Multi-laboratory assessment of the linezolid spectrum of activity using the Kirby-Bauer disk diffusion method: Report of the Zyvox Antimicrobial Potency Study (ZAPS) in the United States

Bacillus vallismortis acts against ginseng root rot by modifying the composition and microecological functions of ginseng root endophytes

Introduction

The endophytic microbiome serves a crucial function as a secondary line of defense against pathogen invasion in plants. This study aimed to clarify the mechanism of action of the ginseng plant growth-promoting rhizobacteria (PGPR) Bacillus vallismortis SZ-4 synergizing with endophytic microorganisms in the prevention and control of root rot.

Methods

Ginseng root samples from a susceptible group (CK) with a disease level of 0-2 and a biocontrol group (BIO) treated with strain SZ-4 were collected. We employed high-throughput sequencing to examine the microbial community structure of ginseng roots at different disease levels, explore beneficial endophytic bacteria, and evaluate the efficacy of strain SZ-4 in mitigating root rot through synergistic interactions with ginseng endophytic flora.

Results

The application of the PGPR B. vallismortis SZ-4 biocontrol fungicide has been found to help ginseng resist Fusarium solani by modulating the richness and structure of endophytic microbial populations. The endophytic bacteria HY-43 and HY-46 isolated from ginseng roots treated with B. vallismortis SZ-4 were identified as Bacillus velezensis based on morphological, physiological, and biochemical characteristics, as well as 16S rDNA and gyrB sequencing analyses. The endophytic bacteria HY-43 and HY-46 were combined with strain SZ-4 to generate the bacterial consortia CS4-43 and CS4-46, respectively. Both CS4-43 and CS4-46 significantly enhanced the inhibitory effects of the single strain SZ-4, as well as HY-43 and HY-46, against ginseng root rot, while also promoting plant growth.

Discussion

These findings offers a theoretical foundation for studying the microecological prevention and control of ginseng diseases as well as new insights for conducting research on the efficient and precise management of plant diseases.

Chemical Profile, Antibacterial Activity and Antioxidant Activity of Bark Volatile Oil of Terminalia arjuna

Terminalia arjuna is an evergreen medicinal plant that belongs to the Combretaceae family of flowering plants. The bark of the plant exhibits antiviral, anticancer, hypocholesterolemic, antioxidant and antimicrobial properties. In this study, composition antibacterial activity, antioxidant activity and cytotoxicity of bark oil of Terminalia arjuna(Roxb.) were reported. Oils were extracted by microwave assisted hydrodistillation where an oil yield of 0.18 % was obtained followed by the identification of 35 compounds by gas chromatography mass spectrometry. The most abundant volatiles were furfural (11.11 %), isoeugenol (9.99 %), p-ethylguaiacol (9.97 %), α-cadinol (9.57 %), and estragole (9.47 %). The oil was further evaluated against ten different drug resistant strains where oil showed significant activity against all pathogens and the highest activity was found against Acinetobacter baumannii(22 mm), Klebsiella pneumoniae (22 mm) and Staphylococcus aureus(22 mm) in a concentration-dependent manner. Antioxidant activity evaluation demonstrated 68 % radical scavenging activity by the volatile oil as compared to 81 % of the standard, ascorbic acid at a concentration of 1000 μg. Cytotoxicity studies were conducted to see the effect of sample on the expression level of a housekeeping gene, Glyceraldehyde 3-phosphate dehydrogenase where it did not affect the normal transcription of the gene.

Mechanisms of Surfactin from Bacillus subtilis SF1 against Fusarium foetens: A Novel Pathogen Inducing Potato Wilt

Fusarium wilt is a severe and worldwide disease in potato cultivation. In this study, Fusarium foetens was first identified as the pathogen of potato wilt. Bacillus subtilis SF1 has the potential for controlling potato wilt induced by F. foetens, resulting in a mycelium growth inhibition of 52.50 ± 2.59% in vitro and a significant decrease in incidence rate by 45.56% in vivo. This research highlighted the antifungal activity of surfactin from B. subtilis SF1 and attempted to reveal the unknown antifungal mechanisms. Surfactin inhibited F. foetens mycelium growth beyond the concentration of 20 μg/μL. Surfactin-treated mycelium appeared to have morphological malformation. Surfactin enhanced reduced glutathione production and caused the increase in values of the extracellular fluids in OD260 and OD280. Surfactin induced differential protein expression and changed the genes’ transcription levels. Surfactin binds to fungal DNA via groove-binding mode, with a binding constant of Kb 2.97 × 104 M−1. Moreover, B. subtilis SF1 harbored genes encoding plant-promoting determinants, making potato seedlings grow vigorously. The results will help provide a comprehensive understanding of the mechanisms of surfactin against filamentous fungi and the application of surfactin-producing microbial in the biocontrol of plant pathogenic fungi.

Efficacy of Tigecycline and Linezolid Against Pan-Drug-Resistant Bacteria Isolated From Companion Dogs in South Korea

The emergence of multidrug-resistant bacteria in companion animals is an increasing concern in view of the concept of One Health. The antimicrobials linezolid (LZD) and tigecycline (TGC) are effective against multidrug-resistant bacteria isolated from humans; however, thus far, no previous study has evaluated the efficacy of these drugs against bacteria isolated from companion animals. This study aimed to evaluate the efficacy of LZD and TGC against bacteria that were isolated from companion dogs and showed resistance to all classes of antimicrobial agents. Clinical samples (auditory channel, eye, skin, and urine) were collected from dogs that visited the Veterinary Medical Teaching Hospital of Konkuk University (Seoul, South Korea) from October 2017 to September 2020. In total, 392 bacterial isolates were obtained, of which 85 were resistant to all classes of antimicrobial agents tested and were, therefore, considered potentially pan-drug resistant (PDR). The susceptibility of isolates to LZD and TGC was determined by the disk diffusion method and interpreted using the Clinical Laboratory Standards Institute guidelines. In total, 95.6% (43/45) and 97.8% (44/45) of gram-positive isolates were susceptible to LZD and TGC, respectively, whereas 82.5% (33/40) of gram-negative isolates were sensitive to TGC. In conclusion, both agents showed favorable efficacy, with the susceptibility rates for all potential PDR bacteria, except Pseudomonas spp., ranging from 72.7 to 100%. Thus, these drugs may serve as excellent antimicrobial options for veterinary medicine in the future.

The global prevalence of Daptomycin, Tigecycline, Quinupristin/Dalfopristin, and Linezolid-resistant Staphylococcus aureus and coagulase-negative staphylococci strains: a systematic review and meta-analysis

OBJECTIVE

Methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-resistant coagulase-negative Staphylococcus (MRCoNS) are among the main causes of nosocomial infections, which have caused major problems in recent years due to continuously increasing spread of various antibiotic resistance features. Apparently, vancomycin is still an effective antibiotic for treatment of infections caused by these bacteria but in recent years, additional resistance phenotypes have led to the accelerated introduction of newer agents such as linezolid, tigecycline, daptomycin, and quinupristin/dalfopristin (Q/D). Due to limited data availability on the global rate of resistance to these antibiotics, in the present study, the resistance rates of S. aureus, Methicillin-resistant S. aureus (MRSA), and CoNS to these antibiotics were collected.

