising alternative for clinical treatment of multidrug-resistant bacterial infections. Here, we investigated the protective effects of phage BUCT700 as prophylactic and therapeutic agents in Galleria mellonella models of infection, respectively. This study demonstrates that phage therapy can provide protection in targeting S. maltophilia-related infection, especially as prophylaxis.

Coping with the ESKAPE pathogens: Evolving strategies, challenges and future prospects

Globally, the ESKAPE pathogens (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter species) are the major cause of nosocomial infections. These pathogens are multidrug resistant, and their negative impacts have brought serious health challenges and economic burden on many countries worldwide. Thus, this narrative review exploits different emerging alternative therapeutic strategies including combination antibiotics, antimicrobial peptides ((AMPs), bacteriophage and photodynamic therapies used in the treatment of the ESKAPE pathogens, their merits, limitations, and future prospects. Our findings indicate that ESKAPE pathogens exhibit resistance to drug using different mechanisms including drug inactivation by irreversible enzyme cleavage, drug-binding site alteration, diminution in permeability of drug or drug efflux increment to reduce accumulation of drug as well as biofilms production. However, the scientific community has shown significant interest in using these novel strategies with numerous benefits although they have some limitations including but not limited to instability and toxicity of the therapeutic agents, or the host developing immune response against the therapeutic agents. Thus, comprehension of resistance mechanisms of these pathogens is necessary to further develop or modify these approaches in order to overcome these health challenges including the barriers of bacterial resistance.

Characterisation and sequencing of the novel phage Abp95, which is effective against multi-genotypes of carbapenem-resistant Acinetobacter baumannii

Acinetobacter baumannii has become one of the most challenging conditional pathogens in health facilities. It causes various infectious diseases in humans, such as wound or urinary tract infections and pneumonia. Phage therapy has been used as an alternative strategy for antibiotic-resistant A. baumannii infections and has been approved by several governments. Previously, we have reported two potential phage therapy candidates, Abp1 and Abp9, both of which are narrow-host-range phages. In the present study, we screened and isolated 22 A. baumannii bacteriophages from hospital sewage water and determined that Abp95 has a wide host range (29%; 58/200). The biological and genomic characteristics and anti-infection potential of Abp95 were also investigated. Abp95 belongs to the Myoviridae family, with a G+C content of 37.85% and a genome size of 43,176 bp. Its genome encodes 77 putative genes, none of which are virulence, lysogeny, or antibiotic resistance genes. Abp95 was found to accelerate wound healing in a diabetic mouse wound infection model by clearing local infections of multidrug-resistant A. baumannii. In conclusion, the lytic phage Abp95, which has a wide host range, demonstrates potential as a candidate for phage therapy against multiple sequence types of carbapenem-resistant A. baumannii.

Morphological, biological and genomic characterization of lytic phages against Streptococcus agalactiae causing streptococcosis in tilapia

Streptococcus agalactiae, a highly invasive pathogen causing streptococcosis, is a major disease imparting devastating effect in the aquaculture, worldwide. As bacteriophage therapy is getting more attention recently, as an alternative viable biocontrol agent to antibiotic and vaccine, this study aimed to isolate and purify obligately lytic bacteriophages and study its morphological, genetic and biological characteristics. Host range analysis of the four bacteriophages isolated in this study, such as Phage- 12 P, 15 F, 16 E and 20D exhibited 100% infectivity to S. agalactiae serotype Ia, a predominant serotype infecting fish. Morphotype of the phages was revealed by HR-TEM and found that the phage 20D belong to the family Myoviridae and the phages 12 P, 15 F, 16 E belonged to the family Siphoviridae with typical head and tail structure. Lytic potential of the phages were ascertained by multiplicity of infection and one step lytic curve and it is found that the phages exhibit high burst size at an MOI of 0.01. Random amplified polymorphic DNA revealed the genetic diversity of these four phages with distinct banding pattern. The phages were found to be lytic with the absence of genes coding for integrase, transposase and recombinase on PCR based screening. Phages exhibited stability and viability at various physic-chemical parameters such as temperature ranging from 4 to 45 °C, pH of 4-12 and salinity ranging from 0 to 6%. Thus the present study revealed that S. agalactiae specific phages such as Phage- 12 P, 15 F, 16 E and 20D are highly stable and potential to eliminate the S. agalactiae serotype Ia infecting fish. After the complete characterization of the phages by whole genome sequencing and exploring the defense function against S. agalactiae infection in vivo, it may be applied as a therapeutic agent against S. agalactiae infection in aquaculture.

Animal model testing for efficacy and adverse effects of bacteriophages against Acinetobacter baumannii

This study aimed to conduct a detailed study on murine model testing of bacteriophage against Acinetobacter baumannii. These bacteriophages were tested not only for their efficacy in healing wound of murine models infected with multidrug resistant A. baumannii but were also studied for any derangement in hematological parameters as well as liver and kidney function. The study also included any histological changes observed in hepatic and renal tissues of the bacteriophage treated murine animals. This experimental study was conducted at Institute of Basic Medical Sciences, Khyber Medical University, Peshawar and Institute of Pure and Applied Biology, Department of Microbiology and Molecular Genetics, Bahauddin Zakariya University, Multan. A. baumannii isolates were obtained from the Microbiology Department, Armed Forces Institute of Pathology, Rawalpindi. Antimicrobial susceptibility was done by using standard procedures and as per Clinical Laboratory Standards Institute guidelines. Bacteriophages were isolated from sewage water samples collected from different hospitals in Multan. These bacteriophages were characterized and finally used for treating the murine model and efficacy of phage as a therapeutic option was determined by using superficial rat wound model. In this study, the isolated lytic bacteriophage was effective in relatively faster wound healing of the infected animals. Moreover, there were no significant hematological or renal and hepatic profile changes in treated animals. Histology of renal and hepatic tissues was also normal as compared to control animals. Our study concluded that the isolated phage could serve as an attractive therapeutic candidate to combat the deadly multidrug resistant A. baumannii.

