A combined pharmacodynamic quantitative and qualitative model reveals the potent activity of daptomycin and delafloxacin against Staphylococcus aureus biofilms

Comparison of the in vitro activities of delafloxacin and comparators against Staphylococcus epidermidis clinical strains involved in osteoarticular infections: a CRIOGO multicentre retrospective study

OBJECTIVES

Staphylococcus epidermidis bone and joint infections (BJIs) on material are often difficult to treat. The activity of delafloxacin has not yet been studied on S. epidermidis in this context. The aim of this study was to assess its in vitro activity compared with other fluoroquinolones, against a large collection of S. epidermidis clinical strains.

METHODS

We selected 538 S. epidermidis strains isolated between January 2015 and February 2023 from six French teaching hospitals. One hundred and fifty-two strains were ofloxacin susceptible and 386 were ofloxacin resistant. Identifications were performed by MS and MICs were determined using gradient concentration strips for ofloxacin, levofloxacin, moxifloxacin and delafloxacin.

RESULTS

Ofloxacin-susceptible strains were susceptible to all fluoroquinolones. Resistant strains had higher MICs of all fluoroquinolones. Strains resistant to ofloxacin (89.1%) still showed susceptibility to delafloxacin when using the Staphylococcus aureus 2021 CA-SFM/EUCAST threshold of 0.25 mg/L. In contrast, only 3.9% of the ofloxacin-resistant strains remained susceptible to delafloxacin with the 0.016 mg/L S. aureus breakpoint according to CA-SFM/EUCAST guidelines in 2022. The MIC50 was 0.094 mg/L and the MIC90 was 0.38 mg/L.

CONCLUSIONS

We showed low delafloxacin MICs for ofloxacin-susceptible S. epidermidis strains and a double population for ofloxacin-resistant strains. Despite the absence of breakpoints for S. epidermidis, delafloxacin may be an option for the treatment of complex BJI, including strains with MICs of ≤0.094 mg/L, leading to 64% susceptibility. This study underlines the importance for determining specific S. epidermidis delafloxacin breakpoints for the management of BJI on material.

Carboxylated nanofibrillated cellulose empowers moxifloxacin to overcome Staphylococcus aureus biofilm in bacterial keratitis

Bacterial keratitis is one of the vision-threatening ocular diseases that is increasing at an alarming rate due to antimicrobial resistance. One of the primary causes of antimicrobial resistance could be biofilm formation, which alters the mechanism and physiology of the microorganisms. Even a potent drug fails to inhibit biofilm due to the extracellular polysaccharide matrix surrounding the bacteria, inhibiting the permeation of drugs. Therefore, we aimed to develop carboxylated nanocellulose fibers loaded with moxifloxacin (Mox-cNFC) as a novel drug delivery system to treat bacterial corneal infection. Nanocellulose fibers were fabricated using a two-step method involving citric acid hydrolysis followed by TEMPO oxidation to introduce carboxylated groups (1.12 mmol/g). The Mox-cNFC particles showed controlled drug release till 40 h through diffusion. In vitro biofilm inhibition studies showed the particle's ability to disrupt the biofilm matrix and enhance the drug penetration to achieve optimal concentrations that inhibit the persister cells (without increasing minimum inhibitory concentration), thereby reducing the bacterial drug-resistant property. In vivo studies revealed the therapeutic potential of Mox-cNFC to treat Staphylococcus aureus-induced bacterial keratitis with once-a-day treatment, unlike neat moxifloxacin. Mox-cNFC could improve patient compliance by reducing the frequency of instillation and a controlled drug release to prevent toxicity.

Synthesis and Staphylococcus aureus biofilm inhibitory activity of indolenine-substituted pyrazole and pyrimido[1,2-b]indazole derivatives

Staphylococcus aureus is a highly adaptable opportunistic pathogen that can form biofilms and generate persister cells, leading to life-threatening infections that are difficult to treat with antibiotics alone. Therefore, there is a need for an effective S. aureus biofilm inhibitor to combat this public health threat. In this study, a small library of indolenine-substituted pyrazoles and pyrimido[1,2-b]indazole derivatives were synthesised, of which the hit compound exhibited promising antibiofilm activities against methicillin-susceptible S. aureus (MSSA ATCC 29213) and methicillin-resistant S. aureus (MRSA ATCC 33591) at concentrations significantly lower than the planktonic growth inhibition. The hit compound could prevent biofilm formation and eradicate mature biofilms of MSSA and MRSA, with a minimum biofilm inhibitory concentration (MBIC50) value as low as 1.56 µg/mL and a minimum biofilm eradication concentration (MBEC50) value as low as 6.25 µg/mL. The minimum inhibitory concentration (MIC) values of the hit compound against MSSA and MRSA were 50 µg/mL and 25 µg/mL, respectively, while the minimum bactericidal concentration (MBC) values against MSSA and MRSA were > 100 µg/mL. Preliminary structure-activity relationship analysis reveals that the fused benzene ring and COOH group of the hit compound are crucial for the antibiofilm activity. Additionally, the compound was not cytotoxic to human alveolar A549 cells, thus highlighting its potential as a suitable candidate for further development as a S. aureus biofilm inhibitor.

New Antimicrobials for Gram-Positive Sustained Infections: A Comprehensive Guide for Clinicians

Antibiotic resistance is a public health problem with increasingly alarming data being reported. Gram-positive bacteria are among the protagonists of severe nosocomial and community infections. The objective of this review is to conduct an extensive examination of emerging treatments for Gram-positive infections including ceftobiprole, ceftaroline, dalbavancin, oritavancin, omadacycline, tedizolid, and delafloxacin. From a methodological standpoint, a comprehensive analysis on clinical trials, molecular structure, mechanism of action, microbiological targeting, clinical use, pharmacokinetic/pharmacodynamic features, and potential for therapeutic drug monitoring will be addressed. Each antibiotic paragraph is divided into specialized microbiological, clinical, and pharmacological sections, including detailed and appropriate tables. A better understanding of the latest promising advances in the field of therapeutic options could lead to the development of a better approach in managing antimicrobial therapy for multidrug-resistant Gram-positive pathogens, which increasingly needs to be better stratified and targeted.

Daptomycin as an option for lock therapy: a systematic literature review

Aim: To review preclinical and clinical data relevant to daptomycin lock therapy in catheter-related bloodstream infection (CRBSI). Methods: Systematic review in PubMed, Scopus and clinical trial registries. Results: Preclinical data demonstrate daptomycin lock solution stability and compatibility with heparin, good biofilm penetration, bactericidal activity against biofilm-embedded bacteria, and high efficacy in vitro and in animal catheter infection models. Clinical data remain limited (two case reports and five case series totaling n = 65 CRBSI episodes), albeit promising (successful catheter salvage in about 80% of cases). Conclusion: Despite theoretical advantages of daptomycin, clinical data remain scarce. Comparative studies versus alternative lock solutions are needed, as well as studies to define optimal daptomycin lock regimen (including optimal concentration, dwell time and lock duration).

Updated Review on Clinically-Relevant Properties of Delafloxacin

The extensive use of fluoroquinolones has been consequently accompanied by the emergence of bacterial resistance, which triggers the necessity to discover new compounds. Delafloxacin is a brand-new anionic non-zwitterionic fluoroquinolone with some structural particularities that give it attractive proprieties: high activity under acidic conditions, greater in vitro activity against Gram-positive bacteria-even those showing resistance to currently-used fluoroquinolones-and nearly equivalent affinity for both type-II topoisomerases (i.e., DNA gyrase and topoisomerase IV). During phases II and III clinical trials, delafloxacin showed non-inferiority compared to standard-of-care therapy in the treatment of acute bacterial skin and skin structure infections and community-acquired bacterial pneumonia, which resulted in its approval in 2017 by the Food and Drug Administration for indications. Thanks to its overall good tolerance, its broad-spectrum in vitro activity, and its ease of use, it could represent a promising molecule for the treatment of bacterial infections.

