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

Evaluation of the efficacy of sulbactam combination therapy for monomicrobial and polymicrobial pulmonary infections caused by multidrug-resistant Acinetobacter baumannii

The efficacy in treatment of monomicrobial versus polymicrobial Acinetobacter baumannii (mono-AB vs poly-AB) pulmonary infections remains unclear. This study mainly investigated the efficacy of sulbactam combination regimens against mono-AB and poly-AB pulmonary infections. A multicenter retrospective study of adult patients who received sulbactam or cefoperazone/sulbactam for multidrug-resistant A. baumannii (MDRAB) between August 2021 and July 2023 was conducted. The outcomes of 7-day microbiological efficacy and 14-day clinical efficacy were measured. A total of 366 patients were enrolled, including 75 mono-AB patients. Among the 291 poly-AB cases, 82 patients were co-infected with Pseudomonas aeruginosa and 76 patients with Klebsiella pneumoniae. All A. baumannii isolates exhibited multidrug resistance. The antibiotics demonstrating the highest sensitivity against these isolates were polymyxins and tigecycline, with sensitivity rates of 91.25% and 71.63%, respectively. In the multivariable analysis, patients receiving sulbactam-based treatment for poly-AB pulmonary infections exhibited significantly higher microbial clearance of A. baumannii compared with those with mono-AB infections. Microbial efficacy analysis of A. baumannii co-infection with K. pneumoniae or P. aeruginosa showed similar results to overall poly-AB infections. Sulbactam doses ≥ 8 g/day showed the best microbiological and clinical efficacy. Sulbactam combined with tigecycline and/or polymyxins demonstrated significantly better microbiological efficacy compared with sulbactam alone. Sulbactam combined with polymyxins resulted in better microbiological and clinical efficacy than when combined with tigecycline. In conclusion, patients with poly-AB lung infections exhibit a higher microbial clearance rate of A. baumannii following treatment compared with those with mono-AB infections. A daily dose ≥8 g sulbactam may be optimal for treating MDRAB pneumonia. The combination of sulbactam and polymyxins demonstrates significant advantages over other sulbactam-containing regimens in terms of microbiological and clinical efficacy.IMPORTANCEThis is the first multicenter retrospective study to investigate the efficacy of sulbactam combination regimens in the treatment of monomicrobial and polymicrobial AB-related pulmonary infections. Our study found that patients receiving sulbactam-based treatment for poly-AB pulmonary infections exhibited significantly higher microbial clearance of A. baumannii compared with those with mono-AB infections. Microbial efficacy analysis of A. baumannii co-infection with K. pneumoniae or P. aeruginosa showed similar results to overall poly-AB infections. These findings are significantly important for further analyzing the potential mechanisms underlying the differences in efficacy between antimicrobial treatments for monomicrobial and polymicrobial infections, as well as for optimizing clinical antimicrobial combination strategies.

Management of multidrug-resistant gram-negative bacilli infections in adult solid organ transplant recipients: GESITRA-IC/SEIMC, CIBERINFEC, and SET recommendations update

Multidrug-resistant (MDR) Gram-negative bacilli (GNB) infections in solid organ transplant (SOT) recipients continue to pose a significant threat despite advances in diagnostics and treatments. The last international consensus guidelines of the Spanish Society of Infectious Diseases and Clinical Microbiology (SEIMC) on the management of MDR GNB in adult solid organ transplant (SOT) recipients were published in 2018, underscoring the need for an update to incorporate recent advances, particularly the availability of new drugs that may improve the current standard of care. A working group consisting of members from the Study Group of Infection in Transplantation and Immunocompromised Hosts (GESITRA-IC) of SEIMC, the Center for Biomedical Research Network in Infectious Diseases (CIBERINFEC) and the Spanish Society of Transplantation (SET) developed consensus-based recommendations for managing MDR GNB infections during the transplant procedure. Recommendations were categorized based on evidence quality and strength, utilizing the Grading of Recommendations Assessment, Development and Evaluation (GRADE) system. The final recommendations were endorsed through a consensus meeting and approved by the expert panel.

Antibiotic killing of drug-induced bacteriostatic cells

There is a long-standing belief that bacteriostatic drugs are inherently antagonistic to the action of bactericidal antibiotics. This belief is primarily because the action of most bactericidal antibiotics requires the target bacteria to be growing. Since bacteriostatic drugs stop the growth of treated bacteria, these drugs would necessarily work against one another. Our results question this long-standing belief by demonstrating conditions where sequential treatment with a bacteriostatic then bactericidal antibiotic is as or more effective than treatment with a bactericidal drug alone. These results raise the need to investigate the pharmacodynamics of the joint action of bacteriostatic and bactericidal antibiotics in vitro and in vivo.

Current and novel therapies for management of Acinetobacter baumannii-associated pneumonia

Acinetobacter baumannii is a common pathogen associated with hospital-acquired pneumonia showing increased resistance to carbapenem and colistin antibiotics nowadays. Infections with A. baumannii cause high patient fatalities due to their capability to evade current antimicrobial therapies, emphasizing the urgency of developing viable therapeutics to treat A. baumannii-associated pneumonia. In this review, we explore current and novel therapeutic options for overcoming therapeutic failure when dealing with A. baumannii-associated pneumonia. Among them, antibiotic combination therapy administering several drugs simultaneously or alternately, is one promising approach for optimizing therapeutic success. However, it has been associated with inconsistent and inconclusive therapeutic outcomes across different studies. Therefore, it is critical to undertake additional clinical trials to ascertain the clinical effectiveness of different antibiotic combinations. We also discuss the prospective roles of novel antimicrobial therapies including antimicrobial peptides, bacteriophage-based therapy, repurposed drugs, naturally-occurring compounds, nanoparticle-based therapy, anti-virulence strategies, immunotherapy, photodynamic and sonodynamic therapy, for utilizing them as additional alternative therapy while tackling A. baumannii-associated pneumonia. Importantly, these innovative therapies further require pharmacokinetic and pharmacodynamic evaluation for safety, stability, immunogenicity, toxicity, and tolerability before they can be clinically approved as an alternative rescue therapy for A. baumannii-associated pulmonary infections.

Comparative effectiveness and safety of colistin-based versus high-dose ampicillin/sulbactam-based combination therapy for nosocomial pneumonia caused by carbapenem-resistant Acinetobacter baumannii

Differences exist between Infectious Diseases Society of America guidance and European Society of Clinical Microbiology and Infectious Diseases guidelines on treating pneumonia caused by carbapenem-resistant Acinetobacter baumannii (CRAB). This study compared the outcomes of colistin-based and high-dose ampicillin/sulbactam-based combination therapies in patients with CRAB nosocomial pneumonia. A retrospective cohort study was conducted at a university-affiliated hospital in South Korea. Patients received either a colistin-based regimen with a loading dose followed by a maintenance dose (June 2021-May 2022) or a high-dose ampicillin/sulbactam-based regimen with sulbactam 9 g/day (October 2022-September 2023). The primary outcome was 28-day all-cause mortality; secondary outcomes included 14-day/28-day clinical success rates and 14-day/28-day kidney injury based on the Risk, Injury, Failure, Loss, End-stage renal disease score. Logistic and Poisson regression analyses were used to compare outcomes between groups. Among 179 patients enrolled in the study, 84 received the colistin-based regimen and 95 received the high-dose ampicillin/sulbactam-based regimen. The ampicillin/sulbactam group showed significantly lower 28-day mortality (20% vs. 61%; adjusted relative risk [aRR] = 0.16, 95% CI 0.08-0.32). Clinical success rates were higher in the ampicillin/sulbactam group at both 14 days (39% vs. 23%; aRR = 2.19, 95% CI 1.10-4.37) and 28 days (55% vs. 32%; aRR = 2.71, 95% CI 1.14-5.20). Additionally, 28-day kidney injury was lower in the ampicillin/sulbactam group (0.63 ± 1.16 vs. 1.06 ± 1.35; aRR = 0.56, 95% CI 0.40-0.79). High-dose ampicillin/sulbactam-based combination therapy demonstrates superior outcomes over colistin-based combination therapy for CRAB nosocomial pneumonia, including lower mortality, higher clinical success rates, and reduced kidney injury.

Fighting resistance with redundancy: a path forward for treating antimicrobial-resistant infections?

Carbapenem-resistant Acinetobacter baumannii (CRAB) remains a major threat, with high mortality and limited effective treatments. Sulbactam-durlobactam has emerged as a promising therapy against CRAB. Sulbactam-durlobactam was combined with imipenem-cilastatin in a clinical trial that led to its United States Food and Drug Administration approval. However, the additive benefit of imipenem remains uncertain. In a recent study (Antimicrob Agents Chemother 69:e01627-24, 2025, https://doi.org/10.1128/aac.01627-24), Veeraraghavan and colleagues provide convincing mechanistic evidence that adding imipenem to sulbactam-durlobactam enhances bacterial killing, likely through complementary inhibition of penicillin binding proteins, leveraging the concept of target redundancy.

