In vitro activity of tigecycline (GAR-936) tested against 11,859 recent clinical isolates associated with community-acquired respiratory tract and gram-positive cutaneous infections

Risk factors for tigecycline-induced hypofibrinogenaemia

WHAT IS KNOWN AND OBJECTIVE

Hypofibrinogenaemia is major treatment-related adverse event associated with tigecycline therapy, which in some cases can result in treatment termination. We aimed to identify the risk factors for tigecycline-induced hypofibrinogenaemia.

METHODS

We retrospectively retrieved 426 Chinese patients who were undergoing tigecycline therapy ≥ 3 days.

RESULTS AND DISCUSSION

There were 426 patients treated with tigecycline. The mean age was 60.31 ± 19.23 years, and 299 (70.19%) patients were male. Of the patients, 50.5% developed hypofibrinogenaemia and 10.1% of patients developed bleeding. Compared with before treatment, fibrinogen (FIB) significantly decreased after tigecycline was used while prothrombin time (PT), activated partial thromboplastin time (APTT) and thrombin time (TT) significantly increased (all P < .001). There was no statistically significant difference in platelet count, hepatic function, and renal function before and after tigecycline treatment (all P > .05). In analysing relevant risk factors, extension of the tigecycline treatment course was found to be the main risk factor for tigecycline-induced hypofibrinogenaemia. Regardless of whether patients received the standard dose or high dose of tigecycline, the long treatment course group (>14 days) had more patients with hypofibrinogenaemia than the routine treatment course group (52.21% vs 40.74%, 48.81% vs 19.44%, all P < .05). Renal failure (whether requiring or not requiring dialysis) is also a risk factor for tigecycline-induced hypofibrinogenaemia (OR [95% CI]: 2.450 [1.335-4.496]).

WHAT IS NEW AND CONCLUSION

Tigecycline administration has been related to hypofibrinogenaemia, especially patients with renal failure and when long treatment course of tigecycline are used. We recommend that coagulation function be closely monitored in patients with the aforementioned risk factors for tigecycline-induced hypofibrinogenaemia to ensure patient safety.

Tigecycline

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Tigecycline treatment causes a decrease in fibrinogen levels

The objective of this study was to assess the impact of tigecycline treatment on coagulation parameters, specifically fibrinogen, in patients with severe infections. We examined 20 cases of tigecycline-treated patients with severe infections, including hospital-acquired pneumonia, complicated intra-abdominal infections, complicated skin and soft tissue infections, and bloodstream infections. We monitored the relative markers of coagulation and renal and liver function before, during, and after treatment. Fibrinogen (FIB) levels decreased significantly after the use of tigecycline and normalized after the cessation of treatment. FIB levels significantly decreased in the patients treated with the recommended dose or a higher treatment dose. The FIB levels decreased more in the higher-treatment-dose group. There was no difference in the decrease in FIB levels or the FIB level recovery by age. Prothrombin time (PT), activated partial thromboplastin time (APTT), and thrombin time (TT) were prolonged after tigecycline use. The TT decreased after the cessation of treatment, and the PT and APTT also decreased but not to a significant level. There was no change in platelet, alanine aminotransferase (ALT), or creatinine (Cr) levels associated with treatment. The use of tigecycline was associated with decreased FIB levels, which returned to normal after the cessation of treatment. A high-dose treatment group showed greater decreases in FIB levels than did patients treated with the recommended dose. The decline in FIB was not related to patient age. The use of tigecycline was associated with prolonged PT, APTT, and TT.

Tigecycline: a novel glycylcycline antibiotic

Tigecycline, the first-in-class glycylcycline, was developed to recapture the broad spectrum of activity of the tetracycline class and to treat patients with difficult-to-treat bacterial infections. Tigecycline's in vitro spectrum of activity encompasses aerobic, facultative and anaerobic Gram-positive and -negative bacteria, including antimicrobial-resistant bacteria such as methicillin-resistant Staphylococcus aureus, vancomycin-resistant Enterococcus faecalis and Enterococcus faecium, and extended-spectrum beta-lactamase-producing Enterobacteriaceae. Clinical trials involving patients with complicated skin and skin-structure infections and complicated intra-abdominal infections, including patients infected with methicillin-resistant S. aureus, demonstrated that tigecycline was bacteriologically and clinically effective with mild-to-moderate gastrointestinal adverse events (i.e., nausea, vomiting and diarrhea) the most commonly reported. Tigecycline is a promising new broad-spectrum parenteral monotherapy for the treatment of patients with Gram-positive and -negative bacterial infections.

Resistance and the management of complicated skin and skin structure infections: the role of ceftobiprole

Antimicrobial resistant bacteria are an increasing concern due to the resulting increase in morbidity, mortality, and health-care costs associated with the administration of inadequate or delayed antimicrobial therapy. The implications of inadequate antimicrobial therapy in complicated skin and skin structure infections (cSSSIs) have gained more attention recently, most likely due to the recent emergence of community-acquired methicillin resistant Staphylococcus aureus (MRSA) and the already high prevalence of MRSA in the nosocomial setting. Due to the continuous threat of resistance arising and the limitations of currently available agents for the treatment of cSSSIs, it is necessary to develop new antimicrobials for this indication. Ceftobiprole medocaril, the prodrug of ceftobiprole, is a parental investigational cephalosporin for the treatment of cSSSIs displaying a wide-spectrum of activity against both Gram-positive and Gram-negative species, including MRSA. Ceftobiprole displays noncomplex linear pharmacokinetics, is eliminated primarily by glomerular filtration, and distributes to extracellular fluid. Additionally, it has been shown that the extent of distribution to the site of action with regard to cSSSIs, ie, the extracellular space fluid of subcutaneous adipose tissue and skeletal muscle, is expected to be efficacious, as free concentrations meet efficacy targets for most pathogens. Similar to other beta-lactams, it displays an excellent safety and tolerability profile with the primary adverse events being dysgeusia in healthy volunteers, resulting from the conversion of the prodrug to the active, and nausea in patients. Ceftobiprole has demonstrated noninferiority in two large-scale pivotal studies comparing it to vancomycin, clinical cure rates 93.3% vs 93.5%, respectively, or vancomycin plus ceftazidime, clinical cure rates 90.5% vs 90.2%, respectively. Given the pharmacokinetic and pharmacodynamic properties, ceftobiprole is a promising new agent for the treatment of cSSSIs and has the potential to be used as a single agent for empiric treatment.

