Tigecycline for the treatment of multidrug-resistant Enterobacteriaceae: a systematic review of the evidence from microbiological and clinical studies

Complete nucleotide sequence of Klebsiella pneumoniae multidrug resistance plasmid pKP048, carrying blaKPC-2, blaDHA-1, qnrB4, and armA

The Klebsiella pneumoniae multidrug resistance plasmid pKP048 was completely sequenced. This plasmid carries several important resistance determinants, such as bla(KPC-2), bla(DHA-1), qnrB4, and armA, which confer resistance to carbapenems, cephalosporins, fluoroquinolones, and aminoglycosides, respectively. Analysis of the finished 151,188-bp sequence data revealed 163 putative genes, 108 of which were assigned functions such as replication, stable inheritance, antibiotic resistance, a mobile element, conjugal transfer, and a restriction-modification system, showing the strong phylogenetic mosaicism and plasticity of the plasmid.

Antimicrobial susceptibility of multidrug-resistant (MDR) and extensively drug-resistant (XDR) Enterobacteriaceae isolates to fosfomycin

The advancing antimicrobial drug resistance among Enterobacteriaceae renders the evaluation of potential novel therapeutic options necessary. We sought to evaluate the in vitro antimicrobial activity of fosfomycin against multidrug-resistant (MDR) Enterobacteriaceae isolates. Antimicrobial susceptibility to fosfomycin and 12 additional antibiotics of MDR Enterobacteriaceae isolates collected between November 2007 and April 2009 at the University Hospital of Heraklion, Crete, Greece, was examined using the Etest method. A total of 152 MDR Enterobacteriaceae isolates were studied, including Klebsiella pneumoniae (76.3%), Escherichia coli (17.1%), Proteus mirabilis (4.6%) and other species (2.0%). Antimicrobial susceptibility rates were highest for fosfomycin (92.8%), tigecycline (92.1%) and colistin (73.0%) followed by imipenem (35.5%), tetracycline (20.4%), gentamicin (19.7%), trimethoprim/sulfamethoxazole (12.5%) and ciprofloxacin (10.5%). Of the 152 isolates, 85 (55.9%) were extensively drug-resistant (XDR), of which 78 (91.8%) remained susceptible to fosfomycin. Susceptibility to fosfomycin of the 79 carbapenemase-producing, 34 extended-spectrum beta-lactamase-producing and 24 metallo-beta-lactamase-producing isolates was 94.9%, 94.1% and 83.3%, respectively. In conclusion, in this study fosfomycin exhibited good in vitro antimicrobial activity against MDR and XDR Enterobacteriaceae. We suggest further evaluation of the potential clinical utility of fosfomycin against infections caused by these pathogens.

In vitro activity of tigecycline against 2423 clinical isolates and comparison of the available interpretation breakpoints

MICs to tigecycline and 12 antimicrobials were performed by microdilution method, against 2423 nonduplicate pathogens recently isolated in 17 Greek hospitals. The Food and Drug Administration (FDA) and European Committee on Antimicrobial Susceptibility Testing (EUCAST) criteria were used comparatively for interpretation of tigecycline MICs. Tigecycline exhibited potent in vitro activity against the majority of the isolates tested. (MIC(90) values of 0.5, 1, 2, 0.125, 1, 0.25, 0.125, and 1 mg/L were observed for Escherichia coli, Klebsiella pneumoniae, Enterobacter spp., Moraxella catarrhalis, Acinetobacter spp., Staphylococcus aureus, Enterococcus spp., and Streptococcus pneumoniae isolates, respectively.) Tigecycline activity was the same, irrespective of the resistance profile to other antimicrobials (Gram-negative pathogens susceptible or resistant to imipenem, Enterococcus spp., S. aureus, or S. pneumoniae isolates, susceptible or resistant to vancomycin, methicillin or penicillin, respectively). Interpretation using EUCAST and FDA breakpoints differed among isolates of K. pneumoniae and Enterobacter spp. having tigecycline MICs of 2 to 4 mg/L. In conclusion, tigecycline exhibited potent activity against pathogens recently isolated in a region that experiences high antimicrobial resistance rates. Indications that the available criteria might categorize differently tigecycline susceptibility status in K. pneumoniae and Enterobacter spp. isolates were also detected.

