The Association Between Empirical Antibiotic Treatment and Mortality in Severe Infections Caused by Carbapenem-resistant Gram-negative Bacteria: A Prospective Study

Innovative Antibiotic Therapies for Carbapenem-Resistant Gram-Negative Bacterial Infections: Clinical Efficacy, Safety, and Comparative Studies

This review provides an overview of recent research and advancements in infection prevention and the treatment of drug-resistant bacterial diseases. Cefiderocol, a novel siderophore cephalosporin, has demonstrated effectiveness against carbapenem-resistant bacteria such as Pseudomonas aeruginosa and Acinetobacter baumannii. Clinical trials, including APEKS-NP and CREDIBLE-CR, affirm its efficacy for hospital-acquired pneumonia (HAP) but highlight concerns over increased mortality due to severe renal complications. Cefiderocol has shown superior outcomes in complicated urinary tract infections (cUTI) compared to imipenem-cilastatin. A comparison of colistin monotherapy versus combination therapy with meropenem for carbapenem-resistant infections revealed no significant improvement in clinical outcomes with combination therapy but noted delays in resistance development. Colistin-rifampicin combination therapy showed potential benefits for colistin-resistant Acinetobacter baumannii, although results were not statistically significant. SPR206, a polymyxin derivative, and durlobactam, a β-lactamase inhibitor, show promise in addressing these resistant strains, with durlobactam demonstrating efficacy in combination with sulbactam and imipenem-cilastatin. Additional studies investigated antibiotic strategies for resistant infections, including cefoperazone-sulbactam versus combination therapy with tigecycline, and examined infection-prevention strategies in surgical settings, comparing chlorhexidine-alcohol and povidone-iodine. This research highlights the importance of optimizing treatment regimens and infection-control measures across various healthcare settings, including neonatology and surgical care.

Colistin Use for the Treatment of Multi-Drug-Resistant Gram-Negative Severe Infections in ICU Patients: A Single-Center Study

Background: Colistin is increasingly used to treat severe infections caused by multi-drug-resistant (MDR) bacteria, particularly in critically ill patients. Its effectiveness, especially in monotherapy, remains controversial. This study aimed to evaluate the effectiveness and toxicity of colistin therapy in severe MDR infections. Methods: This retrospective study included patients treated with colistin (CMS) at the ICU. Patients' treatments were divided into four subgroups: monotherapy vs. combination therapy, empirical vs. targeted therapy, intravenous vs. intravenous plus inhaled therapy, and standard doses with and without a loading dose. The primary outcome was clinical cure. Secondary outcomes included microbiological eradication, survival rate, and drug-related toxicity, particularly acute kidney injury (AKI). Exclusion criteria included Gram-positive infection, inhaled therapy alone, use of colistin <5 days. Results: A total of 150 patients (mean age 60 ± 18 years, APACHE II score 17 ± 10) were included. The most frequent condition was hospital-acquired pneumonia (n = 140, 93.3%). The most common pathogen was MDR Acinetobacter baumannii (n = 146, 97.3%). In most patients, colistin therapy was targeted (n = 113, 75.3%) and combined with other antibiotics (n = 124, 82.7%). Inhaled CMS was added in 47 (31.3%) patients. Mean duration of therapy was 10 ± 4 days. Clinical cure occurred in 64 (42.7%) patients, microbiological eradication in 20 (13.3%). AKI developed in 65 (53.7%) patients. Inhaled CMS improved the clinical cure rates (57.4% vs. 37.0%, p = 0.003). Conclusions: Intravenous CMS was mainly used for MDR Acinetobacter baumannii-related pneumonia. Clinical cure was observed in 42.7% of patients, but renal toxicity was high. Combining intravenous and inhaled CMS may improve outcomes.

