Survey of infections due to Staphylococcus species: frequency of occurrence and antimicrobial susceptibility of isolates collected in the United States, Canada, Latin America, Europe, and the Western Pacific region for the SENTRY Antimicrobial Surveillance Program, 1997-1999

Benzyl alcohol and ethanol can enhance the pathogenic potential of clinical Staphylococcus epidermidis strains

BACKGROUND

Staphylococcus epidermidis is the most frequent cause of health care-associated infections, particularly in neonates and patients with indwelling catheters. The pathogenesis of infections caused by this organism is associated with its ability to form biofilms. We hypothesized that alcohol used in skin disinfectants, as well as preservative in solutions administered through catheters, can enhance biofilm formation by S epidermidis.

METHODS

We performed polymerase chain reaction (PCR) analysis to investigate the prevalence of ica locus in a collection of 169 commensal and clinical S epidermidis strains. Using a microtiter plate assay, we examined the effect of ethanol and benzyl alcohol on biofilm production. Quantitative real-time reverse transcriptase PCR analysis evaluated quantitative changes in gene expression.

RESULTS

We found that ica-positive but biofilm-negative or low-grade biofilm-positive S epidermidis strains displayed induction or increase in biofilm production after incubation in media supplemented with both ethanol and benzyl alcohol. The expression of the icaADBC operon was up-regulated in the presence of alcohol.

CONCLUSION

Our results suggest that biofilm production and, therefore, the pathogen potential of S epidermidis can be induced by alcohol. Considering the routine use of alcohol-based skin disinfectants and benzyl alcohol-containing solutions in hospitals, the alcohol-inducible biofilm phenotype of S epidermidis has potentially profound clinical ramifications.

A pilot study of high-dose short duration daptomycin for the treatment of patients with complicated skin and skin structure infections caused by gram-positive bacteria

BACKGROUND

Methicillin-susceptible and -resistant (MRSA) Staphylococcus aureus are significant causes of complicated skin and skin structure infections (cSSSI). The bactericidal antibiotic daptomycin is approved for gram-positive cSSSI at 4 mg/kg/day for 7-14 days, but the optimal dose level and duration of therapy have not been firmly established. This pilot study evaluated the efficacy and safety of daptomycin at 10 mg/kg every 24 h for 4 days [high-dose short duration (HDSD) regimen] vs. standard of care therapy with vancomycin or semi-synthetic penicillin for the treatment of cSSSI.

METHODS

This was a semi-single blind, randomised, multicentre, comparative trial. The primary efficacy end-point was the clinical response 7-14 days posttherapy.

RESULTS

One hundred patients were randomised; 48 in each arm were treated. The treatment groups were well balanced with respect to demographics, comorbidities and the type of infection (75% because of MRSA). Overall, clinical success rates were 75.0% (36/48) for daptomycin and 87.5% (42/48) for comparator (95% confidence interval for the difference: -27.9, 2.9). The median duration of comparator therapy was 8 days. Two comparator patients and no daptomycin patients experienced treatment-related serious adverse events requiring hospitalisation.

CONCLUSION

We found that the HDSD regimen had a safety profile similar to that seen in previous studies. Although the differences were not statistically significant, clinical success rates for comparator were higher than for daptomycin. In post hoc analyses HDSD daptomycin performed better in some subgroups (e.g. outpatients) than in others (e.g. certain MRSA infections). These observations require confirmation in larger trials.

Staphylococcus aureus clumping factor A binds to complement regulator factor I and increases factor I cleavage of C3b

The human complement system plays an important role in the control of Staphylococcus aureus infection. For instance, we previously demonstrated that the central complement component deposited on the organism's surface, C3b, can be cleaved by the host complement control protein, factor I, resulting in diminished phagocytosis of S. aureus. In the present study, we have identified clumping factor A (ClfA) from cell wall proteins of S. aureus as a specific protein bound by factor I. Recombinant ClfA (rClfA) containing the full-length A region (peptides 40-559) also bound factor I. We identified an 50-kDa fragment of ClfA that is shed by S. aureus into growth medium. The shed ClfA fragment was derived from the A region of ClfA and bound factor I. rClfA and the shed ClfA fragment increased factor I cleavage of C3b into inactive C3b. Our findings describe a new S. aureus mechanism for modification of host complement activities.

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.

Simvastatin inhibits Staphylococcus aureus host cell invasion through modulation of isoprenoid intermediates

Patients on a statin regimen have a decreased risk of death due to bacterial sepsis. We have found that protection by simvastatin includes the inhibition of host cell invasion by Staphylococcus aureus, the most common etiologic agent of sepsis. Inhibition was due in part to depletion of isoprenoid intermediates within the cholesterol biosynthesis pathway and led to the cytosolic accumulation of the small GTPases CDC42, Rac, and RhoB. Actin stress fiber disassembly required for host invasion was attenuated by simvastatin and by the inhibition of phosphoinositide 3-kinase (PI3K) activity. PI3K relies on coupling to prenylated proteins, such as this subset of small GTPases, for access to membrane-bound phosphoinositide to mediate stress fiber disassembly. Therefore, we examined whether simvastatin restricts PI3K cellular localization. In response to simvastatin, the PI3K isoform p85, coupled to these small-GTPases, was sequestered within the cytosol. From these findings, we propose a mechanism whereby simvastatin restricts p85 localization, inhibiting the actin dynamics required for bacterial endocytosis. This approach may provide the basis for protection at the level of the host in invasive infections by S. aureus.

Community-Acquired Methicillin-Resistant Staphylococcus aureus (CA-MRSA) Colonization and Infection in Intravenous and Inhalational Opiate Drug Abusers

Methicillin-resistant Staphylococcus aureus (MRSA) is a significant pathogen in hospital-acquired and community-acquired infections. We hypothesized that drug abuse is a risk factor for community-acquired MRSA (CA-MRSA) infection, and we employed a rapid multiplex PCR technique for MRSA identification. The study was conducted on MRSA isolates from 60 opiate addicts (intravenous and inhalational drug users) to detect the rate and location of MRSA colonization and infection among them in comparison to 60 non-addict patients and 15 healthy volunteer controls. The proportion of addicts with MRSA colonization (and/or infection) was significantly higher than non-addict patients with MRSA colonization. MRSA colonization was associated with infection in 58% of MRSA-colonized addicts. The MRSA nasal carriage in the addicts was significantly higher than MRSA carriage elsewhere, whether in the addicts group or in the non-addict patients group. Moreover, the nasopharyngeal carriage rate of MRSA among addicts was significantly higher than among the non-addict patients. Increasing the duration of addiction resulted in a significant increase in CA-MRSA colonization in opiate addicts. Both inhalational and intravenous drug use led to significant MRSA colonization in the addict population. In conclusion, this study demonstrated how drug abusers, a high-risk group for infections with MRSA, could be a source or a reservoir of CA-MRSA infection in the non-addict population.