In Vitro Techniques and Measurements of Phage Characteristics That Are Important for Phage Therapy Success

Validated methods for phage selection, host range expansion, and lytic activity determination are indispensable for maximizing phage therapy outcomes. In this review, we describe some relevant methods, highlighting their advantages and disadvantages, and categorize them as preliminary or confirmatory methods where appropriate. Experimental conditions, such as the composition and consistency of culture media, have an impact on bacterial growth and, consequently, phage propagation and the selection of phage-resistant mutants. The phages require different experimental conditions to be tested to fully reveal their characteristics and phage therapy potential in view of their future use in therapy. Phage lytic activity or virulence should be considered as a result of the phage, its host, and intracellular/environmental factors, including the ability of a phage to recognize receptors on the bacterial cell surface. In vitro quantitative and qualitative measurements of phage characteristics, further validated by in vivo experiments, could be incorporated into one system or mathematical model/formula, which could predict a potential successful outcome of clinical applications.

Isolation and Characterization of a Novel Siphoviridae Phage, vB_AbaS_TCUP2199, Infecting Multidrug-Resistant Acinetobacter baumannii

Multidrug-resistant Acinetobacter baumannii (MDRAB) is a pathogen recognized as antimicrobial-resistant bacteria involved in healthcare-associated infections. Resistance to antibiotics has made alternative therapies necessary. Bacteriophage therapy is considered a potential solution to treat MDRAB. In this study, we isolated and characterized the phage vB_AbaS_TCUP2199 (TCUP2199), which can infect MDRAB. Morphological analysis revealed that TCUP2199 belongs to the Siphoviridae family. TCUP2199 has a wide host range, can adsorb rapidly (68.28% in 2 min), and has a burst size of 196 PFU/cell. At least 16 distinct structural proteins were visualized by SDS polyacrylamide gel electrophoresis. A stability test showed that TCUP2199 was stable at 37 °C and pH 7. Genome analysis of TCUP2199 showed that it consists of a double-stranded DNA genome of 79,572 bp with a G+C content of 40.39%, which contains 98 putative open reading frames, none of which is closely related to the bacteriophage genome sequence that was found in the public database. TCUP2199 shows similarity in genomic organization and putative packaging mechanism with Achromobacter phage JWF and Pseudoalteromonas phage KB12-38 based on protein BLAST and phylogenetic analysis. Because of those unique characteristics, we consider TCUP2199 to be a novel phage that is suitable for inclusion in a phage cocktail to treat A. baumannii infection.

Bacteriophage therapeutics to confront multidrug-resistant Acinetobacter baumannii - a global health menace

We have already entered the post-antibiotic era as the outbreaks of numerous multidrug-resistant strains in the community as well as hospital-acquired infections are ringing alarm bells in the health sector. Acinetobacter baumannii is one such pathogen that has been considered a worldwide threat as it acquires multidrug resistance. It is one of the most challenging hospital-acquired pathogens as World Health Organization has listed carbapenem-resistant A. baumannii as a critical priority pathogen with limited therapeutic options. There is an urgent need to develop novel strategies against such pathogens to tackle the global crisis. Bacteriophages (phages), especially the lytic ones have re-emerged as a potential therapeutic approach. This review encompasses vast majority of phages against A. baumannii strains with special references related to single phage or monophage therapy, use of phage cocktails, combination therapy with antibiotics, use of phage-derived enzymes like endolysins and depolymerases to combat the pathogen and explore their therapeutic aspects. The concurrent ecological as well as evolutionary interplay between the phages and host bacteria demands in depth-research and knowledge, so as to utilize the maximum potential of the bacteriophage therapy.

Isolation, Characterization, and Genomic Analysis of Three Novel E. coli Bacteriophages That Effectively Infect E. coli O18

Escherichia coli (E. coli) is one of the most common pathogenic bacteria worldwide. Avian pathogenic E. coli (APEC) causes severe systemic disease in poultry (Colibacillosis), and accordingly, has an extreme risk to the poultry industry and public health worldwide. Due to the increased rate of multi-drug resistance among these bacteria, it is necessary to find an alternative therapy to antibiotics to treat such infections. Bacteriophages are considered one of the best solutions. This study aimed to isolate, characterize, and evaluate the potential use of isolated bacteriophages to control E. coli infections in poultry. Three novel phages against E. coli O18 were isolated from sewage water and characterized in vitro. The genome size of the three phages was estimated to be 44,776 bp, and the electron microscopic analysis showed that they belonged to the Siphoviridae family, in the order Caudovirales. Phages showed good tolerance to a broad range of pH and temperature. The complete genomes of three phages were sequenced and deposited into the GenBank database. The closely related published genomes of Escherichia phages were identified using BLASTn alignment and phylogenetic trees. The prediction of the open reading frames (ORFs) identified protein-coding genes that are responsible for functions that have been assigned such as cell lysis proteins, DNA packaging proteins, structural proteins, and DNA replication/transcription/repair proteins.

The characteristic and potential therapeutic effect of isolated multidrug-resistant Acinetobacter baumannii lytic phage

BACKGROUND

Widespread misuse of antibiotics caused bacterial resistance increasingly become a serious threat. Bacteriophage therapy promises alternative treatment strategies for combatting drug-resistant bacterial infections. In this study, we isolated and characterized a novel, potent lytic bacteriophage against multi-drug resistant (MDR) Acinetobacter baumannii and described the lytic capability and endolysin activity of the phage to evaluate the potential in phage therapy.

METHODS

A novel phage, pIsf-AB02, was isolated from hospital sewage. The morphological analysis, its host range, growth characteristics, stability under various conditions, genomic restriction pattern were systematically investigated. The protein pattern of the phage was analyzed, and the endolysin activity of the phage was determined under the non-denaturing condition on SDS-PAGE. The optimal lytic titer of phage was assessed by co-culture of the phage with clinical MDR A. baumannii isolates. Finally, HeLa cells were used to examine the safety of the phage.