Introduction of a β-leucine residue instead of leucine9 and glycine10 residues in Temporin L for improved cell selectivity, stability and activity against planktonic and biofilm of methicillin resistant S. aureus

Leucine and glycine residues, at the 9th and 10th positions of helical domain of naturally occurring antimicrobial peptide (AMP), Temporin L were substituted with an unnatural amino acid, β-leucine (homovaline) to improve its serum protease stability, haemolytic/cytotoxic properties and reduce the size to some extent. The designed analogue, L9βl-TL showed either equal or improved antimicrobial activity to TL against different microorganisms including the resistant strains. Interestingly, L9βl-TL also exhibited lower haemolytic and cytotoxic activities against human red blood cells and 3T3 cells, respectively. Moreover, L9βl-TL showed antibacterial activity in presence of 25% (v/v) human serum and showed resistance against proteolytic cleavage in presence of it that suggested the serum protease stability of the TL-analogue. L9βl-TL exhibited un-ordered secondary structures in both bacterial and mammalian membrane mimetic lipid vesicles as compared to the helical structures of TL in these environments. However, tryptophan fluorescence studies demonstrated more selective interaction of L9βl-TL with bacterial membrane mimetic lipid vesicles in comparison to non-selective interactions of TL with both kinds of lipid vesicles. Membrane depolarization studies with live MRSA and bacterial membrane-mimetic lipid vesicles suggested a membrane-disrupting mode of action of L9βl-TL. L9βl-TL showed faster bactericidal mechanism compared to TL against MRSA. Interestingly, L9βl-TL was found as more potent than TL either in inhibiting biofilm formation or in eradicating the mature biofilm formed by MRSA. Overall, the present work demonstrates a simple and useful strategy to design of an analogue of TL, with minimal modifications while maintaining its antimicrobial activity with lesser toxicity and higher stability which could be attempted for other AMPs as well.

Efficacy and Toxicity Studies of Novel α-MSH Analogues with Antibiofilm Action and β-Lactam Resensitization Potential against MRSA

Methicillin-resistant Staphylococcus aureus (MRSA), a biofilm-forming recalcitrant pathogen with a multidrug-resistant profile, poses a pandemic threat to human health and is the leading cause of severe infections in both healthcare and community settings. In this study, toward designing novel α-MSH-based peptides with enhanced activity and stability against MRSA, particularly its stationary phase and biofilm, we explored a design approach to augment the hydrophobicity of an 8-mer C-terminal α-MSH(6-13)-based peptide Ana-5 through the incorporation of a bulky unnatural amino acid. The designed Ana-peptides overcame the limitation of diminished activity in biological media and exhibited enhanced antistaphylococcal activity and cell selectivity. With membrane rupture as the primary mode of action, the peptides exhibited inhibitory potential against S. aureus biofilms. Importantly, the peptides did not exhibit any adverse effects in the in vivo toxicity studies and were also able to significantly alleviate bacterial infection in a systemic infection mice model study. Additionally, the peptides retained their activity in the presence of serum and displayed a low propensity toward resistance development in MRSA cells. Moreover, the observed synergistic potential of Ana-10 with conventional antibiotics could be vital in resurrecting discarded antibiotics. Thus, this study provides us with an exciting lead, Ana-10, for further development against biofilm-based chronic S. aureus infections.

Preparation, Characterization, and Staphylococcus aureus Biofilm Elimination Effect of Baicalein-Loaded β-Cyclodextrin-Grafted Chitosan Nanoparticles

BACKGROUND AND PURPOSE

Infections caused by Staphylococcus aureus (S. aureus) colonization in medical implants are resistant to antibiotics due to the formation of bacterial biofilm internal. Baicalein (BA) has been confirmed as an inhibitor of bacterial biofilm with less pronounced effects owing to its poor solubility and absorption. Studies have found that β-cyclodextrin-grafted chitosan (CD-CS) can improve drug efficiency as a drug carrier. Therefore, this research aims to prepare BA-loaded CD-CS nanoparticles (CD-CS-BA-NPs) for S. aureus biofilm elimination enhancement.

METHODS

CD-CS-BA-NPs were prepared via the ultrasonic method. The NPs were characterized using the X-ray diffraction (XRD), Thermo gravimetric analyzer (TGA), Transmission electron microscopy (TEM) and Malvern Instrument. The minimum inhibitory concentration (MIC) of the NPs were investigated. The biofilm models in vivo and in vitro were constructed to assess the S. aureus biofilm elimination ability of the NPs. The Confocal laser method (CLSM) and the Live/Dead kit were employed to explore the mechanism of the NPs in promoting biofilm elimination.

RESULTS

CD-CS-BA-NPs have an average particle size of 424.5 ± 5.16 nm, a PDI of 0.2 ± 0.02, and a Zeta potential of 46.13 ± 1.62 mV. TEM images revealed that the NPs were spherical with uniform distribution. XRD and TGA analysis verified the formation and the thermal stability of the NPs. The NPs with a MIC of 12.5 ug/mL exhibited a better elimination effect on S. aureus biofilm both in vivo and in vitro. The mechanism study demonstrated that the NPs may permeate into the biofilm more easily, thereby improving the biofilm elimination effect of BA.

CONCLUSION

CD-CS-BA-NPs were successfully prepared with enhanced elimination of S. aureus biofilm, which may serve as a reference for future development of anti-biofilm agents.

Antibiofilm Combinatory Strategy: Moxifloxacin-Loaded Nanosystems and Encapsulated N-Acetyl-L-Cysteine

Bacterial biofilms of Staphylococcus aureus, formed on implants, have a massive impact on the increasing number of antimicrobial resistance cases. The current treatment for biofilm-associated infections is based on the administration of antibiotics, failing to target the biofilm matrix. This work is focused on the development of multiple lipid nanoparticles (MLNs) encapsulating the antibiotic moxifloxacin (MOX). The nanoparticles were functionalized with d-amino acids to target the biofilm matrix. The produced formulations exhibited a mean hydrodynamic diameter below 300 nm, a low polydispersity index, and high encapsulation efficiency. The nanoparticles exhibited low cytotoxicity towards fibroblasts and low hemolytic activity. To target bacterial cells and the biofilm matrix, MOX-loaded MLNs were combined with a nanosystem encapsulating a matrix-disruptive agent: N-acetyl-L-cysteine (NAC). The nanosystems alone showed a significant reduction of both S. aureus biofilm viability and biomass, using the microtiter plate biofilm model. Further, biofilms grown inside polyurethane catheters were used to assess the effect of combining MOX-loaded and NAC-loaded nanosystems on biofilm viability. An increased antibiofilm efficacy was observed when combining the functionalized MOX-loaded MLNs and NAC-loaded nanosystems. Thus, nanosystems as carriers of bactericidal and matrix-disruptive agents are a promising combinatory strategy towards the eradication of S. aureus biofilms.

Seaweed Extracts as an Effective Gateway in the Search for Novel Antibiofilm Agents against Staphylococcus aureus

Treatment of biofilm-associated infections has become a major challenge in biomedical and clinical fields due to the failure of conventional treatments in controlling this highly complex and tolerant structure. Therefore, the search for novel antibiofilm agents with increased efficacy as those provided by natural products, presents an urgent need. The aim of this study was to explore extracts derived from three algae (green Ulva lactuca, brown Stypocaulon scoparium, red Pterocladiella capillacea) for their potential antibiofilm activity against Staphylococcus aureus, bacterium responsible for several acute and chronic infections. Seaweed extracts were prepared by successive maceration in various solvents (cyclohexane (CH), dichloromethane (DCM), ethyl acetate (EA), and methanol (MeOH)). The ability of the different extracts to inhibit S. aureus biofilm formation was assessed using colony-forming unit (CFU) counts method supported by epifluorescence microscopic analysis. Effects of active extracts on the biofilm growth cycle, as well as on S. aureus surface hydrophobicity were evaluated. Results revealed the ability of four extracts to significantly inhibit S. aureus biofilm formation. These findings were supported by microscopy analyses. The gradual increase in the number of adherent bacteria when the selected extracts were added at various times (t₀, t_2h, t_4h, t_6h, and t_24h) revealed their potential effect on the initial adhesion and proliferation stages of S. aureus biofilm development. Interestingly, a significant reduction in the surface hydrophobicity of S. aureus treated with dichloromethane (DCM) extract derived from U. lactuca was demonstrated. These findings present new insights into the exploration of seaweeds as a valuable source of antibiofilm agents with preventive effect by inhibiting and/or delaying biofilm formation.