Relative quantitative comparisons of the extracellular protein profiles of Staphylococcus aureus UAMS-1 and its sarA, agr, and sarA agr regulatory mutants using one-dimensional polyacrylamide gel electrophoresis and nanocapillary liquid chromatography coupled with tandem mass spectrometry

One-dimensional polyacrylamide gel electrophoresis followed by nanocapillary liquid chromatography coupled with mass spectrometry was used to analyze proteins isolated from Staphylococcus aureus UAMS-1 after 3, 6, 12, and 24 h of in vitro growth. Protein abundance was determined using a quantitative value termed normalized peptide number, and overall, proteins known to be associated with the cell wall were more abundant early on in growth, while proteins known to be secreted into the surrounding milieu were more abundant late in growth. In addition, proteins from spent media and cell lysates of strain UAMS-1 and its isogenic sarA, agr, and sarA agr regulatory mutant strains during exponential growth were identified, and their relative abundances were compared. Extracellular proteins known to be regulated by the global regulators sarA and agr displayed protein levels in accordance with what is known regarding the effects of these regulators. For example, cysteine protease (SspB), endopeptidase (SspA), staphopain (ScpA), and aureolysin (Aur) were higher in abundance in the sarA and sarA agr mutants than in strain UAMS-1. The immunoglobulin G (IgG)-binding protein (Sbi), immunodominant staphylococcal antigen A (IsaA), IgG-binding protein A (Spa), and the heme-iron-binding protein (IsdA) were most abundant in the agr mutant background. Proteins whose abundance was decreased in the sarA mutant included fibrinogen-binding protein (Fib [Efb]), IsaA, lipase 1 and 2, and two proteins identified as putative leukocidin F and S subunits of the two-component leukotoxin family. Collectively, this approach identified 1,263 proteins (matches of two peptides or more) and provided a convenient and reliable way of identifying proteins and comparing their relative abundances.

Antimicrobial resistance in major pathogens of hospital-acquired pneumonia in Asian countries

Antimicrobial resistance is a worldwide problem. For patients with hospital-acquired or ventilator-associated pneumonia, resistant pathogens pose a significant challenge to successful treatment outcomes and to the cost-effective delivery of health care. In the developing world, antibiotic resistance may be relatively more prevalent compared with Western countries. Common resistant pathogens include methicillin-resistant Staphylococcus aureus, multidrug resistant Pseudomonas aeruginosa, multidrug resistant Acinetobacter species, and extended-spectrum beta-lactamase-producing strains of Escherichia coli and Klebsiella pneumoniae. The emergence of these strains has provided a major impetus toward development of the present consensus treatment recommendations of the Asian HAP Working Group. The following review provides summary data regarding the incidence and prevalence of antibiotic-resistant pathogens in 10 Asian countries.

Rapid screening for carriage of methicillin-resistant Staphylococcus aureus by PCR and associated costs

PCR tests for the rapid and valid detection of methicillin-resistant Staphylococcus aureus (MRSA) are now available. We evaluated the costs associated with contact screening for MRSA carriage in a tertiary-care hospital with low MRSA endemicity. Between 1 October 2005 and 28 February 2006, 232 patients were screened during 258 screening episodes (644 samples) for MRSA carriage by GenoType MRSA Direct (Hain Lifescience GmbH, Nehren, Germany). Conventional culture confirmed all PCR results. According to in-house algorithms, 34 of 258 screening episodes (14.7%) would have qualified for preemptive contact isolation, but such isolation was not done upon negative PCR results. MRSA carriage was detected in 4 (1.5%) of 258 screening episodes (i.e., in four patients), of which none qualified for preemptive contact isolation. The use of PCR for all 258 screening episodes added costs (in Swiss francs [CHF]) of CHF 104,328.00 and saved CHF 38,528.00 (for preemptive isolation). The restriction of PCR screening to the 34 episodes that qualified for preemptive contact isolation and screening all others by culture would have lowered costs for PCR to only CHF 11,988.00, a savings of CHF 38,528.00. Therefore, PCR tests are valuable for the rapid detection of MRSA carriers, but high costs require the careful evaluation of their use. In patient populations with low MRSA endemicity, the broad use of PCR probably is not cost-effective.

Expression of Staphylococcus epidermidis SdrG increases following exposure to an in vivo environment

SdrG is a surface-associated fibrinogen binding protein present in most strains of Staphylococcus epidermidis. Surface expression of SdrG was not detected by flow cytometry or immunofluorescence microscopy on S. epidermidis 0-47 grown in nutrient broth or in the presence of human serum. sdrG transcript levels increased 1 hour following a shift from growth in nutrient broth to growth in the bloodstream of a mouse and resulted in a concomitant increase in protein levels as detected by immunofluorescence microscopy. The environmental signal(s) resulting in the increase in expression is elusive, as growth under conditions known to mimic in vivo conditions (elevated CO(2), iron limitation, human serum, and citrated human blood) did not affect expression of SdrG. Immunizing mice with either the N1N2N3 (amino acids 50 to 597) or N2N3 (amino acids 273 to 597) subdomain of the N-terminal A domain of recombinant SdrG (rSdrG) elicited a robust antibody response; however, only mice vaccinated with rSdrG(N23) exhibited a significant reduction in 0-47 recovered after experimental infection. Since SdrG is expressed early during infection in response to specific host environmental cues present in the bloodstream and since antibodies to it are effective in reducing bacteremia, SdrG possesses attributes of a vaccine component effective against the pathogenic form of the ubiquitous human commensal S. epidermidis.

