Effect of appropriate combination therapy on mortality of patients with bloodstream infections due to carbapenemase-producing Enterobacteriaceae (INCREMENT): a retrospective cohort study

BACKGROUND

The best available treatment against carbapenemase-producing Enterobacteriaceae (CPE) is unknown. The objective of this study was to investigate the effect of appropriate therapy and of appropriate combination therapy on mortality of patients with bloodstream infections (BSIs) due to CPE.

METHODS

In this retrospective cohort study, we included patients with clinically significant monomicrobial BSIs due to CPE from the INCREMENT cohort, recruited from 26 tertiary hospitals in ten countries. Exclusion criteria were missing key data, death sooner than 24 h after the index date, therapy with an active antibiotic for at least 2 days when blood cultures were taken, and subsequent episodes in the same patient. We compared 30 day all-cause mortality between patients receiving appropriate (including an active drug against the blood isolate and started in the first 5 days after infection) or inappropriate therapy, and for patients receiving appropriate therapy, between those receiving active monotherapy (only one active drug) or combination therapy (more than one). We used a propensity score for receiving combination therapy and a validated mortality score (INCREMENT-CPE mortality score) to control for confounders in Cox regression analyses. We stratified analyses of combination therapy according to INCREMENT-CPE mortality score (0-7 [low mortality score] vs 8-15 [high mortality score]). INCREMENT is registered with ClinicalTrials.gov, number NCT01764490.

FINDINGS

Between Jan 1, 2004, and Dec 31, 2013, 480 patients with BSIs due to CPE were enrolled in the INCREMENT cohort, of whom we included 437 (91%) in this study. 343 (78%) patients received appropriate therapy compared with 94 (22%) who received inappropriate therapy. The most frequent organism was Klebsiella pneumoniae (375 [86%] of 437; 291 [85%] of 343 patients receiving appropriate therapy vs 84 [89%] of 94 receiving inappropriate therapy) and the most frequent carbapenemase was K pneumoniae carbapenemase (329 [75%]; 253 [74%] vs 76 [81%]). Appropriate therapy was associated with lower mortality than was inappropriate therapy (132 [38·5%] of 343 patients died vs 57 [60·6%] of 94; absolute difference 22·1% [95% CI 11·0-33·3]; adjusted hazard ratio [HR] 0·45 [95% CI 0·33-0·62]; p<0·0001). Among those receiving appropriate therapy, 135 (39%) received combination therapy and 208 (61%) received monotherapy. Overall mortality was not different between those receiving combination therapy or monotherapy (47 [35%] of 135 vs 85 [41%] of 208; adjusted HR 1·63 [95% CI 0·67-3·91]; p=0·28). However, combination therapy was associated with lower mortality than was monotherapy in the high-mortality-score stratum (30 [48%] of 63 vs 64 [62%] of 103; adjusted HR 0·56 [0·34-0·91]; p=0·02), but not in the low-mortality-score stratum (17 [24%] of 72 vs 21 [20%] of 105; adjusted odds ratio 1·21 [0·56-2·56]; p=0·62).

INTERPRETATION

Appropriate therapy was associated with a protective effect on mortality among patients with BSIs due to CPE. Combination therapy was associated with improved survival only in patients with a high mortality score. Patients with BSIs due to CPE should receive active therapy as soon as they are diagnosed, and monotherapy should be considered for those in the low-mortality-score stratum.

FUNDING

Spanish Network for Research in Infectious Diseases, European Development Regional Fund, Instituto de Salud Carlos III, and Innovative Medicines Initiative.

Microspectrofluorimetry to dissect the permeation of ceftazidime in Gram-negative bacteria

A main challenge in chemotherapy is to determine the in cellulo parameters modulating the drug concentration required for therapeutic action. It is absolutely urgent to understand membrane permeation and intracellular concentration of antibiotics in clinical isolates: passing the membrane barrier to reach the threshold concentration inside the bacterial periplasm or cytoplasm is the pivotal step of antibacterial activity. Ceftazidime (CAZ) is a key molecule of the combination therapy for treating resistant bacteria. We designed and synthesized different fluorescent CAZ derivatives (CAZ*, CAZ**) to dissect the early step of translocation-accumulation across bacterial membrane. Their activities were determined on E. coli strains and on selected clinical isolates overexpressing ß-lactamases. The accumulation of CAZ* and CAZ** were determined by microspectrofluorimetry and epifluorimetry. The derivatives were properly translocated to the periplasmic space when we permeabilize the outer membrane barrier. The periplasmic location of CAZ** was related to a significant antibacterial activity and with the outer membrane permeability. This study demonstrated the correlation between periplasmic accumulation and antibiotic activity. We also validated the method for approaching ß-lactam permeation relative to membrane permeability and paved the way for an original matrix for determining "Structure Intracellular Accumulation Activity Relationship" for the development of new therapeutic candidates.

Aminoglycosides against carbapenem-resistant Enterobacteriaceae in the critically ill: the pitfalls of aminoglycoside susceptibility

INTRODUCTION

The emergence of carbapenem-resistant Enterobacteriaceae (CRE) has brought aminoglycosides to the frontline since an aminoglycoside may be the only antimicrobial to which CRE isolates show in vitro susceptibility. The appropriateness of aminoglycoside-based therapies for severe infections by CRE is discussed considering the current breakpoints and recent pharmacokinetic (PK) studies in critically ill patients. Areas covered: Many aminoglycoside-susceptible CRE isolates present minimal inhibitory concentrations (MICs) at or slightly below the breakpoint of amikacin or gentamicin. However, recent PK studies with these aminoglycosides in critically ill have invariably shown that the PK/pharmacodynamic (PD) target is very unlikely attained even when high doses are administered, if the MICs are near the breakpoint. Expert commentary: While new antimicrobials are not widely available, the authors forecast an increasing use of aminoglycosides as backbone antibiotics against CRE isolates. However, the altered PK of aminoglycosides in critically ill patients severely impairs their predicted efficacy in these patients. Aminoglycoside breakpoints may hide 'aminoglycoside-susceptible' CRE isolates for that aminoglycosides will unlikely be effective if used in monotherapy. Therefore, these breakpoints may need to be revised due to the increasing use of aminoglycosides as backbone antibiotics to treat severe infections by CRE isolates in critically ill patients.

Bloodstream infections in children caused by carbapenem-resistant versus carbapenem-susceptible gram-negative microorganisms: Risk factors and outcome

Carbapenems are often considered the last resort agents reserved for treatment of infections due to highly antimicrobial resistant organisms such as A. baumannii and P. aeruginosa. However, carbapenem-resistant Gram-negative (CRGN) pathogens have become much more prevalent in the last decade. The objective of this study was to determine risk factors for and outcome of bacteremia caused by Gram-negative microorganisms in a pediatric tertiary-care hospital. Among 97 patients with hospital-acquired Gram-negative bacteremia, 66 patients with carbapenem-susceptible Gram-negative pathogens (CSGN) were compared with the remaining 31 with CRGN isolates. The overall clinical response and microbiological response rates were 83.3% and 43.9% in CSGN group, and 54.8% and 32.3% in CRGN group, respectively (P=0.002 and P=0.004, respectively). The treatment failure and relapse rates were 18.2% and 6.1% in CSGN group, and 38.7% and 6.5% in CRGN group, respectively (P=0.03 in each). The infection-related mortality rates were 10.8% in the CSGN group and 32.3% in the CRGN group (P=0.01). The total length of stay in hospital before infection was longer in patients with CRGN bacteremia than that of the CSGN bacteremia (P=0.002). The extended spectrum antibiotic usage prior to infection was significantly different between the groups (P=0.008). Infections due to CRGN are generally associated with poorer patient outcomes. Longer hospital stay and extended spectrum antibiotic usage prior to infection are the most important risk factors for CRGN bacteremia in our cohort.

