Vancomycin-intermediate S. Aureus Research Articles

Classical β-Lactamase Inhibitors Potentiate the Activity of Daptomycin against Methicillin-Resistant Staphylococcus aureus and Colistin against Acinetobacter baumannii.

ABSTRACTWe asked whether beta-lactamase inhibitors (BLIs) increased the activity of daptomycin (DAP) against methicillin-resistant Staphylococcus aureus (MRSA), the peptide antibiotic colistin (COL) against the emerging Gram-negative nosocomial pathogen Acinetobacter baumannii, and the human host defense peptide cathelicidin LL37 against either pathogen. DAP and LL37 kill curves were performed with or without BLIs against MRSA, vancomycin-intermediate S. aureus (VISA), and heterogeneous VISA (hVISA). COL and LL37 kill curves were performed against A. baumannii. Boron-dipyrromethene (BODIPY)-labeled DAP binding to MRSA grown with the BLI tazobactam (TAZ) was assessed microscopically. The combination of COL plus TAZ was studied in a murine model of A. baumannii pneumonia. TAZ alone lacked in vitro activity against MRSA or A. baumannii. The addition of TAZ to DAP resulted in a 2- to 5-log10 reduction in recoverable MRSA CFU at 24 h compared to the recoverable CFU with DAP alone. TAZ plus COL showed synergy by kill curves for 4 of 5 strains of A. baumannii tested. Growth with 20 mg/liter TAZ resulted in 2- to 2.5-fold increases in the intensity of BODIPY-DAP binding to MRSA and hVISA strains. TAZ significantly increased the killing of MRSA and A. baumannii by LL37 in vitro. TAZ increased the activity of COL in a murine model of A. baumannii pneumonia. Classical BLIs demonstrate synergy with peptide antibiotics. Since BLIs have scant antimicrobial activity on their own and are thus not expected to increase selective pressure toward antibiotic resistance, their use in combination with peptide antibiotics warrants further study.

Increasing rate of daptomycin non-susceptible strains of Staphylococcus aureus in patients with atopic dermatitis.

IntroductionDaptomycin is a cyclic lipopeptide that is bactericidal against Staphylococcus aureus, including methicillin-resistant S. aureus (MRSA), vancomycin-intermediate S. aureus (VISA) and vancomycin-resistant S. aureus (VRSA) strains. Daptomycin exerts its antimicrobial effect by a calcium-dependent interaction with the cytoplasmic membrane resulting in depolarization, ion loss and rapid cell death. Unfortunately, loss of daptomycin susceptibility in S. aureus in the clinical setting has been noted.AimTo evaluate the susceptibility profile to daptomycin among S. aureus strains isloted from patients with atopic dermatitis (AD). Another point was to correlate the results obtained by broth microdilution method and Etest, which is commonly applied in clinical setting.Material and methodsOne hundred patients with the diagnosis of atopic dermatitis were microbiologically assessed for the carriage of S. aureus. Antimicrobial susceptibility tests were performed using broth-microdilution (BMD) and Etests for daptomycin.Results Staphylococcus aureus strains were isolated from the majority of our patients, either from the skin (73%) or the anterior nares (75%). Six of the 100 nasal swabs (6%) and 5 of the 100 skin swabs (5%) were positive for methicillin-resistant Staphylococcus aureus (MRSA). A total of 81 of 148 (54.7%) daptomycin non-susceptible isolates of S. aureus were identified by BMD. Only 19 of 81 were also classified as non-susceptible by Etest.ConclusionsClinicians and microbiologists should be aware of the possibility of the emergence of daptomycin non-susceptibility (or increase in minimal inhibitory concentration) during prolonged therapy and closely monitor the susceptibility of persisting isolates that might be recovered during therapy.