METHOD

Several databases including web of science, EMBASE, and Medline (via PubMed), were searched (September 2018) to identify those studies that address MRSA, and CONS resistance to linezolid, tigecycline, daptomycin, and Q/D around the world.

RESULT

Most studies that reported resistant staphylococci were from the United States, Canada, and the European continent, while African and Asian countries reported the least resistance to these antibiotics. Our results showed that linezolid had the best inhibitory effect on S. aureus. Although resistances to this antibiotic have been reported from different countries, however, due to the high volume of the samples and the low number of resistance, in terms of statistical analyzes, the resistance to this antibiotic is zero. Moreover, linezolid, daptomycin and tigecycline effectively (99.9%) inhibit MRSA. Studies have shown that CoNS with 0.3% show the lowest resistance to linezolid and daptomycin, while analyzes introduced tigecycline with 1.6% resistance as the least effective antibiotic for these bacteria. Finally, MRSA and CoNS had a greater resistance to Q/D with 0.7 and 0.6%, respectively and due to its significant side effects and drug-drug interactions; it appears that its use is subject to limitations.

CONCLUSION

The present study shows that resistance to new agents is low in staphylococci and these antibiotics can still be used for treatment of staphylococcal infections in the world.

Aeromonas hydrophila, an Emerging Causative Agent of Freshwater-Farmed Whiteleg shrimp Litopenaeus vannamei

Aeromonas hydrophila is a well-known bacterial pathogen associated with mass mortalities in aquaculture. Yet, few reports are available on whiteleg shrimp-pathogenic A. hydrophila. In the present study, a virulent isolate WS05 was confirmed as a causative agent of diseased freshwater-cultured whiteleg shrimp and showed a mean lethal dose (LD₅₀) value of 4.8 × 10⁴ CFU mL⁻¹. It was identified phenotypically and molecularly as an A. hydrophila strain, and exhibited susceptibility to several veterinary antibiotics extensively used in aquaculture, including cotrimoxazole, doxycycline, florfenicol, neomycin, and tetracycline. In view of the strongest inhibition zone of florfenicol against isolate WS05, the synergistic effect of the combinations of florfenicol and herb extracts was further evaluated, and the result indicated that Punica granatum extract was a potential synergist of florfenicol against isolate WS05 and the fractional inhibitory concentration index (FICI) for the florfenicol-P. granatum extract was calculated as 0.31. When combined with 7.81 mg mL⁻¹P. granatum extract, the minimum inhibitory concentration (MIC) of florfenicol against isolate WS05 was reduced from 0.50 to 0.03 mg L⁻¹, and its activity against isolate WS05 was also enhanced with a significant reduction of ≥3.61 log in cell density after 24 h of treatment compared with that in the single drug treatment. In addition, the protective effect was potentiated by the combination of florfenicol and P. granatum extract, with a cumulative mortality of 36.66% (p < 0.05) and 33.33% (p < 0.05) lower than that in the single treatment with florfenicol and P. granatum extract after the challenge with isolate WS05 for seven days. As far as we know, this is the first study to describe whiteleg shrimp-pathogenic A. hydrophila and suggest P. granatum extract as a potential synergist of florfenicol against the A. hydrophila pathogen.

Preliminary Studies of Chemical and Physical Properties of Two Varieties of Avocado Seeds Grown in Chile

In Chile, the most cultivated avocado varieties are Hass and Negra de la Cruz. The increase in the production of fast food preparations, salads, and avocado oil has generated large amounts of seeds and husks as waste, which may constitute a possible new source of bioactive compounds, of great interest to the food and pharmaceutical industry. Therefore, the objective of this study was to determine different nutritional, biochemical, antimicrobial, and physical properties of the SH and SNC seeds grown in Chile. In SH and SNC, their nutritional composition, lipophilic components, and total phenols (PTs) were determined. The antioxidant and antibacterial activity of extracts were measured in different solvent combinations. In addition, the color change of seeds (ΔE) during the browning, the mechanical resistance to the cut, and their thermal transitions by differential calorimetry (DSC) were determined. The results indicated that SH has a higher protein content and lipophilic components. In the ethanol extract, SNC showed greater antiradical activity and is an inhibitor of Gram (+) bacteria. The SNC browning given by ΔEwas greater and adjusted well to kinetic and enzymatic models. The physical analyses of the seeds indicated that SNC presented higher cut resistance and lower transition temperature (Tg) with a lower thermal fusion of its lipids, which would be due to its higher unsaturated composition. These properties of SH and SNC can be useful for the agrifood, pharmaceutical, and chemical industries.

Ophthalmic Econazole Hydrogels for the Treatment of Fungal Keratitis

Econazole is a feasible alternative treatment in the management of fungal keratitis. Nevertheless, its low water solubility is considered the main limitation to the incorporation into ophthalmic formulations. In this work, econazole nitrate is solubilized by using cyclodextrins to achieve an optimum therapeutic concentration. Phase solubility diagrams suggest α-cyclodextrin as the most effective cyclodextrin and later the inclusion complex formed with this one was characterized in solution by 1D, 2D-NMR, and molecular modeling. Econazole-α-cyclodextrin inclusion complex was included in 2 types of ocular hydrogels: a natural polysaccharides ion-sensitive hydrogel and a hyaluronic acid hydrogel. Both of them show no ocular irritation in the hen's egg test on chorioallantoic membrane assay and a controlled econazole release over time. Permeability studies suggest that hydrogels do not modify the econazole nitrate permeability through bovine cornea in comparison with an econazole-α-cyclodextrin inclusion complex solution. Finally, ocular biopermanence studies performed using positron emission tomography show these hydrogels present a high retention time on the eye. Results suggest the developed formulations have a high potential as vehicles for the econazole topical ocular administration as fungal keratitis treatment.

An investigation of Panax ginseng Meyer growth promotion and the biocontrol potential of antagonistic bacteria against ginseng black spot

Background

Ginseng black spot disease resulting from Alternaria panax Whuetz is a common soil-borne disease, with an annual incidence rate higher than 20–30%. In this study, the bacterial strains with good antagonistic effect against A. panax are screened.

Methods

A total of 285 bacterial strains isolated from ginseng rhizosphere soils were screened using the Kirby–Bauer disk diffusion method and the Oxford cup plate assay. We analyzed the antifungal spectrum of SZ-22 by confronting incubation. To evaluate the efficacy of biocontrol against ginseng black spot and for growth promotion by SZ-22, we performed pot experiments in a plastic greenhouse. Taxonomic position of SZ-22 was identified using morphology, physiological, and biochemical characteristics, 16S ribosomal DNA, and gyrB sequences.

Results

SZ-22 (which was identified as Brevundimonas terrae) showed the strongest inhibition rate against A. panax, which showed 83.70% inhibition, and it also provided broad-spectrum antifungal effects. The inhibition efficacies of the SZ-22 bacterial suspension against ginseng black spot reached 82.47% inhibition, which is significantly higher than that of the 25% suspension concentrate azoxystrobin fungicide treatment (p < 0.05). Moreover, the SZ-22 bacterial suspension also caused ginseng plant growth promotion as well as root enhancement.

