Bactericidal activity of bacteriophage endolysin HY-133 against Staphylococcus aureus in comparison to other antibiotics as determined by minimum bactericidal concentrations and time-kill analysis

[Phage endolysins-a novel class of antibacterial agents with a wide range of applications]

As "enzybiotics," endolysins represent a new class of antibacterial agents that are naturally produced at the end of the lytic cycle in bacteriophage-infected bacterial cells to enable the phage particles formed to be released from the inside of the host cell. Their enzymatic effect on the cell wall peptidoglycan, which leads to lysis of the infected bacteria, can also be exerted externally as an applied agent. While the endolysin activity can be directly effective in Gram-positive bacteria, the endolysin must be modified for activity against Gram-negative bacteria so that it can overcome the outer cell membrane. For this reason, and to optimize endolysin specificity and stability, endolysins are increasingly being genetically modified and produced recombinantly, which is relatively easy to achieve due to their modular structure consisting of lytic and binding domains. Endolysins have already found increasing actual or extensively postulated use for preventive, therapeutic, and diagnostic purposes in human and veterinary medicine as well as in food safety, biotechnology, and the One Health sector; however, this still needs to be better substantiated by valid studies. Although, in contrast to phage therapy, the regulatory aspects can follow the approval procedures also required for other pharmaceuticals, only less than a dozen randomized controlled studies of phases 1 to 3 have been initiated or completed in the field of human medicine. Only very few endolysin formulations approved as medical products are currently available on the market and approval as medicinal drugs is being sought for some endolysins.

Evaluating the antibacterial activity of engineered phage ФEcSw endolysin against multidrug-resistant Escherichia coli strain Sw1

OBJECTIVE

The emergence of bacteriophage-encoded endolysins hold significant promise as novel antibacterial agents, particularly against the growing threat of antibiotic-resistant bacteria. Therefore, we investigated the phage ФEcSw endolysin to enhance the lytic activity against multi-drug-resistant Escherichia coli Sw1 through site-directed mutagenesis (SDM) guided by in silico identification of critical residues.

METHODS

A computational analysis was conducted to elucidate the protein folding pattern, identify the active domains, and recognize critical residues of ФEcSw endolysin. Structural similarity-based docking simulations were employed to identify residues potentially involved in both recognition and cleavage of the bacterial peptidoglycan. Phage endolysin was amplified, cloned, expressed, and purified from phage ФEcSw. Pure endolysin (EL) activity was subsequently validated through SDM.

RESULTS

Our studies revealed both open and closed conformations of ФEcSw endolysin within specific residue ranges (51-60 and 128-141). Notably, the active site was identified and contains the crucial catalytic residues, Glu19 and Asp34. A time-kill assay demonstrated that the holin (HL) - EL effectively reduced E. coli Sw1 growth by 46% within 12 h. Furthermore, treatment with HL, EL, and HL-EL significantly increased bacterial membrane permeability (11%, 74%, and 85%, respectively) within just 1 h. Importantly, SDM identified a double mutant (K19/H34) of the endolysin exhibiting the highest lytic activity compared to the wild-type and other mutants (E19D, E19K, D34E, and D34H) due to increase net charge from +3.23 to +6.29.

CONCLUSIONS

Our findings demonstrate that phage endolysins and HLs or engineered endolysin hold significant potential as therapeutic agents to combat multidrug-resistant bacterial infections.