Telavancin penetration into human epithelial lining fluid determined by population pharmacokinetic modeling and Monte Carlo simulation

Telavancin is an investigational bactericidal lipoglycopeptide with a multifunctional mechanism of action, as demonstrated against methicillin-resistant Staphylococcus aureus. While the plasma pharmacokinetics have been described, the extent of the penetration of the drug into the lung, measured by the epithelial lining fluid (ELF), remains unknown. Population modeling and Monte Carlo simulation were employed to estimate the penetration of telavancin into ELF. Plasma and ELF pharmacokinetic data were obtained from 20 healthy volunteers, and the pharmacokinetic samples were assayed by a validated liquid chromatography-tandem mass spectrometry technique. Concentration-time profiles in plasma and ELF were simultaneously modeled using a three-compartment model with zero-order infusion and first-order elimination and transfer. The model parameters were identified in a population pharmacokinetic analysis (BigNPAG). Monte Carlo simulation of 9,999 subjects was performed to calculate the ELF/plasma penetration ratios by estimating the area under the concentration-time curve (AUC) for the drug in ELF (AUC(ELF)) and for the free drug in plasma (free AUC(plasma)) from zero to infinity after a single dose. After the Bayesian step, the overall fits of the model to the data were good, and plots of predicted versus observed concentrations in plasma and ELF showed slopes and intercepts very close to the ideal values of 1.0 and 0.0, respectively. The median AUC(ELF)/free AUC(plasma) penetration ratio was 0.73, and the 25th and 75th percentile value ratios were 0.43 and 1.24, respectively. In uninfected lung tissue, the median AUC(ELF) is approximately 75% of the free AUC(plasma).

Enzymatic activity of the Staphylococcus aureus SplB serine protease is induced by substrates containing the sequence Trp-Glu-Leu-Gln

Proteases are of significant importance for the virulence of Staphylococcus aureus. Nevertheless, their subset, the serine protease-like proteins, remains poorly characterized. Here presented is an investigation of SplB protease catalytic activity revealing that the enzyme possesses exquisite specificity and only cleaves efficiently after the sequence Trp-Glu-Leu-Gln. To understand the molecular basis for such selectivity, we solved the three-dimensional structure of SplB to 1.8 A. Modeling of substrate binding to the protease demonstrated that selectivity relies in part on a canonical specificity pockets-based mechanism. Significantly, the conformation of residues that ordinarily form the oxyanion hole, an essential structural element of the catalytic machinery of serine proteases, is not canonical in the SplB structure. We postulate that within SplB, the oxyanion hole is only formed upon docking of a substrate containing the consensus sequence motif. It is suggested that this unusual activation mechanism is used in parallel with classical determinants to further limit enzyme specificity. Finally, to guide future development, we attempt to point at likely physiological substrates and thus the role of SplB in staphylococcal physiology.

The human fibrinolytic system is a target for the staphylococcal metalloprotease aureolysin

The major opportunistic pathogen Staphylococcus aureus utilizes the human fibrinolytic system for invasion and spread via plasmin(ogen) binding and non-proteolytic activation. Because S. aureus secretes several proteases recently proposed as virulence factors, we explored whether these enzymes could add to the activation of the host's fibrinolytic system. Exposure of human pro-urokinase [pro-uPA (where uPA is urokinase-type plasminogen activator)] to conditioned growth media from staphylococcal reference strains results in an EDTA-sensitive conversion of the single-chain zymogen into its two-chain active form, an activity not observed in an aureolysin-deficient strain. Using purified aureolysin, we verified the capacity of this thermolysin-like metalloprotease to activate pro-uPA, with a 2.6 x 10(3) M(-1) x s(-1) catalytic efficiency. Moreover, activation also occurs in the presence of human plasma, as well as in conditioned growth media from clinical isolates. Finally, we establish that aureolysin (i) converts plasminogen into angiostatin and mini-plasminogen, the latter retaining its capacity to be activated by uPA and to hydrolyse fibrin, (ii) degrades the plasminogen activator inhibitor-1, and (iii) abrogates the inhibitory activity of alpha(2)-antiplasmin. Altogether, we propose that, in parallel with the staphylokinase-dependent activation of plasminogen, aureolysin may contribute significantly to the activation of the fibrinolytic system by S. aureus, and thus may promote bacterial spread and invasion.

Mechanism and inhibition of saFabI, the enoyl reductase from Staphylococcus aureus

Approximately one-third of the world's population carries Staphylococcus aureus. The recent emergence of extreme drug resistant strains that are resistant to the "antibiotic of last resort", vancomycin, has caused a further increase in the pressing need to discover new drugs against this organism. The S. aureus enoyl reductase, saFabI, is a validated target for drug discovery. To drive the development of potent and selective saFabI inhibitors, we have studied the mechanism of the enzyme and analyzed the interaction of saFabI with triclosan and two related diphenyl ether inhibitors. Results from kinetic assays reveal that saFabI is NADPH-dependent, and prefers acyl carrier protein substrates carrying fatty acids with long acyl chains. On the basis of product inhibition studies, we propose that the reaction proceeds via an ordered sequential ternary complex, with the ACP substrate binding first, followed by NADPH. The interaction of NADPH with the enzyme has been further explored by site-directed mutagenesis, and residues R40 and K41 have been shown to be involved in determining the specificity of the enzyme for NADPH compared to NADH. Finally, in preliminary inhibition studies, we have shown that triclosan, 5-ethyl-2-phenoxyphenol (EPP), and 5-chloro-2-phenoxyphenol (CPP) are all nanomolar slow-onset inhibitors of saFabI. These compounds inhibit the growth of S. aureus with MIC values of 0.03-0.06 microg/mL. Upon selection for resistance, three novel safabI mutations, A95V, I193S, and F204S, were identified. Strains containing these mutations had MIC values approximately 100-fold larger than that of the wild-type strain, whereas the purified mutant enzymes had K i values 5-3000-fold larger than that of wild-type saFabI. The increase in both MIC and K i values caused by the mutations supports the proposal that saFabI is the intracellular target for the diphenyl ether-based inhibitors.