Colistin utilization at a tertiary hospital in South Africa: an opportunity for antimicrobial stewardship practices

Introduction. Colistin (polymyxin E) has emerged as a last-resort treatment option for multidrug-resistant infections.Hypothesis/Gap Statement. Studies on the use, safety and efficacy of colistin in South Africa are limited.Aim. This study aims to describe the use of colistin and its clinical outcomes at a tertiary public hospital in South Africa.Methodology. We conducted a retrospective review of adult and paediatric patients who received parenteral colistin between 2015 and 2019.Results. A total of 69 patients (26 adults, 13 children and 30 neonates) were reviewed. Acinetobacter baumannii was the most common causative pathogen isolated (70.1 %). Colistin was predominately used to treat septicaemia (75.4 %). It was primarily administered as definitive therapy (71.0 %) and as monotherapy (56.5 %). It was used in 11.5 % of adults with infections susceptible to other antibiotics. Loading doses of intravenous colistin were administered in only 15 (57.7 %) adult patients. Neurotoxicity and nephrotoxicity occurred in 5.8 % and 43.5 % of patients, respectively. Clinical cure was achieved in 37 (53.6 %) patients. On multivariate logistic regression analysis, adults [adjusted odds ratio (aOR), 25.54; 95 % CI, 2.73-238.65; P < 0.01] and children (aOR, 8.56; 95 % CI, 1.06-69.10; P < 0.05) had higher odds of death than neonates.Conclusion. The study identified significant stewardship opportunities to improve colistin prescription and administration. Achieving optimal patient outcomes necessitates a multidisciplinary approach and vigilant monitoring of colistin use.

Xpert Carba-R Assay on Flagged Blood Culture Samples: Clinical Utility in Intensive Care Unit Patients with Bacteremia Caused by Enterobacteriaceae

Introduction and background

Rapid molecular diagnostics to predict carbapenem resistance well before the availability of routine drug sensitivity testing (DST) can serve as an antimicrobial stewardship tool in the context of high rates of Carbapenem-resistant Enterobacteriaceae (CRE).

Materials and methods

A retrospective observational study of patients more than 18 years of age on whom Xpert Carba-R (FDA approved for rectal swab specimen) was done on gram-negative bacteria (GNB) flagged blood culture samples, in an Indian intensive care unit between January 2015 and November 2018. We analyzed the performance of Xpert Carba-R in comparison with routine DST.

Results

A total of 164 GNBs were isolated from 160 patients. Klebsiella pneumoniae and Escherichia coli were the predominant isolates. Carba-R was positive in 35.36% of samples and 45.34% were carbapenem-resistant (CR) on routine DST. The distribution of the CR gene was: Oxacillinase (OXA) (50%), NDM (32.7%) followed by OXA and NDM co-expression (15.51%). The sensitivity, specificity, positive likelihood ratio, negative likelihood ratio, positive predictive value, and negative predictive value of Carba-R were 90.74, 93.15, 13.25, 0.10, 83.58 and 96.31% for Enterobacteriaceae. The median time to obtain the Carba-R report was 30 hours 34 minutes vs 74 hours and 20 minutes for routine DST. Based on the Carba-R report, 9.72% of patients had escalation and 27.08% had de-escalation of antibiotics.

Conclusion

Xpert Carba-R serves as a rapid diagnostic tool for predicting carbapenem resistance in intensive care unit patients with bacteremia caused by Enterobacteriaceae.

How to cite this article

Rajendran S, Gopalakrishnan R, Tarigopula A, Kumar DS, Nambi PS, Sethuraman N, et al. Xpert Carba-R Assay on Flagged Blood Culture Samples: Clinical Utility in Intensive Care Unit Patients with Bacteremia Caused by Enterobacteriaceae. Indian J Crit Care Med 2023;27(9):655-662.

An overview of gram-negative bacteria with difficult-to-treat resistance: definition, prevalence, and treatment options

INTRODUCTION

Difficult-to-treat resistance (DTR) is a newly proposed resistance phenotype characterized by resistance to all first-line drugs. The emergence of DTR as a new resistance phenotype has significant implications for clinical practice. This new concept has the potential to be widely used instead of traditional phenotypes.

AREAS COVERED

This study carried out a detailed analysis about the definition, application, and evolution of various resistance phenotypes. We collected all the research articles on Gram-negative bacteria with difficult-to-treat resistance (GNB-DTR), analyzed the DTR in each region and each bacterial species. The advantages and doubts of DTR, the dilemma of GNB-DTR infections and the potential therapeutic strategies are summarized in the review.

