Contemporary causes of skin and soft tissue infections in North America, Latin America, and Europe: Report from the SENTRY Antimicrobial Surveillance Program (1998–2004)

Skin and soft tissue infections

Skin and soft tissue infections are a common cause of hospitalization and use of antibiotic therapy, and may result in significant disability. Infections managed by surgeons may vary from simple, noncomplicated cellulitis to severe necrotizing soft tissue infections. The differentiation of necrotizing infections from nonnecrotizing infections is critical to achieving adequate surgical therapy. An understanding of the changing epidemiology of all complicated skin and soft tissue infections is required for selection of appropriate empiric antibiotic therapy.

In vitro activity of daptomycin against Staphylococci isolated from bacteremia and community-onset skin and soft tissue infections in France: data from two nationwide studies

Staphylococci are a leading cause of skin and soft tissue infections (SSTIs) and bacteremia in France, a country with a high prevalence of oxacillin resistance. We evaluated the in vitro activity of daptomycin compared with reference compounds against 445 Staphylococcus aureus and 53 coagulase-negative Staphylococci (CNS) collected during two large nationwide studies performed in 2006 and 2007. The percentage of oxacillin resistance among S. aureus was 13.6% (SSTIs) and 30.7% (bacteremia). Daptomycin showed lower MIC(90) levels compared to vancomycin, teicoplanin, and linezolid (0.19 mg/L vs. 2, 1.5, and 1 mg/L, respectively), irrespective of oxacillin susceptibility. Amongst the CNS, 64.2% of the isolates originated from clinical bacteremia were resistant to oxacillin and 24.5% to teicoplanin; all but one Staphylococci were susceptible to daptomycin (MIC = 1.5 mg/l). As with linezolid, daptomycin seems to constitute an alternative option to treat some staphylococcal infections in the French context of high oxacillin resistance prevalence and high glycopeptides MIC.

Virulence potential of Escherichia coli isolates from skin and soft tissue infections

Escherichia coli strains frequently are isolated from skin and soft tissue infections (SSTI); however, their virulence potential has not yet been extensively studied. In the present study, we characterized 102 E. coli SSTI strains isolated mostly from surgical and traumatic wounds, foot ulcers, and decubitus. The strains were obtained from the Institute of Microbiology and Immunology, University of Ljubljana, Slovenia. Phylogenetic backgrounds, virulence factors (VFs), and antibiotic resistance profiles were determined. Correlations between VFs and phylogenetic groups were established and analyzed with regard to patient factors. Further, the associations of the three most prevalent antibiotic resistance patterns with virulence potential were analyzed. Our results showed that the majority of the studied strains (64%) [corrected] belonged to the B2 phylogenetic group. The most prevalent VF was ompT (80%), while toxin genes cnf1 and hlyA were found with prevalences of 32 and 30%, respectively. None of the investigated bacterial characteristics were significantly associated with patient gender, age, type of infection, or immunodeficiency. The most prevalent antibiotic resistance pattern was resistance to ampicillin (46%), followed by resistance to tetracycline (25%) and fluoroquinolones (21%). Strains resistant to ciprofloxacin exhibited a significantly reduced prevalence of cnf1 (P < 0.05) and usp (P < 0.01). Our study revealed that E. coli isolates from SSTIs exhibit a remarkable virulence potential that is comparable to that of E. coli isolates from urinary tract infections and bacteremia.

Multicenter evaluation of the in vitro activity of dalbavancin tested against staphylococci and streptococci in 5 European countries: results from the DECIDE Surveillance Program (2007)

