Evaluation of Ceftaroline Alone and in Combination against Biofilm-Producing Methicillin-Resistant Staphylococcus aureus with Reduced Susceptibility to Daptomycin and Vancomycin in an In Vitro Pharmacokinetic/Pharmacodynamic Model

Efficacy of Ceftobiprole and Daptomycin at Bone Concentrations Against Methicillin-Resistant Staphylococcus aureus Biofilm: Results of a Dynamic In Vitro PK/PD Model

Background: The presence of biofilms and low antimicrobial concentrations in bone tissue make prosthetic joint infections (PJI) difficult to treat. Ceftobiprole (CTO) has a potential role in MRSA PJI. This study evaluated the efficacy of ceftobiprole and daptomycin (DAP) alone and in combination against MRSA biofilms at expected bone tissue concentrations. We assessed whether CTO-DAP outperformed DAP combined with a non-anti-MRSA beta-lactam (cefazolin [CZO]). Methods: A dynamic in vitro PK/PD biofilm model (CDC biofilm reactor) was used to simulate concentrations expected in cortical bone at a standard dosing of DAP (10 mg/kg/24 h), CTO (500 mg/8 h), and CZO (2 g/8 h), and assess performance against a 48-h MRSA biofilm from two clinical isolates that cause PJI (MRSA-1811 and MRSA-1733). Time-kill curves using the log change method (Δlog10 CFU/cm2) assessed antimicrobial efficacy over 56 h. Resistance emergence was monitored. Results: Although both monotherapies were active, neither reached bactericidal levels nor was one superior to the other (Δlog10 CFU/cm2 CTO vs. DAP: -1.44 ± 0.25 vs. -1.50 ± 0.01 [p = 0.686] and -1.55 ± 0.74 vs. -0.56 ± 0.36 [p = 0.108] for MRSA-1811 and MRSA-1733, respectively). Only in the MRSA-1811 isolate did the CTO-DAP combination improve the activity of each monotherapy, without achieving a synergistic effect (Δlog10 CFU/cm2: CTO-DAP -2.087 ± 0.048 vs. CTO -1.436 ± 0.249 [p = 0.013] and vs. DAP -1.503 ± 0.011 [p = 0.006]). No combination therapy (CTO-DAP vs. DAP-CZO) outperformed the other in either strain. No resistant bacterial subpopulations appeared with any antibiotic regimen. Conclusions: At clinically relevant concentrations, ceftobiprole and daptomycin showed similar activity against MRSA biofilms. The CTO-DAP combination showed comparable efficacy to DAP-CZO.

A prospective study to evaluate high dose daptomycin pharmacokinetics and pharmacodynamics in Staphylococcus spp. infective endocarditis

Background

Daptomycin pharmacokinetics and pharmacodynamics data relative to higher doses in patients are necessary for clinical practice.

Objectives

A monocentric, prospective study that enrolled patients with a diagnosis of Staphylococcus spp. infective endocarditis treated with daptomycin according to clinical practice, to evaluate the pharmacokinetics/pharmacodynamics of different daptomycin daily doses (group A: 8-10 and group B: 11-12 mg/kg).

Design and methods

A monocentric, prospective, cohort study that enrolled patients with a diagnosis of Staphylococcus spp. infective endocarditis treated with daptomycin. Daptomycin was administered by intravenous infusion over a 30-min period for at least five consecutive days before PK study.

Results

Twenty-two patients were included. Native valve infectious endocarditis (IE) was diagnosed in 9 patients, prosthetic valve IE was diagnosed in 10 patients and 3 patients had concomitant intracardiac device infections. All patients showed a microbiologic response with negative blood cultures by day 5 (1-3 interquartile rate (IQR) 3-8). The median calculated AUC0-24 was 1298 (1-3 IQR 1069-1484) and 1459 (1-3 IQR 1218-1711) µg*h/mL, with the corresponding clearance of 0.49 (1-3 IQR 0.37-0.57) and 0.57 (1-3 IQR 0.40-0.71) L/h, respectively. A value of area under the curve/minimum inhibitory concentration (AUC/MIC) > 666 was reached by all patients; however, 4 out of 15 patients in group A and 1 out of 14 patients in group B did not reach the pharmacokinetic/pharmacodynamic (PK/PD) target of 1061; therefore, AUC/MIC equal to or above 1061 was reached by 73.3% in group A and 92.9% in group B.

Conclusion

From a PK/PD point of view, all patients reached the value of AUC/MIC > 666, while roughly 70% of patients in group A and 90% in group B reached the target value of AUC/MIC>1061. Even if this cut-off value is arbitrary, 11-12 mg/kg daily dose could be taken into consideration in case of serious infections characterised by a high inoculum or in cases of prosthetic valve infections.

Dynamic In Vitro PK/PD Infection Models for the Development and Optimisation of Antimicrobial Regimens: A Narrative Review

The antimicrobial concentration-time profile in humans affects antimicrobial activity, and as such, it is critical for preclinical infection models to simulate human-like dynamic concentration-time profiles for maximal translatability. This review discusses the setup, principle, and application of various dynamic in vitro PK/PD infection models commonly used in the development and optimisation of antimicrobial treatment regimens. It covers the commonly used dynamic in vitro infection models, including the one-compartment model, hollow fibre infection model, biofilm model, bladder infection model, and aspergillus infection model. It summarises the mathematical methods for the simulation of the pharmacokinetic profile of single or multiple antimicrobials when using the serial or parallel configurations of in vitro systems. Dynamic in vitro models offer reliable pharmacokinetic/pharmacodynamic data to help define the initial dosing regimens of new antimicrobials that can be developed further in clinical trials. They can also help in the optimisation of dosing regimens for existing antimicrobials, especially in the presence of emerging antimicrobial resistance. In conclusion, dynamic in vitro infection models replicate the interactions that occur between microorganisms and dynamic antimicrobial exposures in the human body to generate data highly predictive of the clinical efficacy. They are particularly useful for the development new treatment strategies against antimicrobial-resistant pathogens.

Daptomycin and ceftaroline combination for the treatment of persistent methicillin-resistant Staphylococcus aureus bloodstream infections: a case series and literature review

Methicillin-resistant Staphylococcus aureus (MRSA) is challenging to treat due to a lack of guidance for clinicians. The daptomycin and ceftaroline combination is promising for treating persistent MRSA bloodstream infections (BSIs). In this report, we present a case series of 7 patients who failed vancomycin and then were treated with daptomycin and ceftaroline for persistent MRSA BSIs. The median age (IQR) of the included patients was 59 (48-67), with 5 male and 2 female patients. Six patients (85.7%) had a clinical cure for their persistent BSIs. The median time (IQR) for sterilization of MRSA BSIs after initiation of daptomycin and ceftaroline combination was 2 days (1-3). Among the patients who had clinical cures, the median time for clinical cures (IQR) was 6 weeks (4.5-6 weeks). The combination of daptomycin and ceftaroline could be an excellent treatment option for persistent MRSA BSIs.