[Tigecycline for treatment of severe infections in intensive care: a drug use evaluation]

OBJECTIVES

To report our experience of tigecycline use in a medical and surgical intensive care unit. To describe its prescription, microbiology findings, tolerance and efficacy.

STUDY DESIGN

Prospective, observational, single center study.

PATIENTS AND METHODS

All consecutive patients treated with tigecycline were included. Demography, indication of treatment, bacteriology before, during and in the month after treatment and ICU mortality were collected. The main endpoints were clinical and microbiological efficacy and tolerance.

RESULTS

Twenty-four patients were included. In half of the cases, tigecycline was prescribed in monotherapy for a complicated intra-abdominal infection. Overall tolerance of tigecycline was good. Clinical and microbiological cure was obtained in six cases, not obtained in nine, indeterminate in six cases and not evaluable in the three cases of prophylaxis. During the treatment, four bacteria commonly sensitives were shown to be resistant to tigecycline.

CONCLUSION

Our pilot study on 24 patients suggests that tigecycline is well tolerated in critically ill patients. Clinical cure in severe infections was compromised in nine patients essentially because of resistant pathogens suggesting its prescription on antibiogram. However, the impact of association or the increasing doses in severe critically ill patients should be evaluated.

ramR mutations in clinical isolates of Klebsiella pneumoniae with reduced susceptibility to tigecycline

Five Klebsiella pneumoniae isolates with reduced susceptibility to tigecycline (MIC, 2 microg/ml) were analyzed. A gene homologous to ramR of Salmonella enterica was identified in Klebsiella pneumoniae. Sequencing of ramR in the nonsusceptible Klebsiella strains revealed deletions, insertions, and point mutations. Transformation of mutants with wild-type ramR genes, but not with mutant ramR genes, restored susceptibility to tigecycline and repressed overexpression of ramA and acrB. Thus, this study reveals a molecular mechanism for tigecycline resistance in Klebsiella pneumoniae.

Influence of media and testing methodology on susceptibility to tigecycline of Enterobacteriaceae with reported high tigecycline MIC

The tigecycline susceptibility of six different Enterobacteriaceae strains with reported high tigecycline MICs was determined in quintuplicate by four methodologies using Mueller-Hinton agar and broth from six manufacturers. The MICs determined by Etest were a >or=1-fold dilution lower than those determined by broth microdilution and agar dilution, with the highest modal values given by agar dilution. The highest modal MICs were obtained using Oxoid medium, and the lowest inhibition zone values (disc diffusion) were obtained using Oxoid and bioMérieux media. The lowest MICs were obtained by Etest using Difco or Merck media.

Controlling the spread of carbapenemase-producing Gram-negatives: therapeutic approach and infection control

Although the rapid spread of carbapenemase-producing Gram-negatives (CPGNs) is providing the scientific community with a great deal of information about the molecular epidemiology of these enzymes and their genetic background, data on how to treat multidrug-resistant or extended drug-resistant carbapenemase-producing Enterobacteriaceae and how to contain their spread are still surprisingly limited, in spite of the rapidly increasing prevalence of these organisms and of their isolation from patients suffering from life-threatening infections. Limited clinical experience and several in vitro synergy studies seem to support the view that antibiotic combinations should be preferred to monotherapies. But, in light of the data available to date, it is currently impossible to quantify the real advantage of drug combinations in the treatment of these infections. Comprehensive clinical studies of the main therapeutic options, broken down by pathogen, enzyme and clinical syndrome, are definitely lacking and, as carbapenemases keep spreading, are urgently needed. This spread is unveiling the substantial unpreparedness of European public health structures to face this worrisome emergency, although experiences from different countries-chiefly Greece and Israel-have shown that CPGN transmission and cross-infection can cause a substantial threat to the healthcare system. This unpreparedness also affects the treatment of individual patients and infection control policies, with dramatic scarcities of both therapeutic options and infection control measures. Although correct implementation of such measures is presumably cumbersome and expensive, the huge clinical and public health problems related to CPGN transmission, alongside the current scarcity of therapeutic options, seem to fully justify this choice.

