Linezolid resistance since 2001: SENTRY Antimicrobial Surveillance Program

Antibacterial activity of 2-(2',4'-dibromophenoxy)-4,6-dibromophenol from Dysidea granulosa

2-(2′,4′-Dibromophenoxy)-4,6-dibromophenol isolated from the marine sponge Dysidea granulosa (Bergquist) collected off the coast of Lakshadweep islands, Indian Ocean, exhibited potent and broad spectrum in-vitro antibacterial activity, especially against methicillin resistant Staphylococcus aureus (MRSA), methicillin sensitive Staphylococcus aureus (MSSA), vancomycin resistant Enterococci (VRE), vancomycin sensitive Enterococci (VSE) and Bacillus spp. Minimal inhibitory concentration (MIC) was evaluated against 57 clinical and standard strains of Gram positive and Gram negative bacteria. The observed MIC range was 0.117–2.5 μg/mL against all the Gram positive bacteria and 0.5–2 μg/mL against Gram negative bacteria. The in-vitro antibacterial activity observed was better than that of the standard antibiotic linezolid, a marketed anti-MRSA drug. The results establish 2-(2′,4′-dibromophenoxy)-4,6-dibromophenol, as a potential lead molecule for anti-MRSA and anti-VRE drug development.

ZAAPS International Surveillance Program (2007) for linezolid resistance: results from 5591 Gram-positive clinical isolates in 23 countries

The 2007 ZAAPS Program reports the results from the 6th year of oxazolidinone (linezolid) resistance surveillance among Gram-positive pathogens from 23 nations. For 2007, a total of 5591 organisms were systematically sampled from Asia, Australia, Canada, Europe, and Latin America including Staphylococcus aureus (3000 isolates, 38.2% methicillin resistant), coagulase-negative staphylococci (CoNS, 716 isolates), enterococci (906 isolates), Streptococcus pneumoniae (452 isolates), viridans group streptococci (155 isolates), and beta-hemolytic streptococci (362 isolates). The overall linezolid MIC distribution (MIC(50) and MIC(90) at 1 and 2 microg/mL, respectively) was unchanged since 2002. At published linezolid breakpoints (, or = 2 microg/mL), all streptococci were susceptible; however, resistance was observed very rarely among S. aureus (0.03%), CoNS (0.28%), and the enterococci (0.11%, 0.55% intermediate). These oxazolidinone-nonsusceptible isolates occurred in Ireland, Italy, China, and Brazil (9 strains), and the rate was not increased since 2006. The detected mechanism of resistance was G2576 target mutations; no cfr-mediated patterns were observed. Clonal outbreaks with patient-to-patient dissemination were documented in 1 Italian site. Linezolid appears to retain excellent activity against monitored Gram-positive pathogens at a level of >99.8%.

Genome sequencing of linezolid-resistant Streptococcus pneumoniae mutants reveals novel mechanisms of resistance

Linezolid is a member of a novel class of antibiotics, with resistance already being reported. We used whole-genome sequencing on three independent Streptococcus pneumoniae strains made resistant to linezolid in vitro in a step-by-step fashion. Analysis of the genome assemblies revealed mutations in the 23S rRNA gene in all mutants including, notably, G2576T, a previously recognized resistance mutation. Mutations in an additional 31 genes were also found in at least one of the three sequenced genomes. We concentrated on three new mutations that were found in at least two independent mutants. All three mutations were experimentally confirmed to be involved in antibiotic resistance. Mutations upstream of the ABC transporter genes spr1021 and spr1887 were correlated with increased expression of these genes and neighboring genes of the same operon. Gene inactivation supported a role for these ABC transporters in resistance to linezolid and other antibiotics. The hypothetical protein spr0333 contains an RNA methyltransferase domain, and mutations within that domain were found in all S. pneumoniae linezolid-resistant strains. Primer extension experiments indicated that spr0333 methylates G2445 of the 23S rRNA and mutations in spr0333 abolished this methylation. Reintroduction of a nonmutated version of spr0333 in resistant bacteria reestablished G2445 methylation and led to cells being more sensitive to linezolid and other antibiotics. Interestingly, the spr0333 ortholog was also mutated in a linezolid-resistant clinical Staphylococcus aureus isolate. Whole-genome sequencing and comparative analyses of S. pneumoniae resistant isolates was useful for discovering novel resistance mutations.

Bacteremia caused by an Enterococcus faecalis isolate with high-level linezolid resistance in a teenager with Crohn's disease

Linezolid is an antibiotic used to treat highly resistant infections, including vancomycin-resistant enterococci and methicillin-resistant Staphylococcus aureus. Enterococcus faecalis bacteremia occurs in pediatric patients. We present a teenager admitted for bacteremia caused by E faecalis with a distinctive pattern of resistance to linezolid. This organism has the highest MIC to linezolid reported in the literature to date.

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.