A profile of delafloxacin in the treatment of adults with community-acquired bacterial pneumonia

INTRODUCTION

Community-acquired bacterial pneumonia (CABP) is the most common infectious cause of hospital admission in adults, and poses a significant clinical and economic burden. At the same time, antimicrobial resistance is increasing worldwide with only a few new antibiotics developed in recent years. Delafloxacin is an anionic fluoroquinolone available in intravenous and oral formulations and with a broad spectrum of activity targeting Gram-positives, including methicillin-resistant Staphylococcus aureus (MRSA), gram-negative organisms, and atypical and anaerobic organisms. It also has a better adverse event profile compared to other fluoroquinolones.

AREAS COVERED

This article reviews the current epidemiology of CABP, etiologic agents and current resistance rates, current treatment guidelines, characteristics of delafloxacin (chemistry, microbiology, PK/PD), clinical efficacy and safety in pneumonia and other indications, and regulatory affairs.

EXPERT OPINION

: Delafloxacin's susceptibility profile against respiratory pathogens, bioequivalent intravenous and oral formulations and favorable safety profile, support its use for the treatment of CABP. It could be useful as empirical treatment in countries with high rates of penicillin-resistant S. pneumoniae and in patients with suspected or documented pneumonia due to MRSA. In post-influenza staphylococcal bacterial pneumonia, MRSA could be also considered an important pathogen.

Early Clinical Experience with Delafloxacin: A Case Series

BACKGROUND

-The most recently approved fluoroquinolone for use in the US and Europe, delafloxacin (DLX) provides broad-spectrum coverage, improved side effect profile, and excellent potency. Currently approved for the treatment of acute bacterial skin infections and community-acquired pneumonia, DLX may be useful in the treatment of other infections given the longstanding versatility of other fluoroquinolones.

METHODS

-This is a retrospective review of adult patients treated with DLX at The University of Texas Medical Branch, Galveston, TX from January 1, 2018 to February 1, 2020 using pre-existing electronic medical records. Simple statistics were calculated using Microsoft Excel.

RESULTS

-Five patients were prescribed DLX (median age 59 years, 40% female, 100% outpatient) with a median treatment duration of seven days.  Prescriptions were initiated by infectious diseases specialists (2/5, 40%), emergency medicine physicians (2/5, 40%), and ophthalmologists (1/5, 20%).  The most common conditions treated were prosthetic joint infections (PJI) and acute skin and soft tissue infections (each n = 2).  Both PJIs were caused by multi-drug-resistant Staphylococcus epidermidis. Off-label utilization was high (3/5, 60%). No patient experienced any documented treatment failure due to delafloxacin and there were zero reported adverse events.

CONCLUSIONS

-A new antibiotic with valuable characteristics, DLX treatment was highly successful in this case series, including with multiple off-label indications.  Real-world clinical data with delafloxacin are currently scant.  Prospective data would be useful for identifying future clinical niches for this new fluoroquinolone.

Activity of Moxifloxacin Against Biofilms Formed by Clinical Isolates of Staphylococcus aureus Differing by Their Resistant or Persister Character to Fluoroquinolones

Staphylococcus aureus biofilms are poorly responsive to antibiotics. Underlying reasons include a matrix effect preventing drug access to embedded bacteria, or the presence of dormant bacteria with reduced growth rate. Using 18 clinical isolates previously characterized for their moxifloxacin-resistant and moxifloxacin-persister character in stationary-phase culture, we studied their biofilm production and matrix composition and the anti-biofilm activity of moxifloxacin. Biofilms were grown in microtiter plates and their abundance quantified by crystal violet staining and colony counting; their content in polysaccharides, extracellular DNA and proteins was measured. Moxifloxacin activity was assessed after 24 h of incubation with a broad range of concentrations to establish full concentration-response curves. All clinical isolates produced more biofilm biomass than the reference strain ATCC 25923, the difference being more important for those with high relative persister fractions to moxifloxacin, most of which being also resistant. High biofilm producers expressed icaA to higher levels, enriching the matrix in polysaccharides. Moxifloxacin was less potent against biofilms from clinical isolates than from ATCC 25923, especially against moxifloxacin-resistant isolates with high persister fractions, which was ascribed to a lower concentration of moxifloxacin in these biofilms. Time-kill curves in biofilms revealed the presence of a moxifloxacin-tolerant subpopulation, with low multiplication capacity, whatever the persister character of the isolate. Thus, moxifloxacin activity depends on its local concentration in biofilm, which is reduced in most isolates with high-relative persister fractions due to matrix effects, and insufficient to kill resistant isolates due to their high MIC.

Potential Antimicrobial Activity of Galloyl-Flavonoid Glycosides From Woodfordia uniflora Against Methicillin-Resistant Staphylococcus aureus

Antibiotic-resistant infections are a growing problem; to combat multi-drug resistant bacterial infections, antibiotics with novel mechanisms of action are needed. Identification of potent bioactive natural products is an attractive avenue for developing novel therapeutic strategies against bacterial infections. As part of our ongoing research to explore bioactive natural products from diverse resources, we investigated the antimicrobial compounds from Woodfordia uniflora, a flowering shrub unique to the Dhofar region of Oman. The plant has been used as a remedy for skin infections in Oman. However, to date, no study has examined the antimicrobial compounds in W. uniflora. Phytochemical analysis of the methanolic extract of W. uniflora leaves in combination with LC/MS-based analysis allowed us to isolate and identify four flavonoid-type analogs (1–4), procyanidin B3-3-O-gallate (1), rhamnetin 3-O-(6″-galloyl)-β-D-glucopyranoside (2), rhamnetin 3-O-α-L-rhamnopyranoside (3), and quercetin 3-O-(6″-galloyl)-β-D-glucopyranoside (4). The isolates have a novel mechanism of action; the compounds inhibit biofilm formation in methicillin-resistant Staphylococcus aureus (MRSA) and synergize with methicillin. Our metabolite analysis revealed that this synergizing activity by compounds was achieved by remodeling metabolism including central carbon metabolism and glutamine biosynthesis that resulted in abnormal cell formation and reduction in biofilm formation of MRSA. Taken together, these findings provide experimental evidence that rhamnetin 3-O-(6″-galloyl)-β-D-glucopyranoside (2) and quercetin 3-O-(6″-galloyl)-β-D-glucopyranoside (4) can be considered as potential therapeutic agents for the treatment of methicillin-resistant S. aureus-associated diseases.

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

The purpose of the present study was to investigate anti-staphylococcal activity of daptomycin and bacteriophage K, alone or in combination, against biofilm-producers and non-producers S. aureus and S. epidermidis strains, under biofilm forming and cells' proliferation conditions. Daptomycin and bacteriophage K (ATCC 19685B1), in different concentrations, were tested against 10 Staphylococcus aureus and 10 S. epidermidis, characterized by phenotypes and genotypes. The quantitative microtiter plate (crystal violet, CV), methylthiazoltetrazolium (MTT), and growth curve (GC) assays were performed. No statistically significant difference was found between species, whereas daptomycin alone performed better using medium and high concentrations of the drug and bacteriophage K was more active against strains with higher susceptibility, by CV and MTT assays. Best results were achieved using both agents combined in high concentrations. Bacteriophage K was effective within 3.8 and 2.4 h, depending on the concentration used, by the GC assay. Combination of daptomycin with bacteriophage K was more effective against staphylococci, depending on the concentrations used and strains' susceptibility. Further studies are needed to evaluate if this approach might be a choice for prevention or therapy of biofilm-associated infections.

Delafloxacin as a treatment option for community-acquired pneumonia infection

Community-acquired pneumonia (CAP) is a leading cause of morbidity and mortality in adults. Bacterial pathogens are recognized to be frequent causative agents, which makes antibacterial treatment crucial for the evolution of these patients. There are several antimicrobial options available in daily practice. However, bacterial resistance is a problem. The chemical, pharmacokinetic, pharmacodynamics, and safety characteristics of delafloxacin, a fluoroquinolone, are discussed. The data from one phase 3 clinical trial evaluating the use of delafloxacin in adults with community-acquired pneumonia is also discussed, along with findings from other meaningful studies. In vitro data have shown that delafloxacin has broad spectrum activity. Results from phase 2 and phase 3 studies have demonstrated that delafloxacin use is safe. International guidelines have recommended respiratory fluoroquinolones as second option for non-severe cases and must be considered in very severe patients not improving to a betalactam/macrolide combination. Delafloxacin was compared to moxifloxacin in the phase 3 community-acquired pneumonia trial. Serious and life-long adverse events due to fluoroquinolones use have been recently reported. Delafloxacin may possibly replace currently available fluoroquinolones, particularly in the treatment of resistant pathogens, such as ciprofloxacin-resistant P. aeruginosa isolates when other drugs are inefficient.