EXPERT OPINION

Available studies show that the prevalence of GNB-DTR is not optimistic. Unlike traditional resistance phenotypes, DTR is more closely aligned with the clinical treatment perspective and can help with the prompt selection of an appropriate treatment plan. Currently, potential treatment options for GNB-DTR include a number of second-line drugs and novel antibiotics. However, the definition of first-line drugs is inherently dynamic. Therefore, the DTR concept based on first-line drugs needs to be continuously updated and refined, considering the emergence of new antibiotics, resistance characteristics, and pathogen prevalence in different regions.

Duration of Treatment for Pseudomonas aeruginosa Bacteremia: a Retrospective Study

INTRODUCTION

There is no consensus regarding optimal duration of antibiotic therapy for Pseudomonas aeruginosa bacteremia. We aimed to evaluate the impact of short antibiotic course.

METHODS

We present a retrospective multicenter study including patients with P. aeruginosa bacteremia during 2009-2015. We evaluated outcomes of patients treated with short (6-10 days) versus long (11-15 days) antibiotic courses. The primary outcome was a composite of 30-day mortality or bacteremia recurrence and/or persistence. Univariate and inverse probability treatment-weighted (IPTW) adjusted multivariate analysis for the primary outcome was performed. To avoid immortal time bias, the landmark method was used.

RESULTS

We included 657 patients; 273 received a short antibiotic course and 384 a long course. There was no significant difference in baseline characteristics of patients. The composite primary outcome occurred in 61/384 patients in the long-treatment group (16%) versus 32/273 in the short-treatment group (12%) (p = 0.131). Mortality accounted for 41/384 (11%) versus 25/273 (9%) of cases, respectively. Length of hospital stay was significantly shorter in the short group [median 13 days, interquartile range (IQR) 9-21 days, versus median 15 days, IQR 11-26 days, p = 0.002]. Ten patients in the long group discontinued antibiotic therapy owing to adverse events, compared with none in the short group. On univariate and multivariate analyses, duration of therapy was not associated with the primary outcome.

CONCLUSIONS

In this retrospective study, 6-10 days of antibiotic course for P. aeruginosa bacteremia were as effective as longer courses in terms of survival and recurrence. Shorter therapy was associated with reduced length of stay and less drug discontinuation.

The necessity of a loading dose when prescribing intravenous colistin in critically ill patients with CRGNB-associated pneumonia: a multi-center observational study

Background

The importance or necessity of a loading dose when prescribing intravenous colistin has not been well established in clinical practice, and approximate one-third to half of patients with carbapenem-resistant gram-negative bacteria (CRGNB) infection did not receive the administration of a loading dose. The aim of this study is to investigate the efficacy and risk of acute kidney injury when prescribing intravenous colistin for critically ill patients with nosocomial pneumonia caused by CRGNB.

Methods

This was a multicenter, retrospective study that recruited ICU-admitted patients who had CRGNB-associated nosocomial pneumonia and were treated with intravenous colistin. Then, we classified the patients into colistin loading dose (N = 85) and nonloading dose groups (N = 127). After propensity-score matching for important covariates, we compared the mortality rate, clinical outcome and microbiological eradication rates between the groups (N = 67).

Results

The loading group had higher percentages of patients with favorable clinical outcomes (55.2% and 35.8%, p = 0.037) and microbiological eradication rates (50% and 27.3%, p = 0.042) at day 14 than the nonloading group. The mortality rates at days 7, 14 and 28 and overall in-hospital mortality were not different between the two groups, but the Kaplan–Meier analysis showed that the loading group had a longer survival time than the nonloading group. Furthermore, the loading group had a shorter length of hospital stay than the nonloading group (52 and 60, p = 0.037). Regarding nephrotoxicity, there was no significant difference in the risk of developing acute kidney injury between the groups.

Conclusions

The administration of a loading dose is recommended when prescribing intravenous colistin for critically ill patients with nosocomial pneumonia caused by CRGNB.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13054-022-03947-9.