In vitro activity of TR-700, the antibacterial moiety of the prodrug TR-701, against linezolid-resistant strains

TR-701 is the orally active prodrug of TR-700, a novel oxazolidinone that demonstrates four- to eightfold-greater activity than linezolid (LZD) against Staphylococcus and Enterococcus spp. In this study evaluating the in vitro sensitivity of LZD-resistant isolates, TR-700 demonstrated 8- to 16-fold-greater potency than LZD against all strains tested, including methicillin-resistant Staphylococcus aureus (MRSA), strains of MRSA carrying the mobile cfr methyltransferase gene, and vancomycin-resistant enterococci. The MIC(90) for TR-700 against LZD-resistant S. aureus was 2 microg/ml, demonstrating the utility of TR-700 against LZD-resistant strains. A model of TR-700 binding to 23S rRNA suggests that the increased potency of TR-700 is due to additional target site interactions and that TR-700 binding is less reliant on target residues associated with resistance to LZD.

Community-Associated Methicillin-Resistant Staphylococcus aureus in the Pediatric Population

PURPOSE

To review the epidemiology and prevalence of community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA), define the differences between community-acquired and hospital-acquired strains, highlight the advantages and disadvantages of antibiotics commonly used to treat infections caused by this pathogen, and identify strategies to limit the spread of this organism and prevent future outbreaks.

DATA

Literature was accessed through MEDLINE using the search terms community-acquired methicillin-resistant Staphylococcus aureus, community-associated methicillin-resistant Staphylococcus aureus, CA-MRSA, pediatrics, and children. Articles evaluated were published in the English language and limited to human studies. References of literature identified by initial search techniques were reviewed for additional relevant articles.

DATA SYNTHESIS

Community-associated methicillin-resistant Staphylococcus aureus has become a prominent pathogen in pediatric patients in the last ten years. Its increasing prevalence has been reported throughout the United States, and it is the cause of over one half of all skin and soft tissue infections seen in many hospitals and emergency departments. The risk factors for infection with this pathogen differ from those associated with hospital-acquired strains. Mild to moderate infections can generally be treated with oral antibiotics, while more serious infections may require parenteral therapy. Sulfamethoxazole/trimethoprim and clindamycin are the preferred oral agents due to their efficacy, tolerability, well established side effect profiles, and cost. Vancomycin is the standard of care for parenteral therapy, although clindamycin is an acceptable parenteral alternative. More costly agents such as linezolid, daptomycin, and quinupristin/dalfopristin should be reserved for patients with severe infections, multiple allergies, or in strains with unusual resistance patterns. The best way to prevent and control outbreaks is to maintain standard infection control procedures including excellent hand hygiene.

CONCLUSIONS

CA-MRSA is a serious and frequently seen pathogen. Proper antibiotic selection that takes into account patient factors, disease severity, ease of administration, and cost is necessary to maximize favorable patient outcomes.

Linezolid for the treatment of infections caused by Gram-positive pathogens in China

In this randomised, double-blind, comparator-controlled, multicentre study conducted in China, 142 hospitalised patients aged 18-75 years with pneumonia (n=80) or complicated skin and soft-tissue infection (cSSTI) (n=62) due to suspected or known Gram-positive pathogens were randomised (1:1) to receive either linezolid 600mg (n=71) or vancomycin 1g in patients aged < or =60 years or 0.75g in patients aged >60 years (n=71) intravenously every 12h. The duration of treatment was 10-21 days for patients with pneumonia and 7-21 days for patients with cSSTI. Clinical outcomes were assessed at end-of-treatment (EOT) visit and follow-up (FU) visit 7-28 days post therapy. Staphylococcus aureus was the most common pathogen at baseline and most of these isolates were resistant to meticillin. All isolates were susceptible to linezolid and vancomycin. For the evaluable patients, the effective treatment rate for linezolid was higher than that for vancomycin at EOT (86.9% (53/61) vs. 61.7% (37/60)) and at FU (83.1% (49/59) vs. 64.9% (37/57)). Pathogen eradication rates for the microbiologically evaluable patients at FU were 79.2% (42/53) for linezolid and 61.5% (32/52) for vancomycin. The incidence of drug-related adverse events (AEs) was 25.4% (18/71) for linezolid and 16.9% (12/71) for vancomycin. Four (5.6%) linezolid-treated and eight (11.3%) vancomycin-treated patients discontinued the study drug because of an AE. Linezolid was well tolerated and effective for the treatment of infections caused by Gram-positive pathogens, including meticillin-resistant S. aureus.

Antimicrobial activity of DC-159a, a new fluoroquinolone, against 1,149 recently collected clinical isolates

The activity of DC-159a, a novel orally administered fluorinated quinolone, was evaluated by reference broth microdilution or agar dilution methods against 1,149 recently collected clinical isolates from five continents. Against pathogens associated with community-acquired respiratory tract infections (CA-RTIs), the MIC(90)s were 0.12 microg/ml for Streptococcus pneumoniae, 0.015 to 0.03 microg/ml for Haemophilus influenzae, 0.03 microg/ml for Moraxella catarrhalis, and 0.12 microg/ml for beta-hemolytic streptococci. Similarly, DC-159a was potent against various types of staphylococci (MIC(90) range, 0.03 to 2 microg/ml), Enterococcus faecalis (MIC(90), 4 microg/ml), wild-type isolates of the family Enterobacteriaceae (MIC(90) range, 0.06 to 2 microg/ml), wild-type Pseudomonas aeruginosa (MIC(90), 2 microg/ml), and Acinetobacter spp. (MIC(90), 0.12 microg/ml). Fluoroquinolone-nonsusceptible organism subsets usually had elevated DC-159a MICs, but the MICs were often two- to fourfold lower than those of levofloxacin and moxifloxacin. In conclusion, DC-159a appears to possess a balanced broad spectrum of activity that exceeds the activities of the currently marketed fluoroquinolones, especially against pathogens that cause CA-RTIs.

