Minocycline susceptibility breakpoints for Acinetobacter baumannii: do we need to re-evaluate them?

Optimizing Antibiotic Therapy for Stenotrophomonas maltophilia Infections in Critically Ill Patients: A Pharmacokinetic/Pharmacodynamic Approach

Stenotrophomonas maltophilia is an opportunistic, multidrug-resistant non-fermentative Gram-negative bacillus, posing a significant challenge in clinical treatment due to its numerous intrinsic and acquired resistance mechanisms. This study aimed to evaluate the adequacy of antibiotics used for the treatment of S. maltophilia infections in critically ill patients using a pharmacokinetic/pharmacodynamic (PK/PD) approach. The antibiotics studied included cotrimoxazole, levofloxacin, minocycline, tigecycline, cefiderocol, and the new combination aztreonam/avibactam, which is not yet approved. By Monte Carlo simulations, the probability of target attainment (PTA), the PK/PD breakpoints, and the cumulative fraction of response (CFR) were estimated. PK parameters and MIC distributions were sourced from the literature, the European Committee on Antimicrobial Susceptibility Testing (EUCAST), and the SENTRY Antimicrobial Surveillance Program collection. Cefiderocol 2 g q8h, minocycline 200 mg q12h, tigecycline 100 mg q12h, and aztreonam/avibactam 1500/500 mg q6h were the best options to treat empirically infections due to S. maltophilia. Cotrimoxazole provided a higher probability of treatment success for the U.S. isolates than for European isolates. For all antibiotics, discrepancies between the PK/PD breakpoints and the clinical breakpoints defined by EUCAST (or the ECOFF) and CLSI were detected.

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.

Combination eravacycline therapy for ventilator-associated pneumonia due to carbapenem-resistant Acinetobacter baumannii in patients with COVID-19: A case series

BACKGROUND

Carbapenem-resistant Acinetobacter baumannii (CRAB) pneumonia is associated with poor clinical outcomes and increased mortality. Clinical data regarding the optimal treatment of CRAB is limited, and combination therapy is often preferred. Eravacycline has demonstrated in-vitro activity against A. baumannii and has been considered for the treatment of pulmonary infections caused by CRAB.

OBJECTIVE

The objective of this case series was to describe clinical outcomes associated with eravacycline when utilized as part of a combination regimen for the treatment of CRAB pneumonia at a county hospital.

METHODS

A retrospective chart review was conducted from April 1, 2020, to October 1, 2020, which included hospitalized patients ≥18 years of age, diagnosed with coronavirus disease 2019 (COVID-19), with a sputum culture positive for CRAB, and receipt of at least one dose of eravacycline. The primary outcome studied was clinical resolution of CRAB pneumonia. A key secondary outcome was microbiological resolution.

RESULTS

A total of 24 patients received combination eravacycline therapy for a median of 10.5 days. Overall, 17 (71%) patients demonstrated clinical resolution of CRAB pneumonia. Repeat sputum cultures post-treatment were collected in 17 (71%) patients, of which 12 (71%) achieved microbiological resolution. No adverse events attributable to eravacycline were identified.

CONCLUSION

With limited viable salvage treatment options, combination eravacycline therapy showed favorable microbiological and clinical outcomes in patients with CRAB pneumonia. In light of this, eravacycline could be considered as a potential treatment option when designing CRAB pneumonia salvage therapy regimens.

In vitro antimicrobial susceptibility data of global meropenem-resistant Acinetobacter baumannii isolates causing pneumonia: Data from the Antimicrobial Testing Leadership and Surveillance Program, 2014-2021, and re-estimations of susceptibility breakpoints and appropriate dosages of important antibiotics for pneumonia treatment

OBJECTIVES

To evaluate the susceptibility of globally pneumonia-causing meropenem-resistant (MEM-R) Acinetobacter baumannii isolates against important antibiotics and estimate appropriate dosages of indicated antibiotics.

METHODS

We extracted the 2014-2021 Antimicrobial Testing of Leadership Surveillance database regarding the susceptibility of MEM-R A. baumannii isolates causing pneumonia against important antibiotics. The susceptibility and carbapenemase-encoding gene (CPEG) data of pneumonia-causing MEM-R A. baumannii isolates from patients hospitalized in intensive care units of five major regions were analyzed. The susceptibility breakpoints (SBP) recommended by the Clinical and Laboratory Standards Institute (CLSI) in 2022, other necessary criteria [SBP of MIC for colistin, 2 mg/L, in the CLSI 2018; and cefoperazone-sulbactam (CFP-SUL), 16 mg/L], and the pharmacokinetic and pharmacodynamic data of indicated antibiotics were employed.

