Isolation and Characterization of Novel Lytic Bacteriophages Infecting Epidemic Carbapenem-Resistant Klebsiella pneumoniae Strains

Novel strategies for vancomycin-resistant Enterococcus faecalis biofilm control: bacteriophage (vB_EfaS_ZC1), propolis, and their combined effects in an ex vivo endodontic model

BACKGROUND

Endodontic treatment failures are predominantly attributed to Enterococcus faecalis (E. faecalis) infection, a Gram-positive coccus. E. faecalis forms biofilms, resist multiple antibiotics, and can withstand endodontic disinfection protocols. Vancomycin-resistant strains, in particular, are challenging to treat and are associated with serious medical complications.

METHODS

A novel phage, vB_EfaS_ZC1, was isolated and characterized. Its lytic activity against E. faecalis was assessed in vitro through time-killing and biofilm assays. The phage's stability under various conditions was determined. Genomic analysis was conducted to characterize the phage and its virulence. The phage, propolis, and their combination were evaluated as an intracanal irrigation solution against a 4-week E. faecalis mature biofilm, using an ex vivo infected human dentin model. The antibiofilm activity was analyzed using a colony-forming unit assay, field emission scanning electron microscopy, and confocal laser scanning microscopy.

RESULTS

The isolated phage, vB_EfaS_ZC1, a siphovirus with prolate capsid, exhibited strong lytic activity against Vancomycin-resistant strains. In vitro assays indicated its effectiveness in inhibiting planktonic growth and disrupting mature biofilms. The phage remained stable under wide range of temperatures (- 80 to 60 °C), tolerated pH levels from 4 to 11; however the phage viability significantly reduced after UV exposure. Genomic analysis strongly suggests the phage's virulence and suitability for therapeutic applications; neither lysogeny markers nor antibiotic resistance markers were identified. Phylogenetic analysis clustered vB_EfaS_ZC1 within the genus Saphexavirus. The phage, both alone and in combination with propolis, demonstrated potent antibiofilm effects compared to conventional root canal irrigation.

CONCLUSION

Phage vB_EfaS_ZC1 demonstrates a promising therapy, either individually or in combination with propolis, for addressing challenging endodontic infections caused by E. faecalis.

Characterization of the novel cross-genus phage vB_SmaS_QH3 and evaluation of its antibacterial efficacy against Stenotrophomonas maltophilia

Background

Bacteriophages, which are natural bacterial predators, demonstrate potential as safe and effective biological control agents against drug-resistant infections. This study aims to characterize the biological properties of the novel lytic phage vB_SmaS_QH3 and comprehensively evaluate its efficacy in preventing and controlling clinically multidrug resistance Stenotrophomonas maltophilia infections using both in vivo and in vitro models.

Methods

The phage was isolated from hospital sewage using the multidrug resistant S. maltophilia no. 3738 as the host. Transmission electron microscopy (TEM) was used to observe phage morphology, and the host range was determined via spot assays. Proliferation kinetics, including multiplicity of infection (MOI), adsorption rate, and one-step growth curves, were analyzed. Stability was assessed under various physicochemical conditions. Based on Illumina whole-genome sequencing data, bioinformatics tools were employed for gene annotation, functional prediction, and phylogenetic analysis. Antimicrobial activity was assessed using in vitro and in vivo models.

Results

A lytic phage vB_SmaS_QH3 was isolated from hospital sewage. TEM revealed that it belongs to the class Caudoviricetes, featuring an icosahedral head (62 ± 3 nm) and a non-contractile long tail (121 ± 5 nm). Although the phage has a narrow host range, it exhibits cross-genus infectivity, lysing S. maltophilia (11/81) and Pseudomonas aeruginosa (3/24). The optimal MOI for phage vB_SmaS_QH3 is 0.01, with an adsorption rate of 49.16% within 20 min, a latent period of 40 min, a lytic period of 50 min, and a burst size of 41.67 plaque-forming units/cell. The phage remained stable at 4-60°C, at pH 3-11, and in chloroform, but it was completely inactivated following 20-min exposure to UV irradiation. Genomic analysis showed a linear double-stranded DNA genome of 43,085 bp with a GC content of 54.2%, containing 54 predicted ORFs, and no virulence or antibiotic resistance genes were detected. In vitro, vB_SmaS_QH3 effectively inhibited bacterial growth within 9 h. In vivo, it significantly improved the survival rate of Galleria mellonella larvae infected with S. maltophilia, regardless of the treatment timing.

Conclusion

vB_SmaS_QH3 is a narrow host range lytic phage with a safe genome and excellent stability. It exhibits significant antibacterial activity both in vitro and in vivo, making it a promising candidate for therapeutic applications.

Development of a lytic bacteriophage BPK01 impregnated biopolymer (chitosan) hydrogel for combating high-risk strains of carbapenem resistant Klebsiella pneumoniae (CRKP) pathogens- in vitro and in vivo evaluation

Alternative strategies are urgently required to combat the rise of high-risk carbapenem-resistant Klebsiella pneumoniae (CRKP), including blaNDM-positive strains that produce carbapenemase enzymes, which deactivate beta-lactam antibiotics and result in poor treatment outcomes. In this study, we isolated a bacteriophage BPK01, targeting a high-risk strain of Klebsiella pneumoniae (carbapenem-resistant, blaNDM-positive, ST147, capsular type K64, biofilm former). BPK01 demonstrated strong lytic activity (84%) against a panel of genetically characterized CRKP strains (n = 59) from clinical specimens, including pus, urine, sputum, blood, and tracheal aspirates. BPK01 was classified as a Caudoviricetes phage, exhibiting a burst size of 220 virions and a short latent period of 10 min. It demonstrated stability across a range of conditions (temperature, pH, and organic solvents) and effectively disrupted biofilms on silicone catheters. In vivo, BPK01 improved survival rates in the Galleria mellonella infection model and reduced bacterial burden in a murine bacteremia model, underscoring its therapeutic potential. Subsequently, we developed a hydrogel by incorporating BPK01 into a chitosan biopolymer, which demonstrated efficient lytic activity (spot assay, scanning electron microscopy, time kill assay) against CRKP pathogens, stability of biological activity for 6 months of storage, and controlled release kinetics, with the mathematical model Korsmeyer - Peppas being the best fit (R2 = 0.9962). The hydrogel expedited the healing of CRKP-infected lesions in a murine model, suggesting its potential as an effective topical treatment. This study highlights BPK01 as a promising biotherapeutic candidate for treating CRKP infection, with the phage hydrogel offering an ecofriendly and sustainable solution for treating infected lesions. Further research could expand its use in phage cocktails and other formulations for broader CRKP infection management.