RESULTS

The morphological analysis revealed that the pIsf-AB02 phage displays morphology resembling the Myoviridae family. It can quickly destroy 56.3% (27/48) of clinical MDR A. baumannii isolates. This virulent phage could decrease the bacterial host cells (from 10⁸ CFU/ml to 10³ CFU/ml) in 30 min. The optimum stability of the phage was observed at 37 °C. pH 7 is the most suitable condition to maintain phage stability. The 15 kDa protein encoded by pIsf-AB02 was detected to have endolysin activity. pIsf-AB02 did not show cytotoxicity to HeLa cells, and it can save HeLa cells from A. baumannii infection.

CONCLUSION

In this study, we isolated a novel lytic MDR A. baumannii bacteriophage, pIsf-AB02. This phage showed suitable stability at different temperatures and pHs, and demonstrated potent in vitro endolysin activity. pIsf-AB02 may be a good candidate as a therapeutic agent to control nosocomial infections caused by MDR A. baumannii.

Novel lytic bacteriophage vB_GEC_EfS_9 against Enterococcus faecium

Enterococcus spp. is a common commensal microorganism, however, some strains can cause opportunistic infections in humans. Treatment of Enterococcus faecium-related endocarditis, urinary and genital tract infections, meningitis, septicemia, and even neonatal sepsis is often complicated by antibiotic resistance. The spread of multi-resistant bacterial strains has renewed interest in phage therapy, which has many advantages: Its advantages include a much lower frequency of resistance development compared to antibiotics and strict specificity, which allows affecting of only their target microbes without disturbing necessary microbiome. We isolated and characterized a virulent bacteriophage which is active against Enterococcus faecium clinical strains. The phage, which was designated as vB_GEC_EfS_9 was studied in terms of its growth pattern and adsorption rate, as well as its host range. The whole genome of the phage was sequenced and analyzed. Obtained results indicate that phage vB_GEC_EfS_9 is a virulent phage which has a very good potential for therapeutic use against strains of E. faecium.

Isolation, characterization, and effectiveness of bacteriophage Pɸ-Bw-Ab against XDR Acinetobacter baumannii isolated from nosocomial burn wound infection

OBJECTIVES

With emergence of drug resistance, novel approaches such as phage therapy for treatment of bacterial infections have received significant attention. The purpose of this study was to isolate and identify effective bacteriophages on extremely drug-resistant (XDR) bacteria isolated from burn wounds.

MATERIALS AND METHODS

Pathogenic bacteria were isolated from hospitalized patient wounds in specialized burn hospitals in Iran, and their identification was performed based on biochemical testing and sequencing of the gene encoding 16S rRNA. Bacteriophages were isolated from municipal sewage, Isfahan, Iran. The phage morphology was observed by TEM. After detection of the host range, adsorption rate, and one-step growth curve, the phage proteomics pattern and restriction enzyme digestion pattern were analyzed.

RESULTS

All isolates of bacteria were highly resistant to antibiotics. Among isolates, Acinetobacter baumannii strain IAU_FAL101 (GenBank accession number: MW845680), which was an XDR bacterium, showed significant sensitivity to phage Pɸ-Bw-Ab. TEM determined the phage belongs to Siphoviridae. They had double-stranded DNA. This phage showed the highest antibacterial effect at 15 ^°C and pH 7. Analysis of the restriction enzyme digestion pattern showed Pɸ-Bw-Ab phage was sensitive to most of the used enzymes and based on SDS-PAGE, protein profiles were revealed 43 to 90 kDa.

CONCLUSION

Considering the potential ability of the isolated phage, it had an antibacterial impact on other used bacterial spp and also strong antibacterial effects on XDR A. baumannii. Also, it had long latency and low burst size. This phage can be a suitable candidate for phage therapy.

Topically Applied Bacteriophage to Control Multi-Drug Resistant Klebsiella pneumoniae Infected Wound in a Rat Model

(Background): Multi-drug-resistant Klebsiella pneumoniae (MDR-KP) has steadily grown beyond antibiotic control. Wound infection kills many patients each year, due to the entry of multi-drug resistant (MDR) bacterial pathogens into the skin gaps. However, a bacteriophage (phage) is considered to be a potential antibiotic alternative for treating bacterial infections. This research aims at isolating and characterizing a specific phage and evaluate its topical activity against MDR-KP isolated from infected wounds. (Methods): A lytic phage ZCKP8 was isolated by using a clinical isolate KP/15 as a host strain then characterized. Additionally, phage was assessed for its in vitro host range, temperature, ultraviolet (UV), and pH sensitivity. The therapeutic efficiency of phage suspension and a phage-impeded gel vehicle were assessed in vivo against a K. pneumoniae infected wound on a rat model. (Result): The phage produced a clear plaque and was classified as Siphoviridae. The phage inhibited KP/15 growth in vitro in a dose-dependent pattern and it was found to resist high temperature (˂70 °C) and was primarily active at pH 5; moreover, it showed UV stability for 45 min. Phage-treated K. pneumoniae inoculated wounds showed the highest healing efficiency by lowering the infection. The quality of the regenerated skin was evidenced via histological examination compared to the untreated control group. (Conclusions): This research represents the evidence of effective phage therapy against MDR-KP.

Advances in Bacteriophage Therapy against Relevant MultiDrug-Resistant Pathogens

The increase of multiresistance in bacteria and the shortage of new antibiotics in the market is becoming a major public health concern. The World Health Organization (WHO) has declared critical priority to develop new antimicrobials against three types of bacteria: carbapenem-resistant A. baumannii, carbapenem-resistant P. aeruginosa and carbapenem-resistant and ESBL-producing Enterobacteriaceae. Phage therapy is a promising alternative therapy with renewed research in Western countries. This field includes studies in vitro, in vivo, clinical trials and clinical cases of patients receiving phages as the last resource after failure of standard treatments due to multidrug resistance. Importantly, this alternative treatment has been shown to be more effective when administered in combination with antibiotics, including infections with biofilm formation. This review summarizes the most recent studies of this strategy in animal models, case reports and clinical trials to deal with infections caused by resistant A. baumannii, K. pneumoniae, E. coli, and P. aeruginosa strains, as well as discusses the main limitations of phage therapy.