Predictors of mortality in bloodstream infections caused by multidrug-resistant gram-negative bacteria: 4 years of collection

The study was undertaken to describe the profile of patients and the characteristics of all multidrug-resistant gram-negative bacteria (MDR-GNB) and to assess mortality. We examined 138 patients with bloodstream infections (BSIs) caused by MDR-GNB. Clinical characteristics, antibiotic therapy, and in-hospital mortality were analyzed. Survivor and nonsurvivor subgroups were compared to identify predictors of mortality. The in-hospital mortality rate was 25.4%. Univariate analysis revealed that comorbidities and inadequate initial antimicrobial treatment could increase risk of death. In Cox regression analysis, mortality was independently associated with the age (P = .034), hospitalization in an intensive care unit (ICU) (P = .04), invasive procedures (P < .001), and Acute Physiology and Chronic Health Evaluation II scores (P < .001), whereas combination therapy or monotherapy was not associated with mortality (P = .829). Postantibiogram therapy was associated with hospitalization in an ICU (P = .006), Charlson comorbidity index score (P = .003), and inadequate initial antimicrobial treatment (P < .001). MDR-GNB strains and antimicrobial regimens were not the major risk factors of mortality. Inadequate initial antimicrobial treatment, invasive procedures, high Acute Physiology And Chronic Health Evaluation II scores, hospitalization in an ICU, and comorbidities were the important factors responsible for mortality. Although there was no difference between combination therapy and monotherapy in mortality, combined treatment may be more effective than monotherapy for patients in an ICU, with a Charlson comorbidity index score < 4, or inadequate initial antimicrobial treatment.

Monotherapy versus Combination Therapy against Nonbacteremic Carbapenem-resistant Gram-negative Infections: A Retrospective Observational Study

Background:

Superiority of colistin–carbapenem combination therapy (CCCT) over colistin monotherapy (CMT) against carbapenem-resistant Gram-negative bacterial (CRGNB) infections is not conclusively proven.

Aim:

The aim of the current study was to analyze the effectiveness of both strategies against CRGNB nonbacteremic infections.

Design:

This was a retrospective observational cohort study.

Subjects and Methods:

Case record analysis of patients who had CRGNB nonbacteremic infections identified over a period of 4 years (January 2012–December 2015) was done by medical record review at a tertiary care center in India.

Statistical Analysis:

P < 0.05 was considered as significant. Multivariate analysis was performed using Cox regression.

Results:

Out of 153 patients (pneumonia 115, urinary tract infection 17, complicated skin and soft-tissue infection 18, intra-abdominal infection 1, and meningitis 2), 92 patients received CCCT and 61 received CMT. Univariate analysis revealed higher Acute Physiology and Chronic Health Evaluation II (APACHE II) score, pneumonia as the diagnosis, and Klebsiella as the causative organism to be the risk factors for higher 28-day mortality (P = 0.036, 0.006, 0.016, respectively). Combination therapy had no significant impact on mortality (odds ratio [OR] = 0.91, 95% confidence interval [CI] = 0.327–2.535, P = 0.857). Multivariate analysis revealed that higher APACHE II score and infection due to Klebsiella were found to be independent risk factors for higher mortality (OR = 3.16 and 4.9, 95% CI = 1.34–7.4 and 2.19–11.2, P = 0.008 and 0.0001, respectively).

Conclusions:

In our retrospective single-center series of CRGNB nonbacteremic infections, CCCT was not superior to CMT. Multicenter large observational studies or prospective randomized clinical trials are the need of the hour.

Risk factors for mortality in patients with ventilator-associated pneumonia caused by carbapenem-resistant Enterobacteriaceae

Background

The ideal therapeutic option for ventilator associated pneumonia caused by carbapenem-resistant Enterobacteriaceae is not defined. The aim of this study was to assess mortality-associated risk factors in patients with VAP by CRE and determine the outcome of several treatment options.

Methods

This was a retrospective study performed in two tertiary hospitals involving patients with VAP caused by CRE between January 2010 and August 2014. The outcomes were mortality within 30 days of VAP diagnosis and overall mortality during hospital admission. Risk factors for mortality were assessed by comparing variables of survivors and non-survivors.

Results

One hundred and twelve patients with CRE-VAP were included, 73 (65%) male, median age 56 years. The 30-day mortality was 57.1% and the overall hospital mortality was 67%. In the binary logistic regression analysis, only age >50 years was independently associated to increased mortality. Polymyxin was the most used drug (47.5%), followed by tigecycline (29.2%) and aminoglycosides (2.4%). Combined therapy with two active drugs was used by 17 patients (20.8%). No therapeutic option was independently associated to survival. However, combined therapy with two active drugs was superior to the therapy with a single active drug when inappropriate therapy was the comparator (p = 0.044). The addition of carbapenem was not associated with increased survival.

Conclusion

The best therapeutic option for VAP by CRE is still not completely defined, but the therapy with at least two active drugs was superior in this study.

Clinical translation of polymyxin-based combination therapy: Facts, challenges and future opportunities

The emergence and spread of multidrug resistant Gram-negative bacteria has led to a resurgence in the clinical use of polymyxin antibiotics. However, the prevalence of polymyxin resistance is on the rise at an alarming rate, motivating the idea of combination therapy to sustain the revival of these "old" antibiotics. Although ample evidence in favor of combination therapy has emerged, it seems impracticable and confusing to find a promising combination from the diverse reports or gain adequate information on the efficacy and safety profile. With a stagnating discovery pipeline of novel antimicrobials, there is a clear need to fill the knowledge gaps in translating these basic research data to beneficial clinical practice. In this review, we examined the factors and ambiguities that stand as major hurdles in bringing polymyxin combination therapy to bedside care, highlighting the importance and urgency of incorporating translational research insights into areas of difficulty. We also discussed future research priorities that are essential to gather the necessary evidence and insights for promoting the best possible use of polymyxins in combination therapy.

Emerging Issues and Treatment Strategies in Carbapenem-Resistant Enterobacteriaceae (CRE)

Carbapenems are the broadest spectrum antimicrobials utilized in the treatment of serious infections since the 1980s. Soon after their introduction, the discovery of carbapenem-resistant Enterobacteriaceae (CRE) was reported in the 1990s. Invasive CRE infections are associated with high mortality and limited treatment options making care for patients with these infections challenging for clinicians. Current practice has reverted back to the use of "older" antimicrobials, such as the polymyxins, tigecycline, and fosfomycin, to combat invasive CRE infections. However, recent approval of ceftazidime-avibactam has added another treatment option to the current antimicrobial armamentarium. Resistance among the "older" agents is still rare but has been reported. Currently, there are numerous agents that are under investigation as well as combination therapy that looks promising in the treatment of CRE infections.