ICU-Associated Gram-Negative Bloodstream Infection: Risk Factors Affecting the Outcome Following the Emergence of Colistin-Resistant Isolates in a Regional Greek Hospital

Intensive care unit patients may present infections by difficult-to-treat-resistant Gram-negative microorganisms. Colistin resurfaced as a last resort antibiotic for the treatment of multi-drug-resistant Gram-negative bacteria. However, colistin might not improve survival, particularly after the emergence of colistin-resistant isolates. We aimed to (1) examine the first Gram-negative-associated-bloodstream infection (GN-BSI) effect on 28-day mortality and (2) distinguish mortality risk factors. From 1 January 2018 to 31 December 2019, we retrospectively studied all adult patients admitted for more than 48 h in the critical care department of a regional Greek hospital, with prevalent difficult-to-treat Gram-negative pathogens. We examined the patient records for the first GN-BSI. The local laboratory used broth microdilution to evaluate bacterial susceptibility to colistin. Seventy-eight patients fulfilled the entry criteria: adult and first GN-BSI. They developed GN-BSI on day 10 (6-18), while the overall mortality was 26.9%. Thirty-two and 46 individuals comprised the respective colistin-resistant and colistin-sensitive groups. The admission Acute Physiology Assessment and Chronic Health Evaluation II score was associated with acquiring colistin-resistant GN-BSI in the multivariable logistic regression analysis (οdds ratio (CI), 1.11 (1.03-1.21)). Regarding mortality, the index day sequential organ failure assessment score was solely associated with the outcome (hazard-ratio (CI), 1.23 (1.03-1.48), Cox proportional hazard analysis). GN-BSI was often caused by colistin-resistant bacteria. Concerning our data, sepsis severity was the independent predictor of mortality regardless of the colistin-resistance phenotype or empirical colistin treatment.

Non-fermentative gram-negative bloodstream infection in northern Italy: a multicenter cohort study

Background

The management of non-fermentative gram-negative bloodstream infection (NFGN-BSI) offers numerous challenges. In this study the aim is to analyse a large cohort of patients with NFGN-BSI recruited in the northern Italy to describe epidemiology, etiological and susceptibility pattern, therapeutic management and outcome.

Methods

Multicentre retrospective cohort study of patients hospitalised at three large teaching hospitals in northern Italy in a fourth year period.

Results

355 BSI episodes were analyzed, due to P. aeruginosa (72.7%), A. baumannii (16.6%), and Stenotrophomonas maltophilia (10.7%). Overall, 21.4% of isolates were defined as DTR, highest rate among A. baumannii (64.4%). All-cause 30-day mortality rate was 17.5%. Rates of XDR or DTR A. baumannii isolation were significantly higher in non-surviving patients. Independent risk factors for 30-day mortality were: age (HR 1.03, 95%CI 1.00–1.04, p = 0.003), septic shock (HR 2.84, 95%CI 1.67–4.82, p < 0.001) and BSI due to Acinetobacter baumannii (HR 2.23, 95%CI 1.27–3.94, p = 0.005).

Conclusion

The overall prevalence of DTR was high in the NFGN BSI cohort analyzied, mainly among Acinetobacter baumannii episodes (64.4%). Acinetobacter baumannii is showed to be an independent predictor of mortality. These evidences marked the urgent need of new therapeutic options against this pathogen.

Trial registration number: 79/2017/O/OssN. Approved: March14th, 2017.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12879-021-06496-8.

The role of combination therapy in the treatment of severe infections caused by carbapenem resistant gram-negatives: a systematic review of clinical studies

BACKGROUND

Effective treatment of sepsis due to carbapenem-resistant Gram-negative bacteria (CR-GNB) remains a challenge for clinicians worldwide. In recent years, the combination of antibiotics has become the preferred treatment strategy for CR-GNB infection. However, robust evidence to support this approach is lacking. This systematic review aimed at critically evaluating all available antibiotic options for CR-GNB sepsis with particular focus on combination.

