In vitro activity and post-antibiotic effects of linezolid in combination with fosfomycin against clinical isolates of Staphylococcus aureus

Antimicrobial Synergistic Effects of Linezolid and Vancomycin with a Small Synthesized 2-Mercaptobenzothiazole Derivative: A Challenge for MRSA Solving

Methicillin-resistant Staphylococcus aureus (MRSA) emerged as one of the leading causes of persistent human infections and makes it difficult to treat bacteremia, especially with biofilm formation. In this work, we investigated the in vitro synergism between Linezolid (LNZ) and Vancomycin (VAN) with a 2-mercaptobenzothiazole derivative, resulting in a new small-molecule antibacterial compound that we named BTZ2e, on several clinical MRSA, MRSE (methicillin-resistant Staphylococcus epidermidis) and control (ATCC Collection) strains in their planktonic and biofilms cultures. The broth microdilution method evaluated the susceptibility of planktonic cells to each investigated antibiotic combined with BTZ2e. The biofilm's metabolic activity was studied with the XTT reduction assay. As a result, in this study, biofilm formation was significantly suppressed by the BTZ2e treatment. In terms of minimal biofilm inhibitory concentration (MBIC), BTZ2e revealed an MBIC50 value of 32 μg/mL against methicillin-susceptible S. aureus (MSSA) and 16 μg/mL against methicillin-resistant S. aureus ATCC 43300 biofilms. An inhibition range of 32 μg/mL and 256 μg/mL was registered for the clinical isolates. Interestingly, a synergistic effect (FICI ≤ 0.5) was encountered for the combination of BTZ2e with LNZ and VAN on several planktonic and sessile strains. In particular, the best result against planktonic cells emerged as a result of the synergistic association between LNZ and BTZ2e, while against sessile cells, the best synergistic association resulted from VAN and BTZ2e. The consistent results indicate BTZ2e as a promising adjuvant against multi-resistant strains such as MRSA and MRSE.

In silico and in vitro studies of GENT-EDTA encapsulated niosomes: A novel approach to enhance the antibacterial activity and biofilm inhibition in drug-resistant Klebsiella pneumoniae

Klebsiella pneumoniae (Kp) is a common pathogen inducing catheter-related biofilm infections. Developing effective therapy to overcome antimicrobial resistance (AMR) in Kp is a severe therapeutic challenge that must be solved. This study aimed to prepare niosome-encapsulated GENT (Gentamicin) and EDTA (Ethylenediaminetetraacetic acid) (GENT-EDTA/Nio) to evaluate its efficacy toward Kp strains. The thin-film hydration method was used to prepare various formulations of GENT-EDTA/Nio. Formulations were characterized for their physicochemical characteristics. GENT-EDTA/Nio properties were used for optimization with Design-Expert Software. Molecular docking was utilized to determine the antibacterial activity of GENT. The niosomes displayed a controlled drug release and storage stability of at least 60 days at 4 and 25 °C. GENT-EDTA/Nio performance as antimicrobial agents has been evaluated by employing agar well diffusion method, minimum bactericidal concentration (MBC), and minimum inhibitory concentration (MIC) against the Kp bacteria strains. Biofilm formation was investigated after GENT-EDTA/Nio administration through different detection methods, which showed that this formulation reduces biofilm formation. The effect of GENT-EDTA/Nio on the expression of biofilm-related genes (mrkA, ompA, and vzm) was estimated using QRT-PCR. MTT assay was used to evaluate the toxicity effect of niosomal formulations on HFF cells. The present study results indicate that GENT-EDTA/Nio decreases Kp's resistance to antibiotics and increases its antibiotic and anti-biofilm activity and could be helpful as a new approach for drug delivery.