Delafloxacin: A Review in Acute Bacterial Skin and Skin Structure Infections

The global spread of antibacterial-resistant strains, especially methicillin-resistant Staphylococcus aureus (MRSA) for acute bacterial skin and skin structure infections (ABSSSIs), has driven the need for novel antibacterials. Delafloxacin [Quofenix™ (EU); Baxdela^® (USA)], a new fluoroquinolone (FQ), has a unique chemical structure that enhances its antibacterial activity in acidic environments such as occurs in ABSSSIs (including S. aureus infections). Delafloxacin (intravenous and oral formulations) is approved in several countries for the treatment of adults with ABSSSIs (featured indication). In intent-to-treat analyses in pivotal phase 3 trials in adults with ABSSSIs, including those with comorbid disease, intravenous delafloxacin monotherapy (± oral switch after six doses) twice daily was noninferior to intravenous vancomycin + aztreonam for primary endpoints, as specified by the FDA (objective response rate at 48–78 h after initiation of therapy) and the EMA [investigator-assessed clinical cure rate at the follow-up visit at day 14 (± 1 day)]. Delafloxacin was generally well tolerated, with most treatment-related adverse events mild to moderate in severity and few patients discontinuing treatment because of these events. Relative to vancomycin + aztreonam (a non-FQ regimen), delafloxacin treatment was not associated with an increased risk of FQ-associated AEs of special interest. Given its unique chemical structure that confers novel properties relative to other FQ and its broad spectrum of activity against common clinically relevant Gram-positive pathogens, including against MRSA strains (± FQ-resistance mutations), and Gram-negative pathogens, intravenous delafloxacin (± oral switch) provides a novel emerging option for the treatment of adult patients with ABSSSIs.

Harnessing ultrasound-stimulated phase change contrast agents to improve antibiotic efficacy against methicillin-resistant Staphylococcus aureus biofilms

Bacterial biofilms, often associated with chronic infections, respond poorly to antibiotic therapy and frequently require surgical intervention. Biofilms harbor persister cells, metabolically indolent cells, which are tolerant to most conventional antibiotics. In addition, the biofilm matrix can act as a physical barrier, impeding diffusion of antibiotics. Novel therapeutic approaches frequently improve biofilm killing, but usually fail to achieve eradication. Failure to eradicate the biofilm leads to chronic and relapsing infection, is associated with major financial healthcare costs and significant morbidity and mortality. We address this problem with a two-pronged strategy using 1) antibiotics that target persister cells and 2) ultrasound-stimulated phase-change contrast agents (US-PCCA), which improve antibiotic penetration.

We previously demonstrated that rhamnolipids, produced by Pseudomonas aeruginosa, could induce aminoglycoside uptake in gram-positive organisms, leading to persister cell death. We have also shown that US-PCCA can transiently disrupt biological barriers to improve penetration of therapeutic macromolecules. We hypothesized that combining antibiotics which target persister cells with US-PCCA to improve drug penetration could improve treatment of methicillin resistant S. aureus (MRSA) biofilms. Aminoglycosides alone or in combination with US-PCCA displayed limited efficacy against MRSA biofilms. In contrast, the anti-persister combination of rhamnolipids and aminoglycosides combined with US-PCCA dramatically improved biofilm killing. This novel treatment strategy has the potential for rapid clinical translation as the PCCA formulation is a variant of FDA-approved ultrasound contrast agents that are already in clinical practice and the low-pressure ultrasound settings used in our study can be achieved with existing ultrasound hardware at pressures below the FDA set limits for diagnostic imaging.

New-Generation Antibiotics for Treatment of Gram-Positive Infections: A Review with Focus on Endocarditis and Osteomyelitis

Infective endocarditis, osteomyelitis, and osteosynthesis-associated infections are mostly caused by Gram-positive bacteria. They are often difficult to treat and are associated with a poor prognosis. In the past 20 years, nine antibiotic drugs with predominant activity against Gram-positive bacteria have been introduced and approved by the Food and Drug Administration or the European Medicines Agency: ceftaroline, daptomycin, telavancin, dalbavancin, oritavancin, linezolid, tedizolid, delafloxacin, and omadacycline. This narrative review aims to provide an overview on these antibiotics with a special focus on their use in infective endocarditis, osteomyelitis, and osteosynthesis-associated infections. Although some of these approved antibiotics are promising, they should not be used as first- or second-line therapy, awaiting more clinical data.

Biological and Physico-Chemical Characteristics of Arginine-Rich Peptide Gemini Surfactants with Lysine and Cystine Spacers

Ultrashort cationic lipopeptides (USCLs) and gemini cationic surfactants are classes of potent antimicrobials. Our recent study has shown that the branching and shortening of the fatty acids chains with the simultaneous addition of a hydrophobic N-terminal amino acid in USCLs result in compounds with enhanced selectivity. Here, this approach was introduced into arginine-rich gemini cationic surfactants. l-cystine diamide and l-lysine amide linkers were used as spacers. Antimicrobial activity against planktonic and biofilm cultures of ESKAPE (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter spp.) strains and Candida sp. as well as hemolytic and cytotoxic activities were examined. Moreover, antimicrobial activity in the presence of human serum and the ability to form micelles were evaluated. Membrane permeabilization study, serum stability assay, and molecular dynamics were performed. Generally, critical aggregation concentration was linearly correlated with hydrophobicity. Gemini surfactants were more active than the parent USCLs, and they turned out to be selective antimicrobial agents with relatively low hemolytic and cytotoxic activities. Geminis with the l-cystine diamide spacer seem to be less cytotoxic than their l-lysine amide counterparts, but they exhibited lower antibiofilm and antimicrobial activities in serum. In some cases, geminis with branched fatty acid chains and N-terminal hydrophobic amino acid resides exhibited enhanced selectivity to pathogens over human cells.

Destruction of Staphylococcus aureus biofilms by combining an antibiotic with subtilisin A or calcium gluconate

In S. aureus biofilms, bacteria are embedded in a matrix of extracellular polymeric substances (EPS) and are highly tolerant to antimicrobial drugs. We thus sought to identify non-antibiotic substances with broad-spectrum activity able to destroy the EPS matrix and enhance the effect of antibiotics on embedded biofilm bacteria. Among eight substances tested, subtilisin A (0.01 U/mL) and calcium gluconate (CaG, Ca²⁺ 1.25 mmol/L) significantly reduced the biomass of biofilms formed by at least 21/24 S. aureus isolates. Confocal laser scanning microscopy confirmed that they both eliminated nearly all the proteins and PNAG from the matrix. By contrast, antibiotics alone had nearly no effect on biofilm biomass and the selected one (oxytetracycline-OTC) could only slightly reduce biofilm bacteria. The combination of OTC with CaG or subtilisin A led to an additive reduction (average of 2 log₁₀ CFU/mL) of embedded biofilm bacteria on the isolates susceptible to OTC (MBC < 10 μg/mL, 11/24). Moreover, these two combinations led to a reduction of the embedded biofilm bacteria higher than 3 log₁₀ CFU/mL for 20–25% of the isolates. Further studies are now required to better understand the factors that cause the biofilm produced by specific isolates (20–25%) to be susceptible to the combinations.

Recalcitrant Staphylococcus aureus Infections: Obstacles and Solutions

Antibiotic treatment failure of Staphylococcus aureus infections is very common. In addition to genetically encoded mechanisms of antibiotic resistance, numerous additional factors limit the efficacy of antibiotics in vivo Identifying and removing the barriers to antibiotic efficacy are of major importance, as even if new antibiotics become available, they will likely face the same barriers to efficacy as their predecessors. One major obstacle to antibiotic efficacy is the proficiency of S. aureus to enter a physiological state that is incompatible with antibiotic killing. Multiple pathways leading to antibiotic tolerance and the formation of tolerant subpopulations called persister cells have been described for S. aureus Additionally, S. aureus is a versatile pathogen that can infect numerous tissues and invade a variety of cell types, of which some are poorly penetrable to antibiotics. It is therefore unlikely that there will be a single solution to the problem of recalcitrant S. aureus infection. Instead, specific approaches may be required for targeting tolerant cells within different niches, be it through direct targeting of persister cells, sensitization of persisters to conventional antibiotics, improved penetration of antibiotics to particular niches, or any combination thereof. Here, we examine two well-described reservoirs of antibiotic-tolerant S. aureus, the biofilm and the macrophage, the barriers these environments present to antibiotic efficacy, and potential solutions to the problem.

