Colistin Plus Carbapenem versus Colistin Monotherapy in the Treatment of Carbapenem-Resistant Acinetobacter baumannii Pneumonia

Engineering of a decellularized bovine skin coated with antibiotics-loaded electrospun fibers with synergistic antibacterial activity for the treatment of infectious wounds

An ideal antibacterial wound dressing with strong antibacterial behavior versus highly drug-resistant bacteria and great wound-healing capacity is still being developed. There is a clinical requirement to progress the current clinical cares that fail to fully restore the skin structure due to post-wound infections. Here, we aim to introduce a novel two-layer wound dressing using decellularized bovine skin (DBS) tissue and antibacterial nanofibers to design a bioactive scaffold with bio-mimicking the native extracellular matrix of both dermis and epidermis. For this purpose, polyvinyl alcohol (PVA)/chitosan (CS) solution was loaded with antibiotics (colistin and meropenem) and electrospun on the surface of the DBS scaffold to fabricate a two-layer antibacterial wound dressing (DBS-PVA/CS/Abs). In detail, the characterization of the fabricated scaffold was conducted using biomechanical, biological, and antibacterial assays. Based on the results, the fabricated scaffold revealed a homogenous three-dimensional microstructure with a connected pore network, a high porosity and swelling ratio, and favorable mechanical properties. In addition, according to the cell culture result, our fabricated two-layer scaffold surface had a good interaction with fibroblast cells and provided an excellent substrate for cell proliferation and attachment. The antibacterial assay revealed a strong antibacterial activity of DBS-PVA/CS/Abs against both standard strain and multidrug-resistant clinical isolates of Acinetobacter baumannii, Pseudomonas aeruginosa, and Escherichia coli. Our bilayer antibacterial wound dressing is strongly suggested as an admirable wound dressing for the management of infectious skin injuries and now promises to advance with preclinical and clinical research.

Clinical Efficacy of Sitafloxacin-Colistin-Meropenem and Colistin-Meropenem in Patients with Carbapenem-Resistant and Multidrug-Resistant Acinetobacter baumannii Hospital-Acquired Pneumonia (HAP)/Ventilator-Associated Pneumonia (VAP) in One Super-Tertiary Hospital in Bangkok, Thailand: A Randomized Controlled Trial

BACKGROUND

Carbapenem-resistant A. baumannii (CRAB) hospital-acquired pneumonia (HAP)/ventilator-associated pneumonia (VAP) is now a therapeutic problem worldwide.

METHOD

An open-label, randomized, superiority, single-blind trial was conducted in Rajavithi Hospital, a super-tertiary care facility in Bangkok, Thailand. CRAB HAP/VAP patients were randomly assigned to receive either sitafloxacin-colistin-meropenem or colistin-meropenem. Outcomes in the two groups were then assessed with respect to mortality, clinical response, and adverse effects.

RESULT

Between April 2021 and April 2022, 77 patients were treated with combinations of either sitafloxacin plus colistin plus meropenem (n = 40) or colistin plus meropenem (n = 37). There were no significant differences between the two groups with respect to all-cause mortality rates at 7 days and 14 days (respectively, 7.5% vs. 2.7%; p = 0.616, and 10% vs. 10%; p = 1). Patients who received sitafloxacin-colistin-meropenem showed improved clinical response compared with patients who received colistin-meropenem in terms of both intention-to-treat (87.5% vs. 62.2%; p = 0.016) and per-protocol analysis (87.2% vs. 67.7%; p = 0.049). There were no significant differences between the two groups with respect to adverse effects.

CONCLUSIONS

Adding sitafloxacin as a third agent to meropenem plus colistin could improve clinical outcomes in CRAB HAP/VAP with little or no impact on adverse effects. In short, sitafloxacin-meropenem-colistin could be another therapeutic option for combatting CRAB HAP/VAP.

Efficacy of combination therapy with standard-dose carbapenem for treating nosocomial pneumonia caused by carbapenem-resistant Acinetobacter baumannii in intensive care units: A multicentre retrospective propensity score-matched study

Carbapenem-resistant Acinetobacter baumannii (CRAB) infection is common worldwide. Despite carbapenem resistance, standard-dose carbapenems are still used in clinical practice. Hence in this study, we aimed to compare the efficacy and outcomes of a regimen containing standard-dose carbapenems with those of a regimen lacking carbapenems during the treatment of critically ill patients with CRAB nosocomial pneumonia in the intensive care unit (ICU). Initially, 735 patients were recruited for this multicentre retrospective cohort study. After exclusion, time-window bias adjustment, and propensity score matching, multiple clinical outcomes were compared between the carbapenem-containing (CC) (n = 166) and no carbapenem-containing (NCC) (n = 166) groups. The CC group showed a higher risk of clinical failure on day 7 than the NCC group (44.6% vs. 33.1%, P = 0.043). The lengths of ICU stay (21 and 16 days, P = 0.024) and hospital stay (61 and 44 days, P = 0.003) were longer in the CC group than in the NCC group. Multivariate analysis showed that the CC regimen was associated with higher clinical failure (adjusted odds ratio (aOR) = 1.64, 95% CI = 1.05-2.56, P = 0.031) and lower microbiological eradication (aOR = 0.48, 95% CI = 0.23-1.00, P = 0.049) at day 7 than the NCC group. Thus, a regimen containing a standard dose of carbapenem should be prescribed with caution for treating CRAB nosocomial pneumonia in the ICU.

