In Vitro Anti-Biofilm Activity of Bacteriophage K (ATCC 19685-B1) and Daptomycin against Staphylococci

Cholesterol-Rich Antibiotic-Loaded Liposomes as Efficient Antimicrobial Therapeutics

Introduction

Liposomal antibiotics have demonstrated higher bacteriostatic and bactericidal activities than free drugs. In this study, we investigated the effects of cholesterol (Chol) content of liposomes, liposome concentration, and surface coating with polyethylene glycol (PEG) on the antimicrobial activity of moxifloxacin (MOX) liposomes against Staphylococcus epidermidis (ATCC 35984) (S.e).

Methods

MOX-liposome compositions with increasing Chol content were evaluated for their susceptibility to planktonic S.e (growth inhibition, killing, and live-dead staining), as well as against pre-formed biofilms (crystal violet, MTT assay, and confocal microscopy). The MOX-liposomes prepared by active loading were characterized in terms of loading, size distribution, and zeta potential.

Results-Discussion

All liposomes had nano-dimensions ranging in diameter from 92nm to 114nm, with zeta-potential values from -2.30mV to -4.50mV. Planktonic bacteria and established biofilms are significantly more susceptible to MOX-liposomes with higher Chol-content than other liposome-types, and the same MOX dose encapsulated in 10 times higher lipids demonstrated higher antimicrobial activity. Coating the MOX liposomes with PEG did not affect their activity. Flow cytometry showed higher binding of Chol-rich liposomes to bacteria, explaining the higher antimicrobial activity. Interestingly, the integrity of calcein-loaded Chol-rich liposomes was much lower than that of liposomes with low or no Chol during incubation with various strains of S. epidermidis. In vivo results in a zebrafish infection model (bacteremia) confirmed the superior activity of Chol-rich MOX-liposomes compared to the free drug.

Conclusion

The current in vitro and in vivo findings demonstrated the potential of PEGylated and Chol-rich liposomal antibiotics as highly efficient therapeutics for the treatment of S. epidermidis infections.

One-Two Punch: Phage-Antibiotic Synergy Observed against Staphylococcus aureus by Combining Pleurotin and Phage K

The surge in antibiotic-resistant Staphylococcus aureus infections has been deemed a major public health concern. There is an urgent need for novel antimicrobial therapies, chemical and nonantibiotic. The basidiomycota-derived, secondary metabolite pleurotin has been shown to be effective against Gram-positive bacteria, while bacteriophages could be the ultimate nonantibiotic alternative. In this study, the combination of pleurotin and phage K targeting S. aureus was examined. Pleurotin was isolated from the basidiomycota fungus Hohenbuehelia grisea. The cytotoxicity of pleurotin was assessed in two human cell lines in comparison to pleuromutilin, vancomycin, and phage K. The antibiotics were then tested independently or in combination with phage K against two S. aureus strains. Cytotoxicity of pleurotin in human cells was comparable to vancomycin and pleuromutilin. Results suggest that adding phage K has a synergistic effect and can lower the MIC for pleurotin, pleuromutilin, and vancomycin. This demonstrates that pleurotin could be a viable antistaphylococcal drug.

Bacteriophage Resistance, Adhesin's and Toxin's Genes Profile of Staphylococcus aureus Causing Infections in Children and Adolescents

Staphylococcus aureus is a common pathogen, often recovered from children's infections. Βiofilm formation, antimicrobial resistance and production of adhesins and toxins contribute to its virulence. As resistance to antimicrobials rises worldwide, alternative therapies like bacteriophages (among them the well-studied Bacteriophage K) can be helpful. The aim of this study was to determine the bacteriophage and antimicrobial susceptibility and the presence of virulence genes among S. aureus from infections in children and adolescents. Eighty S. aureus isolates were tested for biofilm formation and antimicrobial susceptibility. The presence of two genes of the ica operon (icaA, icaD), adhesin's (fnbA, fnbB, sasG) and toxin's genes (PVL, tst, eta, etb) was tested by PCRs. Susceptibility to Bacteriophage K was determined using a spot assay. Thirteen isolates were methicillin-resistant (MRSA) and 41 were multi-resistant. Twenty-five S. aureus (31.3%) were resistant to Bacteriophage K, mostly from ocular and ear infections. Twelve S. aureus (15%) were PVL-positive, seven (8.8%) positive for tst, 18 (22.5%) were eta-positive and 46 were (57.5%) etb-positive. A total of 66 (82.5%) isolates carried fnbA, 16 (20%) fnbB and 26 (32.5%) sasG. PVL, tst and sasG carriage were more frequent in MRSA. Bacteriophage-susceptible isolates carried more frequently eta (32.7%) and etb (69.1%) compared to phage-resistant S. aureus (0% and 32%, respectively). Although mainly methicillin-sensitive, S. aureus from pediatric infections exhibited high antimicrobial resistance and carriage of virulence genes (especially for exfoliative toxins and fnbA). MRSA was associated with PVL, tst and sasG carriage, whereas Bacteriophage susceptibility was associated with eta and etb. The high level of Bacteriophage K susceptibility highlights its potential use against staphylococcal infections.