The use of linezolid in the treatment of infected total joint arthroplasty

Fourteen patients with a diagnosis of infected total joint arthroplasty treated by 1 or 2-stage revision and a course of oral linezolid were reviewed. Patients were assessed according to McPherson stage, inflammatory markers, nature of surgery, use of antibiotics, pathogen isolated, and outcome at follow-up. Pathogens isolated were coagulase-negative staphylococcus, multiresistant Staphylococcus aureus, Enterobacter cloacae, and mixed growth. McPherson stages were 1 IB2, 1 IA3, 1 II A2, 3IIIA2, 2 IIIB1, 3 IIIB2, 1 IIIB3, 1 IIIC2, and 1 IIIC3. All patients showed resolution of infection, with normalization of inflammatory markers after treatment. Mean length of follow-up is 32.7 months (range, 9-44 months). Comparison is drawn with previous studies highlighting the good results achievable with the use of this antibiotic. Although no substitute for adequate surgical management, it does allow oral treatment and therefore avoids the difficulties associated with long-term intravenous antibiotic therapy.

In vitro susceptibility of viridans group streptococci isolated from blood in southwest Finland in 1993-2004

We studied in vitro activity against invasive viridans group streptococci (VGS) of penicillin and 4 newer antibiotics, i.e. telithromycin, linezolid, levofloxacin and quinupristin-dalfopristin. Also 7 other antibiotics were tested. Antibiotic susceptibility of 263 VGS blood isolates, collected from southwest Finland during a 12-y period was determined. We wished to discover whether there is an increasing trend of antimicrobial resistance among VGS in Finland. Our results showed that penicillin is still a good choice for treating VGS infections based on the considerably low resistance percentage, 2.3%. Also newer antibiotics showed good in vitro activity: susceptibilities for telithromycin, linezolid and levofloxacin were 100%, 98.9% and 94.6%, respectively. However, quinupristin-dalfopristin was not as effective as described in previous studies, with only 57% susceptibility.

Determination of risk factors associated with isolation of linezolid-resistant strains of vancomycin-resistant Enterococcus

OBJECTIVE

To identify independent risk factors associated with isolation of linezolid-resistant, vancomycin-resistant Enterococcus (VRE).

DESIGN

A retrospective, case-case-control study.

SETTING

A tertiary care, academic medical center.Methods. VRE isolates from clinical cultures were retrospectively analyzed for linezolid resistance during our 18-month study period. Clinical data were obtained from electronic patient records, and the risk factors associated with isolation of linezolid-resistant VRE were determined by comparison of 2 case groups with a control group.

RESULTS

A total of 20% of the VRE isolates analyzed during the study period were linezolid resistant, and resistant isolates were most commonly recovered from the urine (40% of resistant isolates). Risk factors found to be associated with isolation of linezolid-resistant VRE were peripheral vascular disease and/or the receipt of a solid organ transplant, total parenteral nutrition, piperacillin-tazobactam, and/or cefepime. Only 25% of patients from whom linezolid-resistant VRE was isolated had previous linezolid exposure, and in the multivariate model this was not found to be a risk factor associated with the isolation of linezolid-resistant VRE.

CONCLUSIONS

The results of this analysis suggest that there is horizontal transmission of linezolid-resistant VRE in our institution and highlight the need for improved infection control measures. Furthermore, the high incidence of linezolid-resistant VRE demands a reassessment of our empirical antibiotic selection for patients infected with VRE.

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.

LEADER surveillance program results for 2006: an activity and spectrum analysis of linezolid using clinical isolates from the United States (50 medical centers)

Surveillance for emerging linezolid resistance among commonly occurring Gram-positive pathogens in the United States began with the 2002 ZAAPS program and more recently (2004) expanded as the LEADER program. The 2006 LEADER program processed 5374 strains from 50 medical centers (100 per site) located within the 9 US census regions; species and number tested by broth microdilution (% linezolid susceptible) included Staphylococcus aureus (2913, >99.9), coagulase-negative staphylococci (CoNSs) (808, 98.4), enterococci (547, 97.4), Streptococcus pneumoniae (546, 100.0), viridans group streptococci (189, 100.0), and beta-hemolytic streptococci (371, 100.0). In addition to 1 linezolid-nonsusceptible S. aureus, 3 strains were daptomycin-nonsusceptible, 4 were quinupristin/dalfopristin-intermediate, 2 were vancomycin-intermediate (vancomycin MIC values, 4 mug/mL), and all were methicillin-resistant S. aureus. Among the linezolid-resistant isolates (1 S. aureus, 13 CoNSs, 3 Enterococcus faecalis, and 10 Enterococcus faecium isolates), all but 3 Staphylococcus epidermidis isolates had the G2567T mutation. Overall, 99.55% of the tested 2006 LEADER program isolates remained susceptible to linezolid at current Clinical and Laboratory Standards Institute breakpoints.