Clinical Effectiveness of Tetracycline-Class Agents Based Regimens in Patients With Carbapenem-Resistant Acinetobacter baumannii Bacteremia: A Single-Center Retrospective Cohort Study

This study evaluated the clinical outcome of carbapenem-resistant Acinetobacter baumannii (CRAB) bacteremia and the clinical effectiveness of tetracyclines-based therapy. In a retrospective cohort study over 5 years period, 108 patients were included in the study. The overall 30-day mortality rate was 71.4%. Pitt's bacteremia score (PBS) (adjusted hazard ratio [aHR], 1.32; 95% confidence interval [CI], 1.22-1.42 per 1-point), colistin-single regimens (aHR, 0.34; 95% CI, 0.17-0.69), and tetracyclines single/tetracyclines-colistin combination regimens (aHR, 0.18; 95% CI, 0.07-0.48) were independently associated with 30-day mortality. Among patients with a PBS < 6, only tetracycline-containing regimens were associated with decreased mortality. Among patients receiving appropriate definite antimicrobials, the tetracyclines-colistin combination (7 of 7, 100%) tended to a higher 30-day survival rate compared to a tetracycline (7 of 12, 57.1%) or colistin single regimen (10 of 22, 41.6%, P = 0.073). Our findings suggest tetracyclines might be effective for treating CRAB infections when combined with colistin.

Microbiologic Cure with a Simplified Dosage of Intravenous Colistin in Adults: A Retrospective Cohort Study

Purpose

Colistin's FDA weight-based dosing (WBD) and frequency are both expressed in a broad range. Therefore, a simplified fixed-dose regimen (SFDR) of intravenous colistin based on three body-weight segments has been established for adults. The SFDR falls within the WBD range of each body-weight segment and accounts for the pharmacokinetic features. This study compared microbiologic cure with colistin SFDR to WBD in critically ill adults.

Patients and Methods

A retrospective cohort study was conducted for colistin orders from January 2014 to February 2022. The study included ICU patients who received intravenous colistin for carbapenem-non-susceptible, colistin-intermediate Gram-negative bacilli infections. Patients received the SFDR after the protocol was implemented, as the WBD was previously used. The primary endpoint was microbiologic cure. Secondary endpoints were 30-day infection recurrence and acute kidney injury (AKI).

Results

Of the 228 screened patients, 84 fulfilled the inclusion and matching criteria (42 in each group). The microbiologic cure rate was 69% with the SFDR and 36% with the WBD [p=0.002]. Infection recurred in four of the 29 patients who had a microbiologic cure with the SFDR (14%), and in six of the 15 patients with WBD (40%); [p=0.049]. AKI occurred in seven of the 36 SFDR patients who were not on hemodialysis (19%) and 15 of the 33 WBD patients (46%); [p=0.021].

Conclusion

In this study, colistin SFDR was associated with a higher microbiologic cure in carbapenem-non-susceptible, colistin-intermediate Gram-negative bacilli infections and with a lower incidence of AKI in critically ill adults compared to WBD.

Polymyxin combination therapy for multidrug-resistant, extensively-drug resistant, and difficult-to-treat drug-resistant gram-negative infections: is it superior to polymyxin monotherapy?

INTRODUCTION

The increasing prevalence of infections with multidrug-resistant (MDR), extensively-drug resistant (XDR) or difficult-to-treat drug resistant (DTR) Gram-negative bacilli (GNB), including Pseudomonas aeruginosa, Acinetobacter baumannii, Klebsiella pneumoniae, Enterobacter species, and Escherichia coli poses a severe challenge.

AREAS COVERED

The rapid growing of multi-resistant GNB as well as the considerable deceleration in development of new anti-infective agents have made polymyxins (e.g. polymyxin B and colistin) a mainstay in clinical practices as either monotherapy or combination therapy. However, whether the polymyxin-based combinations lead to better outcomes remains unknown. This review mainly focuses on the effect of polymyxin combination therapy versus monotherapy on treating GNB-related infections. We also provide several factors in designing studies and their impact on optimizing polymyxin combinations.