A plethora of carbapenem resistance in Acinetobacter baumannii: no end to a long insidious genetic journey

Acinetobacter baumannii, notorious for causing nosocomial infections especially in patients admitted to intensive care unit (ICU) and burn units, is best at displaying resistance to all existing antibiotic classes. Consequences of high potential for antibiotic resistance has resulted in extensive drug or even pan drug resistant A. baumannii. Carbapenems, mainly imipenem and meropenem, the last resort for the treatment of A. baumannii infections have fallen short due to the emergence of carbapenem resistant A. baumannii (CRAB). Though enzymatic degradation by production of class D β-lactamases (Oxacillinases) and class B β-lactamases (Metallo β-lactamases) is the core mechanism of carbapenem resistance in A. baumannii; however over-expression of efflux pumps such as resistance-nodulation cell division (RND) family and variant form of porin proteins such as CarO have been implicated for CRAB inception. Transduction and outer membrane vesicles-mediated transfer play a role in carbapenemase determinants spread. Colistin, considered as the most promising antibacterial agent, nevertheless faces adverse effects flaws. Cefiderocol, eravacycline, new β-lactam antibiotics, non-β-lactam-β-lactamase inhibitors, polymyxin B-derived molecules and bacteriophages are some other new treatment options streamlined.

The clinical path to deliver encapsulated phages and lysins

The global emergence of multidrug-resistant pathogens is shaping the current dogma regarding the use of antibiotherapy. Many bacteria have evolved to become resistant to conventional antibiotherapy, representing a health and economic burden for those afflicted. The search for alternative and complementary therapeutic approaches has intensified and revived phage therapy. In recent decades, the exogenous use of lysins, encoded in phage genomes, has shown encouraging effectiveness. These two antimicrobial agents reduce bacterial populations; however, many barriers challenge their prompt delivery at the infection site. Encapsulation in delivery vehicles provides targeted therapy with a controlled compound delivery, surpassing chemical, physical and immunological barriers that can inactivate and eliminate them. This review explores phages and lysins' current use to resolve bacterial infections in the respiratory, digestive, and integumentary systems. We also highlight the different challenges they face in each of the three systems and discuss the advances towards a more expansive use of delivery vehicles.

Bacteriophages for ESKAPE: role in pathogenicity and measures of control

INTRODUCTION

The quest to combat bacterial infections has dreaded humankind for centuries. Infections involving ESKAPE (Enterococcus spp., Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter spp.) impose therapeutic challenges due to the emergence of antimicrobial drug resistance. Recently, investigations with bacteriophages have led to the development of novel strategies against ESKAPE infections. Also, bacteriophages have been demonstrated to be instrumental in the dissemination of virulence markers in ESKAPE pathogens.

AREAS COVERED

The review highlights the potential of bacteriophage in and against the pathogenicity of antibiotic-resistant ESKAPE pathogens. The review also emphasizes the challenges of employing bacteriophage in treating ESKAPE pathogens and the knowledge gap in the bacteriophage mediated antibiotic resistance and pathogenicity in ESKAPE infections.

EXPERT OPINION

Bacteriophage infection can kill the host bacteria but in survivors can transfer genes that contribute toward the survival of the pathogens in the host and resistance toward multiple antimicrobials. The knowledge on the dual role of bacteriophages in the treatment and pathogenicity will assist in the prediction and development of novel therapeutics targeting antimicrobial-resistant ESKAPE. Therefore, extensive investigations on the efficacy of synthetic bacteriophage, bacteriophage cocktails, and bacteriophage in combination with antibiotics are needed to develop effective therapeutics against ESKAPE infections.

Trends and Development in the Antibiotic-Resistance of Acinetobacter baumannii: A Scientometric Research Study (1991-2019)

Objective

Data visualization software were used to display and analyze the research status, hotspot and development trend of the antibiotic-resistance of Acinetobacter baumannii objectively and comprehensively, so as to provide guidance and reference for the research of the antibiotic-resistant Acinetobacter baumannii.

Materials and Methods

The data of relevant publications on antibiotic-resistant Acinetobacter baumanii from 1991 to 2019 were retrieved from Web of Science (WOS) Core database. VOSviewer and CiteSpace software were used to conduct co-citation visualization network rendering and cluster analysis on the publications’ years, authors, countries, institutions, keywords and citations.

Results

A total of 3915 valid records on the study of antibiotic-resistant Acinetobacter baumanii were retrieved. The number of relevant publications was increasing year after year. The United States is the most influential country in the field, which works closely with other countries and publishes most of the papers. University of Sydney is the leading institution in this area. Bonomo Robert A publishes most of the papers. There are the highest number of publications in the research areas of antimicrobial agents and chemotherapy. “Nucleotide sequence” and “outbreak” were once the hotspots in this field, but recently “bacteriophage”, “biofilm” and “colistin resistance” have become the research hotspots.

Conclusion

Since 1991, the number of publications on antibiotic-resistant Acinetobacter baumannii has grown rapidly, and various countries and institutions have paid close attention to the problem of antibiotic resistance. Countries, institutions and researchers, which have strong influential power, collaborate with each other closely. The future research direction of antibiotic-resistant Acinetobacter baumannii should lie in the further breakthrough of antibacterial peptides, bacteriophage therapy, CRISPR system and various combined therapies.