Phenotypic characteristics and comparative proteomics of Staphylococcus aureus strains with different vancomycin-resistance levels

Reduced vancomycin susceptibility of methicillin-resistant Staphylococcus aureus (MRSA) is a worldwide problem. Unfortunately, its genetic marker and molecular mechanisms remained unknown. This study investigated differential phenotypic characteristic and protein expression profiles among three groups of MRSA isolates, including vancomycin-susceptible S. aureus (VSSA), heterogeneous vancomycin-intermediate S. aureus (hVISA) and vancomycin-intermediate S. aureus (VISA) (n = 7 isolates/group). Phenotypic characteristic revealed significant greater number of isolates with non-spreading colony in VISA as compared to both VSSA and hVISA groups. 2-DE followed by nanoLC-MS/MS analyses revealed increased glyceraldehyde 3-phosphate dehydrogenase (GAPDH) in both hVISA and VISA, whereas 50S ribosomal protein L14 (RplN) and DNA-binding protein II (Hup) were increased only in VISA. The non-spreading colony and GAPDH level of MRSA may be used as the markers for differentiation of VSSA, hVISA and VISA.

Molecular characterization of vancomycin-intermediate Staphylococcus aureus isolates from Tehran

ObjectiveTo determine the prevalence and some genetic characteristics of clinical isolates of Staphylococcus aureus (S. aureus) with reduced susceptibility to vancomycin. MethodsA total of 414 isolates of S. aureus were collected from clinical specimens from hospitals in Tehran. Vancomycin-intermediate S. aureus (VISA) was determined by brain heart infusion agar containing 4 μg/mL vancomycin screening plate and confirmed via E-test. VISA isolates were analysed for vanA, vanB, mecA, staphylococcal cassette chromosome mec types, surface protein A (Spa) types and agr specific groups. ResultsBrain heart infusion agar containing 4 μg/mL vancomycin screening tests revealed that 17.14% (n = 71) of S. aureus isolates were VISA phenotype. Ten of the 71 isolates were confirmed by E-test method (minimal inhibitory concentration was 4 to 8 μg/mL). All VISA isolates were susceptible to linezolid and 6 isolates (60%) were methicillin-resistant S. aureus. Five isolates belonged to agr Group II, 4 belonged to agr Group I and 1 belonged to agr Group III. Spa type t030, and staphylococcal cassette chromosome mec Type III were dominant among VISA isolates. ConclusionsThis study provides further evidence of the global dissemination of VISA isolates and emphasizes to vancomycin susceptibility testing prior to antibiotic therapy.

Activity of tick antimicrobial peptide from Ixodes persulcatus (persulcatusin) against cell membranes of drug-resistant Staphylococcus aureus

Persulcatusin (IP), which is an antimicrobial peptide found in Ixodes persulcatus midgut, is active against Gram-positive bacteria such as Staphylococcus aureus. Multidrug-resistant bacteria in particular methicillin-resistant S. aureus (MRSA), vancomycin-intermediate S. aureus (VISA) and vancomycin-resistant S. aureus (VRSA) are a worldwide clinical concern. In the present study, to explore the potential of IP as a new agent against multidrug-resistant S. aureus infections, we evaluated the antimicrobial activity of IP against multidrug-resistant S. aureus strains by MIC90, morphological observation with scanning electron microscope (SEM), and the calcein leakage assay of membrane integrity. Among the six antimicrobial peptides used in this study, IP exhibited the lowest MIC90 values for both vancomycin-susceptible and -resistant S. aureus strains. The IP MIC90 against a VISA strain was equivalent to vancomycin, while the MIC90 against VRSA was relatively low. SEM observations indicated that bacterial cells exposed to IP were crumpled and showed prominent structural changes. Moreover, IP influenced the cell membranes of both MRSA and VRSA in a mere 5 min, leading to leakage of the preloaded calcein. Although a VISA strain was resistant to the action of IP on cell membrane, the MIC90 of IP was lower than that of Nisin, suggesting that IP had another bactericidal mechanism in addition to cell membrane attack. Our results indicate that the synthetic tick antimicrobial peptide, IP exhibits strong antibacterial activity against multidrug-resistant S. aureus strains, including VRSA, via both cell membrane attack and another unknown mechanism. IP represents a promising candidate for a new anti-VRSA therapy.