Increasing incidence of methicillin-resistant Staphylococcus aureus in hand infections: a 3-year county hospital experience

BACKGROUND

Staphylococcus aureus is the most common cause of skin and soft-tissue infections. Methicillin-resistant S. aureus and community-acquired methicillin-resistant S. aureus have shown an increase in prevalence among soft-tissue infections over the past several years, with overall rates approaching 50 percent at the authors' institution in 2002. The object of this study was to determine the incidence of methicillin-resistant S. aureus with respect to hand infections, the antibiotic resistance pattern of methicillin-resistant S. aureus isolates, and implications for a change in antibiotic treatment algorithms for hand infections.

METHODS

A retrospective chart review of 761 patients with hand infections tracked by International Classification of Diseases, 9th Revision codes for finger or hand abscesses from 2001 to 2003 was performed at Parkland Memorial Hospital, Dallas, Texas. Culture results were obtained from 436 patients and analyzed for type of organism, and sensitivity profiles were obtained for all methicillin-resistant S. aureus isolates.

RESULTS

The median age of 761 patients was 40 years (range, 16 to 77 years); 71 percent were male and 28 percent were female. Of the 436 cultures reviewed, 371 (85 percent) had organisms identified. Methicillin-resistant S. aureus was the dominant single organism in hand infections cultured in all 3 years. The overall methicillin-resistant S. aureus rate was 61 percent of all hand infections in 2003. The percentage of S. aureus isolates identified as methicillin-resistant S. aureus increased from 55 percent to 78 percent over 3 years, up from 34 percent in 2001. Fortunately, 86 percent of these methicillin-resistant S. aureus isolates demonstrated sensitivity to conventional antibiotics, but a trend of resistance is developing.

CONCLUSIONS

The incidence of community-acquired methicillin-resistant S. aureus increased from 34 percent to 61 percent over a 3-year period at the authors' county institution. An increasing trend of resistance patterns among conventional antibiotics was also demonstrated. As a result of this study, the treatment algorithm at Parkland Memorial Hospital has been modified to include abscess drainage accompanied by an antibiotic regimen targeted specifically at methicillin-resistant S. aureus. These data also have implications for broader application regarding simple skin infections and current antibiotic treatment algorithms.

Dual targeting of GyrB and ParE by a novel aminobenzimidazole class of antibacterial compounds

A structure-guided drug design approach was used to optimize a novel series of aminobenzimidazoles that inhibit the essential ATPase activities of bacterial DNA gyrase and topoisomerase IV and that show potent activities against a variety of bacterial pathogens. Two such compounds, VRT-125853 and VRT-752586, were characterized for their target specificities and preferences in bacteria. In metabolite incorporation assays, VRT-125853 inhibited both DNA and RNA synthesis but had little effect on protein synthesis. Both compounds inhibited the maintenance of negative supercoils in plasmid DNA in Escherichia coli at the MIC. Sequencing of DNA corresponding to the GyrB and ParE ATP-binding regions in VRT-125853- and VRT-752586-resistant mutants revealed that their primary target in Staphylococcus aureus and Haemophilus influenzae was GyrB, whereas in Streptococcus pneumoniae it was ParE. In Enterococcus faecalis, the primary target of VRT-125853 was ParE, whereas for VRT-752586 it was GyrB. DNA transformation experiments with H. influenzae and S. aureus proved that the mutations observed in gyrB resulted in decreased susceptibilities to both compounds. Novobiocin resistance-conferring mutations in S. aureus, H. influenzae, and S. pneumoniae were found in gyrB, and these mutants showed little or no cross-resistance to VRT-125853 or VRT-752586 and vice versa. Furthermore, gyrB and parE double mutations increased the MICs of VRT-125853 and VRT-752586 significantly, providing evidence of dual targeting. Spontaneous frequencies of resistance to VRT-752586 were below detectable levels (<5.2x10(-10)) for wild-type E. faecalis but were significantly elevated for strains containing single and double target-based mutations, demonstrating that dual targeting confers low levels of resistance emergence and the maintenance of susceptibility in vitro.

Role of linezolid in the treatment of orthopedic infections

Gram-positive organisms, particularly staphylococci and streptococci, are responsible for the majority of bone and joint infections. The rising incidence of antimicrobial resistance among Staphylococcus aureus, coagulase-negative staphylococci and enterococci means that novel antibiotics with unique mechanisms of antimicrobial activity are needed, especially in orthopedic infections. Linezolid is the first of the oxazolidinones, a new class of antibacterial agents particularly effective against Gram-positive infections including methicillin- and vancomycin-resistant strains. With an excellent oral bioavailability and acceptable safety profile, linezolid offers a valuable alternative to more traditional therapies, such as glycopeptides. No large randomized trials have been published on its use in patients with orthopedic infections, but early results are encouraging. Reported adverse events, especially bone marrow suppression and optic neuropathy seen with prolonged administration, mean that treatment of such patients must be undertaken with careful follow-up of laboratory tests. Until now, little resistance has been reported.

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.

Substituent activity relationship studies on new azolo benzoxazepinyl oxazolidinones

In an effort to discover potent antibacterials based on the entropically favored 'bioactive conformation' approach, a series of novel tricyclic molecules mimicking the conformationally constrained structure of Linezolid is reported. Based on the initial tricyclic molecule 1, the benzazepine derivative 2 was designed where the tricyclic structure had more flexibility around C-N bond compared to 1. While, the molecule 2 was less active, the molecule 3 showed promising antibacterial activity presumably after having obtained rigidity due to pyrrole ring. The syntheses, SAR studies, and evaluation of 3 as a lead compound are reported.