EXPERT OPINION

An abundance of recent in vitro and preclinical in vivo data suggest clinical benefit for polymyxin-drug combination therapies, especially colistin plus meropenem and colistin plus rifampicin, with synergistic killing against MDR, XDR, and DTR P. aeruginosa, K. pneumoniae and A. baumannii. The beneficial effects of polymyxin-drug combinations (e.g. colistin or polymyxin B + carbapenem against carbapenem-resistant K. pneumoniae and carbapenem-resistant A. baumannii, polymyxin B + carbapenem + rifampin against carbapenem-resistant K. pneumoniae, and colistin + ceftolozan/tazobactam + rifampin against PDR-P. aeruginosa) have often been shown in clinical setting by retrospective studies. However, high-certainty evidence from large randomized controlled trials is necessary. These clinical trials should incorporate careful attention to patient's sample size, characteristics of patient's groups, PK/PD relationships and dosing, rapid detection of resistance, MIC determinations, and therapeutic drug monitoring.

Synergetic dual antibiotics-loaded chitosan/poly (vinyl alcohol) nanofibers with sustained antibacterial delivery for treatment of XDR bacteria-infected wounds

Resistance of bacterial pathogens to conventional antibiotics has remained a significant challenge in managing post-wound infections, especially in developing countries. Here, a nanofibrous chitosan/poly (vinyl alcohol) (CS/PVA) mat was designed for controlled delivery of three different concentrations of two antibiotics (colistin/meropenem ratio of 32/64 μg/ml (AB1), 64/128 μg/ml (AB2), and 128/256 (AB3) μg/ml) with synergistic antibacterial activity against ATCC and extensively drug-resistant (XDR) Acinetobacter baumannii clinical isolates. The scaffolds showed a uniform fibrous structure with no bead formation with a sustained release of the antibiotics for one week. The elongation at break, wettability, porosity, and average fiber diameter decreased with increased antibiotics concentrations. Young's modulus and tensile strength showed a significant increase after adding antibiotics. All the constructs showed excellent in vitro cytocompatibility for fibroblasts and biocompatibility in an animal model. The antibacterial assays confirmed the dose-dependent antibacterial activity of the CS/PVA. The scaffolds loaded with AB2 and AB3 showed biocidal properties against ATCC, while only CS/PVA/AB3 had antibacterial activity against XDR clinical isolates. This study suggests the CS/PVA/AB3 nanofibrous scaffold contained 128/256 μg/ml colistin/meropenem as an excellent antibacterial wound dressing for protection of skin wounds from XDR clinical isolates and now promises to proceed with pre-clinical investigations.

Optimal dosing interval of intravenous Colistin monotherapy versus combination therapy: A systematic review and meta-analysis

We aimed to maximize the clinical response and effectiveness of colistin antibiotics in patients with multi-drug (MDR) and extensively drug-resistant (XDR) Gram-negative bacteria, there is an increasing interest in colistin combination therapy with other antibiotics and extended interval dosing regimens. This systematic review and meta-analysis aim is to evaluate if the combination therapy is superior to monotherapy with colistin regarding increased survival and also which dose interval is the most effective to utilize. English language, peer-reviewed journal publications from the first date available to 25 January 2022 were identified by searching the PubMed and Web of Science databases. Forest plots for overall and subgroups and funnel plots were graphed. 42 studies were included in the study. Among them, 38 studies were on combination therapy, and four on dose interval. The overall pooled odds ratio is 0.77 (CI: 0.62; 0.95) (p value < 0.017). The I^2 value was 43% (p value < 0.01). The Begg correlation test of funnel plot asymmetry showed no significant publication bias (0.064). The overall pooled odds ratio for Carbapenem is 0.74 (CI: 0.48; 1.13). A prospective randomized controlled trials (RCT) on 40 adults intensive care unit (ICU) patients with ventilator-associated pneumonia (VAP), comparing the mortality and ICU length of stay of 8- or 24- hour intervals regimens, showed that the ICU length of stay and ICU mortality were; 31.31, 35.3 days, and 32.06, 22.2% in groups 24-h interval and 8- hour interval (p value: 0.39, 0.87), respectively. It seems that combination therapy is associated with drug synergism and increased survival. The extended interval colistin administration may result in higher peak concentration and bacterial eradication. In both cases, we face a dearth of literature.

Prediction of Tissue Exposures of Meropenem, Colistin, and Sulbactam in Pediatrics Using Physiologically Based Pharmacokinetic Modeling

BACKGROUND

The combination of polymyxins, meropenem, and sulbactam demonstrated efficacy against multi-drug-resistant bacillus Acinetobacter baumannii. These three antibiotics are commonly used against major blood, skin, lung, and heart muscle infections.

OBJECTIVE

The objective of this study was to predict drug disposition and extrapolate the efficacy in these tissues using a physiologically based pharmacokinetic modeling approach that linked drug exposures to their target pharmacodynamic indices associated with antimicrobial activities against A. baumannii.