New therapeutic choices for infections caused by methicillin-resistant Staphylococcus aureus

In recent years, a marked increase in the incidence of infections caused by methicillin-resistant Staphylococcus aureus (MRSA) has occurred in many countries. This review addresses the effectiveness and limitations of drugs classically used for the treatment of MRSA, e.g. vancomycin, and also newer anti-MRSA antimicrobials, e.g. second-generation glycolipopeptides, tigecycline, and beta-lactams.

In vitro antibacterial activity of tigecycline against resistant Gram-negative bacilli and enterococci by time-kill assay

This time-kill study was performed with 65 genetically unique clinical isolates of Gram-negative bacilli and enterococci to further define the antibacterial activity of tigecycline. To our knowledge, this is the largest published time-kill study evaluating tigecycline activity to date. Isolates evaluated were 10 meropenem-resistant Acinetobacter baumannii; 15 Escherichia coli, including 10 extended-spectrum beta-lactamase (ESBL) producers; 15 Klebsiella pneumoniae, including 10 ESBL producers; 20 vancomycin-resistant Enterococcus faecium (VRE), including 10 that were linezolid resistant; and 5 vancomycin-susceptible Enterococcus faecalis. Time-kill testing was performed using tigecycline concentrations of 1x, 2x, and 4x MIC with colony-forming units (CFU) per milliliter determined at 0, 4, 8, 12, 24, 36, and 48 h. Tigecycline MICs (microg/mL) were < or =1 for E. coli and K. pneumoniae, regardless of the isolates' ESBL production; A. baumannii, 0.06 to 4; 9/10 (90%) were < or =2; E. faecalis < or =0.12; and VRE < or =0.25, regardless of linezolid susceptibility. In the time-kill assay, tigecycline significantly inhibited bacterial growth when compared with the growth control. The reduction in growth was <3 log(10) CFU/mL for all isolates, indicative of a bacteriostatic effect.

Tigecycline: A review of a new glycylcycline antibiotic

Tigecycline derived from minocycline. It is part of a new class of antibiotics called glycylcyclines. Tigecycline is given intravenously and has activity against a variety of gram-positive and gram-negative bacterial pathogens, many of which are resistant to existing antibiotics. Tigecycline successfully completed phase III trials in which it was at least equal to intravenous vancomycin and aztreonam to treat complicated skin and skin structure infections (cSSSI), and to intravenous imipenem and cilastatin to treat complicated intra-abdominal infections (cIAI). Tigecycline side effects are primarily digestive upset. It should be a valuable addition to the armamentarium to treat even the most resistant pathogens.

Tigecycline: in community-acquired pneumonia

Tigecycline is a first-in-class glycylcycline, broad-spectrum, intravenous antibacterial developed to overcome the two major mechanisms of tetracycline resistance (ribosomal protection and efflux). The drug has been in use since 2005 for complicated intra-abdominal infections, and complicated skin and soft tissue structure infections, but is currently being assessed in the US for community-acquired pneumonia (CAP) in adults. In vitro, tigecycline had good activity against a range of Gram-positive, Gram-negative and atypical community-acquired respiratory tract pathogens implicated in CAP. Compared with other antibacterials, tigecycline has a prolonged post-antibiotic effect against key bacteria and a long serum elimination half-life in humans. The drug effectively penetrates lung tissue. The combined results of two well designed, phase III studies demonstrated that tigecycline 100 mg initially, followed by 50 mg every 12 hours for 7-14 days was not inferior to recommended dosages of levofloxacin in the treatment of hospitalized patients with CAP. Clinical cure rates were 89.7% versus 86.3% in the clinically evaluable population and 81.0% versus 79.7% in the clinical modified intent-to-treat population. Tigecycline was generally well tolerated in patients with CAP.

Postantibiotic effect of tigecycline against 14 gram-positive organisms

The in vitro postantibiotic effects (PAEs), postantibiotic sub-MIC effects (PA-SMEs), and sub-MIC effects of tigecycline were determined for 14 gram-positive and gram-negative organisms. The pneumococcal, staphylococcal, and enterococcal PAEs were 1.9 to 5.1, 2.9 to 5.7, and 3.9 to 6.1 h, respectively, and those for Haemophilus influenzae, Escherichia coli, Klebsiella pneumoniae, Enterobacter cloacae, and Acinetobacter baumannii were 1.1 to 5.0, 1.9 to 2.1, 1.7 to 1.8, 1.0 to 1.7, and 0.7 to 3 h, respectively. The PA-SMEs (four times the MIC) ranged from 6.7 to >11 h for gram-positive organisms and from 2.3 to >11.3 h for gram-negative organisms.

In vitro activity of tigecycline: MICs, MBCs, time-kill curves and post-antibiotic effect

The minimum inhibitory concentrations (MICs), minimum bactericidal concentrations (MBCs), time-kill curves, and postantibiotic effect (PAE) of tigecycline, the first in the glycylcycline class of antibiotics, were evaluated. MICs were determined against 749 clinical isolates. Time-kill curves were performed against two isolates each of Enterococcus faecalis, MSSA, and MRSA. The presence of PAE, against the same isolates, was investigated. MIC(90)s (microg/mL) were the following: Escherichia coli 0.25; Klebsiella spp 0.5; Enterobacter spp 1; Acinetobacter spp. 2; Staphylococcus aureus (MSSA+MRSA) 0.25; CNS (MS+MR) 0.25; vancomycin-susceptible Enterococcus faecalis 0.12. Tigecycline exerted bacteriostatic activity against all the tested isolates, MBC(90)values being 32xMIC. Time-kill experiments showed a marked reduction in bacterial growth. A PAE at 1- to 20-fold the MIC was observed against the two enterococcal isolates (1.5-3.2h, range) and the four staphylococci (1.6-3h, range). Our findings confirm the excellent antimicrobial activity of tigecycline, adding informations on its bacteriostatic activity vs enterococci and staphylococci, whether methicillin-resistant or -susceptible, and its PAE.

In vitro activity of daptomycin and tigecycline against coagulase-negative staphylococcus blood isolates from bone marrow transplant recipients

BACKGROUND AND OBJECTIVE

Multi-resistant coagulase-negative staphylococci (CNS) may cause systemic infections in patients undergoing bone marrow transplantation. Daptomycin, a new lipopeptide, and tigecycline, a new glycylcycline, have excellent activity against Gram-positive bacteria including methicillin-resistant staphylococci. This study presents the in vitro activity of daptomycin and tigecycline compared to vancomycin and fosfomycin against 105 CNS isolated from 76 bone marrow transplant patients with symptomatic bacteremia.