Sulbactam for carbapenem-resistant Acinetobacter baumannii infections: a literature review

Carbapenem-resistant Acinetobacter baumannii (CRAB) is characterized as a critical priority pathogen with restricted therapeutic options. To date, the most effective antimicrobial treatment against this difficult-to-treat bacterial strain has not been established. Sulbactam is a β-lactamase inhibitor with intrinsic activity against this pathogen, however, as a β-lactam, it can be hydrolysed by β-lactamases produced by A. baumannii. High-dose, extended-infusion treatment with sulbactam can overcome this hydrolysis by β-lactamases and is considered an effective therapeutic strategy against CRAB. The aim of this review is to analyse primary and secondary research studies that compare sulbactam-based with other regimens, such as polymyxin-containing regimens, tigecycline-containing regimens and other antimicrobial combinations against CRAB infections, especially ventilator-associated pneumonia (VAP), hospital-acquired pneumonia (HAP) and bacteraemia. Our findings suggest that results are conflicting, mostly because of high heterogeneity among studies. However, in most studies, sulbactam-based regimens have demonstrated comparable, and in several studies more favourable results in contrast to other antimicrobial treatments with respect to clinical cure and mortality in CRAB-associated pneumonia, yet without reaching statistical significance in most cases. The auspicious novel β-lactam/β-lactamase inhibitor combination sulbactam/durlobactam is also discussed, although real-world clinical data regarding its efficacy in CRAB infections are still scarce. More randomized controlled trials comparing sulbactam-based with other regimens are warranted to determine the most effective antimicrobial combination against CRAB infections. Nevertheless, current data suggest that sulbactam could play a major role in this combination treatment.

Nanobiotic Formulations utilizing Quinoline-based-Triazole functionalized Carbon Quantum Dots via Click Chemistry for Combatting Clinical-Resistant Bacterial Pathogens

Therapeutic options for preventing the trajectory of multi-drug resistance bacterial pathogens could rely on the effort to design a novel technique to develop a potent antimicrobial agent to counter the key issue. To curb the current outbreak, we synthesized first generation of antimicrobial amine-modified carbon quantum dots, CQDs-NH2 as carbon precursors followed by hydrothermal carbonization of ethylenediamine/citric acid, and postmodified with propargyl alcohol (CQDs-1) and quinoline derivative; 8-hydroxy quinoline (CQDs-2) through Cu(I)-catalyzed azide-alkyne cycloaddition. The novel clicked 1,2,3-triazole functionalized CQDs-NH2 templates, were evaluated against standard Gram-positive; Staphylococcus aureus (S. aureus), and Gram-negative; Escherichia coli (E. coli), MRSA, along with clinical-resistant diabetic foot PUS swab isolated bacterial pathogens by 96-well method as well as agar-well diffusion method, to unleased the potential antibacterial activity. 1,2,3-triazole functionalized CQDs-NH2 template showed enhanced antibacterial activity against distinct bacterial strains, with minimum inhibitory concentration for standard bacteria, MRSA-bacteria, and clinical resistant bacterial pathogens in the range of 0.25-8, 64-128, and 128-256 μg mL-1 respectively. This nanobiotic template displays good potential through the hybridization of 1,2,3-triazole with antibacterial pharmacophores CQDs-NH2 and quinoline, to overcome drug resistance, reduce toxicity, and improve pharmacokinetic profiles. The findings of this study might have a favorable impact on antibiotic pharmacodynamics and, as a result, nanobiotic dosing regimens as well as clinical outcomes.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1007/s12088-024-01266-x.

Suggested Dosing of Select Beta-lactam Agents for the Treatment of Antimicrobial-Resistant Gram-Negative Infections in Children

The Infectious Diseases Society of America (IDSA) publishes annual guidance on the treatment of antimicrobial-resistant (AMR) gram-negative infections. Within the AMR guidance, suggested dosages of antibiotics for adults infected with AMR pathogens are provided. This document serves as a companion document to the IDSA guidance to assist pediatric specialists with dosing β-lactam agents for the treatment of AMR infections in children. A panel of 13 pediatric infectious diseases specialists, including 11 pharmacists and 2 physicians, reviewed existing pharmacokinetic/pharmacodynamic, animal, and clinical data for newer β-lactam agents that are available in the United States and suggested for the treatment of AMR infections (ie, cefiderocol, ceftazidime-avibactam, ceftazidime-avibactam and aztreonam, ceftolozane-tazobactam, imipenem-cilastatin-relebactam, meropenem-vaborbactam, sulbactam-durlobactam). Suggested dosing for ampicillin-sulbactam is also provided, given complexities in dosing for carbapenem-resistant Acinetobacter baumannii infections. Consensus-based suggested dosing for β-lactam agents used to treat AMR infections in neonates, infants, children, and adolescents and relevant supporting evidence are provided. Content is up to date as of December 1, 2024. Gaps and limitations to existing data are discussed. Optimizing antibiotic dosing is critical to improving the outcomes of children with AMR infections.

Simultaneous determination of three β-Lactam/β-lactamase inhibitor combinations in critically ill patients by UPLC-MS/MS

β-Lactam/β-lactamase inhibitors (BL/BLIs) are widely used in critically ill patients. Recent research has shown the importance of therapeutic drug monitoring (TDM) of BLs, but few studies have highlighted the importance of detecting BLIs in critically ill patients. In our laboratory, we have developed and validated a simple and robust method for the determination of ceftazidime, cefoperazone, piperacillin, avibactam, sulbactam and tazobactam in human plasma by ultra-high performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). Sample preparation was by protein precipitation of 100 µL of sample, followed by chromatographic separation on an ACQUITY UPLC® BEH C18 column (2.1 × 50 mm, 1.7 µm) and mass spectrometric detection using a SHIMADZU 8050CL in multiple reaction monitoring (MRM) mode. The method was fully validated for selectivity, carry-over, linearity, lower limit of quantification, matrix effect, extraction recovery, stability and dilution integrity. The results of the TDM could provide feedback to clinicians and allow timely adjustment of dosing regimens in critically ill patients. The method is suitable for routine TDM and has been successfully applied to the clinical determination of 81 plasma concentrations in 44 patients.

Invasive Klebsiella pneumoniae liver abscess syndrome complicated by carbapenem-resistant Acinetobacter baumannii infection: a case report

Background

A liver abscess caused by hypervirulent Klebsiella pneumoniae can lead to multiple invasive extrahepatic infections, including lung abscesses, endophthalmitis, brain abscesses, and necrotizing fasciitis. This condition, known as Klebsiella pneumoniae liver abscess invasion syndrome, progresses rapidly and is associated with severe illness, high disability rates, and significant mortality. However, bloodstream infections with co-infection involving carbapenem-resistant Acinetobacter baumannii are exceedingly rare.

Case presentation

The Emergency Medicine Department of the First People's Hospital of Kunshan successfully treated a male patient diagnosed with liver, lung, and prostate abscesses. The patient underwent puncture and drainage, with analysis of the drainage fluid, sputum culture, and metagenomic next-generation sequencing (m-NGS) revealing a co-infection with blood-borne Klebsiella pneumoniae and Acinetobacter baumannii. Guided by drug sensitivity test results, the patient received treatment with polymyxin and cefoperazone sodium-sulbactam sodium for infection control and liver protection. The treatment was successful, and the patient fully recovered and was discharged.

Conclusion

By reporting this rare case and highlighting the drug resistance of the bacteria, we propose a new diagnosis and treatment plan for managing Klebsiella pneumoniae combined with carbapenem-resistant Acinetobacter baumannii infection, along with a literature review.

Treatment Approaches for Carbapenem-Resistant Acinetobacter baumannii Infections

Carbapenem-resistant Acinetobacter baumannii has been associated with over three hundred thousand annual deaths globally. It is resistant to most available antibiotics and associated with high morbidity and mortality. No global consensus currently exists for treatment strategies that balance safety and efficacy because of heterogeneity of treatment regimens in current clinical practice and scarcity of large-scale controlled studies arising from difficulties in establishing robust clinical outcomes. This review outlines the epidemiology and resistance mechanisms of carbapenem-resistant A. baumannii, then summarizes available clinical data on each approved agent with activity against this pathogen. Emerging treatment options such as cefiderocol and sulbactam-durlobactam show promise, but their success hinges on comprehensive clinical validation and access in regions most impacted by this pathogen. New therapeutic modalities that are in various stages of clinical development are also discussed.