Current developments and prospects of the antibiotic delivery systems

Antibiotics have remained the cornerstone for the treatment of bacterial infections ever since their discovery in the twentieth century. The uproar over antibiotic resistance among bacteria arising from genome plasticity and biofilm development has rendered current antibiotic therapies ineffective, urging the development of innovative therapeutic approaches. The development of antibiotic resistance among bacteria has further heightened the clinical failure of antibiotic therapy, which is often linked to its low bioavailability, side effects, and poor penetration and accumulation at the site of infection. In this review, we highlight the potential use of siderophores, antibodies, cell-penetrating peptides, antimicrobial peptides, bacteriophages, and nanoparticles to smuggle antibiotics across impermeable biological membranes to achieve therapeutically relevant concentrations of antibiotics and combat antimicrobial resistance (AMR). We will discuss the general mechanisms via which each delivery system functions and how it can be tailored to deliver antibiotics against the paradigm of mechanisms underlying antibiotic resistance.

In Vitro Efficacy of Phage Therapy Against Common Biofilm-forming Pathogens in Orthopedics and Trauma Surgery

Formation of biofilms by bacteria is a major challenge in a clinical setting. The importance of these biofilms increases in specialties where foreign bodies and prosthetic material are used. Orthopaedics is such a speciality and phage therapy could offer additional therapeutic options when dealing with biofilm infections.We conducted a systematic literature review using the PubMed database. We searched for phage activity against biofilms of the most common pathogens found in orthopaedics.The results of the systematic review were broken down into different categories and discussed accordingly. We concentrated on the time the biofilms were allowed to mature, and the surface they were grown on. In addition, we checked the efficacy of bacteriophages compared to antibiotics and when applied simultaneously with antibiotics. We also investigated the source of the phages, how they were tested for sensibility against the biofilms, as well the conditions (pH, temperature) under which they remained active and stable.The data suggests that the in vitro efficacy of phages does not change under a wide spectrum of temperature and pH. To further explore the use of bacteriophages in orthopaedics, we need further studies that test biofilms which matured for several weeks on surfaces that are common in arthroplasty and traumatology.

Daptomycin Liposomes Exhibit Enhanced Activity against Staphylococci Biofilms Compared to Free Drug

The purpose of the present study was to investigate the anti-staphylococcal activity of liposomal daptomycin against four biofilm-producing S. aureus and S. epidermidis clinical strains, three of which are methicillin-resistant. Neutral and negatively charged daptomycin-loaded liposomes were prepared using three methods, namely, thin-film hydration (TFH), a dehydration-rehydration vesicle (DRV) method, and microfluidic mixing (MM); moreover, they were characterized for drug encapsulation (EE%), size distribution, zeta-potential, vesicle stability, drug release, and drug integrity. Interestingly, whilst drug loading in THF and DRV nanosized (by extrusion) vesicles was around 30-35, very low loading (~4%) was possible in MM vesicles, requiring further explanatory investigations. Liposomal encapsulation protected daptomycin from degradation and preserved its bioactivity. Biofilm mass (crystal violet, CV), biofilm viability (MTT), and growth curve (GC) assays evaluated the antimicrobial activity of neutral and negatively charged daptomycin-liposomes towards planktonic bacteria and biofilms. Neutral liposomes exhibited dramatically enhanced inhibition of bacterial growth (compared to the free drug) for all species studied, while negatively charged liposomes were totally inactive. Biofilm prevention and treatment studies revealed high antibiofilm activity of liposomal daptomycin. Neutral liposomes were more active for prevention and negative charge ones for treating established biofilms. Planktonic bacteria as well as the matured biofilms of low daptomycin-susceptible, methicillin-resistant Staphylococcus aureus (MRSA) and Staphylococcus epidermidis (MRSE) strains were almost completely eradicated by liposomal-daptomycin, indicating the need for their further exploration as antimicrobial therapeutics.