Characterization, Antibiofilm, and Depolymerizing Activity of Two Phages Active on Carbapenem-Resistant Acinetobacter baumannii

Acinetobacter baumannii is a leading cause of healthcare-associated infections worldwide. Its various intrinsic and acquired mechanisms of antibiotic resistance make the therapeutic challenge even more serious. One of the promising alternative treatments that is increasingly highlighted is phage therapy, the therapeutic use of bacteriophages to treat bacterial infections. Two phages active against nosocomial carbapenem-resistant A. baumannii strain 6077/12, vB_AbaM_ISTD, and vB_AbaM_NOVI, were isolated from Belgrade wastewaters, purified, and concentrated using CsCl gradient ultracentrifugation. The phages were screened against 103 clinical isolates of A. baumannii from a laboratory collection and characterized based on plaque and virion morphology, host range, adsorption rate, and one-step growth curve. Given that phage ISTD showed a broader host range, better adsorption rate, shorter latent period, and larger burst size, its ability to lyse planktonic and biofilm-embedded cells was tested in detail. Phage ISTD yielded a 3.5- and 2-log reduction in planktonic and biofilm-associated viable bacterial cell count, respectively, but the effect was time-dependent. Both phages produced growing turbid halos around plaques indicating the synthesis of depolymerases, enzymes capable of degrading bacterial exopolysaccharides. Halos tested positive for presence of phages in the proximity of the plaque, but not further from the plaque, which indicates that the observed halo enlargement is a consequence of enzyme diffusion through the agar, independently of the phages. This notion was also supported by the growing halos induced by phage preparations applied on pregrown bacterial lawns, indicating that depolymerizing effect was achieved also on non-dividing sensitive cells. Overall, good rates of growth, fast adsorption rate, broad host range, and high depolymerizing activity, as well as antibacterial effectiveness against planktonic and biofilm-associated bacteria, make these phages good candidates for potential application in combating A. baumannii infections.

Transdermal permeation of bacteriophage particles by choline oleate: potential for treatment of soft-tissue infections

Aim: A sodium alginate-based biohydrogel was prepared integrating choline oleate deep euthetic solvent as facilitator of transdermal delivery and a cocktail of lytic bacteriophages for Acinetobacter baumannii, aiming at treating soft-tissue infections by the aforementioned pathogen. Materials & methods: Two bacteriophages were isolated from a hospital sewage and a wastewater treatment plant sewage in Sorocaba (Brazil), and characterized via SDS-PAGE electrophoresis, transmission electron microscope and evaluation of lytic spectra of the bacteriophage cocktail. The biohydrogel was prepared and characterized by DSC, FTIR, XRD, DESEM, XRT and transdermal permeation of the bacteriophage cocktail. Results & conclusion: The physico-chemical characterization of the biohydrogel produce indicated adequate structural characteristics and ability to promote/facilitate transdermal delivery of bacteriophage particles, thus showing potential for biopharmaceutical applications.

Antibiotic Resistance Profiles, Molecular Mechanisms and Innovative Treatment Strategies of Acinetobacter baumannii

Antibiotic resistance is one of the biggest challenges for the clinical sector and industry, environment and societal development. One of the most important pathogens responsible for severe nosocomial infections is Acinetobacter baumannii, a Gram-negative bacterium from the Moraxellaceae family, due to its various resistance mechanisms, such as the β-lactamases production, efflux pumps, decreased membrane permeability and altered target site of the antibiotic. The enormous adaptive capacity of A. baumannii and the acquisition and transfer of antibiotic resistance determinants contribute to the ineffectiveness of most current therapeutic strategies, including last-line or combined antibiotic therapy. In this review, we will present an update of the antibiotic resistance profiles and underlying mechanisms in A. baumannii and the current progress in developing innovative strategies for combating multidrug-resistant A. baumannii (MDRAB) infections.

Characterization and Genome Structure of Virulent Phage EspM4VN to Control Enterobacter sp. M4 Isolated From Plant Soft Rot

Enterobacter sp. M4 and other bacterial strains were isolated from plant soft rot disease. Virulent phages such as EspM4VN isolated from soil are trending biological controls for plant disease. This phage has an icosahedral head (100 nm in diameter), a neck, and a contractile sheath (100 nm long and 18 nm wide). It belongs to the Ackermannviridae family and resembles Shigella phage Ag3 and Dickeya phages JA15 and XF4. We report herein that EspM4VN was stable from 10°C to 50°C and pH 4 to 10 but deactivated at 70°C and pH 3 and 12. This phage formed clear plaques only on Enterobacter sp. M4 among tested bacterial strains. A one-step growth curve showed that the latent phase was 20 min, rise period was 10 min, and an average of 122 phage particles were released from each absorbed cell. We found the phage’s genome size was 160,766 bp and that it annotated 219 open reading frames. The genome organization of EspM4VN has high similarity with the Salmonella phage SKML-39; Dickeya phages Coodle, PP35, JA15, and Limestone; and Shigella phage Ag3. The phage EspM4VN has five tRNA species, four tail-spike proteins, and a thymidylate synthase. Phylogenetic analysis based on structural proteins and enzymes indicated that EspM4VN was identified as a member of the genus Agtrevirus, subfamily Aglimvirinae, family Ackermannviridae.