Phage-Derived Endolysins Against Resistant Staphylococcus spp.: A Review of Features, Antibacterial Activities, and Recent Applications

Antimicrobial resistance is a significant global public health issue, and the dissemination of antibiotic resistance in Gram-positive bacterial pathogens has significantly increased morbidity, mortality rates, and healthcare costs. Among them, Staphylococcus, especially methicillin-resistant Staphylococcus aureus (MRSA), causes a wide range of diseases due to its diverse pathogenic factors and infection strategies. These bacteria also present significant issues in veterinary medicine and food safety. Effectively managing staphylococci-related problems necessitates a concerted effort to implement preventive measures, rapidly detect the pathogen, and develop new and safe antimicrobial therapies. In recent years, there has been growing interest in using endolysins to combat bacterial infections. These enzymes, which are also referred to as lysins, are a unique class of hydrolytic enzymes synthesized by double-stranded DNA bacteriophages. They possess glycosidase, lytic transglycosylase, amidase, and endopeptidase activities, effectively destroying the peptidoglycan layer and resulting in bacterial lysis. This unique property makes endolysins powerful antimicrobial agents, particularly against Gram-positive organisms with more accessible peptidoglycan layers. Therefore, considering the potential benefits of endolysins compared to conventional antibiotics, we have endeavored to gather and review the characteristics and uses of endolysins derived from staphylococcal bacteriophages, as well as their antibacterial effectiveness against Staphylococcus spp. based on conducted experiments and trials.

Survey of probable synergism between melittin and ciprofloxacin, rifampicin, and chloramphenicol against multidrug-resistant Pseudomonas aeruginosa

Background

The emergence of multidrug-resistant bacteria and also biofilm-associated infections is a great health concern due to the failure of available antibiotics. This has alerted scientists to developing alternative antibiotics. Melittin as an antimicrobial peptide has antibacterial synergistic activity in combining with conventional antibiotics against pathogenic bacteria. Accordingly, this study aimed to assess the synergistic effect of melittin in combination with Ciprofloxacin, Rifampicin, and Chloramphenicol against MDR strains of P. aeruginosa.

Materials and methods

Fifty strains of P. aeruginosa were isolated from clinical specimens. The antibiotic susceptibility of isolates was evaluated by the disk diffusion method. The MIC and MBC of melittin and melittin-antibiotics combination against isolated strains were examined by microdilution method. The probable synergism between melittin and antibiotics was assayed using the FIC protocol. Time-killing kinetics and anti-biofilm effects of melittin and melittin-antibiotics combination were evaluated using time-kill kinetics and crystal violet staining method, respectively. The toxicity of the melittin-antibiotics combination on the HEK293 cell line was also assessed by the MTT assay method.

Results

Out of 50 isolates of P. aeruginosa, 15 strains are considered to be multidrug strains. Among MDR strains of P. aeruginosa, 42.85% were resistant to cefepime and ceftazidime and all urine-originate isolates were resistant to cotrimoxazole. A combination of MIC dose of ciprofloxacin and melittin decreased resistance against ciprofloxacin up to 33%. The ciprofloxacin-melittin combination showed a favorable synergism and anti-biofilm effect and was also 30.3% less toxic than melittin alone at 4 μg/ml against the HEK293 cell line. In contrast to ciprofloxacin, with the melittin-rifampicin and melittin-chloramphenicol combinations, an addition effect occurred, respectively, in 86.66 and 53.33% of MDR strains of P. aeruginosa.

Conclusion

Combining melittin's antibacterial and anti-biofilm properties with traditional antibiotics may offer a novel strategy to address antibiotic resistance in P. aeruginosa. The simultaneous administration of melittin and ciprofloxacin in a single dose has shown a marked increase in antibacterial effectiveness while minimizing toxicity to the HEK293 cell line. It is advisable to conduct additional research to explore the combined antibacterial effects of melittin and ciprofloxacin in a wider range of clinical samples, animal models, and clinical trial settings.

Cannabinoids as Antibacterial Agents: A Systematic and Critical Review of In Vitro Efficacy Against Streptococcus and Staphylococcus

BACKGROUND

Two major bacterial pathogens, Staphylococcus aureus and Streptococcus pyogenes, are becoming increasingly antibiotic-resistant. Despite the urgency, only a few new antibiotics have been approved to address these infections. Although cannabinoids have been noted for their antibacterial properties, a comprehensive review of their effects on these bacteria has been lacking.