Evaluation of automated time-lapse microscopy for assessment of in vitro activity of antibiotics

This study aimed to evaluate the potential of a new time-lapse microscopy based method (oCelloScope) to efficiently assess the in vitro antibacterial effects of antibiotics. Two E. coli and one P. aeruginosa strain were exposed to ciprofloxacin, colistin, ertapenem and meropenem in 24-h experiments. Background corrected absorption (BCA) derived from the oCelloScope was used to detect bacterial growth. The data obtained with the oCelloScope were compared with those of the automated Bioscreen C method and standard time-kill experiments and a good agreement in results was observed during 6-24h of experiments. Viable counts obtained at 1, 4, 6 and 24h during oCelloScope and Bioscreen C experiments were well correlated with the corresponding BCA and optical density (OD) data. Initial antibacterial effects during the first 6h of experiments were difficult to detect with the automated methods due to their high detection limits (approximately 10⁵CFU/mL for oCelloScope and 10⁷CFU/mL for Bioscreen C), the inability to distinguish between live and dead bacteria and early morphological changes of bacteria during exposure to ciprofloxacin, ertapenem and meropenem. Regrowth was more frequently detected in time-kill experiments, possibly related to the larger working volume with an increased risk of pre-existing or emerging resistance. In comparison with Bioscreen C, the oCelloScope provided additional information on bacterial growth dynamics in the range of 10⁵ to 10⁷CFU/mL and morphological features. In conclusion, the oCelloScope would be suitable for detection of in vitro effects of antibiotics, especially when a large number of regimens need to be tested.

Bloodstream infections caused by Klebsiella pneumoniae in onco-hematological patients: clinical impact of carbapenem resistance in a multicentre prospective survey

The aim of this study was to identify risk factors for mortality in patients suffering from hematological malignancies (HMs) with bloodstream infections (BSIs) caused by Klebsiella pneumoniae (KP). We conducted a prospective cohort study on KP BSI in 13 Italian hematological units participating in the HEMABIS registry-SEIFEM group. The outcome measured was death within 21 days of BSI onset. Survivor and non-survivor subgroups were compared and Cox regression analysis was conducted to identify independent predictors of mortality. A total of 278 episodes of KP BSI were included in the study between January 2010 and June 2014. We found that 161 (57.9%) KP isolates were carbapenem resistant (CRKP). The overall 21-day mortality rate was 36.3%. It was significantly higher for patients with CRKP BSI (84/161, 52.2%) than for those with BSI caused by carbapenem susceptible KP (CSKP) (17/117, 14.5%; P < 0.001). Septic shock (HR 3.86), acute respiratory failure (HR 2.32), inadequate initial antimicrobial therapy (HR 1.87) and carbapenem resistance by KP isolates (HR 1.85) were independently associated with mortality. A subanalysis was conducted in only 149 patients with CRKP BSI who had received ≥48 hr of adequate antibiotic therapy, and combination therapy was independently associated with survival (HR 0.32). Our study shows that in recent years carbapenem resistance has dramatically increased in HM patients with KP BSI in Italy and is associated with a worse outcome. The optimal management of such infections and the definition of new empirical/targeted antimicrobial strategies in HM patients can still be considered unmet clinical needs. Am. J. Hematol. 91:1076-1081, 2016. © 2016 Wiley Periodicals, Inc.

Synergistic combinations of polymyxins

The proliferation of extensively drug-resistant Gram-negative pathogens has necessitated the therapeutic use of colistin and polymyxin B. However, treatment failures with polymyxin monotherapies and the emergence of polymyxin resistance have catalysed the search for polymyxin combinations that synergistically kill polymyxin-susceptible and -resistant organisms. This mini-review examines recent (2011-2016) in vitro and in vivo studies that have attempted to identify synergistic polymyxin combinations against Pseudomonas aeruginosa, Klebsiella pneumoniae and Acinetobacter baumannii. Clinical evidence for the use of combination regimens is also discussed.

Polymyxin monotherapy or in combination against carbapenem-resistant bacteria: systematic review and meta-analysis

OBJECTIVES

The objective of this study was to summarize available data on polymyxin-based combination therapy or monotherapy for carbapenem-resistant Gram-negative bacteria.

METHODS

This is a systematic review. We included observational studies and randomized controlled trials (RCTs) comparing polymyxin monotherapy versus polymyxin-based combination therapy in adult patients with infections caused by carbapenem-resistant or carbapenemase-producing Gram-negative bacteria. Only named antibiotic regimens were included. The primary outcome was 30 day mortality. Unadjusted OR (uOR) and adjusted OR where available with 95% CI were pooled in random-effects meta-analyses.

RESULTS

Twenty-two studies including 28 comparisons were included. Polymyxin monotherapy was associated with a uOR of 1.58 (95% CI = 1.03-2.42) for mortality compared with polymyxin/carbapenem combination therapy (seven observational studies, 537 patients), without heterogeneity. Subgrouping studies to serious and critical risk of bias resulted in uORs of 0.94 (95% CI = 0.42-2.09) and 1.94 (95% CI = 1.17-3.23), respectively. Mortality was significantly higher with polymyxin monotherapy compared with combination therapy with tigecycline, aminoglycosides or fosfomycin (potentially double-coverage regimens): uOR of 1.57 (95% CI = 1.06-2.32) overall (10 observational studies and 1 RCT, 585 patients, no heterogeneity) and uOR of 2.09 (95% CI = 1.21-3.6) for Klebsiella pneumoniae bacteraemia (7 observational studies, 285 patients, no heterogeneity); very low quality evidence. Two RCTs and one observational study assessing rifampicin/colistin combination therapy for Acinetobacter baumannii infections showed no difference in mortality compared with colistin monotherapy; moderate quality evidence.

CONCLUSIONS

The significant association observed in observational studies between polymyxin monotherapy and mortality cannot be taken as proof of combination therapy effects due to the low quality of the evidence. The only three RCTs to date show no effect of rifampicin/colistin or fosfomycin/colistin on mortality for Acinetobacter infections.

In vitro antibacterial activity of rifampicin in combination with imipenem, meropenem and doripenem against multidrug-resistant clinical isolates of Pseudomonas aeruginosa

Background

Multidrug-resistant Pseudomonas aeruginosa has emerged as one of the most important healthcare-associated pathogens. Colistin is regarded as the last-resort antibiotic for multidrug-resistant Gram-negative bacteria, but is associated with high rates of acute kidney injury. The aim of this in vitro study is to search for an alternative treatment to colistin for multidrug-resistant P. aeruginosa infections.

Methods

Multidrug and carbapenem-resistant P. aeruginosa isolates were collected between January 2009 and December 2012 at MacKay Memorial Hospital. Minimal inhibitory concentrations (MICs) were determined for various antibiotic combinations. Carbapenemase-producing genes including bla_VIM, other β-lactamase genes and porin mutations were screened by PCR and sequencing. The efficacy of carbapenems (imipenem, meropenem, doripenem) with or without rifampicin was correlated with the type of porin mutation (frameshift mutation, premature stop codon mutation) in multidrug-resistant P. aeruginosa isolates without carbapenemase-producing genes.

Results

Of the 71 multidrug-resistant clinical P. aeruginosa isolates, only six harboured the bla_VIM gene. Imipenem, meropenem and doripenem were significantly more effective (reduced fold-change of MICs) when combined with rifampicin in bla_VIM-negative isolates, especially in isolates with porin frameshift mutation.

Conclusions

Imipenem + rifampicin combination has a low MIC against multidrug-resistant P. aeruginosa, especially in isolates with porin frameshift mutation. The imipenem + rifampicin combination may provide an alternative treatment to colistin for multidrug -resistant P. aeruginosa infections, especially for patients with renal insufficiency.