Potential of a Bacteriophage Isolated from Wastewater in Treatment of Lobar Pneumonia Infection Induced by Klebsiella pneumoniae in Mice

The potential of bacteriophages as alternative treatment for multidrug-resistant (MDR) Klebsiella pneumoniae-related infections has recently gained much interest. The purpose of this research was to isolate and characterize a K. pneumoniae-specific lytic phage with the potential to treat experimental lobar pneumonia induced by K. pneumoniae in mice. A lytic phage was isolated from an urban wastewater sample in Tehran and characterized by transmission electron microscopy (TEM), thermal, pH, and chloroform stability before being employed for treatment of mice infected with K. pneumoniae in an experimental model of lobar pneumonia. BALB/C mice were challenged by intranasal inoculation with 10⁸ colony-forming units (CFU/ml) of K. pneumoniae ATCC 10031 followed by an intraperitoneal injection of the isolated phage using 10¹⁰ and 10⁹ plaque-forming units (PFU/ml) simultaneously or 24 h post infection. Control groups of mice received bacteria or bacteriophage alone. Mice were euthanized daily up to 7 days post infection and examined for abnormality in their lungs and livers followed by determining the number of phages and bacteria in plasma and lung homogenates. The isolated phage (vB_KpnM-Teh.1) belonged to the Myoviridae family, was stable at 37 °C, pH 7, and was resistant to chloroform. Treatment of mice with a single dose of phage simultaneously at the time of infection, or 24 h post infection, resulted in seven and five logs decrease of CFU/ml in the lung homogenates up to 3 days after phage administration, respectively. The isolated phage may have the potential as a therapeutic agent against K. pneumoniae infections.

Bacteriophages, a New Therapeutic Solution for Inhibiting Multidrug-Resistant Bacteria Causing Wound Infection: Lesson from Animal Models and Clinical Trials

Wound infection kills a large number of patients worldwide each year. Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, and Pseudomonas aeruginosa are the most important colonizing pathogens of wounds that, with various virulence factors and impaired immune system, causes extensive tissue damage and nonhealing wounds. Furthermore, the septicemia caused by these pathogens increases the mortality rate due to wound infections. Because of the prevalence of antibiotic resistance in recent years, the use of antibiotics to inhibit these pathogens has been restricted, and the topical application of antibiotics in wound infections increases antibiotic resistance. Therefore, finding a new therapeutic strategy against wound infections is so essential since these infections have a destructive effect on the patient’s mental health and high medical costs. In this review, we discussed the use of phages for the prevention of multidrug-resistant (MDR) bacteria, causing wound infection and their role in wound healing in animal models and clinical trials. The results showed that phages have a high ability to inhibit different wound infections caused by MDR bacteria, heal the wound faster, have lower side effects and toxicity, destroy bacterial biofilm, and they are useful in controlling immune responses. Many studies have used animal models to evaluate the function of phages, and this study appears to have a positive impact on the use of phages in clinical practice and the development of a new therapeutic approach to control wound infections, although there are still many limitations.

Genetic mechanisms of antibiotic resistance and virulence in Acinetobacter baumannii: background, challenges and future prospects

With the advent of the multidrug-resistant era, many opportunistic pathogens including the species Acinetobacter baumannii have gained prominence and pose a major global threat to clinical health care. Pathogenicity in bacteria is genetically regulated by a complex network of transcription and virulence factors and a brief overview of the major investigations on comprehending these processes over the past few decades in A. baumanni are compiled here. Many investigators have employed genome sequencing techniques to identify the regions that contribute to antibiotic resistance and comparative genomics to study sequence similarities to understand evolutionary trends of resistance gene transfers between isolates. A summary of these studies given here provides an insight into the invasion and successful colonization of the species. The individual roles played by different genes, regulators & promoters, enzymes, metal ions as well as mobile elements in influencing antibiotic resistance are briefly discussed. Precautionary measures and prospects for developing future strategies by exploring promising new research targets in effective control of multidrug resistant A. baumannii are also analyzed.

Characterization and genome analysis of novel Klebsiella phage Henu1 with lytic activity against clinical strains of Klebsiella pneumoniae

Klebsiella pneumoniae is an important human pathogen that is associated with a wide range of diseases, including pneumonia and septicemia. Because of the threat of drug-resistant K. pneumoniae to humans, especially carbapenem-resistant K. pneumoniae, which is becoming a growing threat to hospitalized patients, the potential use of phage therapy has generated considerable interest. Henu1, isolated from a sewage sample, was identified as a linear double-stranded DNA phage of 40,352 bp with 53.14% G + C content and 143-bp terminal repeats. The Henu1 genome contains 45 open reading frames, and no tRNA genes were found. K. pneumoniae clinical strains with the capsular types K-1, K-2, and K-57 could be infected by Henu1. No human-virulence-related genes or lysogen-formation gene clusters were detected in this phage genome, suggesting that Henu1 is a virulent phage in its bacterial host and is safe for humans.

Specific and Selective Bacteriophages in the Fight against Multidrug-resistant Acinetobacter baumannii

Acinetobacter baumannii causes serious infections especially in immunocompromised and/or hospitalized patients. Several A. baumannii strains are multidrug resistant and infect wounds, bones, and the respiratory tract. Current studies are focused on finding new effective agents against A. baumannii. Phage therapy is a promising means to fight this bacterium and many studies on procuring and applying new phages against A. baumannii are currently being conducted. As shown in animal models, phages against multidrug-resistant A. baumannii may control bacterial infections caused by this pathogen and may be a real hope to solve this dangerous health problem.

Efficacy of bacteriophage treatment against carbapenem-resistant Acinetobacter baumannii in Galleria mellonella larvae and a mouse model of acute pneumonia

Background

Acinetobacter baumannii is an opportunistic pathogen that causes serious nosocomial infection in intensive care units. In particular, carbapenem-resistant A. baumannii (CRAB) strains have been increasing in the past decade, and they have caused major medical problems worldwide. In this study, a novel A. baumannii lytic phage, the YMC 13/03/R2096 ABA BP (phage Βϕ-R2096), which specifically causes the lysis of CRAB strains, was characterized in detail in vitro and in silico, and the in vivo effectiveness of phage therapy was evaluated using Galleria mellonella and a mouse model of acute pneumonia.

