Helen Giamarellou

Metallo-β-lactamases: a last frontier for β-lactams?

Metallo-β-lactamases are resistance determinants of increasing clinical relevance in Gram-negative bacteria. Because of their broad range, potent carbapenemase activity and resistance to inhibitors, these enzymes can confer resistance to almost all β-lactams. Since the 1990s, several metallo-β-lactamases encoded by mobile DNA have emerged in important Gram-negative pathogens (ie, in Enterobacteriaceae, Pseudomonas aeruginosa, and Acinetobacter baumannii). Some of these enzymes (eg, VIM-1 and NDM-1) have been involved in the recent crisis resulting from the international dissemination of carbapenem-resistant Klebsiella pneumoniae and other enterobacteria. Although substantial knowledge about the molecular biology and genetics of metallo-β-lactamases is available, epidemiological data are inconsistent and clinical experience is still lacking; therefore, several unsolved or debatable issues remain about the management of infections caused by producers of metallo-β-lactamase. The spread of metallo-β-lactamases presents a major challenge both for treatment of individual patients and for policies of infection control, exposing the substantial unpreparedness of public health structures in facing up to this emergency.

Population Pharmacokinetic Analysis of Colistin Methanesulfonate and Colistin after Intravenous Administration in Critically Ill Patients with Infections Caused by Gram-Negative Bacteria

ABSTRACT Colistin is used to treat infections caused by multidrug-resistant gram-negative bacteria (MDR-GNB). It is administered intravenously in the form of colistin methanesulfonate (CMS), which is hydrolyzed in vivo to the active drug. However, pharmacokinetic data are limited. The aim of the present study was to characterize the pharmacokinetics of CMS and colistin in a population of critically ill patients. Patients receiving colistin for the treatment of infections caused by MDR-GNB were enrolled in the study; however, patients receiving a renal replacement therapy were excluded. CMS was administered at a dose of 3 million units (240 mg) every 8 h. Venous blood was collected immediately before and at multiple occasions after the first and the fourth infusions. Plasma CMS and colistin concentrations were determined by a novel liquid chromatography-tandem mass spectrometry method after a rapid precipitation step that avoids the significant degradation of CMS and colistin. Population pharmacokinetic analysis was performed with the NONMEM program. Eighteen patients (6 females; mean age, 63.6 years; mean creatinine clearance, 82.3 ml/min) were included in the study. For CMS, a two-compartment model best described the pharmacokinetics, and the half-lives of the two phases were estimated to be 0.046 h and 2.3 h, respectively. The clearance of CMS was 13.7 liters/h. For colistin, a one-compartment model was sufficient to describe the data, and the estimated half-life was 14.4 h. The predicted maximum concentrations of drug in plasma were 0.60 mg/liter and 2.3 mg/liter for the first dose and at steady state, respectively. Colistin displayed a half-life that was significantly long in relation to the dosing interval. The implications of these findings are that the plasma colistin concentrations are insufficient before steady state and raise the question of whether the administration of a loading dose would benefit critically ill patients.

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 β-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.

Interventions to reduce colonisation and transmission of antimicrobial-resistant bacteria in intensive care units: an interrupted time series study and cluster randomised trial.

Summary Background Intensive care units (ICUs) are high-risk areas for transmission of antimicrobial-resistant bacteria, but no controlled study has tested the effect of rapid screening and isolation of carriers on transmission in settings with best-standard precautions. We assessed interventions to reduce colonisation and transmission of antimicrobial-resistant bacteria in European ICUs. Methods We did this study in three phases at 13 ICUs. After a 6 month baseline period (phase 1), we did an interrupted time series study of universal chlorhexidine body-washing combined with hand hygiene improvement for 6 months (phase 2), followed by a 12–15 month cluster randomised trial (phase 3). ICUs were randomly assigned by computer generated randomisation schedule to either conventional screening (chromogenic screening for meticillin-resistant Staphylococcus aureus [MRSA] and vancomycin-resistant enterococci [VRE]) or rapid screening (PCR testing for MRSA and VRE and chromogenic screening for highly resistant Enterobacteriaceae [HRE]); with contact precautions for identified carriers. The primary outcome was acquisition of resistant bacteria per 100 patient-days at risk, for which we calculated step changes and changes in trends after the introduction of each intervention. We assessed acquisition by microbiological surveillance and analysed it with a multilevel Poisson segmented regression model. We compared screening groups with a likelihood ratio test that combined step changes and changes to trend. This study is registered with ClinicalTrials.gov, number NCT00976638. Findings Seven ICUs were assigned to rapid screening and six to conventional screening. Mean hand hygiene compliance improved from 52% in phase 1 to 69% in phase 2, and 77% in phase 3. Median proportions of patients receiving chlorhexidine body-washing increased from 0% to 100% at the start of phase 2. For trends in acquisition of antimicrobial-resistant bacteria, weekly incidence rate ratio (IRR) was 0·976 (0·954–0·999) for phase 2 and 1·015 (0·998–1·032) for phase 3. For step changes, weekly IRR was 0·955 (0·676–1·348) for phase 2 and 0·634 (0·349–1·153) for phase 3. The decrease in trend in phase 2 was largely caused by changes in acquisition of MRSA (weekly IRR 0·925, 95% CI 0·890–0·962). Acquisition was lower in the conventional screening group than in the rapid screening group, but did not differ significantly (p=0·06). Interpretation Improved hand hygiene plus unit-wide chlorhexidine body-washing reduced acquisition of antimicrobial-resistant bacteria, particularly MRSA. In the context of a sustained high level of compliance to hand hygiene and chlorhexidine bathings, screening and isolation of carriers do not reduce acquisition rates of multidrug-resistant bacteria, whether or not screening is done with rapid testing or conventional testing. Funding European Commission.