Targeted Therapy of Severe Infections Caused by Staphylococcus aureus in Critically Ill Adult Patients: A Multidisciplinary Proposal of Therapeutic Algorithms Based on Real-World Evidence

(1) Introduction: To develop evidence-based algorithms for targeted antibiotic therapy of infections caused by Staphylococcus aureus in critically ill adult patients. (2) Methods: A multidisciplinary team of four experts had several rounds of assessment for developing algorithms concerning targeted antimicrobial therapy of severe infections caused by Staphylococcus aureus in critically ill patients. The literature search was performed by a researcher on PubMed-MEDLINE (until August 2022) to provide evidence for supporting therapeutic choices. Quality and strength of evidence was established according to a hierarchical scale of the study design. Two different algorithms were created, one for methicillin-susceptible Staphylococcus aureus (MSSA) and the other for methicillin-resistant Staphylococcus aureus (MRSA). The therapeutic options were categorized for each different site of infection and were selected also on the basis of pharmacokinetic/pharmacodynamic features. (3) Results: Cefazolin or oxacillin were the agents proposed for all of the different types of severe MSSA infections. The proposed targeted therapies for severe MRSA infections were different according to the infection site: daptomycin plus fosfomycin or ceftaroline or ceftobiprole for bloodstream infections, infective endocarditis, and/or infections associated with intracardiac/intravascular devices; ceftaroline or ceftobiprole for community-acquired pneumonia; linezolid alone or plus fosfomycin for infection-related ventilator-associated complications or for central nervous system infections; daptomycin alone or plus clindamycin for necrotizing skin and soft tissue infections. (4) Conclusions: We are confident that targeted therapies based on scientific evidence and optimization of the pharmacokinetic/pharmacodynamic features of antibiotic monotherapy or combo therapy may represent valuable strategies for treating MSSA and MRSA infections.

Enhancement in Site-Specific Delivery of Chloramphenicol Using Bacterially Sensitive Microparticle Loaded Into Dissolving Microneedle: Potential For Enhanced Effectiveness Treatment of Cellulitis

One of the biggest challenges in infectious disease treatment is the existence of bacterial infections in underskin wound tissue, such as cellulitis. Compared to other treatments, it is harder for antibacterial drugs to penetrate the physical barrier on the affected skin with a nonspecific target, making conventional therapy for cellulitis infection more difficult and considered. In this novel research, we pioneer a combined strategy of dissolving microneedles (MNs) and bacteria-sensitive microparticles (MPs) for enhanced penetration and targeted delivery of chloramphenicol (CHL) to the infection site specifically. The polycaprolactone polymer was used to make MPs because of its sensitivity to bacterial enzyme stimuli. The best microparticle formulation was discovered and optimized using the Design-Expert application. Furthermore, this study evaluated the antibacterial activity of MPs in vitro and in vivo on the mutant Drosophila larval infection model. This strategy shows improvement in the antibacterial activity of MPs and higher retention duration compared to conventional cream formulation, and the inclusion of these MPs into dissolving MNs was able to greatly improve the dermatokinetic characteristics of CHL in ex vivo evaluation. Importantly, the antimicrobial efficacy in an ex vivo infection model demonstrated that, following the use of this strategy, bacterial bioburdens decreased by up to 99.99% after 24 h. The findings offered a proof of concept for the enhancement of CHL dermatokinetic profiles and antimicrobial activities after its preparation into bacteria-sensitive MPs and distribution by MNs. Future research should investigate in vivo effectiveness in an appropriate animal model.

Ultrasound assisted facile synthesis of Boron-Heck coupled sclareol analogs as potential antibacterial agents against Staphylococcus aureus

AIM

To evaluate the antimicrobial capability of sclareol and its derivatives against Staphylococcus aureus and its Methicillin-resistant strain (MRSA).