OBJECTIVE

This systematic review examines the antibacterial activity of cannabinoids against S. aureus, including methicillin-resistant S. aureus (MRSA) and vancomycin-resistant S. aureus (VRSA) strains, and S. pyogenes.

METHODS

Databases, including CINAHL, Cochrane, Medline, Scopus, Web of Science, and LILACS, were searched. Of 3510 records, 24 studies met the inclusion criteria, reporting on the minimum inhibitory concentration (MIC) and minimum bactericidal concentration of cannabinoids.

RESULTS

Cannabidiol (CBD) emerged as the most effective cannabinoid, with MICs ranging from 0.65 to 32 mg/L against S. aureus, 0.5 to 4 mg/L for MRSA, and 1 to 2 mg/L for VRSA. Other cannabinoids, such as cannabichromene, cannabigerol (CBG), and delta-9-tetrahydrocannabinol (Δ9-THC), also exhibited significant antistaphylococcal activity. CBD, CBG, and Δ9-THC also showed efficacy against S. pyogenes, with MICs between 0.6 and 50 mg/L. Synergistic effects were observed when CBD and essential oils from Cannabis sativa when combined with other antibacterial agents.

CONCLUSION

Cannabinoids' antibacterial potency is closely linked to their structure-activity relationships, with features like the monoterpene region, aromatic alkyl side chain, and aromatic carboxylic groups enhancing efficacy, particularly in CBD and its cyclic forms. These results highlight the potential of cannabinoids in developing therapies for resistant strains, though further research is needed to confirm their clinical effectiveness.

Antibacterial and Anti-Biofilm Efficacy of Endolysin LysAB1245 against a Panel of Important Pathogens

Infections caused by antibiotic-resistant bacteria pose a significant global challenge. This study explores the antibacterial effects of a bacteriophage-derived endolysin, LysAB1245, against important pathogens, including Acinetobacter baumannii, Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, and Staphylococcus aureus. We determined the minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) for all tested isolates. A time-kill study was conducted to evaluate the reduction in bacterial survival following treatment with LysAB1245. Additionally, the effects of LysAB1245 on P. aeruginosa K1455 and methicillin-resistant S. aureus (MRSA) NPRC 001R-formed biofilms were investigated. The MIC and MBC of LysAB1245 against all the tested isolates ranged from 4.68 to 9.36 µg/mL and 4.68 to 18.72 µg/mL, respectively. The time-kill study demonstrated more than a 4 log CFU/mL (99.99%) reduction in bacterial survival within 6 h of LysAB1245 treatment at 2MIC. LysAB1245 (1/8-1/2MIC) treatment significantly reduced biofilms formed by P. aeruginosa and MRSA in a concentration-dependent manner. Furthermore, scanning electron and confocal laser scanning microscopy confirmed the potential inhibition effects on 3-day established biofilms formed on abiotic surfaces upon treatment with LysAB1245 at 2MIC. The findings indicate that endolysin LysAB1245 could be employed as a new alternative therapeutic antibacterial and anti-biofilm agent for combating biofilm-related infections.

MRSA compendium of epidemiology, transmission, pathophysiology, treatment, and prevention within one health framework

Staphylococcus aureus is recognized as commensal as well as opportunistic pathogen of humans and animals. Methicillin resistant strain of S. aureus (MRSA) has emerged as a major pathogen in hospitals, community and veterinary settings that compromises the public health and livestock production. MRSA basically emerged from MSSA after acquiring SCCmec element through gene transfer containing mecA gene responsible for encoding PBP-2α. This protein renders the MRSA resistant to most of the β-lactam antibiotics. Due to the continuous increasing prevalence and transmission of MRSA in hospitals, community and veterinary settings posing a major threat to public health. Furthermore, high pathogenicity of MRSA due to a number of virulence factors produced by S. aureus along with antibiotic resistance help to breach the immunity of host and responsible for causing severe infections in humans and animals. The clinical manifestations of MRSA consist of skin and soft tissues infection to bacteremia, septicemia, toxic shock, and scalded skin syndrome. Moreover, due to the increasing resistance of MRSA to number of antibiotics, there is need to approach alternatives ways to overcome economic as well as human losses. This review is going to discuss various aspects of MRSA starting from emergence, transmission, epidemiology, pathophysiology, disease patterns in hosts, novel treatment, and control strategies.