Analysis of a novel phage as a promising biological agent targeting multidrug resistant Klebsiella pneumoniae

The rise of deaths by resistant bacteria is a global threat to public health systems. Klebsiella pneumoniae is a virulent pathogen that causes serious nosocomial infections. The major obstacle to bacterial treatment is antibiotic resistance, which necessitates the introducing of alternative therapies. Phage therapy has been regarded as a promising avenue to fight multidrug-resistant (MDR) pathogens. In the current study, a novel phage vB_KpnP_KP17 was isolated from sewage, and its lytic potential was investigated against K. pneumoniae. The isolated phage vB_KpnP_kP17 was lytic to 17.5% of tested K. pneumoniae isolates. One step growth curve indicated a virulent phage with a short latent period (20 min) and large burst size (331 PFU/cell). Additionally, vB_KpnP_kP17 maintained its activity against planktonic cells over a wide range of pH, temperature and UV irradiation intervals. The potential of vB_KpnP_KP17 as antibiofilm agent was revealed by the biofilm inhibition assay. The isolated phage vB_KpnP_KP17 at multiplicity of infection (MOI) of 10 inhibited more than 50% of attached biofilms of tested K. pneumoniae isolates. The genome of vB_KpnP_kP17 was characterized and found to be a linear dsDNA of 39,936 bp in length and GC content of 52.85%. Additionally, the absence of toxicity, virulence and antibiotic resistance genes further confirms the safety of vB_KpnP_KP17 for clinical applications. These characteristics make vB_KpnP_KP17 of a potential therapeutic value to manage MDR K. pneumoniae infections. Additionally, the formulation of vB_KpnP_KP17 in a cocktail with other lytic phages or with antibiotics could be applied to further limit biofilm-producing K. pneumoniae infections.

Phage Therapy: A Promising Treatment Strategy against Infections Caused by Multidrug-resistant Klebsiella pneumoniae

Klebsiella pneumoniae (KP) is a common and highly pathogenic pathogen, which often causes several serious infections in humans. The rampant and inappropriate use of broad-spectrum antibiotics has fueled a worrisome surge in Multidrug Resistance (MDR) among the strains of K. pneumoniae, which has significantly boosted the risk and complexity of nosocomial infection transmission in clinical settings. Consequently, this situation presents a substantial challenge to the efficacy of anti-infective treatments, making the development of new and innovative therapeutic approaches important. Bacteriophages (phages) are viruses that can infect and kill bacteria. They and their derived products are now being considered as promising alternatives or adjuncts to antimicrobial therapies for treating bacterial infections in humans, which exhibit a remarkable safety profile and precise host specificity. Numerous studies have also unequivocally demonstrated the remarkable potential of phages in effectively combating MDR K. pneumoniae infections both in vitro and in vivo. These studies have explored various approaches to K. pneumoniae phages, such as phage cocktails, phage-derived enzymes, and the synergistic utilization of phages and antibiotics. Therefore, phage therapy is old but not obsolete, particularly in light of the escalating problem of antimicrobial-resistant K. pneumoniae infections. Here, we have presented a comprehensive summary of the current knowledge on phage therapy for K. pneumoniae infections, including phage distribution, in vitro characterization of phages, in vivo investigations, and cases of clinical study. This review highlights the rapid advancements in phage therapy for K. pneumoniae, offering a promising avenue for combating this global public health threat.

Characterizing the bacteriophage PKp-V1 as a potential treatment for ESBL-producing hypervirulent K1 Klebsiella pneumoniae ST258 isolated from veterinary specimens

Background and Aim: The dearth of new antibiotics necessitates alternative approaches for managing infections caused by resistant superbugs. This study aimed to evaluate the lytic potential of the purified bacteriophage PKp-V1 against extended-spectrum β-lactamase (ESBL) harboring hypervirulent Klebsiella pneumoniae (hvKp)-K1 recovered from veterinary specimens. Materials and Methods: A total of 50 samples were collected from various veterinary specimens to isolate K. pneumoniae, followed by antimicrobial susceptibility testing and molecular detection of various virulence and ESBL genes. Multilocus sequence typing of the isolates was performed to identify prevalent sequence types. The bacteriophages were isolated using the double-agar overlay method and characterized using transmission electron microscopy, spot tests, plaque assays, stability tests, and one-step growth curve assays. Results: Among 17 (34%) confirmed K. pneumoniae isolates, 6 (35%) were hvKp, whereas 13 (76%) isolates belonging to the K1 type were positive for the wzy (K1) virulence gene. All (100%) hvKp isolates exhibited the allelic profile of ST258. Overall, PKp-V1 exhibited an 88 % (15/17; (p ≤ 0.05) host range, among which all (100 %; p ≤ 0.01) hvKp isolates were susceptible to PKp-V1. PKp-V1 exhibited a lytic phage titer of 2.4 × 108 plaque forming unit (PFU)/mL at temperatures ranging from 25°C to 37°C. The lytic phage titers of PKp-V1 at pH = 8 and 0.5% chloroform were 2.1 × 108 PFU/mL and 7.2 × 109 PFU/mL, respectively. Conclusion: Although the incidence of ESBL-infected K. pneumoniae in veterinary settings is worrisome, PKp-V1 phages showed considerable lytic action against the host bacterium, indicating the potential of PKp-V1 as a possible alternative therapeutic option against MDR K. pneumoniae. Keywords: antibiotic resistance, bacteriophage, Klebsiella pneumoniae, veterinary.

Characterizing the bacteriophage PKp-V1 as a potential treatment for ESBL-producing hypervirulent K1 Klebsiella pneumoniae ST258 isolated from veterinary specimens

Background and Aim

The dearth of new antibiotics necessitates alternative approaches for managing infections caused by resistant superbugs. This study aimed to evaluate the lytic potential of the purified bacteriophage PKp-V1 against extended-spectrum β-lactamase (ESBL) harboring hypervirulent Klebsiella pneumoniae (hvKp)-K1 recovered from veterinary specimens.

Materials and Methods

A total of 50 samples were collected from various veterinary specimens to isolate K. pneumoniae, followed by antimicrobial susceptibility testing and molecular detection of various virulence and ESBL genes. Multilocus sequence typing of the isolates was performed to identify prevalent sequence types. The bacteriophages were isolated using the double-agar overlay method and characterized using transmission electron microscopy, spot tests, plaque assays, stability tests, and one-step growth curve assays.

Results

Among 17 (34%) confirmed K. pneumoniae isolates, 6 (35%) were hvKp, whereas 13 (76%) isolates belonging to the K1 type were positive for the wzy (K1) virulence gene. All (100%) hvKp isolates exhibited the allelic profile of ST258. Overall, PKp-V1 exhibited an 88 % (15/17; (p ≤ 0.05) host range, among which all (100 %; p ≤ 0.01) hvKp isolates were susceptible to PKp-V1. PKp-V1 exhibited a lytic phage titer of 2.4 × 108 plaque forming unit (PFU)/mL at temperatures ranging from 25°C to 37°C. The lytic phage titers of PKp-V1 at pH = 8 and 0.5% chloroform were 2.1 × 108 PFU/mL and 7.2 × 109 PFU/mL, respectively.

Conclusion

Although the incidence of ESBL-infected K. pneumoniae in veterinary settings is worrisome, PKp-V1 phages showed considerable lytic action against the host bacterium, indicating the potential of PKp-V1 as a possible alternative therapeutic option against MDR K. pneumoniae.

Physiochemical characterization of a potential Klebsiella phage MKP-1 and analysis of its application in reducing biofilm formation

The common intestinal pathogen Klebsiella pneumoniae (K. pneumoniae) is one of the leading causes of fatal superbug infections that can resist the effects of commonly prescribed medicines. The uncontrolled use or misuse of antibiotics has increased the prevalence of drug-resistant K. pneumoniae strains in the environment. In the quest to search for alternative therapeutics for treating these drug-resistant infections, bacteriophages (bacterial viruses) emerged as potential candidates for in phage therapy against Klebsiella. The effective formulation of phage therapy against drug-resistant Klebsiella infections demands thorough characterization and screening of many bacteriophages. To contribute effectively to the formulation of successful phage therapy against superbug infections by K. pneumoniae, this study includes the isolation and characterization of a novel lytic bacteriophage MKP-1 to consider its potential to be used as therapeutics in treating drug-resistant Klebsiella infections. Morphologically, having a capsid attached to a long non-contractile tail, it was found to be a siphovirus that belongs to the class Caudoviricetes and showed infectivity against different strains of the target host bacterium. Comparatively, this double-stranded DNA phage has a large burst size and is quite stable in various physiological conditions. More interestingly, it has the potential to degrade the tough biofilms formed by K. pneumoniae (Klebsiella pneumoniae subsp. pneumoniae (Schroeter) Trevisan [ATCC 15380]) significantly. Thus, the following study would contribute effectively to considering phage MKP-1 as a potential candidate for phage therapy against Klebsiella infection.