Neutrophil microbicides induce a pathogen survival response in community-associated methicillin-resistant Staphylococcus aureus

In recent years, there has been a dramatic increase in the incidence of community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) infections. MW2 (pulsed-field type USA400), the prototype CA-MRSA strain, is highly virulent and has enhanced ability to evade killing by neutrophils. Although progress has been made, the molecular basis for enhanced virulence of CA-MRSA remains incompletely defined. To that end, we studied resistance of MW2 to key microbicides of human neutrophils. Hydrogen peroxide (H2O2), hypochlorous acid, and azurophilic granule proteins had significant bacteriostatic but limited staphylocidal activity toward MW2 under the conditions tested. An MW2-specific microarray revealed common changes in S. aureus gene expression following exposure to each microbicide, such as up-regulation of transcripts involved in gene regulation (e.g., saeRS and kdpDE) and stress response. Azurophilic granule proteins elicited the greatest number of changes in MW2 transcripts, including up-regulation of mRNAs encoding multiple toxins and hemolysins (e.g., hlgA, hlgB, hlgC, hla, lukS-PV, lukF-PV, sec4, and set17-26). Notably, H2O2 triggered up-regulation of transcripts related to heme/iron uptake (e.g., isdA, isdB, and isdCDEFsrtBisdG), and an isogenic isdAB-negative strain of MW2 had increased susceptibility to H2O2 (p<0.001) and human neutrophils (p<0.05) compared with the wild-type parental strain. These findings reveal a S. aureus survival response wherein Iron-regulated surface determinant (Isd) proteins are important for resistance to innate host defense. Collectively, the data provide an enhanced view of the mechanisms used by S. aureus to circumvent destruction by the innate immune system.

Molecular epidemiology of clinically significant antibiotic resistance genes

Antimicrobials were first introduced into medical practice a little over 60 years ago and since that time resistant strains of bacteria have arisen in response to the selective pressure of their use. This review uses the paradigm of the evolution and spread of beta-lactamases and in particular beta-lactamases active against antimicrobials used to treat Gram-negative infections. The emergence and evolution particularly of CTX-M extended-spectrum beta-lactamases (ESBLs) is described together with the molecular mechanisms responsible for both primary mutation and horizontal gene transfer. Reference is also made to other significant antibiotic resistance genes, resistance mechanisms in Gram-negative bacteria, such as carbepenamases, and plasmid-mediated fluoroquinolone resistance. The pathogen Staphylococcus aureus is reviewed in detail as an example of a highly successful Gram-positive bacterial pathogen that has acquired and developed resistance to a wide range of antimicrobials. The role of selective pressures in the environment as well as the medical use of antimicrobials together with the interplay of various genetic mechanisms for horizontal gene transfer are considered in the concluding part of this review.

Enhanced susceptibility to infections in a diabetic wound healing model

Background

Wound infection is a common complication in diabetic patients. The progressive spread of infections and development of drug-resistant strains underline the need for further insights into bacterial behavior in the host in order to develop new therapeutic strategies. The aim of our study was to develop a large animal model suitable for monitoring the development and effect of bacterial infections in diabetic wounds.

Methods

Fourteen excisional wounds were created on the dorsum of diabetic and non-diabetic Yorkshire pigs and sealed with polyurethane chambers. Wounds were either inoculated with 2 × 10⁸ Colony-Forming Units (CFU) of Staphylococcus aureus or injected with 0.9% sterile saline. Blood glucose was monitored daily, and wound fluid was collected for bacterial quantification and measurement of glucose concentration. Tissue biopsies for microbiological and histological analysis were performed at days 4, 8, and 12. Wounds were assessed for reepithelialization and wound contraction.

Results

Diabetic wounds showed a sustained significant infection (>10⁵ CFU/g tissue) compared to non-diabetic wounds (p < 0.05) over the whole time course of the experiment. S. aureus-inoculated diabetic wounds showed tissue infection with up to 8 × 10⁷ CFU/g wound tissue. Non-diabetic wounds showed high bacterial counts at day 4 followed by a decrease and no apparent infection at day 12. Epidermal healing in S. aureus-inoculated diabetic wounds showed a significant delay compared with non-inoculated diabetic wounds (59% versus 84%; p < 0.05) and were highly significant compared with healing in non-diabetic wounds (97%; p < 0.001).

Conclusion

Diabetic wounds developed significantly more sustained infection than non-diabetic wounds. S. aureus inoculation leads to invasive infection and significant wound healing delay and promotes invasive co-infection with endogenous bacteria. This novel wound healing model provides the opportunity to closely assess infections during diabetic wound healing and to monitor the effect of therapeutical agents in vivo.

Linezolid versus glycopeptide or beta-lactam for treatment of Gram-positive bacterial infections: meta-analysis of randomised controlled trials

Linezolid has been approved for the treatment of patients with infections caused by Gram-positive cocci that are resistant to traditionally used antibiotics, including glycopeptides. This oxazolidinone antibiotic has been reported to have excellent pharmacokinetics and effectiveness. We did a meta-analysis of randomised controlled trials (RCTs) to clarify whether linezolid is superior to glycopeptides or beta-lactams for the treatment of Gram-positive infections. 12 RCTs, involving 6093 patients, were included. Overall, with respect to treatment success, linezolid was more effective than glycopeptides or beta-lactams (odds ratio [OR] 1.41 [95% CI 1.11-1.81]). Mortality was similar between the groups (OR 0.97 [0.79-1.19]). Linezolid was more effective than comparators in patients with skin and soft-tissue infections (OR 1.67 [1.31-2.12]) and bacteraemia (OR 2.07 [1.13-3.78]). However, there was no difference in treatment success for patients with pneumonia (OR 1.03 [0.75-1.42]). Treatment with linezolid was not associated with more adverse effects in general (OR 1.40 [0.95-2.06]); however, thrombocytopenia was recorded more commonly in patients receiving linezolid (OR 11.72 [3.66-37.57]). Although linezolid is more effective than its comparators for the empirical treatment of selected patients, several points, such as the use of less potent antistaphylococcal beta-lactams, the same all-cause mortality, and the higher probability of thrombocytopenia, should be taken into account and may limit the use of linezolid to specific patient populations or infections that are difficult to treat with other antibiotics.

An antidote for Staphylococcus aureus pneumonia?

Methicillin-resistant Staphylococcus aureus (MRSA) is the leading cause of bacterial infections in the United States. Severe invasive MRSA infections, which include pneumonia, are difficult to treat because the bacteria are resistant to antibiotics. A new report now shows that immunization against alpha-hemolysin (Hla), a cytolytic toxin secreted by most S. aureus strains, protects mice against lethal pneumonia. This finding represents the first successful vaccine strategy for the treatment of staphylococcal pneumonia.