METHODS

An adult physiologically based pharmacokinetic model was developed for meropenem, colistin, and sulbactam and scaled to pediatrics accounting for both renal and non-renal clearances. The model reliability was evaluated by comparing simulated plasma and tissue drug exposures to observed data. Target pharmacodynamic indices were used to evaluate whether pediatric and adult dosing regimens provided sufficient coverage.

RESULTS

The modeled plasma drug exposures in adults and pediatric patients were consistent with reported literature data. The mean fold errors for meropenem, colistin, and sulbactam were in the range of 0.710-1.37, 0.981-1.47, and 0.647-1.39, respectively. Simulated exposures in the blood, skin, lung, and heart were consistent with reported penetration rates. In a virtual pediatric population aged from 2 to < 18 years, the interpretive breakpoints were achieved in 85-90% of subjects for their targeted pharmacodynamic indices after administration of pediatric dosing regimens consisting of 30 mg/kg of meropenem, and 40 mg/kg of sulbactam three times daily as a 3-h or continuous infusion and 5 mg/kg/day of colistin base activity.

CONCLUSIONS

The physiologically based pharmacokinetic modeling supports pediatric dosing regimens of meropenem/colistin/sulbactam in a co-administration setting against infections in the blood, lung, skin, and heart tissues due to A. baumannii.

Acinetobacter baumannii complex, national laboratory-based surveillance in South Africa, 2017 to 2019

Objective

We aimed to provide an analysis of A. baumannii complex (ABC) isolated from blood cultures in South Africa.

Materials and methods

ABC surveillance was conducted from 1 April 2017 to 30 September 2019 at 19 hospital sites from blood cultures of any age and sex. Organism identification was performed using the MALDI-TOF MS and antimicrobial susceptibility testing (AST), MicroScan Walkaway System. We confirmed colistin resistance with Sensititre, FRCOL panel, and selected for whole-genome sequencing.

Results

During the study period, we identified 4822 cases of ABC, of which 2152 cases were from 19 enhanced surveillance sites were reported during the enhanced surveillance period (1 August 2018 to 30 September 2019). Males accounted for 54% (2611/4822). Of the cases with known age, 41% (1968/4822) were infants (< 1-year-old). Seventy-eight percent (1688/2152) of cases had a known hospital outcome, of which 36% (602/1688) died. HIV status was known for 69% (1168/1688) of cases, and 14% (238/1688) were positive. Eighty-two percent (1389/1688) received antimicrobial treatment in admission. Three percent (35/1389) of cases received single colistin. Four percent (75/2033) were resistant to colistin. At least 75% of the isolates (1530/2033) can be classified as extensively drug-resistant (XDR), with resistance to most antibiotics except for colistin. The majority, 83% (20/24), of the colistin-resistant isolates were of the sequence type (ST) 1. Resistance genes, both plasmid- and chromosomal- mediated were not observed. Although all isolates had, nine efflux pump genes related to antimicrobial resistance.

Conclusion

Our surveillance data contributed to a better understanding of the natural course of A. baumannii disease, the patient characteristics among infants, and the level of resistance. At least two-thirds of the isolates were extensively drug-resistant, and four percent of isolates were resistant to colistin.

Diagnosis and management of infections caused by multidrug-resistant bacteria: guideline endorsed by the Italian Society of Infection and Tropical Diseases (SIMIT), the Italian Society of Anti-Infective Therapy (SITA), the Italian Group for Antimicrobial Stewardship (GISA), the Italian Association of Clinical Microbiologists (AMCLI) and the Italian Society of Microbiology (SIM)

Management of patients with infections caused by multidrug-resistant organisms is challenging and requires a multidisciplinary approach to achieve successful clinical outcomes. The aim of this paper is to provide recommendations for the diagnosis and optimal management of these infections, with a focus on targeted antibiotic therapy. The document was produced by a panel of experts nominated by the five endorsing Italian societies, namely the Italian Association of Clinical Microbiologists (AMCLI), the Italian Group for Antimicrobial Stewardship (GISA), the Italian Society of Microbiology (SIM), the Italian Society of Infectious and Tropical Diseases (SIMIT) and the Italian Society of Anti-Infective Therapy (SITA). Population, Intervention, Comparison and Outcomes (PICO) questions about microbiological diagnosis, pharmacological strategies and targeted antibiotic therapy were addressed for the following pathogens: carbapenem-resistant Enterobacterales; carbapenem-resistant Pseudomonas aeruginosa; carbapenem-resistant Acinetobacter baumannii; and methicillin-resistant Staphylococcus aureus. A systematic review of the literature published from January 2011 to November 2020 was guided by the PICO strategy. As data from randomised controlled trials (RCTs) were expected to be limited, observational studies were also reviewed. The certainty of evidence was classified using the GRADE approach. Recommendations were classified as strong or conditional. Detailed recommendations were formulated for each pathogen. The majority of available RCTs have serious risk of bias, and many observational studies have several limitations, including small sample size, retrospective design and presence of confounders. Thus, some recommendations are based on low or very-low certainty of evidence. Importantly, these recommendations should be continually updated to reflect emerging evidence from clinical studies and real-world experience.