Carbapenem-resistant Acinetobacter baumannii raises global alarm for new antibiotic regimens

Carbapenem-resistant Acinetobacter baumannii (CRAB) is a top-priority pathogen causing a nosocomial infection that increases morbidity and mortality. Treatment options for CRAB are relatively limited by pharmacokinetic restrictions, such as substantial toxicity. Therefore, we must better understand this pathogen to develop new treatments and control strategies. The review aims to provide an overview of the current understanding of acquired, adaptive, and intrinsic Carbapenem-resistant pathways in A. baumannii, as well as its consequences on healthcare systems, particularly critical care units. The review also provides insights into how CRAB infections are currently managed worldwide and why novel therapeutic regimens are needed. The peculiarity of A. baumannii and its often reported virulence factors have been discussed further. In conclusion, the purpose of this review is to emphasize the current knowledge on CRAB, as it causes major worry in the field of nosocomial infections as well as overall public health.

The challenges of difficult-to-treat Acinetobacter infections

SUMMARYInfections due to Acinetobacter spp. are among the most difficult to treat. Most are resistant to standard antibiotics, and there is difficulty in distinguishing colonizers from pathogens. This mini-review examines the available antibiotics that exhibit activity against these organisms and provides guidance as to which cultures are relevant and how to treat active infections. Antibiograms describing resistance mechanisms and the minimum inhibitory concentration (MIC) are essential to determine which agent or combination of agents should be used after confirmation of infection, utilizing clinical parameters and biomarkers such as procalcitonin. Directed therapy should be prompt as despite its reputation as a colonizer, the attributable mortality is high. However, although combination therapy is advised, no specific combination has definite evidence of superiority.

Combination therapy strategies against multidrug resistant bacteria in vitro and in vivo

Exploring effective combination antibacterial therapies has become a research focus. This study selected seven common antibiotics to perform a series of tests on different Gram-negative bacteria isolated from clinical samples of chronic obstructive pulmonary disease patients. More than 70% of the strains exhibited multidrug resistance but remained sensitive to polymyxin B. The checkerboard assay revealed a significant synergistic effect between polymyxin B and tetracycline against different resistant strains, with fractional inhibitory concentration index values consistently below 0.5. Further time-kill curve analysis demonstrated that the use of minimal inhibit concentration of polymyxin B or tetracycline alone had limited bactericidal effects, while their combination significantly reduced bacterial counts by 2-3 log colony-forming units within 12 h. Additionally, the survival rate of larvae treated with the polymyxin B and tetracycline combination was significantly higher than that of the mono-therapy and untreated groups. In brief, this study demonstrates that the combination of polymyxin B and tetracycline exhibits potent antibacterial activity against multidrug resistant Gram-negative bacteria both in vitro and in vivo.

Effect of colistin combined with sulbactam: 9 g versus 12 g per day on mortality in the treatment of carbapenems resistant Acinetobacter baumannii pneumonia: A randomized controlled trial

BACKGROUND

The current treatment recommendation involves administering a high dose of sulbactam alongside at least one additional agent. However, there remains a lack of data regarding the optimal dosage of sulbactam. We investigated whether administering sulbactam at a dosage of 12 g/day decreases the mortality rate among patients with CRAB pneumonia compared to 9 g/day.

METHODS

The study was an open-label, superiority, randomized controlled trial conducted at Phramongkutklao Hospital between September 2019 and September 2023 in patients diagnosed with CRAB. Participants were randomly assigned to receive a combination of colistin with either 9 or 12 g/day of sulbactam. The primary endpoint was the all-cause mortality rate at 28 days postrandomization.

RESULTS

Among the 138 participants, there was a trend towards a lower mortality rate in the 12 g/day group (59.4% vs. 47.8%; P = 0.158). After adjusting for factors associated with mortality, a lower mortality was observed in the 12 g/day group (adjusted HR 0.54 [95% CI 0.33-0.87]; P = 0.0110). The microbiological cure rate at day 7 was higher in the 12 g/day group (73.2% vs. 89.4%; P = 0.02).

CONCLUSIONS

Colistin in combination with sulbactam at a dosage of 12 g/day may improve mortality compared to 9 g/day.

Isolation, characterization, and potential application of Acinetobacter baumannii phages against extensively drug-resistant strains

One of the significant issues in treating bacterial infections is the increasing prevalence of extensively drug-resistant (XDR) strains of Acinetobacter baumannii. In the face of limited or no viable treatment options for extensively drug-resistant (XDR) bacteria, there is a renewed interest in utilizing bacteriophages as a treatment option. Three Acinetobacter phages (vB_AbaS_Ftm, vB_AbaS_Eva, and vB_AbaS_Gln) were identified from hospital sewage and analyzed for their morphology, host ranges, and their genome sequences were determined and annotated. These phages and vB_AbaS_SA1 were combined to form a phage cocktail. The antibacterial effects of this cocktail and its combinations with selected antimicrobial agents were evaluated against the XDR A. baumannii strains. The phages exhibited siphovirus morphology. Out of a total of 30 XDR A. baumannii isolates, 33% were sensitive to vB_AbaS_Ftm, 30% to vB_AbaS_Gln, and 16.66% to vB_AbaS_Eva. When these phages were combined with antibiotics, they demonstrated a synergistic effect. The genome sizes of vB_AbaS_Ftm, vB_AbaS_Eva, and vB_AbaS_Gln were 48487, 50174, and 50043 base pairs (bp), respectively, and showed high similarity. Phage cocktail, when combined with antibiotics, showed synergistic effects on extensively drug-resistant (XDR) strains of A. baumannii. However, the need for further study to fully understand the mechanisms of action and potential limitations of using these phages is highlighted.

A retrospective study of the efficacy of sulbactam in the treatment of patients with extensively drug-resistant Acinetobacter baumannii infections

PURPOSE

Sulbactam (SBT) is one of the most significant treatments for patients with extensively drug-resistant Acinetobacter baumannii (XDR-AB). However, the efficacy and safety of SBT and its high dose regimen has not been well documented. This retrospective study aimed to assess the efficacy and safety of SBT-based treatment, particularly at high-dose (≥ 6 g/day), for XDR-AB infection.

METHOD

A total of 52 XDR-AB infected patients treated with intravenous SBT at Peking Union Medical College Hospital were included. The primary outcome was 28-day all-cause mortality, while the secondary outcome was 14-day clinical response and the time of response. The formulation of SBT in our study is 0.5 g per vial.

RESULTS

Among the patients, the 28-day all-cause mortality rate was 36.5% (19/52), and the favorable 14-day clinical response rate was 59.6% (31/52). The 28-day mortality was independently associated coinfection with gram-positive bacteria (GPB) and a shorter duration of therapy. Patients with intracranial infection might have a longer survival time. A favorable 14-day clinical response was associated with the dose of SBT, and a longer treatment duration. However, the higher creatinine clearance (CrCl) associated with a worse clincal response. In addition, a higher SBT dosage was significantly correlated with a shorter time to clinical response. No adverse effects related were reported.

CONCLUSION

The single-agent formulation of SBT emerges as a promising alternative for the treatment of XDR-AB infection, such as intracranial infection, particularly at high doses (≥ 6 g/day). Besides, longer duration of treatment correlates with higher survival rate and better favorable clinical response. Higher CrCl negatively correlates with favorable clinical response.

Antibacterial Therapy Options for Infections Caused by Carbapenem-Resistant Acinetobacter baumannii

The review presents current treatment regimens for infections associated with carbapenem-resistant Acinetobacter baumannii, which are leading nosocomial pathogens exhibiting multidrug resistance to available antibacterial drugs. To date, widely used beta-lactam antibiotics, including carbapenems, have lost their effectiveness in combating acinetobacter infections, while new antibiotics remain poorly available to patients. Therefore, the only measure to combat the antibiotic resistance of carbapenem-resistant A. baumannii is to evaluate the efficiency of combination therapy in vitro and in vivo, which is of particular interest to Russian and foreign researchers.

Sulbactam-durlobactam for the treatment of Acinetobacter baumannii-calcoaceticus complex

INTRODUCTION

Infections with Acinetobacter baumannii-calcoaceticus complex (ABC) pose difficulty for clinicians given a limited arsenal of effective antimicrobials. Sulbactam/durlobactam provides a novel treatment option for patients experiencing hospital- or ventilator-acquired pneumonia with susceptible strains.

AREAS COVERED

This review provides a comprehensive discussion of sulbactam/durlobactam, including basic characteristics, in vitro activity, and clinical trial data supporting its use for the treatment of ABC. Manufacturer's data, published literature to date, and conference data are utilized in this review.

EXPERT OPINION

Sulbactam/durlobactam offers clinicians a new and effective treatment option for resistant ABC infection. Sulbactam, when combined with durlobactam, displays enhanced potency against ABC isolates, which has translated into positive clinical outcomes observed in clinical trials and post-marketing case studies. Although overall treatment indications and clinical experience are limited to date, sulbactam/durlobactam offers a familiar and favorable safety profile in comparison with alternative agents. Factors associated with use of combination antibiotic therapy, availability of commercial drug susceptibility testing, and cost-effectiveness are all currently key considerations for sulbactam/durlobactam use.