Clinical epidemiology, treatment and prognostic factors of extensively drug-resistant Acinetobacter baumannii ventilator-associated pneumonia in critically ill patients

Limited data exist regarding prognostic factors and optimal antimicrobial treatment of infections caused by extensively drug-resistant Acinetobacter baumannii (XDR-AB). This retrospective cohort study included 93 adult patients who developed ventilator-associated pneumonia (VAP) due to XDR-AB in the ICU of the University Hospital of Heraklion, Greece, from October 2012 to April 2015. XDR-AB isolates were mainly susceptible to colistin (93.5%) and tigecycline (25.8%), whereas 6 (6.5%) were pandrug-resistant. Prior to infection, patients had long durations of mechanical ventilation and hospital stay and multiple exposures to antibiotics. Median Charlson co-morbidity and APACHE II scores were 2 and 17, respectively. Mortality at 28 days of infection onset was high (34.4%) despite high rates of in-vitro-active empirical (81.7%) and definitive (90.3%) treatment. Active colistin-based combination therapy (n = 55) and monotherapy (n = 29) groups had similar 28-day mortality (27.6% vs. 30.9%, respectively) and Kaplan-Meier survival estimates over time. In multivariable Cox regression, advanced age (aHR = 1.05 per year increase, 95% CI 1.02-1.09), rapidly fatal underlying disease (aHR = 2.64, 95% CI 0.98-9.17) and APACHE II score (aHR = 1.06 per unit increase, 95% CI 0.99-1.14) were identified as independent predictors of 28-day mortality, but no difference in mortality hazards between the active colistin-based combination therapy and monotherapy groups was produced (aHR = 0.88, 95% CI 0.35-2.38). These results support the use of colistin as a first-line agent against VAP in settings where XDR-AB is endemic, but oppose the introduction of colistin-based combination therapy as standard treatment.

Ten key points for the appropriate use of antibiotics in hospitalised patients: a consensus from the Antimicrobial Stewardship and Resistance Working Groups of the International Society of Chemotherapy

The Antibiotic Stewardship and Resistance Working Groups of the International Society for Chemotherapy propose ten key points for the appropriate use of antibiotics in hospital settings. (i) Get appropriate microbiological samples before antibiotic administration and carefully interpret the results: in the absence of clinical signs of infection, colonisation rarely requires antimicrobial treatment. (ii) Avoid the use of antibiotics to 'treat' fever: use them to treat infections, and investigate the root cause of fever prior to starting treatment. (iii) Start empirical antibiotic treatment after taking cultures, tailoring it to the site of infection, risk factors for multidrug-resistant bacteria, and the local microbiology and susceptibility patterns. (iv) Prescribe drugs at their optimal dosing and for an appropriate duration, adapted to each clinical situation and patient characteristics. (v) Use antibiotic combinations only where the current evidence suggests some benefit. (vi) When possible, avoid antibiotics with a higher likelihood of promoting drug resistance or hospital-acquired infections, or use them only as a last resort. (vii) Drain the infected foci quickly and remove all potentially or proven infected devices: control the infection source. (viii) Always try to de-escalate/streamline antibiotic treatment according to the clinical situation and the microbiological results. (ix) Stop unnecessarily prescribed antibiotics once the absence of infection is likely. And (x) Do not work alone: set up local teams with an infectious diseases specialist, clinical microbiologist, hospital pharmacist, infection control practitioner or hospital epidemiologist, and comply with hospital antibiotic policies and guidelines.

Antibiotic strategies in the era of multidrug resistance

The rapid emergence and dissemination of antibiotic-resistant microorganisms in ICUs worldwide threaten adequate antibiotic coverage of infected patients in this environment. The causes of this problem are multifactorial, but the core issues are clear: the emergence of antibiotic resistance is highly correlated with selective pressure resulting from inappropriate use of these drugs. Because a significant increase in mortality is observed when antibiotic therapy is delayed in infected ICU patients, initial therapy should be broad enough to cover all likely pathogens. Receipt of unnecessary prolonged broad-spectrum antibiotics, however, should be avoided. Local microbiologic data are extremely important to predict the type of resistance that may be present for specific causative bacteria, as is prior antibiotic exposure, and antibiotic choices should thus be made at an individual patient level.

Activity of Colistin in Combination with Meropenem, Tigecycline, Fosfomycin, Fusidic Acid, Rifampin or Sulbactam against Extensively Drug-Resistant Acinetobacter baumannii in a Murine Thigh-Infection Model

Few effective therapeutic options are available for treating severe infections caused by extensively drug-resistant Acinetobacter baumannii (XDR-AB). Using a murine thigh-infection model, we examined the in vivo efficacy of colistin in combination with meropenem, tigecycline, fosfomycin, fusidic acid, rifampin, or sulbactam against 12 XDR-AB strains. Colistin, tigecycline, rifampin, and sulbactam monotherapy significantly decreased bacterial counts in murine thigh infections compared with those observed in control mice receiving no treatment. Colistin was the most effective agent tested, displaying bactericidal activity against 91.7% of strains at 48 h post-treatment. With strains showing a relatively low minimum inhibitory concentration (MIC) for meropenem (MIC ≤ 32 mg/L), combination therapy with colistin plus meropenem caused synergistic inhibition at both 24 h and 48 h post-treatment. However, when the meropenem MIC was ≥64 mg/L, meropenem did not significantly alter the efficacy of colistin. The addition of rifampin and fusidic acid significantly improved the efficacy of colistin, showing a synergistic effect in 100% and 58.3% of strains after 24 h of treatment, respectively, while the addition of tigecycline, fosfomycin, or sulbactam did not show obvious synergistic activity. No clear differences in activities were observed between colistin-rifampin and colistin-fusidic acid combination therapy with most strains. Overall, our in vivo study showed that administering colistin in combination with rifampin or fusidic acid is more efficacious in treating XDR-AB infections than other combinations. The colistin-meropenem combination may be another appropriate option if the MIC is ≤32 mg/L. Further clinical studies are urgently needed to confirm the relevance of these findings.

Beyond Susceptible and Resistant, Part III: Treatment of Infections due to Gram-Negative Organisms Producing Carbapenemases

Carbapenemases are enzymes that are capable of inactivating all or almost all beta-lactam antimicrobial agents. These enzymes are frequently coexpressed with other resistance mechanisms to non-beta-lactams, leading to extremely drug-resistant pathogens. Once a curiosity, these enzymes have spread into organisms that are among the most common causes of infection, such as Klebsiella pneumoniae and Escherichia coli. Identification of these organisms has proved challenging for clinical microbiology laboratories, leading to revisions in susceptibility standards for carbapenems. Although currently a rare cause of infection in children, these carbapenem-resistant Enterobacteriaceae (CRE) are becoming endemic in a variety of healthcare settings. Management of infections due to CRE is complicated by a lack of effective treatment options and clinical data on their effectiveness. Treatment of CRE infections in children is particularly challenging because therapeutic options for CRE lack adequate data on dosing and safety in children. Use of unconventional combination treatment regimens, including agents to which the organism is resistant in vitro, may provide some benefit in the treatment of severe CRE infection. Fortunately, several agents with the potential for treatment of CRE infections have been recently approved or are in late clinical development, although few data will be available in the short term to inform use in children.

Multidrug-resistant bacteria in hematology patients: emerging threats

Multidrug-resistant (MDR) bacteria, particularly Gram negatives, such as Enterobacteriaceae resistant to third-generation cephalosporins or carbapenems and MDR Pseudomonas aeruginosa, are increasingly frequent in hematology patients. The prevalence of different resistant species varies significantly between centers. Thus, the knowledge of local epidemiology is mandatory for deciding the most appr-opriate management protocols. In the era of increasing antibiotic resistance, empirical therapy of febrile neutropenia should be individualized. A de-escalation approach is recommended in case of severe clinical presentation in patients who are at high risk for infection with a resistant strain. Targeted therapy of an MDR Gram negative usually calls for a combination treatment, although no large randomized trials exist in this setting. Infection control measures are the cornerstone of limiting the spread of MDR pathogens in hematology units.