In vitro identification of underutilized β-lactam combinations against methicillin-resistant Staphylococcus aureus bacteremia isolates

Methicillin-resistant Staphylococcus aureus (MRSA) bacteremia is a serious clinical challenge with high mortality rates. Antibiotic combination therapy is currently used in cases of persistent infection; however, the limited development of new antibiotics will likely increase the need for combination therapy, and better methods are needed for identifying effective combinations for treating persistent bacteremia. To identify pairwise combinations with the most consistent potential for benefit compared to monotherapy with a primary anti-MRSA agent, we conducted a systematic study with an in vitro high-throughput methodology. We tested daptomycin and vancomycin each in combination with gentamicin, rifampicin, cefazolin, and oxacillin, and ceftaroline with daptomycin, gentamicin, and rifampicin. Combining cefazolin with daptomycin lowered the daptomycin concentration required to reach 95% growth inhibition (IC95) for all isolates tested and lowered daptomycin IC95 below the sensitivity breakpoint for five out of six isolates that had daptomycin minimum inhibitory concentrations at or above the sensitivity breakpoint. Similarly, vancomycin IC95s were decreased when vancomycin was combined with cefazolin for 86.7% of the isolates tested. This was a higher percentage than was achieved by adding any other secondary antibiotic to vancomycin. Adding rifampicin to daptomycin or vancomycin did not always reduce IC95s and failed to produce synergistic interaction in any of the isolates tested; the addition of rifampicin to ceftaroline was frequently synergistic and always lowered the amount of ceftaroline required to reach the IC95. These analyses rationalize further in vivo evaluation of three drug pairs for MRSA bacteremia: daptomycin+cefazolin, vancomycin+cefazolin, and ceftaroline+rifampicin.IMPORTANCEBloodstream infections caused by methicillin-resistant Staphylococcus aureus (MRSA) have a high mortality rate despite the availability of vancomycin, daptomycin, and newer antibiotics including ceftaroline. With the slow output of the antibiotic pipeline and the serious clinical challenge posed by persistent MRSA infections, better strategies for utilizing combination therapy are becoming increasingly necessary. We demonstrated the value of a systematic high-throughput approach, adapted from prior work testing antibiotic combinations against tuberculosis and other mycobacteria, by using this approach to test antibiotic pairs against a panel of MRSA isolates with diverse patterns of antibiotic susceptibility. We identified three antibiotic pairs-daptomycin+cefazolin, vancomycin+cefazolin, and ceftaroline+rifampicin-where the addition of the second antibiotic improved the potency of the first antibiotic across all or most isolates tested. Our results indicate that these pairs warrant further evaluation in the clinical setting.

Synergistic bactericidal effects of phage-enhanced antibiotic therapy against MRSA biofilms

Methicillin-resistant Staphylococcus aureus (MRSA) causes biofilm-related medical device infections. Phage-antibiotic combinations offer potential therapy due to proven in vitro antibiofilm efficacy. We evaluated phage-antibiotic synergy against biofilms using modified checkerboard and 24-h time-kill assays. Humanized-simulated daptomycin (DAP) (10, 8, and 6 mg/kg q24h) and ceftaroline (CPT) (600 mg q12h) were combined with Intesti13, Sb-1, and Romulus phages (tMOI 1, q12h). Assays were conducted in 168-h biofilm reactor models against DAP non-susceptible (DNS) vancomycin intermediate S. aureus (VISA) MRSA D712 and DAP-susceptible MRSA 8014. Synergistic activity and bactericidal activity were defined as ≥2log10 CFU/mL reduction from antibiotic-only regimens and ≥3log10 CFU/mL decrease from baseline at 24 h. Differences were analyzed by one-way analysis of variance with Tukey's post hoc test (P ≤ 0.05 is considered significant). Surviving bacteria were examined for antibiotic minimum biofilm inhibitory concentration (MBIC) changes and phage susceptibility. In 168-h biofilm models, humanized DAP 10 mg/kg + CPT, combined with a 2-phage cocktail (Intesti13 + Sb-1) against D712, and a 3-phage cocktail (Intesti13 + Sb-1 + Romulus) against 8014, demonstrated synergistic bactericidal activity. At 168 h, bacteria were minimally detectable [2log10 CFU/cm2 (-Δ4.23 and -Δ4.42 log10 CFU/cm2; both P < 0.001)]. Antibiotic MBIC remained unchanged compared to baseline across various time points. None of the tested bacteria at 168 h exhibited complete phage resistance. This study reveals bactericidal efficacy of DAP + CPT with 2-phage and 3-phage cocktails against DNS VISA and MRSA isolates (D712 and 8014) in biofilm models, maintaining susceptibility. Further research is needed for diverse strains and durations, aligning with infection care.

IMPORTANCE

The prevalence of biofilm-associated medical device infections caused by methicillin-resistant Staphylococcus aureus (MRSA) presents a pressing medical challenge. The latest research demonstrates the potential of phage-antibiotic combinations (PACs) as a promising solution, notably in vitro antibiofilm efficacy. By adopting modified checkerboard and 24-h time-kill assays, the study investigated the synergistic action of phages combined with humanized-simulated doses of daptomycin (DAP) and ceftaroline (CPT). The results were promising: a combination of DAP, CPT, and either a 2-phage or 3-phage cocktail effectively exhibited bactericidal activity against both DAP non-susceptible vancomycin intermediate S. aureus MRSA and DAP-susceptible MRSA strains within 168-h biofilm models. Moreover, post-treatment evaluations revealed no discernible rise in antibiotic resistance or complete phage resistance. This pioneering work suggests the potential of PACs in addressing MRSA biofilm infections, setting the stage for further expansive research tailored to diverse bacterial strains and treatment durations.

Antibiofilm approaches as a new paradigm for treating infections

The lack of effective antibiotics for drug-resistant infections has led the World Health Organization to declare antibiotic resistance a global priority. Most bacterial infections are caused by microbes growing in structured communities called biofilms. Bacteria growing in biofilms are less susceptible to antibiotics than their planktonic counterparts. Despite their significant clinical implications, bacterial biofilms have not received the attention they warrant, with no approved antibiotics specifically designed for their eradication. In this paper, we aim to shed light on recent advancements in antibiofilm strategies that offer compelling alternatives to traditional antibiotics. Additionally, we will briefly explore the potential synergy between computational approaches, including the emerging field of artificial intelligence, and the accelerated design and discovery of novel antibiofilm molecules in the years ahead.

Phage-antibiotic combinations against multidrug-resistant Pseudomonas aeruginosa in in vitro static and dynamic biofilm models

Biofilm-producing Pseudomonas aeruginosa infections pose a severe threat to public health and are responsible for high morbidity and mortality. Phage-antibiotic combinations (PACs) are a promising strategy for combatting multidrug-resistant (MDR), extensively drug-resistant (XDR), and difficult-to-treat P. aeruginosa infections. Ten MDR/XDR P. aeruginosa strains and five P. aeruginosa-specific phages were genetically characterized and evaluated based upon their antibiotic susceptibilities and phage sensitivities. Two selected strains, AR351 (XDR) and I0003-1 (MDR), were treated singly and in combination with either a broad-spectrum or narrow-spectrum phage, phage EM-T3762627-2_AH (EM), or 14207, respectively, and bactericidal antibiotics of five classes in biofilm time-kill analyses. Synergy and/or bactericidal activity was demonstrated with all PACs against one or both drug-resistant P. aeruginosa strains (average reduction: -Δ3.32 log10 CFU/cm2). Slightly improved ciprofloxacin susceptibility was observed in both strains after exposure to phages (EM and 14207) in combination with ciprofloxacin and colistin. Based on phage cocktail optimization with four phages (EM, 14207, E20050-C (EC), and 109), we identified several effective phage-antibiotic cocktails for further analysis in a 4-day pharmacokinetic/pharmacodynamic in vitro biofilm model. Three-phage cocktail, EM + EC + 109, in combination with ciprofloxacin demonstrated the greatest biofilm reduction against AR351 (-Δ4.70 log10 CFU/cm2 from baseline). Of remarkable interest, the addition of phage 109 prevented phage resistance development to EM and EC in the biofilm model. PACs can demonstrate synergy and offer enhanced eradication of biofilm against drug-resistant P. aeruginosa while preventing the emergence of resistance.