Combination Versus Monotherapy for Carbapenem-Resistant Acinetobacter Species Serious Infections: A Prospective IPTW Adjusted Cohort Study

INTRODUCTION

International guidelines recommend definitive combination antibiotic therapy for the management of serious infections involving carbapenem-resistant Acinetobacter (CRAB) species. The commonly available combination options include high-dose sulbactam, polymyxins, tetracyclines, and cefiderocol. Scanty prospective data exist to support this approach.

METHODS

Patients with CRAB bacteraemia, ventilator-associated pneumonia (VAP), or both were categorized based on whether they received combination therapy or monotherapy. The 30-day mortality was compared between the two groups. Inverse probability treatment weighting (IPTW) was done using propensity score (PS) for a balanced comparison between groups.

RESULTS

Between January 2021 and May 2023, of the 161 patients with CRAB bacteraemia (n = 55, 34.2%), VAP (n = 46, 28.6%), or both (n = 60, 37.3%) who received appropriate intravenous antibiotic therapy, 70% (112/161) received monotherapy, and the rest received combination therapy. The overall 30-day mortality was 62% (99/161) and not different (p = 0.76) between the combination therapy (31/49, 63.3%) and monotherapy (68/112, 60.7%) groups. The propensity score matching using IPTW did not show a statistical difference (p = 0.47) in 30-day mortality for receiving combination therapy with an adjusted odds ratio (OR) P of 1.29 (0.64, 2.58).

CONCLUSION

Combination therapy for CRAB infections needs further study in a randomised controlled trial, as this observational study showed no difference in 30-day mortality between monotherapy and combination therapy.

Outcomes of adult patients with multidrug-resistant Acinetobacter baumannii ventilator-associated pneumonia treated with monotherapy versus combination therapy in a tertiary hospital

We compared clinical outcomes of patients who received monotherapy and combination therapy for treatment of MDR A. baumannii VAP. 170 patients were included. Vasopressor use and mortality rate were higher for combination therapy (69.3% versus 28.6%, p=0.024; 67.5% versus 14.3%, p=0.007; respectively). Majority received polymyxin B-based combination therapy, with higher mortality than those without polymyxin B (80.2% versus 19.8%, p=0.043). After adjusting for vasopressor use, monotherapy, dual combination, and triple combination therapy were not associated with mortality (aHR 0.24, 95% CI 0.03 to 1.79, p=0.169; aHR 1.26, 95% CI 0.79 to 2.00, p=0.367; aHR 0.93, 95% CI 0.57 to 1.49, p=0.744; respectively). There was no difference in adverse effects and length of stay between the two groups. Mortality from MDR A. baumannii VAP was high and not associated with monotherapy or combination therapy after adjustment for vasopressor use. Antibiotic regimens other than those containing polymyxin are urgently needed for the treatment of these infections.

Successful Treatment of Carbapenem-Resistant Acinetobacter baumannii Meningitis With Sulbactam-Durlobactam

BACKGROUND

The treatment of carbapenem-resistant Acinetobacter baumannii/calcoaceticus complex (CRAB) presents significant treatment challenges.

METHODS

We report the case of a 42-year-old woman with CRAB meningitis who experienced persistently positive cerebrospinal fluid (CSF) cultures for 13 days despite treatment with high-dose ampicillin-sulbactam and cefiderocol. On day 13, she was transitioned to sulbactam-durlobactam and meropenem; 4 subsequent CSF cultures remained negative. After 14 days of sulbactam-durlobactam, she was cured of infection. Whole genome sequencing investigations identified putative mechanisms that contributed to the reduced cefiderocol susceptibility observed during cefiderocol therapy. Blood and CSF samples were collected pre-dose and 3-hours post initiation of a sulbactam-durlobactam infusion.

RESULTS

The CRAB isolate belonged to sequence type 2. An acquired blaOXA-23 and an intrinsic blaOXA-51-like (ie, blaOXA-66) carbapenemase gene were identified. The paradoxical effect (ie, no growth at lower cefiderocol dilutions but growth at higher dilutions) was observed by broth microdilution after 8 days of cefiderocol exposure but not by disk diffusion. Potential markers of resistance to cefiderocol included mutations in the start codon of piuA and piuC iron transport genes and an A515V substitution in PBP3, the primary target of cefiderocol. Sulbactam and durlobactam were detected in CSF at both timepoints, indicating CSF penetration.

CONCLUSIONS

This case describes successful treatment of refractory CRAB meningitis with the administration of sulbactam-durlobactam and meropenem and highlights the need to be cognizant of the paradoxical effect that can be observed with broth microdilution testing of CRAB isolates with cefiderocol.

Optimizing Treatment Strategies for Carbapenem-Resistant Acinetobacter Baumannii-Associated Pneumonia: A Multicenter Study in Chinese Hospitals

Purpose

To evaluate the clinical outcomes and safety of tigecycline (TGC) plus cefoperazone/sulbactam (CPS) or TGC monotherapy in patients with hospital-acquired pneumonia (HAP) caused by Carbapenem-Resistant Acinetobacter baumannii (CRAB).

Methods

This was a retrospective analysis of multicenter data from 62 Chinese hospitals with CRAB HAP. Risk factors for receiving TGC with CPS therapy and predictors of mortality were assessed using multivariate logistic and Cox regression analyses, respectively. Propensity score matching (PSM) evaluated the efficacy and safety of antimicrobial regimens.

Results

A total of the 180 patients were included, with 95 receiving TGC monotherapy and 85 receiving combination therapy. Multivariate logistic regression analysis revealed that older age (P = 0.011), and intensive care unit (ICU) admission (P = 0.007) were significant risk factors for combination therapy. Multivariate Cox regression demonstrated that combination therapy was associated with a significantly higher risk of 90-day mortality (P = 0.031). Patients in the standard-dose TGC (SDT) plus CPS subgroup had significantly higher rates of SOFA scores ≥ 7 (P = 0.009) and MV used (P = 0.028), as well as higher 30-/90-day mortality compared to high-dose TGC (HDT) plus CPS group. TGC plus CPS significantly reduced CRP levels (P = 0.009), while the variations in ALT, TBIL, Cr, Hb, and PLT levels did not differ between different antimicrobial regimens after PSM.

Conclusion

HDT and CPS combination therapy was more effective in patients with advanced age and more severe condition. Safety profiles of different antimicrobial regimens were similar with liver, kidneys, and coagulation functions.

Treatment of multidrug-resistant Gram-negative bloodstream infections in critically ill patients: an update

PURPOSE OF REVIEW

This review describes the latest information in the management of bloodstream infections caused by multidrug-resistant Gram-negative bacilli (MDRGNB) in critically ill patients.

RECENT FINDINGS

The prevalence of bloodstream infections due to MDRGNB is high, and they pose a significant risk in critically ill patients. Recently, novel antimicrobial agents, including new β-lactam/β-lactamase inhibitor combinations and cefiderocol, have been introduced for treating these infections. Concurrently, updated guidelines have been issued to aid in treatment decisions. Prompt diagnosis and identification of resistance patterns are crucial for initiating effective antibiotic therapy. Current studies, especially with observational design, and with limited sample sizes and patients with bacteremia, suggest that the use of these new antibiotics is associated with improved outcomes in critically ill patients with MDRGNB bloodstream infections.

SUMMARY

For critically ill patients with bloodstream infections caused by MDRGNB, the use of newly developed antibiotics is recommended based on limited observational evidence. Further randomized clinical trials are necessary to determine the most effective antimicrobial therapies among the available options.

Comparing the Outcomes of Cefoperazone/Sulbactam-Based and Non-Cefoperazone/Sulbactam-Based Therapeutic Regimens in Patients with Multiresistant Acinetobacter baumannii Infections-A Meta-Analysis

The addition of sulbactam restores the complete range of cefoperazone activity against bacteria and extends its spectrum of action to include the Acinetobacter species. The effectiveness of cefoperazone/sulbactam against multiresistant Acinetobacter baumannii has not been investigated. The purpose of the current meta-analysis was to compare the efficacy of cefoperazone/sulbactam-based therapeutic regimens and non-cefoperazone/sulbactam-based therapeutic regimens in the treatment of multiresistant Acinetobacter baumannii infections. The current meta-analysis of 10 retrospective studies provides evidence that cefoperazone/sulbactam-based therapeutic regimens are superior to non-cefoperazone/sulbactam-based therapeutic regimens in terms of 30-day mortality and clinical improvement in patients with multiresistant Acinetobacter baumannii infections. The risk of mortality was reduced by 38% among multiresistant Acinetobacter baumannii infections in patients who received cefoperazone/sulbactam-based therapeutic regimens. The cefoperazone/sulbactam-based combination therapy was superior to the cefoperazone/sulbactam monotherapy in terms of 30-day mortality when both therapeutic regimens were compared to the tigecycline monotherapy in patients with multiresistant Acinetobacter baumannii infections.