In vitro synergistic effects of various combinations of vancomycin and non-beta-lactams against Staphylococcus aureus with reduced susceptibility to vancomycin

The aim of our study was to determine the potential for synergistic effect of vancomycin combined with a non–beta-lactam agent and of combinations of orally available non-beta-lactam agents against vancomycin-intermediate S. aureus (VISA) and heterogeneous VISA (hVISA). Three VISA isolates, three hVISA isolates, and two vancomycin-susceptible S. aureus (VSSA) isolates were used. The combinations included vancomycin and one of clindamycin, ciprofloxacin, gentamicin, rifampicin, or trimethoprim/sulfamethoxazole. Pairwise combinations among five non–beta-lactam agents were also tested for synergy. Synergy was determined using time-kill curves at 24h. Vancomycin combined with either ciprofloxacin or gentamicin showed synergy against some isolates of VISA, hVISA and VSSA. Vancomycin combined with trimethoprim/sulfamethoxazole showed synergy against VISA and hVISA. Among orally available non-beta-lactam agents, only ciprofloxacin combined with either clindamycin or trimethoprim/sulfamethoxazole showed synergy against one isolate of VISA.

Multiple healthcare-associated infections in a patient with Crohn's disease: Case report

Background and Objective: Healthcare-associated infections (HAIs) are the main cause of death in hospitalized individuals worldwide, related with preexisting disease and invasive procedures. The present study aimed to identify the microorganisms in a immunosuppressed patient and their antimicrobial resistance profile. Case report: A 33-year-old man with Crohn's disease was admitted in a hospital for an enterostomy and cholecystectomy, with postoperative fever and gastrointestinal bleeding. Infections of the urinary tract, into the bloodstream and associated with vascular catheter were evaluated by collect of urine, blood and secretions from catheter tips, individually plated on specific media for direct identification and antibiogram in VITEK® 2. Two different vascular catheters samples and a hemoculture revealed Staphylococcus aureus strains β-lactamases producers, with macrolide-lincosamide-streptogramin B (MLS B) and methicillin resistance phenotypes (MRSA), and one indication of VISA (Vancomycin-intermediate S. aureus). Pseudomonas aeruginosa and P. luteola were detected in catheter tips with different resistance profile, whereas Trichosporon asahii and Klebsiella pneumonia (ciprofloxacin/levofloxacin resistant) were isolated from urine. Amikacin, meropenem polymyxin B, piperacillin/tazobactam, ciprofloxacin, cefepime and amphotericin B were administered to this patient. Conclusions: The patient survived even after multiple infections with pathogens usually envolved in HAIs and mortality in brazilian hospitals.

Antibacterial activity of the novel semisynthetic lantibiotic NVB333 in vitro and in experimental infection models.

NVB333 is a novel semisynthetic lantibiotic derived from the amide coupling of 3,5-dichlorobenzylamine to the C-terminal of deoxyactagardine B. The in vitro activity of NVB333 includes efficacy against clinically relevant pathogens including methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococcus spp. NVB333 shows no cross-resistance with other antibiotics tested and a very low propensity for resistance development. After intravenous dosing NVB333 has high exposure in mouse plasma and shows generally improved in vivo activity compared with vancomycin in mouse infection models despite modest MIC values. In thigh infection models, promising efficacy was demonstrated against several strains of S. aureus including methicillin-resistant S. aureus (MRSA) and vancomycin-intermediate S. aureus (VISA) strains, and against Enterococcus faecalis UNT126-3. Area under the concentration curve (AUC)/MIC was shown to be the best predictor of efficacy against S. aureus UNT103-3 with an AUC/MIC of 138 (uncorrected for protein binding) achieving a static effect. NVB333 was also effective in a disseminated infection model where it conferred complete survival from the MRSA strain ATCC 33591. NVB333 showed rather modest lung penetration after intravenous dosing (AUC in lung 2-3% of plasma AUC), but because of very high plasma exposure, therapeutic levels of compound were achieved in the lung. Efficacy at least equal to vancomycin was demonstrated against an MRSA strain (UNT084-3) in a bronchoalveolar infection model. The impressive in vivo efficacy of NVB333 and strong resistance prognosis makes this compound an interesting candidate for development for treating systemic Gram-positive infections.