METHODS AND RESULTS

A new series of Boron-Heck-coupled sclareol analogs were prepared by structural modifications at C-15 terminal double bond of sclareol using ultrasonication. The structural modifications were designed to keep the stereochemistry of all the five chiral centres of sclareol intact. A two-step reaction scheme consisting of Boron-Heck coupling of sclareol followed by Wittig reaction was carried out to produce novel sclareol congeners for antintimicrobial evaluation. Three compounds SAJ-1, SAJ-2 and SB-11 exhibited strong antibacterial activity against Staphylococcus aureus and Methicillin-resistant strain (MRSA) with MIC values between 3 to 11 μM. Among all the screened compounds, SAJ-1 and SAJ-2 showed the best anti-biofilm profiles against both the strains. Moreover SAJ-1 and SAJ-2 acted synergistically with streptomycin against S. aureus while creating varying outcomes in combination with ciprofloxacin, penicillin, and ampicillin. SAJ-1 also acted synergistically with ampicillin against S. aureus, while SB-11 showed synergism with ciprofloxacin against both pathogens. Moreover, SAJ-1 and SAJ-2 also inhibited staphyloxanthin production in S. aureus and MRSA and induced post-antibiotic effects against both pathogens.

CONCLUSIONS

It can be inferred that SAJ-1, SAJ-2 and SB-11 may act as potential chemical entities for the development of antibacterial substances. The study revealed that SAJ-1 and SAJ-2 are most suitable sclareol analogs for further studies towards the development of antibacterial substances.

SIGNIFICANCE AND IMPACT OF THE STUDY

SAJ-1, SAJ-2 and SB-11 show promising antibacterial properties against Staphylococcus aureus. Efforts should be made and more research should be done, utilising in vivo models to determine their efficacy as antibiotics.

Comprehensive insight into anti-staphylococcal and anti-enterococcal action of brominated and chlorinated pyrazine-based chalcones

The greatest threat and medicinal impact within gram-positive pathogens are posed by two bacterial genera, Staphylococcus and Enterococcus. Chalcones have a wide range of biological activities and are recognized as effective templates in medicinal chemistry. This study provides comprehensive insight into the anti-staphylococcal and anti-enterococcal activities of two recently published brominated and chlorinated pyrazine-based chalcones, CH-0y and CH-0w. Their effects against 4 reference and 12 staphylococcal and enterococcal clinical isolates were evaluated. Bactericidal action, the activity in combination with selected conventional antibiotics, the study of post-antimicrobial effect (PAE, PAE/SME), and in vitro and in vivo toxicity, were included. In CH-0y, anti-staphylococcal activity ranging from MIC = 15.625 to 62.5 μM, and activity against E. faecium from 31.25 to 62.5 μM was determined. In CH-0w, anti-staphylococcal activity ranging from 31.25 to 125 μM, and activity against E. faecium and E. faecalis (62.5 μM) was revealed. Both CH-0y and CH-0w showed bactericidal action, beneficial impact on bacterial growth delay within PAE and PAE/SME studies, and non/low toxicity in vivo. Compared to CH-0w, CH-0y seems to have higher anti-staphylococcal and less toxic potential. In conclusion, chalcones CH-0y and CH-0w could be considered as structural pattern for future adjuvants to selected antibiotic drugs.

Nanobiotic formulations as promising advances for combating MRSA resistance: susceptibilities and post-antibiotic effects of clindamycin, doxycycline, and linezolid

Antimicrobial activity and post-antibiotic effects (PAEs) are both important parameters in determination of the dosage regimen of antimicrobial agents. In the present study, antimicrobial activity and PAEs of clindamycin, doxycycline, linezolid, and their nanobiotic formulations were evaluated against two methicillin resistant Staphylococcus aureus clinical isolates (MRSA) encoded (MRSA-S1 and MRSA-S2). Nanobiotic formulations increased the susceptibility of MRSA isolates by 4–64 folds as compared to their conventional ones. The PAE values were determined after exposure of MRSA isolates for 1 h to 10× the MICs of the tested antibiotics. The duration of PAEs were recorded after bacterial growth in Mueller Hinton broth (MHB) free from antibiotic has been restored. The PAE values for MRSA-S1 were 2.5 h for the conventional antibiotics. However, the PAEs for nanobiotics were 4 h for both clindamycin and linezolid, while 3 h for doxycycline. For MRSA-S2, linezolid and linezolid nanobiotics PAEs were 3 h. PAEs of clindamycin and clindamycin nanobiotics were 3.75 h and 4 h, respectively. Doxycycline and doxycycline nanobiotics revealed the same PAEs patterns of 3.5 h. The findings of the current study may positively influence the pharmacodynamics of the antibiotics and consequently the dosage regimen of nanobiotics as well as on their clinical outcome.