Fosfomycin for the treatment of multidrug-resistant, including extended-spectrum beta-lactamase producing, Enterobacteriaceae infections: a systematic review

Rising rates of resistance to antimicrobial drugs among Enterobacteriaceae limit the choice of reliably active forms of these drugs. We evaluated the evidence on fosfomycin as a treatment option for infections caused by members of the family Enterobacteriaceae with advanced resistance to antimicrobial drugs, including producers of extended-spectrum beta-lactamase (ESBL). We systematically reviewed studies evaluating the antimicrobial activity, or the clinical effectiveness of fosfomycin. 17 antimicrobial-susceptibility studies were found and included in our Review, accounting for 5057 clinical isolates of Enterobacteriaceae with advanced resistance to antimicrobial drugs (4448 were producers of ESBL); 11 of the 17 studies reported that at least 90% of the isolates were susceptible to fosfomycin. Using a provisional minimum inhibitory concentration susceptibility breakpoint of 64 mg/L or less, 1604 (96.8%) of 1657 Escherichia coli isolates producing ESBL were susceptible to fosfomycin. Similarly, 608 (81.3%) of 748 Klebsiella pneumoniae isolates producing ESBL were susceptible to fosfomycin. In two clinical studies, oral treatment with fosfomycin-trometamol was clinically effective against complicated or uncomplicated lower urinary tract infections caused by ESBL-producing E coli in, cumulatively, 75 (93.8%) of the 80 patients evaluated. Initial clinical data support the use of fosfomycin for the treatment of urinary tract infections caused by these pathogens, although further research is needed.

Infections by pandrug-resistant gram-negative bacteria: clinical profile, therapeutic management, and outcome in a series of 21 patients

Clinical reports on infections by pandrug-resistant (PDR) bacteria are scarce. This observational case series study was conducted during a 2-year period at a university hospital. Patients infected by PDR gram-negative bacteria comprised the study cohort. An isolate was defined as PDR if it was resistant to all antibiotic classes available for empirical treatment. A total of 21 patients infected by PDR gram-negative bacteria were recorded. The mean APACHE II score on admission was 18.8, the mean Charlson comorbidity index was 2.9, and 20 (95.2%) patients had a history of intensive care unit hospitalization. All patients had recent exposure to multiple antibiotics (median, 6 antibiotic groups). Infections occurred at a mean of 41.5 days after admission. The mean length of stay after infection was 54.6 days and 5 (23.8%) patients died due to the infection. Treatment was mainly based on a colistin-containing regimen (47.6%) or tigecycline (33.3%). All patients treated with tigecycline had total resolution of the infection and a notably shorter length of hospital stay after infection. In conclusion, PDR gram-negative bacterial infections are associated with considerable prolongation of hospitalization and mortality, although the mortality is not as high as that expected. Tigecycline appears to be effective for the successful treatment of PDR infections

Antibacterial susceptibility testing in the clinical laboratory

This article familiarizes the clinician with the principles of bacterial susceptibility testing and reporting to facilitate communication with the clinical microbiology laboratory. As resistance continues to emerge among a wide range of clinically relevant bacteria, the complexity of this communication increases. This updated version provides an overview of the important susceptibility concerns for most commonly isolated bacterial pathogens.