Current therapies and challenges for the treatment of Staphylococcus aureus biofilm-related infections

Staphylococcus aureus is a major cause of nosocomial and community-acquired infections and contributes to significant increase in morbidity and mortality especially when associated with medical devices and in biofilm form. Biofilm structure provides a pathway for the enrichment of resistant and persistent phenotypes of S. aureus leading to relapse and recurrence of infection. Minimal diffusion of antibiotics inside biofilm structure leads to heterogeneity and distinct physiological activity. Additionally, horizontal gene transfer between cells in proximity adds to the challenges associated with eradication of biofilms. This narrative review focuses on biofilm-associated infections caused by S. aureus, the impact of environmental conditions on biofilm formation, interactions inside biofilm communities, and the clinical challenges that they present. Conclusively, potential solutions, novel treatment strategies, combination therapies, and reported alternatives are discussed.

Evaluation of Omadacycline Alone and in Combination with Rifampin against Staphylococcus aureus and Staphylococcus epidermidis in an In Vitro Pharmacokinetic/Pharmacodynamic Biofilm Model

Biofilm-associated infections lead to substantial morbidity. Omadacycline (OMC) is a novel aminomethylcycline with potent in vitro activity against Staphylococcus aureus and Staphylococcus epidermidis, but data surrounding its use in biofilm-associated infections are lacking. We investigated the activity of OMC alone and in combination with rifampin (RIF) against 20 clinical strains of staphylococci in multiple in vitro biofilm analyses, including an in vitro pharmacokinetic/pharmacodynamic (PK/PD) CDC biofilm reactor (CBR) model (simulating human exposures). The observed MICs for OMC demonstrated potent activity against the evaluated strains (0.125 to 1 mg/L), with an increase of MICs generally observed in the presence of biofilm (0.25 to >64 mg/L). Furthermore, RIF was shown to reduce OMC biofilm MICs (bMICs) in 90% of strains, and OMC plus RIF combination in biofilm time-kill analyses (TKAs) exhibited synergistic activity in most of the strains. Within the PK/PD CBR model, OMC monotherapy primarily displayed bacteriostatic activity, while RIF monotherapy generally exhibited initial bacterial eradication, followed by rapid regrowth likely due to the emergence of RIF resistance (RIF bMIC, >64 mg/L). However, the combination of OMC plus RIF produced rapid and sustained bactericidal activity in nearly all the strains (3.76 to 4.03 log10 CFU/cm2 reductions from starting inoculum in strains in which bactericidal activity was reached). Furthermore, OMC was shown to prevent the emergence of RIF resistance. Our data provide preliminary evidence that OMC in combination with RIF could be a viable option for biofilm-associated infections with S. aureus and S. epidermidis. Further research involving OMC in biofilm-associated infections is warranted.

Safety and Efficacy of a Single Procedure of Extraction and Reimplantation of Infected Cardiovascular Implantable Electronic Device (CIED) in Comparison with Deferral Timing: An Observational Retrospective Multicentric Study

(1) Background: Infections are among the most frequent and life-threatening complications of cardiovascular implantable electronic device (CIED) implantation. The aim of this study is to compare the outcome and safety of a single-procedure device extraction and contralateral implantation versus the standard-of-care (SoC) two-stage replacement for infected CIEDs. (2) Methods: We retrospectively included 66 patients with CIED infections who were treated at two Italian hospitals. Of the 66 patients enrolled in the study, 27 underwent a single procedure, whereas 39 received SoC treatment. All patients were followed up for 12 months after the procedure. (3) Results: Considering those lost to follow-up, there were no differences in the mortality rates between the two cohorts, with survival rates of 81.5% in the single-procedure group and 84.6% in the SoC group (p = 0.075). (4) Conclusions: Single-procedure reimplantation associated with an active antibiofilm therapy may be a feasible and effective therapeutic option in CIED-dependent and frail patients. Further studies are warranted to define the best treatment regimen and strategies to select patients suitable for the single-procedure reimplantation.

Cas12a/Guide RNA-Based Platforms for Rapidly and Accurately Identifying Staphylococcus aureus and Methicillin-Resistant S. aureus

In order to ensure the prevention and control of methicillin-resistant Staphylococcus aureus (MRSA) infection, rapid and accurate detection of pathogens and their resistance phenotypes is a must. Therefore, this study aimed to develop a fast and precise nucleic acid detection platform for identifying S. aureus and MRSA. We initially constructed a CRISPR-Cas12a detection system by designing single guide RNAs (sgRNAs) specifically targeting the thermonuclease (nuc) and mecA genes. To increase the sensitivity of the CRISPR-Cas12a system, we incorporated PCR, loop-mediated isothermal amplification (LAMP), and recombinase polymerase amplification (RPA). Subsequently, we compared the sensitivity and specificity of the three amplification methods paired with the CRISPR-Cas12a system. Finally, the clinical performance of the methods was tested by analyzing the fluorescence readout of 111 clinical isolates. In order to visualize the results, lateral-flow test strip technology, which enables point-of-care testing, was also utilized. After comparing the sensitivity and specificity of three different methods, we determined that the nuc-LAMP-Cas12a and mecA-LAMP-Cas12a methods were the optimal detection methods. The nuc-LAMP-Cas12a platform showed a limit of detection (LOD) of 10 aM (~6 copies μL-1), while the mecA-LAMP-Cas12a platform demonstrated a LOD of 1 aM (~1 copy μL-1). The LOD of both platforms reached 4 × 103 fg/μL of genomic DNA. Critical evaluation of their efficiencies on 111 clinical bacterial isolates showed that they were 100% specific and 100% sensitive with both the fluorescence readout and the lateral-flow readout. Total detection time for the present assay was approximately 80 min (based on fluorescence readout) or 85 min (based on strip readout). These results indicated that the nuc-LAMP-Cas12a and mecA-LAMP-Cas12a platforms are promising tools for the rapid and accurate identification of S. aureus and MRSA. IMPORTANCE The spread of methicillin-resistant Staphylococcus aureus (MRSA) poses a major threat to global health. Isothermal amplification combined with the trans-cleavage activity of Cas12a has been exploited to generate diagnostic platforms for pathogen detection. Here, we describe the design and clinical evaluation of two highly sensitive and specific platforms, nuc-LAMP-Cas12a and mecA-LAMP-Cas12a, for the detection of S. aureus and MRSA in 111 clinical bacterial isolates. With a limit of detection (LOD) of 4 × 103 fg/μL of genomic DNA and a turnaround time of 80 to 85 min, the present assay was 100% specific and 100% sensitive using either fluorescence or the lateral-flow readout. The present assay promises clinical application for rapid and accurate identification of S. aureus and MRSA in limited-resource settings or at the point of care. Beyond S. aureus and MRSA, similar CRISPR diagnostic platforms will find widespread use in the detection of various infectious diseases, malignancies, pharmacogenetics, food contamination, and gene mutations.

Daptomycin synergistic properties from in vitro and in vivo studies: a systematic review

INTRODUCTION

Daptomycin is a bactericidal lipopeptide antibiotic approved for the treatment of systemic infections (i.e. skin and soft tissue infections, bloodstream infections, infective endocarditis) caused by Gram-positive cocci. It is often prescribed in association with a partner drug to increase its bactericidal effect and to prevent the emergence of resistant strains during treatment; however, its synergistic properties are still under evaluation.

METHODS

We performed a systematic review to offer clinicians an updated overview of daptomycin synergistic properties from in vitro and in vivo studies. Moreover, we reported all in vitro and in vivo data evaluating daptomycin in combination with other antibiotic agents, subdivided by antibiotic classes, and a summary graph presenting the most favourable combinations at a glance.