Novel nanobiotic formulations of clindamycin, doxycycline, and linezolid were evaluated for the post-antibiotic effects against biofilm forming methicillin resistant Staphylococcus aureus (MRSA).

Development and Validation of an HPLC-UV Method for Quantitation of Linezolid: Application to Resistance Study Using in vitro PK/PD Model

Background

Linezolid (LNZ), an oxazolidinone antibiotic, has 100% oral bioavailability and favorable activities against gram-positive pathogens. The in vitro PK/PD model was developed based on concentrations obtained with routine doses in humans can be used to guide dose optimization in the clinic.

Methods

In this study, we employed an in vitro PK/PD model to simulate the changes in the plasma concentration of linezolid in the human body against a clinical isolate of MRSA in vitro. A high-performance liquid chromatography (HPLC)-UV method was applied to measure the concentration of linezolid. Bacterial samples were collected at different times from the central compartment for count.

Results

The chromatographic separation was carried out with an AichromBond-AQC18 column(250mm×4.6mm, 5μm), using a mobile phase of water with 0.1% formic acid:acetonitrile 70:30 (v/v), followed by detection at 254 nm, and a single detection run was completed within 10 min. The method was validated by estimating the precision and accuracy for the inter- and intra-day analyses in the concentration range of 0.25-32 mg/L. The method was linear over the investigated range of 0.125-32 mg/L, with all correlation coefficients R² = 0.9999. The intra-day and inter-day precisions were within 7.598%, and the method recovery ranged from 90.912% to 106.459%. In vitro PK/PD model, both the absorption and elimination of linezolid being simulated can be precisely controlled by computer. In the control group, the bacterial reached 7.9 Log10CFU/mL in the first 48h and maintained until the end, indicating that the colonies grew well in vitro PK/PD model. In the linezolid 600 mg q12h administration group, the colony decreased to 2.39 Log10CFU/mL at 24h, showing a good bactericidal effect; however, the colonies resumed growth to the initial level in 48h, indicating an emergence of resistance.

Conclusion

We successfully established an in vitro infection PK/PD model and developed an HPLC-UV method to determine linezolid concentration for resistance investigation. The results suggest that the 600 mg q12h dosing regimen may no longer be applicable and requires optimization.

Drug resistance reversal potential of multifunctional thieno[3,2-c]pyran via potentiation of antibiotics in MDR P. aeruginosa

We explored the antibacterial potential (alone and combination) against multidrug resistant (MDR) Pseudomonas aeruginosa isolates KG-P2 using synthesized thieno[3,2-c]pyran-2-ones in combination with different antibiotics. Out of 14 compounds, two compounds (3g and 3l) abridged the MIC of tetracycline (TET) by 16 folds. Compounds was killing the KG-P2 cells, in time dependent manner, lengthened post-antibiotic effect (PAE) of TET and found decreased the mutant prevention concentration (MPC) of TET. In ethidium bromide efflux experiment, two compounds repressed the drug transporter (efflux pumps) which is further supported by molecular docking of these compounds with efflux complex MexAB-OprM. In another study, these compounds inhibited the synthesis of biofilm.