Macrolides, ketolides, and glycylcyclines: azithromycin, clarithromycin, telithromycin, tigecycline

The advanced macrolides, azithromycin and clarithromycin, and the ketolide, telithromycin, are structural analogs of erythromycin. They have several distinct advantages when compared with erythromycin, including enhanced spectrum of activity, more favorable pharmacokinetics and pharmacodynamics, once-daily administration, and improved tolerability. Clarithromycin and azithromycin are used extensively for the treatment of respiratory tract infections, sexually transmitted diseases, and Helicobacter pylori-associated peptic ulcer disease. Telithromycin is approved for the treatment of community-acquired pneumonia. Severe hepatotoxicity has been reported with the use of telithromycin.

Tigecycline for the treatment of patients with community-acquired pneumonia requiring hospitalization

Pneumonia, along with influenza, is the leading cause of mortality associated with infectious diseases in the USA. Tigecycline is a novel antimicrobial agent that is active against a broad spectrum of pathogens. Our objective is to review the literature about the efficacy of tigecycline in community-acquired pneumonia (CAP). Data from various sources, including Pubmed, the European Medicines Agency (EMEA) and the US FDA were appraised. Tigecycline was found to be noninferior compared with levofloxacin for the treatment of patients with bacterial CAP requiring hospitalization. Recently, the drug was approved for the treatment of these patients by the FDA, but owing to some concerns, its application in the EMEA has been withdrawn. In addition, in a recent study concerns were expressed about the efficacy of tigecycline in the lungs using the current dosage. More data are needed about the pharmacokinetics of tigecycline in the lungs and its efficacy in severe CAP.

Combined ramR mutation and presence of a Tn1721-associated tet(A) variant in a clinical isolate of Salmonella enterica serovar Hadar resistant to tigecycline

A Salmonella enterica serovar Hadar strain resistant to tigecycline (MIC, 16 microg/ml) was isolated. Molecular characterization revealed the presence of a plasmid-borne tet(A) variant associated with Tn1721 mediating a rise of the MIC for tigecycline when transferred to Escherichia coli. Additionally, a truncating mutation in ramR was detected. Transformation with wild-type ramR but not with the mutated ramR lowered the MIC for tigecycline. Characterization of this Salmonella isolate implicates ramR in resistance to tigecycline.

Natural product scaffolds as leads to drugs

Numerous ‘scaffolds’ that have been identified in natural product structures have led to very significant numbers of approved drugs and drug candidates for a multiplicity of diseases over the years. In this mini-review, we discuss the base scaffolds (chemical skeletons) that we feel have produced very significant numbers of agents as drugs or drug leads and, in a number of cases, compounds that can be used as chemical synthons or that present activities in biological areas that were not obvious from their earlier history.

Multidrug-resistant Gram-negative infections: what are the treatment options?

The emergence of multidrug-resistant (MDR) Gram-negative bacilli creates a challenge in the treatment of nosocomial infections. While the pharmaceutical pipeline is waning, two revived old antibacterials (colistin and fosfomycin), a newer one (tigecycline) and an 'improved' member of an existing class (doripenem) are the only therapeutic options left. The class of polymyxins, known since 1947 and represented mostly by polymyxin B and polymyxin E (colistin), has recently gained a principal role in the treatment of the most problematic MDR Gram-negative pathogens (such as Pseudomonas aeruginosa, Acinetobacter baumannii, Klebsiella pneumoniae and Stenotrophomonas maltophilia). Future prospective studies are needed to answer important clinical questions, such as the possible benefit of combination with other antimicrobials versus monotherapy, the efficacy of colistin in neutropenic hosts and the role of inhaled colistin. As new pharmacokinetic data emerge, clarification of the pharmacokinetic/pharmacodynamic (PK/PD) profile of colistin as well as appropriate dosing seems urgent, while development of resistance must be carefully monitored. Fosfomycin tromethamine, a synthetic salt of fosfomycin discovered in 1969, has regained attention because of its in vitro activity against extended-spectrum beta-lactamase (ESBL)-producing Enterobacteriaceae and MDR P. aeruginosa. Although in use for decades in oral and parenteral formulations for a variety of infections without significant toxicity, its clinical utility in MDR infections remains to be explored in future studies. Tigecycline, the first representative of the new class of glycylcyclines, holds promise in infections from MDR K. pneumoniae (K. pneumoniae carbapenemase [KPC]- and ESBL-producing strains) and Enterobacteriaceae with various mechanisms of resistance. The in vitro activity of tigecycline against A. baumannii makes it a tempting option, as it is currently the most active compound against MDR strains along with colistin. However, the usual minimum inhibitory concentration values of this pathogen are approximately 2 mg/L and compromise clinical outcomes based on PK/PD issues. Its advantageous penetration into various tissues is useful in infections of the skin and soft tissues as well as intra-abdominal infections (official indications), whereas low serum concentrations compromise its use in bloodstream infections. Therefore, prospective studies with dose escalation are urgently needed, as well as clarification of its role in nosocomial pneumonia, after poor results in the study of ventilator-associated pneumonia. Finally, doripenem, the recently licensed member of the carbapenems (without significant spectrum alterations from the ascendant members) seems to possess a lower potential for resistance selection and a more favourable pharmacokinetic profile when given as an extended infusion. The latter strategy could prove helpful in overcoming low level resistance of A. baumannii and P. aeruginosa strains.