Investigation on rifampicin administration from the standpoint of pharmacokinetics/pharmacodynamics in a neutropenic murine thigh infection model.

The purpose of this study was to examine the pharmacokinetics/pharmacodynamics of rifampicin against methicillin-susceptible Staphylococcus aureus (MSSA), methicillin-resistant S.aureus (MRSA), and vancomycin-intermediate S.aureus (VISA) in a neutropenic murine thigh infection model. Three S.aureus isolates (MSSA [ATCC 25923], MRSA and VISA [Mu50]) with rifampicin MIC 0.06 to >256μg/mL were tested. The efficacy was calculated as the change in bacterial density. A maximum effect model was used to determine the PK/PD index that best described the dose-response data. The area under the curve (AUC)/MIC and maximum concentration of drug in serum (Cmax/MIC) were the best correlated with invivo efficacy (AUC/MIC, R(2)=0.96; Cmax/MIC, R(2)=0.97) for S.aureus ATCC 25923 strain, and the dose fractionation-response study did not show significantly different antimicrobial activity (p=0.10). The AUC/MIC values associated with stasis and 1-log kill for the S.aureus ATCC 25923 strain were 386 and 952, respectively. On the other hand, no antimicrobial efficacy was observed against two strains (MRSA and VISA) with MIC of 128μg/mL or more. Rifampicin demonstrated concentration-dependent killing. The AUC/MIC was a predictive PK/PD index.

First Report on Vancomycin-Resistant Staphylococcus aureus in Bovine and Caprine Milk.

The present investigation was carried out to study the vancomycin resistance pattern of Staphylococcus aureus isolates (n = 274) obtained from 352 milk samples of bovine (269) and caprine (63) clinical and subclinical mastitis from different districts of West Bengal, India. Of them, seven isolates (vancomycin-resistant S. aureus [VRSA] 1-7) exhibited resistance to vancomycin. Minimum inhibitory concentration of vancomycin (MICvan) for VRSA2 and VRSA3 was ≥16 μg/ml; thus categorized as VRSA. For rest of the isolates, MICvan was 8 μg/ml and they were grouped as vancomycin intermediate S. aureus (VISA). Even though all the isolates were resistant to cefoxitin and oxacillin and possessed mecA gene, none of them carried vancomycin resistance gene. Furthermore, all the seven isolates were subjected to Staphylococcal cassette chromosome mec (SCCmec) typing, Staphylococcal protein A (spa) typing, and enterobacterial repetitive intergenic consensus polymerase chain reaction. All the isolates except VRSA3 and VRSA4 from Kolkata district exhibited diverse genetic lineage, irrespective of their host and antibiotic resistance pattern. These two isolates showed clonal similarity (MRSA-SCCmec-V-spa t267) with methicillin-resistant S. aureus (MRSA) strains previously reported in human and animal infection. Isolation of VRSA and VISA could probably be due to intensive use of vancomycin in healthcare premises, which might have led to the development of glycopeptide-resistant strains and thereafter, further disseminated in the environment, including livestock farms. Detection of VRSA in milk is a serious concern as it may further cause health problems in the consumers. This is the first ever report of VRSA in food animals, even though the pathogen is otherwise prevalent in humans.

Transcriptional profiling of the two-component regulatory system VraSR in Staphylococcus aureus with low-level vancomycin resistance