Conclusion

Although the results of the outdoor pot-culture method were influenced by the pathogen inoculum density, the cropping history of the field site, and the weather conditions, B. terrae SZ-22 controlled ginseng black spot and promoted ginseng growth successfully. This study provides resource for the biocontrol of ginseng black spot.

Synthesis and biological activities of some new (Nα-dinicotinoyl)-bis-L-leucyl linear and macrocyclic peptides

A series of linear and macrocyclic peptides 3–12 were synthesized using 3,5-pyridinedicarboxylic acid (1) as starting material and screened for their antimicrobial, anti-inflammatory and anticancer activities. Bis-ester 3 was prepared from 1 and l-leucine methyl ester. Hydrazinolysis and hydrolysis of dipeptide methyl ester 3 with hydrazine hydrate or 1 N sodium hydroxide afforded compounds 4 and 5, respectively. Cyclization of the dipeptide 5 with l-lysine methyl ester afforded cyclic pentapeptide ester 6. Compounds 7–9 were synthesized by reacting hydrazide 4 with phthalic anhydride, 1,8-naphthalene anhydride or acetophenone derivatives. Treatment of acid hydrazide 4 with aromatic aldehydes or tetraacid dianhydrides afforded the corresponding bis-dipeptide hydrazones 10a–e and macrocyclic peptides 11 and 12, respectively. The structures of newly synthesized compounds were confirmed by IR, ¹H-NMR, MS spectral data and elemental analysis. The detailed synthesis, spectroscopic data, biological and pharmacological activities of the synthesized compounds was reported.

Linezolid update: stable in vitro activity following more than a decade of clinical use and summary of associated resistance mechanisms

Linezolid, approved for clinical use since 2000, has become an important addition to the anti-Gram-positive infection armamentarium. This oxazolidinone drug has in vitro and in vivo activity against essentially all Gram-positive organisms, including methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant enterococci (VRE). The in vitro activity of linezolid was well documented prior to its clinical application, and several ongoing surveillance studies demonstrated consistent and potent results during the subsequent years of clinical use. Emergence of resistance has been limited and associated with invasive procedures, deep organ involvement, presence of foreign material and mainly prolonged therapy. Non-susceptible organisms usually demonstrate alterations in the 23S rRNA target, which remain the main resistance mechanism observed in enterococci; although a few reports have described the detection of cfr-mediated resistance in Enterococcus faecalis. S. aureus isolates non-susceptible to linezolid remain rare in large surveillance studies. Most isolates harbour 23S rRNA mutations; however, cfr-carrying MRSA isolates have been observed in the United States and elsewhere. It is still uncertain whether the occurrences of such isolates are becoming more prevalent. Coagulase-negative isolates (CoNS) resistant to linezolid were uncommon following clinical approval. Surveillance data have indicated that CoNS isolates, mainly Staphylococcus epidermidis, currently account for the majority of Gram-positive organisms displaying elevated MIC results to linezolid. In addition, these isolates frequently demonstrate complex and numerous resistance mechanisms, such as alterations in the ribosomal proteins L3 and/or L4 and/or presence of cfr and/or modifications in 23S rRNA. The knowledge acquired during the past decades on this initially used oxazolidinone has been utilized for developing new candidate agents, such as tedizolid and radezolid, and as linezolid patents soon begin to expire, generic brands will certainly become available. These events will likely establish a new chapter for this successful class of antimicrobial agents.

In vitro activity of fosfomycin in combination with linezolid against clinical isolates of methicillin-resistant Staphylococcus aureus

The objective of this paper was to investigate the in vitro effects of fosfomycin combined with linezolid against methicillin-resistant Staphylococcus aureus (MRSA). A total of 102 MRSA isolates isolated from clinical specimens of human infections from three hospitals in China were studied. The microdilution checkerboard method was used to determine whether combinations act synergistically against these isolates. The susceptibility results for fosfomycin and linezolid were interpreted according to the guidelines of the Clinical and Laboratory Standards Institute. Synergy and indifference were defined as a fractional inhibitory concentration index of ⩽0.5 and >0.5 but ⩽4, respectively. The combination of fosfomycin and linezolid demonstrated the following interactions: 98.04% (100/102) synergism; 1.96% (2/102) indifference; no antagonism was seen. Thus, the combination between fosfomycin and linezolid shows synergism for most of the MRSA isolates tested in this study. If these findings are confirmed in further in vitro or in vivo studies, the above combination could be tested clinically for difficulty to treat MRSA infections, particularly those warranting prolonged oral therapy.

Antimicrobial properties and elution kinetics of linezolid from polymethylmethacrylate

Polymethylmethacrylate (PMMA) impregnated with antibiotics is widely used in the treatment of osteomyelitis and infected arthroplasties. With the emergence of resistant bacterial strains, linezolid, which is active against gram-positive bacteria and toward which resistance has been scarce, has been suggested as an alternative. In the current in vitro study, the authors sought to determine and compare the efficacy and elution kinetics of linezolid from PMMA. Polymethylmethacrylate beads impregnated with linezolid, vancomycin, or gentamicin alone and in combinations were placed in suspensions of vancomycin-resistant enterococci, methicillin-resistant Staphylococcus aureus, Klebsiella pneumoniae, Escherichia coli, and Staphylococcus epidermidis. The leaching out concentrations of antibiotics and growth inhibitory time in days were recorded. The mechanical strength of cement beads was evaluated in accordance with International Standard 5833. The growth inhibitory time of linezolid was significantly longer than that of vancomycin and gentamicin for methicillin-resistant S aureus, vancomycin-resistant enterococci, and S epidermidis. The combination of linezolid with gentamicin and vancomycin significantly increased the growth inhibitory time compared with either antibiotic used alone. Linezolid alone or in combination with vancomycin and gentamicin showed satisfactory elution kinetics and antimicrobial activity in vitro without compromising the mechanical strength of PMMA. Future research evaluating the in vivo profile of linezolid-loaded PMMA in experimental animals is needed before it can be considered for human use.

Linezolid surveillance program results for 2008 (LEADER Program for 2008)

The LEADER Program was initiated in 2004 and monitors emerging linezolid resistance in sampled US medical centers. This report summarizes the data obtained in 2008, the 5th consecutive year. A total of 57 institutions participated in 2008 representing all 9 US census regions with 100 target organisms per site (6113 isolates, 101.9% compliance to protocol design). The organisms tested by reference broth microdilution methods were Staphylococcus aureus (3156), coagulase-negative staphylococci (CoNS; 856), enterococci (901), Streptococcus pneumoniae (619), and viridans group (223) or beta-hemolytic streptococci (358); also, D-test was used to determine inducible clindamycin resistance in Staphylococcus aureus. Linezolid remained very potent against all sampled species with MIC(90) results ranging from 1 microg/mL (streptococci and CoNS) to 2 microg/mL (Staphylococcus aureus and enterococci). Only 0.36% of sampled strains were nonsusceptible to linezolid, a slight decrease from 0.45% and 0.44% in 2006 and 2007, respectively. The nonsusceptible strains (22) were Staphylococcus aureus (3), CoNS (14), and Enterococcus faecium (5) each with defined target mutations (G2576T in 19 strains; T2504A in 1 strain), mobile cfr element (1 strain Staphylococcus epidermidis with an identical pulsed-field gel electrophoresis pattern to a cfr-positive Staphylococcus epidermidis isolated from the same center in LEADER 2007), or an unknown (1 strain) mechanism. The mobile cfr resistance found in a Staphylococcus aureus strain in 2007 was not observed in 2008. In conclusion, linezolid activity sampled by the 5th year of this LEADER Program showed sustained potency and spectrum (99.64% susceptibility levels). The nonsusceptible strain isolation rates remained stable and the plasmid-mediated ribosomal-based resistance mechanism that emerged in Staphylococcus aureus and Staphylococcus epidermidis strains in 2007 showed no evidence of dissemination or increased prevalence. However, there was evidence of cfr persistence with the S. epidermidis strain. The LEADER Program continues to be an effective and sensitive surveillance tool to detect and monitor novel oxazolidinone resistance phenotypes and genotypes.