In vitro activities of moxifloxacin and tigecycline against bacterial isolates associated with intraabdominal infections at a medical center in Taiwan, 2001-2006

A total of 569 nonduplicate isolates recovered from patients with community-onset or hospital-onset intraabdominal infections (IAIs) from 2001 to 2006 were studied. These included 28 Staphylococcus aureus and 541 Gram-negative isolates (33.6% Escherichia coli, 29.0% Klebsiella pneumoniae, 8.1% Acinetobacter baumannii, and 6.3% Pseudomonas aeruginosa). Minimum inhibitory concentrations (MICs) of the isolates to moxifloxacin, imipenem, and ciprofloxacin were determined using the agar dilution method and to tigecycline using the broth microdilution method. Extended-spectrum beta-lactamase (ESBL) producers were found in 15.5% (29 out of 182) of E. coli, 15.3% (24 out of 157) of K. pneumoniae, and 15.4% (2 out of 13) of K. oxytoca isolates. More than 85% of Enterobacteriaceae were susceptible to moxifloxacin, but this percentage was lower among E. coli (78%). The percentage of E. coli (K. pneumoniae) isolates that were not susceptible to moxifloxacin was 6% (0%) in 2001, 39% (17%) in 2003, and 21% (14%) in 2006. Tigecycline exhibited good in vitro activities against all S. aureus and >95% of all Enterobacteriaceae tested. Among the 24 isolates of ESBL-producing K. pneumoniae, 4 had tigecycline MICs > or = 2 microg/ml. Eighty percent of A. baumannii isolates exhibited tigecycline MICs of < or = 2 microg/ml. This study found that moxifloxacin and tigecycline exhibited good in vitro activity against bacterial isolates causing IAIs.

Novel genetic environment of the carbapenem-hydrolyzing beta-lactamase KPC-2 among Enterobacteriaceae in China

Thirty-nine bla(KPC)-producing isolates of the family Enterobacteriaceae with carbapenem resistance or reduced carbapenem susceptibility were obtained from inpatients from eight hospitals in six cities of three provinces in eastern China. The pulsed-field gel electrophoresis analysis of all 36 Klebsiella pneumoniae isolates revealed six major patterns. The resistant plasmids of most isolates were successfully transferred by conjugation and evaluated experimentally to be 40 to 180 kb in size. A 20.2-kb bla(KPC)-surrounding nucleotide sequence from plasmid pKP048 has been obtained and contains an integration structure of a Tn3-based transposon and partial Tn4401 segment, with the gene order Tn3-transposase, Tn3-resolvase, ISKpn8, the bla(KPC-2) gene, and the ISKpn6-like element. The chimera of several transposon-associated elements indicated a novel genetic environment of the K. pneumoniae carbapenemase beta-lactamase gene in isolates from China.