The objective of this study was to comprehensively identify the target genes regulated by the two-component regulatory system VraSR in Staphylococcus aureus and to clarify the role of VraSR in low-level vancomycin resistance. Expression of vraS was determined by real-time quantitative reverse transcriptase PCR (qRT-PCR). A clinical heterogeneous vancomycin-intermediate S. aureus (hVISA) strain B6D and a vancomycin-intermediate S. aureus (VISA) strain D7 that was induced from a meticillin-resistant S. aureus strain were selected to construct vraSR null mutants by allelic replacement. The vraSR-complemented strain B6D_c was also constructed by allelic replacement. Genes differentially expressed in the wild-type, vraSR null mutant and complemented strains were detected using RNA-Seq and were validated by qRT-PCR. Compared with vancomycin-susceptible S. aureus strains, expression of vraS was upregulated in all four isogenic hVISA strains. Vancomycin minimum inhibitory concentrations (MICs) in the vraSR null mutants B6D-ΔvraSR and D7-ΔvraSR were significantly lower than in the wild-type strains B6D and D7 and the complemented strain B6D_c. RNA-Seq and qRT-PCR data showed that expression of genes encoding FmtA protein, foldase protein PrsA, capsular polysaccharide biosynthesis glycosyltransferase, TcaA, a putative membrane protein, and six hypothetical proteins was down regulated in both vraSR-null mutants B6D-ΔvraSR and D7-ΔvraSR. Most of these differentially expressed proteins are involved in cell wall biosynthesis, which is associated with vancomycin resistance in S. aureus. In conclusion, VraSR plays an important role in S. aureus strains with low-level vancomycin resistance. PrsA, FmtA, glycosyltransferase and TcaA are regulated directly or indirectly by VraSR.

Repurposing auranofin for the treatment of cutaneous staphylococcal infections

The scourge of multidrug-resistant bacterial infections necessitates the urgent development of novel antimicrobials to address this public health challenge. Drug repurposing is a proven strategy to discover new antimicrobial agents; given that these agents have undergone extensive toxicological and pharmacological analysis, repurposing is an effective method to reduce the time, cost and risk associated with traditional antibiotic innovation. In this study, the in vitro and in vivo antibacterial activities of an antirheumatic drug, auranofin, was investigated against multidrug-resistant Staphylococcus aureus. The results indicated that auranofin possesses potent antibacterial activity against all tested strains of S. aureus, including meticillin-resistant S. aureus (MRSA), vancomycin-intermediate S. aureus (VISA) and vancomycin-resistant S. aureus (VRSA), with minimum inhibitory concentrations (MICs) ranging from 0.0625μg/mL to 0.125μg/mL. In vivo, topical auranofin proved superior to conventional antimicrobials, including fusidic acid and mupirocin, in reducing the mean bacterial load in infected wounds in a murine model of MRSA skin infection. In addition to reducing the bacterial load, topical treatment of auranofin greatly reduced the production of inflammatory cytokines, including tumour necrosis factor-α (TNFα), interleukin-6 (IL-6), interleukin-1 beta (IL-1β) and monocyte chemoattractant protein-1 (MCP-1), in infected skin lesions. Moreover, auranofin significantly disrupted established in vitro biofilms of S. aureus and Staphylococcus epidermidis, more so than the traditional antimicrobials linezolid and vancomycin. Taken together, these results support that auranofin has potential to be repurposed as a topical antimicrobial agent for the treatment of staphylococcal skin and wound infections.

Digital antimicrobial susceptibility testing using the MilliDrop technology.

We present the MilliDrop Analyzer (MDA), a droplet-based millifluidic system for digital antimicrobial susceptibility testing (D-AST), which enables us to determine minimum inhibitory concentrations (MICs) precisely and accurately. The MilliDrop technology was validated by using resazurin for fluorescence readout, for comparison with standard methodology, and for conducting reproducibility studies. In this first assessment, the susceptibility of a reference Gram-negative strain Escherichia coli ATCC 25922 to gentamicin, chloramphenicol, and nalidixic acid were tested by the MDA, VITEK®2, and broth microdilution as a reference standard. We measured the susceptibility of clinically relevant Gram-positive strains of Staphylococcus aureus to vancomycin, including vancomycin-intermediate S. aureus (VISA), heterogeneous vancomycin-intermediate S. aureus (hVISA), and vancomycin-susceptible S. aureus (VSSA) strains. The MDA provided results which were much more accurate than those of VITEK®2 and standard broth microdilution. The enhanced accuracy enabled us to reliably discriminate between VSSA and hVISA strains.

Phenotypic Characteristics of Vancomycin-Non-Susceptible Staphylococcus aureus.