Comparison of cefiderocol and colistin-based regimens for the treatment of severe infections caused by carbapenem-resistant Acinetobacter baumannii: a systematic review with meta-analysis and trial sequential analysis

BACKGROUND

There are multiple antibiotic regimens for the treatment of carbapenem-resistant Acinetobacter baumannii (CRAB) in clinical practice. We conducted this meta-analysis to compare the efficacy and safety of cefiderocol-based regimens and colistin-based regimens in the treatment of CRAB infections.

METHODS

Two authors independently searched the PubMed, Web of Science, Embase, and Cochrane databases from their establishment to April 15, 2024, to search for randomized controlled trials (RCTs) or cohort studies, and compared the clinical efficacy and safety of cefiderocol-based regimens and colistin-based regimens in the treatment of CRAB infections. The Newcastle Ottawa Scale (NOS) checklist was used to evaluate the quality of the included studies. The primary outcome was all-cause mortality, and subgroup analysis was conducted on the basis of the site of infection and the risk of bias in the studies. Trial sequential analysis (TSA) was then conducted.

RESULTS

Six observational studies were included, with 251 cases in the cefiderocol-based group and 372 cases in the colistin-based group. Compared to the colistin-based group, the cefiderocol-based group had lower all-cause mortality (RR = 0.71, 95% CI: 0.54-0.92, P = 0.01) and 30-day mortality (RR = 0.64, 95% CI: 0.43-0.95, P = 0.03). However, for the 14-day and 28-day mortality rates, there was no statistically significant difference between two groups. According to the subgroup analysis, among patients with bloodstream infection (BSI), the cefiderocol-based group had lower all-cause mortality, but it did not reduce the mortality of ventilator-associated pneumonia (VAP) patients. The result of TSA showed that our conclusions are reliable. There was no significant statistical difference in the microbiological cure rate, clinical cure rate, or duration of hospitalization. In addition, the cefiderocol-based group did not have an increased incidence of acute kidney injury (AKI).

CONCLUSIONS

Compared with the colistin-based regimens, the cefiderocol-based regimens were significantly associated with a lower risk of mortality in CRAB-infected patients, especially for patients with BSI. However, they did not show any advantages in terms of the clinical cure rate or microbiological cure rate, nor did they reduce the incidence of AKI.

PROSPERO REGISTRATION NUMBER

CRD42023487213.

Antibiotic killing of drug-induced bacteriostatic cells

Synopsis

Background

There is a long-standing belief that bacteriostatic drugs are inherently antagonistic to the action of bactericidal antibiotics. This belief is primarily due to the fact that the action of most bactericidal antibiotics requires the target bacteria to be growing. Since bacteriostatic drugs stop the growth of treated bacteria, these drugs would necessarily work against one another. We have recently shown that bacteria treated with high concentrations of bacteriostatic drugs retain some metabolic activity, dividing on average once per day.

Objectives

We seek to determine if this low level of growth is sufficient to allow for bactericidal antibiotics of different classes to still kill after bacteria are treated with bacteriostatic drugs.

Methods

We first treated Escherichia coli and Staphylococcus aureus with two different bacteriostatic drugs, followed by one of three bactericidal drugs of three different classes. The density of these bacteria was tracked over six days to determine the amount of killing that occurred.

Results

Our results question this long-standing belief by demonstrating conditions where sequential treatment with a bacteriostatic then bactericidal antibiotic is as or more effective than treatment with a bactericidal drug alone.

Conclusions

These results raise the need to investigate the pharmacodynamics of the joint action of bacteriostatic and bactericidal antibiotics in vitro and in vivo.

Ampicillin-Sulbactam for Carbapenem-Susceptible Acinetobacter baumannii Pneumonia: A Case for High-Dose, Continuous Infusion Dosing Strategy in the Trauma ICU

Background: The optimal ampicillin-sulbactam dosing regimen for carbapenem-susceptible Acinetobacter baumannii isolates in critically ill trauma patients has not been clearly defined. One strategy to provide the adequate sulbactam dose includes high-dose continuous infusion. Case(s) Description: We present three cases of critically ill trauma patients with augmented renal clearance treated with high-dose ampicillin-sulbactam through an intravenous continuous infusion for ventilator-associated pneumonia. All A. baumannii isolates were susceptible to sulbactam with low minimum inhibitory concentrations. All achieved clinical cure at the end of therapy and no recurrent pneumonia was noted. No clinically substantial adverse effect attributable to ampicillin-sulbactam therapy occurred. Discussion: There is limited evidence to endorse high-dose, continuous infusion ampicillin-sulbactam for treatment of infections caused by carbapenem-susceptible A. baumannii. This report presents three critically ill trauma patients with augmented renal clearance that achieved positive clinical outcomes with higher doses of ampicillin-sulbactam administered through a continuous infusion.

Treatment of infections caused by carbapenem-resistant Acinetobacter baumannii

Patients with severe carbapenem-resistant Acinetobacter baumannii (CRAB) infections currently face significant treatment challenges. When patients display signs of infection and the clinical suspicion of CRAB infections is high, appropriate treatment should be immediately provided. However, current treatment plans and clinical data for CRAB are limited. Inherent and acquired resistance mechanisms, as well as host factors, significantly restrict options for empirical medication. Moreover, inappropriate drug coverage can have detrimental effects on patients. Most existing studies have limitations, such as a restricted sample size, and are predominantly observational or non-randomized, which report significant variability in patient infection severity and comorbidities. Therefore, a gold-standard therapy remains lacking. Current and future treatment options of infections due to CRAB were described in this review. The dose and considerable side effects restrict treatment options for polymyxins, and high doses of ampicillin-sulbactam or tigecycline appear to be the best option at the time of initial treatment. Moreover, new drugs such as durlobactam and cefiderocol have substantial therapeutic capabilities and may be effective salvage treatments. Bacteriophages and antimicrobial peptides may serve as alternative treatment options in the near future. The advantages of a combination antimicrobial regimen appear to predominate those of a single regimen. Despite its significant nephrotoxicity, colistin is considered a primary treatment and is often used in combination with antimicrobials, such as tigecycline, ampicillin-sulbactam, meropenem, or fosfomycin. The Infectious Diseases Society of America (IDSA) has deemed high-dose ampicillin-sulbactam, which is typically combined with high-dose tigecycline, polymyxin, and other antibacterial agents, the best option for treating serious CRAB infections. A rational combination of drug use and the exploration of new therapeutic drugs can alleviate or prevent the effects of CRAB infections, shorten hospital stays, and reduce patient mortality.

Treatment of infections caused by multidrug-resistant Gram-negative bacilli: A practical approach by the Italian (SIMIT) and French (SPILF) Societies of Infectious Diseases

INTRODUCTION

The emergence of multidrug-resistant Gram-negative bacilli and the development of new antibiotics have complicated the selection of optimal regimens. International guidelines are valuable tools, but are limited by the scarcity of high-quality randomized trials in many situations.

METHODS

A panel of experts from the French and Italian Societies of Infectious Diseases aimed to address unresolved issues in clinical practice based on their experience, an updated literature review and open discussions.

RESULTS

The panel reached consensus for the following 'first choices': (i) cefepime for ventilator-acquired pneumonia due to AmpC β-lactamase-producing Enterobacterales; (ii) the β-lactam/β-lactamase inhibitor combination most active in vitro, or cefiderocol combined with fosfomycin, and aerosolized colistin or aminoglycosides, for severe pneumonia due to Pseudomonas aeruginosa resistant to ceftolozane-tazobactam; (iii) high-dose piperacillin-tazobactam (including loading dose and continuous infusion) for complicated urinary tract infections (cUTIs) caused by extended-spectrum β-lactamase-producing Enterobacterales with piperacillin-tazobactam minimum inhibitory concentration (MIC) ≤8 mg/L; (iv) high-dose cefepime for cUTIs due to AmpC β-lactamase-producing Enterobacterales other than Enterobacter spp. if cefepime MIC ≤2 mg/L; (v) ceftolozane-tazobactam or ceftazidime-avibactam plus metronidazole for intra-abdominal infections (IAIs) due to third-generation cephalosporin-resistant Enterobacterales; (vi) ceftazidime-avibactam plus aztreonam plus metronidazole for IAIs due to metallo-β-lactamase-producing Enterobacterales; (vii) ampicillin-sulbactam plus colistin for bloodstream infections (BSIs) caused by carbapenem-resistant Acinetobacter baumannii; (viii) meropenem-vaborbactam for BSIs caused by Klebsiella pneumoniae carbapenemase-producing Enterobacterales; and (ix) ceftazidime-avibactam plus fosfomycin for neurological infections caused by carbapenem-resistant P. aeruginosa.