From clinical microbiology to infection pathogenesis: how daring to be different works for Staphylococcus lugdunensis

Staphylococcus lugdunensis has gained recognition as an atypically virulent pathogen with a unique microbiological and clinical profile. S. lugdunensis is coagulase negative due to the lack of production of secreted coagulase, but a membrane-bound form of the enzyme present in some isolates can result in misidentification of the organism as Staphylococcus aureus in the clinical microbiology laboratory. S. lugdunensis is a skin commensal and an infrequent pathogen compared to S. aureus and S. epidermidis, but clinically, infections caused by this organism resemble those caused by S. aureus rather than those caused by other coagulase-negative staphylococci. S. lugdunensis can cause acute and highly destructive cases of native valve endocarditis that often require surgical treatment in addition to antimicrobial therapy. Other types of S. lugdunensis infections include abscess and wound infection, urinary tract infection, and infection of intravascular catheters and other implanted medical devices. S. lugdunensis is generally susceptible to antimicrobial agents and shares CLSI antimicrobial susceptibility breakpoints with S. aureus. Virulence factors contributing to this organism's heightened pathogenicity remain largely unknown. Those characterized to date suggest that the organism has the ability to bind to and interact with host cells and to form biofilms on host tissues or prosthetic surfaces.

Rapid detection of the pandemic methicillin-resistant Staphylococcus aureus clone ST 239, a dominant strain in Asian hospitals

We describe and validate a novel PCR assay to detect the pandemic hospital-acquired methicillin-resistant Staphylococcus aureus (HA-MRSA) lineage ST 239. Results based on previously uncharacterized isolates from a hospital in northeast Thailand support the view that at least 90% of HA-MRSA isolates in mainland Asia correspond to ST 239 or close relatives.

How complicated skin and soft tissue infections are treated in Italy: economic evaluation of inpatient intravenous antibiotic treatment in seven hospitals

OBJECTIVES

Complicated skin and soft tissue infections (cSSTIs) are a common cause of morbidity at hospital level. This study aimed to evaluate the costs and outcomes of inpatient intravenous antibiotic therapy for the treatment of cSSTI in seven Italian hospitals.

METHODS

A total of 307 patients were enrolled in a retrospective, multicentre, incidence-based, observational study. The target population consisted of hospitalised patients eligible to receive intravenous antibiotic therapy for cSSTI. Direct hospital costs were measured through a microcosting approach.

RESULTS

Failure of initial antibiotic therapy occurred in 23% of patients. Average antibiotic treatment lasted 12.2 days; the average full cost of admission totalled euro5,530. If the initial antibiotic regimen fails to eradicate the infectious organism, the length of stay extends for 7 days and costs increase by euro2,850 per patient. Nevertheless, when taking into account the lower intensity of care during the last days of treatment, savings reduce costs to euro671 per patient. These could be increased by euro74 for each hospital day avoided because of faster antibiotic action.

CONCLUSIONS

Efforts should be made to minimise the risk of selecting wrong antibiotics and to identify the quickest antibiotic in eradicating the infection.

Genotypic characteristics of Staphylococcus aureus isolates from a multinational trial of complicated skin and skin structure infections

The impact of bacterial genetic characteristics on the outcome of patients with Staphylococcus aureus infections is uncertain. This investigation evaluated potential associations between bacterial genotype and clinical outcome using isolates collected as part of an international phase 2 clinical trial (FAST II) evaluating telavancin for the treatment of complicated skin and skin structure infections (cSSSI). Ninety S. aureus isolates from microbiologically evaluable patients with cSSSI enrolled in the FAST II trial from 11 sites in the United States (56 isolates, or 62%) and 7 sites in South Africa (34 isolates, or 38%) were examined for staphylococcal cassette chromosome mec, agr, and the presence of 31 virulence genes and subjected to pulsed-field gel electrophoresis (PFGE). South African methicillin-susceptible S. aureus (MSSA) isolates were more likely to carry certain virulence genes, including sdrD (P = 0.01), sea (P < 0.01), and pvl (P = 0.01). All 44 (49%) methicillin-resistant S. aureus (MRSA) isolates were from the United States; 37 (84%) were strain USA 300 by PFGE. In the United States, MRSA isolates were more likely than MSSA isolates to carry genes for sdrC (P = 0.03), map/eap (P = 0.05), fnbB (P = 0.11), tst (P = 0.02), sea (P = 0.04), sed (P = 0.04), seg (P = 0.11), sej (P = 0.11), agr (P = 0.09), V8 (P = 0.06), sdrD, sdrE, eta, etb, and see (P < 0.01 for all). MRSA isolates were more often clonal than MSSA isolates by PFGE. Isolates from patients who were cured were significantly more likely to contain the pvl gene than isolates from patients that failed or had indeterminate outcomes (79/84 [94%] versus 3/6 [50%]; P = 0.01). S. aureus strains from different geographic regions have different distributions of virulence genes.

Daptomycin and tigecycline: a review of clinical efficacy in the antimicrobial era

There is a clinical need for new treatment options as a result of continued increase in the expression of resistance among bacterial pathogens. A number of compounds currently in development show promise. However, in some cases, there is concern that resistance may develop quickly to new compounds that are based on existing antimicrobial agents. Therefore, daptomycin, a novel lipopeptide with a unique mode of action, is of particular interest. It has rapid bactericidal activity against growing and stationary-phase bacteria, once-daily dosing regimen, and has a low potential for the development of resistance. It has been approved for the treatment of complicated skin and soft tissue infections caused by Gram-positive bacteria, and registration for treatment of infective endocarditis and bacteraemia is anticipated. Daptomycin is a welcome addition to the antimicrobial armamentarium for the treatment of bacterial infections. Tigecycline is a new glycyclcycline antimicrobial recently approved for use in the USA, Europe and elsewhere. While related to the tetracyclines, tigecycline overcomes many of the mechanisms responsible for resistance to this class. It is a novel broad spectrum glycylcycline with good activity against Gram-positive, many Gram-negative, anaerobic, and some atypical pathogens that has been developed to address this need. It is efficacious in complicated skin and soft tissue infections and in intra-abdominal infections. This review aims to summarise the key clinical data of daptomycin and tigecycline which hold promise for widespread clinical use in the next decade.