Results

The A. baumannii phage Βϕ-R2096 was isolated from sewage water using CRAB clinical strains selected from patients at a university hospital in South Korea. The complete genome of the phage Βϕ-R2096, which belongs to the Myoviridae family, was analyzed. Phage Βϕ-R2096 inhibited bacterial growth in a dose-dependent manner and exhibited high bacteriolytic activity at MOI = 10. In the evaluation of its therapeutic potential against CRAB clinical isolates using two in vivo models, phage Βϕ-R2096 increased the survival rates of both G. mellonella larvae (from 0 to 50% at 24 h) and mice (from 30% with MOI = 0.1 to 100% with MOI = 10 for 12 days) in post-infection of CRAB. In particular, phage Βϕ-R2096 strongly ameliorated histologic damage to infected lungs, with bacterial clearance in the lungs observed on day 3 postinfection in the mouse acute pneumonia model. Moreover, in vivo studies revealed no mortality or serious side effects in phage-treated groups.

Conclusion

The results of this study strongly suggest that phage Βϕ-R2096, a novel A. baumannii lytic phage, could be an alternative antibacterial agent to control CRAB infections. This study is the first report to compare in vivo evaluations (G. mellonella larvae and a mouse acute pneumonia model) of the therapeutic efficacy of a phage against CRAB infections.

Electronic supplementary material

The online version of this article (10.1186/s12866-019-1443-5) contains supplementary material, which is available to authorized users.

A Novel Phage PD-6A3, and Its Endolysin Ply6A3, With Extended Lytic Activity Against Acinetobacter baumannii

With widespread abuse of antibiotics, bacterial resistance has increasingly become a serious threat. Acinetobacter baumannii has emerged as one of the most important hospital-acquired pathogens worldwide. Bacteriophages (also called “phages”) could be used as a potential alternative therapy to meet the challenges posed by such pathogens. Endolysins from phages have also been attracting increasing interest as potential antimicrobial agents. Here, we isolated 14 phages against A. baumannii, determined the lytic spectrum of each phage, and selected one with a relatively broad host range, named vB_AbaP_PD-6A3 (PD-6A3 for short), for its biological characteristics. We over-expressed and purified the endolysin (Ply6A3) from this phage and tested its biological characteristics. The PD-6A3 is a novel phage, which can kill 32.4% (179/552) of clinical multidrug resistant A. baumannii (MDRAB) isolates. Interestingly, in vitro, this endolysin could not only inhibit A. baumannii, but also that of other strains, such as Escherichia coli and methicillin-resistant Staphylococcus aureus (MRSA). We found that lethal A. baumannii sepsis mice could be effectively rescued in vivo by phage PD-6A3 and endolysin Ply6A3 intraperitoneal injection. These characteristics reveal the promising potential of phage PD-6A3 and endolysin Ply6A3 as attractive candidates for the control of A. baumannii-associated nosocomial infections.

Skin and Soft Tissue Models for Acinetobacter baumannii Infection

Multidrug-resistant A. baumannii are important Gram-negative pathogens causing persistent wound infections in both wounded and burned victims, which often result in secondary complications such as delayed wound healing, skin graft failure, and sometimes more serious outcomes such as sepsis and amputation. The choice of antibiotics to remediate these A. baumannii infections is becoming limited; and therefore, there has been a renewed interest in the research and development of new antibacterials targeting this pathogen. However, the evaluation of safety and efficacy is made more difficult by the lack of well-established in vivo models. This chapter describes established rodent and large animal models that have been used to investigate and develop treatments for A. baumannii skin and soft tissue infections.

New Treatment Options against Carbapenem-Resistant Acinetobacter baumannii Infections

Carbapenem-resistant Acinetobacter baumannii (CRAB) is a perilous nosocomial pathogen causing substantial morbidity and mortality. Current treatment options for CRAB are limited and suffer from pharmacokinetic limitations, such as high toxicity and low plasma levels. As a result, CRAB is declared as the top priority pathogen by the World Health Organization for the investment in new drugs. This urgent need for new therapies, in combination with faster FDA approval process, accelerated new drug development and placed several drug candidates in the pipeline. This article reviews available information about the new drugs and other therapeutic options focusing on agents in clinical or late-stage preclinical studies for the treatment of CRAB, and it evaluates their expected benefits and potential shortcomings.

Bacteriophage Therapy: Clinical Trials and Regulatory Hurdles

Increasing reports of antimicrobial resistance and limited new antibiotic discoveries and development have fuelled innovation in other research fields and led to a revitalization of bacteriophage (phage) studies in the Western world. Phage therapy mainly utilizes obligately lytic phages to kill their respective bacterial hosts, while leaving human cells intact and reducing the broader impact on commensal bacteria that often results from antibiotic use. Phage therapy is rapidly evolving and has resulted in cases of life-saving therapeutic use and multiple clinical trials. However, one of the biggest challenges this antibiotic alternative faces relates to regulations and policy surrounding clinical use and implementation beyond compassionate cases. This review discusses the multi-drug resistant Gram-negative pathogens of highest critical priority and summarizes the current state-of-the-art in phage therapy targeting these organisms. It also examines phage therapy in humans in general and the approaches different countries have taken to introduce it into clinical practice and policy. We aim to highlight the rapidly advancing field of phage therapy and the challenges that lie ahead as the world shifts away from complete reliance on antibiotics.

Characterization of bacteriophage HN48 and its protective effects in Nile tilapia Oreochromis niloticus against Streptococcus agalactiae infections

Streptococcus agalactiae is a causative agent responsible for massive mortalities of tilapia that has led to catastrophic losses to tilapia culture globally. Bacteriophages represent a new class of antimicrobials against bacteria. In this study, we characterized the bacteriophage HN48, which formed small and round-transparent plaques on a double-layer plate. With a hexagonal head and a long tail, this phage may belong to the Caudovirales according to the International Committee on Taxonomy of Viruses. HN48 was found to have a relatively wide and highly specific host range, to be sensitive to high temperature (60-80°C) and low pH (3-5), and to be relatively stable at alkaline pH (8-10). Intraperitoneal injection with HN48 had no adverse effects on tilapia and effectively inactivated the bacteria in the kidney. Fish that received phage therapy had 60% ± 3.3% survival rates and a delayed mean death time of about 3 days when compared to the control group. To the best of knowledge, this is the first study of tilapia streptococcal phage. Overall, the results indicated that phage HN48 could prevent tilapia from experimental S. agalactiae infection, suggesting it has the potential to control this disease.