The clinical impact of linezolid susceptibility reporting in patients with vancomycin-resistant enterococci

Linezolid remains a mainstay of therapy for vancomycin-resistant enterococci (VREs), but resistance has emerged. We describe a cohort of 20 patients with linezolid-intermediate or resistant VRE (LIRVRE) reported by Etest and disk diffusion testing, 18 of whom demonstrated linezolid susceptibility by agar dilution on further investigation. Patients with reported LIRVRE were matched based on culture site and enterococcal species to patients with linezolid-susceptible VRE (LSVRE) in a 1:3 ratio. Patients with reported LIRVRE developed more nosocomial infections (P = .04), had more central lines placed (P = .04), and underwent more computed tomography scans related to VRE infection (P = .02). Multivariate analysis revealed increased surgical procedures related to VRE infections (P = .008), increased linezolid use during hospital stay (P = .03), and delayed culture and susceptibility results compared with those with LSVRE (P = .006). Therefore, inaccurate detection and reporting of LIRVRE by disk diffusion and Etest is associated with increased patient morbidity and resource use.

Management of Community-Associated Methicillin-ResistantStaphylococcus aureusInfections in Children

In recent years, community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) has emerged as a pathogen in children without established risk factors, and its prevalence in the United States is increasing. Although many CA-MRSA infections are mild, primarily involving the skin and soft tissues, the organism can cause serious, invasive, and life-threatening infections. To provide a comprehensive review of the epidemiology, clinical features, therapy, and prevention of CA-MRSA infections in children, we performed MEDLINE (1966-January 2006) and Cochrane Library searches, and reviewed abstracts for relevance to S. aureus infections. Only articles pertaining to CA-MRSA infections in pediatrics were closely examined. As a genetically distinct pathogen, CA-MRSA is generally susceptible to multiple non-beta-lactam antimicrobials. The optimal treatment for CA-MRSA infections in pediatric patients has not been well studied. Common antibiotics used include clindamycin, trimethoprim-sulfamethoxazole, vancomycin, and rifampin. Rational empiric antimicrobial therapy for infections caused by S. aureus requires consideration of the possibility of methicillin resistance. The local prevalence and susceptibilities of CA-MRSA, severity of infection, and individual risk factors should be considered in selecting treatment.

Epidemiological Profile of Linezolid‐Resistant Coagulase‐Negative Staphylococci

BACKGROUND

Surveillance studies have shown that <0.1% of coagulase-negative staphylococci are linezolid resistant; however, at our institution, 4% of such organisms were found to be resistant. We investigated the risk factors for and the epidemiological profile of linezolid-resistant coagulase-negative staphylococci.

METHODS

Susceptibility testing and pulsed-field gel electrophoresis were performed to analyze the genetic relatedness of both linezolid-resistant and linezolid-susceptible isolates. Clinical data were retrieved from medical records, and a case-case-control study was performed to identify unique risk factors for linezolid resistance.

RESULTS

Isolates recovered from 25 patients with linezolid-resistant coagulase-negative staphylococci were examined; all but 1 of the isolates were identified as Staphylococcus epidermidis, and all but 1 had a minimum inhibitory concentration of linezolid of >256 microg/mL. Pulsed-field gel electrophoresis showed that 21 (84%) of 25 linezolid-resistant isolates exhibited genetic relatedness, whereas linezolid-susceptible isolates were of diverse clones. Unique, independent predictors of linezolid resistance included receipt of linezolid in the 3 months preceding isolation of the coagulase-negative staphylococci (odds ratio, 20.6; 95% confidence interval, 5.8-73.0).

CONCLUSION

Linezolid-resistant coagulase-negative staphylococci have emerged at our institution and are predominately of a single clone. We believe that the most likely scenario to explain this emergence is that person-to-person spread of linezolid-resistant coagulase-negative staphylococci led to establishment of skin colonization with the strain. Subsequent use of linezolid was followed by selection of the linezolid-resistant strain, which then became the dominant skin flora. The potential for a parallel scenario involving clonal dissemination followed by selection of linezolid-resistant methicillin-resistant Staphylococcus aureus is a real possibility.

Performance accuracy of antibacterial and antifungal susceptibility test methods: report from the College of American Pathologists Microbiology Surveys Program (2001-2003)

CONTEXT

The College of American Pathologists Microbiology Surveys Program provides external proficiency samples that monitor the performance of nearly 3000 laboratories that perform and report antimicrobial susceptibility tests.

OBJECTIVE

To summarize results obtained with bacterial and yeast challenge samples (2001 through 2003).

DESIGN

One organism every 4 months was tested by surveys participants against antibacterials/antifungals by routinely used methods. Reports were graded by interpretive category (susceptible, intermediate, resistant) based on an 80% consensus of referees/participants.