Linezolid versus vancomycin for the treatment of gram-positive bacterial infections: meta-analysis of randomised controlled trials

This review aimed to compare data regarding the effectiveness and safety of linezolid and vancomycin in the treatment of gram-positive bacterial infections. PubMed and other databases were searched to identify relevant randomised controlled trials (RCTs). Nine RCTs studying 2489 clinically assessed patients were included in the meta-analysis. Overall, there was no difference between linezolid and vancomycin regarding treatment success in clinically assessed patients [odds ratio (OR)=1.22, 95% confidence interval (CI) 0.99-1.50]. Linezolid was more effective than vancomycin in patients with skin and soft-tissue infections (OR=1.40, 95% CI 1.01-1.95). However, there was no difference in treatment success for patients with bacteraemia (OR=0.88, 95% CI 0.49-1.58) or pneumonia (OR=1.16, 95% CI 0.85-1.57). Linezolid was associated with better eradication rates in all microbiologically assessed patients compared with vancomycin (OR=1.33, 95% CI 1.03-1.71). There was no difference in total adverse effects possibly or probably related to the study drugs (OR=1.14, 95% CI 0.82-1.59). However, nephrotoxicity was recorded more commonly in patients receiving vancomycin (OR=0.31, 95% CI 0.13-0.74). In conclusion, linezolid is as effective as vancomycin in patients with gram-positive infections. There is superior clinical and microbiological outcome with linezolid in complicated skin and soft-tissue infections caused by Staphylococcus aureus.

United States resistance surveillance results for linezolid (LEADER Program for 2007)

The LEADER Program (2007) monitors for emerging linezolid resistance in sampled US medical centers, initiated in 2004. For the current reported year, the number of sites participating was increased from 50 to 60 institutions representing all 9 US census regions with 100 target organisms per site (6305 isolates, 105.1% compliance to protocol design). The organisms tested by reference broth microdilution methods were Staphylococcus aureus (3318), coagulase negative staphylococci (CoNS, 1020), enterococci (705), Streptococcus pneumoniae (622), and viridans group (249) or beta-hemolytic streptococci (391); also, D-test was used to determine inducible clindamycin resistance in S. aureus strains. Linezolid remained very potent against all sampled species with MIC(90) results ranging from 1 microg/mL (streptococci and CoNS) to 2 microg/mL (S. aureus and enterococci). Only 0.44% of sampled strains were nonsusceptible to linezolid, compared with 0.45% in 2006. The nonsusceptible strains (23) were usually staphylococci (20) or Enterococcus faecium (8), each with defined target mutations (G2576T, 24 strains) or a novel mobile cfr element in staphylococci (2 strains). In conclusion, linezolid activity sampled by the 4th year of this LEADER Program showed sustained potency and spectrum (99.56% susceptibility). Although the nonsusceptible strain isolation rates remained stable, a new plasmid-mediated ribosomal-based resistance mechanism emerged in S. aureus and Staphylococcus epidermidis strains from Arizona and Ohio. The LEADER Program appears to be an effective and sensitive surveillance tool to detect novel resistance phenotypes and genotypes.

Pharmacokinetics of linezolid in human non-inflamed vitreous after systemic administration

OBJECTIVES

To determine the concentration-time curves of linezolid in serum and vitreous from 24 patients undergoing vitrectomy.

METHODS

Vitrectomy was performed 1, 2, 4, 8 and 12 h after infusion of 600 mg of linezolid in 20 patients divided into groups of four. Four additional patients were studied 12 h after two separate oral doses of 600 mg of linezolid. Serum samples were obtained 1 h after linezolid administration to determine C(max); vitreous and a second serum sample were taken simultaneously during the vitrectomy in all patients, and the concentrations of linezolid in vitreous (C(v)) and serum (C(s)) were determined.

RESULTS

Among patients who received one intravenous dose of 600 mg of linezolid, the highest mean C(v) was observed at 4 and 8 h following linezolid administration (3.4 and 3.7 mg/L). The highest mean C(v) was observed in patients who received two oral doses of 600 mg of linezolid separated by 12 h (4.5 mg/L), which was higher than the MIC(90) for Staphylococcus epidermidis. The highest C(v)/C(s) ratio was reached 12 h after administration of one and two doses (2.4 and 1.5, respectively).

CONCLUSIONS

Microbiologically significant concentrations of linezolid can be achieved in the vitreous of the non-inflamed human eye after intravenous administration of 600 mg, and it is even better after two doses of 600 mg. It appears that linezolid accumulates in the vitreous, achieving potentially useful steady-state concentrations. An evaluation of clinical efficacy is needed to confirm the perceived utility based on the pharmacokinetics.

Zyvox® Annual Appraisal of Potency and Spectrum Program Results for 2006: an activity and spectrum analysis of linezolid using clinical isolates from 16 countries

The Zyvox Annual Appraisal of Potency and Spectrum Program has completed its fifth year of monitoring for emerging resistance to linezolid and other Gram-positive active agents on the continents of Europe, Asia, Australia, and Latin America. In 2006, 4216 Gram-positive isolates from 16 nations were submitted for analysis from 6 organism groups including Staphylococcus aureus (54.0%), coagulase-negative staphylococci (CoNS) (14.6%), enterococci (10.0%), Streptococcus pneumoniae (9.4%), viridans group streptococci (5.0%), and beta-hemolytic streptococci (7.0%). Linezolid retained potent activity against S. aureus (MIC(50) and MIC(90), 2 microg/mL; 39.8% methicillin resistant) and CoNS (MIC(50) and MIC(90), 1 microg/mL; 74.3% methicillin resistant). Despite endemicity of vancomycin-resistant enterococci (up to 30.0%) in several nations, linezolid inhibited >99% of strains at </=2 microg/mL (modal MIC, 1 microg/mL). Among streptococci, all linezolid MIC values were </=2 microg/mL. Rare instances of linezolid-resistance were detected in enterococci (2 isolates, China and Germany) and CoNS (3 isolates, Italy and Brazil); 2 CoNS and 1 Enterococcus faecium had documented G2576T mutations. Overall, linezolid remained active against 99.88% of tested strains from this global collection.