METHODS

We systematically searched published literature from January 1945 until December 2018 for observational comparative and non-comparative studies and randomized trials examining any antibiotic option for CR-GNB. Studies were included if reporting microbiologically-confirmed infection caused by Acinetobacter baumannii, Enterobacteriaceae/Klebsiella spp., or Pseudomonas aeruginosa, reporting at least one of the study outcomes, and definitive antibiotic treatment. Carbapenem-resistance was defined as phenotypically-detected in vitro resistance to at least one of the following carbapenems: doripenem, ertapenem, imipenem, meropenem. Each antibiotic regimen was classified as "defined" when at least the molecular class(es) composing the regimen was detailed. Primary outcomes were 30-day and attributable mortality. Bayesian network meta-analysis (NMA) approach was selected for quantitative synthesis to explore feasibility of pooling data on antibiotic regimens.

RESULTS

A total of 6306 records were retrieved and 134 studies including 11,546 patients were included: 54 studies were on Acinetobacter, 52 on Enterobacteriaceae/Klebsiella, 21 on mixed Gram-negative, and 7 on Pseudomonas. Nine (7%) were RCTs; 19 prospective cohorts (14%), 89 (66%) retrospective, and 17 (13%) case series. Forty-one studies (31%) were multicentric. Qualitative synthesis showed an heterogeneous and scattered reporting of key-clinical and microbiological variables across studies. Ninety-two distinct antibiotic regimens were identified with 47 of them (51%, 5863 patients) not reporting any details on numbers, type, dosage and in vitro activity of the included antibiotic molecules. The NMAs could not be performed for any of the selected outcome given the presence of too many disconnected components.

CONCLUSION

The existing evidence is insufficient to allowing for the formulation of any evidence-based therapeutic recommendation for CR-GNB sepsis. Future studies must provide a standardized definition of antibiotic regimen to drive recommendations for using combination of antibiotics that can be reliably applied to clinical practice.

Effect on 30-day mortality and duration of hospitalization of empirical antibiotic therapy in CRGNB-infected pneumonia

BACKGROUND

The objective of this study was to investigate whether unreasonable empirical antibiotic treatment (UEAT) had an impact on 30-day mortality and duration of hospitalization in bacterial pneumonia caused by carbapenem-resistant gram-negative bacteria (CRGNB).

METHODS

This was a retrospective cohort study involving CRGNB-infected pneumonia. All CRGNB-infected pneumonia patients received empirical and targeted antibiotic treatment (TAT), and they were divided into reasonable empirical antibiotic treatment (REAT) and UEAT according to whether the empirical antibiotic treatment (EAT) was reasonable. The data of the two groups were compared to analyze their influence on the 30-day mortality and hospitalization time in CRGNB-infected pneumonia patients. Moreover, we also considered other variables that might be relevant and conducted multivariable regression analysis of 30-day mortality and duration of hospitalization in CRGNB-infected pneumonia patients.

RESULTS

The study collected 310 CRGNB-infected pneumonia patients, the most common bacterium is Acinetobacter baumannii (211/310 [68%]), the rest were Klebsiella pneumoniae (46/310 [15%]), Pseudomonas aeruginosa and others (53/310 [17%]). Among them, 76/310 (24.5%) patients received REAT. In the analysis of risk factors, dementia, consciousness were risk factors of 30-day mortality, pulmonary disease, hemodynamic support at culture taken day and recent surgery were risk factors for longer hospital stay. The analysis of 30-day mortality showed that UEAT was not associated with 30-day mortality for the 30-day mortality of REAT and UEAT were 9 of 76 (11.84%) and 36 of 234 (15.38%) (P = 0.447), respectively. Meanwhile, there was difference between REAT and UEAT (P = 0.023) in the analysis of EAT on hospitalization time in CRGNB-infected pneumonia patients.

CONCLUSIONS

UEAT was not associated with 30-day mortality while was related to duration of hospitalization in CRGNB-infected pneumonia patients, in which Acinetobacter baumanniii accouned for the majority.