Dalbavancin is an antimicrobial lipoglycopeptide agent that has proven activity against Gram-positive pathogens and a once weekly dosing advantage compared with other agents in the glycopeptide class. The most common pathogens isolated from skin and skin structure infections (SSSIs) include Staphylococcus aureus and beta-hemolytic streptococci (betaHS), and dalbavancin has demonstrated excellent activity against these species. This study used 18 medical center laboratories in 5 European countries to assess the activity of dalbavancin, vancomycin, and teicoplanin against S. aureus, coagulase-negative staphylococci (CoNS), and betaHS. The rank order of potency was dalbavancin (MIC(50), 0.06 microg/mL) > teicoplanin (MIC(50), 0.5 microg/mL) > vancomycin (MIC(50), 2 microg/mL) and dalbavancin (MIC(50), 0.06 microg/mL) > teicoplanin and vancomycin (MIC(50), 2 microg/mL) against S. aureus and CoNS, respectively. Dalbavancin was the most active glycopeptide tested against betaHS with all strains inhibited by < or = 0.12 microg/mL. Susceptibility to other antimicrobial classes was also evaluated with noticeable differences demonstrated between countries. Higher methicillin-resistant S. aureus (MRSA) rates were observed in Italy (44.2%) and the United Kingdom (36.8%) compared with other countries, but resistance to erythromycin (51.6-83.1%) and clindamycin (5.7-68.4%) among MRSA also varied significantly between countries. The excellent contemporary activity of dalbavancin against common Gram-positive pathogens collected in European countries suggests that dalbavancin could have a role in the treatment of various types of SSSIs.

Daptomycin for the treatment of enterococcal bacteraemia: results from the Cubicin Outcomes Registry and Experience (CORE)

Enterococcal infections are a common cause of nosocomial bloodstream infections. Vancomycin resistance and the emergence of linezolid resistance necessitate alternative therapies. Studies in vitro as well as animal and case studies suggest that daptomycin may be effective in enterococcal infections. Patients with positive blood cultures for enterococci in the Cubicin((R)) Outcomes Registry and Experience (CORE) 2005-2006 were identified. Patients with endocarditis, intracardiac foreign body infections or non-speciated enterococci were excluded. Outcome was assessed using protocol-defined criteria. Of 159 patients included in the efficacy population, Enterococcus faecium and Enterococcus faecalis were isolated in 120 (75.5%) and 39 (24.5%) patients, respectively. Vancomycin resistance was detected in 91% and 23% of patients with E. faecium and E. faecalis infections, respectively. Prior to daptomycin, 94/159 (59.1%) and 35/159 (22.0%) patients had received vancomycin and linezolid, respectively. Daptomycin was first-line therapy in 27/159 cases (17%). Success was observed in 139/159 patients (87%) and in 104/120 (87%) and 35/39 (90%) patients with E. faecium and E. faecalis infections, respectively. Among the safety population (n=211), 20 (9.5%) experienced 28 adverse events possibly related to daptomycin, 8 of which were considered serious. Daptomycin may be a useful agent for treating enterococcal bacteraemia caused by E. faecium or E. faecalis. Further studies are warranted.

Antimicrobial resistance in Europe and its potential impact on empirical therapy

The problem of microbial drug resistance is a major public health concern, due to its global dimension and alarming magnitude, although the epidemiology of resistance can exhibit remarkable geographical variability and rapid temporal evolution. The major resistance issues overall are those related to methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant enterococci (VRE), Enterobacteriaceae producing extended-spectrum beta-lactamases, and multidrug-resistant Pseudomonas aeruginosa and Acinetobacter baumannii. Europe is not free from any of these issues, although their impact may be significantly different in different countries. MRSA rates are high in several European countries, but seem to have levelled off in some settings. Diffusion of VRE is still irregular. The most alarming resistance trends are those observed for Enterobacteriaceae and the Gram-negative non-fermenters, with a generalized increase in rates of resistance to the most important anti-Gram-negative agents (beta-lactams and fluoroquinolones) and the circulation of strains showing multidrug resistance phenotypes.

Antimicrobial drug use and resistance in Europe

Routine surveillance data indicate a relation between use and resistance and support interventions designed to reduce antimicrobial consumption at a national level in Europe.

Our study confronts the use of antimicrobial agents in ambulatory care with the resistance trends of 2 major pathogens, Streptococcus pneumoniae and Escherichia coli, in 21 European countries in 2000–2005 and explores whether the notion that antimicrobial drug use determines resistance can be supported by surveillance data at national aggregation levels. The data obtained from the European Surveillance of Antimicrobial Consumption and the European Antimicrobial Resistance Surveillance System suggest that variation of consumption coincides with the occurrence of resistance at the country level. Linear regression analysis showed that the association between antimicrobial drug use and resistance was specific and robust for 2 of 3 compound pathogen combinations, stable over time, but not sensitive enough to explain all of the observed variations. Ecologic studies based on routine surveillance data indicate a relation between use and resistance and support interventions designed to reduce antimicrobial drug consumption at a national level in Europe.