RESULTS

The most common antibacterial test methods/systems were Vitek (38%-43%), MicroScan (39%-43%), and the disk diffusion test (14%-15%), although Etest was most used for fastidious species. YeastOne was the dominant antifungal test (50%-55%). Antifungal results demonstrated continuous, improved accuracy (83%-88%), highest for YeastOne (96%) and broth microdilution (95%) methods. Antibacterial test accuracy was consistently greater than 97% against gram-positive organism challenges and greater than 98% against gram-negative challenges. For gram-negative strains with well-characterized resistance mechanisms, the accuracy by method was disk diffusion greater than broth microdilution greater than automated systems. Major problems identified were (1) Haemophilus influenzae control ranges require re-evaluation, (2) overuse of beta-lactamase tests, (3) errors among Enterococcus faecium against penicillins (Vitek 2, MicroScan), (4) false-susceptible results with trimethoprim/sulfamethoxazole against coagulase-negative staphylococci (MicroScan), (5) macrolide false-susceptibility for beta-hemolytic streptococcus (MicroScan), (6) flawed reporting for antimicrobials not active at the infection site, (7) use of outdated interpretive criteria, and (8) failure to follow Clinical and Laboratory Standards Institute testing/reporting recommendations.

CONCLUSIONS

Susceptibility tests were generally performing satisfactorily as measured by the surveys, but serious errors were identified with some drug/organism combinations that may require action by the Clinical and Laboratory Standards Institute and/or the Food and Drug Administration.

In vitro characterization of the antibacterial spectrum of novel bacterial type II topoisomerase inhibitors of the aminobenzimidazole class

Antibiotics with novel mechanisms of action are becoming increasingly important in the battle against bacterial resistance to all currently used classes of antibiotics. Bacterial DNA gyrase and topoisomerase IV (topoIV) are the familiar targets of fluoroquinolone and coumarin antibiotics. Here we present the characterization of two members of a new class of synthetic bacterial topoII ATPase inhibitors: VRT-125853 and VRT-752586. These aminobenzimidazole compounds were potent inhibitors of both DNA gyrase and topoIV and had excellent antibacterial activities against a wide spectrum of problematic pathogens responsible for both nosocomial and community-acquired infections, including staphylococci, streptococci, enterococci, and mycobacteria. Consistent with the novelty of their structures and mechanisms of action, antibacterial potency was unaffected by commonly encountered resistance phenotypes, including fluoroquinolone resistance. In time-kill assays, VRT-125853 and VRT-752586 were bactericidal against Staphylococcus aureus, Streptococcus pneumoniae, Enterococcus faecalis, and Haemophilus influenzae, causing 3-log reductions in viable cells within 24 h. Finally, similar to the fluoroquinolones, relatively low frequencies of spontaneous resistance to VRT-125853 and VRT-752586 were found, a property consistent with their in vitro dual-targeting activities.

Burn wound infections

Burns are one of the most common and devastating forms of trauma. Patients with serious thermal injury require immediate specialized care in order to minimize morbidity and mortality. Significant thermal injuries induce a state of immunosuppression that predisposes burn patients to infectious complications. A current summary of the classifications of burn wound infections, including their diagnosis, treatment, and prevention, is given. Early excision of the eschar has substantially decreased the incidence of invasive burn wound infection and secondary sepsis, but most deaths in severely burn-injured patients are still due to burn wound sepsis or complications due to inhalation injury. Burn patients are also at risk for developing sepsis secondary to pneumonia, catheter-related infections, and suppurative thrombophlebitis. The introduction of silver-impregnated devices (e.g., central lines and Foley urinary catheters) may reduce the incidence of nosocomial infections due to prolonged placement of these devices. Improved outcomes for severely burned patients have been attributed to medical advances in fluid resuscitation, nutritional support, pulmonary and burn wound care, and infection control practices.

Linezolid-resistant Staphylococcus aureus in two pediatric patients receiving low-dose linezolid therapy

We report 2 sisters with hyper-IgE syndrome treated with daily suppressive dosages of linezolid (LZD) who developed LZD-resistant Staphylococcus aureus carrying the G2576T mutation in the 23S rRNA gene. Molecular typing suggested transmission of the resistant strain from one sister to the other. LZD-susceptible S. aureus was isolated 2 months after LZD discontinuation. LZD-resistant S. aureus remains rare but may occur while receiving suppressive therapy.

Burn wound infections

Burns are one of the most common and devastating forms of trauma. Patients with serious thermal injury require immediate specialized care in order to minimize morbidity and mortality. Significant thermal injuries induce a state of immunosuppression that predisposes burn patients to infectious complications. A current summary of the classifications of burn wound infections, including their diagnosis, treatment, and prevention, is given. Early excision of the eschar has substantially decreased the incidence of invasive burn wound infection and secondary sepsis, but most deaths in severely burn-injured patients are still due to burn wound sepsis or complications due to inhalation injury. Burn patients are also at risk for developing sepsis secondary to pneumonia, catheter-related infections, and suppurative thrombophlebitis. The introduction of silver-impregnated devices (e.g., central lines and Foley urinary catheters) may reduce the incidence of nosocomial infections due to prolonged placement of these devices. Improved outcomes for severely burned patients have been attributed to medical advances in fluid resuscitation, nutritional support, pulmonary and burn wound care, and infection control practices.