Flexible Microneedle Array Patch for Chronic Wound Oxygenation and Biofilm Eradication

Chronic nonhealing wounds are a growing socioeconomic problem that affects more than 6 million people annually solely in the United States. These wounds are colonized by bacteria that often develop into biofilms that act as a physical and chemical barrier to therapeutics and tissue oxygenation leading to chronic inflammation and tissue hypoxia. Although wound debridement and vigorous mechanical abrasion techniques are often used by clinical professionals to manage and remove biofilms from wound surfaces, such methods are highly nonselective and painful. In this study, we have developed a flexible polymer composite microneedle array that can overcome the physicochemical barriers (i.e., bacterial biofilm) present in chronic nonhealing wounds and codeliver oxygen and bactericidal agents. The polymeric microneedles are made by using a facile UV polymerization process of polyvinylpyrrolidone and calcium peroxide onto a flexible polyethylene terephthalate substrate for conformable attachment onto different locations of the human body surface. The microneedles effectively elevate the oxygen levels from 8 to 12 ppm once dissolved over the course of 2 h while also providing strong bactericidal effects on both liquid and biofilm bacteria cultures of both Gram-positive (Staphylococcus aureus) and Gram-negative (Pseudomonas aeruginosa) bacterial strains commonly found in dermal wounds. Furthermore, the results from the ex vivo assay on a porcine wound model indicated successful insertion of the microneedles into the tissue while also providing effective bactericidal properties against both Gram-positive and Gram-negative within the complex tissue matrix. Additionally, the microneedles demonstrate high levels of cytocompatibility with less than 10% of apoptosis throughout 6 days of continuous exposure to human dermal fibroblast cells. The demonstrated flexible microneedle array can provide a better approach for increasing the effectiveness of topical tissue oxygenation as well as the treatment of infected wounds with intrinsically antibiotic resistant biofilms.

Synergistic effect of curcumin-Cu and curcumin-Ag nanoparticle loaded niosome: Enhanced antibacterial and anti-biofilm activities

In the current study, for the first time, the synergistic activity of curcumin and silver/copper nanoparticles (NPs) was studied against Staphylococcus aureus and Pseudomonas aeruginosa. Moreover, a unique combination of curcumin and silver/copper NPs in free and encapsulated forms was prepared and delivered through a niosomal system. For this purpose, different niosomal formulations of curcumin and metal NPs were prepared by thin film hydration method. Then, the dual drug-loaded niosomes were dispersed in chitosan hydrogel in order to widen its applications. The effect of the molar ratios of lipid to drug and surfactant to cholesterol was investigated to find the optimized noisomal nanoparticles in terms of size, polydispersity index (PDI), and entrapment efficiency (EE). The size and PDI values were measured by dynamic light scattering (DLS). Morphology and in vitro drug release kinetics of niosomes were examined by scanning and transmission electron microscopy (SEM, TEM) and dialysis method, respectively. The drug-loaded niosomes and their hydrogel counterpart were screened for investigating their antibacterial activity against S. aureus and P. aeruginosa by disk diffusion, minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) assays. Furthermore, anti-biofilm assay and expression of biofilm-associated genes by Real-time PCR were performed to evaluate the anti-biofilm effect of NPs. In this study, the drug-loaded niosomal formulations showed good entrapment efficiencies (EE) with a sustained release profile over 72 h. Moreover, compared to free drugs, the optimized niosomal formulations increased antibacterial activity against the bacteria via promotion in the inhibition zone and reduction in MIC and MBC values. Interestingly, gel-based niosomal formulations increased the inhibition zone by about 6 mm and significantly decreased MIC and MBC values compared to niosomal formulations. Also, biofilm eradication of curcumin-metal NPs encapsulated into niosomal hydrogel was highest compared to free and niosomal drugs. Overall, curcumin-Cu or curcumin-Ag nanoparticle loaded niosomes incorporated in hydrogel hold great promise for biomedical applications.

In vitro and in vivo Antibacterial Activity of Linezolid Plus Fosfomycin Against Staphylococcus aureus with Resistance to One Drug

Objective

The purpose of this study is to assess the in vitro/vivo activities of linezolid plus fosfomycin against Staphylococcus aureus (S. aureus) isolates with varying susceptibility to the study drugs.