CONCLUSIONS

These expert choices were based on the necessary balance between antimicrobial stewardship principles and the need to provide optimal treatment for individual patients in each situation.

Improving Outcomes in Nosocomial Pneumonia: Recent Evidence and More Challenges

Nosocomial pneumonia (NP) represents a leading nosocomial infection and results in substantial morbidity and cost. Over the last several years, the evidence has evolved which directs our approach to NP. Specifically, the definition of NP and classification of its various subtypes has expanded to capture nuances among various phenotypes of this syndrome. For example, segregating those with hospital-acquired pneumonia (HAP) based on whether they subsequently require mechanical ventilation has been shown to be important. Likewise, newer data indicate the true economic cost of NP and underscore the diverse range of pathogens that can cause NP. Moreover, multidrug-resistant (MDR) bacteria have become a major threat in NP. Fortunately, newer simple preventive strategies have been tested and found to be effective at reducing the incidence of NP. Should prevention fail, a range of new antibiotics have been formally studied in NP and found to be effective. Some of these novel agents have relatively broad ranges of activity and are in vitro active against select MDR organisms. Others, however, are narrower in spectrum and directed against specific problem bacteria. In short, the literature in the field of NP has progressed rapidly, and clinicians require a clear appreciation of these changes so as to improve patient outcomes.

Optimizing Treatment for Carbapenem-Resistant Acinetobacter baumannii Complex Infections: A Review of Current Evidence

Carbapenem-resistant Acinetobacter baumannii complex (CRAB) poses a significant global health challenge owing to its resistance to multiple antibiotics and limited treatment options. Polymyxin-based therapies have been widely used to treat CRAB infections; however, they are associated with high mortality rates and common adverse events such as nephrotoxicity. Recent developments include numerous observational studies and randomized clinical trials investigating antibiotic combinations, repurposing existing antibiotics, and the development of novel agents. Consequently, recommendations for treating CRAB are undergoing significant changes. The importance of colistin is decreasing, and the role of sulbactam, which exhibits direct antibacterial activity against A. baumannii complex, is being reassessed. High-dose ampicillin-sulbactam-based combination therapies, as well as combinations of sulbactam and durlobactam, which prevent the hydrolysis of sulbactam and binds to penicillin-binding protein 2, have shown promising results. This review introduces recent advancements in CRAB infection treatment based on clinical trial data, highlighting the need for optimized treatment protocols and comprehensive clinical trials to combat the evolving threat of CRAB effectively.

Treatment Strategies of Colistin Resistance Acinetobacter baumannii Infections

Acinetobacter baumannii has emerged as a pressing challenge in clinical practice, mainly due to the development of resistance to multiple antibiotics, including colistin, one of the last-resort treatments. This review highlights all the possible mechanisms of colistin resistance and the genetic basis contributing to this resistance, such as modifications to lipopolysaccharide or lipid A structures, alterations in outer membrane permeability via porins and heteroresistance. In light of this escalating threat, the review also evaluates available treatment options. The development of new antibiotics (cefiderocol, sulbactam/durlobactam) although not available everywhere, and the use of various combinations and synergistic drug combinations (including two or more of the following: a polymyxin, ampicillin/sulbactam, carbapenems, fosfomycin, tigecycline/minocycline, a rifamycin, and aminoglycosides) are discussed in the context of overcoming colistin resistance of A. baumannii infections. Although most studied combinations are polymyxin-based combinations, non-polymyxin-based combinations have been emerging as promising options. However, clinical data remain limited and continued investigation is essential to determine optimal therapeutic strategies against colistin-resistant A. baumannii.

Current treatment options for pneumonia caused by carbapenem-resistant Acinetobacter baumannii

PURPOSE OF REVIEW

The purpose of this review is to briefly summarize the challenges associated with the treatment of pneumonia caused by carbapenem-resistant Acinetobacter baumannii (CRAB), discuss its carbapenem-resistance, and review the literature supporting the current treatment paradigm and therapeutic options.

RECENT FINDINGS

In a multicenter, randomized, and controlled trial the novel β-lactam-β-lactamase inhibitor sulbactam-durlobactam was compared to colistin, both in addition to imipenem-cilastatin. The drug met the prespecified criteria for noninferiority for 28-day all-cause mortality while demonstrating higher clinical cure rates in the treatment of CRAB pneumonia. In an international, randomized, double-blind, placebo controlled trial colistin monotherapy was compared to colistin combined with meropenem. In this trial, combination therapy was not superior to monotherapy in the treatment of drug-resistant gram-negative organisms including CRAB pneumonia.

SUMMARY

CRAB pneumonia is a preeminent public health threat without an agreed upon first line treatment strategy. Historically, there have been drawbacks to available treatment modalities without a clear consensus on the first-line treatment regimen. CRAB pneumonia is a top priority for the continued development of antimicrobials, adjuvant therapies and refinement of current treatment strategies.

Carbapenem-resistant Acinetobacter baumannii and Ventilator-associated Pneumonia; Epidemiology, Risk Factors, and Current Therapeutic Approaches

Acinetobacter baumannii is one of the primary pathogens responsible for healthcare-associated infections. It is related to high rates of morbidity and mortality globally, mainly because of its high capacity to develop resistance to antimicrobials. Nowadays, carbapenem-resistant A. baumannii (CRAB) has increased and represents a significant concern among carbapenem-resistant organisms. It is also a key pathogen associated with ventilator-associated pneumonia. CRAB was placed on the critical group of the universal priority list of the World Health Organization for antibiotic-resistant bacteria, to mention the importance of research development and the urgency of new antibiotics. Patients with severe CRAB infections currently face significant treatment challenges. Some approaches have been taken to deal with CRAB, such as combination therapy and the synergistic effect of certain antibiotics, but the best antibiotic regimen is still unknown. In this narrative review, we attempt to clarify the issues, including epidemiology, risk factors, and current treatment options for CRAB.

Current Therapeutic Approaches for Multidrug-Resistant and Extensively Drug-Resistant Acinetobacter baumannii Infections

The treatment of Acinetobacter baumannii infections remains a challenge for physicians worldwide in the 21st century. The bacterium possesses a multitude of mechanisms to escape the human immune system. The consequences of A. baumannii infections on morbidity and mortality, as well on financial resources, remain dire. Furthermore, A. baumannii superinfections have also occurred during the COVID-19 pandemic. While prevention is important, the antibiotic armamentarium remains the most essential factor for the treatment of these infections. The main problem is the notorious resistance profile (including resistance to carbapenems and colistin) that this bacterium exhibits. While newer beta lactam/beta-lactamase inhibitors have entered clinical practice, with excellent results against various infections due to Enterobacteriaceae, their contribution against A. baumannii infections is almost absent. Hence, we have to resort to at least one of the following, sulbactam, polymyxins E or B, tigecycline or aminoglycosides, against multidrug-resistant (MDR) and extensively drug-resistant (XDR) A. baumannii infections. Furthermore, the notable addition of cefiderocol in the fight against A. baumannii infections represents a useful addition. We present herein the existing information from the last decade regarding therapeutic advances against MDR/XDR A. baumannii infections.

Characterization of bacteriophage vB_AbaS_SA1 and its synergistic effects with antibiotics against clinical multidrug-resistant Acinetobacter baumannii isolates

Acinetobacter baumannii is a major cause of nosocomial infections globally. The increasing prevalence of multidrug-resistant (MDR) A. baumannii has become an important public health concern. To combat drug resistance, alternative methods such as phage therapy have been suggested. In total, 30 MDR A. baumannii strains were isolated from clinical specimens, and their antibiotic susceptibilities were determined. The Acinetobacter phage vB_AbaS_SA1, isolated from hospital sewage, was characterized. In addition to its plaque size, particle morphology, and host range, its genome sequence was determined and annotated. Finally, the antibacterial effects of phage alone, antibiotics alone, and phage/antibiotic combinations were assessed against the A. baumannii strains. Phage vB_AbaS_SA1 had siphovirus morphology, showed a latent period of 20 min, and a 250 PFU/cell (plaque forming unit/cell) burst size. When combined with antibiotics, vB_AbaS_SA1 (SA1) showed a significant phage-antibiotic synergy effect and reduced the overall effective concentration of antibiotics in time-kill assessments. The genome of SA1 is a linear double-stranded DNA of 50 108 bp in size with a guanine-cytosine (GC) content of 39.15%. Despite the potent antibacterial effect of SA1, it is necessary to perform additional research to completely elucidate the mechanisms of action and potential constraints associated with utilizing this bacteriophage.