Linezolid in prophylaxis against experimental aortic valve endocarditis due to Streptococcus oralis or Enterococcus faecalis

There are no experimental studies regarding the prophylactic efficacy of linezolid against infective endocarditis. Nonbacterial thrombotic endocarditis of the aortic valve was induced in rabbits by the insertion of a polyethylene catheter. Twenty-four hours later, animals were randomly assigned to a control group, and groups receiving either ampicillin (two doses of 40 mg/kg of body weight each, given intravenously, 2 h apart) or linezolid (a single per os dose of 75 mg/kg). The first dose of ampicillin and the single dose of linezolid were administered 0.5 and 1 h, respectively, prior to the intravenous inoculation of approximately 10(7) CFU of Streptococcus oralis or Enterococcus faecalis. Linezolid peak levels in rabbit serum were similar to the peak serum levels in humans following a 600-mg oral dose of linezolid. Linezolid prevented endocarditis in 87% of S. oralis-challenged rabbits (P < 0.001 versus controls; P = 0.026 versus ampicillin). In rabbits challenged with E. faecalis, linezolid prevented endocarditis in 73% (P = 0.003 versus controls; P = 0.049 versus ampicillin). Ampicillin prevented endocarditis due to S. oralis or due to E. faecalis in 47% (P = 0.005 versus controls) and in 30% (P = not significant versus controls) of the challenged animals, respectively. In conclusion, linezolid was effective as prophylaxis against endocarditis caused by a strain of S. oralis and to a lesser degree against that caused by a strain of E. faecalis. Its prophylactic efficacy was superior to that of ampicillin.

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.

Structure-based drug design meets the ribosome

The high-resolution structures of the bacterial ribosomal subunits and those of their complexes with antibiotics have advanced significantly our understanding of small-molecule interactions with RNA. The wealth of RNA structural data generated by these structures has allowed computational chemists to employ a drug discovery paradigm focused on RNA-based targets. The structures also show how target-based resistance affects antibiotics acting at the level of the ribosome. Not only are the sites pinpointed where different classes of antibiotics inhibit protein synthesis, but their orientations, relative dispositions, and unique mechanisms of action are also revealed at the atomic level. Both the 30S and the 50S ribosomal subunits have been shown to be "targets of targets", offering several adjacent, functionally relevant binding pockets for antibiotics. It is the detailed knowledge of these validated locations, or ribofunctional loci, plus the mapping of the resistance hot-spots that allow the rational design of next-generation antibacterials. When the structural information is combined with a data-driven computational toolkit able to describe and predict molecular properties appropriate for bacterial cell penetration and drug-likeness, a structure-based drug design approach for novel antibacterials shows great promise.

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).

Clinical Characteristics of Linezolid-Resistant Staphylococcus aureus Infections

Case reports have previously identified linezolid resistance in 6 clinical isolates of Staphylococcus aureus. We describe an additional case and discuss clinical characteristics of these patients. Invasive procedures, deep organ involvement, and presence of foreign material were predominant in these cases. Resistance followed prolonged (>21 days) linezolid therapy in most cases. The development of resistance to linezolid should be taken into account when selecting this drug as a therapeutic option.

Antimicrobial resistance of nosocomial strains of Staphylococcus aureus in Russia: results of a prospective study

A total of 879 Staphylococcus aureus clinical isolates from 17 medical institutions in different regions of Russia were tested. Susceptibility to 18 antimicrobials was determined by agar dilution in accordance with the NCCLS recommendations. The most potent antimicrobials were glycopeptides, linezolid, and fusidic acid, to which no resistance was found. Other antimicrobials with low frequency of non-susceptibility were mupirocin (0.3%), trimethoprim/sulfamethoxazole (0.8%), quinupristin/dalfopristin (1.8%) and rifampicin (7.0%). Fluoroquinolones displayed moderate activity (5.8% of non-susceptible strains to moxifloxacin, 9.1% to levofloxacin, 13.1% to ciprofloxacin). High rates of non-susceptibility were found to clindamycin (27.1%), gentamicin (30.7%), tetracycline (37.1%), erythromycin (39.6%) and chloramphenicol (43.1%). The prevalence of oxacillin-resistant S. aureus (ORSA) was 33.5% and varied from 0% to 89.5% in different hospitals. ORSA were isolated most frequently in the burn units (77.5%), intensive care units (54.8%), trauma and orthopedics units (42.1%). This is the first multicenter study published of antimicrobial resistance of S. aureus in Russia which meets international standards.

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.

Antimicrobial activity of isoprenoid-substituted xanthones from Cudrania cochinchinensis against vancomycin-resistant enterococci

Ten xanthones with one or two isoprenoid groups and a prenylated benzophenone isolated from roots of Cudrania cochinchinensis (Moraceae) were tested for their antimicrobial activities against vancomycin-resistant enterococci (VRE). Among these compounds, gerontoxanthone H exhibited considerable antibacterial activity against five VRE strains (VanA, VanB and VanC) (MICs = 1.56 microg/ml). Four xanthones, 1,3,7-trihydroxy-2-prenylxanthone, gerontoxanthone I, alvaxanthone and isoalvaxanthone, showed weaker antibacterial activity against these VREs (MICs = 3.13-6.25 microg/ml). .

Trimethoprim-sulfamethoxazole as a viable treatment option for infections caused by methicillin-resistant Staphylococcus aureus

OBJECTIVE

To review available data regarding the efficacy of trimethoprim-sulfamethoxazole (TMP-SMX) for the treatment of infections caused by methicillin-resistant Staphylococcus aureus (MRSA).