MATERIAL AND METHODS

Blood stream isolates of Staphylococcus epidermidis (n = 102) and Staphylococcus haemolyticus (n = 3) from bone marrow transplant patients were collected from 2000 to 2006. The susceptibility of all isolates was tested using methods of the Clinical Laboratory Standards Institute.

RESULTS

The minimal inhibitory concentrations MIC(50) and MIC(90) were 0.125 microg/mL and 0.25 microg/mL for daptomycin, 0.25 and 0.5 microg/mL for tigecycline, 1 microg/mL and 2 microg/mL for vancomycin, and 8 microg/mL and >256 microg/mL for fosfomycin, respectively. MIC values of tested agents were similar for both methicillin-sensitive and methicillin-resistant S. epidermidis strains.

CONCLUSIONS

All CNS isolates were susceptible to the new antistaphylococcal agents daptomycin and tigecycline. Although vancomycin had been used over the past 30 yr at our bone marrow transplant unit all CNS were still susceptible to vancomycin.

Capability of 11 antipneumococcal antibiotics to select for resistance by multistep and single-step methodologies

Testing of 12 pneumococcal strains with differing resistotypes [including tet(M) positive] showed that tigecycline, amoxicillin-clavulanate, imipenem, and ceftriaxone did not select for resistant clones after 50 sequential subcultures. By comparison, azithromycin, clarithromycin, clindamycin, telithromycin, levofloxacin, moxifloxacin, and gemifloxacin did show resistant clones. Tigecycline also yielded a low frequency of resistance in single-step tests compared to all beta-lactams, macrolides/ketolides, and quinolones tested.

Prevalence and regional variation in meticillin-resistant Staphylococcus aureus (MRSA) in the USA and comparative in vitro activity of tigecycline, a glycylcycline antimicrobial

The Tigecycline Evaluation and Surveillance Trial (T.E.S.T.) is a surveillance study established in 2004 to monitor the activity of tigecycline, the first glycylcycline, and comparator agents [β-lactams (including penicillins, cephalosporins and carbapenems), glycopeptides, tetracyclines, fluoroquinolones and oxazolidinones] against Gram-positive and Gram-negative pathogens worldwide. This report examines 1692 isolates of Staphylococcus aureus collected in the continental United States between January 2004 and September 2005. Meticillin-resistant S. aureus (MRSA) accounted for 52.0 % of isolates. Prevalence of MRSA by state ranged from 12.5 % in New Hampshire to 100 % in Kentucky. All isolates were susceptible to tigecycline, linezolid and vancomycin. In vitro, tigecycline was potent against both meticillin-susceptible S. aureus (MSSA) (MIC50 and MIC90=0.12 μg ml−1) and MRSA (MIC50=0.12 μg ml−1; MIC90=0.25 μg ml−1). Only a single isolate was resistant to three or more antimicrobial classes. Ninety-six isolates (5.7 %) were susceptible to the complete antimicrobial panel.

Tigecycline: in-vitro performance as a predictor of clinical efficacy

The incidence of nosocomial disease caused by Gram-negative pathogens is increasing, and infections caused by Enterobacter, Klebsiella, Acinetobacter, Escherichia coli and Pseudomonas aeruginosa are more commonly refractive to traditional antimicrobial agents, including aminoglycosides, fluoroquinolones and broad-spectrum cephalosporins. The most important mechanism of resistance to beta-lactam antibiotics among Gram-negative bacilli involves the production of beta-lactamases. Extended-spectrum beta-lactamases are particularly worrisome, since they are often associated with multidrug resistance phenotypes, which can pose a significant therapeutic challenge. Novel agents for the treatment of Gram-negative infections are uncommon, as recent emphasis has been placed on the development of agents targeting drug-resistant strains of Gram-positive bacteria, e.g., streptococci, enterococci and staphylococci. Tigecycline, a semi-synthetic derivative of minocycline, has a unique and novel mechanism of action, which not only allows this agent to overcome the well-known tet gene-encoded resistance mechanisms, but also maintains its activity against Gram-negative pathogens producing a broad array of extended-spectrum beta-lactamases. Tigecycline is the first example of a new class of glycylcyclines with activity against a wide range of clinically important Gram-negative pathogens. Tigecycline has potent antimicrobial activity, and has been associated with an excellent therapeutic response in animal infection models and recently reported clinical trials, which reflect the effectiveness of tigecycline against pathogens causing intra-abdominal, skin and soft-tissue infections, including susceptible or multidrug-resistant strains of most Enterobacteriaceae, as well as anaerobic pathogens.

Clonal diversity and resistance mechanisms in tetracycline-nonsusceptible Streptococcus pneumoniae isolates in Poland

The frequency of tetracycline resistance in Streptococcus pneumoniae isolates in Poland is one of the highest in Europe. The aim of this study was to analyze the clonal diversity and resistance determinants of tetracycline-nonsusceptible S. pneumoniae isolates identified in Poland and to investigate the effect of tetracycline resistance on their susceptibilities to tigecycline, doxycycline, and minocycline. We have analyzed 866 pneumococcal isolates collected from 1998 to 2003 from patients with respiratory tract diseases, and 242 of these (27.9%) were found to be resistant to tetracycline. All of the resistant isolates were characterized by testing of their susceptibilities to other antimicrobials, serotyping, pulsed-field gel electrophoresis (PFGE), and identification of tetracycline resistance genes and transposons. Selected isolates representing the main PFGE types were analyzed by multilocus sequence typing. Among the isolates investigated, 27 serotypes and 146 various PFGE patterns, grouped into 90 types, were discerned. The most common PFGE type, corresponding to serotype 19F and sequence type 423, was represented by 22.3% of all of the tetracycline-resistant isolates. The tet(M) gene was the sole resistance gene in the group of isolates studied, and in over 96% of the isolates, the Tn916 family of tet(M)-containing conjugative transposons was detected. Several isolates contained specific variants of the transposons, the Tn1545-like, Tn3872-like, or Tn2009-like element. The correlation between the MICs of tetracycline, doxycycline, and minocycline was revealed, whereas no cross-resistance to tetracycline and tigecycline was observed.