Methods

The increasing concentration stepwise method was used to induce S. aureus resistant strains. The in vitro antibacterial activity of linezolid combined with fosfomycin against S. aureus in vitro was studied by time-kill curve and PAE. The transmission electron microscopy (TEM) was employed to observe the cell morphology of bacteria treated with drug, and the changes of cell wall thickness were recorded. The Galleria mellonella infection model was established to demonstrate the in vivo efficacy of linezolid and fosfomycin against S. aureus with varying susceptibility.

Results

The antibiotic combination showed excellent synergistic or additive effects on the original and the linezolid-resistant strain, but showed indifferent effect for fosfomycin-resistant strain. TEM images showed that fosfomycin alone and in combined could reduce the cell wall thickness of the strains resistant to linezolid and cell lysis, while linezolid increases the cell wall thickness of the strains resistant to fosfomycin. In the Galleria mellonella infection model, the survival rate of the antibiotic combined was improved compared with that of the single drug. There was a good correlation between in vivo efficacy and in vitro susceptibility.

Conclusion

The type of interaction expressed in the test combination was highly dependent on fosfomycin resistance.

Synergistic Combination of Linezolid and Fosfomycin Closing Each Other's Mutant Selection Window to Prevent Enterococcal Resistance

Enterococci, the main pathogens associated with nosocomial infections, are resistant to many common antibacterial drugs including β-lactams, aminoglycosides, etc. Combination therapy is considered an effective way to prevent bacterial resistance. Preliminary studies in our group have shown that linezolid combined with fosfomycin has synergistic or additive antibacterial activity against enterococci, while the ability of the combination to prevent resistance remains unknown. In this study, we determined mutant prevention concentration (MPC) and mutant selection window (MSW) of linezolid, fosfomycin alone and in combination including different proportions for five clinical isolates of Enterococcus and characterized the resistance mechanism for resistant mutants. The results indicated that different proportions of linezolid combined with fosfomycin had presented different MPCs and MSWs. Compared with linezolid or fosfomycin alone, the combination can restrict the enrichment of resistant mutants at a lower concentration. A rough positive correlation between the selection index (SI) of the two agents in combination and the fractional inhibitory concentration index (FICI) of the combination displayed that the smaller FICI of linezolid and fosfomycin, the more probable their MSWs were to close each other. Mutations in ribosomal proteins (L3 and L4) were the mechanisms for linezolid resistant mutants. Among the fosfomycin-resistant mutants, only two strains have detected the MurA gene mutation related to fosfomycin resistance. In conclusion, the synergistic combination of linezolid and fosfomycin closing each other’s MSW could effectively suppress the selection of enterococcus resistant mutants, suggesting that the combination may be an alternative for preventing enterococcal resistance. In this study, the resistance mechanism of fosfomycin remains to be further studied.

Synergistic Effects from Combination of Cryptotanshinone and Fosfomycin Against Fosfomycin-Susceptible and Fosfomycin-Resistant Staphylococcus aureus

Purpose

Fosfomycin is now widely used to treat methicillin-resistant S. aureus due to its unique antibacterial activity. However, fosfomycin-resistant S. aureus has rapidly emerged, it is urgent to find new treatments to eliminate fosfomycin-resistant S. aureus infection. The purpose of this study was to analyze the activity of cryptanshinone, a traditional Chinese medicine monomer, in combination with fosfomycin against fosfomycin-sensitive S. aureus (FSSA) and fosfomycin-resistant S. aureus (FRSA).

Methods

The MICs of fosfomycin and/or cryptanshinone were determined by agar dilution assay and checkerboard microdilution assay. Furthermore, synergistic effects from fosfomycin and/or cryptanshinone were analyzed by the time-kill assay in vitro.

Results

The combination of fosfomycin and cryptotanshinone had a synergistic effect on most (71.43%) of the FRSA and had a partial (28.57%) synergistic effect on a small part. In addition, time sterilization curve verified synergistic activity between cryptanshinone and fosfomycin against FSSA and FRSA, especially when fosfomycin was added for a second time.