Activity of linezolid against 3,251 strains of uncommonly isolated gram-positive organisms: report from the SENTRY Antimicrobial Surveillance Program

Linezolid was tested against 32 species of uncommonly isolated gram-positive organisms (3,251 strains) by reference MIC methods and found to be highly active (MIC50 range, 0.25 to 2 microg/ml; MIC90 range, 0.25 to 2 microg/ml). Only one isolate (viridans group streptococcus; 0.03% of tested strains) was resistant to linezolid.

Contemporary activity of meropenem and comparator broad-spectrum agents: MYSTIC program report from the United States component (2005)

The Meropenem Yearly Susceptibility Test Information Collection Program is a 9-year-old antimicrobial resistance surveillance network of more than 100 medical centers worldwide, including 15 sites in the United States (US) that monitors the susceptibility of Gram-negative and Gram-positive bacterial pathogens especially to carbapenems. In 2005, the antimicrobial activity of 11 broad-spectrum agents was assessed against 2910 bacterial isolates (2493 Gram-negative and 417 staphylococci) submitted from the US medical centers to a reference laboratory using Clinical and Laboratory Standards Institute susceptibility testing methods and interpretative criteria. Meropenem continued to demonstrate 1) high potency with MIC(90) values 4- to 16-fold lower than imipenem against the Enterobacteriaceae, 2) equal activity against Pseudomonas aeruginosa, 3) 2-fold less activity compared with imipenem against Acinetobacter spp., and 4) 4- to 8-fold less activity compared with imipenem against the oxacillin-susceptible staphylococci. The wide spectrum of activity for carbapenems against Enterobacteriaceae (1657 strains) was confirmed by the overall rank order by percentage susceptibility at breakpoint criteria: imipenem (98.9%) > meropenem (98.7%) > cefepime (97.6%) > piperacillin/tazobactam (92.0%) > ceftriaxone (91.2%) > aztreonam (90.6%) > gentamicin = tobramycin (90.5%) > ceftazidime (90.4%) > levofloxacin (84.9%) > ciprofloxacin (83.9%). Against Acinetobacter spp. isolates, only tobramycin (92.0% susceptible) and carbapenems (92.0-85.6%) exhibited acceptable levels of activity. A continued increase in the resistance rate for both ciprofloxacin and levofloxacin was observed with highest rates found among indole-positive Proteae species (36.5-33.3%) and Escherichia coli (21.6-20.4%) isolates, some documented by molecular typing methods as clonally related. Ongoing surveillance of meropenem and other broad-spectrum antimicrobial agents appears warranted to monitor the potency and spectrum of activity against indicated Gram-negative and-positive pathogens causing serious infections in the hospital setting, and to detect the emergence of new or novel resistance mechanisms that could compromise clinical utility (serine and metallo-carbapenemases).

In vitro activity of linezolid against key gram-positive organisms isolated in the united states: results of the LEADER 2004 surveillance program

Since the approval of linezolid in 2000, sporadic reports of resistance have been given and a greater understanding of the underlying mechanisms of resistance has been gained. However, since these developments, an updated status of the in vitro activity of linezolid against gram-positive organisms from the United States has not been reported. The LEADER 2004 surveillance initiative was undertaken to obtain current and representative data on the activity of linezolid against key species, including isolates with significant resistance phenotypes. Organisms were isolated during 2004 and included 2,872 Staphylococcus aureus, 496 coagulase-negative staphylococcus (CNS), 428 Enterococcus faecalis, 196 Enterococcus faecium, and 422 Streptococcus pneumoniae isolates. All S. aureus isolates (54.2% oxacillin resistant) were susceptible to linezolid (MIC90 = 2 microg/ml); MIC distributions were consistent, regardless of oxacillin or multidrug resistance status. For CNS, one nonsusceptible isolate was encountered (Staphylococcus epidermidis; MIC = 32 microg/ml), but overall, the MIC(90) (1 microg/ml) was lower than that obtained with S. aureus. For E. faecalis and E. faecium, 99.5% and 96.4% of isolates, respectively, were linezolid susceptible. Both species had an MIC90 of 2 microg/ml, and MIC distributions did not vary with the vancomycin susceptibility status of the populations analyzed. Linezolid nonsusceptibility was not encountered among the S. pneumoniae isolates. These findings indicate that linezolid nonsusceptibility has remained rare among staphylococci and uncommon and sporadic among enterococci. Nonetheless, careful and ongoing monitoring of the in vitro effectiveness of linezolid will be needed so that any changes to the current status may be detected as soon as possible.

Oxazolidinone susceptibility patterns in 2004: report from the Zyvox® Annual Appraisal of Potency and Spectrum (ZAAPS) Program assessing isolates from 16 nations

OBJECTIVES

To investigate the activity of linezolid (an oxazolidinone), a potent choice for community- and hospital-acquired infections, via a worldwide surveillance network called the Zyvox Annual Appraisal of Potency and Spectrum (ZAAPS) Program.

METHODS

A total of 4098 Gram-positive strains were collected from 42 laboratories located in North America (five sites in Canada), South America (10 sites), Europe (16 sites) and the Far East (11 sites). Each country or site submitted 200 isolates (Canada submitted 200 isolates for each of five sites; total 1000) for confirmation of organism identification and reference MIC processing. Nearly 25 comparator agents were tested along with quality control strains, and interpretative criteria from the CLSI, formerly the NCCLS, M100-S15 were applied. No linezolid resistance was detected in strains from 16 monitored countries in 2004.

RESULTS

Linezolid remained highly active against Streptococcus pneumoniae, viridans group and beta-haemolytic streptococci (MIC90, 1 mg/L). Against Staphylococcus aureus, linezolid showed 99.5% of results at 0.5-2 mg/L with only one isolate at 4 mg/L. Oxacillin-resistant S. aureus rates varied between nations and ranged from 1.4% in Sweden to 29.5% in the UK to 65.2% in Mexico. Linezolid MIC values were generally one log2 dilution step lower for coagulase-negative staphylococci (CoNS) when compared with S. aureus. No CoNS strains produced a linezolid result at 4 mg/L. Compared with ZAAPS 2002 and 2003 results for enterococci where seven resistant strains were identified, the 2004 data revealed no resistance and 98.1% of linezolid MIC results were at 1 or 2 mg/L. Vancomycin-resistant enterococci (5.3% overall) varied markedly by country including a high of 47.2% in Korea.

CONCLUSIONS

Linezolid continues to be effective in vitro against Gram-positive pathogens from five continents and no oxazolidinone-resistant strains were identified among the 4098 systemically collected strains (2004) or among 20 158 non-United States isolates for the entire ZAAPS Program (2002-04).

[Antimicrobial susceptibility of the uropathogens in out patients in Goiânia City, Goiás State]

Due to the fact that the number of multiresistant microorganisms which cause cystitis is increasing, the objective of this study was to identify the pathogens that cause urinary tract infection in women and determine antimicrobial susceptibility. We analyzed 442 urine samples from June 2002 to August 2003. Identification through biochemical and enzymatic assays, and the antibiogram by Disk diffusion method were performed. Out of these samples, 78 were positive for urinary tract infection (17.6%). Escherichia coli were the microorganisms that most frequently caused infections (67.9%). Gram-negative bacteria exhibited resistance to amoxicillin in 74.6% of the cases. Most were ceftazidime and gentamicin sensitive. Gram-positive bacteria were resistant in 72.7% of the samples to ampicillin, and they were trimethoprim/sulfamethoxazole, vancomycin and linezolid sensitive. It was concluded that investigation of bacterial resistance is necessary to provide information for new therapeutic options.