Exploration of Bacterial Re-Growth as In Vitro Phenomenon Affecting Methods for Analysis of the Antimicrobial Activity of Chimeric Bacteriophage Endolysins

Drug alternatives to combat methicillin-resistant Staphylococcus aureus (MRSA) in human and animal healthcare are urgently needed. Recently, the recombinant bacteriophage endolysins, PRF-119 and its successor substance HY-133, have proven to be highly active against various S. aureus clonal lineages and to exhibit a very rapid bactericidal effect when standard methods for susceptibility testing are applied. Along with subsequent growth curve experiments, a re-growth phenomenon was observed in vitro necessitating its clarification for the assessment of the agent’s stability and activity as well as for methodological aspects of endolysin testing in general. Distinct in vitro parameters were comparatively examined applying also scanning electron microscopy, fluorescence assays and SDS-PAGE analysis. The shape and material of the culture vessels as well as the shaking conditions were identified as factors influencing the in vitro stability and activity of HY-133. The highest function maintenance was observed in plain centrifuge tubes. Based on this, the conditions and parameters of assays for testing the antimicrobial activities of phage endolysins were determined and adjusted. In particular, shear forces should be kept to a minimum. Our results form the basis for both future test standardization and re-growth-independent experiments as prerequisites for exact determination of the antimicrobial activities of engineered endolysins.

Treating Bacterial Infections with Bacteriophage-Based Enzybiotics: In Vitro, In Vivo and Clinical Application

Over the past few decades, we have witnessed a surge around the world in the emergence of antibiotic-resistant bacteria. This global health threat arose mainly due to the overuse and misuse of antibiotics as well as a relative lack of new drug classes in development pipelines. Innovative antibacterial therapeutics and strategies are, therefore, in grave need. For the last twenty years, antimicrobial enzymes encoded by bacteriophages, viruses that can lyse and kill bacteria, have gained tremendous interest. There are two classes of these phage-derived enzymes, referred to also as enzybiotics: peptidoglycan hydrolases (lysins), which degrade the bacterial peptidoglycan layer, and polysaccharide depolymerases, which target extracellular or surface polysaccharides, i.e., bacterial capsules, slime layers, biofilm matrix, or lipopolysaccharides. Their features include distinctive modes of action, high efficiency, pathogen specificity, diversity in structure and activity, low possibility of bacterial resistance development, and no observed cross-resistance with currently used antibiotics. Additionally, and unlike antibiotics, enzybiotics can target metabolically inactive persister cells. These phage-derived enzymes have been tested in various animal models to combat both Gram-positive and Gram-negative bacteria, and in recent years peptidoglycan hydrolases have entered clinical trials. Here, we review the testing and clinical use of these enzymes.

Endolysin, a Promising Solution against Antimicrobial Resistance

Antimicrobial resistance (AMR) is a global crisis for human public health which threatens the effective prevention and control of ever-increasing infectious diseases. The advent of pandrug-resistant bacteria makes most, if not all, available antibiotics invalid. Meanwhile, the pipeline of novel antibiotics development stagnates, which prompts scientists and pharmacists to develop unconventional antimicrobials. Bacteriophage-derived endolysins are cell wall hydrolases which could hydrolyze the peptidoglycan layer from within and outside of bacterial pathogens. With high specificity, rapid action, high efficiency, and low risk of resistance development, endolysins are believed to be among the best alternative therapeutic agents to treat multidrug resistant (MDR) bacteria. As of now, endolysins have been applied to diverse aspects. In this review, we comprehensively introduce the structures and activities of endolysins and summarize the latest application progress of recombinant endolysins in the fields of medical treatment, pathogen diagnosis, food safety, and agriculture.