High-Dose Daptomycin and Clinical Applications

OBJECTIVE

To evaluate evidence for high-dose daptomycin (doses ≥ 8 mg/kg/d).

DATA SOURCES

A PubMed/MEDLINE literature search was performed (January 2000 to December 2020) using the search terms daptomycin, high dose, and dosing. Review article references and society guidelines were reviewed.

STUDY SELECTION AND DATA EXTRACTION

Clinical trials, observational studies, retrospective studies, meta-analyses, and systematic reviews reporting on high-dose daptomycin were included.

DATA SYNTHESIS

Experimentally, daptomycin outperforms other antimicrobials for high inoculum and biofilm-associated infections. Clinically, high-dose daptomycin is supported as salvage and first-line therapy for endocarditis and bacteremia, primarily when caused by methicillin-resistant Staphylococcus aureus (when vancomycin minimum inhibitory concentration is >1 mg/L) and Enterococcus. High-dose daptomycin appears effective for osteomyelitis and central nervous system infections, although comparative studies are lacking. High dosing in renal replacement therapy requires considering clearance modality to achieve exposures like normal renal function. Weight-based dosing in obesity draws concern for elevated exposures, although high doses have not been evaluated kinetically in obesity. Some data show benefits of high doses in overweight populations. Burn patients clear daptomycin more rapidly, and high doses may only achieve drug exposures similar to standard doses (6 mg/kg).

RELEVANCE TO PATIENT CARE AND CLINICAL PRACTICE

This review analyzes the efficacy and safety of high-dose daptomycin in serious gram-positive infections. Discussion of specific infectious etiologies and patient populations should encourage clinicians to evaluate their daptomycin dosing standards.

CONCLUSIONS

The efficacy of high-dose daptomycin and limited safety concerns encourage clinicians to consider high-dose daptomycin more liberally in severe gram-positive infections.

Novel approaches for the treatment of methicillin-resistant Staphylococcus aureus: Using nanoparticles to overcome multidrug resistance

Methicillin-resistant Staphylococcus aureus (MRSA) causes serious infections in both community and hospital settings, with high mortality rates. Treatment of MRSA infections is challenging because of the rapidly evolving resistance mechanisms combined with the protective biofilms of S. aureus. Together, these characteristic resistance mechanisms continue to render conventional treatment modalities ineffective. The use of nanoformulations with unique modes of transport across bacterial membranes could be a useful strategy for disease-specific delivery. In this review, we summarize treatment approaches for MRSA, including novel techniques in nanoparticulate designing for better therapeutic outcomes; and facilitate an understanding that nanoparticulate delivery systems could be a robust approach in the successful treatment of MRSA.

Successful Development of Bacteriocins into Therapeutic Formulation for Treatment of MRSA Skin Infection in a Murine Model

The emergence of antibiotic-resistant pathogens has caused a serious worldwide problem in infection treatment in recent years. One of the pathogens is methicillin-resistant Staphylococcus aureus (MRSA), which is a major cause of skin and soft tissue infections. Alternative strategies and novel sources of antimicrobials to solve antibiotic resistance problems are urgently needed. In this study, we explored the potential of two broad-spectrum bacteriocins, garvicin KS and micrococcin P1, in skin infection treatments.

The emergence of antibiotic-resistant pathogens has caused a serious worldwide problem in infection treatment in recent years. One of the pathogens is methicillin-resistant Staphylococcus aureus (MRSA), which is a major cause of skin and soft tissue infections. Alternative strategies and novel sources of antimicrobials to solve antibiotic resistance problems are urgently needed. In this study, we explored the potential of two broad-spectrum bacteriocins, garvicin KS and micrococcin P1, in skin infection treatments. The two bacteriocins acted synergistically with each other and with penicillin G in killing MRSA in vitro. The MICs of the antimicrobials in the three-component mixture were 40 ng/ml for micrococcin P1 and 2 μg/ml for garvicin KS and penicillin G, which were 62, 16, and at least 1,250 times lower than their MICs when assessed individually. To assess its therapeutic potential further, we challenged the three-component formulation in a murine skin infection model with the multidrug-resistant luciferase-tagged MRSA Xen31, a strain derived from the clinical isolate S. aureus ATCC 33591. Using the tagged-luciferase activity as a reporter for the presence of Xen31 in wounds, we demonstrated that the three-component formulation was efficient in eradicating the pathogen from treated wounds. Furthermore, compared to Fucidin cream, which is an antibiotic commonly used in skin infection treatments, our formulation was also superior in terms of preventing resistance development.

Evaluation of Staphylococcal Bacteriophage Sb-1 as an Adjunctive Agent to Antibiotics Against Rifampin-Resistant Staphylococcus aureus Biofilms

Rifampin plays a crucial role in the treatment of staphylococcal implant-associated infection, as it is the only antibiotic capable of eradicating Staphylococcus aureus biofilms. However, the emergence of rifampin resistance strongly limits its use. Combinatorial therapy of antibiotics and bacteriophages may represent a strategy to overcome the resistance. Here, we evaluated the activity of staphylococcal bacteriophage Sb-1 in combination with different antibiotics against the biofilms of 10 rifampin-resistant S. aureus clinical strains, including MRSA and MSSA. S. aureus biofilms formed on porous glass beads were exposed to antibiotics alone or combined with Sb-1 simultaneously or staggered (first Sb-1 for 24 h followed by antibiotic). Recovered bacteria were detected by measuring growth-related heat production at 37°C (isothermal microcalorimetry) and the biofilm eradication was assessed by sonication of beads and plating of the resulting sonication fluid. Minimum biofilm eradication concentration (MBEC) was defined as the lowest concentration of antibiotic required to kill all adherent bacteria, resulting in absence of growth after plating the sonication fluid. Tested antibiotics presented high MBEC values when administered alone (64 to > 1,024 μg/ml). The simultaneous or staggered combination of Sb-1 with daptomycin showed the highest activity against all MRSA biofilms, whereas the exposure to Sb-1 with vancomycin showed no improved anti-biofilm activity. Staggered administration of Sb-1 and flucloxacillin, cefazolin, or fosfomycin improved the antibiofilm activity in four out of six MSSA, whereas simultaneous exposure exhibited similar or lesser synergy. In conclusion, the combinatorial effect of Sb-1 and antibiotics enabled to eradicate rifampin-resistant S. aureus biofilms in vitro.

Lipidated Short Analogue of α-Melanocyte Stimulating Hormone Exerts Bactericidal Activity against the Stationary Phase of Methicillin-Resistant Staphylococcus aureus and Inhibits Biofilm Formation

Stationary phase Staphylococcus aureus, especially methicillin-resistant S. aureus (MRSA), has been widely associated with many persistent infections as well as biofilm-associated infections, which are challenging due to their increasing antibiotic resistance. α-Melanocyte stimulating hormone (α-MSH) is an antimicrobial peptide (AMP) with well-established potent activity against S. aureus , but little is known about its antimicrobial efficacy against the stationary phase of the bacteria. We investigated the in vitro activities of two palmitoylated analogues, Pal-α-MSH(6-13) and Pal-α-MSH(11-13), of the C-terminal fragments of α-MSH against biofilm-producing strains of methicillin-sensitive S. aureus (MSSA) and MRSA. While both the peptides demonstrated anti-staphylococcal efficacy, Pal-α-MSH(11-13) emerged as the most effective AMP as palmitoylation led to a remarkable enhancement in its activity against stationary phase bacteria. Similar to α-MSH, both the designed analogues were membrane-active and exhibited improved bacterial membrane depolarization and permeabilization, as further confirmed via electron microscopy studies. Of the two peptides, Pal-α-MSH(11-13) was able to retain its activity in the presence of standard microbiological media, which otherwise is a major limiting factor toward the therapeutic use of α-MSH-based peptides. More importantly, Pal-α-MSH(11-13) was also highly effective in inhibiting the formation of biofilms. Furthermore, it did not lead to resistance development in MRSA cells even upon 18 serial passages at sub-MIC concentrations. These observations support the potential use of Pal-α-MSH(11-13) in the treatment of planktonic as well as sessile S. aureus infections.