RESULTS

A total of 92 studies and 1087 isolates (723 Staphylococcus aureus, 68 Staphylococcus epidermidis, 179 Enterococcus faecium, 105 Enterococcus faecalis, 12 Enterococcus durans) were included. Synergism accounted for 30.9% of total interactions, while indifferent effect was the most frequently observed interaction (41.9%). Antagonistic effect accounted for 0.7% of total interactions. The highest synergistic rates against S. aureus were observed with daptomycin in combination with fosfomycin (55.6%). For S. epidermidis and Enterococcus spp., the most effective combinations were daptomycin plus ceftobiprole (50%) and daptomycin plus fosfomycin (63.6%) or rifampicin (62.8%), respectively.

FUTURE PERSPECTIVES

We believe this systematic review could be useful for the future updates of guidelines on systemic infections where daptomycin plays a key role.

Synergistic effect of antibiotic combinations on Staphylococcus aureus biofilms and their persister cell populations

Treatment of staphylococcal infections is difficult due to multidrug resistance with their persister forms posing an added threat of recalcitrant infections. Antibiotic combinations are widely studied as an alternative strategy to combat them; therefore, they merit further investigation into their effect on the number of persister cells. In the present study, the fractional inhibitory concentrations of antibiotic combinations ciprofloxacin-daptomycin, ciprofloxacin-vancomycin, daptomycin-tobramycin, and tobramycin-vancomycin (checkerboard assay) were determined against two previously studied clinical (S48 and J6) and one standard (NCIM 5021) isolate of Staphylococcus aureus. They showed synergistic effects with a 2 to 256-fold reduction in MICs. All combinations also resulted in inhibition and disruption of biofilms in a concentration-dependent manner. All antibiotic combinations, except ciprofloxacin-daptomycin, showed total biofilm inhibition at 100X MICs. Similarly, antibiotic combination at 100X MIC showed 77–97% disruption of preformed biofilms. Time-kill assays performed at a 100X MIC combination against stationary-phase cells showed a two to six log₁₀ reduction in CFU followed by a plateau indicating the presence of persisters. Significant differences were observed in persister cell fraction remaining after treatment with antibiotic combinations compared to monotherapies (p < 0.05) and therefore merit further investigation in clinical use for treatment against persisters.

pH variation in medical implant biofilms: Causes, measurements, and its implications for antibiotic resistance

The advent of implanted medical devices has greatly improved the quality of life and increased longevity. However, infection remains a significant risk because bacteria can colonize device surfaces and form biofilms that are resistant to antibiotics and the host's immune system. Several factors contribute to this resistance, including heterogeneous biochemical and pH microenvironments that can affect bacterial growth and interfere with antibiotic biochemistry; dormant regions in the biofilm with low oxygen, pH, and metabolites; slow bacterial growth and division; and poor antibody penetration through the biofilm, which may also be regions with poor acid product clearance. Measuring pH in biofilms is thus key to understanding their biochemistry and offers potential routes to detect and treat latent infections. This review covers the causes of biofilm pH changes and simulations, general findings of metabolite-dependent pH gradients, methods for measuring pH in biofilms, effects of pH on biofilms, and pH-targeted antimicrobial-based approaches.

Biofilm and Planktonic Antibiotic Resistance in Patients With Acute Exacerbation of Chronic Rhinosinusitis

INTRODUCTION

The recalcitrant nature of patients with acute exacerbation of chronic rhinosinusitis (AECRS) potentially involves persisting colonization of the sinonasal mucosa by bacterial biofilms. Biofilms are known to be highly resistant to antibiotics, which may trigger or maintain chronic inflammation in the sinonasal mucosa. However, little is known about the relationship between the minimum inhibitory concentration (MIC) and antibiofilm concentrations of bacteria obtained from AECRS patients.

MATERIAL AND METHODS

Thirty bacterial strains from 25 patients with AECRS were identified and underwent MIC determination (VITEK^® 2). The planktonic isolates were submitted to an in vitro formation of biofilms (Modified Calgary Biofilm Device) and determination of minimum biofilm inhibitory concentration (MBIC) and minimum biofilm eradication concentration (MBEC) for amoxicillin, amoxicillin/clavulanic acid, clarithromycin, and levofloxacin. MIC of the planktonic forms was compared with MBIC and MBEC levels, according to the breakpoints established by the Clinical Laboratory Standards Institute guidelines.

RESULTS

The main bacteria retrieved was S. aureus (60%), followed by other Gram-positive and Gram-negative bacteria in lower frequencies. 76.7% of strains formed biofilm in vitro (n=23/30). The planktonic isolates presented high rates of resistance for amoxicillin (82.6%) and clarithromycin (39.1%), and lower rates for amoxicillin/clavulanic acid (17.4%). The biofilm-forming bacteria counterparts presented higher levels of MBIC and MBEC compared to the MIC levels for amoxicillin, amoxicillin/clavulanic acid, and clarithromycin. Levofloxacin was highly effective against both planktonic and biofilm forms. Planktonic resistant forms were associated with levels of antibiofilm concentrations (MBIC and MBEC).

CONCLUSIONS

Biofilm-forming bacteria from AECRS patients are prevalent, and biofilm forms are highly resistant to antibiotics compared to their planktonic counterparts. Antibiotic resistance observed in planktonic forms is a good indicator of biofilm resistance, although near 20% of susceptible planktonic bacteria can produce antibiotic tolerant biofilms.

Orthopaedic Implant-Associated Staphylococcal Infections: A Critical Reappraisal of Unmet Clinical Needs Associated with the Implementation of the Best Antibiotic Choice

Infections associated with orthopaedic implants represent a major health concern characterized by a remarkable incidence of morbidity and mortality. The wide variety of clinical scenarios encountered in the heterogeneous world of infections associated with orthopaedic implants makes the implementation of an optimal and standardized antimicrobial treatment challenging. Antibiotic bone penetration, anti-biofilm activity, long-term safety, and drug choice/dosage regimens favouring outpatient management (i.e., long-acting or oral agents) play a major role in regards to the chronic evolution of these infections. The aim of this multidisciplinary opinion article is to summarize evidence supporting the use of the different anti-staphylococcal agents in terms of microbiological and pharmacological optimization according to bone penetration, anti-biofilm activity, long-term safety, and feasibility for outpatient regimens, and to provide a useful guide for clinicians in the management of patients affected by staphylococcal infections associated with orthopaedic implants Novel long-acting lipoglycopeptides, and particularly dalbavancin, alone or in combination with rifampicin, could represent the best antibiotic choice according to real-world evidence and pharmacokinetic/pharmacodynamic properties. The implementation of a multidisciplinary taskforce and close cooperation between microbiologists and clinicians is crucial for providing the best care in this scenario.

Bacterial biofilm infections, their resistance to antibiotics therapy and current treatment strategies

Nearly 80% of human chronic infections are caused due to bacterial biofilm formation. This is the most leading cause for failure of medical implants resulting in high morbidity and mortality. In addition, biofilms are also known to cause serious problems in food industry. Biofilm impart enhanced antibiotic resistance and become recalcitrant to host immune responses leading to persistent and recurrent infections. It makes the clinical treatment for biofilm infections very difficult. Reduced penetration of antibiotic molecules through EPS, mutation of the target site, accumulation of antibiotic degrading enzymes, enhanced expression of efflux pump genes are the probable causes for antibiotics resistance. Accordingly, strategies like administration of topical antibiotics and combined therapy of antibiotics with antimicrobial peptides are considered for alternate options to overcome the antibiotics resistance. A number of other remediation strategies for both biofilm inhibition and dispersion of established biofilm have been developed. The metallic nanoparticles and their oxides have recently gained a tremendous thrust as antibiofilm therapy for their unique features. This present comprehensive review gives the understanding of antibiotic resistance mechanisms of biofilm and provides an overview of various currently available biofilm remediation strategies, focusing primarily on the applications of metallic nanoparticles and their oxides.