Colistin Monotherapy versus Colistin plus Meropenem Combination Therapy for the Treatment of Multidrug-Resistant Acinetobacter baumannii Infection: A Meta-Analysis

(1) Introduction: Colistin combination therapy with other antibiotics is a way to enhance colistin activity. The purpose of this meta-analysis was to compare the efficacy and safety of treatment with colistin monotherapy versus colistin plus meropenem combination therapy in patients with drug-resistant Acinetobacter baumannii infection. (2) Methods: All studies were included if they reported one or more of the following outcomes: clinical improvement, complete microbiological response, 14-day mortality, hospital mortality, or nephrotoxicity. (3) Results: Three randomized controlled trials and seven retrospective studies were included in the meta-analysis. Colistin monotherapy has similar rates of clinical improvement, 14-day mortality, hospital mortality, and nephrotoxicity as colistin plus meropenem combination therapy. Regarding complete microbiological response, the colistin plus meropenem combination was better than colistin monotherapy. (4) Discussion: Previous meta-analyses demonstrated heterogeneity in study quality and a lack of evidence supporting the use of colistin-based combination therapy. Our meta-analysis clearly showed that colistin combined with meropenem was not superior to colistin monotherapy for the treatment of Acinetobacter baumannii infection. (5) Conclusions: The efficacy and safety of treatment with colistin monotherapy and that of colistin plus meropenem combination therapy in patients with drug-resistant Acinetobacter baumannii infection were comparable. The majority of the evidence was obtained from nonrandomized studies, and high-quality randomized controlled trials are needed to confirm the role of colistin plus meropenem combination therapy in the treatment of multidrug-resistant Acinetobacter baumannii infection.

Complicated carbapenem-resistant infections: a treatment pathway analysis in Italian sites

INTRODUCTION

Efforts to curb a growing prevalence of carbapenem resistance are prominent worldwide and especially in countries where high levels of carbapenem resistance are reported, such as Italy. Complicated infections, including complicated urinary tract infections (cUTI), complicated intra-abdominal infections (cIAI), and hospital-acquired/ventilator-associated bacterial pneumonia (HABP/VABP), are often caused by carbapenem-resistant Gram-negative (CRGN) bacteria and as such, these infection sites and their causative bacteria are important areas of focus for healthcare practitioners seeking to follow good antimicrobial stewardship practices. The aim of this study was to assess the clinical management and associated clinical and economic outcomes of patients with cUTI, cIAI, and HABP/VABP resulting from CRGN bacteria in Italy.

METHODS

We first conducted a hospital survey focusing on Gram-negative infections and their antibacterial susceptibility profile in four participating Italian hospitals. The second part of the study involved a non-interventional, retrospective single cohort chart review of 100 patients with cUTI, cIAI, or HABP/VABP caused by CRGN bacteria, in which patient characteristics, index hospitalization characteristics, infection characteristics, patient outcomes, treatment pathways, and healthcare resource use were assessed.

RESULTS

The hospital survey demonstrated carbapenem resistance in approximately 17% of complicated infections, mostly associated with Acinetobacter baumannii. The non-interventional, retrospective cohort component showed that complicated CRGN infections were hospital- or healthcare-acquired in 99.0% of cases and were most often caused by Klebsiella pneumoniae (66.0%). Despite the carbapenem-resistant nature of the included infections, carbapenems were used in 19.0% of patients as empirical therapy, in 43.0% as late empirical (i.e. immediately before receipt of susceptibility test results), and in 64.0% as targeted therapy (post-susceptibility test result receipt). Colistin was used in 61.0% of patients after susceptibility results were available. High clinical and economic burden was evident, with the average length of hospital stay being greater than 50 days, clinical cure achievement in only 43.0% of patients, and an overall mortality rate of 65.0% by the end of the follow-up period.

CONCLUSION

Our results reflect the considerable burden associated with complicated CRGN infections in Italy and the limitations in current treatment strategies. Our study pinpoints potential areas for improvement. For example, regular and detailed local surveillance and state of the art microbial diagnostic capabilities might aid and hasten clinical decision-making and facilitate improved antimicrobial stewardship when treating complex CRGN infections. New therapeutic options which more appropriately address CRGN infections may assist in improving outcomes which are important to both patients and healthcare providers.