Activities of dalbavancin against a worldwide collection of 81,673 gram-positive bacterial isolates

Dalbavancin, a long-acting lipoglycopeptide, was evaluated against 81,673 isolates of staphylococci, enterococci, and streptococci collected from 33 countries during worldwide resistance surveillance (2002 to 2007). Regardless of susceptibility to oxacillin, comparable potencies for dalbavancin against Staphylococcus aureus and coagulase-negative staphylococci from all countries were noted (MIC(90), 0.06 to 0.12 microg/ml). Vancomycin-susceptible Enterococcus spp. had dalbavancin MIC(90)s comparable to those for staphylococci, whereas vancomycin-resistant strains were more resistant (MIC(50), >4 microg/ml). beta-Hemolytic and viridians group streptococci were very susceptible to dalbavancin (MIC(90), <or=0.03 microg/ml). Overall, dalbavancin was >or=16-fold more active than vancomycin against the monitored gram-positive species.

Management and Treatment Considerations for Infections Caused by Methicillin-Resistant Staphylococcus aureus

Infections caused by methicillin-resistant Staphylococcus aureus have been documented since the 1960s. Four decades later, this microorganism has evolved from a pathogen found primarily in the health care environment to a major pathogen of community-acquired infections. Interestingly, the community-acquired methicillin-resistant Staphylococcus aureus isolates tend to be genetically distinct from their health-care–acquired relatives, have a propensity to be more virulent, yet be susceptible to more antibiotics. Furthermore, infections caused in the pediatric population have a susceptibility pattern that differs from those found in adults. With an increase in infections caused by methicillin-resistant Staphylococcus aureus, empiric therapy should contain an agent with activity against this microorganism. Currently several options exist for the treatment of skin and skin structure infections, yet very few options are available for the treatment of more invasive diseases caused by methicillin-resistant Staphylococcus aureus. This article will review the history of methicillin-resistant Staphylococcus aureus, Staphylococcus aureus economic considerations, and the current plus future treatment options for these infections.

Central roles for IL-2 and MCP-1 following intranasal exposure to SEB: a new mouse model

Murine models for bacterial superantigens like staphylococcal enterotoxin B (SEB) have to date been rather cumbersome. The reasons include: (1) necessary use of potentiating agents such as actinomycin D, d-galactosamine, lipopolysaccharide (LPS), or viruses; (2) high toxin amounts required to elicit effects; and/or (3) generation of phenotypic-stable transgenic animals. Our study employed readily available C3H/HeJ (TLR4 negative, LPS-nonresponsive) mice with intranasal and intraperitoneal administration of low microgram quantities of SEB. These animals responded to SEB with severe lung inflammation and hypothermia, culminating in death. A survey of cytokines/chemokines in sera and lungs after lethal intoxication revealed that monocyte chemoattractant protein-1 and interleukin-2 were associated with effects in this model. In contrast, SEB had minimal effects upon congenic (TLR4 positive, LPS-responsive) C3H/OuJ mice. Lethality of SEB in C3H/HeJ mice was neutralized with SEB-specific antibodies, suggesting potential utility of this model for future therapeutic studies.

In vitro activity of ceftobiprole against pathogens from two phase 3 clinical trials of complicated skin and skin structure infections

In phase 3 clinical trials for ceftobiprole treatment of complicated skin and skin structure infections, 1,219 gram-positive and 276 gram-negative aerobic baseline pathogens were identified. Ceftobiprole inhibited all staphylococcal isolates, including methicillin-resistant strains, at MICs of </=4 mug/ml. Against Enterobacteriaceae and Pseudomonas aeruginosa isolates, the potency of ceftobiprole was similar to that of cefepime.