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.

An Outbreak of Infection due to β-Lactamase Klebsiella pneumoniae Carbapenemase 2–Producing K. pneumoniae in a Greek University Hospital: Molecular Characterization, Epidemiology, and Outcomes

BACKGROUND We describe the emergence and spread of Klebsiella pneumoniae carbapenemase 2 (KPC-2)-producing K. pneumoniae at a Greek University hospital. METHODS Isolates with a carbapenem minimum inhibitory concentration >1 microg/mL and a negative EDTA-imipenem disk synergy test result were submitted to boronic acid disk test and to polymerase chain reaction (PCR) for KPC gene and sequencing. Records from patients who had KPC-2-producing K. pneumoniae isolated were retrospectively reviewed. Clinical isolates were submitted to molecular typing using pulsed-field gel electrophoresis, and the beta-lactamase content was studied using isoelectric focusing and PCR. RESULTS From January 2007 through December 2008, 50 patients (34 in the intensive care unit [ICU]) were colonized (n = 32) or infected (n = 18) by KPC-2-producing K. pneumoniae. Increasing prevalence of KPC-2-producing K. pneumoniae coincided with decreasing prevalence of metallo-beta lactamase-producing isolates in our ICU. Multidrug resistance characterized the studied isolates, with colistin, gentamicin, and fosfomycin being the most active agents. Besides KPC-2, clinical isolates encoded TEM-1-like, SHV-11, SHV-12, CTX-M-15, and LEN-19 enzymes. Four different clonal types were detected; the predominant one comprised 41 single patient isolates (82%). Sporadic multiclonal cases of KPC-2-producing K. pneumoniae infection were identified from September 2007 through May 2008. The outbreak strain was introduced in February 2008 and disseminated rapidly by cross-transmission; 38 patients (76%) were identified after August 2008. Fourteen cases of bacteremia, 2 surgical site infections, 2 lower respiratory tract infections (1 bacteremic), and 1 urinary tract infection were identified. Most patients received a colistin-containing combination treatment. Crude mortality was 58.8% among ICU patients and 37.5% among non-ICU patients, but attributable mortality was 22.2% and 33.3%, respectively. CONCLUSIONS The emergence of KPC-2-producing K. pneumoniae in Greek hospitals creates an important challenge for clinicians and hospital epidemiologists, because it is added to the already high burden of antimicrobial resistance.

Acinetobacter baumannii: a universal threat to public health?

Acinetobacter spp. are non-fermentative, strictly aerobic, Gram-negative microorganisms with a confusing taxonomic history. The Acinetobacter baumannii-Acinetobacter calcoaceticus complex is the species most commonly isolated from clinical specimens. It is ubiquitous in nature and has been found as part of the normal skin, throat and rectal flora as well as in food and body lice. It colonises patients in Intensive Care Units and contaminates inanimate hospital surfaces and devices as well as wounds, including war injuries. Although a frequent coloniser, Acinetobacter can be the cause of severe and sometimes lethal infections, mostly of nosocomial origin, predominantly ventilator-associated pneumonia. Bacteraemic infections are rare but may evolve to septic shock. Acinetobacter also emerges as a cause of nosocomial outbreaks and is characterised by increasing antimicrobial multiresistance. Antibiotic use, especially carbapenems and third-generation cephalosporins, is recognised as the most important risk factor for multiresistance. Described resistance mechanisms include hydrolysis by beta-lactamases, alterations in outer membrane proteins and penicillin-binding proteins, and increased activity of efflux pumps. Today, Acinetobacter resistant to carbapenems, aminoglycosides and fluoroquinolones presents a challenge to the clinician. However, sulbactam, tigecycline and colistin represent the current therapeutic approaches, which are associated with satisfactory efficacy.