Bacteriophage entrapped chitosan microgel for the treatment of biofilm-mediated polybacterial infection in burn wounds

Staphylococcus aureus (S. aureus) and Pseudomonas aeruginosa (P. aeruginosa) bacteria are most commonly present in burn wound infections. Multidrug resistance (MDR) and biofilm formation make it difficult to treat these infections. Bacteriophages (BPs) are proven as an effective therapy against MDR as well as biofilm-associated wound infections. In the present work, a naturally inspired bacteriophage cocktail loaded chitosan microparticles-laden topical gel has been developed for the effective treatment of these infections. Bacteriophages against MDR S. aureus (BPSAФ1) and P. aeruginosa (BPPAФ1) were isolated and loaded separately and in combination into the chitosan microparticles (BPSAФ1-CHMPs, BPPAФ1-CHMPs, and MBP-CHMPs), which were later incorporated into the SEPINEO™ P 600 gel (BPSAФ1-CHMPs-gel, BPPAФ1-CHMPs-gel, and MBP-CHMPs-gel). BPs were characterized for their morphology, lytic activity, burst size, and hemocompatibility, and BPs belongs to Caudoviricetes class. Furthermore, BPSAФ1-CHMPs, BPPAФ1-CHMPs, and MBP-CHMPs had an average particle size of 1.19 ± 0.11, 1.42 ± 0.21, and 2.84 ± 0.28 μm, respectively, and expressed promising in vitro antibiofilm eradication potency. The ultrasound and photoacoustic imaging in infected burn wounds demonstrated improved wound healing reduced inflammation and increased oxygen saturation following treatment with BPs formulations. The obtained results suggested that the incorporation of the BPs in the MP-gel protected the BPs, sustained the BPs release, and improved the antibacterial activity.

How Do Phages Disrupt the Structure of Enterococcus faecalis Biofilm?

Biofilms are composed of multicellular communities of microbial cells and their self-secreted extracellular polymeric substances (EPS). The viruses named bacteriophages can infect and lyze bacterial cells, leading to efficient biofilm eradication. The aim of this study was to analyze how bacteriophages disrupt the biofilm structure by killing bacterial cells and/or by damaging extracellular polysaccharides, proteins, and DNA. The use of colorimetric and spectrofluorimetric methods and confocal laser scanning microscopy (CLSM) enabled a comprehensive assessment of phage activity against E. faecalis biofilms. The impact of the phages vB_Efa29212_2e and vB_Efa29212_3e was investigated. They were applied separately or in combination on 1-day and 7-day-old biofilms. Phages 2e effectively inhibited the growth of planktonic cells with a limited effect on the biofilm. They did not notably affect extracellular polysaccharides and proteins; however, they increased DNA levels. Phages 3e demonstrated a potent and dispersing impact on E. faecalis biofilms, despite being slightly less effective than bacteriophages 2e against planktonic cells. Phages 3e reduced the amount of extracellular polysaccharides and increased eDNA levels in both 1-day-old and 7-day-old biofilm cultures. Phage cocktails had a strong antimicrobial effect on both planktonic and biofilm-associated bacteria. A significant reduction in the levels of polysaccharides, proteins, and eDNA in 1-day-old biofilm samples was noted, which confirms that phages interfere with the structure of E. faecalis biofilm by killing bacterial cells and affecting extracellular polymer levels.

A Bacteriophage Microgel Effectively Treats the Multidrug-Resistant Acinetobacter baumannii Bacterial Infections in Burn Wounds

Multidrug-resistant (MDR) Acinetobacter baumannii (A. baumannii) is one of the major pathogens present in burn wound infections. Biofilm formation makes it further challenging to treat with clinically available antibiotics. In the current work, we isolated the A. baumannii-specific bacteriophages (BPABΦ1), loaded into the chitosan microparticles followed by dispersion in gel, and evaluated therapeutic efficacy against MDR A. baumannii clinical strains. Isolated BPABΦ1 were found to belong to the Corticoviridae family, with burst size 102.12 ± 2.65 PFUs per infected host cell. The BPABΦ1 loaded chitosan microparticles were evaluated for quality attributes viz. size, PDI, surface morphology, in vitro release, etc. The developed formulation exhibited excellent antibiofilm eradication potential in vitro and effective wound healing after topical application.