Tigecycline: a glycylcycline antimicrobial agent

BACKGROUND

Tigecycline, the first glycylcycline to be approved by the US Food and Drug Administration, is a structural analogue of minocycline that was designed to avoid tetracycline resistance mediated by ribosomal protection and drug efflux. It is indicated for the treatment of complicated skin and skin-structure infections and complicated intra-abdominal infections and is available for intravenous administration only.

OBJECTIVE

This article summarizes the in vitro and in vivo activities and pharmacologic and pharmacokinetic properties of tigecycline, and reviews its clinical efficacy and tolerability profile.

METHODS

Relevant information was identified through a search of MEDLINE (1966-April 2006), Iowa Drug Information Service (1966-April 2006), and International Pharmaceutical Abstracts (1970-April 2006) using the terms tigecycline, GAR-936, and glycylcycline. Also consulted were abstracts and posters from meetings of the Infectious Diseases Society of America and the Interscience Conference on Antimicrobial Agents and Chemotherapy (1999-2006) and documents provided for formulary consideration by the US manufacturer of tigecycline.

RESULTS

Like the tetracyclines, tigecycline binds to the 30S subunit of bacterial ribosomes and inhibits protein synthesis by preventing the incorporation of amino acid residues into elongating peptide chains. In vitro, tigecycline exhibits activity against a wide range of clinically significant gram-positive and gram-negative bacteria, including multidrug-resistant strains (eg, oxacillin-resistant Staphylococcus aureus, vancomycin-resistant enterococci, extended-spectrum beta-lactamase-producing Enterobacteriaceae), and anaerobes (eg, Bacteroides spp). In pharmacokinetic studies in human adults, tigecycline had a large Vd (7-9 L/kg), was moderately bound to plasma protein (71%-89%), had an elimination t(1/2) of 42.4 hours, and was eliminated primarily by biliary/fecal (59%) and renal (33%) excretion. Dose adjustment did not appear to be necessary based on age, sex, renal function, or mild to moderate hepatic impairment (Child-Pugh class A-B). In patients with severe hepatic impairment (Child-Pugh class C), the maintenance dose should be reduced by 50%. In 4 Phase III clinical trials in patients with complicated skin and skin-structure infections and complicated intra-abdominal infections, tigecycline was reported to be noninferior to its comparators (vancomycin + aztreonam in 2 studies and imipenem/cilastatin in 2 studies), with clinical cure rates among clinically evaluable patients of >80% (P < 0.001 for noninferiority). The most frequently reported (> or =5 %) adverse events with tigecycline were nausea (28.5%), vomiting (19.4%), diarrhea (11.6%), local IV-site reaction (8.2%), infection (6.7%), fever (6.3%), abdominal pain (6.0%), and headache (5.6%). The recommended dosage of tigecycline is 100 mg IV given as a loading dose, followed by 50 mg IV g12h for 5 to 14 days.

CONCLUSIONS

In clinical trials, tigecycline was effective for the treatment of complicated skin and skin-structure infections and complicated intra-abdominal infections. With the exception of gastrointestinal adverse events, tigecycline was generally well tolerated. With a broad spectrum of activity that includes multidrug-resistant gram-positive and gram-negative pathogens, tigecycline may be useful in the treatment of conditions caused by these pathogens.

Tigecycline: first of a new class of antimicrobial agents

Tigecycline is the first commercially available member of the glycylcyclines, a new class of antimicrobial agents. The glycylcyclines are derivatives of the tetracycline antibiotics, with structural modifications that allow for potent gram-positive, gram-negative, and anaerobic activity, including certain multidrug-resistant strains. The enhanced activity can be attributed to stronger binding affinity and enhanced protection against several mechanisms of resistance that affect other antibiotic classes such as tetracyclines. Tigecycline exhibits generally bacteriostatic action by reversibly binding to the 30S ribosomal subunit and inhibiting protein translation. In vitro activity has been demonstrated against multidrug-resistant gram-positive pathogens including methicillin-resistant and glycopeptide-intermediate and -resistant Staphylococcus aureus, as well as vancomycin-resistant enterococci. Multidrug-resistant gram-negative pathogens, such as Acinetobacter baumannii and extended-spectrum beta-lactamase-producing Klebsiella pneumoniae and Escherichia coli, are typically highly susceptible to tigecycline. The drug also has displayed significant activity against many clinically important anaerobic organisms. This agent demonstrates a predictable pharmacokinetic profile and minimal drug interactions, and is generally well tolerated, with nausea being the most common adverse event. It was approved in June 2005 for the treatment of complicated skin and skin structure infections (SSSIs) and complicated intraabdominal infections. Currently, a limited number of broad-spectrum antimicrobials are available to combat multidrug-resistant organisms. The addition of new agents is essential to limiting the spread of these pathogens and improving outcomes in patients with these types of infections. Tigecycline has demonstrated promising results in initial in vitro and clinical studies for SSSIs and complicated intraabdominal infections; however, further clinical experience will clarify its role as a broad-spectrum agent.

Activity of tigecycline against clinical isolates of Staphylococcus aureus and extended-spectrum β-lactamase-producing Escherichia coli in Granada, Spain

We evaluated the in vitro activity of tigecycline using the Etest and disk diffusion method according to Clinical and Laboratory Standards Institute guidelines against clinical isolates of methicillin-susceptible Staphylococcus aureus (MSSA) and methicillin-resistant S. aureus (MRSA) as well as for CTX-M-9 extended-spectrum beta-lactamase (ESBL)-producing Escherichia coli and SHV ESBL-producing E. coli. All isolates were susceptible to tigecycline according to US Food and Drug Administration cut-off points. There were no differences in the activity of tigecycline between MSSA and MRSA isolates or between the presence of either type of ESBL. For each type of microorganism studied, we established the equation relating the minimum inhibitory concentration to the diameter of the zone of inhibition.