Background:Staphylococcus aureus, with reduced vancomycin susceptibility, is probably under the regulation of several genes and various express phenotypes.Objectives:This study aimed to investigate the phenotypic differences between vancomycin-susceptible S. aureus (VSSA), vancomycin-intermediate S. aureus (VISA), and heterogeneous VISA (hVISA) isolates.Materials and Methods:A total of 130 methicillin-resistant S. aureus (MRSA) isolates were studied, including 49 VSSA, 28 hVISA, and 5 VISA isolates from blood cultures and 48 isolates (two VSSA, six hVISA, and 40 VISA) derived in vitro (laboratory-induced/sub-passaged). Their phenotypes were examined using a coagulase tube test, colony spreading on soft agar, and urease activity. The SCCmec and agr typing were performed using multiplex PCR.Results:Most of the MRSA isolates were SCCmec III-agr I (84.5%), followed by SCCmec II-agr II (11.8%). The average plasma coagulation time of vancomycin-non-susceptible isolates was longer than that of the susceptible isolates (12 vs. 2.6 hours). Four hVISA (P = 0.023) and nine VISA (P < 0.001) isolates yielded a negative coagulase test after 24-hour incubation. The percentage of VSSA isolates showing non-spreading colonies (accessory gene regulator (agr) dysfunction) was significantly lower than in the VISA group (P = 0.013), but no significant difference was found between VSSA and hVISA. The VISA group showed higher urease activity than that of the VSSA and hVISA groups (P = 0.002).Conclusions:There were diverse phenotypic changes among vancomycin-non-susceptible S. aureus isolates. This may be due to the variety of related regulatory systems. The diversity of phenotypic expression may result in its misidentification in routine laboratory checks.

Cleistochlamys kirkii chemical constituents: Antibacterial activity and synergistic effects against resistant Staphylococcus aureus strains

Ethnopharmacological relevanceCleistochlamys kirkii (Benth) Oliv., (Annonaceae) is a medicinal plant traditionally used in Mozambique to treat infectious diseases. Aims of the studyTo find antibacterial lead compounds from C. kirkii and provide scientific validation for its use in traditional medicine. Materials and methodsThrough bioassay-guided fractionation, nine compounds (1–9), with different scaffolds, were isolated from the methanol extract of C. kirkii whose structures were identified by spectroscopic methods. Compounds 1–9 were evaluated for their in vitro antibacterial activity against a panel of eight Gram-positive, including five drug-resistant strains of Staphylococcus aureus, vancomycin-resistant Enterococcus faecalis, and two Gram-negative bacteria strains. Minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) were determined.A chemosensitization assay, using the checkerboard method, was also performed in order to evaluate the type of interaction of compounds with antibiotics/compounds against two S. aureus resistant strains (ATCC 9144 and CIP 106760) and a susceptible strain (ATCC 6538). ResultsDichamanetin (3), a rare C-benzylated flavanone, was very active against all the Gram-positive strains tested, displaying MIC values in the range of 1–7.5μg/mL. The C-benzylated flavanones chamanetin (1), isochamanetin (2), and the α,β-unsaturated lactone (−)-cleistenolide (6) also showed relevant antibacterial activity against some of the Gram-positive strains assayed. Compounds 4, 5, and 7–9 have shown no significant activity at the concentration ranges tested. In the combination with antibiotics, polycarpol (8) (MIC 125μg/mL) showed a strong synergistic effect against the methicillin-resistant S. aureus ATCC 9144. When combined with oxacillin (MIC 125μg/mL), compound 8 reduced the MIC to 1.5μg/mL (FICI=0.11). Similarly, it reduced the MIC of amoxicillin (MIC 250μg/mL) to 7.5μg/mL (FICI=0.18). Synergy was also obtained when this compound was combined with both β-lactam antibiotics (FICI=0.30) and with vancomycin (FICI=0.24) against vancomycin-intermediate S. aureus (VISA) CIP 106760. Remarkable, compound 8 was also able to reduce synergistically the MIC value of dichamanetin (3) (FICI=0.18) against this strain. ConclusionsThese results suggested that C. kirkii constituents may be valuable as a leads for restoring antibiotic activity against resistant S. aureus strains.