Biofilm Formation in Methicillin-Resistant Staphylococcus aureus Isolated in Cystic Fibrosis Patients Is Strain-Dependent and Differentially Influenced by Antibiotics

Cystic fibrosis (CF) is a genetic disease with lung abnormalities making patients particularly predisposed to pulmonary infections. Staphylococcus aureus is the most frequently identified pathogen, and multidrug-resistant strains (MRSA, methicillin-resistant S. aureus) have been associated with more severe lung dysfunction leading to eradication recommendations. Diverse bacterial traits and adaptive skills, including biofilm formation, may, however, make antimicrobial therapy challenging. In this context, we compared the ability of a collection of genotyped MRSA isolates from CF patients to form biofilm with and without antibiotics (ceftaroline, ceftobiprole, linezolid, trimethoprim, and rifampicin). Our study used standardized approaches not previously applied to CF MRSA, the BioFilm Ring test® (BRT®), the Antibiofilmogram®, and the BioFlux™ 200 system which were adapted for use with the artificial sputum medium (ASM) mimicking conditions more relevant to the CF lung. We included 63 strains of 10 multilocus sequence types (STs) isolated from 35 CF patients, 16 of whom had chronic colonization. The BRT® showed that 27% of the strains isolated in 37% of the patients were strong biofilm producers. The Antibiofilmogram® performed on these strains showed that broad-spectrum cephalosporins had the lowest minimum biofilm inhibitory concentrations (bMIC) on a majority of strains. A focus on four chronically colonized patients with inclusion of successively isolated strains showed that ceftaroline, ceftobiprole, and/or linezolid bMICs may remain below the resistance thresholds over time. Studying the dynamics of biofilm formation by strains isolated 3years apart in one of these patients using BioFlux™ 200 showed that inhibition of biofilm formation was observed for up to 36h of exposure to bMIC and ceftaroline and ceftobiprole had a significantly greater effect than linezolid. This study has brought new insights into the behavior of CF MRSA which has been little studied for its ability to form biofilm. Biofilm formation is a common characteristic of prevalent MRSA clones in CF. Early biofilm formation was strain-dependent, even within a sample, and not only observed during chronic colonization. Ceftaroline and ceftobiprole showed a remarkable activity with a long-lasting inhibitory effect on biofilm formation and a conserved activity on certain strains adapted to the CF lung environment after years of colonization.

Biofilm Time-Kill Curves to Assess the Bactericidal Activity of Daptomycin Combinations against Biofilm-Producing Vancomycin-Resistant Enterococcus faecium and faecalis

INTRODUCTION

E. faecium and E. faecalis are responsible for 13.9% of hospital-acquired infections with frequent resistance to vancomycin (82.6% of E. faecium, 9.5% of E. faecalis). Medical device infections secondary to enterococci often require combination therapy due to impaired activity against biofilm embedded cells. In vitro data demonstrate synergistic activity of daptomycin combinations. Using a novel, biofilm time-kill approach, we evaluated whether daptomycin combinations maintained synergy against biofilm-producing E. faecium and E. faecalis.

METHODS

Broth microdilution (BMD) and biofilm MIC (bMIC) values for daptomycin, ampicillin, ceftriaxone, fosfomycin, and rifampin were determined against biofilm-producing E. faecium and E. faecalis. Daptomycin combination bMIC values were determined in the presence of biologic concentrations of other antimicrobials. Synergy was evaluated against two E. faecalis (R6981, R7808) and two E. faecium (5938 and 8019) using a previously described biofilm time-kill method. Synergy was defined as ≥2 log10 CFU/cm2 reduction over the most active agent alone. Bactericidal activity was defined as ≥3 log10 CFU/cm2 reduction.

RESULTS

Daptomycin bMICs were 2-8-fold higher than BMD. In the presence of other antimicrobials, daptomycin bMICs were reduced ≥ two-fold in dilutions. Ceftriaxone and ampicillin demonstrated the most potent combinations with daptomycin, yielding synergy against three of four strains. Daptomycin plus rifampin was synergistic against E. faecium 5938 and E. faecalis 6981 and produced bactericidal kill. The combination of daptomycin plus fosfomycin displayed synergy solely against E. faecalis 6981.

CONCLUSIONS

Daptomycin combinations with beta-lactams demonstrated promising synergistic activity against both E. faecium and E. faecalis. While daptomycin plus rifampin yielded bactericidal results, the effect was not seen across all organisms. These combinations warrant further evaluation to determine the optimal dose and response.

Pulse Dosing of Antibiotic Enhances Killing of a Staphylococcus aureus Biofilm

Biofilms are highly tolerant to antibiotics and underlie the recalcitrance of many chronic infections. We demonstrate that mature Staphylococcus aureus biofilms can be substantially sensitized to the treatment by pulse dosing of an antibiotic – in this case, oxacillin. Pulse (periodic) dosing was compared to continuous application of antibiotic and was studied in a novel in vitro flow system which allowed for robust biofilm growth and tractable pharmacokinetics of dosing regimens. Our results highlight that a subpopulation of the biofilm survives antibiotic without becoming resistant, a population we refer to as persister bacteria. When oxacillin was continuously present the persister level did not decline, but, importantly, providing correctly timed periodic breaks decreased the surviving population. We found that the length of the periodic break impacted efficacy, and there was an optimal length that sensitized the biofilm to repeat treatment without allowing resistance expansion. Periodic dosing provides a potential simple solution to a complicated problem.

Benzyl isocyanate isolated from the leaves of Psidium guajava inhibits Staphylococcus aureus biofilm formation

Benzyl isocyanate (BIC), from methanol extract of Psidium guajava leaves, exhibited substantial anti-biofilm activities against Staphylococcus aureus, the common bacterial pathogen in nosocomial infections. Major components of the extract included eugenol, BIC, phenyl-2-methoxy-4-(1-propenyl)-acetate and 2,5-pyrrolidinedione,1-penta-3-4-dienyl, analyzed by GC-MS and HPLC studies. BIC exhibited substantial anti-biofilm activitiy against S. aureus, established by assaying biofilm formation, biofilm metabolic activity, bacterial adherence to hydrocarbons, exopolysaccharide formation, and optical and scanning electron microscopic studies. BIC significantly downregulated the important biofilm markers of S. aureus, viz., icaAD, sarA and agr, observed by quantitative real time polymerase chain reaction analysis. Molecular docking studies revealed thermodynamically favorable interaction of BIC with IcaA, SarA and Agr, having Gibbs energy values of -8.45, -9.09 and -10.29 kcal mol^-1, respectively. BIC after binding to IcaR, the repressor of IcaA, influences its binding to target DNA site (E_shape, -157.27 kcal mol^-1). The results are considered to demonstrate anti-biofilm potential of BIC against bacterial infections.

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.