Guiding antibiotics towards their target using bacteriophage proteins

Novel therapeutic strategies against difficult-to-treat bacterial infections are desperately needed, and the faster and cheaper way to get them might be by repurposing existing antibiotics. Nanodelivery systems enhance the efficacy of antibiotics by guiding them to their targets, increasing the local concentration at the site of infection. While recently described nanodelivery systems are promising, they are generally not easy to adapt to different targets, and lack biocompatibility or specificity. Here, nanodelivery systems are created that source their targeting proteins from bacteriophages. Bacteriophage receptor-binding proteins and cell-wall binding domains are conjugated to nanoparticles, for the targeted delivery of rifampicin, imipenem, and ampicillin against bacterial pathogens. They show excellent specificity against their targets, and accumulate at the site of infection to deliver their antibiotic payload. Moreover, the nanodelivery systems suppress pathogen infections more effectively than 16 to 32-fold higher doses of free antibiotics. This study demonstrates that bacteriophage sourced targeting proteins are promising candidates to guide nanodelivery systems. Their specificity, availability, and biocompatibility make them great options to guide the antibiotic nanodelivery systems that are desperately needed to combat difficult-to-treat infections.

Therapeutic efficacy of a K5-specific phage and depolymerase against Klebsiella pneumoniae in a mouse model of infection

Klebsiella pneumoniae has become one of the most intractable gram-negative pathogens infecting humans and animals due to its severe antibiotic resistance. Bacteriophages and protein products derived from them are receiving increasing amounts of attention as potential alternatives to antibiotics. In this study, we isolated and investigated the characteristics of a new lytic phage, P1011, which lyses K5 K. pneumoniae specifically among 26 serotypes. The K5-specific capsular polysaccharide-degrading depolymerase dep1011 was identified and expressed. By establishing murine infection models using bovine strain B16 (capable of supporting phage proliferation) and human strain KP181 (incapable of sustaining phage expansion), we explored the safety and efficacy of phage and dep1011 treatments against K5 K. pneumoniae. Phage P1011 resulted in a 60% survival rate of the mice challenged with K. pneumoniae supporting phage multiplication, concurrently lowering the bacterial burden in their blood, liver, and lungs. Unexpectedly, even when confronted with bacteria impervious to phage multiplication, phage therapy markedly decreased the number of viable organisms. The protective efficacy of the depolymerase was significantly better than that of the phage. The depolymerase achieved 100% survival in both treatment groups regardless of phage propagation compatibility. These findings indicated that P1011 and dep1011 might be used as potential antibacterial agents to control K5 K. pneumoniae infection.

Isolation and characterization of a relatively broad-spectrum phage against Escherichia coli

Multiple pathogenic types or serotypes restrict treatment for colibacillosis. In addition, rising antibiotic resistance has heightened public awareness to prevent and control pathogenic Escherichia coli. The bacteriophage is a viable technique to treat colibacillosis as an alternative to antibiotics. In this study, PH444, a relatively broad-spectrum obligate lytic phage, was screened from 48 Shiga toxin-producing Escherichia coli (STEC) phages isolated from farm manure samples and sewage samples in order to conduct genome-wide analysis, biological characterization, and a bacterial challenge experiment in milk. The results demonstrated that PH444 was a T7-like phage with a double-stranded DNA of 115,111 bp that belongs to the Kuravirus and was stable at temperatures between 4 and 50 °C and a pH range of 3 to 11. After adding PH444, the bacterial load in milk could be reduced from 3 × 103 PFU/ mL to zero within 1 h. In consideration of the biological properties of phage PH444, it was, therefore, demonstrated that PH444 has the potential to be used in phage biocontrol.

Longitudinal monitoring reveals the emergence and spread of blaGES-5-harboring carbapenem-resistant Klebsiella quasipneumoniae in a Hong Kong hospital wastewater discharge line

Testing hospital wastewater (HWW) is potentially an effective, long-term approach for monitoring trends in antimicrobial resistance (AMR) patterns in health care institutions. Over a year, we collected wastewater samples from the clinical and non-clinical sites of a tertiary hospital and from a downstream wastewater treatment plant (WWTP). We focused on the extent of carbapenem resistance among Enterobacteriaceae isolates given their clinical importance. Escherichia coli and Klebsiella spp. were the most frequently isolated Enterobacteriaceae species at all sampling sites. Additionally, a small number of isolates belonging to ESKAPE pathogens (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter species), except K. pneumoniae, were detected. Of the 232 Klebsiella spp. isolates, 100 (43.1 %) were multi-drug resistant (MDR), with 46 being carbapenem-resistant. Most of these carbapenem-resistant isolates were K. quasipneumoniae (CRKQ) (n = 44). All CRKQ isolates were isolated from the wastewater of a clinical site that includes intensive care units, which also yielded significantly more multi-drug resistant isolates compared to all other sampling sites. Among the CRKQ isolates, blaGES-5 genes (n = 42) were the primary genetic determinant of carbapenem resistance. Notably, three different CRKQ isolates, collected within the same month in HWW and the influent and effluent flow of the WWTP, shared >99 % sequence similarity between their blaGES-5 genes and between their flanking regions and upstream integron-integrase region. The influent isolate was phylogenetically close to K. quasipnuemoniae isolates from wastewater collected in Japan. Its blaGES-5 gene and surrounding sequences were > 99 % identical to blaGES-24 genes found in the Japanese isolates. Our results suggest that testing samples from sites located closer to hospitals could support antibiotic stewardship programs compared to samples collected further downstream. Moreover, testing samples collected regularly from WWTPs may reflect the local and global spread of pathogens and their resistances.

Morphological, biological, and genomic characterization of Klebsiella pneumoniae phage vB_Kpn_ZC2

BACKGROUND

Bacteriophages (phages) are one of the most promising alternatives to traditional antibiotic therapies, especially against multidrug-resistant bacteria. Klebsiella pneumoniae is considered to be an opportunistic pathogen that can cause life-threatening infections. Thus, this study aims at the characterization of a novel isolated phage vB_Kpn_ZC2 (ZCKP2, for short).

METHODS

The phage ZCKP2 was isolated from sewage water by using the clinical isolate KP/08 as a host strain. The isolated bacteriophage was purified and amplified, followed by testing of its molecular weight using Pulse-Field Gel Electrophoresis (PFGE), transmission electron microscopy, antibacterial activity against a panel of other Klebsiella pneumoniae hosts, stability studies, and whole genome sequencing.