Multicentre open-label randomised controlled trial to compare colistin alone with colistin plus meropenem for the treatment of severe infections caused by carbapenem-resistant Gram-negative infections (AIDA): a study protocol

INTRODUCTION

The emergence of antibiotic-resistant bacteria has driven renewed interest in older antibacterials, including colistin. Previous studies have shown that colistin is less effective and more toxic than modern antibiotics. In vitro synergy studies and clinical observational studies suggest a benefit of combining colistin with a carbapenem. A randomised controlled study is necessary for clarification.

METHODS AND ANALYSIS

This is a multicentre, investigator-initiated, open-label, randomised controlled superiority 1:1 study comparing colistin monotherapy with colistin-meropenem combination therapy for infections caused by carbapenem-resistant Gram-negative bacteria. The study is being conducted in 6 centres in 3 countries (Italy, Greece and Israel). We include patients with hospital-associated and ventilator-associated pneumonia, bloodstream infections and urosepsis. The primary outcome is treatment success at day 14, defined as survival, haemodynamic stability, stable or improved respiratory status for patients with pneumonia, microbiological cure for patients with bacteraemia and stability or improvement of the Sequential Organ Failure Assessment (SOFA) score. Secondary outcomes include 14-day and 28-day mortality as well as other clinical end points and safety outcomes. A sample size of 360 patients was calculated on the basis of an absolute improvement in clinical success of 15% with combination therapy. Outcomes will be assessed by intention to treat. Serum colistin samples are obtained from all patients to obtain population pharmacokinetic models. Microbiological sampling includes weekly surveillance samples with analysis of resistance mechanisms and synergy. An observational trial is evaluating patients who met eligibility requirements but were not randomised in order to assess generalisability of findings.

ETHICS AND DISSEMINATION

The study was approved by ethics committees at each centre and informed consent will be obtained for all patients. The trial is being performed under the auspices of an independent data and safety monitoring committee and is included in a broad dissemination strategy regarding revival of old antibiotics.

TRIAL REGISTRATION NUMBER

NCT01732250 and 2012-004819-31; Pre-results.

Treatment options for infections caused by carbapenem-resistant Enterobacteriaceae: can we apply "precision medicine" to antimicrobial chemotherapy?

INTRODUCTION

For the past three decades, carbapenems played a central role in our antibiotic armamentarium, trusted to effectively treat infections caused by drug-resistant bacteria. The utility of this class of antibiotics has been compromised by the emergence of resistance especially among Enterobacteriaceae.

AREAS COVERED

We review the current mainstays of pharmacotherapy against infections caused by carbapenem-resistant Enterobacteriaceae (CRE) including tigecycline, aminoglycosides, and rediscovered 'old' antibiotics such as fosfomycin and polymyxins, and discuss their efficacy and potential toxicity. We also summarize the contemporary clinical experience treating CRE infections with antibiotic combination therapy. Finally, we discuss ceftazidime/avibactam and imipenem/relebactam, containing a new generation of beta-lactamase inhibitors, which may offer alternatives to treat CRE infections. We critically evaluate the published literature, identify relevant clinical trials and review documents submitted to the United States Food and Drug Administration.

EXPERT OPINION

Defining the molecular mechanisms of resistance and applying insights about pharmacodynamic and pharmacokinetic properties of antibiotics, in order to maximize the impact of old and new therapeutic approaches should be the new paradigm in treating infections caused by CRE. A concerted effort is needed to carry out high-quality clinical trials that: i) establish the superiority of combination therapy vs. monotherapy; ii) confirm the role of novel beta-lactam/beta-lactamase inhibitor combinations as therapy against KPC- and OXA-48 producing Enterobacteriaceae; and, iii) evaluate new antibiotics active against CRE as they are introduced into the clinic.

Tigecycline Treatment for Carbapenem-Resistant Enterobacteriaceae Infections: A Systematic Review and Meta-Analysis

Carbapenem-resistant Enterobacteriaceae (CRE) infections are prevalent worldwide; they have few effective treatments and this jeopardizes public health. Clinicians often use tigecycline to combat CRE, but its clinical efficacy remains controversial. Therefore, to compare the efficacy and safety of tigecycline in treating CRE infections compared with that of other antimicrobial agents, and to evaluate whether combination therapy and high-dose regimens are beneficial, we performed a systematic review and meta-analysis. PubMed and Embase were searched for controlled trials or cohort studies reporting the efficacy and/or safety of tigecycline-based regimens to treat CRE infections. Statistical analyses were performed using the Comprehensive Meta-Analysis V2.2. All meta-analyses were performed based on fixed- or random-effects model, and the I method was used to assess heterogeneity. Twenty-one controlled studies and 5 single-arm studies were included in this systematic review. With regard to the controlled studies, the tigecycline groups did not differ significantly from the control groups in terms of overall mortality (Odds ratio (OR) = 0.96 [95% confidence interval (CI) = 0.75-1.22; P = 0.73]), clinical response rate (OR = 0.58 [95% CI = 0.31-1.09; P = 0.09]), or microbiological response rate (OR = 0.46 [95% CI = 0.15-1.44; P = 0.18]). Subgroup analyses showed that 30-day mortality was significantly lower in patients who received tigecycline combination therapy than in those who received monotherapy (OR = 1.83 [95% CI = 1.07-3.12; P = 0.03]) and other antibiotic regimens (OR = 0.59 [95% CI = 0.39-0.88; P = 0.01]), respectively. In addition, high-dose tigecycline regimens differed significantly from standard dose schedules in terms of ICU mortality (OR = 12.48 [95% CI = 2.06-75.43; P = 0.006]). The results of the 5 single-arm studies corroborated the findings of the controlled studies. Our results indicated that the efficacy of tigecycline in treating CRE infections is similar to that of other antibiotics. Tigecycline combination therapy and high-dose regimens may be more effective than monotherapy and standard-dose regimens, respectively. Nonetheless, considering that the current available evidence is limited, well-designed randomized controlled trials are urgently needed to clarify the comparative efficacy of tigecycline in treating CRE infections.

Is colistin effective in the treatment of infections caused by multidrug-resistant (MDR) or extremely drug-resistant (XDR) gram-negative microorganisms in children?

The increasing incidence of infections caused by multidrug-resistant (MDR) or extremely drug-resistant (XDR) gram-negative organisms has led to the reemergence of colistin use. Clinical and demographic data were collected on 94 pediatric patients diagnosed with MDR or XDR gram-negative infections and treated with either a colistin-containing regimen (colistin group) or at least one antimicrobial agent other than colistin (noncolistin group). The overall clinical response rates were 65.8% in the colistin group and 70.0% in the noncolistin group (P = 0.33). The infection-related mortality rates were 11% in the colistin group and 13.3% in the noncolistin group (P = 0.74). There was no statistically significant difference in nephrotoxicity in the colistin and noncolistin groups. Colistin therapy was at least as effective and as safe as beta-lactam antibiotics or quinolones, with or without aminoglycosides, in the treatment of infections caused by gram-negative organisms and may be a therapeutic option in children.

Dynamic interaction of colistin and meropenem on a WT and a resistant strain of Pseudomonas aeruginosa as quantified in a PK/PD model

OBJECTIVES

Combination therapy can be a strategy to ensure effective bacterial killing when treating Pseudomonas aeruginosa, a Gram-negative bacterium with high potential for developing resistance. The aim of this study was to develop a pharmacokinetic/pharmacodynamic (PK/PD) model that describes the in vitro bacterial time-kill curves of colistin and meropenem alone and in combination for one WT and one meropenem-resistant strain of P. aeruginosa.