Future strategies for treating Staphylococcus aureus bloodstream infections

Bloodstream infections are potentially life-threatening diseases. They can cause serious secondary infections, such as infective endocarditis and osteomyelitis, and may result in severe sepsis. One of the most critical determinants of survival is the induction of timely and effective antibiotic therapy. One of the leading causes of bloodstream infections is Staphylococcus aureus, with an increasing proportion of isolates being resistant to methicillin. Methicillin-resistant S. aureus (MRSA) is associated with greater morbidity and mortality rates than methicillin-sensitive S. aureus (MSSA). Standard-of-care antibiotic treatments for S. aureus bloodstream infections are limited by toxicity and/or differential efficacy against MRSA and MSSA, which makes the choice of empirical therapy difficult. New management strategies are required to address the challenges raised by S. aureus bloodstream infections and MRSA in particular. These may include the use of techniques that allow the early identification of complications arising from S. aureus bacteraemia, rapid pathogen identification to enable the administration of appropriate antibiotic therapy, and the identification of new drugs with novel modes of action that may circumvent antibiotic resistance and enable effective empirical treatment of both MSSA and MRSA infections.

Mechanisms of antibiotic resistance in Staphylococcus aureus

Staphylococcus aureus can exemplify better than any other human pathogen the adaptive evolution of bacteria in the antibiotic era, as it has demonstrated a unique ability to quickly respond to each new antibiotic with the development of a resistance mechanism, starting with penicillin and methicillin, until the most recent, linezolid and daptomycin. Resistance mechanisms include enzymatic inactivation of the antibiotic (penicillinase and aminoglycoside-modification enzymes), alteration of the target with decreased affinity for the antibiotic (notable examples being penicillin-binding protein 2a of methicillin-resistant S. aureus and D-Ala-D-Lac of peptidoglycan precursors of vancomycin-resistant strains), trapping of the antibiotic (for vancomycin and possibly daptomycin) and efflux pumps (fluoroquinolones and tetracycline). Complex genetic arrays (staphylococcal chromosomal cassette mec elements or the vanA operon) have been acquired by S. aureus through horizontal gene transfer, while resistance to other antibiotics, including some of the most recent ones (e.g., fluoroquinolones, linezolid and daptomycin) have developed through spontaneous mutations and positive selection. Detection of the resistance mechanisms and their genetic basis is an important support to antibiotic susceptibility surveillance in S. aureus.

Activity of dalbavancin tested against Staphylococcus spp. and beta-hemolytic Streptococcus spp. isolated from 52 geographically diverse medical centers in the United States

Dalbavancin is a lipoglycopeptide antimicrobial agent with a potency significantly better than that of vancomycin when tested against staphylococci and streptococci. These two pathogens are common causes of skin and skin structure infections (SSSIs), and dalbavancin has been approved for the treatment of moderate to severe SSSIs. This study generated susceptibility data for staphylococci and beta-hemolytic streptococci from 52 U.S. medical centers that locally tested dalbavancin, vancomycin, and other antimicrobial class representatives to assess the potency of dalbavancin and the overall contemporary activities of commonly prescribed agents. Locally generated data showed that oxacillin-resistant staphylococci (57.0% overall) had slightly higher dalbavancin MIC(90) values (0.19 microg/ml) than oxacillin-susceptible strains (0.125 microg/ml). This potency was 8- to 16-fold greater than that for vancomycin. beta-Hemolytic streptococci had MIC(90) values ranging between <or=0.016 and 0.064 microg/ml (highest for group B isolates). Levofloxacin, gentamicin, and tetracycline were active against oxacillin-susceptible staphylococci (82 to 99% susceptible), with lower susceptibility rates seen for the oxacillin-resistant strains. Linezolid coverage was >98% against staphylococci. Erythromycin resistance was high for staphylococci (30.6 to 94.1%) with inducible clindamycin resistance rates of 26.0% and 55.0% for oxacillin-susceptible and -resistant Staphylococcus aureus, respectively. Beta-hemolytic streptococci had a 20.2% erythromycin resistance rate and a 60% inducible clindamycin resistance rate but were highly susceptible to other tested agents. Etest reading errors were apparent and skewed results towards slightly higher dalbavancin MICs, requiring further education on how to interpret Etest method results for this compound. Current disk diffusion breakpoint criteria for oxacillin susceptibility for S. aureus showed a very-major-error rate of 2.3% and only a 0.9% minor-error rate when cefoxitin was used to predict oxacillin susceptibility. Dalbavancin demonstrated excellent potency and activity (100% susceptibility at proposed breakpoints) against common causes of SSSI pathogens in this U.S. multicenter study sample.