RESULTS

Phage ZCKP2 belongs morphologically to siphoviruses as indicated from the Transmission Electron Microscopy microgram. The Pulsed Field Gel Electrophoresis and the phage sequencing estimated the phage genome size of 48.2 kbp. Moreover, the absence of lysogeny-related genes, antibiotic resistance genes, and virulence genes in the annotated genome suggests that phage ZCKP2 is safe for therapeutic use. Genome-based taxonomic analysis indicates that phage ZCKP2 represents a new family that has not been formally rated yet. In addition, phage ZCKP2 preserved high stability at different temperatures and pH values (-20 - 70 °C and pH 4 - 9). For the antibacterial activity, phage ZCKP2 maintained consistent clear zones on KP/08 bacteria along with other hosts, in addition to effective bacterial killing over time at different MOIs (0.1, 1, and 10). Also, the genome annotation predicted antibacterial lytic enzymes. Furthermore, the topology of class II holins was predicted in some putative proteins with dual transmembrane domains that contribute significantly to antibacterial activity. Phage ZCKP2 characterization demonstrates safety and efficiency against multidrug-resistant K. pneumoniae, hence ZCKP2 is a good candidate for further in vivo and phage therapy clinical applications.

Genomic and functional characterization of carbapenem-resistant Klebsiella pneumoniae from hospital wastewater

BACKGROUND

The emergence of carbapenem-resistant Klebsiella pneumoniae (CRKP) attracted extensive attention. Information on CRKP from hospital wastewater (HWW) is limited. The aims of this study were to investigate the genomic characteristics and to evaluate the survivability characteristics of 11 CRKP from HWW in a Chinese teaching hospital in Fujian province.

RESULTS

A total of 11 CRKP from HWW were recovered in this study. All CRKP from HWW were resistant to most antibiotics. Comparative genetic analysis demonstrated that all CRKP isolates were clustered into the three distinct phylogenetic clades and clade 2 and clade 3 were mixtures of samples collected from both HWW and clinical settings. Varieties of resistance genes, virulence genes and plasmid replicon types were detected in CRKP from HWW. In vitro transfer of bla_KPC-2 was successful for 3 bla_KPC-2-positive CRKP from HWW with high conjugation frequency. Our study demonstrated that the genetic environments of bla_KPC-2 shared core structure with ISKpn27-bla_KPC-2-ISKpn6. Group analysis showed that CRKP from HWW had a lower survivability in serum compared to clinical CRKP (p < 005); and CRKP from HWW had no significant difference in survivability in HWW compared to clinical CRKP (p > 005).

CONCLUSIONS

We analyzed the genomic and survivability characteristics of CRKP from HWW in a Chinese teaching hospital. These genomes represent a significant addition of genomic data from the genus and could serve as a valuable resource for future genomic studies about CRKP from HWW.

Characterization and Comparative Genomic Analysis of Three Virulent E. coli Bacteriophages with the Potential to Reduce Antibiotic-Resistant Bacteria in the Environment

The emerging global crisis of antibiotic resistance demands new alternative antibacterial solutions. Although bacteriophages have been used to combat bacterial infections for over a century, a dramatic boost in phage studies has recently been observed. In the development of modern phage applications, a scientific rationale is strongly required and newly isolated phages need to be examined in detail. In this study, we present the full characterization of bacteriophages BF9, BF15, and BF17, with lytic activity against extended-spectrum β-lactamases (ESBLs)- and AmpC β-lactamases (AmpC)-producing Escherichia coli, the prevalence of which has increased significantly in livestock in recent decades, representing a great hazard to food safety and a public health risk. Comparative genomic and phylogenetic analysis indicated that BF9, BF15, and BF17 represent the genera Dhillonvirus, Tequatrovirus, and Asteriusvirus, respectively. All three phages significantly reduced in vitro growth of their bacterial host and retained the ability to lyse bacteria after preincubation at wide ranges of temperature (−20–40 °C) and pH (5–9). The results described herein indicate the lytic nature of BF9, BF15, and BF17, which, along with the absence of genes encoding toxins and bacterial virulence factors, represents an undoubted asset in terms of future phage application.

Isolation, characterization, therapeutic potency, and genomic analysis of a novel bacteriophage vB_KshKPC-M against carbapenemase-producing Klebsiella pneumoniae strains (CRKP) isolated from Ventilator-associated pneumoniae (VAP) infection of COVID-19 patients

BACKGROUND

Carbapenem-resistant Klebsiella pneumoniae (CRKP) is a significant clinical problem, given the lack of therapeutic options. The CRKP strains have emerged as an essential worldwide healthcare issue during the last 10 years. Global expansion of the CRKP has made it a significant public health hazard. We must consider to novel therapeutic techniques. Bacteriophages are potent restorative cases against infections with multiple drug-resistant bacteria. The Phages offer promising prospects for the treatment of CRKP infections.

OBJECTIVE

In this study, a novel K. pneumoniae phage vB_KshKPC-M was isolated, characterized, and sequenced, which was able to infect and lyse Carbapenem-resistant K. pneumoniae host specifically.

METHODS

One hundred clinical isolates of K. pneumoniae were collected from patients with COVID-19 associated with ventilator-associated acute pneumonia hospitalized at Shahid Beheshti Hospital, Kashan, Iran, from 2020 to 2021. Initially, all samples were cultured, and bacterial isolates identified by conventional biochemical tests, and then the ureD gene was used by PCR to confirm the isolates. The Antibiotic susceptibility test in the disc diffusion method and Minimum inhibitory concentrations for Colistin was done and interpreted according to guidelines. Phenotypic and molecular methods determined the Carbapenem resistance of isolates. The blaKPC, blaNDM, and blaOXA-23 genes were amplified for this detection. Biofilm determination of CRKP isolates was performed using a quantitative microtiter plate (MTP) method. The phage was isolated from wastewater during the summer season at a specific position from Beheshti Hospital (Kashan, Iran). The sample was processed and purified against the bacterial host, a CRKP strain isolated from a patient suffering from COVID-19 pneumoniae and resistance to Colistin with high potency for biofilm production. This isolate is called Kp100. The separated phages were diluted and titration by the double overlay agar plaque assay. The separate Phage is concentrated with 10% PEG and stored at -80 °C until use. The phage host range was identified by the spot test method. The purified phage morphology was determined using a transmission electron microscope. The phage stability tests (pH and temperature) were analyzed. The effect of cationic ions on phage adsorption was evaluated. The optimal titer of bacteriophage was determined to reduce the concentration of the CRKP strain. One-step growth assays were performed to identify the purified phage burst's latent cycle and size. The SDS-PAGE was used for phage proteins analysis. Phage DNA was extracted by chloroform technique, and the whole genome of lytic phage was sequenced using Illumina HiSeq technology (Illumina, San Diego, CA). For quality assurance and preprocessing, such as trimming, Geneious Prime 2021.2.2 and Spades 3.9.0. The whole genome sequence of the lytic phage is linked to the GenBank database accession number. RASTtk-v1.073 was used to predict and annotate the ORFs. Prediction of ORF was performed using PHASTER software. ResFinder is used to assess the presence of antimicrobial resistance and virulence genes in the genome. The tRNAs can-SE v2.0.6 is used to determine the presence of tRNA in the genome. Linear genome comparisons of phages and visualization of coding regions were performed using Easyfig 2.2.3 and Mauve 2.4.0. Phage lifestyles were predicted using the program PHACTS. Phylogenetic analysis and amino acid sequences of phage core proteins, such as the major capsid protein. Phylogenies were reconstructed using the Neighbor-Joining method with 1000 bootstrap repeat. HHpred software was used to predict depolymerase. In this study, GraphPad Prism version 9.1 was used for the statistical analysis. Student's t-test was used to compare the sets and the control sets, and the significance level was set at P ≤ 0.05.