Application of a Loading Dose of Colistin Methanesulfonate in Critically Ill Patients: Population Pharmacokinetics, Protein Binding, and Prediction of Bacterial Kill

ABSTRACT A previous pharmacokinetic study on dosing of colistin methanesulfonate (CMS) at 240 mg (3 million units [MU]) every 8 h indicated that colistin has a long half-life, resulting in insufficient concentrations for the first 12 to 48 h after initiation of treatment. A loading dose would therefore be beneficial. The aim of this study was to evaluate CMS and colistin pharmacokinetics following a 480-mg (6-MU) loading dose in critically ill patients and to explore the bacterial kill following the use of different dosing regimens obtained by predictions from a pharmacokinetic-pharmacodynamic model developed from an in vitro study on Pseudomonas aeruginosa. The unbound fractions of colistin A and colistin B were determined using equilibrium dialysis and considered in the predictions. Ten critically ill patients (6 males; mean age, 54 years; mean creatinine clearance, 82 ml/min) with infections caused by multidrug-resistant Gram-negative bacteria were enrolled in the study. The pharmacokinetic data collected after the first and eighth doses were analyzed simultaneously with the data from the previous study (total, 28 patients) in the NONMEM program. For CMS, a two-compartment model best described the pharmacokinetics, and the half-lives of the two phases were estimated to be 0.026 and 2.2 h, respectively. For colistin, a one-compartment model was sufficient and the estimated half-life was 18.5 h. The unbound fractions of colistin in the patients were 26 to 41% at clinical concentrations. Colistin A, but not colistin B, had a concentration-dependent binding. The predictions suggested that the time to 3-log-unit bacterial kill for a 480-mg loading dose was reduced to half of that for the dose of 240 mg.

Interactions of colistin and rifampin on multidrug-resistant Acinetobacter baumannii

The increased incidence of nosocomial infections by multidrug-resistant Acinetobacter spp creates demand on the application of some combinations of older antimicrobials on that species. The in vitro activities of colistin and of rifampin and of their interaction were tested on 39 nosocomial isolates of Acinetobacter baumannii. All isolates were resistant to ampicillin/sulbactam, to 3(rd) and 4(th) generation cephalosporins, to amikacin and to ciprofloxacin. MICs were determined by a microdilution technique and interactive studies between 1x or 4x MIC of colistin and rifampin were performed by the time-kill assay. Rifampin was applied at a concentration of 2 microg/mL which is equal to its mean serum level. All isolates were inhibited by colistin and only 15.2% by rifampin. Synergy between 1x MIC of colistin and rifampin was detected in 15.4% of isolates at 6 h of growth and in 51.3% of isolates at 24 h of growth. Synergy between 4x MIC of colistin and rifampin was detected in 15.4% of isolates at 6 h of growth and in 66.7% of isolates at 24 h of growth. It is concluded that colistin is highly active on multidrug-resistant Acinetobacter spp and its activity on A.baumannii is increased in the presence of rifampin, so that their administration might be proposed for nosocomial infections by these isolates.

Multidrug-resistant and extensively drug-resistant Gram-negative pathogens: current and emerging therapeutic approaches

Introduction: In the era of multidrug-resistant, extensively drug-resistant (XDR) and even pandrug-resistant Gram-negative microorganisms, the medical community is facing the threat of untreatable infections particularly those caused by carbapenemase-producing bacteria, that is, Klebsiella pneumoniae, Pseudomonas aeruginosa and Acinetobacter baumannii. Therefore, all the presently available antibiotics, as well as for the near future compounds, are presented and discussed. Areas covered: Current knowledge concerning mechanisms of action, in vitro activity and interactions, pharmacokinetic/pharmacodynamics, clinical efficacy and toxicity issues for revived and novel antimicrobial agents overcoming current resistance mechanisms, including colistin, tigecycline, fosfomycin, temocillin, carbapenems, and antibiotics still under development for the near future such as plazomicin, eravacycline and carbapenemase inhibitors is discussed. Expert opinion: Colistin is active in vitro and effective in vivo against XDR carbapenemase-producing microorganisms in the critically ill host, whereas tigecycline, with the exception of P. aeruginosa, has a similar spectrum of activity. The efficacy of combination therapy in bacteremias and ventilator-associated pneumonia caused by K. pneumoniae carbapenemase producers seems to be obligatory, whereas in cases of P. aeruginosa and A. baumannii its efficacy is questionable. Fosfomycin, which is active against P. aeruginosa and K. pneumoniae, although promising, shares poor experience in XDR infections. The in vivo validity of the newer potent compounds still necessitates the evaluation of Phase III clinical trials particularly in XDR infections.