The Emerging Role of β-Lactams in the Treatment of Methicillin-Resistant Staphylococcus aureus Bloodstream Infections

Methicillin-resistant Staphylococcus aureus (MRSA) bloodstream infections (BSI) are associated with substantial morbidity and mortality. Monotherapy with first-line antimicrobials such as vancomycin (VAN; glycopeptide) and daptomycin (DAP; lipopeptide) are inadequate in some cases due to reduced antibiotic susceptibilities or therapeutic failure. In recent years, β-lactam antibiotics have emerged as a potential option for combination therapy with VAN and DAP that may meet an unmet therapeutic need for MRSA BSI. Ceftaroline (CPT), the only commercially available β-lactam in the United States with intrinsic in vitro activity against MRSA, has been increasingly studied in the setting of VAN and DAP failures. Novel combinations of first-line agents (VAN and DAP) with β-lactams have been the subject of many recent investigations due to in vitro findings such as the "seesaw effect," where β-lactam susceptibility may be improved in the presence of decreased glycopeptide and lipopeptide susceptibility. The combination of CPT and DAP, in particular, has become the focus of many scientific evaluations, due to intrinsic anti-MRSA activities and potent in vitro synergistic activity against various MRSA strains. This article reviews the available literature describing these innovative therapeutic approaches for MRSA BSI, focusing on preclinical and clinical studies, and evaluates the potential benefits and limitations of each strategy.

Impact of Daptomycin Dose Exposure Alone or in Combination with β-Lactams or Rifampin against Vancomycin-Resistant Enterococci in an In Vitro Biofilm Model

Enterococcus faecium strains are commonly resistant to vancomycin and β-lactams. In addition, E. faecium often causes biofilm-associated infections and these infections are difficult to treat. In this context, we investigated the activity of dosing regimens using daptomycin (DAP) (8, 10, 12, and 14 mg/kg of body weight/day) alone and in combination with ceftaroline (CPT), ampicillin (AMP), ertapenem (ERT), and rifampin (RIF) against 2 clinical strains of biofilm-producing vancomycin-resistant Enterococcus faecium (VREfm), namely, strains S447 and HOU503, in an in vitro biofilm model. HOU503 harbors common LiaS and LiaR substitutions, whereas S447 lacks mutations associated with the LiaFSR pathway. MIC results demonstrated that both strains were susceptible to DAP and resistant to CPT, AMP, ERT, and RIF. The 168-h pharmacokinetic/pharmacodynamic (PK/PD) CDC biofilm reactor models (simulating human antibiotic exposures) were used with titanium and polyurethane coupons to evaluate the efficacy of antibiotic combinations. DAP 12 and 14 achieved bactericidal activity against S447 but lacked such effect against HOU503. Addition of ERT and RIF enhanced DAP activity, allowing DAP 8 and 10 plus ERT or RIF to produce bactericidal activity against both strains at 168 h. While DAP 8 and 10 plus CPT improved killing, they did not reach bactericidal reduction against S447. Combination of AMP, CPT, ERT, or RIF resulted in enhanced and bactericidal activity for DAP against HOU503 at 168 h. Our data provide further support for the use of combinations of DAP with AMP, ERT, CPT, and RIF in infections caused by biofilm producing VREfm. Further research involving DAP combinations against biofilm-producing enterococci is warranted.

Multicenter Cohort of Patients With Methicillin-Resistant Staphylococcus aureus Bacteremia Receiving Daptomycin Plus Ceftaroline Compared With Other MRSA Treatments

Background

Daptomycin and ceftaroline (DAP-CPT) have been used for persistent methicillin-resistant Staphylococcus aureus bacteremia (MRSAB), but have rarely been compared with other therapies. This study provides an exploratory analysis of patients placed on DAP-CPT vs standard of care (SOC) for MRSAB.

Methods

This is a retrospective, matched cohort study MRSAB patients at 4 hospitals in the United States. Patients receiving DAP-CPT for ≥72 hours at any point in therapy were matched 2:1 when possible, 1:1 otherwise, to SOC, first by infection source, then age and renal function. SOC was empiric treatment with vancomycin or daptomycin and any subsequent combination antibiotic(s), except for DAP-CPT.

Results

Fifty-eight patients received DAP-CPT with 113 matched SOC. Ninety-six percent of SOC received vancomycin, and 56% (63/113) escalated therapy at least once in the treatment course. Twenty-four patients received DAP-CPT within 72 hours of index culture; 2 (8.3%) died within 30 days vs 14.2% (16/113) with SOC (P > .05). Subgroup analysis identified numerically lower mortality in DAP-CPT patients with a Charlson comorbidity index ≥3, endovascular source, and receipt of DAP-CPT within 72 hours of index culture. The median MRSAB duration was 9.3 vs 4.8 days for DAP-CPT and SOC, respectively. DAP-CPT was initiated on day 6 on average; after receipt of DAP-CPT, MRSAB duration was 3.3 days.

Conclusions

DAP-CPT treatment is often delayed in MRSAB. Combination therapy may be more beneficial if initiated earlier, particularly in patients at higher risk for mortality. Blinded, randomized, prospective studies are needed to eliminate selection bias inherent in retrospective analyses when examining DAP-CPT vs SOC.

Phenotypic and Genotypic Characteristics of Methicillin-Resistant Staphylococcus aureus (MRSA) Related to Persistent Endovascular Infection

Persistent methicillin-resistant Staphylococcus aureus (MRSA) bacteremia (PB) represents an important subset of S. aureus infection and correlates with poor clinical outcomes. MRSA isolates from patients with PB differ significantly from those of resolving bacteremia (RB) with regard to several in vitro phenotypic and genotypic profiles. For instance, PB strains exhibit less susceptibility to cationic host defense peptides and vancomycin (VAN) killing under in vivo-like conditions, greater damage to endothelial cells, thicker biofilm formation, altered growth rates, early activation of many global virulence regulons (e.g., sigB, sarA, sae and agr) and higher expression of purine biosynthesis genes (e.g., purF) than RB strains. Importantly, PB strains are significantly more resistant to VAN treatment in experimental infective endocarditis as compared to RB strains, despite similar VAN minimum inhibitory concentrations (MICs) in vitro. Here, we review relevant phenotypic and genotypic characteristics related to the PB outcome. These and future insights may improve our understanding of the specific mechanism(s) contributing to the PB outcome, and aid in the development of novel therapeutic and preventative measures against this life-threatening infection.

Evaluation of Telavancin Alone and Combined with Ceftaroline or Rifampin against Methicillin-Resistant Staphylococcus aureus in an In Vitro Biofilm Model

Infections caused by biofilm-producing methicillin-resistant Staphylococcus aureus (MRSA) bacteria are challenging due to increasing antibiotic resistance. Synergistic activities of lipopeptides and lipoglycopeptides with β-lactams have been demonstrated for MRSA, but little is known about biofilm-embedded organisms. Our objective was to evaluate two telavancin (TLV) dosage regimens (7.5 mg/kg of body weight and 10 mg/kg every 24 h [q24h]) alone and in combination with ceftaroline (CPT) (600 mg every 8 h [q8h]) or rifampin (RIF) (450 mg every 12 h [q12h]) against two biofilm-producing MRSA strains (494 and N315). Pharmacokinetic/pharmacodynamic CDC biofilm reactor models with polyurethane coupons were used to evaluate the efficacies of the antibiotic combinations over 72 h. Overall, there were no significant differences observed between the two TLV dosing regimens either alone or in combination with RIF or CPT against these strains. Both TLV dosing regimens and CPT alone demonstrated killing but did not reach bactericidal reduction at 72 h. However, both TLV regimens in combination with RIF demonstrated enhanced activity against both strains, with a rapid decrease in CFU/ml at 4 h that was bactericidal and maintained over the 72-h experiment (-Δ3.75 log10 CFU/ml from baseline; P < 0.0001). Of interest, no enhanced activity was observed for TLV combined with CPT. No development of resistance was observed in any of the combination models. However, resistance to RIF developed as early as 24 h, with MIC values exceeding 32 mg/liter. Our results show that TLV plus RIF displayed therapeutic improvement against biofilm-producing MRSA. These results suggest that TLV at 7.5 and 10 mg/kg q24h are equally effective in eradicating biofilm-associated MRSA strains in vitro.