Evaluation of a new chromogenic medium for the detection of methicillin-resistant Staphylococcus aureus carriage on nasal and perianal specimens

A new chromogenic medium, denim blue (DB), was compared with methicillin-resistant Staphylococcus aureus (MRSA) Select (MRSAS) for detection of MRSA from surveillance specimens. On DB, MRSA colonies are larger (0.57-0.8 versus 0.45-0.6 mm at 18 and 24 h, respectively). Despite this, sensitivities of DB were 77% and 96% at 18 and 24 h, respectively, and those of MRSAS were 63% and 97.5%. Specificities were significantly higher for MRSAS than DB. The study demonstrates that DB and MRSA are equal for the detection of MRSA from surveillance specimens provided the plates are read after 24 h of incubation. Positive predictive values of both media were less than 95% requiring confirmation of MRSA, by another method, from all new patients.

Emergence in Brazil of methicillin-resistant Staphylococcus aureus isolates carrying SCCmecIV that are related genetically to the USA800 clone

An increasing incidence of nosocomial infections caused by non-multiresistant methicillin-resistant Staphylococcus aureus (nMMRSA) has been reported worldwide. The present study genotyped nMMRSA isolates obtained from hospitals in two cities in Brazil. The hospital isolates displayed pulsed-field gel electrophoresis (PFGE) patterns that were similar to those of the USA100 (ST5-SCCmecII) and USA 800 (ST5-SCCmecIV) strains, which are related to the New York/Japan and paediatric clones, respectively. Carriage of SCCmecIV and the classification by multilocus sequence typing (MLST) of a representative of this PFGE pattern in clonal complex 5 (CC5) confirmed the genetic relationship of the Brazilian isolates with USA800. The USA800-related Brazilian isolates were responsible for severe nosocomial infections in compromised adults and elderly patients in Brazil. A higher growth rate, an ability to form biofilm on inert polystyrene surfaces and the presence of the egc locus may have contributed, at least in part, to the fitness of these organisms as global nosocomial pathogens.

Epidemiology of staphylococcal resistance

An understanding of the prevalence of resistant Staphylococcus aureus and the risk factors for infection with resistant isolates is essential to help clinicians choose appropriate antibiotic therapy. Selection pressure due to prior and inappropriate antibiotic use of any kind seems to be the main driving force behind the increasing rates of multidrug resistance in methicillin-resistant S. aureus (MRSA) strains. Resistance to glycopeptide antibiotics in MRSA has also emerged in recent years, along with increased use of vancomycin to treat serious infections due to MRSA. Infections due to MRSA are associated with significantly increased morbidity, mortality, length of hospital stay, and costs, compared with infections due to methicillin-susceptible S. aureus, despite adjustment for disease severity and initially appropriate antibiotic treatment. Improvements in the preparation and dissemination of antibiograms, along with adequate public reporting of MRSA trends, are needed to address the challenge of choosing appropriate initial antibiotic treatment for MRSA infections.

Staphylococcus aureus is a major pathogen in acute bacterial rhinosinusitis: a meta-analysis

BACKGROUND

Acute bacterial rhinosinusitis is a common health problem in the United States. Appropriate recommendations for the treatment of acute bacterial rhinosinusitis are based on the prevalence and expected antimicrobial susceptibilities of specific pathogens.

METHODS

A meta-analysis was performed on the English language literature from the period 1990-2006, including prospective studies of antibiotic therapy for acute bacterial rhinosinusitis for which sinus cultures were required in the form of either maxillary sinus taps or middle meatal cultures. Weighted mean culture rates for Streptococcus pneumoniae, Haemophilus influenzae, Moraxella catarrhalis, and Staphylococcus aureus were abstracted from the included articles and compared according to culture technique.

RESULTS

Culture rates (i.e., the percentage of patients with positive culture results) were 32.7% for S. pneumoniae, 31.6% for H. influenzae, 10.1% for S. aureus, and 8.8% for M. catarrhalis. No statistically significant difference was seen between the culture rates for S. aureus and M. catarrhalis. Analysis of the effect of culture technique on the culture rates revealed no statistically significant difference.

CONCLUSIONS

The prevalence of S. aureus among sinus cultures warrants its reconsideration as a major pathogen in acute bacterial rhinosinusitis. As a result, increasing trends of drug-resistant strains may complicate antibiotic recommendations.

Phase 2 study of ceftaroline versus standard therapy in treatment of complicated skin and skin structure infections

Ceftaroline, the bioactive metabolite of ceftaroline fosamil (previously PPI-0903, TAK-599), is a broad-spectrum cephalosporin with potent in vitro activity against multidrug-resistant gram-positive aerobic pathogens, including methicillin-resistant Staphylococcus aureus. A randomized, observer-blinded study to evaluate the safety and efficacy of ceftaroline versus standard therapy in treating complicated skin and skin structure infections (cSSSI) was performed. Adults with cSSSI, including at least one systemic marker of inflammation, were randomized (2:1) to receive intravenous (i.v.) ceftaroline (600 mg every 12 h) or i.v. vancomycin (1 g every 12 h) with or without adjunctive i.v. aztreonam (1 g every 8 h) for 7 to 14 days. The primary outcome measure was the clinical cure rate at a test-of-cure (TOC) visit 8 to 14 days after treatment. Secondary outcomes included the microbiological success rate (eradication or presumed eradication) at TOC and the clinical relapse rate 21 to 28 days following treatment. Of 100 subjects enrolled, 88 were clinically evaluable; the clinical cure rate was 96.7% (59/61) for ceftaroline versus 88.9% (24/27) for standard therapy. Among the microbiologically evaluable subjects (i.e., clinically evaluable and having had at least one susceptible pathogen isolated at baseline), the microbiological success rate was 95.2% (40/42) for ceftaroline versus 85.7% (18/21) for standard therapy. Relapse occurred in one subject in each group (ceftaroline, 1.8%; standard therapy, 4.3%). Ceftaroline exhibited a very favorable safety and tolerability profile, consistent with that of marketed cephalosporins. Most adverse events from ceftaroline were mild and not related to treatment. Ceftaroline holds promise as a new therapy for treatment of cSSSI and other serious polymicrobial infections.