In vitro activity of tigecycline against isolates from patients enrolled in phase 3 clinical trials of treatment for complicated skin and skin-structure infections and complicated intra-abdominal infections

The in vitro activity of tigecycline was evaluated against 4913 baseline pathogens isolated from 1986 patients enrolled in 4 pivotal phase 3 clinical trials. The trials, which were conducted in 38 countries worldwide, involved patients with complicated skin and skin-structure infections or complicated intra-abdominal infections. Tigecycline was active against the most prevalent pathogens for each infection type, including gram-positive and gram-negative strains of both aerobic and anaerobic bacteria (MICs, < or =2 microg/mL for most pathogens). The spectrum of activity of tigecycline included important pathogens, such as Staphylococcus aureus (including methicillin-resistant S. aureus), Streptococcus pyogenes, Escherichia coli, Klebsiella pneumoniae, and Bacteroides fragilis. A few genera, such as Pseudomonas aeruginosa and members of the tribe Proteeae, were generally less susceptible to tigecycline than were other gram-negative pathogens. The susceptibility of the pathogens to tigecycline was similar for isolates obtained from patients enrolled in the studies of complicated skin and skin-structure infection or of complicated intra-abdominal infection. For most pathogens, the susceptibility to tigecycline was similar across all geographic regions. The excellent expanded broad-spectrum activity of tigecycline demonstrated in vitro against clinical isolates confirmed its potential utility for pathogens associated with complicated skin and skin-structure infections or complicated intra-abdominal infections.

Successful salvage therapy with tigecycline after linezolid failure in a liver transplant recipient with MRSA pneumonia

Pulmonary infections are a significant cause of morbidity and mortality after liver transplantation. Infections with methicillin-resistant Staphylococcus aureus (MRSA) have increased in the last 10 years. Mortality may exceed 80% in liver transplant recipients who develop MRSA pneumonia. A 57-year-old male following living-donor liver transplantation developed a right-sided MRSA pneumonia 6 weeks after transplantation, which required artificial ventilation for 14 weeks. Initially, pneumonia was treated with linezolid. However, after 12 days under current therapy, the infection spread out to both lungs. At that time. we initiated the treatment with tigecycline. Under this therapy, the patient could be cured from MRSA pneumonia and was extubated. We detected no tigecycline related hepatotoxic effect. In conclusion, this case suggests that tigecycline may be useful in the salvage therapy of pneumonia due to MRSA after linezolid failure.

Antimicrobial activity of tigecycline against recent isolates of respiratory pathogens from Asian countries

In vitro activities of tigecycline were compared with 15 other comparator agents against recent clinical isolates of respiratory pathogens (623 Streptococcus pneumoniae, 105 Staphylococcus aureus, 92 Klebsiella pneumoniae, and 84 Haemophilus influenzae isolates) collected from 11 Asian countries. All isolates of S. pneumoniae from Asian countries were susceptible to tigecycline regardless of penicillin susceptibility with MIC90 of <or=0.06 mg/L. Both methicillin-resistant and methicillin-susceptible S. aureus isolates were susceptible to tigecycline with very low MIC90 values (0.25 and 0.12 mg/L, respectively). Tigecycline was also active against K. pneumoniae (98.9% susceptible; MIC50, 1 mg/L; MIC90, 2 mg/L) including 10 extended-spectrum beta-lactamase-producing isolates and H. influenzae (100% susceptible; MIC50 and MIC90, 0.12 mg/L) from Korea. Data confirmed that tigecycline has an excellent in vitro activity against drug-resistant clinical isolates of respiratory pathogens from Asian countries.

Tigecycline: a novel glycylcycline

Antibacterials have been in clinical use for almost 60 years; however, the effectiveness of these valuable agents has been diminished by widespread emergence of bacterial resistance. Tigecycline is the first in a new class of glycylcyclines with activity against a wide range of clinically important pathogens. Tigecycline has demonstrated potent microbiological activity and excellent therapeutic response in animal infection models and in recently reported phase III human clinical trials. It is effective against intra-abdominal and skin and soft tissue infections caused by susceptible or multidrug-resistant staphylococci, enterococci or streptococci as well as most Enterobacteriaceae and anaerobic pathogens. In clinical trials nausea and vomiting were the most common adverse events and were of a magnitude typical of those observed with tetracyclines in general. Additionally, tigecycline has proven to be efficacious in animal models of infection, including pneumonia, endocarditis and peritonitis. Tigecycline is only available as an intravenous agent and distributes extensively in tissues. Administration of a 100mg loading dose of tigecycline followed by twice-daily doses of 50mg yielded an apparent volume of distribution of 7-10 L/kg. Systemic clearance ranged from 0.2 to 0.3 L/h/kg and its half-life varied from 37 to 67 hours. The pharmacokinetics of tigecycline appear unaffected by sex, age, renal disease or the presence of food. Data from animal studies would suggest that time above the minimum inhibitory concentration is the pharmacodynamic factor that best correlates with bacterial eradication. The efficacy, safety profile and pharmacodynamic attributes of tigecycline support its continuing clinical development as empirical parenteral treatment of challenging nosocomial and community-acquired infections, including those caused by proven or suspected resistant pathogens.

Tigecycline: A new glycylcycline antimicrobial agent

PURPOSE

The pharmacology, spectrum of activity, pharmacokinetics, clinical efficacy, adverse events, dosage and administration, drug interactions, and place in therapy of tigecycline are reviewed.

SUMMARY

Tigecycline is the first of a new class of antimicrobials, the glycylcyclines, to receive approved labeling from the Food and Drug Administration. Similar to tetracyclines, glycylcyclines contain the central four-ring carbocyclic skeleton, with a substitution at the D-9 position. This substitution confers expanded broad-spectrum activity and defense against antimicrobial efflux pumps and ribosomal protection mechanisms. Tigecycline covers a broad spectrum of gram-positive (including resistant isolates), gram-negative (including extended-spectrum beta-lactamase producing organisms), and anaerobic pathogens. It does not exhibit activity against Pseudomonas aeruginosa and Proteus species. Clinical efficacy has been demonstrated in complicated skin and skin structure infections and intraabdominal infections. Tigecycline is administered intravenously and exhibits linear pharmacokinetics. The drug does not undergo extensive metabolism and works independently of the cytochrome P-450 isoenzyme system and therefore does not affect medications metabolized by these enzymes. Tigecycline is administered as a 100-mg i.v. loading dose followed by 50 mg i.v. every 12 hours. Hepatic dosage adjustment is necessary for severe disease; however, no dosage adjustments are necessary for patients with renal impairment.

CONCLUSION

Tigecycline is an alternative agent available for the treatment of resistant gram-negative and gram-positive infections, especially in patients with a history of a penicillin allergy or antimicrobial-related toxicities.