Can β-Lactam Antibiotics Be Resurrected to Combat MRSA?

The use of β-lactam antibiotics to treat infections caused by Staphylococcus aureus has been severely compromised by the acquisition by horizontal gene transfer of a gene that encodes the β-lactam-insensitive penicillin-binding protein PBP2a. This allows methicillin-resistant S. aureus (MRSA) to proliferate in the presence of β-lactam antibiotics. Paradoxically the dependence on PBP2a for the essential transpeptidase activity in cell wall peptidoglycan biosynthesis is the 'Achilles heel' of MRSA. Compounds that disrupt the divisome, wall teichoic acid, and functional membrane microdomains act synergistically with β-lactams against MRSA. These include drugs such as statins that are widely used in human medicine. The antibiotics vancomycin and daptomycin are also synergistic with β-lactams, and combinations have been employed to treat persistent MRSA infections. An additional benefit of exposing MRSA to β-lactams could be a reduction in virulence mediated by interfering with the global regulator Agr. The mechanistic basis of synergy is discussed, and the possibility that β-lactams can be resurrected to combat MRSA infections is explored.

Treatment strategies for persistent methicillin-resistant Staphylococcus aureus bacteraemia

WHAT IS KNOWN AND OBJECTIVE

Treatment of methicillin-resistant Staphylococcus aureus (MRSA) bacteraemia is a long-standing challenge to health care, often complicated by metastatic infections, treatment failure and mortality. When MRSA bacteraemia persists despite adequate initial treatment, current Infectious Diseases Society of America guidelines recommend evaluation and removal of possible sources of infection. In addition, a change in therapy may be considered. The objective of this review was to explore the therapeutic options for the treatment of persistent MRSA bacteraemia.

METHODS

A literature search of PubMed, MEDLINE and Google Scholar was performed using the following search terms: [methicillin-resistant Staphylococcus aureus OR MRSA] AND [bacteraemia OR bloodstream infection] AND [persistent OR persistence OR refractory OR treatment failure OR salvage] AND treatment. We evaluated relevant, adult, English-language, peer-reviewed studies published between 1985 and May 2018. In vitro and animal studies were considered as supportive of in vivo data.

RESULTS AND DISCUSSION

Randomized, controlled trials are lacking. However, case series and case reports support multiple treatment options including high-dose daptomycin in combination with an antistaphylococcal β-lactam, ceftaroline, trimethoprim-sulfamethoxazole (TMP-SMX) or fosfomycin; ceftaroline alone or in combination with vancomycin or TMP-SMX; linezolid alone or in combination with a carbapenem, or telavancin.

WHAT IS NEW AND CONCLUSION

Given the heterogeneity of the data, a preferred regimen has not emerged. Prescribers must take into consideration recent exposure, source control, and available synergy and clinical data. Further comparative trials are needed to establish a preferred regimen and the creation of a universal treatment algorithm.

Combination of Tedizolid and Daptomycin against Methicillin-Resistant Staphylococcus aureus in an In Vitro Model of Simulated Endocardial Vegetations

Methicillin-resistant Staphylococcus aureus (MRSA) is a major pathogen responsible for health care-associated infections, and treatment options are limited. Tedizolid (TZD) is a novel oxazolidinone antibiotic with activity against MRSA. Previously, daptomycin (DAP) has demonstrated synergy with other antibiotics against MRSA. We sought to determine the efficacy of the combination of TZD and DAP against MRSA in an in vitro model of simulated endocardial vegetations (SEVs). TZD simulations of 200 mg once daily and DAP simulations of 6 mg/kg of body weight and 10 mg/kg once daily were tested alone and in the combinations TZD plus DAP at 6 mg/kg or DAP at 10 mg/kg against two clinical strains of MRSA, 494 and 67. These regimens were tested in SEV models over 8 days to determine the antibacterial activity of the regimens and whether synergy or antagonism might be present between the agents. Against both strains 494 and 67 and at both DAP dose regimens, the combination of TZD and DAP was antagonistic at 192 h. In all cases, DAP alone was statistically superior to DAP plus TZD. When the combination was stopped after 96 h, transitioning to DAP at 6 mg/kg or DAP at 10 mg/kg alone resulted in better antibacterial activity than either of the TZD-plus-DAP combinations, further demonstrating antagonistic effects. Against MRSA, we demonstrated that TZD and DAP have antagonistic activity that hinders their overall antimicrobial efficacy. The exact nature of this antagonistic relationship is still undetermined, but its presence warrants further study of the potentially harmful grouping of the two antibiotics in clinical use.

Phenylthiazoles with tert-Butyl side chain: Metabolically stable with anti-biofilm activity

A new series of phenylthiazoles with t-butyl lipophilic component was synthesized and their antibacterial activity against a panel of multidrug-resistant bacterial pathogens was evaluated. Five compounds demonstrated promising antibacterial activity against methicillin-resistant staphylococcal strains and several vancomycin-resistant staphylococcal and enterococcal species. Additionally, three derivatives 19, 23 and 26 exhibited rapid bactericidal activity, and remarkable ability to disrupt mature biofilm produced by MRSA USA300. More importantly, a resistant mutant to 19 couldn't be isolated after subjecting MRSA to sub-lethal doses for 14 days. Lastly, this new series of phenylthiazoles possesses an advantageous attribute over the first-generation compounds in their stability to hepatic metabolism, with a biological half-life of more than 9 h.

The current role of glycopeptides in the treatment of methicillin-resistant Staphylococcus aureus (MRSA) infections in not neutropenic adults: the viewpoint of a group of Italian experts

Staphylococcus aureus is still an important problem in clinical and therapeutic area, worldwide. In Italy, in recent years, methicillin resistance remained stable, yet considerably high, the percentage of strains of MRSA being around 40%. It was deemed interesting and timely to carry out a consensus conference using the RAND/UCLA method to collect the opinion of a group of experts in infectious diseases on the role of glycopeptides in the management of MRSA infections within several clinical scenarios and namely in pneumonia, bacteremia and endocarditis, joint replacement infections, skin and soft tissue infections, diabetic foot, abdominal infections and central nervous system infections. The scenarios proposed by the Scientific Committee have been validated by a group of experts in infectious diseases and then voted in three meetings of infectious disease specialists. The results obtained on each individual condition were analyzed and therapeutic recommendations on each of these were released.

Update on the Role of Infection and Biofilms in Wound Healing: Pathophysiology and Treatment

BACKGROUND

Chronic wounds, and among these infected diabetic foot ulcers, are a worldwide problem. The poor treatment outcomes result in high healthcare costs, amputations, a decreased quality of life, and an increased mortality. These outcomes are influenced by several factors, including biofilm formation. A biofilm consists of pathogenic bacteria that are encased in an exopolysaccharide layer and communicate through secretion of signaling molecules. Bacteria that live in a biofilm are refractory to host responses and treatment.

METHODS

We performed a nonsystematic review of the currently published to-date medical biofilm literature. The review summarizes the evidence of biofilm in chronic wounds, the role of biofilm in wound healing, detection of biofilm, and available antibiofilm treatments. Articles containing basic science and clinical research, as well as systematic reviews, are described and evaluated. The articles have variable levels of evidence. All articles have been peer reviewed and meet the standards of evidence-based medicine.