Human vitreous distribution of linezolid after a single oral dose

PURPOSE

To evaluate the relationship between vitreous linezolid concentrations versus both time and serum concentrations after a single 600 mg oral dose.

METHODS

Two groups of six subjects undergoing a pars plana vitrectomy indicated by macular pucker or full thickness macular hole were given a single tablet of linezolid before surgery. The early group underwent vitrectomy at random times before the time of maximum serum linezolid concentration (i.e., 77 minutes) and the late group underwent vitrectomy at random times afterward. Each patient had a serum sample drawn shortly before and after vitrectomy and the vitreous specimen was sampled at the initiation of surgery.

RESULTS

The early group and late group had mean vitreous linezolid concentrations of 0.06 mcg/mL and 1.25 mcg/mL, respectively. The vitreous linezolid concentration showed a strong correlation to the interpolated serum concentration (R2 = 0.74, P < 0.01) at the time of vitrectomy.

CONCLUSION

The study demonstrates that linezolid penetrates the blood-retina barrier in noninflamed eyes. Because the vitreous concentrations appeared to exponentially trend upward with time and 33% of the late group achieved sufficient MIC90 levels for the common pathogens found in postoperative endophthalmitis, adequate concentrations might be achieved with an altered dosing regimen to achieve higher serum steady state levels. Further study is warranted.

Trends in linezolid susceptibility patterns: report from the 2002–2003 worldwide Zyvox Annual Appraisal of Potency and Spectrum (ZAAPS) Program

Linezolid is an important oxazolidinone antimicrobial for the treatment of infections caused by Gram-positive cocci, especially vancomycin-resistant enterococci and oxacillin-resistant Staphylococcus aureus (ORSA). Since its introduction, however, ribosomal mutations have been detected that produce resistance; thus, longitudinal surveillance remains necessary to monitor for emerging resistance in all geographic areas of oxazolidinone use. The 2003 Zyvox Annual Appraisal of Potency and Spectrum (ZAAPS) Program compared linezolid minimum inhibitory concentration (MIC) results with 13-15 comparator antimicrobial agents (8089 isolates) and also with results from an earlier surveillance period (2002). Sampling institutions in the United States of America (USA), Canada, Europe (seven nations), South America (three nations) and the Asia-Pacific (three nations) referred 200 Gram-positive cocci to the central laboratory for MIC processing and identification confirmation. Linezolid resistance (MIC > or = 8 mg/L) was established by alternative susceptibility testing methods as well as by ribosomal target characterisation. Concurrent drug use data were collected. Linezolid activity against the six major organism groups did not vary between years or geographic areas. In contrast, penicillin resistance increased 2% in Streptococcus pneumoniae; macrolide resistance was stable among beta-haemolytic streptococci (19-21%), but increased in S. pneumoniae (+2%); ORSA rates increased 4%; and vancomycin resistance in enterococci was present, but varied markedly by region. Non-clonal linezolid-resistant isolates were detected, each having the same G2576U 23S rRNA target mutation. Furthermore, the first linezolid-resistant, non-USA isolate (S. aureus in Greece) was observed, apparently related to linezolid use. In 2003, near complete activity for linezolid against Gram-positive isolates was again documented (99.93% susceptible) in the ZAAPS Program. Rare linezolid-resistant isolates were identified among enterococci, limited to USA strains. Limited correlations of linezolid resistance to drug use continues, with an average consumption rate of 0.63DDD/100 patient days (a 50% increase since 2002), and indicates the important role of hospital hygiene practice in preventing the dissemination of oxazolidinone resistances, should they be detected.

Trends in linezolid susceptibility patterns in 2002: Report from the worldwide Zyvox Annual Appraisal of Potency and Spectrum Program

Oxazolidinones have become reliable clinical and candidate antimicrobial agents to be utilized for infections caused by multidrug-resistant Gram-positive cocci, especially vancomycin-resistant enterococci and methicillin-resistant staphylococci. However, mutational resistance of the ribosomal target has been described for several species. Longitudinal surveillance remains necessary to monitor for this evolving linezolid resistance pattern. A survey of linezolid and several comparison Gram-positive focused agents was initiated in 2002 (7971 strains, >99.0% compliance) for 54 participating sites in the United States, Canada, Europe (6 nations), Latin America (2 nations), and the Asia Pacific (2 nations). The 5 and 25 sites in Canada and the United States, respectively, submitted 200 strains each to a central laboratory for organism identification/confirmation and reference MIC processing. The 10 remaining nations had 200 strain samples from 1 to 4 separate institutions. Linezolid resistance (MIC >/= 8 microg/mL) was confirmed by alternative susceptibility testing methods (Etest, AB BIO Disk, Solna, Sweden; disk diffusion method) and target mutation characterization by PCR and sequence analysis. Linezolid activity against the 6 major organism groups did not vary between geographic areas. A total of 98.1% of linezolid MIC values were between 0.5 and 2 microg/mL, and only 0.5% of results were at 4 microg/mL, which included 32 Staphylococcus aureus (0.9%) and 5 (0.5%) enterococcal isolates. Linezolid resistance was detected in only 4 isolates (0.05%): 1 each Staphylococcus aureus, Staphylococcus epidermidis, Enterococcus faecium, and a viridans group Streptococcus. All 4 isolates had a G2576U mutation in the 23S rRNA target. Linezolid activity as outlined by these Zyvox Annual Appraisal of Potency and Spectrum (ZAAPS) Program results demonstrate sustained, near complete activity against contemporary Gram-positive isolates on 4 monitored continents and in centers utilizing oxazolidinones. Rare linezolid-resistant strains were identified in the United States only (0.05% resistance overall).

Résistance au linézolide de Staphylococcus aureus avant inscription au livret du médicament

Resistance to antibiotics is a global problem in geriatric centres.

OBJECTIVE

The aim of this study was to determine the frequency of the resistance to linezolid in Staphylococcus aureus strains before its release in a geriatric centre.

METHOD

From 03-01-01 to 03-04-30 linezolid was included in the panel of antibiotics tested in S. aureus strains. The susceptibilities were estimated by the disk diffusion test in routine clinical microbiology practice.

RESULTS

A total of 213 strains of S. aureus was analysed. All of them were susceptible to the following antibiotics: linezolid, cotrimoxazol, fosfomycin, and glycopeptides. The meticillin-resistant S. aureus (MRSA) represented 67.1% (60.3-73.3) strains. The resistance to pefloxacin, tobramycin and erythromycin concerned 92.3% (86.3-95.9), 73.4% (65.3-80.3) and 31.5% (24.1-39.8) of MRSA strains respectively. The MRSA strains were less resistant to the following antimicrobial drugs: gentamicin 7.0% (3.6-12.8), fusidic acid 2.1% (0.5-6.5) and rifampicin 1.4% (0.2-5.5). The resistance concerning at the same time gentamicin, pefloxacin and fucidic acid represented 2.1% (0.5-6.5) of SARM strains, rifampicin was not interested.