Induction of Viable but Non-Culturable State in Clinically Relevant Staphylococci and Their Detection with Bacteriophage K

Prosthetic joint infections are frequently associated with biofilm formation and the presence of viable but non-culturable (VBNC) bacteria. Conventional sample culturing remains the gold standard for microbiological diagnosis. However, VBNC bacteria lack the ability to grow on routine culture medium, leading to culture-negative results. Bacteriophages are viruses that specifically recognize and infect bacteria. In this study, we wanted to determine if bacteriophages could be used to detect VBNC bacteria. Four staphylococcal strains were cultured for biofilm formation and transferred to low-nutrient media with different gentamycin concentrations for VBNC state induction. VBNC bacteria were confirmed with the BacLight^TM viability kit staining. Suspensions of live, dead, and VBNC bacteria were incubated with bacteriophage K and assessed in a qPCR for their detection. The VBNC state was successfully induced 8 to 19 days after incubation under stressful conditions. In total, 6.1 to 23.9% of bacteria were confirmed alive while not growing on conventional culturing media. During the qPCR assay, live bacterial suspensions showed a substantial increase in phage DNA. No detection was observed in dead bacteria or phage non-susceptible E. coli suspensions. However, a reduction in phage DNA in VBNC bacterial suspensions was observed, which confirmed the detection was successful based on the adsorption of phages.

Biofilms: Formation, Research Models, Potential Targets, and Methods for Prevention and Treatment

Due to the continuous rise in biofilm-related infections, biofilms seriously threaten human health. The formation of biofilms makes conventional antibiotics ineffective and dampens immune clearance. Therefore, it is important to understand the mechanisms of biofilm formation and develop novel strategies to treat biofilms more effectively. This review article begins with an introduction to biofilm formation in various clinical scenarios and their corresponding therapy. Established biofilm models used in research are then summarized. The potential targets which may assist in the development of new strategies for combating biofilms are further discussed. The novel technologies developed recently for the prevention and treatment of biofilms including antimicrobial surface coatings, physical removal of biofilms, development of new antimicrobial molecules, and delivery of antimicrobial agents are subsequently presented. Finally, directions for future studies are pointed out.

Moxifloxacin Liposomes: Effect of Liposome Preparation Method on Physicochemical Properties and Antimicrobial Activity against Staphylococcus epidermidis

The aim of this study was the development of optimal sustained-release moxifloxacin (MOX)-loaded liposomes as intraocular therapeutics of endophthalmitis. Two methods were compared for the preparation of MOX liposomes; the dehydration–rehydration (DRV) method and the active loading method (AL). Numerous lipid-membrane compositions were studied to determine the potential effect on MOX loading and retention in liposomes. MOX and phospholipid contents were measured by HPLC and a colorimetric assay for phospholipids, respectively. Vesicle size distribution and surface charge were measured by DLS, and morphology was evaluated by cryo-TEM. The AL method conferred liposomes with higher MOX encapsulation compared to the DRV method for all the lipid compositions used. Cryo-TEM showed that both liposome types had round vesicular structure and size around 100–150 nm, while a granular texture was evident in the entrapped aqueous compartments of most AL liposomes, but substantially less in DRV liposomes; X-ray diffraction analysis demonstrated slight crystallinity in AL liposomes, especially the ones with highest MOX encapsulation. AL liposomes retained MOX for significantly longer time periods compared to DRVs. Lipid composition did not affect MOX release from DRV liposomes but significantly altered drug loading/release in AL liposomes. Interestingly, AL liposomes demonstrated substantially higher antimicrobial potential towards S. epidermidis growth and biofilm susceptibility compared to corresponding DRV liposomes, indicating the importance of MOX retention in liposomes on their activity. In conclusion, the liposome preparation method/type determines the rate of MOX release from liposomes and modulates their antimicrobial potential, a finding that deserves further in vitro and in vivo exploitation.