Synergistic Effects of Pulsed Lavage and Antimicrobial Therapy Against Staphylococcus aureus Biofilms in an in-vitro Model

Background: Prosthetic joint infections (PJI) are difficult to treat complications of joint arthroplasty. Debridement with implant retention is a common treatment strategy and frequently involves the use of pulsed lavage (PL). However, PL effects on biofilms and antibiotic activity have been scarcely studied in-vitro. We report the effects of PL, vancomycin or flucloxacillin used independently or in combination against Staphylococcus aureus biofilms. Methods: Biofilms of 3 methicillin-susceptible (MSSA) and of 3 methicillin-resistant (MRSA) S. aureus were grown on Ti6Al4V coupons in TGN (TSB + 1%glucose + 2%NaCl). After 24 h, PL was applied to half of the samples (50 mL saline from 5 cm). Samples were either reincubated for 24 h in TGN or TGN + flucloxacillin or vancomycin. Analyses included CFUs counts, biomass assays or fluorescence microscopy. Results: PL transiently reduced bacterial counts by 3-4 Log₁₀ CFU/coupon, but bacterial regrowth to baseline levels was seen after 24 h. At 20 mg/L, flucloxacillin reduced both the CFU counts (3 Log₁₀ CFU/coupon) and biomass (-70%) in one MSSA only, while vancomycin had no effects against MRSA. PL combined with a 24 h reincubation with vancomycin or flucloxacillin at 20 mg/L was synergistic (-5 to 6.5 Log₁₀ CFU/coupon; 81-100% biomass reduction). Fluorescence microscopy confirmed that PL removed most of the biofilm and that subsequent antibiotic treatment partially killed bacteria. Conclusions: While PL only transiently reduces the bacterial load and antibiotics at clinically relevant concentrations show no or limited activity on biofilms, their combination is synergistic against MRSA and MSSA biofilms. These results highlight the need for thorough PL before antibiotic administration in PJI.

Tedizolid-Rifampicin Combination Prevents Rifampicin-Resistance on in vitro Model of Staphylococcus aureus Mature Biofilm

Staphylococcus aureus infections associated with implanted medical devices are difficult to treat and require long-lasting antibiotic therapies, especially when device removal is not possible or easy such as in the case of joint prostheses. Biofilm formation is a major cause of treatment failure and infection recurrence. This study aimed to test, for the first time, the in vitro combination of tedizolid plus rifampicin on methicillin-sensitive (MSSA ATCC 6538) and methicillin-resistant (MRSA ATCC 43300) S. aureus mature biofilm. Here, we demonstrated that the combination of tedizolid with rifampicin significantly disaggregated pre-formed biofilm of both strains, reduced their metabolic activity and exerted bactericidal activity at clinically meaningful concentrations. Notably, tedizolid was able to completely prevent the emergence of resistance to rifampicin. Moreover these effects were similar to those obtained with daptomycin plus rifampicin, a well-known and widely used combination. Preliminary results on some MRSA clinical isolates confirmed the efficacy of this combination in reducing biofilm biomass and preventing rifampicin resistance onset. Further in vivo studies are needed to confirm the validity of this promising therapeutic option that can be useful against biofilm-associated S. aureus infections.

Polydopamine Linking Substrate for AMPs: Characterisation and Stability on Ti6Al4V

Infections are common complications in joint replacement surgeries. Eradicated infections can lead to implant failure. In this paper, analogues of the peptide KR-12 derived from the human cathelicidin LL-37 were designed, synthesised, and characterised. The designed antimicrobial peptides (AMPs) were attached to the surface of a titanium alloy, Ti6Al4V, by conjugation to a polydopamine linking substrate. The topography of the polydopamine coating was evaluated by electron microscopy and coating thickness measurements were performed with ellipsometry and Atomic Force Microscopy (AFM). The subsequently attached peptide stability was investigated with release profile studies in simulated body fluid, using both fluorescence imaging and High-Performance Liquid Chromatography (HPLC). Finally, the hydrophobicity of the coating was characterised by water contact angle measurements. The designed AMPs were shown to provide long-term bonding to the polydopamine-coated Ti6Al4V surfaces.

Activity of Antibiotics against Pseudomonas aeruginosa in an In Vitro Model of Biofilms in the Context of Cystic Fibrosis: Influence of the Culture Medium

Pseudomonas aeruginosa is a major cause of respiratory biofilm-related infections in patients with cystic fibrosis. We developed an in vitro pharmacodynamic model to study the activity of antipseudomonal antibiotics against PAO1 biofilms grown in artificial sputum medium with agar [ASM(+)] versus that against biofilms grown in Trypticase soy broth supplemented with glucose and NaCl (TGN). We measured bacterial counts, metabolic activity (fluorescein diacetate [FDA] hydrolysis), and biomass (crystal violet absorbance). Biofilms grew slower in ASM(+) than in TGN but reached the same CFU counts and metabolic activity in both media and a slightly higher biomass after 48 h in ASM(+) than in TGN. The concentration-response curves of the antibiotics after 24 h of incubation with mature biofilms showed maximal effects ranging from a 3 (ciprofloxacin)- to a 1.5 (ceftazidime, meropenem)-log₁₀-CFU decrease, with tobramycin and colistin showing intermediate values. These maximal reductions in the numbers of CFU were similar in both media for ciprofloxacin and β-lactams but lower in ASM(+) than in TGN for tobramycin and colistin; they were reached at concentrations lower than the human maximum concentration in plasma for ciprofloxacin and β-lactams only. The reductions in metabolic activity and in biomass were low in both media. Small-colony variants were selected by tobramycin in ASM(+) and by ciprofloxacin in both media. The model was then successfully applied to 4 isolates from patients with cystic fibrosis. These biofilms showed CFU counts similar to those of PAO1 biofilms in ASM(+) but a higher biomass than PAO1 biofilms in ASM(+) and moderate differences in their susceptibility to antibiotics from that of PAO1 biofilms grown in this medium. This model proved useful to establish the pharmacodynamic profile of drugs against P. aeruginosa biofilms in the context of cystic fibrosis.

In vitro activities of telithromycin against Staphylococcus aureus biofilms compared with azithromycin, clindamycin, vancomycin and daptomycin

Introduction. Staphylococcus aureus biofilms are difficult to treat and the effect of telithromycin treatment is still unclear.Aim. This study aimed to explore the effect of telithromycin against Staphylococcus aureus biofilms compared with azithromycin, clindamycin, vancomycin and daptomycin.Methodology. Eight methicillin-susceptible and eight methicillin-resistant S. aureus isolates (MSSA and MRSA, respectively) were used for this study. Biofilm biomasses were detected by crystal violet staining and the adherent cells in the established biofilms were quantified by determination of colony-forming units (c.f.u.). The RNA levels of biofilm formation-related genes were determined by RT-qPCR.Results. Telithromycin [8× minimum inhibitory concentration (MIC)] eradicated more established biofilms than azithromycin or clindamycin in the four MSSA isolates, and eliminated the established biofilms of six MRSA isolates more effectively than vancomycin or daptomycin. Telithromycin (8× MIC) killed more adherent cells in the established biofilms than azithromycin or clindamycin in the six MSSA isolates, and killed more adherent cells than vancomycin in all eight MRSA isolates. Daptomycin also showed an excellent effect on the adherent cells of MRSA isolates, with similarresults to telithromycin. The effect of a subinhibitory concentration of telithromycin (1/4× MIC) was significantly superior to that of azithromycin or clindamycin, inhibiting the biofilm formation of six MSSA isolates and seven MRSA isolates more effectively than vancomycin or daptomycin. The RNA levels of agrA, agrC, clfA, icaA and sigB decreased when treated with telithromycin (1/4× MIC).Conclusions. Telithromycin is more effective than azithromycin, clindamycin, vancomycin, or daptomycin against S. aureus biofilms.