RESULTS

Applying the aforementioned criteria, we observed the susceptible rates of colistin, minocycline, and CFP-SUL against the pneumonia-causing MEM-R A. baumannii isolates globally (n = 2905) were 93.2%, 69.1%, and 26.3%, respectively. Minocycline was significantly more active in vitro (MIC ≤4 mg/L) against the pneumonia-causing MEM-R A. baumannii isolates collected from North and South America compared to those from other regions (>90% vs. 58-72%). Additionally, blaOXA-23 and blaOXA-72 were the predominant CPEG in pneumonia-causing MEM-R A. baumannii isolates.

CONCLUSIONS

After deliberative estimations, dosages of 200 mg minocycline intravenously every 12 h (SBP, 8 mg/L), 100 mg tigecycline intravenously every 12 h (SBP, 1 mg/L), and 160 mg nebulized colistin methanesulphonate every 8 h (SBP, 2 mg/L) are needed for the effective treatment of pneumonia-causing MEM-R A. baumannii isolates.

Trends in the susceptibility of U.S. Acinetobacter baumannii-calcoaceticus species complex and Stenotrophomonas maltophilia isolates to minocycline, 2014-2021

IMPORTANCE

Acinetobacter baumannii-calcoaceticus species complex and Stenotrophomonas maltophilia are opportunistic, non-fermentative Gram-negative organisms that can cause serious hospital-acquired infections in immunocompromised patients. These pathogens are inherently resistant to several common drug classes and often acquire other resistance mechanisms, making them difficult to treat. In this study, we analyzed the trends of susceptibility of over 2,500 U.S. bacterial isolates collected from hospitalized patients over an 8-year period to minocycline, which is used to treat infections caused by these pathogens. These in vitro data suggest that minocycline is a useful treatment option for infections caused by Acinetobacter baumannii-calcoaceticus species complex or Stenotrophomonas maltophilia.

Laboratory Surveillance of Acinetobacter spp. Bloodstream Infections in a Tertiary University Hospital during a 9-Year Period

Multidrug-resistant Acinetobacter baumannii infections have become a threat for public health worldwide. The aim of the present study was to follow-up resistance patterns of Acinetobacter spp. bloodstream isolates in a Tertiary University Hospital over the last nine years, from 2014 to 2022. Susceptibility patterns were followed for the following antimicrobial agents: amikacin, gentamicin, tobramycin, ciprofloxacin, levofloxacin, imipenem, meropenem, tigecycline, trimethoprim/sulfamethoxazole, and colistin. Minimal inhibitory concentration (MIC) values to ampicillin/sulbactam, cefepime, ceftazidime, minocycline, piperacillin/tazobactam were evaluated from 2020 to 2023. During the study period, 853 Acinetobacter spp. bloodstream infections (BSIs) were recorded, accounting for 5.36% of all BSIs. A. baumannii was isolated in 795 cases (93.2%), during the study period. Most BSIs were recorded in adult intensive care units (ICU) (46.2%) and medical wards (42%). Among A. baumannii isolates, 4.5% were multidrug-resistant, 84.7% were extensively drug-resistant, and 8.5% were pandrug-resistant. Resistance to carbapenems was over 95%. Resistance to tigecycline increased significantly during the last years of the study (2020-2022); A. baumannii isolates with MIC ≤ 2 μg/mL accounted for 28.5% of all isolates. Resistance to colistin exhibited an increasing pattern up to 42.2% in 2022. Increasing resistance rates and the evolution of pandrug-resistant isolates call for the urgent application of preventive and response actions.

Minocycline Susceptibility and tetB Gene in Carbapenem-Resistant Acinetobacter baumannii in Taiwan

Purpose

In this study, we evaluated the minocycline susceptibility rate in carbapenem-resistant Acinetobacter baumannii (CRAB) clinical strains, and the association between tetB carriage and minocycline susceptibility in CRAB.

Patients and Methods

A total of 100 genetically unrelated CRAB clinical strains from bloodstream infection were randomly collected from a medical center in Taiwan. An argument for a new minocycline susceptibility breakpoint of 1 mg/L was suggested based on pharmacokinetic (PK) and pharmacodynamic (PD) studies. Strains with minocycline minimum inhibitory concentrations (MICs) of >1 mg/L were classified as PK-PD non-susceptible. TetB carriage was detected by polymerase chain reaction (PCR).