RESULTS

Phage vB_KshKPC-M is assigned to the Siphoviridae, order Caudovirales. It was identified as a linear double-stranded DNA phage of 54,378 bp with 50.08% G + C content, had a relatively broad host range (97.7%), a short latency of 20 min, and a high burst size of 260 PFU/cell, and was maintained stable at different pH (3-11) and temperature (45-65 °C). The vB_KshKPC-M genome contains 91 open-reading frames. No tRNA, antibiotic resistance, toxin, virulence-related genes, or lysogen-forming gene clusters were detected in the phage genome. Comparative genomic analysis revealed that phage vB_KshKPC-M has sequence similarity to the Klebsiella phages, phage 13 (NC_049844.1), phage Sushi (NC_028774.1), phage vB_KpnD_PeteCarol (OL539448.1) and phage PWKp14 (MZ634345.1).

CONCLUSION

The broad host range and antibacterial activity make it a promising candidate for future phage therapy applications. The isolated phage was able to lyse most of the antibiotic-resistant clinical isolates. Therefore, this phage can be used alone or as a phage mixture in future studies to control and inhibit respiratory infections caused by these bacteria, especially in treating respiratory infections caused by resistant strains in sick patients.

Characterization and genome analysis of phage vB_KpnS_SXFY507 against Klebsiella pneumoniae and efficacy assessment in Galleria mellonella larvae

Carbapenem-resistant Klebsiella pneumoniae is one of the primary bacterial pathogens that pose a significant threat to global public health because of the lack of available therapeutic options. Phage therapy shows promise as a potential alternative to current antimicrobial chemotherapies. In this study, we isolated a new Siphoviridae phage vB_KpnS_SXFY507 against KPC-producing K. pneumoniae from hospital sewage. It had a short latent period of 20 min and a large burst size of 246 phages/cell. The host range of phage vB_KpnS_SXFY507 was relatively broad. It has a wide range of pH tolerance and high thermal stability. The genome of phage vB_KpnS_SXFY507 was 53,122 bp in length with a G + C content of 49.1%. A total of 81 open-reading frames (ORFs) and no virulence or antibiotic resistance related genes were involved in the phage vB_KpnS_SXFY507 genome. Phage vB_KpnS_SXFY507 showed significant antibacterial activity in vitro. The survival rate of Galleria mellonella larvae inoculated with K. pneumoniae SXFY507 was 20%. The survival rate of K. pneumonia-infected G. mellonella larvae was increased from 20 to 60% within 72 h upon treatment with phage vB_KpnS_SXFY507. In conclusion, these findings indicate that phage vB_KpnS_SXFY507 has the potential to be used as an antimicrobial agent for the control of K. pneumoniae.

Characterization of Klebsiella pneumoniae bacteriophages, KP1 and KP12, with deep learning-based structure prediction

Concerns over Klebsiella pneumoniae resistance to the last-line antibiotic treatment have prompted a reconsideration of bacteriophage therapy in public health. Biotechnological application of phages and their gene products as an alternative to antibiotics necessitates the understanding of their genomic context. This study sequenced, annotated, characterized, and compared two Klebsiella phages, KP1 and KP12. Physiological validations identified KP1 and KP12 as members of Myoviridae family. Both phages showed that their activities were stable in a wide range of pH and temperature. They exhibit a host specificity toward K. pneumoniae with a broad intraspecies host range. General features of genome size, coding density, percentage GC content, and phylogenetic analyses revealed that these bacteriophages are distantly related. Phage lytic proteins (endolysin, anti-/holin, spanin) identified by the local alignment against different databases, were subjected to further bioinformatic analyses including three-dimensional (3D) structure prediction by AlphaFold. AlphaFold models of phage lysis proteins were consistent with the published X-ray crystal structures, suggesting the presence of T4-like and P1/P2-like bacteriophage lysis proteins in KP1 and KP12, respectively. By providing the primary sequence information, this study contributes novel bacteriophages for research and development pipelines of phage therapy that ultimately, cater to the unmet clinical and industrial needs against K. pneumoniae pathogens.

Characterization and comprehensive genome analysis of novel bacteriophage, vB_Kpn_ZCKp20p, with lytic and anti-biofilm potential against clinical multidrug-resistant Klebsiella pneumoniae

Introduction

The rise of infections by antibiotic-resistant bacterial pathogens is alarming. Among these, Klebsiella pneumoniae is a leading cause of death by hospital-acquired infections, and its multidrug-resistant strains are flagged as a global threat to human health, which necessitates finding novel antibiotics or alternative therapies. One promising therapeutic alternative is the use of virulent bacteriophages, which specifically target bacteria and coevolve with them to overcome potential resistance. Here, we aimed to discover specific bacteriophages with therapeutic potential against multiresistant K. pneumoniae clinical isolates.

Methods and Results

Out of six bacteriophages that we isolated from urban and medical sewage, phage vB_Kpn_ZCKp20p had the broadest host range and was thus characterized in detail. Transmission electron microscopy suggests vB_Kpn_ZCKp20p to be a tailed phage of the siphoviral morphotype. In vitro evaluation indicated a high lytic efficiency (30 min latent period and burst size of ∼100 PFU/cell), and extended stability at temperatures up to 70°C and a wide range of (2-12) pH. Additionally, phage vB_Kpn_ZCKp20p possesses antibiofilm activity that was evaluated by the crystal violet assay and was not cytotoxic to human skin fibroblasts. The whole genome was sequenced and annotated, uncovering one tRNA gene and 33 genes encoding proteins with assigned functions out of 85 predicted genes. Furthermore, comparative genomics and phylogenetic analysis suggest that vB_Kpn_ZCKp20p most likely represents a new species, but belongs to the same genus as Klebsiella phages ZCKP8 and 6691. Comprehensive genomic and bioinformatics analyses substantiate the safety of the phage and its strictly lytic lifestyle.

Conclusion

Phage vB_Kpn_ZCKp20p is a novel phage with potential to be used against biofilm-forming K. pneumoniae and could be a promising source for antibacterial and antibiofilm products, which will be individually studied experimentally in future studies.

Characterization of Novel Klebsiella Phage PG14 and Its Antibiofilm Efficacy

The increasing frequency of infections caused by multidrug-resistant Klebsiella pneumoniae demands the development of unconventional therapies. Here, we isolated, characterized, and sequenced a Klebsiella phage PG14 that infects and lyses carbapenem-resistant K. pneumoniae G14. Phage PG14 showed morphology similar to the phages belonging to the family Siphoviridae. The adsorption curve of phage PG14 showed more than 90% adsorption of phages on a host within 12 min. A latent period of 20 min and a burst size of 47 was observed in the one step growth curve. Phage PG14 is stable at a temperature below 30°C and in the pH range of 6 to 8. The PG14 genome showed no putative genes associated with virulence and antibiotic resistance. Additionally, it has shown lysis against 6 out of 13 isolates tested, suggesting the suitability of this phage for therapeutic applications. Phage PG14 showed more than a 7-log cycle reduction in K. pneumoniae planktonic cells after 24 h of treatment at a multiplicity of infection (MOI) of 10. The phage PG14 showed a significant inhibition and disruption of biofilm produced by K. pneumoniae G14. The promising results of this study nominate phage PG14 as a potential candidate for phage therapy. IMPORTANCE Klebsiella pneumoniae is one of the members of the ESKAPE (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter species) group of pathogens and is responsible for nosocomial infections. The global increase of carbapenem-resistant K. pneumoniae has developed a substantial clinical threat because of the dearth of therapeutic choices available. K. pneumoniae is one of the commonly found bacteria responsible for biofilm-related infections. Due to the inherent tolerance of biofilms to antibiotics, there is a growing need to develop alternative strategies to control biofilm-associated infections. This study characterized a novel bacteriophage PG14, which can inhibit and disrupt the K. pneumoniae biofilm. The genome of phage PG14 does not show any putative genes related to antimicrobial resistance or virulence, making it a potential candidate for phage therapy. This study displays the possibility of treating infections caused by multidrug-resistant (MDR) isolates of K. pneumoniae using phage PG14 alone or combined with other therapeutic agents.