Efficacies of Colistin-Carbapenem versus Colistin-Tigecycline in Critically Ill Patients with CR-GNB-Associated Pneumonia: A Multicenter Observational Study

Background: Evaluating the options for antibiotic treatment for carbapenem-resistant Gram-negative bacteria (CR-GNB)-associated pneumonia remains crucial. We compared the therapeutic efficacy and nephrotoxicity of two combination therapies, namely, colistin + carbapenem (CC) versus colistin + tigecycline (CT), for treating CR-GNB-related nosocomial pneumonia in critically ill patients. Methods: In this multicenter, retrospective, and cohort study, we recruited patients admitted to intensive care units and diagnosed with CR-GNB-associated nosocomial pneumonia. We divided the enrolled patients into CC (n = 62) and CT (n = 59) groups. After propensity score matching (n = 39), we compared the therapeutic efficacy by mortality, favorable outcome, and microbiological eradication and compared nephrotoxicity by acute kidney injury between groups. Results: There was no significant difference between the CC and CT groups regarding demographic characteristics and disease severities as assessed using the Acute Physiology and Chronic Health Evaluation (APACHE) II score, Sequential Organ Failure Assessment (SOFA) score, and other organ dysfunction variables. Therapeutic efficacy was non-significantly different between groups in all-cause mortality, favorable outcomes, and microbiological eradication at days 7, 14, and 28; as was the Kaplan-Meier analysis of 28-day survival. For nephrotoxicity, both groups had similar risks of developing acute kidney injury, evaluated using the Kidney Disease Improving Global Outcomes criteria (p = 1.000). Conclusions: Combination therapy with CC or CT had similar therapeutic efficacy and risk of developing acute kidney injury for treating CR-GNB-associated nosocomial pneumonia in critically ill patients.

Treatment of patients with serious infections due to carbapenem-resistant Acinetobacter baumannii: How viable are the current options?

This review critically appraises the published microbiologic and clinical data on the treatment of patients with carbapenem-resistant Acinetobacter baumannii infections. Despite being recognized as an urgent threat pathogen by the CDC and WHO, optimal treatment of patients with serious CRAB infections remains ill-defined. Few commercially available agents exhibit reliable in vitro activity against CRAB. Historically, polymyxins have been the most active agents in vitro, though interpretations of susceptibility data are difficult given issues surrounding MIC testing methodologies and lack of correlation between MICs and clinical outcomes. Most available preclinical and clinical data involve use of polymyxins, tetracyclines, and sulbactam, alone and in combination. As the number of viable treatment options is limited, combination therapy with a polymyxin is often used for patients with CRAB infections, despite the significant risk of nephrotoxicity. However, no treatment regimen has been found to reduce mortality, which exceeds 40% across most studies, or substantially improve clinical response. While some newer agents, such as eravacycline and cefiderocol, have demonstrated in vitro activity, clinical efficacy has not been fully established. New agents with clinically relevant activity against CRAB isolates and favorable toxicity profiles are sorely needed.

Acinetobacter baumannii Infections in Hospitalized Patients, Treatment Outcomes

Background Acinetobacter baumannii (AB), an opportunistic pathogen, could develop into serious infections with high mortality and financial burden. The debate surrounding the selection of effective antibiotic treatment necessitates studies to define the optimal approach. This study aims to compare the clinical outcomes of commonly used treatment regimens in hospitalized patients with AB infections to guide stewardship efforts. Material and methods: Ethical approval was obtained, 320 adult patients with confirmed AB infections admitted to our tertiary care facility within two years were enrolled. The treatment outcomes were statistically analyzed to study the relation between antibiotic regimens and 14, 28, and 90-day mortality as the primary outcomes using binary logistic regression—using R software—in addition to the length of hospitalization, adverse events due to antibiotic treatment, and 90-day recurrence as secondary outcomes. Results: Among 320 patients, 142 (44%) had respiratory tract, 105 (33%) soft tissue, 42 (13%) urinary tract, 22 (7%) bacte iemia, and other infections 9 (3%). Nosocomial infections were 190 (59%) versus community-acquired. Monotherapy was significantly associated with lower 28-day (p < 0.05, OR:0.6] and 90-day (p < 0.05, OR:0.4) mortality rates, shorter length of stay LOS (p < 0.05, Median: −12 days] and limited development of adverse events (p < 0.05, OR:0.4). Subgroup analysis revealed similar results ranging from lower odds of mortality, adverse events, and shorter LOS to statistically significant correlation to monotherapy. Meropenem (MEM) and piperacillin/tazobactam (PIP/TAZ) monotherapies showed non-significant high odd ratios of mortalities, adverse events, and disparate LOS. There was a statistical correlation between most combined therapies and adverse events, and longer LOS. Colistin based and colistin/meropenem (CST/MEM) combinations were superior in terms of 14-day mortality (p = 0.05, OR:0.4) and (p < 0.05, OR:0.4) respectively. Pip/Taz and MEM-based combined therapies were associated with statistically non-significant high odd ratios of mortalities. Tigecycline (TGC)-based combinations showed a significant correlation to mortalities (p < 0.05, OR:2.5). Conclusion: Monotherapy was associated with lower mortality rates, shorter LOS, and limited development of adverse events compared to combined therapies. Colistin monotherapy, colistin/meropenem, and other colistin combinations showed almost equivalent mortality outcomes. Patients on combined therapy were more susceptible to adverse events and comparable LOS. The possible adverse outcomes of PIP/TAZ and MEM-based therapies in the treatment of MDRAB infections and the association of TGC with a higher mortality rate raise doubts about their treatment role.