Design and Selection of Engineered Lytic Proteins With Staphylococcus aureus Decolonizing Activity

Staphylococcus aureus causes various infections in humans and animals, the skin being the principal reservoir of this pathogen. The widespread occurrence of methicillin-resistant S. aureus (MRSA) limits the elimination and treatment of this pathogen. Phage lytic proteins have been proven as efficient antimicrobials against S. aureus. Here, a set of 12 engineered proteins based on endolysins were conceptualized to select the most optimal following a stepwise funnel approach assessing parameters including turbidity reduction, minimum inhibitory concentration (MIC), time-kill curves, and antibiofilm assays, as well as testing their stability in a broad range of storage conditions (pH, temperature, and ionic strength). The engineered phage lysins LysRODIΔAmi and ClyRODI-H5 showed the highest specific lytic activity (5 to 50 times higher than the rest), exhibited a shelf-life up to 6 months and remained stable at temperatures up to 50°C and in a pH range from 3 to 9. LysRODIΔAmi showed the lower MIC values against all staphylococcal strains tested. Both proteins were able to kill 6 log units of the strain S. aureus Sa9 within 5 min and could remove preformed biofilms (76 and 65%, respectively). Moreover, LysRODIΔAmi could prevent biofilm formation at low protein concentrations (0.15–0.6 μM). Due to its enhanced antibiofilm properties, LysRODIΔAmi was selected to effectively remove S. aureus contamination in both intact and disrupted keratinocyte monolayers. Notably, this protein did not demonstrate any toxicity toward human keratinocytes, even at high concentrations (22.1 μM). Finally, a pig skin ex vivo model was used to evaluate treatment of artificially contaminated pig skin using LysRODIΔAmi (16.5 μg/cm²). Following an early reduction of S. aureus, a second dose of protein completely eradicated S. aureus. Overall, our results suggest that LysRODIΔAmi is a suitable candidate as antimicrobial agent to prevent and treat staphylococcal skin infections.

Engineered endolysin-based "artilysins" for controlling the gram-negative pathogen Helicobacter pylori

Helicobacter pylori infection can cause a variety of gastrointestinal diseases. In severe cases, there is a risk of gastric cancer. Antibiotics are often used for clinical treatment of H. pylori infections. However, because of antibiotic overuse in recent years and the emergence of multidrug-resistant bacteria, there is an urgent need to develop new treatment methods and drugs to achieve complete eradication of H. pylori. Endolysins and holins encoded by bacterial viruses (i.e., phages) represent a promising avenue of investigation. These lyase-based antibacterial drugs act on the bacterial cell wall to destroy the bacteria. Currently, a type of endolysin that has been studied more frequently acts on the amide bond between peptidoglycans, and holin is a transmembrane protein that can punch holes in the cell membrane. However, as a Gram-negative bacterium, H. pylori possesses a layer of impermeable lipopolysaccharides on the cell wall, which prevents endolysin interaction with the cell wall. Therefore, we designed a genetic linkage between an endolysin enzyme and a holin enzyme with a section of polypeptides (e.g., polycations and hydrophobic peptides) that enable penetration of the outer membrane. These complexes were designated "artilysins" and were efficiently expressed in Escherichia coli. In vitro bacteriostasis experiments showed that the purified artilysins had strong bacteriostatic effects on H. pylori. In addition, the surface of H. pylori was perforated and destroyed, as confirmed by electron microscopy, which was proved that artilysins had bacteriolytic effect on H. pylori.