Evaluation of tedizolid against Staphylococcus aureus and enterococci with reduced susceptibility to vancomycin, daptomycin or linezolid.

Tedizolid displays potent activity against Gram-positive pathogens. In vitro studies against clinical isolates of Staphylococcus aureus and enterococci demonstrated improved tedizolid activity over linezolid. However, this is not well-characterized against a large collection of resistant isolates, including vancomycin-intermediate S. aureus (VISA), heterogeneous VISA (hVISA), daptomycin-non-susceptible (DNS) S. aureus, linezolid-resistant (LR) S. aureus and VRE. Therefore, our objective was to determine tedizolid activity versus other agents, against MRSA and VRE with various resistance phenotypes. In total, 302 MRSA (75 DNS, 100 VISA, 120 hVISA and 7 LR) and 220 VRE [100 Enterococcus faecalis (all susceptible to daptomycin and linezolid) and 120 E. faecium (25 DNS and 10 LR)] were evaluated. LR isolates were analysed for the cfr gene. MICs of tedizolid, linezolid, ampicillin, clindamycin, daptomycin, gentamicin, levofloxacin, oxacillin, tigecycline, trimethoprim/sulfamethoxazole and vancomycin were determined in accordance with CLSI guidelines. Tedizolid MIC90 values for hVISA, VISA and DNS were 0.5 mg/L (versus 4, 4 and 2 mg/L, respectively, for linezolid). The tedizolid MIC range for LR MRSA was 0.063-1 mg/L. Two LR MRSA possessed the cfr gene with tedizolid MICs of 0.125 and 0.25 mg/L (linezolid MICs of 16 and 8 mg/L). The tedizolid MIC90 for vancomycin-resistant E. faecalis and E. faecium was 0.25 and 1 mg/L, respectively; three dilutions lower for E. faecalis and two dilutions lower for E. faecium compared with linezolid. Tedizolid MICs demonstrate activity against isolates with decreased susceptibility to alternative agents, including linezolid. Tedizolid may be a viable treatment option in clinical situations with MDR Gram-positive pathogens.

Repurposing Non-Antimicrobial Drugs and Clinical Molecules to Treat Bacterial Infections.

There is a pressing need to develop novel antimicrobials to circumvent the scourge of antimicrobial resistance. The objective of this study is to identify non-antibiotic drugs with potent antimicrobial activity, within an applicable clinical range. A library, containing 727 FDA approved drugs and small molecules, was screened against ESKAPE pathogens (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter cloacae). Drugs that showed antimicrobial activity in an applicable clinical range were further tested in vitro and in vivo in an infected mouse model. The initial screening identified 24 non-antibiotic drugs and clinical molecules active against Gram-positive pathogens including methicillin- resistant S. aureus (MRSA) and vancomycin-resistant enterococcus (VRE) isolates. Two non-antibiotic drugs showed activity against Gram-negative pathogens. Among the active non-antibiotic drugs, only ebselen (EB) and 5-fluoro-2'-deoxyuridine (FdUrd), showed bactericidal activity, in an applicable clinical range, against multi-drug-resistant Staphylococcus isolates including MRSA, vancomycin-resistant S. aureus (VRSA), and vancomycin-intermediate S. aureus (VISA). The minimum inhibitory concentration at which 90% of clinical isolates of S. aureus were inhibited (MIC90) was found to be 0.25 and 0.0039mg/L for EB and FdUrd, respectively. Treatment with EB orally significantly increased mice survival in a lethal model of septicemic MRSA infection by (60%) compared to that of control. FdUrd oral and intraperitoneal treatment significantly enhanced mouse survival by 60% and 100%, respectively. These data encourage screening and repurposing of non-antibiotic drugs and clinical molecules to treat multidrug-resistant bacterial infections.

Antibiofilm and membrane-damaging potential of cuprous oxide nanoparticles against Staphylococcus aureus with reduced susceptibility to vancomycin.