CONCLUSION

Linezolid was effective in vitro in S. aureus strains regardless their susceptibilities in meticillin. According to its effectiveness in vivo, linezolid may be of use for the treatment of infections due to MRSA. However, there has been two reports of resistance of MRSA in clinical infections. The use of linezolid has to follow the instructions and it should be carefully monitored.

Vancomycin-resistant Enterococcus faecium endocarditis in a premature infant successfully treated with linezolid

A 4 1/2-month-old, 26-week premature infant with multiple complications of prematurity required a central venous catheter for venous access and antibiotic treatment of bacterial nosocomial infections. He developed tricuspid valve endocarditis with vegetation caused by Enterococcus faecium resistant to ampicillin, vancomycin and quinupristin-dalfopristin but susceptible to linezolid. He was successfully treated with linezolid intravenously (7 weeks) and then orally (2 weeks).

Quinupristin-dalfopristin resistance in Streptococcus pneumoniae: novel L22 ribosomal protein mutation in two clinical isolates from the SENTRY antimicrobial surveillance program

Resistance to quinupristin-dalfopristin (Q/D) among gram-positive cocci has been very uncommon. Two clinical isolates among 8,837 (0.02%) Streptococcus pneumoniae isolates were discovered in 2001 to 2002 with Q/D MICs of 4 micro g/ml. Each had a 5-amino-acid tandem duplication (RTAHI) in the L22 ribosomal protein gene (rplV) preventing synergistic ribosomal binding of the streptogramin combination. Similar gene duplication has been reported in Q/D-resistant Staphylococcus aureus.

Clinical Pharmacokinetics of Linezolid, a Novel Oxazolidinone Antibacterial

Linezolid is the first antibacterial to be approved from the oxazolidinone class. The drug has substantial antimicrobial activity against Gram-positive organisms such as streptococci, staphylococci and enterococci, including species resistant to conventional antibacterial treatment. Linezolid is fully bioavailable following oral administration when compared with intravenous administration. Maximum plasma linezolid concentrations are usually achieved between 1 and 2 hours after oral administration. Food slightly decreases the rate, but not the extent, of absorption. The distribution of linezolid is approximately equivalent to total body water, and there is low protein binding (31%) to serum albumin. The elimination half-life of linezolid is 5-7 hours, and twice-daily administration of 400-600 mg provides steady-state concentrations in the therapeutic range. Linezolid is mainly cleared by non-renal clearance to two metabolites and renal clearance of the parent compound. Approximately 50% of an administered dose appears in the urine as the two major metabolites, and approximately 35% appears as parent drug. A small degree of nonlinearity has been observed, with a 30% decrease in clearance after a 5-fold increase in dose. The nonlinearity is not relevant over the therapeutic dosage range. Plasma linezolid concentrations in elderly patients, patients with mild to moderate hepatic impairment or mild to severe renal impairment are similar to those achieved in young or healthy volunteers. Higher concentrations are observed in women as compared with men, but the difference is not sufficient to warrant an adjustment in dosage. In patients with severe renal impairment requiring haemodialysis, the exposure to the two primary metabolites was 7 to 8-fold higher than in patients with normal renal function. Therefore, linezolid should be used with caution in patients with severe renal insufficiency. A higher clearance of linezolid was found in children as compared with adults, and therefore higher daily dosages per kg bodyweight are required in children. There is no pharmacokinetic interaction when linezolid is coadministered with aztreonam, gentamicin or warfarin. Linezolid is a mild, reversible, inhibitor of monoamine oxidases A and B. Coadministration of linezolid with the adrenergic agents pseudoephedrine and phenylpropanolamine resulted in increases in blood pressure relative to these agents alone or to placebo. The degree of the change in blood pressure was within that associated with normal daily activities. No interaction was observed when linezolid was coadministered with the serotonergic agent dextromethorphan.

Multicentre assessment of linezolid antimicrobial activity and spectrum in Europe: report from the Zyvox antimicrobial potency study (ZAPS-Europe)

OBJECTIVE

To evaluate the in vitro spectrum and activity of linezolid, a recent oxazolidinone, according to well-controlled surveillance data from 42 medical centers in 13 countries throughout Europe.

METHODS

Participants tested the susceptibility of 125 clinical strains of enterococcal and staphylococcal species against 13 drugs using reference broth microdilution trays or the standardized disk diffusion method of the National Committee for Clinical Laboratory Standards (NCCLS). Streptococcal species (n = 25 at each center) were tested against six drugs using E test (AB BIODISK, Solna, Sweden). Quality assurance testing was conducted using NCCLS-recommended strains and verification of resistance to linezolid and other selected agents was performed by retesting strains at the regional (Europe) and international (USA) monitor sites.

RESULTS

A total of 5598 strains from throughout Europe (91% compliance) were tested. Vancomycin resistance was reported in only 0.6 and 3.0% of Enterococcus faecalis and E. faecium, respectively. Penicillin resistance occurred in 25.1% of Streptococcus pneumoniae; 4.9% at the high-level (> or =2 mg/L). The MIC90 for linezolid was 1 mg/L for streptococci and 2 mg/L for enterococci and staphylococci. Using the US FDA- and EUCAST-recommended susceptible breakpoints for linezolid, there were no confirmed reports of linezolid resistance [minimum inhibitory concentration (MIC), > or =8 mg/L]. The distribution of linezolid MIC values was unimodal and varied between 0.25 and 1 mg/L for streptococci (>90% of isolates), and between 1 and 2 mg/L for staphylococci (>90%) and enterococci (>95%). There were no differences in linezolid susceptibility in the vancomycin-, oxacillin-, or penicillin-resistant subsets of strains when compared to susceptible organism populations.

CONCLUSIONS

Compared to the North American component of this study, there was substantially less vancomycin resistance among E. faecium isolates (Europe 3.0% vs. North America 63.4%). While the occurrence of penicillin-resistant S. pneumoniae in Europe and North America was similar (25.1% vs. 29.7%), the recovery of high-level penicillin-resistant strains was nearly three-fold higher in North America (4.9% vs. 13.2%). Only linezolid was universally active against all the tested Gram-positive isolates at </=4 mg/L.

In vitro evaluation of AZD2563, a novel oxazolidinone, against 603 recent staphylococcal isolates

AZD2563, a novel oxazolidinone, and a selection of comparator drugs that included linezolid, erythromycin, clindamycin, quinolones, and gentamicin were tested against 384 Staphylococcus aureus (176 oxacillin-resistant S. aureus [ORSA]) and 219 coagulase-negative staphylococci (CoNS; 162 oxacillin resistant) by reference microdilution (all strains) and agar dilution (30 strains) methods. The following results were noted for AZD2563. (Note that, for comparison only, a breakpoint of < or =4 microg/ml [the breakpoint of linezolid] was used for this study, although a susceptibility breakpoint for AZD2563 has not been determined.) For S. aureus, the MIC at which 50% of the isolates tested are inhibited (MIC(50)) was 1 microg/ml, the MIC(90) was 2 microg/ml, and the percent susceptibility was 100%. For CoNS, the MIC(50) was 0.5 microg/ml, the MIC(90) was 1 microg/ml, and the percent susceptibility was 100%. ORSA and OR-CoNS strains were equally inhibited by AZD2563 and linezolid. AZD2563 demonstrated antistaphylococcal activity comparable to that of linezolid.