METHODS

In vitro time-kill curve experiments were conducted with a P. aeruginosa WT (ATCC 27853) (MICs: meropenem 1 mg/L; colistin 1 mg/L) and a meropenem-resistant type (ARU552) (MICs: meropenem 16 mg/L; colistin 1.5 mg/L). PK/PD models characterizing resistance were fitted to the observed bacterial counts in NONMEM. The final model was applied to predict the bacterial killing of ARU552 for different combination dosages of colistin and meropenem.

RESULTS

A model with compartments for growing and resting bacteria, where the bacterial killing by colistin reduced with continued exposure and a small fraction (0.15%) of the start inoculum was resistant to meropenem, characterized the bactericidal effect and resistance development of the two antibiotics. For a typical patient, a loading dose of colistin combined with a high dose of meropenem (2000 mg q8h) was predicted to result in a pronounced kill of the meropenem-resistant strain over 24 h.

CONCLUSIONS

The developed PK/PD model successfully described the time course of bacterial counts following exposures to colistin and meropenem, alone and in combination, for both strains, and identified a dynamic drug interaction. The study illustrates the application of a PK/PD model and supports high-dose combination therapy of colistin and meropenem to overcome meropenem resistance.

Bloodstream infections in internal medicine

Bloodstream infections (BSI) carry a heavy burden of morbidity and mortality in modern internal medicine wards (IMW). These wards are often filled with elderly subjects with several risk factors for BSI, such as multiple comorbidities, polypharmacy, immunosuppression, and indwelling devices. Diagnosing BSI in such a setting might require a high degree of suspicion, since the clinical presentation could be affected by underlying conditions and concomitant medications, which might delay the administration of an appropriate antimicrobial therapy, an event strongly and unfavorably influencing survival. Furthermore, selecting the appropriate antimicrobial therapy to treat these patients is becoming an increasingly complex task in which all possible benefits and costs should be carefully analyzed from patient and public health perspectives. Only a specialized, continuous, and interdisciplinary approach could really improve the management of IMW patients in an era of increasing antimicrobial resistance and complexity of care.

Laboratory diagnosis, clinical management and infection control of the infections caused by extensively drug-resistant Gram-negative bacilli: a Chinese consensus statement

Extensively drug-resistant (XDR) Gram-negative bacilli (GNB) are defined as bacterial isolates susceptible to two or fewer antimicrobial categories. XDR-GNB mainly occur in Enterobacteriaceae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Stenotrophomonas maltophilia. The prevalence of XDR-GNB is on the rise in China and in other countries, and it poses a major public health threat as a result of the lack of adequate therapeutic options. A group of Chinese clinical experts, microbiologists and pharmacologists came together to discuss and draft a consensus on the laboratory diagnosis, clinical management and infection control of XDR-GNB infections. Lists of antimicrobial categories proposed for antimicrobial susceptibility testing were created according to documents from the Clinical Laboratory Standards Institute (CLSI), the European Committee on Antimicrobial Susceptibility Testing (EUCAST) and the United States Food and Drug Administration (FDA). Multiple risk factors of XDR-GNB infections are analyzed, with long-term exposure to extended-spectrum antimicrobials being the most important one. Combination therapeutic regimens are summarized for treatment of XDR-GNB infections caused by different bacteria based on limited clinical studies and/or laboratory data. Most frequently used antimicrobials used for the combination therapies include aminoglycosides, carbapenems, colistin, fosfomycin and tigecycline. Strict infection control measures including hand hygiene, contact isolation, active screening, environmental surface disinfections, decolonization and restrictive antibiotic stewardship are recommended to curb the XDR-GNB spread.

Antimicrobial resistance: one world, one fight!

The lack of new antibiotic classes calls for a cautious use of existing agents. Yet, every 10 min, almost two tons of antibiotics are used around the world, all too often without any prescription or control. The use, overuse and misuse of antibiotics select for resistance in numerous species of bacteria which then renders antimicrobial treatment ineffective. Almost all countries face increased antimicrobial resistance (AMR), not only in humans but also in livestock and along the food chain. The spread of AMR is fueled by growing human and animal populations, uncontrolled contamination of fresh water supplies, and increases in international travel, migration and trade. In this context of global concern, 68 international experts attending the fifth edition of the World HAI Resistance Forum in June 2015 shared their successes and failures in the global fight against AMR. They underlined the need for a “One Health” approach requiring research, surveillance, and interventions across human, veterinary, agricultural and environmental sectors. This strategy involves concerted actions on several fronts. Improved education and increased public awareness are a well-understood priority. Surveillance systems monitoring infections need to be expanded to include antimicrobial use, as well as the emergence and spread of AMR within clinical and environmental samples. Adherence to practices to prevent and control the spread of infections is mandatory to reduce the requirement of antimicrobials in general care and agriculture. Antibiotics need to be banned as growth promoters for farm animals in countries where it has not yet been done. Antimicrobial stewardship programmes in animal husbandry have proved to be efficient for minimising AMR, without compromising productivity. Regarding the use of antibiotics in humans, new tools to provide highly specific diagnoses of pathogens can decrease diagnostic uncertainty and improve clinical management. Finally, infection prevention and control measures – some of them as simple as hand hygiene – are essential and should be extended beyond healthcare settings. Aside from regulatory actions, all people can assist in AMR reduction by limiting antibiotic use for minor illnesses. Together, we can all work to reduce the burden of AMR.

Controlling bacterial infections by inhibiting proton-dependent processes

Bacterial resistance to antibiotics is recognized as one of the greatest threats in modern healthcare, taking a staggering toll worldwide. New approaches for controlling bacterial infections must be designed, eventually combining multiple strategies for complimentary therapies. This review explores an old/new paradigm for multi-targeted antibacterial therapy, focused at disturbing bacterial cytoplasmic membrane functions at sub minimal inhibitory concentrations, namely through superficial physical alterations of the bilayer, thereby perturbing transmembrane signals transduction. Such a paradigm may have the advantage of fighting the infection while avoiding many of the known resistance mechanisms. This article is part of a Special Issue entitled: Antimicrobial peptides edited by Karl Lohner and Kai Hilpert.

Polymyxin B versus colistin: an update

Polymyxin B and colistin (polymyxin E) are polypeptide antibiotics that were developed in the 1940s, but fell into disfavor due to their high toxicity rates. These two antibiotics were previously regarded to be largely equivalent, due to similarities in their chemical structure and spectrum of activity. In recent years, several pertinent differences, especially in terms of potency and disposition, have been revealed between polymyxin B and colistin. These differences are mainly attributed to the fact that polymyxin B is administered parenterally in its active form, while colistin is administered parenterally as an inactive pro-drug, colistimethate. In this review, we summarize the similarities and differences between polymyxin B and colistin. We also discuss the potential clinical implications of these findings, and provide our perspectives on how polymyxins should be employed to preserve their utility in this era of multi-drug resistance.

Ceftazidime-avibactam for the treatment of complicated urinary tract infections and complicated intra-abdominal infections

Treatment of complicated urinary tract infections and complicated intra-abdominal infections is increasingly difficult due to the rising prevalence of multidrug-resistant Gram-negative bacteria. Ceftazidime-avibactam is a combination of the established third-generation cephalosporin ceftazidime with avibactam, a novel non-β-lactam β-lactamase inhibitor, which restores the activity of ceftazidime against many β-lactamase-producing Gram-negative bacteria, including extended-spectrum β-lactamases and Klebsiella pneumoniae carbapenemases. Clinical and nonclinical studies supporting the safety and efficacy of ceftazidime-avibactam include microbiological surveillance studies of clinically relevant pathogens, in vivo animal models of infection, pharmacokinetic/pharmacodynamic target attainment analyses, Phase I clinical pharmacology studies, and Phase II/III studies in the treatment of complicated intra-abdominal infections and complicated urinary tract infections, including patients with ceftazidime-nonsusceptible Gram-negative infections.