Bacteriophage-encoded enzymes destroying bacterial cell membranes and walls, and their potential use as antimicrobial agents

Appearance of pathogenic bacteria resistant to most, if not all, known antibiotics is currently one of the most significant medical problems. Therefore, development of novel antibacterial therapies is crucial for efficient treatment of bacterial infections in the near future. One possible option is to employ enzymes, encoded by bacteriophages, which cause destruction of bacterial cell membranes and walls. Bacteriophages use such enzymes to destroy bacterial host cells at the final stage of their lytic development, in order to ensure effective liberation of progeny virions. Nevertheless, to use such bacteriophage-encoded proteins in medicine and/or biotechnology, it is crucial to understand details of their biological functions and biochemical properties. Therefore, in this review article, we will present and discuss our current knowledge on the processes of bacteriophage-mediated bacterial cell lysis, with special emphasis on enzymes involved in them. Regulation of timing of the lysis is also discussed. Finally, possibilities of the practical use of these enzymes as antibacterial agents will be underlined and perspectives of this aspect will be presented.

Identification of Eltrombopag as a Repurposing Drug Against Staphylococcus epidermidis and its Biofilms

Staphylococcus epidermidis is a common cause of nosocomial infections, and readily adheres to medical apparatus to form biofilms consisting of highly resistant persister cells. Owing to the refractory infections caused by S. epidermidis biofilms and persisters in immunosuppressed patients, it is crucial to develop new antimicrobials. In the present study, we analyzed the antimicrobial effects of the thrombopoietin receptor agonist eltrombopag (EP) against S. epidermidis planktonic cells, biofilms, and persister cells. EP was significantly toxic to S. epidermidis with the minimal inhibitory concentration of 8 μg/ml, and effectively inhibited the biofilms and persisters in a strain-dependent manner. In addition, EP was only mildly toxic to mammalian cells after 12 to 24 h treatment. It also partially synergized with vancomycin against S. epidermidis, which enhanced its antimicrobial effects and reduced its toxicity to mammalian cells. Taken together, EP is a potential antibiotic for treating refractory infections caused by S. epidermidis.

Resistance to peptidoglycan-degrading enzymes

The spread of bacterial strains resistant to commonly used antibiotics urges the development of novel antibacterial compounds. Ideally, these novel antimicrobials should be less prone to the development of resistance. Peptidoglycan-degrading enzymes are a promising class of compounds with a fundamentally different mode of action compared to traditionally used antibiotics. The difference in the mechanism of action implies differences both in the mechanisms of resistance and the chances of its emergence. To critically assess the potential of resistance development to peptidoglycan-degrading enzymes, we review the available evidence for the development of resistance to these enzymes in vitro, along with the known mechanisms of resistance to lysozyme, bacteriocins, autolysins, and phage endolysins. We conclude that genetic determinants of resistance to peptidoglycan-degrading enzymes are unlikely to readily emerge de novo. However, resistance to these enzymes would probably spread by the horizontal transfer between intrinsically resistant and susceptible species. Finally, we speculate that the higher cost of the therapeutics based on peptidoglycan degrading enzymes compared to classical antibiotics might result in less misuse, which in turn would lead to lower selective pressure, making these antibacterials less prone to resistance development.

Characterization of Clinical MRSA Isolates from Northern Spain and Assessment of Their Susceptibility to Phage-Derived Antimicrobials