Isolation and characterization of a novel phage vB_ValP_VA-RY-3 infecting Vibrio alginolyticus

Vibrio alginolyticus is a common foodborne pathogen existing both in contaminated seafood and the environment and can cause serious mortality in aquaculture facilities. Bacteriophages can be used as an alternative bio-control agent to eliminate and reduce pathogens. In this study, a novel lytic phage, designated vB_ValP_VA-RY-3 (referred to as S1R3Y), was isolated from sewage collected in Dalian, China. The linear double-stranded DNA genome of phage S1R3Y is 40.271 kb, which has a mol% G + C content of 43.98, containing 51 ORFs with a T7-like genomic organization. It shared the closest relationship with phage vB_CsaP_Ss1, but the homology coverage is just 6%. S1R3Y lacks tRNA and no known virulence or lysogenic genes were found. S1R3Y had a burst size of 147 PFU/cell and is stable under different temperatures (4-56 °C) and pH (5.0-7.0). A comparison of its genomic features and phylogenetic analysis revealed that phage S1R3Y is a novel member of the order Caudovirales, family Podoviridae. Our results suggest that phage S1R3Y may represent a potential therapeutic agent against Vibrio alginolyticus.

Identification of a phage-derived depolymerase specific for KL47 capsule of Klebsiella pneumoniae and its therapeutic potential in mice

Klebsiella pneumoniae is one of the major pathogens causing global multidrug-resistant infections. Therefore, strategies for preventing and controlling the infections are urgently needed. Phage depolymerase, often found in the tail fiber protein or the tail spike protein, is reported to have antibiofilm activity. In this study, phage P560 isolated from sewage showed specific for capsule locus type KL47 K. pneumoniae, and the enlarged haloes around plaques indicated that P560 encoded a depolymerase. The capsule depolymerase, ORF43, named P560dep, derived from phage P560 was expressed, purified, characterized and evaluated for enzymatic activity as well as specificity. We reported that the capsule depolymerase P560dep, can digest the capsule polysaccharides on the surface of KL47 type K. pneumoniae, and the depolymerization spectrum of P560dep matched to the host range of phage P560, KL47 K. pneumoniae. Crystal violet staining assay showed that P560dep was able to significantly inhibit biofilm formation. Further, a single dose (50 μg/mouse) of depolymerase intraperitoneal injection protected 90%-100% of mice from lethal challenge before or after infection by KL47 carbapenem-resistant K. pneumoniae. And pathological changes were alleviated in lung and liver of mice infected by KL47 type K. pneumoniae. It is demonstrated that depolymerase P560dep as an attractive antivirulence agent represents a promising tool for antimicrobial therapy.

Convergence of MCR-8.2 and Chromosome-Mediated Resistance to Colistin and Tigecycline in an NDM-5-Producing ST656 Klebsiella pneumoniae Isolate From a Lung Transplant Patient in China

We characterized the first NDM-5 and MCR-8.2 co-harboring ST656 Klebsiella pneumoniae clinical isolate, combining with chromosomal gene-mediated resistance to colistin and tigecycline. The K. pneumoniae KP32558 was isolated from the bronchoalveolar lavage fluid from a lung transplant patient. Complete genome sequences were obtained through Illumina HiSeq sequencing and nanopore sequencing. The acquired resistance genes and mutations in chromosome-encoded genes associated with colistin and tigecycline resistance were analyzed. Comparative genomic analysis was conducted between mcr-8.2-carrying plasmids. The K. pneumoniae KP32558 was identified as a pan-drug resistant bacteria, belonging to ST656, and harbored plasmid-encoded blaNDM-5 and mcr-8.2 genes. The blaNDM-5 gene was located on an IncX3 type plasmid. The mcr-8.2 gene was located on a conjugative plasmid pKP32558-2-mcr8, which had a common ancestor with another two mcr-8.2-carrying plasmids pMCR8_020135 and pMCR8_095845. The MIC of KP32558 for colistin was 256 mg/L. The mcr-8.2 gene and mutations in the two-component system, pmrA and crrB, and the regulator mgrB, had a synergistic effect on the high-level colistin resistance. The truncation in the acrR gene, related to tigecycline resistance, was also identified. K. pneumoniae has evolved a variety of complex resistance mechanisms to the last-resort antimicrobials, close surveillance is urgently needed to monitor the prevalence of this clone.

Duck sewage source coliphage P762 can lyse STEC and APEC

Multiple pathogenic types or serotypes restrict treatment for colibacillosis. In addition, rising antibiotic resistance has heightened public awareness to prevent and control pathogenic Escherichia coli. The bacteriophage is a viable technique to treat colibacillosis as an alternative to antibiotics. P762, a coliphage isolated from duck farm sewage, was demonstrated to cloud lyse Shiga toxin-producing Escherichia Coli serotypes O157 and non-O157 (17/39), Avian pathogenic E. coli covered serotype O78, O83, and O9 (5/19), and other pathogenic Escherichia coli (5/17). Additional fundamental biological characteristics analysis revealed that P762 is stable at pH 3 ~ 11 and temperature between 4 °C and 60 °C, and its optimum multiplicity of infection (MOI) is 0.1. The one-step curve of P762 exhibited three bursts of growth stage: two rapid and one slow stage. Furthermore, the first rapid burst size is 80 CFU/PFU, the burst size of the slow stage is 10 CFU/PFU, and the second rapid burst size is about 990 CFU/PFU. In addition, P762 can form a "halo" on a double agar plate, implying that the phage secretes depolymerase. With 95.14% identity and 90% query coverage, genome sequence analysis revealed that P762 is most closely related to Escherichia phage DY1, which belongs to the genus Kayfunavirus. After screening using RAST and VFDB, no virulence factors were discovered in P762. In vitro antibacterial tests revealed that P762 has high bactericidal activity in lettuce leaves contaminated with STEC. In conclusion, phage P762 might be employed in the future to prevent and control pathogenic Escherichia coli.

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.

Characterization and Genomic Analysis of a Novel Drexlervirial Bacteriophage IME268 with Lytic Activity Against Klebsiella pneumoniae

Introduction

Klebsiella pneumoniae, a multidrug resistant bacterium, that causes nosocomial infections including septicemia, pneumonia etc. Bacteriophages are potential antimicrobial agents for the treatment of antibiotic resistant bacteria.