Therapeutic applications of tigecycline in the management of complicated skin and skin structure infections

Complicated skin and skin structure infections encompass a diverse range of diseases frequently caused by Gram-positive pathogens, and most commonly by Staphylococcus aureus and Streptococcus pyogenes. Treatment of these infections represents a growing clinical challenge as increases in multi-drug-resistant organisms and cross-resistance to antimicrobial therapy have made empiric therapeutic choices more difficult, particularly for patients with known risk factors or who are immunocompromised. Complicating this issue has been the relative lack of new agents with antimicrobial potency against prevalent resistant species such as meticillin resistant S. aureus (MRSA). Tigecycline, a novel glycylcycline, is a broad-spectrum antibiotic with potent microbiological activity against the wide variety of organisms implicated in the aetiology of complicated skin and skin structure infections. Recent phase III clinical data confirm previous observations on the safety and efficacy of tigecycline for the treatment of complicated skin and skin structure infections. Tigecycline was shown to be non-inferior to combination vancomycin-aztreonam regimens and exhibited high clinical success rates. MIC(90) values for tigecycline were uniformly low for both susceptible and resistant pathogens. Adverse events were similar in incidence for both patient populations, with nausea and vomiting reported more frequently with tigecycline treated patients while rash and elevated liver transaminases were most commonly observed in the vancomycin-aztreonam treatment group. Tigecycline helps to address the urgent need for new antimicrobial agents to combat the emergence of multi-drug-resistant Gram-positive pathogens. Current clinical, microbiological and safety data support the use of tigecycline as a valuable therapeutic option in the treatment of complicated skin and skin structure infections.

Management of a large healthcare-associated outbreak of Panton-Valentine leucocidin-positive meticillin-resistant Staphylococcus aureus in Germany

We report the largest documented healthcare-associated outbreak of Panton-Valentine leucocidin-positive meticillin-resistant Staphylococcus aureus (PVL(+) MRSA) in Europe. Six index patients from three long-term care facilities (LTCFs) were screened positive for PVL(+) MRSA in 2004 on admission to a community hospital in Germany. The purpose of this prospective study was to describe the prevalence of PVL(+) MRSA in the LTCFs before and after infection control interventions. Screening for MRSA with or without PVL was performed in all three LTCFs in 2004 [453 residents, 240 healthcare workers (HCWs)] and 2005 (440 residents, 192 HCWs). Swabs from anterior nares and wounds, if applicable, were collected. Colonised residents and staff were treated with mupirocin nasal ointment and topical antiseptics, and staff were provided with hygiene education. Total MRSA carrier rate of residents and HCWs in 2004 was 11.3% (PVL(+) MRSA 9.1%, PVL(-) MRSA 2.2%). There were comparable carrier rates between residents and HCWs in each LTCF. All PVL(+) MRSA isolates were of clonal origin (MLST 22) representing a novel spa sequence type t310. A decrease in total MRSA prevalence (from 11.3 to 5.5%) and PVL(+) MRSA (from 9.1 to 3.3%) was observed in 2005. The rate of PVL(-) MRSA remained unaffected. No symptomatic skin infections were noted among residents or HCWs. In this outbreak incomplete control of PVL(+) MRSA presumably resulted from difficult and delayed detection and decolonisation of carriers, incomplete compliance with control measures and lack of enforcement by public health authorities.

Partial characterization of bacteriocins produced by human Lactococcus lactis and Pediococccus acidilactici isolates

AIMS

The aim of this study was to isolate bacteriocin-producing lactic acid bacteria (LAB) from human intestine.

METHODS AND RESULTS

A total of 111 LAB were isolated from human adult stool and screened for their bacteriocin production. Neutralized cell-free supernatants from Lactococcus lactis subsp. lactis MM19 and Pediococcus acidilactici MM33 showed antimicrobial activity. The antimicrobials in the supernatant from a culture of L. lactis inhibited Enterococcus faecium, various species of Lactobacillus and Staphylococcus aureus; while those in the supernatant from a culture of P. acidilactici inhibited Enterococcus spp., some lactobacilli and various serotypes of Listeria monocytogenes. The antimicrobial metabolites were heat-stable and were active over a pH range of 2-10. The antimicrobial activities of the supernatants of both bacteria were inhibited by many proteases but not by catalase. The plate overlay assay allowed an approximation of size between 3.5 and 6 kDa for both antimicrobial substances.

CONCLUSIONS

As the antagonistic factor(s) produced by L. lactis MM19 and P. acidilactici MM33 were sensitive to proteolytic enzymes, it could be hypothesized that bacteriocins were involved in the inhibitory activities. Inhibition spectrum and biochemical analysis showed that these bacteria produced two distinct bacteriocins.

SIGNIFICANCE AND IMPACT OF THE STUDY

We are the first to isolate bacteriocin-producing strains of Pediococcus and Lactococcus from human intestine. These strains might be useful for control of enteric pathogens.

Nationwide trends in molecular epidemiology of methicillin-resistant Staphylococcus aureus, Finland, 1997-2004

Background

In Finland, the annual number of MRSA notifications to the National Infectious Disease Register (NIDR) has constantly increased since 1995, and molecular typing has revealed numerous outbreak isolates of MRSA. We analyzed the data on MRSA notifications of the NIDR, and MRSA isolates were identified mainly by pulsed-field gel electrophoresis (PFGE) at the National Reference Laboratory (NRL) in Finland during 1997–2004. One isolate representative of each major PFGE type was further characterized by multilocus sequence (MLST)-, staphylococcal cassette chromosome mec (SCCmec)-, and Panton-Valentine leukocidin (PVL)-typing.

Results

The annual number of MRSA notifications to the NIDR rose over ten-fold, from 120 in 1997 to 1458 in 2004, and the proportion of MRSA among S. aureus blood isolates tripled, from <1% during 1997–2003 to 2.8% in 2004. During the same period of time, 253 different strains among 4091 MRSA isolates were identified by PFGE: 215 were sporadic and 38 outbreak/epidemic strains, including 24 new strains. Two epidemic strains resembling internationally recognized MRSA clones accounted for most of the increase: FIN-16 (ST125:IA) from <1% in 1997 to 25% in 2004, and FIN-21 (ST228:I) from 6% in 2002 to 28% in 2004. Half of the ten most common strains carried SCCmec IV or V.