How to tailor recommendations on the treatment of multi-drug resistant Gram-negative infections at country level integrating antibiotic stewardship principles within the GRADE-ADOLOPMENT framework

Promoting the optimal use of antibiotics through evidence-based recommendations should be regarded as a crucial step in the global fight against antimicrobial resistance. Within this scope, several guidelines and guidance documents for antibiotic therapy have been published in recent years. All documents underline the limitations of existing evidence and remark on the need for tailoring recommendations at the national level, based on local epidemiology, availability of diagnostics and drugs, and antimicrobial stewardship principles. The GRADE-ADOLOPMENT methodology is an evidence-based methodology that allows the adoption, adaptation, and update of existing recommendations to specific settings without performing de novo systematic reviews and grading of the evidence. However, procedures to integrate this evidence with stewardship principles, countries' surveillance data, and capacity in terms of diagnostics and antibiotics' availability have never been defined. This Personal View provides the first example of a country's calibration of international evidence-based guidance documents on treating infections caused by multidrug-resistant bacteria. A panel of experts convened by the Italian Medicine Agency (AIFA) used the GRADE methodology for systematically extracting and evaluating 100 recommendations on the treatment of infections due to multidrug-resistant Gram-negative bacteria from 11 guidance documents and 24 systematic reviews. The ADOLOPMENT procedure was used to calibrate the existing recommendations to the national context, leading to the adoption of 64, the adaptation of 27, and the rejection of nine recommendations. We discuss the technical details of the GRADE-ADOLOPMENT application, the calibration process, and the human resources required to support such an effort. This Personal View also covers the challenges of integrating antibiotic stewardship principles in evidence-based recommendations for treating infections with very limited therapeutic and diagnostic options. The details presented here could support the easy transferability of the methodology to other countries and settings, particularly where the incidence of antibiotic-resistant infections is high.

Epidemiology and antimicrobial resistance trends of Acinetobacter species in the United Arab Emirates: a retrospective analysis of 12 years of national AMR surveillance data

INTRODUCTION

Acinetobacter spp., in particular A. baumannii, are opportunistic pathogens linked to nosocomial pneumonia (particularly ventilator-associated pneumonia), central-line catheter-associated blood stream infections, meningitis, urinary tract infections, surgical-site infections, and other types of wound infections. A. baumannii is able to acquire or upregulate various resistance determinants, making it frequently multidrug-resistant, and contributing to increased mortality and morbidity. Data on the epidemiology, levels, and trends of antimicrobial resistance of Acinetobacter spp. in clinical settings is scarce in the Gulf Cooperation Council (GCC) and Middle East and North Africa (MENA) regions.

METHODS

A retrospective 12-year analysis of 17,564 non-duplicate diagnostic Acinetobacter spp. isolates from the United Arab Emirates (UAE) was conducted. Data was generated at 317 surveillance sites by routine patient care during 2010-2021, collected by trained personnel and reported by participating surveillance sites to the UAE National AMR Surveillance program. Data analysis was conducted with WHONET.

RESULTS

Species belonging to the A. calcoaceticus-baumannii complex were mostly reported (86.7%). They were most commonly isolated from urine (32.9%), sputum (29.0%), and soft tissue (25.1%). Resistance trends to antibiotics from different classes during the surveillance period showed a decreasing trend. Specifically, there was a significant decrease in resistance to imipenem, meropenem, and amikacin. Resistance was lowest among Acinetobacter species to both colistin and tigecycline. The percentages of multidrug-resistant (MDR) and possibly extensively drug-resistant (XDR) isolates was reduced by almost half between the beginning of the study in 2010 and its culmination in 2021. Carbapenem-resistant Acinetobacter spp. (CRAB) was associated with a higher mortality (RR: 5.7), a higher admission to ICU (RR 3.3), and an increased length of stay (LOS; 13 excess inpatient days per CRAB case), as compared to Carbapenem-susceptible Acinetobacter spp.

CONCLUSION

Carbapenem-resistant Acinetobacter spp. are associated with poorer clinical outcomes, and higher associated costs, as compared to carbapenem-susceptible Acinetobacter spp. A decreasing trend of MDR Acinetobacter spp., as well as resistance to all antibiotic classes under surveillance was observed during 2010 to 2021. Further studies are needed to explore the reasons and underlying factors leading to this remarkable decrease of resistance over time.

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.

How to treat severe Acinetobacter baumannii infections

PURPOSE OF REVIEW

To update the management of severe Acinetobacter baumannii infections (ABI), particularly those caused by multi-resistant isolates.

RECENT FINDINGS

The in vitro activity of the various antimicrobial agents potentially helpful in treating ABI is highly variable and has progressively decreased for many of them, limiting current therapeutic options. The combination of more than one drug is still advisable in most circumstances. Ideally, two active first-line drugs should be used. Alternatively, a first-line and a second-line drug and, if this is not possible, two or more second-line drugs in combination. The emergence of new agents such as Cefiderocol, the combination of Sulbactam and Durlobactam, and the new Tetracyclines offer therapeutic options that need to be supported by clinical evidence.

SUMMARY

The apparent limitations in treating infections caused by this bacterium, the rapid development of resistance, and the serious underlying situation in most cases invite the search for alternatives to antibiotic treatment, the most promising of which seems to be bacteriophage therapy.

Guidelines for the diagnosis, treatment, prevention and control of infections caused by carbapenem-resistant gram-negative bacilli

The dissemination of carbapenem-resistant Gram-negative bacilli (CRGNB) is a global public health issue. CRGNB isolates are usually extensively drug-resistant or pandrug-resistant, resulting in limited antimicrobial treatment options and high mortality. A multidisciplinary guideline development group covering clinical infectious diseases, clinical microbiology, clinical pharmacology, infection control, and guideline methodology experts jointly developed the present clinical practice guidelines based on best available scientific evidence to address the clinical issues regarding laboratory testing, antimicrobial therapy, and prevention of CRGNB infections. This guideline focuses on carbapenem-resistant Enterobacteriales (CRE), carbapenem-resistant Acinetobacter baumannii (CRAB), and carbapenem-resistant Pseudomonas aeruginosa (CRPA). Sixteen clinical questions were proposed from the perspective of current clinical practice and translated into research questions using PICO (population, intervention, comparator, and outcomes) format to collect and synthesize relevant evidence to inform corresponding recommendations. The grading of recommendations, assessment, development and evaluation (GRADE) approach was used to evaluate the quality of evidence, benefit and risk profile of corresponding interventions and formulate recommendations or suggestions. Evidence extracted from systematic reviews and randomized controlled trials (RCTs) was considered preferentially for treatment-related clinical questions. Observational studies, non-controlled studies, and expert opinions were considered as supplementary evidence in the absence of RCTs. The strength of recommendations was classified as strong or conditional (weak). The evidence informing recommendations derives from studies worldwide, while the implementation suggestions combined the Chinese experience. The target audience of this guideline is clinician and related professionals involved in management of infectious diseases.

Antimicrobial Peptides in Infectious Diseases and Beyond-A Narrative Review

Despite recent medical research and clinical practice developments, the development of antimicrobial resistance (AMR) significantly limits therapeutics for infectious diseases. Thus, novel treatments for infectious diseases, especially in this era of increasing AMR, are urgently needed. There is ongoing research on non-classical therapies for infectious diseases utilizing alternative antimicrobial mechanisms to fight pathogens, such as bacteriophages or antimicrobial peptides (AMPs). AMPs are evolutionarily conserved molecules naturally produced by several organisms, such as plants, insects, marine organisms, and mammals, aiming to protect the host by fighting pathogenic microorganisms. There is ongoing research regarding developing AMPs for clinical use in infectious diseases. Moreover, AMPs have several other non-medical applications in the food industry, such as preservatives, animal husbandry, plant protection, and aquaculture. This review focuses on AMPs, their origins, biology, structure, mechanisms of action, non-medical applications, and clinical applications in infectious diseases.

Antimicrobial Resistance in Ventilator-Associated Pneumonia: Predictive Microbiology and Evidence-Based Therapy

Ventilator-associated pneumonia (VAP) is a serious intensive care unit (ICU)-related infection in mechanically ventilated patients that is frequent, as more than half of antibiotics prescriptions in ICU are due to VAP. Various risk factors and diagnostic criteria for VAP have been referred to in different settings. The estimated attributable mortality of VAP can go up to 50%, which is higher in cases of antimicrobial-resistant VAP. When the diagnosis of pneumonia in a mechanically ventilated patient is made, initiation of effective antimicrobial therapy must be prompt. Microbiological diagnosis of VAP is required to optimize timely therapy since effective early treatment is fundamental for better outcomes, with controversy continuing regarding optimal sampling and testing. Understanding the role of antimicrobial resistance in the context of VAP is crucial in the era of continuously evolving antimicrobial-resistant clones that represent an urgent threat to global health. This review is focused on the risk factors for antimicrobial resistance in adult VAP and its novel microbiological tools. It aims to summarize the current evidence-based knowledge about the mechanisms of resistance in VAP caused by multidrug-resistant bacteria in clinical settings with focus on Gram-negative pathogens. It highlights the evidence-based antimicrobial management and prevention of drug-resistant VAP. It also addresses emerging concepts related to predictive microbiology in VAP and sheds lights on VAP in the context of coronavirus disease 2019 (COVID-19).