Methicillin-resistant Staphylococcus aureus (MRSA) is a prevalent nosocomial pathogen, causing a wide range of diseases. The increased frequency of MRSA isolates in hospitals and the emergence of vancomycin resistance have sparked the search for new control strategies. This study aimed to characterize sixty-seven MRSA isolates collected from both infected patients and asymptomatic carriers in a Spanish hospital. RAPD-PCR allowed the identification of six genetic patterns. We also investigated the presence of genes involved in producing adhesins, toxins and the capsule; the biofilm; and antimicrobial resistance. A notable percentage of the isolates carried virulence genes and showed medium-high ability to form biofilms. Next, we assessed the strains' susceptibility to two phages (phiIPLA-C1C and phiIPLA-RODI) and one endolysin (LysRODI). All strains were resistant to phiIPLA-C1C, and most (70.2%) were susceptible to phiIPLA-RODI. Regarding LysRODI, all strains displayed susceptibility, although to varying degrees. There was a correlation between endolysin susceptibility and the random amplification of polymorphic DNA (RAPD) profile or the presence of some virulence genes (fnbA, eta, etb, PVL and czr), but that was not observed with biofilm-forming ability, strain origin or phage sensitivity. Taken together, these findings can help to explain the factors influencing endolysin effectiveness, which will contribute to the development of efficient therapies targeting MRSA infections.

Synthesis, Characterization, and Pharmacodynamics Study of Enrofloxacin Mesylate

Introduction

Enrofloxacin is used in the treatment of a wide variety of bacterial infections in mammals. However, its poor solubility limits the clinical use.

Methods

In order to improve the solubility of enrofloxacin, the enrofloxacin mesylate (EM) were obtained by a chemical synthesis method. The characterization of EM was carried out using ultraviolet scan (UV), synchronous thermal analysis (SDT), fourier transform infrared spectrometer (FTIR) and mass spectrometry (MS), nuclear magnetic resonance (NMR) and X-ray powder diffraction analysis (XRPD). Acute toxicity of EM in Kunming mice was studied. Besides, pharmacokinetic studies were performed in New Zealand rabbits at a single oral dose of 10 mg/kg, and the antibacterial activity of EM was also evaluated.

Results

EM was successfully synthesized and purified. The stoichiometric ratio of mesylate to enrofloxacin was 1:1 and the aqueous solubility of EM was 483.01±4.06 mg/mL, the solubility of EM was about 2000 times higher than enrofloxacin. The oral lethal dose (LD₅₀) of EM was 1168.364 mg/kg, and the pharmacokinetics indicated that the oral relative bioavailability of EM was about 1.79 times and 1.48 times higher than that of enrofloxacin and enrofloxacin hydrochloride, respectively. In addition, the in vitro antibacterial activity of EM was not significantly changed compared with enrofloxacin and enrofloxacin hydrochloride.

Conclusion

EM has higher solubility, low toxicity for oral use, and increases the oral bioavailability in rabbit. This study may be of benefit for the development of new enrofloxacin drugs.

In Vitro Activity of the Bacteriophage Endolysin HY-133 against Staphylococcus aureus Small-Colony Variants and Their Corresponding Wild Types

Nasal carriage of methicillin-susceptible (MSSA) and methicillin-resistant Staphylococcus aureus (MRSA) represents both a source and a risk factor for subsequent infections. However, existing MRSA decolonization strategies and antibiotic treatment options are hampered by the duration of administration and particularly by the emergence of resistance. Moreover, beyond classical resistance mechanisms, functional resistance as the formation of the small-colony variant (SCV) phenotype may also impair the course and treatment of S. aureus infections. For the recombinant bacteriophage endolysin HY-133, rapid bactericidal and highly selective in vitro activities against MSSA and MRSA has been shown. In order to assess the in vitro efficacy of HY-133 against the SCV phenotype, minimal inhibitory (MIC) and minimal bactericidal concentrations (MBC) were evaluated on clinical SCVs, their isogenic wild types, as well as on genetically derived and gentamicin-selected SCVs. For all strains and growth phases, HY-133 MIC and MBC ranged between 0.12 and 1 mg/L. Time-kill studies revealed a fast-acting bactericidal activity of HY-133 resulting in a ≥3 - log10 decrease in CFU/mL within 1 h compared to oxacillin, which required 4⁻24 h. Since the mode of action of HY-133 was independent of growth phase, resistance pattern, and phenotype, it is a promising candidate for future S. aureus decolonization strategies comprising rapid activity against phenotypic variants exhibiting functional resistance.