Conclusion

The predominant MRSA strains seem to change over time, which encourages us to continue implementing active control measures with each new MRSA case.

Activation of inhibitors by sortase triggers irreversible modification of the active site

Sortases anchor surface proteins to the cell wall of Gram-positive pathogens through recognition of specific motif sequences. Loss of sortase leads to large reductions in virulence, which identifies sortase as a target for the development of antibacterials. By screening 135,625 small molecules for inhibition, we report here that aryl (beta-amino)ethyl ketones inhibit sortase enzymes from staphylococci and bacilli. Inhibition of sortases occurs through an irreversible, covalent modification of their active site cysteine. Sortases specifically activate this class of molecules via beta-elimination, generating a reactive olefin intermediate that covalently modifies the cysteine thiol. Analysis of the three-dimensional structure of Bacillus anthracis sortase B with and without inhibitor provides insights into the mechanism of inhibition and reveals binding pockets that can be exploited for drug discovery.

From Multifunctionalized Poly(ethylene imine)s toward Antimicrobial Coatings

Primary amine groups of branched poly(ethylene imine) (PEI) were functionalized with quaternary ammonium groups, alkyl chains of different length, allylic and benzylic groups in a one-step reaction, using a carbonate coupler. The structure of the obtained amphiphilic polymers was determined by means of 1H and 13C NMR spectroscopy. Depending on their hydrophilic/hydrophobic balance, the obtained polymers can be used as water-soluble disinfectants and for antimicrobial coating materials. The bactericidal properties of some of the amphiphilic polymers against Gram-negative and Gram-positive bacteria were investigated. Minimal inhibitory concentrations (log 4 reduction of bacterial growth) against Escherichia coli and Bacillus subtilis were determined in the range of 0.3-0.4 mg/mL and 0.03-0.04 mg/mL for water-soluble polymers. Glass slides coated with functionalized PEIs showed a reduction of colony forming units of at least 95%, at best 99.9%, against E. coli and B. subtilis.

Rapid recontamination with MRSA of the environment of an intensive care unit after decontamination with hydrogen peroxide vapour

Meticillin-resistant Staphylococcus aureus (MRSA) persists in the hospital environment and conventional cleaning procedures do not necessarily eliminate contamination. A prospective study was conducted on an intensive care unit to establish the level of environmental contamination with MRSA, assess the effectiveness of hydrogen peroxide vapour (HPV) decontamination and determine the rate of environmental recontamination. MRSA was isolated from 11.2% of environmental sites in the three months preceding the use of HPV and epidemiological typing revealed that the types circulating within the environment were similar to those colonising patients. After patient discharge and terminal cleaning using conventional methods, MRSA was isolated from five sites (17.2%). After HPV decontamination but before the readmission of patients, MRSA was not isolated from the environment. Twenty-four hours after readmitting patients, including two colonized with MRSA, the organism was isolated from five sites. The strains were indistinguishable from a strain with which a patient was colonized but were not all confined to the immediate vicinity of the colonized patient. In the eight weeks after the use of HPV, the environment was sampled on a weekly basis and MRSA was isolated from 16.3% sites. Hydrogen peroxide vapour is effective in eliminating bacteria from the environment but the rapid rate of recontamination suggests that it is not an effective means of maintaining low levels of environmental contamination in an open-plan intensive care unit.

Slime production and antibiotic susceptibility in staphylococci isolated from clinical samples

A total of 187 isolates from several clinical specimens were identified to species level as 129 Staphylococcus aureus strains and 58 coagulase-negative staphylococci (CNS) strains by the API Staph System (Biomerieux). Slime production was detected both by the conventional Christensen's method as well as by the Congo red agar method. Seventy-two strains of staphylococci isolates (38.5%) were found to be slime producers by Christensen's test tube method whereas 58 strains (31%) were slime positive with Congo red agar method. There was no statistically significant difference between the two methods for the detection of slime production (P > 0.05). Susceptibility of isolates against antimicrobial agents was tested by the disk diffusion method. Staphylococcal species had resistance to one or more antibiotics. Among the various antimicrobial agents, oxacillin (71.1%) and erythromycin (47.1%) showed higher resistance than most of the agents used against all isolates. Oxacillin resistant S. aureus (ORSA) and oxacillin resistant coagulase-negative staphylococci (ORCNS), 97 (75.2%) and 36 (62.1%) respectively were frequently observed in strains isolated from clinical materials. Among the ORSA strains, two strains were resistant to vancomycin. Moreover, 96 (74.4%) of 129 S. aureus strains were positive for beta-lactamase enzyme. However, 78 (81.25%) of 96 beta-lactamase positive S. aureus strains were beta-lactamase positive ORSA isolates, but none of them had vancomycin resistance.

Early switch from vancomycin to oral linezolid for treatment of gram-positive heart valve endocarditis

BACKGROUND

Patients with complicated gram-positive endocarditis are usually treated with a combination of surgical procedure and long-term antibiotic therapy with intravenous vancomycin. However, oral linezolid offers the potential for an early switch from intravenous vancomycin to oral linezolid therapy.

METHODS

We conducted a retrospective study from February 2002 to August 2005 to determine the potential for early switch from intravenous vancomycin to oral linezolid in patients surgically treated for a left-sided active gram-positive endocarditis.

RESULTS

Fourteen patients were identified; average age was 52 +/- 16 years. There were 10 (85%) and 2 (15%) cases of native and prosthetic valve endocarditis, respectively. Patients were operated on 3 to 10 days after diagnosis. There were no cases of operative mortality. Mean follow-up was 20.8 +/- 7.0 months. Two (14%) patients died of noncardiac causes during follow-up. The mean intensive care unit length of stay was 3.1 +/- 2.3 days, and mean hospital length of stay was 10.5 +/- 3.4 days. No cases of recurrent endocarditis or periprosthetic leakage were observed.

CONCLUSIONS

The combination of aggressive surgical treatment and the early switch from intravenous vancomycin to oral linezolid for treatment of active gram-positive heart valve endocarditis is safe and effective, and reduces infection relapses, vancomycin use, hospital length of stay, and economic costs.