Navigating Available Treatment Options for Carbapenem-Resistant Acinetobacter baumannii-calcoaceticus Complex Infections

Carbapenem-resistant Acinetobacter baumannii-calcoaceticus complex (CRAB) is one of the top-priority pathogens for new antibiotic development. Unlike other antibiotic-resistant threats, none of the available therapies have been shown to consistently reduce mortality or improve patient outcomes in clinical trials. Antibiotic combination therapy is routinely used in clinical practice; however, the preferred combination has not been defined. This narrative review focuses on evidence-based solutions for the treatment of invasive CRAB infections. We dissect the promise and perils of traditional agents used in combination, such as colistin, sulbactam, and the tetracyclines, and offer clinical pearls based on our interpretation of the available data. Next, we investigate the merits of newly developed β-lactam agents like cefiderocol and sulbactam-durlobactam, which have demonstrated contrasting results in recent randomized clinical trials. The review concludes with the authors' perspective on the evolving treatment landscape for CRAB infections, which is complicated by limited clinical data, imperfect treatment options, and a need for future clinical trials. We propose that effective treatment for CRAB infections requires a personalized approach that incorporates host factors, the site of infection, pharmacokinetic-pharmacodynamic principles, local molecular epidemiology of CRAB isolates, and careful interpretation of antibiotic susceptibility testing results. In most clinical scenarios, a dose-optimized, sulbactam-based regimen is recommended with the addition of at least one other in vitro active agent. Should sulbactam-durlobactam receive regulatory approval, recommendations will need to be re-evaluated with the most recent evidence.

Cefiderocol-Based versus Colistin-Based Regimens for Severe Carbapenem-Resistant Acinetobacter baumannii Infections: A Propensity Score-Weighted, Retrospective Cohort Study during the First Two Years of the COVID-19 Pandemic

BACKGROUND

A large increase in multi-drug-resistant Acinetobacter baumannii, especially carbapenem-resistant strains, occurred during the first two years of the COVID-19 pandemic, posing important challenges in its treatment. Cefiderocol appeared to be a good option for the treatment of Carbapenem-resistant Acinetobacter baumannii (CR-Ab), but to date, the guidelines and evidence available are conflicting.

METHODS

We retrospectively included a group of patients with CR-Ab infections (treated with colistin- or cefiderocol-based regimens) at Padua University Hospital (August 2020-July 2022) and assessed predictors of 30-day mortality, and differences in microbiological and clinical treatment. To evaluate the difference in outcomes, accounting for the imbalance in antibiotic treatment allocation, a propensity score weighting (PSW) approach was adopted.

RESULTS

We included 111 patients, 68% males, with a median age of 69 years (IQR: 59-78). The median duration of antibiotic treatment was 13 days (IQR:11-16). In total, 60 (54.1%) and 51 (45.9%) patients received cefiderocol- and colistin-based therapy, respectively. Notably, 53 (47.7%) patients had bloodstream infections, while 58 (52.3%) had pneumonia. Colistin was combined in 96.1%, 80.4%, and 5.8% of cases with tigecycline, meropenem, and fosfomycin, respectively. Cefiderocol was combined in 13.3%, 30%, and 18.3% of cases with fosfomycin, tigecycline, and meropenem, respectively. At the baseline, the two treatment groups significantly differed in age (patients treated with colistin were significantly older), the prevalence of diabetes and obesity (more frequent in the group treated with colistin), length of stay (longer in the group receiving cefiderocol), and type of infection (BSI were more frequent in the group receiving cefiderocol). The proportion of patients who developed acute kidney injury was significantly higher in the colistin group. By using PSW, no statistically significant differences emerged for mortality or clinical and microbiological cure between the two groups. No independent predictors were detected for hospital mortality or clinical cure, while for the length of stay, the only selected predictor was age, with a non-linear effect (p-value 0.025 for non-linearity) on the prolongation of hospital stay of 0.25 days (95% CI 0.10-0.39) at increasing ages (calculated over the IQR).

CONCLUSIONS

Cefiderocol treatment did not differ in terms of main outcomes and safety profile from colistin-based regimens. More prospective studies with a larger number of patients are required to confirm our results.

Enhanced bacterial killing with a combination of sulbactam/minocycline against dual carbapenemase-producing Acinetobacter baumannii

Carbapenem-resistant Acinetobacter baumannii (CRAB) is often difficult to treat. Considering the current circumstances, there is an unquestionable need for new therapeutic options to treat CRAB infections. In the present study, the synergistic activity of sulbactam-based combination was determined against genetically characterized CRAB isolates. Non-duplicate CRAB isolates (n = 150) recovered from blood culture and endotracheal aspirates were included in this study. The minimum inhibitory concentrations (MICs) of tetracyclines (minocycline, tigecycline, eravacycline) and their comparators (meropenem, sulbactam, cefoperazone/sulbactam, ceftazidime/avibactam, and colistin) were determined using the microbroth dilution method. Six isolates were tested for the synergistic activity of various sulbactam-based combinations using time-kill experiments. Tigecycline and minocycline showed a wide spread of MICs with most isolates in the range of 1 to 16 mg/L. The MIC₉₀ of eravacycline (0.5 mg/L) was four dilutions lower than that of tigecycline (8 mg/L). Minocycline with sulbactam was the most active dual combination against OXA-23 like (n = 2) and NDM with OXA-23 like producers (n = 1), which resulted in ≥ 2 log₁₀ kill. The combination of ceftazidime-avibactam with sulbactam showed ≥ 3 log₁₀ kill against all the three tested OXA-23 like producing CRAB isolates, but showed no activity against dual carbapenemase producers. Sulbactam with meropenem showed ≥ 2 log₁₀ kill against one OXA-23 like producing CRAB isolate. The findings suggest that sulbactam-based combination may confer therapeutic benefits against CRAB infections.

The known-unknown: third- and fourth-generation cephalosporins combined with sulbactam

Despite the presence of more than 100 different antibacterials in the therapeutic arsenal, beta-lactam antibiotics, in general, and the third-generation cephalosporins, in particular, remain the main option for the treatment of the most of infections in inpatients. At the same time, the widespread and oftentimes inappropriate use of the third-generation cephalosporins in Russian hospitals lead to the emergence and spread of antimicroabial resistance. The review covers the problems of antibiotic resistance to cephalosporins due to the production of beta-lactamases, the role of beta-lactamase inhibitors in overcoming this type of resistance, options for combinations of cephalosporins with beta-lactamase inhibitors, in vitro activity of cefotaxime/sulbactam and cefepime/sulbactam, the results of clinical studies, and the role of the above combinations in the treatment of infections in the hospital.

A fresh pH-responsive imipenem-loaded nanocarrier against Acinetobacter baumannii with a synergetic effect

In recent years, the treatment of Acinetobacter baumannii infections has become a pressing clinical challenge due to its increasing incidence and its serious pathogenic risk. The research and development of new antibacterial agents for A. baumannii have attracted the attention of the scientific community. Therefore, we have constructed a new pH-responsive antibacterial nano-delivery system (Imi@ZIF-8) for the antibacterial treatment of A. baumannii. Due to its pH-sensitive characteristics, the nano-delivery system offers an improved release of the loaded imipenem antibiotic at the acidic infection site. Based on the high loading capacity and positive charge of the modified ZIF-8 nanoparticles, they are excellent carriers and are suitable for imipenem loading. The Imi@ZIF-8 nanosystem features synergistic antibacterial effects, combining ZIF-8 and imipenem to eliminate A. baumannii through different antibacterial mechanisms. When the loaded imipenem concentration reaches 20 µg/mL, Imi@ZIF-8 is highly effective against A. baumannii in vitro. Imi@ZIF-8 not only inhibits the biofilm formation of A. baumannii but also has a potent killing effect. Furthermore, in mice with celiac disease, the Imi@ZIF-8 nanosystem demonstrates excellent therapeutic efficacy against A. baumannii at imipenem concentrations of 10 mg/kg, and it can inhibit inflammatory reaction and local leukocyte infiltration. Due to its biocompatibility and biosafety, this nano-delivery system is a promising therapeutic strategy in the clinical treatment of A. baumannii infections, providing a new direction for the treatment of antibacterial infections.