Methods and Results

In this study, a novel bacteriophage IME268 was isolated from hospital sewage against clinical multi-drug resistant Klebsiella pneumoniae. Transmission electron microscopy and genomic characterization of this phage exhibited it belongs to the Webervirus genus, Drexlerviridae family. Phage IME268 possessed a double-stranded DNA genome composed of 49,552bp with a GC content of 50.5%. The phage genome encodes 77 open reading frames, out of 44 are hypothetical proteins while 33 had assigned putative functions. No tRNA, virulence related or antibiotic resistance genes were found in phage genome. Comparative genomic analysis showed that phage IME268 has 95% identity with 87% query cover with other phages in NCBI database. Multiplicity of infection, one step growth curve and host range of phage were also measured.

Conclusion

According to findings, Phage IME268 is a promising biological agent that infects Klebsiella pneumoniae and can be used in future phage therapies.

Occurrence of Hypervirulent Klebsiella pneumoniae in Clinical Settings and Lytic Potential of Bacteriophages Against the Isolates

Background: Antibiotic resistance is a major health hazard around the globe. Hypervirulent Klebsiella Pneumoniae (hvKp) is associated with hospital-acquired and community-acquired infections. Since there is a lack of new antibiotics against multidrug-resistant (MDR) pathogens, phage therapy might provide an alternative approach to confer antibiotic resistance. Objectives: This study aimed to estimate the occurrence of hvKp and characterize the bacteriophage against the hvKp prevalence in clinical settings, which might be used as an alternative to antibiotics. Methods: Different clinical samples (n = 50) were collected to isolate K. pneumoniae, and the assessment of multidrug resistance was carried out based on the Clinical and Laboratory Standards Institute guidelines (2020). The bacteriophage was isolated from hospital waste, and the double agar overlay method was used for phage purification and propagation. Spot test and one-step curve were performed to determine host-phage interactions. For the evaluation of phage stability in environmental conditions, the phage was incubated at various ranges of temperature, pH, and chloroform. Results: Out of the collected samples, 22 (44%) isolates were confirmed as K. pneumoniae. Among confirmed K. pneumoniae isolates, a total of 11 (50%) isolates were detected as hvKp. Moreover, 14 (64%) isolates were detected as MDR, out of which 5 (35%) isolates were among hvKp phenotypes. Maximum resistance was observed against ampicillin (86%) followed by ceftriaxone (81%) which was the highest among cephalosporins. The isolated bacteriophage showed a broad host range, short latent period, and stability. Overall, 16 isolates (85%) of K. pneumoniae were susceptible to phage infection, among which 12 isolates were MDR (75%); however, all 5 (100%) hvKp isolates were susceptible to phage infection. One-step growth analysis revealed a burst size of 190 phages/host bacterial cells with a short latent period of 24 minutes. Conclusions: Altogether, the significant prevalence of hvKp was estimated in clinical settings, and the isolated bacteriophage showed significant lytic activity as it killed all the hvKp strains. Phage therapy might be exploited and used as a potential alternative therapeutic approach against infections caused by this resistant pathogen.

Occurrence of Hypervirulent Klebsiella pneumoniae in Clinical Settings and Lytic Potential of Bacteriophages Against the Isolates

Background: Antibiotic resistance is a major health hazard around the globe. Hypervirulent Klebsiella Pneumoniae (hvKp) is associated with hospital-acquired and community-acquired infections. Since there is a lack of new antibiotics against multidrug-resistant (MDR) pathogens, phage therapy might provide an alternative approach to confer antibiotic resistance. Objectives: This study aimed to estimate the occurrence of hvKp and characterize the bacteriophage against the hvKp prevalence in clinical settings, which might be used as an alternative to antibiotics. Methods: Different clinical samples (n = 50) were collected to isolate K. pneumoniae, and the assessment of multidrug resistance was carried out based on the Clinical and Laboratory Standards Institute guidelines (2020). The bacteriophage was isolated from hospital waste, and the double agar overlay method was used for phage purification and propagation. Spot test and one-step curve were performed to determine host-phage interactions. For the evaluation of phage stability in environmental conditions, the phage was incubated at various ranges of temperature, pH, and chloroform. Results: Out of the collected samples, 22 (44%) isolates were confirmed as K. pneumoniae. Among confirmed K. pneumoniae isolates, a total of 11 (50%) isolates were detected as hvKp. Moreover, 14 (64%) isolates were detected as MDR, out of which 5 (35%) isolates were among hvKp phenotypes. Maximum resistance was observed against ampicillin (86%) followed by ceftriaxone (81%) which was the highest among cephalosporins. The isolated bacteriophage showed a broad host range, short latent period, and stability. Overall, 16 isolates (85%) of K. pneumoniae were susceptible to phage infection, among which 12 isolates were MDR (75%); however, all 5 (100%) hvKp isolates were susceptible to phage infection. One-step growth analysis revealed a burst size of 190 phages/host bacterial cells with a short latent period of 24 minutes. Conclusions: Altogether, the significant prevalence of hvKp was estimated in clinical settings, and the isolated bacteriophage showed significant lytic activity as it killed all the hvKp strains. Phage therapy might be exploited and used as a potential alternative therapeutic approach against infections caused by this resistant pathogen.

Occurrence of Hypervirulent Klebsiella pneumoniae in Clinical Settings and Lytic Potential of Bacteriophages Against the Isolates

Background: Antibiotic resistance is a major health hazard around the globe. Hypervirulent Klebsiella Pneumoniae (hvKp) is associated with hospital-acquired and community-acquired infections. Since there is a lack of new antibiotics against multidrug-resistant (MDR) pathogens, phage therapy might provide an alternative approach to confer antibiotic resistance. Objectives: This study aimed to estimate the occurrence of hvKp and characterize the bacteriophage against the hvKp prevalence in clinical settings, which might be used as an alternative to antibiotics. Methods: Different clinical samples (n = 50) were collected to isolate K. pneumoniae, and the assessment of multidrug resistance was carried out based on the Clinical and Laboratory Standards Institute guidelines (2020). The bacteriophage was isolated from hospital waste, and the double agar overlay method was used for phage purification and propagation. Spot test and one-step curve were performed to determine host-phage interactions. For the evaluation of phage stability in environmental conditions, the phage was incubated at various ranges of temperature, pH, and chloroform. Results: Out of the collected samples, 22 (44%) isolates were confirmed as K. pneumoniae. Among confirmed K. pneumoniae isolates, a total of 11 (50%) isolates were detected as hvKp. Moreover, 14 (64%) isolates were detected as MDR, out of which 5 (35%) isolates were among hvKp phenotypes. Maximum resistance was observed against ampicillin (86%) followed by ceftriaxone (81%) which was the highest among cephalosporins. The isolated bacteriophage showed a broad host range, short latent period, and stability. Overall, 16 isolates (85%) of K. pneumoniae were susceptible to phage infection, among which 12 isolates were MDR (75%); however, all 5 (100%) hvKp isolates were susceptible to phage infection. One-step growth analysis revealed a burst size of 190 phages/host bacterial cells with a short latent period of 24 minutes. Conclusions: Altogether, the significant prevalence of hvKp was estimated in clinical settings, and the isolated bacteriophage showed significant lytic activity as it killed all the hvKp strains. Phage therapy might be exploited and used as a potential alternative therapeutic approach against infections caused by this resistant pathogen.

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.