Extended-spectrum beta-lactamase-producing organisms

Extended-spectrum beta-lactamases (ESBLs), which hydrolyse extended-spectrum cephalosporins and are inhibited by clavulanic acid, are spreading among Enterobacteriaceae. The CTX-M enzymes are replacing SHV and TEM enzymes as the prevalent type of ESBLs, principally in community-acquired infections caused by Escherichia coli. Associated infectious syndromes include mainly urinary tract infections, and secondly bloodstream and intra-abdominal infections, and may be serious enough to warrant hospitalisation. Affected patients commonly have various underlying risk factors. This is also observed in hospital-acquired infections. The rates of ESBL-expression among nosocomial Enterobacteriaceae isolates, particularly Klebsiella pneumoniae, have risen substantially in several countries. The hospital epidemiology of these infections is often complex; multiple clonal strains causing focal outbreaks may co-exist with sporadic ones. Relevant infection-control measures should focus on reducing patient-to-patient transmission via the inanimate environment, hospital personnel, and medical equipment. Wise use of antibiotics is also essential. The available therapeutic options for the treatment of ESBL-associated infections are limited by drug resistance conferred by the ESBLs, along with frequently observed co-resistance to various antibiotic classes, including cephamycins, fluoroquinolones, aminoglycosides, tetracyclines, and trimethoprim/sulfamethoxazole. Relevant clinical data regarding the effectiveness of different regimens for ESBL-associated infections are limited. Although certain cephalosporins may appear active in vitro, associated clinical outcomes are often suboptimal. beta-Lactam/beta-lactamase inhibitor combinations may be of value, but the supporting evidence is weak. Carbapenems are regarded as the agents of choice, and may be more effective than fluoroquinolones for serious infections. Tigecycline and polymyxins have substantial antimicrobial activity against ESBL-producing Enterobacteriaceae, and, along with fosfomycin, merit further evaluation.

In vivo pharmacodynamic profile of tigecycline against phenotypically diverse Escherichia coli and Klebsiella pneumoniae isolates

Tigecycline is a glycylcycline with activity against Enterobacteriaceae, including multidrug-resistant isolates of Klebsiella pneumoniae and Escherichia coli producing extended-spectrum beta-lactamase (ESBL) and carbapenemases. Herein, we used an in vivo murine thigh model to characterize the pharmacodynamic profile of tigecycline against genotypically and phenotypically diverse K. pneumoniae and E. coli isolates. Doses of 3.125 to 300 mg/kg, divided 1 to 6 times daily, were administered subcutaneously against six (two nonresistant, one carbapenemase, and three ESBL producing) K. pneumoniae strains and five (two nonresistant and three ESBL producing) E. coli strains. The phenotypic profile (reported tigecycline MIC) for all isolates ranged from 0.125 to 2 microg/ml. Mean correlation coefficients of free (f) drug exposures (percentage of the dosing interval that free drug concentration remained above the MIC [fT>MIC], the ratio of the free drug area under the concentration-time curve/MIC [fAUC/MIC], and the ratio of maximum concentration of free drug in serum/MIC) for all 11 isolates were 0.595, 0.969, and 0.897, respectively. The fAUC/MIC was the pharmacodynamic parameter that best described the efficacy of tigecycline against both E. coli and K. pneumoniae. Interestingly, reductions in the number of CFU were noted even though doses achieved an fT>MIC of 0%. With respect to fAUC/MIC in the neutropenic model, the cumulative 80% and 50% effective pharmacodynamic indexes (EI(80) and EI(50)) for all 11 isolates were 8.4 and 4.7, respectively. An experiment in nonneutropenic mice infected with an ESBL-producing E. coli and K. pneumoniae isolate resulted in the lowest tigecycline fAUC/MIC EI(80) and EI(50) values at 1.8 and 1.0 for E. coli and 1.7 and 1.6 for K. pneumoniae. While the phenotypic profile of tigecycline appeared to drive efficacy irrespective of ESBL or carbapenemase production, the presence of a competent immune system markedly reduced this required exposure.