Streptococcus mutans and Actinomyces naeslundii Interaction in Dual-Species Biofilm

The study of bacterial interaction between Streptococcus mutans and Actinomyces naeslundii may disclose important features of biofilm interspecies relationships. The aim of this study was to characterize-with an emphasis on biofilm formation and composition and metabolic activity-single- and dual-species biofilms of S. mutans or A. naeslundii, and to use a drip flow reactor (DFR) to evaluate biofilm stress responses to 0.2% chlorhexidine diacetate (CHX). Single- and dual-species biofilms were grown for 24 h. The following factors were evaluated: cell viability, biomass and total proteins in the extracellular matrix, 2,3-bis(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide-"XTT"-reduction and lactic acid production. To evaluate stress response, biofilms were grown in DFR. Biofilms were treated with CHX or 0.9% sodium chloride (NaCl; control). Biofilms were plated for viability assessment. Confocal laser-scanning microscopy (CLSM) was also performed. Data analysis was carried out at 5% significance level. S. mutans viability and lactic acid production in dual-species biofilms were significantly reduced. S. mutans showed a higher resistance to CHX in dual-species biofilms. Total protein content, biomass and XTT reduction showed no significant differences between single- and dual-species biofilms. CLSM images showed the formation of large clusters in dual-species biofilms. In conclusion, dual-species biofilms reduced S. mutans viability and lactic acid production and increased S. mutans' resistance to chlorhexidine.

Antibiotic Resistance, Biofilm Formation, and Intracellular Survival As Possible Determinants of Persistent or Recurrent Infections by Staphylococcus aureus in a Vietnamese Tertiary Hospital: Focus on Bacterial Response to Moxifloxacin

Resistance is notoriously high in Asia but may not entirely explain therapeutic failures. Specific modes of bacterial life, such as biofilm or intracellular survival, may also contribute to the persistent and/or recurrent character of infections. Most Staphylococcus aureus isolates form biofilm and many survive and even thrive intracellularly. We collected 36 nonduplicate S. aureus isolates (including 18 methicillin-resistant S. aureus) from patients with clinical evidence of persistent or recurrent infections in a large tertiary Vietnamese hospital. We examined their antibiotic resistance profile (minimal inhibitory concentration determination) and clonal relatedness (spa and agr typing, pulsed field gel electrophoresis profiles). We then assessed the activity of moxifloxacin in both biofilms and infected phagocytes (moxifloxacin previously proved to be one of the most active antibiotics against reference strains in these models). spa-types t189 and t437 and agr group I were the most frequent. Among the 36 isolates, 30 were multidrug resistant but 30 were recovered from patients having received an active drug. All tested isolates produced biofilm and survived inside phagocytes. At its human C_max, moxifloxacin was inactive on biofilms made by moxifloxacin-susceptible as well as moxifloxacin-resistant isolates. It caused only a modest intracellular colony-forming unit decrease against moxifloxacin-susceptible isolates and was inactive against those resistant to moxifloxacin. While our data confirm for this collection the high resistance levels and prevalence of endemic spa- or agr- types in Asia, they show that tolerance in both biofilm and phagocytes are correlated and markedly limit moxifloxacin activity, which goes in line with the suggested role of these modes of life in persistence or recurrence of infections.

Minimum information guideline for spectrophotometric and fluorometric methods to assess biofilm formation in microplates

The lack of reproducibility of published studies is one of the major issues facing the scientific community, and the field of biofilm microbiology has been no exception. One effective strategy against this multifaceted problem is the use of minimum information guidelines. This strategy provides a guide for authors and reviewers on the necessary information that a manuscript should include for the experiments in a study to be clearly interpreted and independently reproduced. As a result of several discussions between international groups working in the area of biofilms, we present a guideline for the spectrophotometric and fluorometric assessment of biofilm formation in microplates. This guideline has been divided into 5 main sections, each presenting a comprehensive set of recommendations. The intention of the minimum information guideline is to improve the quality of scientific communication that will augment interlaboratory reproducibility in biofilm microplate assays.

Clinical Pharmacokinetics and Pharmacodynamics of Delafloxacin

Delafloxacin has recently received approval by the US Food and Drug Administration for the treatment of acute bacterial skin and skin structure infections. This article provides a balanced and comprehensive systematic critique of the literature in order to provide an up-to-date summary of its clinical pharmacology. Oral delafloxacin is rapidly absorbed and exhibits comparable exposure characteristics (300 mg intravenous versus 450 mg oral) between the two formulations, allowing easy transition from intravenous to oral therapy. The bioavailability is high (60-70%) and absorption is not affected by food intake, although further studies are required under clinically relevant conditions. Delafloxacin is primarily excreted renally (thus requiring renal dose adjustment in the setting of renal dysfunction), but also undergoes metabolism by uridine diphosphate-glucuronosyltransferase enzymes in the formation of a conjugated metabolite. Few drug-drug interaction studies have been identified, although more systematic characterizations in vitro and in vivo are warranted. Delafloxacin is a concentration-dependent bactericidal agent that has in vitro susceptibility for gram-positive (notably potent activity against methicillin-resistant Staphylococcus aureus), gram-negative, and anaerobic organisms. In addition to acute bacterial skin and skin structure infections, the clinical utility of delafloxacin has also been studied in community-acquired pneumonia, acute exacerbation of chronic bronchitis, and gonorrhea, with potentially promising findings. Given its mild side effect profile, including an apparent lack of association with clinically important QTc prolongation, delafloxacin is generally well tolerated.

Emerging antibiotics for community-acquired pneumonia

Introduction: Community-acquired pneumonia is the most common infection leading to hospitalization and death in all age groups, especially in elderly populations. Increasing antibiotic resistance among the common bacterial pathogens associated with community-acquired pneumonia, especially Streptococcus pneumoniae and staphylococci, has made its empirical treatment increasingly problematic, highlighting the need for effective antibiotic therapy.Areas covered: We searched PubMed and ClinicalTrials.gov for English-language reports of phase III clinical trials conducted between 2000 and 2019 concerning the antibiotic treatment of community-acquired pneumonia. We provide a summary of the latest approved drugs for this indication and highlight emerging drugs with a potential indication.Expert opinion: Ceftaroline (a new cephalosporine) and omadacycline (a cycline alternative), either parenterally or orally, are the only two new antibiotics to have been approved by the FDA for the treatment of community-acquired pneumonia in the last five years. Among the antimicrobials in development, Lefamulin (the first pleuromutilin), is currently in phase III development. Among the known antibiotic classes, solithromycin (a macrolide), nemonoxacin (a quinolone), and delafloxacin and zabofloxacin (both fluoroquinolones), have been studied in phase II and III in clinical trials. The availability of these new antibiotics may offer opportunities to improve the empirical treatment for community-acquired pneumonia.

Antimicrobial resistance in methicillin-resistant Staphylococcus aureus to newer antimicrobial agents

Infections caused by methicillin-resistant Staphylococcus aureus (MRSA) result in significant morbidity and mortality for patients in both community and health care settings. This is primarily due to the difficulty in treating MRSA, which is often resistant to multiple classes of antibiotics. Understanding the mechanisms of antimicrobial resistance (AMR) in MRSA provides insight into the optimal use of antimicrobial agents in clinical practice and also underpins critical aspects of antimicrobial stewardship programs. In this review we delineate the mechanisms, prevalence, and clinical importance of resistance to antibiotics licensed in the past 20 years that target MRSA, as well as new drugs in the pipeline which are likely to be licensed soon. Current gaps in scientific knowledge about MRSA resistance mechanisms are discussed, and topics in the epidemiology of AMR in S. aureus that require further investigation are highlighted.

Clinical review of delafloxacin: a novel anionic fluoroquinolone

Delafloxacin is a novel anionic fluoroquinolone (FQ) approved for treatment of acute bacterial skin and skin structure infections (ABSSSIs) caused by a number of Gram-positive and Gram-negative organisms including MRSA and Pseudomonas aeruginosa. The unique chemical structure of delafloxacin renders it a weak acid and results in increased potency in acidic environments. In Phase III studies, delafloxacin had similar outcomes to comparator regimens for treatment of ABSSSIs, and was well tolerated overall. Similar to other FQs, delafloxacin is available in both intravenous and oral formulations, but differs in that delafloxacin exerts a minimal effect on cytochrome P450 enzymes and on the corrected QT interval. This novel FQ has the potential to be utilized across a wide variety of clinical settings; however, post-marketing surveillance and long-term safety and resistance data will be essential to identify optimal use scenarios.