Conclusion

These data suggest that cryptanshinone combined with fosfomycin could be a novel treatment for FRSA and provide a new direction for the treatment of bacterial infections in the future.

Fosfomycin as Partner Drug for Systemic Infection Management. A Systematic Review of Its Synergistic Properties from In Vitro and In Vivo Studies

Fosfomycin is being increasingly prescribed for multidrug-resistant bacterial infections. In patients with systemic involvement, intravenous fosfomycin is usually administered as a partner drug, as part of an antibiotic regimen. Hence, the knowledge of fosfomycin pharmacodynamic interactions (synergistic, additive, indifferent and antagonistic effect) is fundamental for a proper clinical management of severe bacterial infections. We performed a systematic review to point out fosfomycin’s synergistic properties, when administered with other antibiotics, in order to help clinicians to maximize drug efficacy optimizing its use in clinical practice. Interactions were more frequently additive or indifferent (65.4%). Synergism accounted for 33.7% of total interactions, while antagonism occurred sporadically (0.9%). Clinically significant synergistic interactions were mostly distributed in combination with penicillins (51%), carbapenems (43%), chloramphenicol (39%) and cephalosporins (33%) in Enterobactaerales; with linezolid (74%), tetracyclines (72%) and daptomycin (56%) in Staphylococcus aureus; with chloramphenicol (53%), aminoglycosides (43%) and cephalosporins (36%) against Pseudomonas aeruginosa; with daptomycin (97%) in Enterococcus spp. and with sulbactam (75%) and penicillins (60%) and in Acinetobacter spp. fosfomycin-based antibiotic associations benefit from increase in the bactericidal effect and prevention of antimicrobial resistances. Taken together, the presence of synergistic interactions and the nearly total absence of antagonisms, make fosfomycin a good partner drug in clinical practice.

Synergy of Linezolid with Several Antimicrobial Agents against Linezolid-Methicillin-Resistant Staphylococcal Strains

Linezolid is a synthetic oxazolydinone active against multi-resistant Gram-positive cocci that inhibits proteins synthesis by interacting with the 50S ribosomal subunit. Although linezolid-resistant strains are infrequent, several outbreaks have been recently described, associated with prolonged treatment with the antibiotic. As an alternative to monotherapy, the combination of different antibiotics is a commonly used option to prevent the selection of resistant strains. In this work, we evaluated combinations of linezolid with classic and new aminoglycosides (amikacin, gentamicin and plazomicin), carbapenems (doripenem, imipenem and meropenem) and fosfomycin on several linezolid- and methicillin-resistant strains of Staphylococcus aureus and S. epidermidis, isolated in a hospital intensive care unit in Madrid, Spain. Using checkerboard and time-kill assays, interesting synergistic effects were encountered for the combination of linezolid with imipenem in all the staphylococcal strains, and for linezolid-doripenem in S.epidermidis isolates. The combination of plazomicin seemed to also have a good synergistic or partially synergistic activity against most of the isolates. None of the combinations assayed showed an antagonistic effect.

Bacterially sensitive nanoparticle-based dissolving microneedles of doxycycline for enhanced treatment of bacterial biofilm skin infection: A proof of concept study

The presence of bacterial biofilms in wounds is a main issue in the healing process. Conventional therapy of bacterial biofilms is hampered by the poor penetration of antibacterial agents through the physical barrier on the infected skin and the non-specific target of antibacterial agents. Here, we present a combination approach of bacterial sensitive nanoparticles (NPs) and dissolving microneedles (MNs) of doxycycline (DOX) for improved biofilm penetration and specifically delivering DOX to the infection site. The NPs were prepared from poly(lactic-co-glycolic acid) and poly (Ɛ-caprolactone) decorated with chitosan. The release of DOX was improved with the presence of bacterial producing biofilm up to 7-fold. The incorporation of these NPs into dissolving MNs was able to significantly enhance the dermatokinetic profiles of DOX, indicated by higher retention time compared to needle-free patches. Importantly, the antibiofilm activity in ex vivo biofilm model showed that after 48 h, the bacterial bioburdens decreased up to 99.99% following the application of this approach. The results presented here assist as proof of principle for the improvement of dermatokinetic profiles and antibiofilm activities of DOX, following its formulation into bacterial sensitive NPs and delivery via MN. Future studies must explore in vivo efficacy in a suitable animal model.