Unresolved issues in the identification and treatment of carbapenem-resistant Gram-negative organisms

PURPOSE OF REVIEW

Carbapenem-resistant organisms (CROs), including Pseudomonas aeruginosa, Acinetobacter baumannii and Enterobacterales, are a threat worldwide. This review will cover mechanisms of resistance within CROs and challenges with identification and treatment of these organisms while pointing out unresolved issues and ongoing challenges.

RECENT FINDINGS

The treatment of CROs has expanded through newer therapeutic options. Guided utilization through genotypic and phenotypic testing is necessary in order for these drugs to target the appropriate mechanisms of resistance and select optimal antibiotic therapy.

SUMMARY

Identification methods and treatment options need to be precisely understood in order to limit the spread and maximize outcomes of CRO infections.

A Comparison of Colistin versus Colistin Plus Meropenem for the Treatment of Carbapenem-Resistant Acinetobacter baumannii in Critically Ill Patients: A Propensity Score-Matched Analysis

Carbapenem-resistant Acinetobacter baumannii (CRAB), an important nosocomial pathogen, occurs particularly in the intensive care unit (ICU). Thus, the aim of this study was to compare the efficacy and safety of documented treatment with colistin monotherapy versus colistin plus meropenem in critically ill patients with CRAB infections at Chiang Mai University Hospital (CMUH). We conducted a retrospective cohort study of critically ill patients with CRAB infections in an ICU from 2015 to 2017, who received colistin monotherapy versus colistin plus meropenem. After propensity score matching, an adjusted odds ratio (aOR) of a 30-day mortality rate in patients who received colistin plus meropenem was 0.43 compared to those who received colistin monotherapy (95% CI, 0.23–0.82, p = 0.01). aORs of clinical response and microbiological response were also higher in patients who received colistin plus meropenem (1.81, 95% CI 1.01–3.26, p = 0.048 and 2.08, 95% CI 1.11–3.91, p = 0.023, respectively). There was no significant difference in nephrotoxicity (aOR, 0.76, 95% CI, 0.43–1.36, p = 0.363) between colistin monotherapy and colistin plus meropenem. In conclusion, the addition of meropenem to colistin caused a reduction in 30-day mortality, higher clinical and microbiological responses, and did not increase nephrotoxicity compared to colistin monotherapy. Furthermore, 30-day mortality was significantly related with age, receiving vasopressor, having malignancy, and the APACHE II score.

Comparative efficacy and safety of combination therapy with high-dose sulbactam or colistin with additional antibacterial agents for multiple drug-resistant and extensively drug-resistant Acinetobacter baumannii infections: A systematic review and network meta-analysis

OBJECTIVES

This study aimed to compare the efficacy and safety of combination therapy with high-dose sulbactam or colistin with additional antibacterial agents for treating multidrug-resistant or extensively drug-resistant Acinetobacter baumannii (MDR-AB or XDR-AB) infections.

METHODS

We systematically searched PubMed, Embase, Cochrane, and Web of Science (through March 30, 2020) for studies that examined high-dose sulbactam or colistin with additional antibacterial agents as therapy for patients with infections with MDR-AB and XDR-AB. Through a network meta-analysis (NMA), using both direct and indirect evidence, we determined risk ratios and 95% confidence intervals. Primary outcomes included clinical improvement, clinical cure, microbiological eradication, and mortality from any cause. Secondary outcomes included nephrotoxicity.

RESULTS

The NMA included 18 studies and 1835 patients. We found that high-dose sulbactam (≥6 g per day), combined with another single antibacterial agent (levofloxacin or tigecycline), which were the highest ranking in clinical improvement and clinical cure. Still colistin-based combination in drug-resistant Acinetobacter baumannii therapy occupied the main position (the number of studies and patients) in most studies. Colistin combined with additional antibacterial agents was associated with a higher risk of nephrotoxicity.

CONCLUSIONS

Therapeutic regimens including high-dose sulbactam in combination with additional antibacterial agents (including colistin) might be one of the promising options for the treatment of MDR-AB or XDR-AB infections and high-quality study will be needed to confirm clinical efficacy.