Considerations About Antimicrobial Stewardship in Settings with Epidemic Extended-Spectrum β-Lactamase-Producing or Carbapenem-Resistant Enterobacteriaceae

Infections caused by gram-negative bacteria (GNB) resistant to multiple classes of antibiotics are increasing in many hospitals. Extended-spectrum β-lactamase (ESBL)-producing and carbapenem-resistant Enterobacteriaceae in particular are now endemic in many parts of the world and represent a serious public health threat. In this era, antimicrobial stewardship programs are essential as targeted and responsible use of antibiotics improves patient outcomes and hopefully limits the selective pressure that drives the further emergence of resistance. However, some stewardship strategies aimed at promoting carbapenem-sparing regimens remain controversial and are difficult to implement when resistance rates to non-carbapenem antibiotics are increasing. Coordinated efforts between stewardship programs and infection control are essential for reversing conditions that favor the emergence and dissemination of multidrug-resistant GNB within the hospital and identifying extra-institutional "feeder reservoirs" of resistant strains such as long-term care facilities, where colonization is common despite limited numbers of serious infections. In settings where ESBL resistance is endemic, the cost-effectiveness of expanded infection control efforts and antimicrobial stewardship is still unknown. Once a patient has been colonized, selective oral or digestive decontamination may be considered, but evidence supporting its effectiveness is limited in patients who are already colonized or in centers with high rates of resistance. Moreover, temporary success at decolonization may be associated with a higher risk of relapse with strains that are resistant to the decolonizing antibiotics.

Polymyxin B in Combination with Antimicrobials Lacking In Vitro Activity versus Polymyxin B in Monotherapy in Critically Ill Patients with Acinetobacter baumannii or Pseudomonas aeruginosa Infections

There is no clinical evidence supporting the use of polymyxin B in combination with another antimicrobial for infections caused by extensively drug-resistant Acinetobacter baumannii or Pseudomonas aeruginosa isolates. We developed a cohort study of patients in two intensive care units from teaching hospitals to evaluate treatment with intravenous polymyxin B for ≥48 h for severe A. baumannii or P. aeruginosa infections. Covariates potentially associated with 30-day mortality were evaluated in a Cox proportional hazards model. A total of 101 patients were included; 33 (32.7%) were treated with polymyxin B in combination with an antimicrobial lacking in vitro activity and 68 (67.3%) with polymyxin B in monotherapy. The overall 30-day mortality was 59.4% (60 patients), comprising 42.4% (14 of 33) and 67.6% (46 of 68) in combination and monotherapy groups, respectively (P = 0.03). The mortality rates were 18.5/1,000 patient days and 36.4/1,000 patient days in the combination and monotherapy groups, respectively (P = 0.02). Combination therapy was independently associated with lower 30-day mortality (hazard ratio, 0.33; 95% confidence interval, 0.17 to 0.64; P = 0.001). Creatinine clearance of ≥60 ml/min was also a protective factor, while a higher acute physiology and chronic health evaluation (APACHE II) score and polymicrobial infection were associated with increased mortality. The results did not change after adding a propensity score for prescribing combination therapy into the model. The protective effect remained when only combination with β-lactam or carbapenem was considered and in both subgroups of patients: those with A. baumannii infection and those with lower respiratory tract infections. To our knowledge, this is the first clinical study to show a benefit of combination over monotherapy with polymyxin B for severe extensively drug-resistant A. baumannii or P. aeruginosa infections.

Efficacy of Appropriate Antimicrobial Therapy on the Survival of Patients With Carbapenem Nonsusceptible Klebsiella Pneumoniae Infection: A Multicenter Study in Taiwan

The impact of antimicrobial treatment on the outcome of carbapenem nonsusceptible Klebsiella pneumoniae (CnsKP) infections needs to be elucidated. This nationwide, multicenter study was conducted to evaluate the impact of appropriate antimicrobial therapy on 14-day mortality among patients with CnsKP infection in Taiwan.Patients with CnsKP infections from 11 medical centers and 4 regional hospitals in Taiwan were enrolled in 2013. Carbapenem nonsusceptibility was defined as a minimum inhibitory concentration of ≥2 mg/L for imipenem or meropenem. Predictors of 14-day mortality were determined using the Cox proportional regression model. The influence of infection severity on the impact of appropriate use of antimicrobials on 14-day mortality was determined using the Acute Physiology and Chronic Health Evaluation (APACHE) II score.Overall 14-day mortality was 31.8% (49/154). Unadjusted mortality for appropriate antimicrobial therapy was 23.1% (18/78 patients). Appropriate therapy was independently associated with reduced mortality (hazard ratio [HR], 0.44; 95% confidence interval [CI], 0.24-0.80; P = 0.007). A subgroup analysis revealed that the benefit of appropriate therapy was limited to patients with higher APACHE II scores (HR for patients with scores >15 and ≤35, 0.46; 95% CI 0.23-0.92; and for those with scores >35, 0.14; 95% CI, 0.02-0.99).In conclusion, appropriate antimicrobial therapy significantly reduces 14-day mortality for CnsKP infections. Survival benefit is more notable among more severely ill patients.

Treatment of MDR-Gram negative infections in the 21st century: a never ending threat for clinicians

The spread of antimicrobial resistance among Gram negative bacteria has dramatically reduced the current therapeutic opportunities and hampered the perspectives of drug discovery pipeline. Several unmet needs concerning the optimal therapeutic approaches to severe infections caused by the leading multi-drug-resistant GNB are still unresolved, mainly in relationship with the difficulty in the design of prospective comparative studies. Therefore a perspective of how the main resistance patterns and the related infections can be managed in the absence of more definitive data is mandatory.

Three Dimensional Checkerboard Synergy Analysis of Colistin, Meropenem, Tigecycline against Multidrug-Resistant Clinical Klebsiella pneumonia Isolates

The spread of carbapenem-non-susceptible Klebsiella pneumoniae strains bearing different resistance determinants is a rising problem worldwide. Especially infections with KPC (Klebsiella pneumoniae carbapenemase) - producers are associated with high mortality rates due to limited treatment options. Recent clinical studies of KPC-blood stream infections revealed that colistin-based combination therapy with a carbapenem and/or tigecycline was associated with significantly decreased mortality rates when compared to colistin monotherapy. However, it remains unclear if these observations can be transferred to K. pneumoniae harboring other mechanisms of carbapenem resistance. A three-dimensional synergy analysis was performed to evaluate the benefits of a triple combination with meropenem, tigecycline and colistin against 20 K. pneumoniae isolates harboring different β-lactamases. To examine the mechanism behind the clinically observed synergistic effect, efflux properties and outer membrane porin (Omp) genes (ompK35 and ompK36) were also analyzed. Synergism was found for colistin-based double combinations for strains exhibiting high minimal inhibition concentrations against all of the three antibiotics. Adding a third antibiotic did not result in further increased synergistic effect in these strains. Antagonism did not occur. These results support the idea that colistin-based double combinations might be sufficient and the most effective combination partner for colistin should be chosen according to its MIC.