Results

Fifty-five (55%) CRAB strains were susceptible to minocycline according to the Clinical and Laboratory Standards Institute (CLSI) criteria, among which 98.2% (54/55) were PK-PD non-susceptible. The minocycline MIC_50/90 was 4/16 mg/L. Ninety-seven (97%) strains carried tetB. All of the tetB-positive strains and 66.7% (2/3) of the tetB-negative strains were PK-PD non-susceptible. By statistical analysis, tetB carriage was significantly correlated with PK-PD non-susceptibility (P = 0.03) and a higher minocycline MIC (P = 0.02). The sensitivity and specificity of the tetB PCR for predicting PK-PD non-susceptibility were 98% and 100%, respectively.

Conclusion

At our institute, most CRAB strains were PK-PD non-susceptible and most carried tetB gene. Recognizing the minocycline MIC and tetB status may be essential when using minocycline to treat CRAB-related infections.

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.

Pandrug-resistant Gram-negative bacteria: a systematic review of current epidemiology, prognosis and treatment options

BACKGROUND

The literature on the epidemiology, mortality and treatment of pandrug-resistant (PDR) Gram-negative bacteria (GNB) is scarce, scattered and controversial.

OBJECTIVES

To consolidate the relevant literature and identify treatment options for PDR GNB infections.

METHODS

A systematic search in MEDLINE, Scopus and clinical trial registries was conducted. Studies reporting PDR clinical isolates were eligible for review if susceptibility testing for all major antimicrobials had been performed. Characteristics and findings of retrieved studies were qualitatively synthesized.

RESULTS

Of 81 studies reviewed, 47 (58%) were published in the last 5 years. The reports reflected a worldwide dissemination of PDR GNB in 25 countries in 5 continents. Of 526 PDR isolates reported, Pseudomonas aeruginosa (n=175), Acinetobacter baumannii (n=172) and Klebsiella pneumoniae (n=125) were most common. PDR GNB were typically isolated in ICUs, but several studies demonstrated wider outbreak potential, including dissemination to long-term care facilities and international spread. All-cause mortality was high (range 20%-71%), but appeared to be substantially reduced in studies reporting treatment regimens active in vitro. No controlled trial has been performed to date, but several case reports and series noted successful use of various regimens, predominantly synergistic combinations, and in selected patients increased exposure regimens and newer antibiotics.

CONCLUSIONS

PDR GNB are increasingly being reported worldwide and are associated with high mortality. Several treatment regimens have been successfully used, of which synergistic combinations appear to be most promising and often the only available option. More pharmacokinetic/pharmacodynamic and outcome studies are needed to guide the use of synergistic combinations.

In Vitro Activity of Minocycline Against Multidrug-Resistant Acinetobacter baumannii Isolates-Evaluation of Clinical Breakpoints and Review of Literature

Therapeutic options for the treatment of infections by multidrug-resistant Acinetobacter baumannii strains are often limited. Minocycline (MIN) is an old antibiotic, with excellent activity against A. baumannii isolates, which can be administered orally. Currently, there is no single criterion regarding the breakpoints for MIN and A. baumannii. The activity of MIN was examined against a collection of A. baumannii isolates recovered from 15 hospitals of 6 countries of South America. A review of the literature was also performed. In our series and most of the studies, the percentages of MIN susceptible isolates exceeded 50%, regardless of the breakpoints utilized (4-2 or 1 μg/mL). However, a greater number of isolates not harboring Tet B were considered resistant with the breakpoints of 1 or 2 μg/mL, whereas isolates with tet(B) genes were still detected with minimum inhibitory concentration below all breakpoints considered. Tetracycline susceptibility may be used as a screening to discriminate the populations with and without acquired resistance mechanisms to MIN. In this study, MIN-resistant subpopulations were found in isolates harboring Tet B, with MIC ≤1 μg/mL, and their frequency increased after incubation with MIN. These subpopulations were not detected in isolates not harboring Tet B. The clinical correlation of these subpopulations should be evaluated in future studies.