Acquired Genetic Elements that Contribute to Antimicrobial Resistance in Frequent Gram-Negative Causative Agents of Healthcare-Associated Infections

Antimicrobial resistance (AMR) is a worldwide public health problem that reduces therapeutic options and increases the risk of death. The causative agents of healthcare-associated infections (HAIs) are drug-resistant microorganisms of the nosocomial environment, which have developed different mechanisms of AMR. The hospital-associated microbiota has been proposed to be a reservoir of genes associated with AMR and an environment where the transfer of genetic material among organisms may occur. The ESKAPE group (Enterococcus faecalis and Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter aerogenes and Escherichia coli) is a frequent causative agents of HAIs. In this review, we address the issue of acquired genetic elements that contribute to AMR in the most frequent Gram-negative of ESKAPE, with a focus on last resort antimicrobial agents and the role of transference of genetic elements for the development of AMR.

The effectiveness and nephrotoxicity of loading dose colistin combined with or without meropenem for the treatment of carbapenem-resistant A. baumannii

INTRODUCTION

Acinetobacter baumannii has emerged as an important nosocomial pathogen worldwide. In Thailand, the incidence and mortality rate of carbapenem-resistant A. baumannii (CRAB) is continuously increasing. This organism is a common pathogen that can cause HAP and VAP. CRAB tends to be susceptible to only colistin, so colistin would be the last line of treatment for CRAB. The recent data from in-vitro studies found that colistin and meropenem combination therapy could exert synergistic effects. However, some in-vivo studies have shown no significant difference in antibacterial effect between colistin monotherapy and colistin plus meropenem. Moreover, the clinical data are recently limited and not clear. Thus, the objective of this study was to compare clinical outcome, microbiological response, mortality rate and nephrotoxicity between loading dose (LD) colistin monotherapy and LD colistin-meropenem for treatment of infection caused by CRAB in Maharaj Nakorn Chiang Mai Hospital.

MATERIALS AND METHODS

This study is a retrospective analytical study. The data were collected from patients who received LD colistin monotherapy or LD colistin plus meropenem combination therapy for treatment of CRAB from 1 January 2013 to 31 August 2017 at Maharaj Nakorn Chiang Mai Hospital. A total of 324 patients met the inclusion criteria. The data were analyzed by descriptive statistics and inferential statistics, and were adjusted for confounding factors by logistic regression analysis.

RESULTS

The adjusted OR of good clinical outcome of patients who received LD colistin plus meropenem was 1.05 times that of patients who received loading dose colistin monotherapy (95%CI 0.62-1.74, p=0.860). Patients who received LD colistin plus meropenem had 0.93 times (adjusted OR) mortality rate at the end of treatment compared to patients who received LD colistin monotherapy (95%CI=0.51-1.71, p=0.935). In addition, microbiological response was defined as eradication of pre-treatment isolated pathogens in post-treatment cultures. Patients who received LD colistin plus meropenem could eradicate pathogens 1.28 times more than LD colistin monotherapy (95% CI=0.74-2.20, p=0.371). Also there was no significant difference in nephrotoxicity (adjusted OR=0.84, 95% CI 0.52-1.36, p=0.492) between LD colistin monotherapy and LD colistin plus meropenem.

CONCLUSION

There were no significant differences in effectiveness and nephrotoxicity of LD colistin monotherapy versus LD colistin plus meropenem for treatment of CRAB infection, so colistin combination therapy was not necessary for the management of infection caused by CRAB.

Insights into Acinetobacter baumannii: A Review of Microbiological, Virulence, and Resistance Traits in a Threatening Nosocomial Pathogen

Being a multidrug-resistant and an invasive pathogen, Acinetobacter baumannii is one of the major causes of nosocomial infections in the current healthcare system. It has been recognized as an agent of pneumonia, septicemia, meningitis, urinary tract and wound infections, and is associated with high mortality. Pathogenesis in A. baumannii infections is an outcome of multiple virulence factors, including porins, capsules, and cell wall lipopolysaccharide, enzymes, biofilm production, motility, and iron-acquisition systems, among others. Such virulence factors help the organism to resist stressful environmental conditions and enable development of severe infections. Parallel to increased prevalence of infections caused by A. baumannii, challenging and diverse resistance mechanisms in this pathogen are well recognized, with major classes of antibiotics becoming minimally effective. Through a wide array of antibiotic-hydrolyzing enzymes, efflux pump changes, impermeability, and antibiotic target mutations, A. baumannii models a unique ability to maintain a multidrug-resistant phenotype, further complicating treatment. Understanding mechanisms behind diseases, virulence, and resistance acquisition are central to infectious disease knowledge about A. baumannii. The aims of this review are to highlight infections and disease-producing factors in A. baumannii and to touch base on mechanisms of resistance to various antibiotic classes.