Activity of Antibiotics against Staphylococcus aureus in an In Vitro Model of Biofilms in the Context of Cystic Fibrosis: Influence of the Culture Medium

Staphylococcus aureus is a highly prevalent pathogen in the respiratory tract of young patients with cystic fibrosis (CF) and causes biofilm-related infections. Here, we set up an in vitro model of a biofilm grown in Trypticase soy broth supplemented with glucose and NaCl (TGN) or in artificial sputum medium (ASM) and used it to evaluate on a pharmacodynamic basis the activity of antibiotics used in CF patients and active on staphylococci (meropenem, vancomycin, azithromycin, linezolid, rifampin, ciprofloxacin, tobramycin). Rheological studies showed that ASM was more elastic than viscous, as was also observed for sputa from CF patients, with elastic and viscous moduli being, respectively, similar to and slightly lower than those of CF sputa. Biofilms formed by methicillin-sensitive S. aureus strain ATCC 25923 and methicillin-resistant S. aureus strain ATCC 33591 reached maturity after 24 h, with biomass (measured by crystal violet staining) and metabolic activity (assessed by following resazurin metabolization) being lower in ASM than in TGN and viability (assessed by bacterial counts) being similar in both media. Full concentration-response curves of antibiotics obtained after 24 h of incubation of biofilms showed that all antibiotics were drastically less potent and less efficient in ASM than in TGN toward viability, metabolic activity, and biomass. Tobramycin selected for small-colony variants, specifically in biofilms grown in ASM; the auxotrophism of these variants could not be established. These data highlight the major influence exerted by the culture medium on S. aureus responsiveness to antibiotics in biofilms. The use of ASM may help to determine effective drug concentrations or to evaluate new therapeutic options against biofilms in CF patients.

Profile of a Novel Anionic Fluoroquinolone-Delafloxacin

Fluoroquinolones have been in clinical use for over 50 years with significant efficacy. However, increasing resistance and emergence of some marked adverse events have limited their usage. The most recently approved class member, delafloxacin, is the only available anionic (non-zwitterionic) fluoroquinolone. Its unique molecular structure provides improved in vitro activity against most Gram-positive pathogens, including quinolone-resistant strains, which is further enhanced at acid pH. Delafloxacin shows favorable pharmacological properties, with about 60% bioavailability after oral administration, only mild inhibition of cytochrome P450 3A, and no evidence of cardiac- or phototoxicity in healthy volunteers (tested against positive controls). Its twice daily dosing, suitability for intravenous, oral, or switch dosing, the lack of many clinically significant drug-drug interactions, and acceptable adverse event profile in registration clinical trials supports its use in the treatment of acute bacterial skin and skin structure infections, and potentially in other infections, where resistance to other agents, safety, and/or the need for early discharge is of concern.

Role of Rifampin against Staphylococcal Biofilm Infections In Vitro, in Animal Models, and in Orthopedic-Device-Related Infections

Rifampin has been used as an agent in combination therapy in orthopedic device-related infections (ODRI) for almost three decades. The aim of this review is to provide data regarding the role of rifampin against biofilm infection in vitro, in animal models, and in clinical ODRI. Available data are gathered in order to present the rational use of rifampin combinations in patients with periprosthetic joint infection (PJI). The role of rifampin is well defined in patients with PJI and is indicated in those who fulfill the Infectious Diseases Society of America criteria for debridement and implant retention or one-stage exchange. It should be used with care because of the danger of rapid emergence of resistance. Potential drug interactions should be considered.

Fatty Acid Potassium Had Beneficial Bactericidal Effects and Removed Staphylococcus aureus Biofilms while Exhibiting Reduced Cytotoxicity towards Mouse Fibroblasts and Human Keratinocytes

Wounds frequently become infected or contaminated with bacteria. Potassium oleate (C18:1K), a type of fatty acid potassium, caused >4 log colony-forming unit (CFU)/mL reductions in the numbers of Staphylococcus aureus and Escherichia coli within 10 min and a >2 log CFU/mL reduction in the number of Clostridium difficile within 1 min. C18:1K (proportion removed: 90.3%) was significantly more effective at removing Staphylococcus aureus biofilms than the synthetic surfactant detergents sodium lauryl ether sulfate (SLES) (74.8%, p < 0.01) and sodium lauryl sulfate (SLS) (78.0%, p < 0.05). In the WST (water-soluble tetrazolium) assay, mouse fibroblasts (BALB/3T3 clone A31) in C18:1K (relative viability vs. control: 102.8%) demonstrated a significantly higher viability than those in SLES (30.1%) or SLS (18.1%, p < 0.05). In a lactate dehydrogenase (LDH) leakage assay, C18:1K (relative leakage vs. control: 108.9%) was found to be associated with a significantly lower LDH leakage from mouse fibroblasts than SLES or SLS (720.6% and 523.4%, respectively; p < 0.05). Potassium oleate demonstrated bactericidal effects against various species including Staphylococcus aureus, Escherichia coli, Bacillus cereus, and Clostridium difficile; removed significantly greater amounts of Staphylococcus aureus biofilm material than SLES and SLS; and maintained fibroblast viability; therefore, it might be useful for wound cleaning and peri-wound skin.

Transcriptome analysis of silver nanoparticles treated Staphylococcus aureus reveals potential targets for biofilm inhibition

The biofilms of Staphylococcus aureus on the implanted materials and chronic wounds are life-threatening and are a substantial financial burden on the healthcare system. Silver nanoparticles (SNP), known for their multi-level physiological effects in planktonic cells could be a promising agent in the treatment of biofilm-related infections also. To gain insight into the effects of SNP on various physiological processes in biofilms we studied the transcriptome of Staphylococcus aureus ATCC 29213. To distinguish between 'nanoparticles-specific' and 'ion-specific' effect of silver, we performed a comparative analysis of the functional genes in response to Ag⁺. As compared to untreated biofilms, 21% (i.e. 629 genes) and 28.5% (i. e. 830 genes) of the total functional coding genes were differentially regulated upon exposure to SNP and Ag⁺. Genes encoding capsular polysaccharides, intercellular adhesion, virulence were downregulated in SNP and Ag⁺ treated biofilms. Genes involved in carbohydrate, protein metabolism including DNA and RNA synthesis, oxidative stress etc. were differentially expressed. Further, activation of efflux pumps and multidrug export proteins was observed, which clearly indicates the presence of metal stress resistance determinants in S. aureus. Silver blocked the integration of mobile genetic elements in S. aureus genome. Our study points out quorum sensing and virulence determinants as possible targets for inhibition of biofilms possibly with/without existing antibiotics. However, further studies on these aspects are warranted. Scanning electron microscopy (SEM) and confocal microscopy revealed changes in biofilm morphology, architecture and thickness in presence of silver nanoparticles and ionic silver, substantiating the transcriptome data.

Characterization of Biofilms Formed by Foodborne Methicillin-Resistant Staphylococcus aureus

The objective of this study was to evaluate the capacity of 49 methicillin resistant Staphylococcus aureus (MRSA) from foods of animal origin (42 from dairy products and 7 from meat and meat products) to form biofilms. Overall, a higher biofilm biomass was observed for those MRSA strains harboring SCCmec type IV, while 8 MRSA strains (5 from dairy products and 3 from meat and meat products) were classified as strong biofilm formers in standard Tryptic Soy Broth medium. When a prolonged incubation period (48 h) was applied for those 8 MRSA strains, an increased biofilm biomass accumulation was observed during the time course, whereas the number of viable cells within the biofilms decreased as the biomass increased. The capacity of biofilm production correlated pretty well between the experiments using polystyrene microtiter plates and stainless steel micro-well plates, and significant higher values were observed in stainless steel when glucose was added to TSB during the enrichment. Biofilms were further characterized by confocal laser scanning microscope (CLSM), confirming that proteins and α-polysaccharides were the predominant components inside the extracellular polymeric matrix of biofilms formed by MRSA strains. In conclusion, our results confirm that MRSA isolates from foods of animal origin have significant capacity for forming biofilms with a high protein content, which can play a key role for the successful dissemination of MRSA lineages via food. Knowledge of the capacity of MRSA strains to produce biofilms, as well as characterization of the main MRSA biofilms matrix components, can help both to counteract the mechanisms involved in biofilm formation and resistance and to define more rational control strategies by using tailor-made cleaning agents.