Parenteral Fosfomycin for the Treatment of Multidrug Resistant Bacterial Infections: The Rise of the Epoxide

Fosfomycin was initially discovered in 1969 but has recently gained renewed interest for the treatment of multidrug-resistant (MDR) bacterial infections, particularly in the United States. Its unique mechanism of action, bactericidal activity, broad spectrum of activity, and relatively safe and tolerable adverse effect profile make it a great addition to the dwindling antibiotic armamentarium. Fosfomycin contains a three-membered epoxide ring with a direct carbon to phosphorous bond that bypasses the intermediate oxygen bond commonly present in other organophosphorous compounds; this structure makes the agent unique from other antibiotics. Despite nearly 50 years of parenteral fosfomycin use in Europe, fosfomycin has retained stable activity against most pathogens. Furthermore, fosfomycin demonstrated in vitro synergy in combination with other cell wall-active antibiotics (e.g., β-lactams, daptomycin). These combinations may offer respite for severe infections due to MDR gram-positive and gram-negative bacteria. The intravenous (IV) formulation is currently under review in the United States, and apropos, this review collates more contemporary evidence (i.e., studies published between 2000 and early 2019) in anticipation of this development. The approval of IV fosfomycin provides another option for consideration in the management of MDR infections. Its unique structure will give rise to a promising epoxide epoch in the battle against MDR bacteria.

Cationic antimicrobial peptides: alternatives and/or adjuvants to antibiotics active against methicillin-resistant Staphylococcus aureus and multidrug-resistant Pseudomonas aeruginosa

BACKGROUND

Methicillin-resistant Staphylococcus aureus and multidrug-resistant Pseudomonas aeruginosa are becoming difficult to treat with antibiotics whereas Cationic Antimicrobial Peptides (CAMPs) represent promising alternatives. The effects of four CAMPs (LL-37: human cathelicidin, CAMA: cecropin(1-7)-melittin A(2-9) amide, magainin-II and nisin) were investigated against clinical and laboratory S. aureus (n = 10) and P. aeruginosa (n = 11) isolates either susceptible or resistant to antibiotics. Minimal Inhibitory Concentrations (MICs), Minimal Bactericidal Concentrations (MBCs), and bacterial survival rates (2 h post-treatment) were determined by microbroth dilution. The antipseudomonal effects of the antibiotics colistin or imipenem combined to LL-37 or CAMA were also studied. The toxicity of CAMPs used alone and in combination with antibiotics was evaluated on two human lung epithelial cell lines by determining the quantity of released cytoplasmic lactate dehydrogenase (LDH). Attempts to induce bacterial resistance to gentamicin, LL-37 or CAMA were also performed.

RESULTS

The results revealed the rapid antibacterial effect of LL-37 and CAMA against both antibiotic susceptible and resistant strains with almost a total reduction in bacterial count 2 h post-treatment. Magainin-II and nisin were less active against tested strains. When antibiotics were combined with LL-37 or CAMA, MICs of colistin decreased up to eight-fold and MICs of imipenem decreased up to four-fold. Cytotoxicity assays revealed non-significant LDH-release suggesting no cell damage in all experiments. Induction of bacterial resistance to LL-37 was transient, tardive and much lower than that to gentamicin and induction of resistance to CAMA was not observed.

CONCLUSION

This study showed the potent and rapid antibacterial activity of CAMPs on both laboratory and clinical isolates of S. aureus and P. aeruginosa either susceptible or resistant to antibiotics. Most importantly, CAMPs synergized the efficacy of antibiotics, had non toxic effects on human cells and were associated with transient and low levels of induced resistance.