In vitro activity of the siderophore cephalosporin, cefiderocol, against molecularly characterized, carbapenem-non-susceptible Gram-negative bacteria from Europe

Objectives

Many carbapenem-resistant (CR) Gram-negative (GN) pathogens exhibit MDR, meaning few therapeutic options are available for CR-GN infections. Cefiderocol, a siderophore cephalosporin, has demonstrated in vitro efficacy against CR-GN bacteria. In the SIDERO-CR-2014–2016 surveillance study, European clinical isolates comprising carbapenem-non-susceptible (CarbNS) Enterobacterales and MDR non-fermenters were tested against cefiderocol and comparators.

Methods

Cefiderocol MICs were determined using iron-depleted CAMHB, and comparators using CAMHB, per recommended CLSI methodology. Carbapenemase gene profiles were determined using PCR.

Results

Isolates (N = 870) from 23 European countries comprised CarbNS Enterobacterales (n = 457), MDR Pseudomonas aeruginosa (n = 177) and MDR Acinetobacter baumannii (n = 236). The most common carbapenemases were KPC (52%), OXA-48-like (19%), VIM (14%) and NDM (8%) in Enterobacterales, VIM (41%) in P. aeruginosa and OXA-23-like (57%) and OXA-24/40-like (37%) in A. baumannii. Most carbapenemase-producing isolates (65%) co-carried ESBLs. Approximately half of P. aeruginosa isolates were negative for carbapenemases, compared with 10% of Enterobacterales and 3% of A. baumannii. A similar proportion of Enterobacterales were susceptible to cefiderocol (81.6%; 79.0% of VIM producers; 51.4% of NDM producers; based on EUCAST breakpoint values) compared with comparator antimicrobial agents, including colistin (76.4%; 93.5% of VIM producers; 78.4% of NDM producers) and ceftazidime/avibactam (76.6%; 1.6% of VIM producers; 2.7% of NDM producers). Of P. aeruginosa isolates, 98.3% were susceptible to cefiderocol (100% of VIM producers), similar to colistin (100%). Against A. baumannii, 94.9% had cefiderocol MIC ≤2 mg/L and 93.6% of isolates were susceptible to colistin.

Conclusions

Cefiderocol demonstrated potent activity against CarbNS and MDR GN bacteria, including non-fermenters and a wide variety of MBL- and serine-β-lactamase-producing strains.

A Real-World Study Comparing Various Antimicrobial Regimens for Bloodstream Infections Caused by Carbapenem-Resistant Gram-Negative Bacilli in a Tertiary Hospital, Shanghai, China, from 2010 to 2017

Background

We conducted a real-world analysis of the effectiveness of different antibiotic regimens for bloodstream infections (BSIs) caused by carbapenem-resistant gram-negative bacilli (CR-GNB) in a Chinese population.

Methods

A retrospective observational study was conducted between January 2010 and December 2017. Patients with BSIs caused by CR-GNB confirmed by in vitro susceptibility tests were enrolled, and patient medical record data on antimicrobial agents and microbiological and clinical outcomes were extracted.

Results

A total of 175 individuals were included; 127 individuals (72.6%) received combination therapy (two or more antibiotics), while 48 individuals (27.4%) received monotherapy (single antibiotic). The all-cause 28-day mortality was 20.0%. Treatment success or presumed success rates were very similar between the monotherapy and combination therapy groups (58.3% versus 59.1%; P = 0.931). Combination therapy had a higher success rate trend than monotherapy in septic shock patients (40.7% versus 18.2%; P = 0.268). Improved therapeutic effects were observed in the active agent-containing group, although the differences were not significant.

Conclusion

Combination therapy likely has better therapeutic effects on critical BSIs caused by CR-GNB than monotherapy. Choosing a proper active agent in an antimicrobial regime is relatively crucial to the ultimate treatment outcome.

Considerations for Empiric Antimicrobial Therapy in Sepsis and Septic Shock in an Era of Antimicrobial Resistance

Patients with sepsis present across a spectrum of infection sites and severity of illnesses requiring complex decision making at the bedside as to when prompt antibiotics are indicated and which regimen is warranted. Many hemodynamically stable patients with sepsis and low acuity of illness may benefit from further work up before initiating therapy, whereas patients with septic shock warrant emergent broad-spectrum antibiotics. The precise empiric regimen is determined by assessing patient and epidemiological risk factors, likely source of infection based on presenting signs and symptoms, and severity of illness. Hospitals should implement quality improvement measures to aid in the rapid and accurate diagnosis of septic patients and to ensure antibiotics are given to patients in an expedited fashion after antibiotic order.