Investigational new drugs for the treatment of resistant pneumococcal infections

Antibiotic resistance in Streptococcus pneumoniae is not only increasing with penicillin but also with other antimicrobial classes including the macrolides, tetracyclines and sulfonamides. This trend with antibiotic resistance has highlighted the need for the further development of new anti-infectives for the treatment of pneumococcal infections, particularly against multi-drug resistant pneumococci. Several new drugs with anti-pneumococcal activity are at various stages of development and will be discussed in this review. Two new cephalosporins with activity against S. pneumoniae include ceftobiprole and RWJ-54428. Faropenem is in a new class of beta-lactam antibiotics called the penems. Structurally, the penems are a hybrid between the penicillins and cephalosporins. Sitafloxacin and garenoxacin are two new quinolones that are likely to have a role in treating pneumococcal infections. Oritavancin and dalbavancin are glycopeptides with activity against methicillin-resistant S. aureus and vancomycin-resistant Enterococcus spp. as well as multi-drug resistant pneumococci. Tigecycline is the first drug in a new class of anti-infectives called the glycycyclines that has activity against penicillin-resistant pneumococci.

In vitro activities of tigecycline, ertapenem, isepamicin, and other antimicrobial agents against clinically isolated organisms in Taiwan

This study evaluated the in vitro activities of tigecycline, ertapenem, isepamicin, and other comparators against 861 bacterial isolates recovered from patients treated in three major teaching hospitals in 2003. MICs to antimicrobial agents were determined by the agar dilution method. High rates of oxacillin resistance (58%) in Staphylococcus aureus (60 isolates), and vancomycin resistance (21%) and quinupristin-dalfopristin non-susceptibility (39%) in Enterococcus faecium (34 isolates) were found. Carbapenems had excellent in vitro activities (>or=98% susceptibility) against the 419 isolates of Enterobacteriaceae, with the MIC(50) and MIC(90) of imipenem, meropenem, and ertapenem being 0.25 and 4 mg/L, 0.03 and 0.12 mg/L, and 0.03 and 0.5 mg/L, respectively. For, Pseudomonas aeruginosa (74 isolates) and Burkholderia cepacia (21 isolates), meropenem (MIC(90), 0.25, 2, and 4 mg/L, respectively) had better in vitro activities than imipenem (MIC(90), 8, 4, and 32 mg/L, respectively) and ertapenem (MIC(90), 0.5, >32, and 32 mg/L, respectively). Isepamicin had a similar activity with amikacin against all Enterobacteriaceae, Pseudomonas aeruginosa, B. cepacia, and Acinetobacter baumannii, except for C. freundii isolates in which isepamicin had an eight-fold activity better than amikacin. Tigecycline had excellent in vitro activities against all isolates tested (MIC(90), <or=1 mg/L) including 14 pandrugresistant A. baumannii isolates (MICs, 1-4 mg/L), except for Proteus mirabilis (59 isolates; MIC(90), 8 mg/L), Bacteroides fragilis (60 isolates; MIC(90), 8 mg/L), P. aeruginosa (MIC(90), 16 mg/L), and B. cepacia (21 isolates; MIC(90), 16 mg/L). Tigecycline, carbapenems, and isepamicin exhibited better or comparable in vitro activities against a wide spectrum of commonly encountered bacteria than other comparator antimicrobials and may represent therapeutic options for infections due to multidrug-resistant pathogens.

The antimicrobial armamentarium: evaluating current and future treatment options

The development and introduction of new antibiotics has, unfortunately, not kept pace with the development of bacterial resistance, and the need for new agents is becoming acute. Although some currently marketed agents remain valuable tools in the treatment of infectious diseases, few new drugs have reached the market in the last decade. In recent years, antibiotics with activity against certain problematic resistant bacteria such as methicillin-resistant Staphylococcus aureus, including linezolid and daptomycin, have been approved for clinical practice. Recently, tigecycline, a minocycline derivative, received approval by the United States Food and Drug Administration for treatment of complicated skin and skin structure and intraabdominal infections; the agent is also active against a variety of multidrug-resistant bacteria. Of the other agents in phase III development, ceftobiprole--a cephalosporin, and faropenem and doripenem--both carbapenems, have wide antibacterial spectra. Antimicrobial agents in the pipeline with marked gram-positive activity include dalbavancin, telavancin, and oritavancin.

Epidemiological MIC cut-off values for tigecycline calculated from Etest MIC values using normalized resistance interpretation

OBJECTIVES

To apply the normalized resistance interpretation (NRI) method to Etest MIC results which have higher precision than conventional log2 dilution MIC tests due to the inclusion of intermediate values. If successful, NRI might provide an objective tool for the definition of epidemiological MIC cut-off values.

METHODS

MICs of tigecycline and other antimicrobial agents were determined for 4771 clinical isolates comprising five Gram-positive and 13 Gram-negative species or species groups using the Etest. Histograms of MIC values were constructed for each species and NRI calculations were applied to them. An upper MIC limit of 2.5 SD above the theoretical mean of the normalized distribution was used for setting the epidemiological cut-off values.

RESULTS

Calculated cut-off values for wild-type strains were between 0.11 and 0.96 mg/L for Gram-positive species, and between 0.44 and 8.3 mg/L for Gram-negative species, except for Pseudomonas aeruginosa, which had a cut-off value of 450 mg/L, consistent with earlier reports on the lack of activity of tigecycline against this species.

CONCLUSIONS

NRI offers an objective method for the analysis of MICs produced using Etests and the determination of epidemiological MIC cut-off values.

Activity of tigecycline tested against a global collection of Enterobacteriaceae, including tetracycline-resistant isolates