Characterization and genome analysis of novel Klebsiella phage BUCT556A with lytic activity against carbapenemase-producing Klebsiella pneumoniae

Carbapenem-resistant Klebsiella pneumoniae (CRKP) have spread globally and led to the limited choice of antimicrobial treatment of K. pneumoniae-induced infections. Bacteriophages are considered as an effective strategy against bacterial infections. In this study, we isolated a novel Klebsiella phage BUCT556A with lytic activity against KPC-producing K. pneumoniae, which was a multi-drug resistant isolate. Phage BUCT556A had a symmetrical head and a long, non-contractile tail, belonging to the family Siphoviridae, order Caudoviridae. Phage BUCT556A had a relatively narrow host range, and a medium burst size of 91 PFU/cell. It was stable at broad temperature/pH range, and exhibited good tolerance to chloroform. The genome of phage BUCT556A was a 49, 376-bp linear double-stranded DNA molecule with average G + C content of 50.2%, and contained 75 open reading frames. There was no tRNA, antibiotic resistance, toxin, virulence related genes or lysogen-formation gene clusters detected in the genome of phage BUCT556A. Phylogenetic analyses based on the major capsid protein Mcp suggested that this phage had a close relationship with Klebsiella phage KLPN1. Together, through phenotypic combined with genomic DNA sequencing and analyses, our study suggests that phage BUCT556A has the potential to be used as a bacterial treatment tool for multidrug-resistant strains K. pneumoniae.

Treatment for carbapenem-resistant Enterobacterales infections: recent advances and future directions

Carbapenem-resistant Enterobacterales (CRE) are a growing threat to human health worldwide. CRE often carry multiple resistance genes that limit treatment options and require longer durations of therapy, are more costly to treat, and necessitate therapies with increased toxicities when compared with carbapenem-susceptible strains. Here, we provide an overview of the mechanisms of resistance in CRE, the epidemiology of CRE infections worldwide, and available treatment options for CRE. We review recentlyapproved agents for the treatment of CRE, including ceftazidime-avibactam, meropenem-vaborbactam, imipenem-relebactam, cefiderocol, and novel aminoglycosides and tetracyclines. We also discuss recent advances in phage therapy and antibiotics that are currently in development targeted to CRE. The potential for the development of resistance to these therapies remains high, and enhanced antimicrobial stewardship is imperative both to reduce the spread of CRE worldwide and to ensure continued access to efficacious treatment options.

Identification of a phage-derived depolymerase specific for KL64 capsule of Klebsiella pneumoniae and its anti-biofilm effect

The increasing prevalence of Carbapenem-resistant Klebsiella pneumoniae (CRKP) poses a serious threat to global health. Phages and phage-derived enzymes gained increasing attention for controling CRKP infections. In this study, a lytic phage P510 infecting KL64 type K. pneumoniae was isolated and characterized. Whole genome analysis and electron microscopy analysis showed that phage P510 belonged to genus Przondovirus, family Autographiviridae, the order Caudovirales. The tail fiber protein of the phage was predicted to encode capsule depolymerase. Further analysis demonstrated that recombinant depolymerase P510dep had polysaccharide-degrading activity against KL64-types capsule of K. pneumoniae, and its lysis spectrum matched to host range of phage P510. We also demonstrated that the recombinant depolymerase was able to significantly inhibit biofilm formation. The discovery of the phage-derived depolymerase lays the foundation for controlling the spread of CRKPs.

Bacteriophage Therapy of Bacterial Infections: The Rediscovered Frontier

Antibiotic-resistant infections present a serious health concern worldwide. It is estimated that there are 2.8 million antibiotic-resistant infections and 35,000 deaths in the United States every year. Such microorganisms include Acinetobacter, Enterobacterioceae, Pseudomonas, Staphylococcus and Mycobacterium. Alternative treatment methods are, thus, necessary to treat such infections. Bacteriophages are viruses of bacteria. In a lytic infection, the newly formed phage particles lyse the bacterium and continue to infect other bacteria. In the early 20th century, d'Herelle, Bruynoghe and Maisin used bacterium-specific phages to treat bacterial infections. Bacteriophages are being identified, purified and developed as pharmaceutically acceptable macromolecular "drugs," undergoing strict quality control. Phages can be applied topically or delivered by inhalation, orally or parenterally. Some of the major drug-resistant infections that are potential targets of pharmaceutically prepared phages are Pseudomonas aeruginosa, Mycobacterium tuberculosis and Acinetobacter baumannii.

Extended Spectrum Beta-Lactamase-Resistant Determinants among Carbapenem-Resistant Enterobacteriaceae from Beef Cattle in the North West Province, South Africa: A Critical Assessment of Their Possible Public Health Implications

Carbapenems are considered to be the last resort antibiotics for the treatment of infections caused by extended-spectrum beta-lactamase (ESBL)-producing strains. The purpose of this study was to assess antimicrobial resistance profile of Carbapenem-resistant Enterobacteriaceae (CRE) isolated from cattle faeces and determine the presence of carbapenemase and ESBL encoding genes. A total of 233 faecal samples were collected from cattle and analysed for the presence of CRE. The CRE isolates revealed resistance phenotypes against imipenem (42%), ertapenem (35%), doripenem (30%), meropenem (28%), cefotaxime, (59.6%) aztreonam (54.3%) and cefuroxime (47.7%). Multidrug resistance phenotypes ranged from 1.4 to 27% while multi antibiotic resistance (MAR) index value ranged from 0.23 to 0.69, with an average of 0.40. Escherichia coli (E. coli), Klebsiella pneumoniae (K. pneumoniae), Proteus mirabilis (P. mirabilis) and Salmonella (34.4, 43.7, 1.3 and 4.6%, respectively) were the most frequented detected species through genus specific PCR analysis. Detection of genes encoding carbapenemase ranged from 3.3% to 35% (blaKPC, blaNDM, blaGES, blaOXA-48, blaVIM and blaOXA-23). Furthermore, CRE isolates harboured ESBL genes (blaSHV (33.1%), blaTEM (22.5%), blaCTX-M (20.5%) and blaOXA (11.3%)). In conclusion, these findings indicate that cattle harbour CRE carrying ESBL determinants and thus, proper hygiene measures must be enforced to mitigate the spread of CRE strains to food products.

Characterization and genome analysis of Klebsiella phage P509, with lytic activity against clinical carbapenem-resistant Klebsiella pneumoniae of the KL64 capsular type

The increasing population infected by carbapenem-resistant Klebsiella pneumoniae necessitates the development of alternative therapies. In this study, we isolated, characterized, and sequenced a bacteriophage, P509, which was able to specifically infect and lyse carbapenem-resistant K. pneumoniae of K locus type KL64. A one-step growth curve experiment showed that the latent time period of phage P509 was 5 min, and the burst size was about 85 phage particles/cell. Stability tests confirmed that P509 was stable over a wide range of temperatures (4 to 50 °C) and pH (3 to 11) conditions. Phage P509 was identified as a linear double-stranded DNA phage with a genome of 40,954 bp with 53.2% G + C content, encoding 50 predicted proteins. Genomic and morphological analysis suggested that P509 belonged to the genus Przondovirus, family Autographiviridae, order Caudovirales. Further analysis showed that no virulence-related genes or lysogen-formation gene clusters were detected in the genome, suggesting that P509 is a lytic phage, making it potentially suitable for clinical applications. In vitro, the number of viable cells in three phage-treated groups (MOI = 0.1, 0.01, 0.001) decreased by 3.75 log₁₀ CFU/ml, 3.32 log₁₀ CFU/ml and 3.21 log₁₀ CFU/ml, respectively, after 80 min of incubation, in comparison to that in the untreated group. Based on these characteristics, phage P509 may be a promising candidate for future phage therapy applications.