Characterization of Resistance in Gram-Negative Urinary Isolates Using Existing and Novel Indicators of Clinical Relevance: A 10-Year Data Analysis

Classical resistance classifications (multidrug resistance [MDR], extensive drug resistance [XDR], pan-drug resistance [PDR]) are very useful for epidemiological purposes, however, they may not correlate well with clinical outcomes, therefore, several novel classification criteria (e.g., usual drug resistance [UDR], difficult-to-treat resistance [DTR]) were introduced for Gram-negative bacteria in recent years. Microbiological and resistance data was collected for urinary tract infections (UTIs) retrospectively, corresponding to the 2008.01.01–2017.12.31. period. Isolates were classified into various resistance categories (wild type/susceptible, UDR, MDR, XDR, DTR and PDR), in addition, two new indicators (modified DTR; mDTR and mcDTR) and a predictive composite score (pMAR) were introduced. Results: n = 16,240 (76.8%) outpatient and n = 13,386 (69.3%) inpatient UTI isolates were relevant to our analysis. Citrobacter-Enterobacter-Serratia had the highest level of UDR isolates (88.9%), the Proteus-Providencia-Morganella group had the highest mDTR levels. MDR levels were highest in Acinetobacter spp. (9.7%) and Proteus-Providencia-Morganella (9.1%). XDR- and DTR-levels were higher in non-fermenters (XDR: 1.7%–4.7%. DTR: 7.3%–7.9%) than in Enterobacterales isolates (XDR: 0%–0.1%. DTR: 0.02%–1.5%). Conclusions: The introduction of DTR (and its’ modifications detailed in this study) to the bedside and in clinical practice will definitely lead to substantial benefits in the assessment of the significance of bacterial resistance in human therapeutics.

Prognostic Utility of the New Definition of Difficult-to-Treat Resistance Among Patients With Gram-Negative Bloodstream Infections

Background

To compare the prognostic utility of the new definition of difficult-to-treat resistance (DTR) vs established definitions in a cohort of patients with Gram-negative bloodstream infections (GNBSIs).

Methods

This was a retrospective single-center study of adult patients with monomicrobial GNBSI, hospitalized from 2013 to 2016. DTR was defined as isolate demonstrating intermediate or resistant phenotype to all reported agents in the carbapenem, beta-lactam, and fluoroquinolone classes. Carbapenem resistance (CR) was defined according to 2015 Centers for Disease Control and Prevention criteria. Each isolate was further classified according to the Magiorakos et al. criteria as non-multidrug-resistant (non-MDR), MDR, extensively drug-resistant (XDR), or pan-drug-resistant (PDR). The primary outcome was all-cause 30-day mortality.

Results

Overall, 1576 patients were analyzed. Enterobacteriaceae accounted for 88.7% of BSIs, with Escherichia coli (n = 941) and Klebsiella pneumoniae (n = 326) being the most common pathogens. Pseudomonas aeruginosa was the most common nonfermentative bacteria (n = 130, 8.2%). Overall, 11% of strains were defined as DTR and 13% as CR. Episodes were further classified as non-MDR (68.8%), MDR (21.9%), XDR (8.8%), and PDR (0.4%). The prevalence rates of DTR, CR, and XDR were similar among Enterobacteriaceae and Acinetobacter baumannii, whereas they differed in P. aeruginosa. All the analyzed resistance definitions significantly improved prediction of 30-day mortality when introduced into a baseline multivariate model, to a similar degree: 9%, 10%, and 11% for DTR, Magiorakos, and CR definitions, respectively.

Conclusions

DTR seems a promising tool to identify challenging GNBSIs, mainly those due to P. aeruginosa. With the availability of new agents for CR infections, further multicenter assessments of DTR are needed.