Multidrug-Resistant Organisms: Considerations in Antibiotic Selection and Administration

Managing infections caused by multidrug-resistant organisms is a significant clinical challenge. Multidrug-resistant organisms' treatment is complicated in the pediatric population because of the lack of primary data, treatment guidelines, rapidly changing pharmacokinetic/pharmacodynamic parameters, and fewer approved antibiotic indications and dosing guidance. Treatment decisions must incorporate available pediatric data, clinical experience, and careful extrapolation from adult data while considering the unique challenges faced by children with complicated infections.

Colistin and Fusidic Acid, a Novel Potent Synergistic Combination for Treatment of Multidrug-Resistant Acinetobacter baumannii Infections

The spread of multidrug-resistant Acinetobacter baumannii (MDRAB) has led to the renaissance of colistin (COL), often the only agent to which MDRAB remains susceptible. Effective therapy with COL is beset with problems due to unpredictable pharmacokinetics, toxicity, and the rapid selection of resistance. Here, we describe a potent synergistic interaction when COL was combined with fusidic acid (FD) against A. baumannii. Synergy in vitro was assessed against 11 MDRAB isolates using disc diffusion, checkerboard methodology (fractional inhibitory concentration index [FICI] of ≤ 0.5, susceptibility breakpoint index [SBPI] of >2), and time-kill methodology (≥2 log10 CFU/ml reduction). The ability of FD to limit the emergence of COL resistance was assessed in the presence and absence of each drug alone and in combination. Synergy was demonstrated against all strains, with an average FICI and SBPI of 0.064 and 78.85, respectively. In time-kill assays, COL-FD was synergistic and rapidly bactericidal, including against COL-resistant strains. Fusidic acid prevented the emergence of COL resistance, which was readily selected with COL alone. This is the first description of a novel COL-FD regimen for the treatment of MDRAB. The combination was effective at low concentrations, which should be therapeutically achievable while limiting toxicity. Further studies are warranted to determine the mechanism underlying the interaction and the suitability of COL-FD as an unorthodox therapy for the treatment of multidrug-resistant Gram-negative infections.

Treatment Options for Carbapenem-Resistant Enterobacteriaceae Infections

This article provides a comprehensive review of currently available treatment options for infections due to carbapenem-resistant Enterobacteriaceae (CRE). Antimicrobial resistance in Gram-negative bacteria is an emerging and serious global public health threat. Carbapenems have been used as the "last-line" treatment for infections caused by resistant Enterobacteriaceae, including those producing extended spectrum ß-lactamases. However, Enterobacteriaceae that produce carbapenemases, which are enzymes that deactivate carbapenems and most other ß-lactam antibiotics, have emerged and are increasingly being reported worldwide. Despite this increasing burden, the most optimal treatment for CRE infections is largely unknown. For the few remaining available treatment options, there are limited efficacy data to support their role in therapy. Nevertheless, current treatment options include the use of older agents, such as polymyxins, fosfomycin, and aminoglycosides, which have been rarely used due to efficacy and/or toxicity concerns. Optimization of dosing regimens and combination therapy are additional treatment strategies being explored. Carbapenem-resistant Enterobacteriaceae infections are associated with poor outcomes and high mortality. Continued research is critically needed to determine the most appropriate treatment.

Global dissemination of extensively drug-resistant carbapenemase-producing Enterobacteriaceae: clinical perspectives on detection, treatment and infection control

The prevalence of carbapenem-resistant Gram-negative bacilli is on the rise worldwide, posing a major public health threat. Previously, this was mostly a problem in Pseudomonas and Acinetobacter, but during the last decade, carbapenem resistance has escalated in medically important species such as Klebsiella pneumoniae and Escherichia coli. In particular, the rising trend in E. coli is of concern, as this may lead to almost untreatable community-acquired infections. Resistance is conferred by carbapenemases, which are beta-lactamases that can breakdown essentially all beta-lactams. Moreover, bacteria carrying these resistance determinants are often resistant to other treatment options, due to the frequent co-acquisition of non-beta-lactam resistance genes located on the same mobile genetic elements. The detection of carbapenemase-producing Enterobacteriaceae (CPE) is a challenge, because some carbapenemases produce relatively discrete levels of carbapenem resistance. Current clinical evidence for treatment guidance is limited and based on retrospective observational studies and case reports. Existing data support the use of combination therapy for treatment of severe infections caused by CPE. Combination regimens including colistin, carbapenems, tigecycline, aminoglycosides and fosfomycin have been used. Randomized controlled studies of combination regimens are ongoing and may help to determine the optimal therapy. Novel beta-lactamase inhibitors may also have a role in future treatment of these infections. Strict infection control measures including isolation or cohort care of affected patients as well as contact tracing and active screening are needed to curb the spread of CPE. In this review, we provide a clinical perspective on the management of patients infected or colonized with CPE.

Activity of antimicrobial combinations against KPC-2-producing Klebsiella pneumoniae in a rat model and time-kill assay

This study evaluated the efficacy of tigecycline (TIG), polymyxin B (PMB), and meropenem (MER) in 80 rats challenged with Klebsiella pneumoniae carbapenemase (KPC)-producing K. pneumoniae infection. A time-kill assay was performed with the same strain. Triple therapy and PMB+TIG were synergistic, promoted 100% survival, and produced negative peritoneal cultures, while MER+TIG showed lower survival and higher culture positivity than other regimens (P = 0.018) and was antagonistic. In vivo and in vitro studies showed that combined regimens, except MER+TIG, were more effective than monotherapies for this KPC-producing strain.

Impact of combination antimicrobial therapy on mortality risk for critically ill patients with carbapenem-resistant bacteremia

There are limited treatment options for carbapenem-resistant Gram-negative infections. Currently, there are suggestions in the literature that combination therapy should be used, which frequently includes antibiotics to which the causative pathogen demonstrates in vitro resistance. This case-control study evaluated risk factors associated with all-cause mortality rates for critically ill patients with carbapenem-resistant Gram-negative bacteremia. Adult patients who were admitted to an intensive care unit with sepsis and a blood culture positive for Gram-negative bacteria resistant to a carbapenem were included. Patients with polymicrobial, recurrent, or breakthrough infections were excluded. Included patients were classified as survivors (controls) or nonsurvivors (cases) at 30 days after the positive blood culture. Of 302 patients screened, 168 patients were included, of whom 90 patients died (53.6% [cases]) and 78 survived (46.4% [controls]) at 30 days. More survivors received appropriate antibiotics (antibiotics with in vitro activity) than did nonsurvivors (93.6% versus 53.3%; P < 0.01). Combination therapy, defined as multiple appropriate agents given for 48 h or more, was more common among survivors than nonsurvivors (32.1% versus 7.8%; P < 0.01); however, there was no difference in multiple-agent use when in vitro activity was not considered (including combinations with carbapenems) (87.2% versus 80%; P = 0.21). After adjustment for baseline factors with multivariable logistic regression, combination therapy was independently associated with decreased risk of death (odds ratio, 0.19 [95% confidence interval, 0.06 to 0.56]; P < 0.01). These data suggest that combination therapy with multiple agents with in vitro activity is associated with improved survival rates for critically ill patients with carbapenem-resistant Gram-negative bacteremia. However, that association is lost if in vitro activity is not considered.

Is combination therapy for carbapenem-resistant Klebsiella pneumoniae the new standard of care?

Carbapenem-resistant Klebsiella pneumoniae causes serious nosocomial infections and therapeutic options are limited. There is increasing evidence suggesting that combination antibiotic therapy is more effective than monotherapy and leads to better outcomes. However, questions remain about which regimen is optimal and how to balance the potential benefits of combination therapy versus the risks and possible complications (e.g., toxicity, increased costs, Clostridium difficile infection). Well-designed randomized clinical trials are needed to clarify these issues.