Steadily increasing resistance among the Enterobacteriaceae to beta-lactams, fluoroquinolones, aminoglycosides, tetracyclines, and trimethoprim/sulfamethoxazole has compromised the utility of these commonly used antimicrobial classes for many community- or hospital-acquired infections. The development of tigecycline, the sentinel representative of a novel class of broad-spectrum agents (the glycylcyclines), represents an important milestone in addressing this critical need. Resistance to tigecycline might be expected to occur via the same mechanisms that produce tetracycline resistance; however, tigecycline remains stable and largely unaffected by the commonly occurring efflux and ribosomal protection resistance mechanisms. In this study, an international collection of Enterobacteriaceae (11327 isolates; 32.8% tetracycline-resistant) from global surveillance studies (2000-2004) were evaluated against tigecycline and other comparator antimicrobials. Although the most active agents were the carbapenems and aminoglycosides (97.5-99.7% susceptible), tigecycline displayed high potency (MIC50 and MIC90, 0.25 and 1 microg/mL) with 95.7% of all strains being inhibited at < or =2 microg/mL. Despite higher MIC values observed with Serratia spp. and Proteae, between 90.5% and 97.5% of isolates were inhibited by < or =4 microg/mL of tigecycline. Tetracycline-resistant populations demonstrated only modest decreases in potency to tigecycline, which appeared to be species-dependent (up to 2-fold only for Escherichia coli, Salmonella spp., Shigella spp., and Panteoa agglomerans; and up to 4-fold for Klebsiella spp., Enterobacter spp., and Citrobacter spp.). Among E. coli (263 isolates) and Klebsiella spp. (356) that meet recognized screening definitions for extended-spectrum beta-lactamase production, 100.0% and 94.4% were inhibited by tigecycline at 2 microg/mL, respectively. These findings confirm that tigecycline exhibits potency, breadth of spectrum, and stability to the commonly occurring resistance mechanisms found in contemporary Enterobacteriaceae isolates, attributes that make this parenteral agent an attractive candidate for use against serious infections produced by these species.

Antimicrobial activity of tigecycline tested against organisms causing community-acquired respiratory tract infection and nosocomial pneumonia

Emerging antimicrobial resistance among respiratory tract pathogens has created a critical need for development of new antimicrobial agents that are not affected by the commonly occurring genetic resistance mechanisms. Tigecycline, a novel broad-spectrum parenteral glycylcycline, has been shown to be active against many of Gram-positive, Gram-negative, atypical, and anaerobic organisms, including strains highly resistant to commonly prescribed antimicrobials and was recently approved by the US Food and Drug Administration for treating infections of skin and skin structures, and for intra-abdominal infections. In this study, tigecycline spectrum and potency were evaluated against a global collection of pathogens (2000-2004) recovered from community-acquired respiratory infections (7580 strains) or from hospitalized patients with pneumonia (3183 strains). Among community-acquired infections, the ranking pathogens were Haemophilus influenzae (52.9%; 21% ampicillin-resistant), Streptococcus pneumoniae (39.2%; 23.7% penicillin-nonsusceptible), and Moraxella catarrhalis (7.9%). Tigecycline displayed potent activity by inhibiting 100% of the 3 species at clinically achievable concentrations (2, 1, and 0.5 microg/mL, respectively). The 10 most prevalent pathogens producing 94.3% of pneumonias in hospitalized patients were Staphylococcus aureus (48.5% of strains; 49.4% oxacillin-resistant), Pseudomonas aeruginosa (15.6%), Klebsiella spp. (5.6%), S. pneumoniae (4.6%), Acinetobacter spp. (4.5%), Enterobacter spp. (4.0%), Escherichia coli (3.8%), Serratia marcescens (2.5%), Enterococcus spp. (2.3%), Stenotrophomonas maltophilia (1.8%), and beta-hemolytic streptococci (1.1%). At a concentration of 4 microg/mL, tigecycline inhibited >96% of these pathogens (exception, P. aeruginosa). S. aureus was readily inhibited by tigecycline (MIC50 and MIC90, 0.25 and 0.5 microg/mL, respectively) with all strains inhibited at < or =1 microg/mL. Streptococci recovered from hospitalized patients (beta-hemolytic and S. pneumoniae) were also very susceptible to tigecycline with the highest MIC being 0.12 microg/mL. All E. coli (including 13.3% with an extended-spectrum beta-lactamase [ESBL] phenotype) were inhibited by < or =1 microg/mL, and all Klebsiella (25.8% ESBL phenotype) and Enterobacter spp. plus 97.0% of Serratia spp. were inhibited by < or =4 microg/mL. Tigecycline was also active against Acinetobacter spp. and S. maltophilia strains (MIC50 and MIC90, 1 and 4 microg/mL, respectively). Further clinical studies should consider the role that tigecycline may play in the therapy for severe respiratory tract infections, both of nosocomial and community origin.

Antimicrobial activity of tigecycline tested against nosocomial bacterial pathogens from patients hospitalized in the intensive care unit

The antimicrobial activity of tigecycline and selected antimicrobials was evaluated against bacterial pathogens isolated from patients hospitalized in intensive care units (ICUs) worldwide. A total of 9093 isolates were consecutively collected in >70 medical centers in North America (4157), South America (1830), Europe (3034), and the Asia-Australia (72) areas. The isolates were collected from the bloodstream (68.5%), respiratory tract (13.6%), skin/soft tissue (5.5%), and urinary tract (2.0%) infections in the 2000-2004 period, and susceptibility was tested by reference broth microdilution methods. The most frequently isolated pathogens were Staphylococcus aureus (32.1%), Enterococcus spp. (13.7%), coagulase-negative staphylococci (CoNS; 13.0%), Pseudomonas aeruginosa (8.4%), and Escherichia coli (7.9%). All Gram-positive pathogens (5665) were inhibited at < or =1 microg/mL of tigecycline. Resistance to oxacillin was detected in 43.5% of Staphylococcus aureus and in 85.0% of CoNS, and resistance to vancomycin was observed in 18.6% of enterococci. Tigecycline was very active against Enterobacteriaceae (1876 strains tested) with an MIC90 of < or =1 microg/mL, except for Serratia spp. (2 microg/mL). Extended-spectrum beta-lactamase (ESBL) phenotype was detected in 10% of E. coli and 31% of Klebsiella spp., whereas 28% of Enterobacter spp. were resistant to ceftazidime (AmpC enzyme production). These resistance phenotypes did not adversely affect tigecycline activity. Tigecycline and trimethoprim/sulfamethoxazole were the most active compounds against Stenotrophomonas maltophilia (MIC90, 2 and 1 microg/mL respectively). Tigecycline was also active against Acinetobacter spp. (MIC90, 1 microg/mL), but P. aeruginosa showed decreased susceptibility to tigecycline (MIC90, 16 microg/mL). In summary, isolates from ICU patients worldwide showed high rates of antimicrobial resistance. The most alarming problems detected were vancomycin resistance among enterococci, ESBL-mediated beta-lactam resistance and fluoroquinolone resistance among Enterobacteriaceae, and carbapenem resistance among P. aeruginosa and Acinetobacter spp. Tigecycline exhibited potent in vitro activity against most of clinically important pathogenic bacteria (except P. aeruginosa) isolated from ICU patients and may represent an excellent option for the treatment of infections in this clinical environment.