Multidrug Resistant Acinetobacter baumannii: Resistance by Any Other Name Would Still be Hard to Treat

PURPOSE OF REVIEW

Acinetobacter baumannii (AB) is an infamous nosocomial pathogen with a seemingly limitless capacity for antimicrobial resistance, leading to few treatment options and poor clinical outcomes. The debatably low pathogenicity and virulence of AB are juxtaposed by its exceptionally high rate of infection-related mortality, likely due to delays in time to effective antimicrobial therapy secondary to its predilection for resistance to first-line agents. Recent studies of AB and its infections have led to a burgeoning understanding of this critical microbial threat and provided clinicians with new ammunition for which to target this elusive pathogen. This review will provide an update on the virulence, resistance, diagnosis, and treatment of multidrug resistant (MDR) AB.

RECENT FINDINGS

Advances in bacterial genomics have led to a deeper understanding of the unique mechanisms of resistance often present in MDR AB and how they may be exploited by new antimicrobials or optimized combinations of existing agents. Further, improvements in rapid diagnostic tests (RDTs) and their more pervasive use in combination with antimicrobial stewardship interventions have allowed for more rapid diagnosis of AB and decreases in time to effective therapy. Unfortunately, there remains a paucity of high-quality clinical data for which to inform the optimal treatment of MDR AB infections. In fact, recently completed studies have failed to identify a combination regimen that is consistently superior to monotherapy, despite the benefits demonstrated in vitro. Encouragingly, new and updated guidelines offer strategies for the treatment of MDR AB and may help to harmonize the use of high toxicity agents such as the polymyxins. Finally, new antimicrobial agents such as eravacycline and cefiderocol have promising in vitro activity against MDR AB but their place in therapy for these infections remains to be determined. Notwithstanding available clinical trial data, polymyxin-based combination therapies with either a carbapenem, minocycline, or eravacycline remain the treatment of choice for MDR, particularly carbapenem-resistant, AB. Incorporating antimicrobial stewardship intervention with RDTs relevant to MDR AB can help avoid potentially toxic combination therapies and catalyze the most important modifiable risk factor for mortality-time to effective therapy. Further research efforts into pharmacokinetic/pharmacodynamic-based dose optimization and clinical outcomes data for MDR AB continue to be desperately needed.

Early Intravenous Colistin Therapy as a Favorable Prognostic Factor for 28-day Mortality in Patients with CRAB Bacteremia: a Multicenter Propensity Score-Matching Analysis

BACKGROUND

Carbapenem-resistant Acinetobacter baumannii (CRAB) infection is associated with high mortality. One of the strategies to reduce the mortality in patients with CRAB infections is to use intravenous colistin early but the effect of this strategy has not been proven. Therefore, we investigated the association of early colistin therapy with 28-day mortality in patients with CRAB bacteremia.

METHODS

This retrospective multicenter propensity score-matching analysis was conducted in the Korea by reviewing the medical records of adult patients with CRAB bacteremia between January 2012 and March 2015. Early colistin therapy was defined as intravenous colistin administration for > 48 hours within five days after the blood culture collection. To identify the risk factors associated with the 28-day mortality in CRAB bacteremia, the clinical variables of the surviving patients were compared to those of the deceased patients.

RESULTS

Of 303 enrolled patients, seventy-six (25.1%) patients received early colistin therapy. The 28-day mortality was 61.4% (186/303). Fatal or rapidly-fatal McCabe classifications, intensive care unit admission, Sequential Organ Failure Assessment scores ≥ 8, vasopressor use, and acute kidney injury were statistically independent poor prognostic factors. Catheter-related infection and early colistin therapy (adjusted odds ratio [aOR], 0.45; 95% confidence interval [CI], 0.21-0.94) were independent favorable prognostic factors associated with 28-day mortality in patients with CRAB bacteremia. Early colistin therapy was still significantly associated with lower 28-day mortality in the propensity score-matching analysis (aOR, 0.31; 95% CI, 0.11-0.88).

CONCLUSION

This study suggests that early colistin therapy might help reduce the mortality of patients with CRAB bacteremia.