Treatment options for K. pneumoniae, P. aeruginosa and A. baumannii co-resistant to carbapenems, aminoglycosides, polymyxins and tigecycline: an approach based on the mechanisms of resistance to carbapenems

The management of carbapenem-resistant infections is often based on polymyxins, tigecycline, aminoglycosides and their combinations. However, in a recent systematic review, we found that Gram-negative bacteria (GNB) co-resistant to carbapanems, aminoglycosides, polymyxins and tigecycline (CAPT-resistant) are increasingly being reported worldwide. Clinical data to guide the treatment of CAPT-resistant GNB are scarce and based exclusively on few case reports and small case series, but seem to indicate that appropriate (in vitro active) antimicrobial regimens, including newer antibiotics and synergistic combinations, may be associated with lower mortality. In this review, we consolidate the available literature to inform clinicians dealing with CAPT-resistant GNB about treatment options by considering the mechanisms of resistance to carbapenems. In combination with rapid diagnostic methods that allow fast detection of carbapenemase production, the approach proposed in this review may guide a timely and targeted treatment of patients with infections by CAPT-resistant GNB. Specifically, we focus on the three most problematic species, namely Klebsiella pneumoniae, Pseudomonas aeruginosa and Acinetobacter baumannii. Several treatment options are currently available for CAPT-resistant K. pneumonia. Newer β-lactam-β-lactamase combinations, including the combination of ceftazidime/avibactam with aztreonam against metallo-β-lactamase-producing isolates, appear to be more effective compared to combinations of older agents. Options for P. aeruginosa (especially metallo-β-lactamase-producing strains) and A. baumannii remain limited. Synergistic combination of older agents (e.g., polymyxin- or fosfomycin-based synergistic combinations) may represent a last resort option, but their use against CAPT-resistant GNB requires further study.

Isothermal microcalorimetry minimal inhibitory concentration testing in extensively drug resistant Gram-negative bacilli: a multicentre study

OBJECTIVES

To evaluate the performance of an isothermal microcalorimetry (IMC) method for determining the MICs among extensively drug-resistant Gram-negative bacilli.

METHODS

A collection of 320 clinical isolates (n = 80 of each) of Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa and Acinetobacter baumannii from Sweden, Spain, Italy and the Netherlands were tested. The MICs were determined using the IMC device calScreener (Symcel, Stockholm, Sweden) and ISO-broth microdilution as the reference method. Essential agreement, categorical agreement, very major errors (VME), major errors (ME) and minor (mE) errors for each antibiotic were determined.

RESULTS

Data from 316 isolates were evaluated. Four errors (two ME, one VME, one mE) among 80 K. pneumoniae, six errors (four ME, one VME, one mE) among 79 E. coli, 15 errors (seven VME, three ME, five mE) among 77 P. aeruginosa and 18 errors (12 VME, two ME, four mE) among 80 A. baumannii were observed. Average essential agreement and categorical agreement of the IMC method were 96.6% (95% confidence interval, 94.2-99) and 97.1% (95% confidence interval, 95.4-98.5) respectively when the MICs were determined at the end of 18 hours. Categorical agreement of the IMC method for prediction of MIC by the end of 8 hours for colistin, meropenem, amikacin, ciprofloxacin and piperacillin/tazobactam were 95%, 91.4%, 94%, 95.2% and 93.7% respectively.

CONCLUSIONS

The IMC method could accurately determine the MICs among extensively drug-resistant clinical isolates of E. coli, K. pneumoniae, P. aeruginosa and A. baumannii isolates.

The Role of Minocycline in the Treatment of Nosocomial Infections Caused by Multidrug, Extensively Drug and Pandrug Resistant Acinetobacter baumannii: A Systematic Review of Clinical Evidence

Treatment options for multidrug resistant Acinetobacter baumannii strains (MDR-AB) are limited. Minocycline has been used alone or in combination in the treatment of infections associated with AB. A systematic review of the clinical use of minocycline in nosocomial infections associated with MDR-AB was performed according to the PRISMA-P guidelines. PubMed-Medline, Scopus and Web of Science ^TM databases were searched from their inception until March 2019. Additional Google Scholar free searches were performed. Out of 2990 articles, 10 clinical studies (9 retrospective case series and 1 prospective single center trial) met the eligibility criteria. In total, 223 out of 268 (83.2%) evaluated patients received a minocycline-based regimen; and 200 out of 218 (91.7%) patients with available data received minocycline as part of a combination antimicrobial regimen (most frequently colistin or carbapenems). Pneumonia was the most common infection type in the 268 cases (80.6% with 50.4% ventilator-associated pneumonia). The clinical and microbiological success rates following minocycline treatment were 72.6% and 60.2%, respectively. Mortality was 20.9% among 167 patients with relevant data. In this systematic review, minocycline demonstrated promising activity against MDR-AB isolates. This review sets the ground for further studies exploring the role of minocycline in the treatment of MDR-AB associated infections.