Bacteriophage therapy as an alternative treatment for human infections. A comprehensive review

Bacteriophages, or phages, are viruses that infect bacteria. They were discovered around a century ago and have been used ever since for therapeutic purposes, particularly in former Soviet Union countries. Their use in Western countries was abandoned after the discovery and broad use of penicillin. The rising problem of antimicrobial resistance has revived interest in bacteriophage therapy. The aim of this article is to provide a comprehensive review of all aspects of natural phage therapy.

Characterization of Two Novel Bacteriophages Infecting Multidrug-Resistant (MDR) Acinetobacter baumannii and Evaluation of Their Therapeutic Efficacy in Vivo

Acinetobacter baumannii is emerging as a challenging nosocomial pathogen due to its rapid evolution of antibiotic resistance. We report characterization of two novel bacteriophages, PBAB08 and PBAB25, infecting clinically isolated, multidrug-resistant (MDR) A. baumannii strains. Both phages belonged to Myoviridae of Caudovirales as their morphology observed under an electron microscope. Their genomes were double stranded linear DNAs of 42,312 base pairs and 40,260 base pairs, respectively. The two phages were distinct from known Acinetobacter phages when whole genome sequences were compared. PBAB08 showed a 99% similarity with 57% sequence coverage to phage AB1 and PBAB25 showed a 97% similarity with 78% sequence coverage to phage IME_AB3. BLASTN significant alignment coverage of all other known phages were <30%. Seventy six and seventy genes encoding putative phage proteins were found in the genomes of PBAB08 and PBAB25, respectively. Their genomic organizations and sequence similarities were consistent with the modular theory of phage evolution. Therapeutic efficacy of a phage cocktail containing the two and other phages were evaluated in a mice model with nasal infection of MDR A. baumannii. Mice treated with the phage cocktail showed a 2.3-fold higher survival rate than those untreated in 7 days post infection. In addition, 1/100 reduction of the number of A. baumannii in the lung of the mice treated with the phage cocktail was observed. Also, inflammatory responses of mice which were injected with the phage cocktail by intraperitoneal, intranasal, or oral route was investigated. Increase in serum cytokine was minimal regardless of the injection route. A 20% increase in IgE production was seen in intraperitoneal injection route, but not in other routes. Thus, the cocktail containing the two newly isolated phages could serve as a potential candidate for therapeutic interventions to treat A. baummannii infections.

Recent advances on topical antimicrobials for skin and soft tissue infections and their safety concerns

Antimicrobial resistance of disease-related microorganisms is considered a worldwide prevalent and serious issue which increases the failure of treatment outcomes and leads to high mortality. Considering that the increased resistance to systemic antimicrobial therapy often needs of the use of more toxic agents, topical antimicrobial therapy emerges as an attractive route for the treatment of infectious diseases. The topical antimicrobial therapy is based on the absorption of high drug doses in a readily accessible skin surface, resulting in a reduction of microbial proliferation at infected skin sites. Topical antimicrobials retain the following features: (a) they are able to escape the enzymatic degradation and rapid clearance in the gastrointestinal tract or the first-pass metabolism during oral administration; (b) alleviate the physical discomfort related to intravenous injection; (c) reduce possible adverse effects and drug interactions of systemic administrations; (d) increase patient compliance and convenience; and (e) reduce the treatment costs. Novel antimicrobials for topical application have been widely exploited to control the emergence of drug-resistant microorganisms. This review provides a description of antimicrobial resistance, common microorganisms causing skin and soft tissue infections, topical delivery route of antimicrobials, safety concerns of topical antimicrobials, recent advances, challenges and future prospective in topical antimicrobial development.

Phage therapy: awakening a sleeping giant

For a century, bacterial viruses called bacteriophages have been exploited as natural antibacterial agents. However, their medicinal potential has not yet been exploited due to readily available and effective antibiotics. After years of extensive use, both properly and improperly, antibiotic-resistant bacteria are becoming more prominent and represent a worldwide public health threat. Most importantly, new antibiotics are not progressing at the same rate as the emergence of resistance. The therapeutic modality of bacteriophages, called phage therapy, offers a clinical option to combat bacteria associated with diseases. Here, we discuss traditional phage therapy approaches, as well as how synthetic biology has allowed for the creation of designer phages for new clinical applications. To implement these technologies, several key aspects and challenges still need to be addressed, such as narrow spectrum, safety, and bacterial resistance. We will summarize our current understanding of how phage treatment elicits mammalian host immune responses, as well bacterial phage resistance development, and the potential impact each will have on phage therapy effectiveness. We conclude by discussing the need for a paradigm shift on how phage therapy strategies are developed.

Biology of Acinetobacter baumannii: Pathogenesis, Antibiotic Resistance Mechanisms, and Prospective Treatment Options

Acinetobacter baumannii is undoubtedly one of the most successful pathogens responsible for hospital-acquired nosocomial infections in the modern healthcare system. Due to the prevalence of infections and outbreaks caused by multi-drug resistant A. baumannii, few antibiotics are effective for treating infections caused by this pathogen. To overcome this problem, knowledge of the pathogenesis and antibiotic resistance mechanisms of A. baumannii is important. In this review, we summarize current studies on the virulence factors that contribute to A. baumannii pathogenesis, including porins, capsular polysaccharides, lipopolysaccharides, phospholipases, outer membrane vesicles, metal acquisition systems, and protein secretion systems. Mechanisms of antibiotic resistance of this organism, including acquirement of β-lactamases, up-regulation of multidrug efflux pumps, modification of aminoglycosides, permeability defects, and alteration of target sites, are also discussed. Lastly, novel prospective treatment options for infections caused by multi-drug resistant A. baumannii are summarized.