Tigecycline activity tested against 26,474 bloodstream infection isolates: a collection from 6 continents

The activity of tigecycline (formerly GAR936), a novel glycylcycline, was tested against recent bloodstream infection (BSI) pathogen isolates from 6 continents. Frequency of clinical occurrence of these pathogens was determined and their antibiograms assessed using reference broth microdilution methods. A total of 26474 strains were tested for tigecycline susceptibility according to the Clinical and Laboratory Standards Institute (formerly the National Committee for Clinical Laboratory Standards) by the M7-A6 guidelines with interpretations from M100-S15 and the package insert. The rank order of pathogens was Staphylococcus aureus (33.1%), Escherichia coli (14.0%), coagulase-negative staphylococci (13.5%), Enterococcus spp. (12.3%), Klebsiella spp. (5.7%), Pseudomonas aeruginosa (4.2%), Enterobacter spp. (3.0%), beta-hemolytic streptococci (2.9%), Streptococcus pneumoniae (2.3%), and viridans group streptococci (1.4%). Tigecycline exhibited a broader spectrum of activity against BSI isolates when compared to ciprofloxacin, tetracycline, aminoglycosides, and many beta-lactams (imipenem). Tigecycline was highly active against most pathogens tested, including staphylococci (MIC(90), 0.5 microg/mL), enterococci (MIC90, 0.25 microg/mL), streptococci (MIC(90), < or =0.12 microg/mL), Escherichia coli (MIC90, 0.25 microg/mL), Klebsiella spp. (MIC90, 1 mmicrog/mL), and Enterobacter spp. (MIC(90), 2 mmicrog/mL), but showed limited inhibition of Pseudomonas aeruginosa (MIC90, 16 microg/mL) and indole-positive or indole-negative Proteae (MIC90, 4-8 microg/mL). In summary, tigecycline exhibited a wide spectrum of antimicrobial potency versus BSI isolates collected worldwide. Serious infections in nosocomial environments should benefit from tigecycline use among the investigational phase 3 agents focused toward resistant strains.

Antimicrobial agents for treatment of serious infections caused by resistant Staphylococcus aureus and enterococci

As clinicians increasingly contend with infections due to staphylococci or enterococci resistant to, or failing treatment with, traditional antimicrobial agents, understanding the potential roles of older as well as more recently introduced antimicrobial agents becomes important. Older agents, such as clindamycin and trimethoprim-sulfamethoxazole, have been used to treat infections due to community-acquired methicillin-resistant Staphylococcus aureus. Among the licensed agents, quinupristin-dalfopristin, linezolid, daptomycin, and tigecycline are active in vitro against most strains of methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococcus faecium, but these agents differ in their approved clinical indications. New agents currently under investigation may further expand treatment options.

Tigecycline: what is it, and where should it be used?

Tigecycline is the first glycylcycline to be launched and is one of the very few new antimicrobials with activity against Gram-negative bacteria. It evades acquired efflux and target-mediated resistance to classical tetracyclines, but not chromosomal efflux in Proteeae and Pseudomonas. Cmax+ is low, but tissue penetration is excellent and the compound has shown equivalence to imipenem/cilastatin in intra-abdominal infection and to vancomycin plus aztreonam in skin and skin structure infection. Tigecycline may prove particularly useful for treatment of surgical wound infections, where both gut organisms and MRSA are likely pathogens. It is also likely to find a role in the treatment of infections due to multiresistant pathogens, including Acinetobacter spp. and ESBL producers, as well as MRSA and enterococci.

Tigecycline

New antimicrobial agents are urgently needed for clinical use due to the increasing prevalence and spread of multidrug-resistant bacteria that are commonly responsible for serious and life-threatening diseases. The need to develop new agents that effectively overcome existing mechanisms of resistance displayed by bacteria resistant to currently available drugs has become paramount. Tigecycline, the first in a new class of antimicrobials, the glycylcyclines, is an analogue of minocycline with additional properties that negate most mechanisms mediating resistance to the tetracyclines. In vitro testing has revealed that tigecycline has activity against vancomycin-resistant enterococci, methicillin-resistant Staphylococcus aureus, penicillin-resistant Streptococcus pneumoniae and many species of multidrug-resistant Gram-negative bacteria, although resistance to tigecycline by Pseudomonas aeruginosa and reduced susceptibility among Proteus species do occur. Tigecycline is being evaluated in multicentre Phase III clinical trials for therapy of many serious and life-threatening infections in which multidrug-resistant bacterial organisms may be found. Tigecycline appears to hold promise as a novel expanded spectrum antibiotic.

Potency and spectrum of tigecycline tested against an international collection of bacterial pathogens associated with skin and soft tissue infections (2000–2004)

The antimicrobial activity of tigecycline, a novel glycylcycline, was evaluated against 5289 bacterial isolates recovered from hospitalized patients with skin and soft tissue infections during 2000-2004. Strains were submitted from >70 medical centers in North America, Latin America, and Europe, and were tested centrally using reference broth microdilution methods. The top 10 ranking pathogens (95% of total) recovered included Staphylococcus aureus (55.2%), Enterococcus spp. (9.6%), Pseudomonas aeruginosa (6.4%), Escherichia coli (5.6%), beta-hemolytic streptococci (5.0%), coagulase-negative staphylococci (4.9%), Enterobacter spp. (2.8%), Klebsiella spp. (2.6%), Proteus mirabilis (1.7%), and indole-positive Proteae (1.2%). All staphylococci (S. aureus and coagulase-negative staphylococci), enterococci, beta-hemolytic streptococci, viridans group streptococci, and E. coli were inhibited by < or =2 microg/mL of tigecycline; in addition, 97% of Klebsiella spp., 95% of Enterobacter spp., and 97% of Acinetobacter spp. were inhibited at this concentration. Only P. aeruginosa and all Proteae (MIC90, 16 microg/mL) displayed elevated MIC values to tigecycline. The broad spectrum of activity exhibited by this glycylcycline included tetracycline-resistant organism subsets, as well as oxacillin-resistant S. aureus, vancomycin-resistant enterococci, and extended-spectrum beta-lactamase-producing enteric bacilli strains. Tigecycline represents a new choice among broad-spectrum parenteral agents for the common Gram-positive and -negative pathogens producing serious infections of skin and soft tissues.