The antimicrobial effects of copper ions and salts are well known, but the effects of cuprous oxide nanoparticles (Cu2O-NPs) on staphylococcal biofilms have not yet been clearly revealed. The present study evaluated Cu2O-NPs for their antibacterial and antibiofilm activities against heterogeneous vancomycin-intermediate Staphylococcus aureus (hVISA) and vancomycin-intermediate S. aureus (VISA). Nanoscaled Cu2O, generated by solution phase technology, contained Cu2O octahedral nanoparticles. Field emission electron microscopy demonstrated particles with sizes ranging from 100 to 150 nm. Cu2O-NPs inhibited the growth of S. aureus and showed antibiofilm activity. The MICs and minimum biofilm inhibitory concentrations ranged from 625 μg/ml to 5,000 μg/ml and from 2,500 μg/ml to 10,000 μg/ml, respectively. Exposure of S. aureus to Cu2O-NPs caused leakage of the cellular constituents and increased uptake of ethidium bromide and propidium iodide. Exposure also caused a significant reduction in the overall vancomycin-BODIPY (dipyrromethene boron difluoride [4,4-difluoro-4-bora-3a,4a-diaza-s-indacene] fluorescent dye) binding and a decrease in the viable cell count in the presence of 7.5% sodium chloride. Cu2O-NP toxicity assessment by hemolysis assay showed no cytotoxicity at 625 to 10,000 μg/ml concentrations. The results suggest that Cu2O-NPs exert their action by disruption of the bacterial cell membrane and can be used as effective antistaphylococcal and antibiofilm agents in diverse medical devices.

Profile of oritavancin and its potential in the treatment of acute bacterial skin structure infections

Oritavancin, a semisynthetic derivative of the glycopeptide antibiotic chloroeremomycin, received the US Food and Drug Administration approval for the treatment of acute bacterial skin and skin structure infections caused by susceptible Gram-positive bacteria in adults in August 2014. This novel second-generation semisynthetic lipoglycopeptide antibiotic has activity against a broad spectrum of Gram-positive bacteria, including methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-intermediate S. aureus (VISA), and vancomycin-resistant Enterococcus. Oritavancin inhibits bacterial cell wall synthesis and is rapidly bactericidal against many Gram-positive pathogens. The long half-life of this drug enables a single-dose administration. Oritavancin is not metabolized in the body, and the unchanged drug is slowly excreted by the kidneys. In two large Phase III randomized, double-blind, clinical trials, oritavancin was found to be non-inferior to vancomycin in achieving the primary composite end point in the treatment of acute Gram-positive skin and skin structure infections. Adverse effects noted were mostly mild with nausea, headache, and vomiting being the most common reported side effects. Oritavancin has emerged as another useful antimicrobial agent for treatment of acute Gram-positive skin and skin structure infections, including those caused by MRSA and VISA.

Survival of vancomycin-intermediate Staphylococcus aureus on hospital surfaces

Contaminated surfaces play an important role in the transmission of certain pathogens that are responsible for healthcare-associated infections. Although previous studies have shown that meticillin-resistant Staphylococcus aureus (MRSA) can survive on dry surfaces at room temperature, no published data regarding vancomycin-intermediate S. aureus (VISA) are available to date. To compare the survival time on different types of surfaces, cell-surface hydrophobicity, adherence to abiotic surfaces and biofilm formation of meticillin-susceptible S. aureus (MSSA), MRSA and VISA. Survival of the S. aureus strains was tested on latex, cotton fabric, vinyl flooring and formica. Cell-surface hydrophobicity was determined using the hydrocarbon interaction affinity method. Adhesion to abiotic surfaces was tested on granite, latex (gloves), glass, vinyl flooring and formica. Biofilm formation was evaluated at 6, 12, 24 and 48 h. All of the samples survived on the vinyl flooring and formica for at least 40 days. VISA survived on both surfaces for more than 45 days. All of the strains were highly hydrophobic. VISA adhered to latex, vinyl flooring and formica. Biofilm formation increased for all of the tested strains within 6-24 h. VISA present high survival, adherence and cell-surface hydrophobicity. Therefore, as the treatment of patients with VISA is a significant challenge for clinicians, greater care with cleaning and disinfection of different types of surfaces in healthcare facilities is recommended because these may become important reservoirs of multi-resistant pathogens.