RESULTS

Both animal and human studies have identified biofilm in chronic wounds and have suggested that healing might be influenced by its presence. A promising development in biofilm detection is rapid molecular diagnostics combined with direct microscopy. This technique, rather than classic culture, might support individualized treatment in the near future. A wide range of treatments for chronic wounds also influence biofilm formation. Several agents that specifically target biofilm are currently being researched.

CONCLUSIONS

Biofilm formation has a substantial role in chronic wounds. Several diagnostic and therapeutic methods against biofilm are currently being developed.

Antibiotic treatment of biofilm infections

Bacterial biofilms are associated with a wide range of infections, from those related to exogenous devices, such as catheters or prosthetic joints, to chronic tissue infections such as those occurring in the lungs of cystic fibrosis patients. Biofilms are recalcitrant to antibiotic treatment due to multiple tolerance mechanisms (phenotypic resistance). This causes persistence of biofilm infections in spite of antibiotic exposure which predisposes to antibiotic resistance development (genetic resistance). Understanding the interplay between phenotypic and genetic resistance mechanisms acting on biofilms, as well as appreciating the diversity of environmental conditions of biofilm infections which influence the effect of antibiotics are required in order to optimize the antibiotic treatment of biofilm infections. Here, we review the current knowledge on phenotypic and genetic resistance in biofilms and describe the potential strategies for the antibiotic treatment of biofilm infections. Of note is the optimization of PK/PD parameters in biofilms, high-dose topical treatments, combined and sequential/alternate therapies or the use antibiotic adjuvants.

Ceftaroline for the treatment of methicillin-resistant Staphylococcus aureus bacteremia

PURPOSE

The utility of ceftaroline for the treatment of methicillin-resistant Staphylococcus aureus bacteremia (MRSAB) is reviewed.

SUMMARY

Ceftaroline was originally approved for the treatment of community-acquired bacterial pneumonia (CABP) and acute bacterial skin and skin structure infections (ABSSSIs) but recently received an additional approval for the treatment of S. aureus bacteremia (SAB) associated with ABSSSIs. Ceftaroline has demonstrated efficacy for the treatment of MRSAB, including isolates with elevated minimum inhibitory concentrations to conventional therapy when used alone or in combination with other agents. In multiple studies, ceftaroline has displayed rapid bloodstream eradication, even in the setting of refractory MRSAB or infective endocarditis. The clinical resolution of MRSAB or SAB in patients who received ceftaroline ranged from 31.0% to 83.3%; studies used varying definitions for clinical resolution and included differing proportions of patients with endocarditis. The use of ceftaroline in treatment-refractory patients and assorted populations makes absolute effectiveness difficult to determine. Ceftaroline has been shown to be effective in patients who have not responded to other agents for MRSAB, making it an attractive option for such patients. Although the approved dosing regimen for ceftaroline fosamil is 600 mg every 12 hours for patients with normal renal function for the treatment of ABSSSIs and CABP, there is some debate about whether more frequent doses (i.e., every 8 hours) are needed for MRSAB.

CONCLUSION

Ceftaroline has been used to successfully treat SAB, including endocarditis. Therapy with ceftaroline may be considered when antibiotic resistance or previous treatment failure precludes the use of first-line agents.

Efficacy of ceftaroline versus vancomycin in an experimental foreign-body and systemic infection model caused by biofilm-producing methicillin-resistant Staphylococcus epidermidis

In this study, the efficacy of ceftaroline versus vancomycin against biofilm-producing methicillin-resistant Staphylococcus epidermidis (MRSE) in a murine model of foreign-body and systemic infection was compared. Two bacteraemic biofilm-producing MRSE strains were used (SE284 and SE385). The minimum inhibitory concentrations (MICs) for strains SE284 and SE385, were, respectively, 0.25 mg/L and 0.5 mg/L for ceftaroline and 4 mg/L and 2 mg/L for vancomycin. The in vitro bactericidal activities of ceftaroline and vancomycin were evaluated using time-kill curves. A foreign-body and systemic infection model in neutropenic female C57BL/6 mice was used to ascertain in vivo efficacy. Animals were randomly allocated into three groups (n = 15) without treatment (controls) or treated with ceftaroline 50 mg/kg every 8 h or vancomycin 110 mg/kg every 6 h. In vitro, ceftaroline showed concentration-dependent bactericidal activity, whilst vancomycin presented time-dependent activity. In the experimental in vivo model, ceftaroline and vancomycin decreased the liver and catheter bacterial concentrations (P <0.05) and increased survival (P <0.05) for both strains. In conclusion, ceftaroline is as effective as vancomycin in the treatment of experimental foreign-body and systemic infection caused by biofilm-producing MRSE.

Susceptibility patterns of Staphylococcus aureus biofilms in diabetic foot infections

BACKGROUND

Foot infections are a major cause of morbidity in people with diabetes and the most common cause of diabetes-related hospitalization and lower extremity amputation. Staphylococcus aureus is by far the most frequent species isolated from these infections. In particular, methicillin-resistant S. aureus (MRSA) has emerged as a major clinical and epidemiological problem in hospitals. MRSA strains have the ability to be resistant to most β-lactam antibiotics, but also to a wide range of other antimicrobials, making infections difficult to manage and very costly to treat. To date, there are two fifth-generation cephalosporins generally efficacious against MRSA, ceftaroline and ceftobripole, sharing a similar spectrum. Biofilm formation is one of the most important virulence traits of S. aureus. Biofilm growth plays an important role during infection by providing defence against several antagonistic mechanisms. In this study, we analysed the antimicrobial susceptibility patterns of biofilm-producing S. aureus strains isolated from diabetic foot infections. The antibiotic minimum inhibitory concentration (MIC) was determined for ten antimicrobial compounds, along with the minimum biofilm inhibitory concentration (MBIC) and minimum biofilm eradication concentration (MBEC), followed by PCR identification of genetic determinants of biofilm production and antimicrobial resistance.

RESULTS

Results demonstrate that very high concentrations of the most used antibiotics in treating diabetic foot infections (DFI) are required to inhibit S. aureus biofilms in vitro, which may explain why monotherapy with these agents frequently fails to eradicate biofilm infections. In fact, biofilms were resistant to antibiotics at concentrations 10-1000 times greater than the ones required to kill free-living or planktonic cells. The only antibiotics able to inhibit biofilm eradication on 50 % of isolates were ceftaroline and gentamicin.

CONCLUSIONS

The results suggest that the antibiotic susceptibility patterns cannot be applied to biofilm established infections. Selection of antimicrobial therapy is a critical step in DFI and should aim at overcoming biofilm disease in order to optimize the outcomes of this complex pathology.

When sepsis persists: a review of MRSA bacteraemia salvage therapy

MRSA bacteraemia (MRSAB), including infective endocarditis, carries a high mortality rate, with up to 50% of patients failing initial therapy with vancomycin and requiring salvage therapy. Persistent MRSAB can be difficult to successfully eliminate, especially when source control is not possible due to an irremovable focus or the bacteraemia still persists despite surgical intervention. Although vancomycin and daptomycin are the only two antibiotics approved by the US FDA for the treatment of patients with MRSAB as monotherapy, the employment of novel strategies is required to effectively treat patients with persistent MRSAB and these may frequently involve combination drug therapy. Treatment strategies that are reviewed in this manuscript include vancomycin combined with a β-lactam, daptomycin-based therapy, ceftaroline-based therapy, linezolid-based therapy, quinupristin/dalfopristin, telavancin, trimethoprim/sulfamethoxazole-based therapy and fosfomycin-based therapy. We recommend that combination antibiotic therapy be considered for use in MRSAB salvage treatment.