Spectrum and potency evaluation of a new oxazolidinone, linezolid: report from the SENTRY Antimicrobial Surveillance Program, 1998-2000

Resistance (R) among Gram-positive cocci has escalated in the last two decades to levels necessitating the development and use in the newer drug classes, oxazolidinones (linezolid) and streptogramins (quinupristin/dalfopristin [Q/D]). The SENTRY Antimicrobial Surveillance Program has monitored these classes before, during and after their release by various regulatory agencies. Over 30,000 Gram-positive strains were tested against >30 drugs by reference broth microdilution methods between 1998-2000 in four geographic regions (Asia-Western Pacific [APAC], Europe [EU], Latin America [LA], North America [NA]). The tested strains were 23,188 staphylococci; 5,103 enterococci and 2,045 streptococci. Among staphylococci, linezolid was active against all isolates (MICs, < or =4 microg/ml) regardless of susceptibility patterns of other antimicrobial agents. Similar results were noted for vancomycin (includes one VISA from Hong Kong), teicoplanin, and Q/D (<1% R). Gatifloxacin had the widest spectrum among fluoroquinolones (FQ) against Staphylococcus aureus (1.5-9.2% R) and coagulase-negative staphylococci (0.8-4.0%). Linezolid was also active against all enterococci (MIC50 and (90,) 2 microg/ml). Q/D was active against only 75.3% of vancomycin-resistant enterococci (VRE). The VRE rate was highest in NA (12.4%) > EU (3.2%) > LA (1.6%) > APAC (1.3%). Among streptococci, linezolid was consistently active (MIC(90,) 1 microg/ml) as were the glycopeptides and Q/D. Variable penicillin-R (MIC, > or = 2 microg/ml) was observed among regions: EU (32.5%) > APAC (15.1%) > LA (13.8%) > NA (9.6%), and macrolide-R was higher in EU (40.3%). Ciprofloxacin-R at > or =4 microg/ml in streptococcal strains was noted world wide highest in viridans group streptococci (18.4-25.6%). Linezolid remained active (MIC, < or =4 microg/ml) against all Gram-positive species strains tested in the SENTRY Program (1998-2000). Q/D, glycopeptides and newer FQ compounds were generally less effective in vitro. It remains a prudent practice to continue surveillance programs to detect emerging resistance patterns and recognize significant regional variations in the oxazolidinone susceptibilities.

A multicenter evaluation of linezolid antimicrobial activity in North America

Overall, 141 centers in North America enrolled in this international surveillance study designed to evaluate the in vitro antimicrobial activity and spectrum of linezolid, a new oxazolidinone. Each participant tested the susceptibility of clinical isolates of staphylococcal species (n = 85) against 12 drugs, and enterococcal species (n = 40) against 6 drugs using reference broth microdilution trays; and of streptococcal species (n = 25) against 6 drugs using Etests (AB BIODISK, Solna, Sweden). Quality control testing was conducted using recommended strains, and verification of resistance to linezolid and select other agents was performed by a regional monitor. Of the 20,161 isolates collected from sites across the United States (US; n = 132) and Canada (n = 9), 18,307 were included in this analysis. Oxacillin resistance occurred in 38.7 and 70.6% of Staphylococcus aureus and coagulase-negative staphylococcal (CoNS) isolates, respectively. Vancomycin resistance was reported in 65.9 and 2.6% of Enterococcus faecium and E. faecalis, respectively. Penicillin resistance occurred in 37.2% of Streptococcus pneumoniae, 17.5% constituting high-level resistance (MIC, > or =2 microg/ml). The MIC(90) for linezolid was 1 microg/ml for streptococci, 2 microg/ml for enterococci and CoNS isolates, and 4 microg/ml for S. aureus. Using the US FDA-recommended susceptible breakpoints for linezolid, there were no confirmed reports of linezolid resistance (i.e., MIC > or =8 microg/ml). The occurrence of linezolid MICs was unimodal and generally varied between, 1-4 microg/ml for staphylococci (94% of recorded results), 1-2 microg/ml for enterococci (93%), and 0.5-1 microg/ml for streptococci (85%). Susceptibility to linezolid was not influenced by susceptibility to other antiicrobials such as vancomycin, beta-lactams or macrolides. Only linezolid was universally active against essentially all tested Gram-positive specimens. The unimodal susceptibility pattern is indicative of excellent and near complete activity against key Gram-positive pathogens including multiply resistant strains, but surveillance for emerging resistances (rare) and the performance of routine susceptibility tests to guide patient therapy seems prudent.

In vitro evaluation of AZD2563, a new oxazolidinone, tested against unusual gram-positive species

The recently introduced oxazolidinone, linezolid, has a spectrum and potency directed against Gram-positive organisms, including antimicrobial-resistant isolates. The newest agent in this class, AZD2563 was tested against uncommonly isolated Gram-positive species to establish the breadth of its spectrum. By reference broth microdilution methods, 120 strains were tested (48 Corynebacterium spp., 10 species; 27 Listeria spp., 2 species; 11 Micrococcus spp., 2 species; 23 Bacillus spp., 3 species; 6 Stomatococcus mucilaginosus and one strain each of 5 other species) against AZD2563 and compared to eight other agents. The AZD2563/linezolid MIC(50;) % inhibited at < or =4 microg/mL were: for corynebacteria (0.25/0.25 microg/mL; 100/100%), Listeria spp. (2/2 microg/mL; 100/100%), Micrococcus spp. (1/1 microg/mL; 100/100%), Bacillus spp. (0.5/1 microg/mL; 100/100%), and S mucilaginosus (0.5/1 microg/mL; 100/100%). Using the MIC(90) values, AZD2563 was slightly more potent than linezolid (two-fold). Only four genus- species groups had AZD2563 MICs of strains at 2 microg/mL (Aerococcus, Leuconostoc, Listeria, Rhodococcus), all other isolates were inhibited by < or = 1 microg/mL. The AZD2563 potency and spectrum versus these rarer species was at least equal to linezolid, including some strains resistant to penicillins, macrolides-lincosamides, and fluoroquinolones.

Linezolid-resistant Enterococcus faecium isolated from a patient without prior exposure to an oxazolidinone: report from the SENTRY Antimicrobial Surveillance Program

A patient case report describes an Enterococcus faecium strain isolated from a blood culture that was resistant to linezolid (MIC, 8 microg/mL; G2576U mutation of 23S rRNA). Co-resistances were identified for vancomycin, ampicillin, macrolides, fluoroquinolones, chloramphenicol, rifampin, gentamicin (high-level), nitrofurantoin and trimethoprim/sulfamethoxazole. Etest (AB BIODISK, Solna, Sweden) and disk diffusion results also detected the oxazolidinone resistance pattern. Laboratories should be aware of the rare possibility of these strains occurring during linezolid therapy or spontaneously (this case) in contemporary practice, and have in vitro susceptibility methods available capable of detecting oxazolidinone resistance.