DATA SOURCES

A MEDLINE search was performed (January 1966-December 2003) using the search terms Staphylococcus aureus , sulfamethoxazole, trimethoprim, co-trimoxazole, and methicillin resistance. Abstracts from infectious diseases meetings also were reviewed.

DATA SYNTHESIS

The reported rate of TMP-SMX resistance in S. aureus is highly variable. From a mechanistic standpoint, TMP-SMX resistance among MRSA appears to be distinct from multidrug resistance, although some anecdotal reports suggest otherwise. Clonal outbreaks of MRSA resistant to TMP-SMX have been described; of these, the Brazilian clone has more often been resistant to TMP-SMX than the Iberian clone. Rates of TMP-SMX resistance are particularly high in institutions serving large numbers of patients infected by the human immunodeficiency virus, due to increased exposure for Pneumocystis prophylaxis. Limited studies and case reports have found TMP-SMX useful against infections caused by MRSA.

CONCLUSIONS

A large body of anecdotal data, but only one randomized clinical trial, indicates the effectiveness of TMP-SMX as a treatment for MRSA infections. Double-blind, randomized controlled trials are needed to compare the two available oral agents-TMP-SMX and linezolid-against MRSA.

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).

Mechanisms of action of newer antibiotics for Gram-positive pathogens

Certain Gram-positive bacteria, including meticillin-resistant Staphylococcus aureus, vancomycin-resistant enterococci, and quinolone-resistant Streptococcus pneumoniae have achieved the status of "superbugs", in that there are few or no antibiotics available for therapy against these pathogens. Only a few classes of novel antibiotics have been introduced in the past 40 years, and all since 1999, including the streptogramin combination quinupristin/dalfopristin (Synercid), the oxazolidinone linezolid, and the lipopeptide daptomycin. This review discusses the mechanisms of antibiotic action against Gram-positive pathogens, and resistance counter-mechanisms developed by Gram-positive bacteria, with emphasis on the newer agents.

Tigecycline: clinical evidence and formulary positioning

Tigecycline, is a novel broad-spectrum glycylcycline antibiotic, which has activity against a broad range of Gram-positive, Gram-negative, atypical, anaerobic and antibiotic-resistant bacteria. This includes activity against MRSA, VRE and penicillin resistant Streptococcus pneumoniae. Whilst exhibiting antibacterial activities typical of earlier tetracyclines, it has more potent activity against tetracycline-resistant organisms. Although a bacteriostatic compound in vitro, its effectiveness in clinical trials suggests that traditional laboratory thinking about using bacteriostatic drugs in serious infections needs to be revised. Unlike existing tetracyclines, tigecycline is only available as an intravenous preparation, is administered twice daily although its long half life and post-antibiotic effect may make once daily dosing possible, appears to have good tissue penetration (e.g. skin) and requires no adjustment in the presence of renal or hepatic diseases. It is efficacious in complicated skin and soft tissue infections and in intra-abdominal infections. In three trials, it was well tolerated despite increased frequency of nausea and vomiting. In the light of these early clinical data and the likelihood that this agent will become available for clinical use within the next 12-24 months, this review aims to summarise the key clinical data and potential formulary considerations for the future use of this agent, subject to further clinical trials and publication of clinical human data.

Effects of positional and geometrical isomerism on the biological activity of some novel oxazolidinones

Some novel oxazolidinone derivatives with benzotriazole as pendant have been synthesized and tested for antibacterial activity. Linearly attached benzotriazole derivative showed more potency compared to angular one in vitro. Out of E/Z-isomers of angularly attached derivatives E-isomer was found to be more potent than Z-isomer. Either less active or inactive molecules were obtained, when benzotriazole was replaced with benzimidazole, benzthiazole, or benzoxazole. Finally, thioacetamide analogue of linear compound gave a lead having activity similar to linezolid in vitro.

Antimicrobial activity of tigecycline (GAR-936) tested against 3498 recent isolates of Staphylococcus aureus recovered from nosocomial and community-acquired infections

Tigecycline is a novel 9-t-butylglycylamido derivative of minocycline that has demonstrated activity against a variety of Gram-positive and -negative bacterial pathogens. In vitro activity of tigecycline and comparator agents was determined for 3498 recent (2000-2003) strains of Staphylococcus aureus recovered from patients with either nosocomial or community-acquired infections. Oxacillin-susceptible and -resistant S. aureus from both patient populations displayed identical results for tigecycline (MIC(50) and MIC(90) results at 0.25 and 0.5 mg/L, respectively) and all strains were inhibited by 1 mg/L or less. While co-resistances to other antimicrobial classes were present in oxacillin-resistant strains, susceptibility to tigecycline remained unaffected, making the compound an attractive candidate for treatment of serious hospital as well as community-acquired staphylococcal infections.

Molecular detection of linezolid resistance in Enterococcus faecium and Enterococcus faecalis by use of 5' nuclease real-time PCR compared to a modified classical approach

A nucleotide transversion from guanine to uracil in the 23S rRNA confers linezolid resistance. We describe a real-time PCR using two Taqman probes that detects a single mutated allele among the genomes of Enterococcus faecium and Enterococcus faecalis. Results were confirmed by a classical approach involving LabChip technology assayed with an Agilent Bioanalyzer 2100.