Hydroxyhexylitaconic acids as potent IMP-type metallo-ß-lactamase inhibitors for controlling carbapenem resistance in Enterobacterales.

Metallo-ß-lactamases (MBLs) represent one of the main causes of carbapenem resistance in the order Enterobacterales. To combat MBL-producing carbapenem-resistant Enterobacterales, the development of MBL inhibitors can restore carbapenem efficacy for such resistant bacteria. Microbial natural products are a promising source of attractive seed compounds for the development of antimicrobial agents. Here, we report that hydroxyhexylitaconic acids (HHIAs) produced by a member of the genus Aspergillus can suppress carbapenem resistance conferred by MBLs, particularly IMP (imipenemase)-type MBLs. HHIAs were found to be competitive inhibitors with micromolar orders of magnitude against IMP-1 and showed weak inhibitory activity toward VIM-2, while no inhibitory activity against NDM-1 was observed despite the high dosage. The elongated methylene chains of HHIAs seem to play a crucial role in exerting inhibitory activity because itaconic acid, a structural analog without long methylene chains, did not show inhibitory activity against IMP-1. The addition of HHIAs restored meropenem and imipenem efficacy to satisfactory clinical levels against IMP-type MBL-producing Escherichia coli and Klebsiella pneumoniae clinical isolates. Unlike EDTA and Aspergillomarasmine A, HHIAs did not cause the loss of zinc ions from the active site, resulting in the structural instability of MBLs. X-ray crystallography and in silico docking simulation analyses revealed that two neighboring carboxylates of HHIAs coordinated with two zinc ions in the active sites of VIM-2 and IMP-1, which formed a key interaction observed in MBL inhibitors. Our results indicated that HHIAs are promising for initiating the design of potent inhibitors of IMP-type MBLs.IMPORTANCEThe number and type of metallo-ß-lactamase (MΒL) are increasing over time. Carbapenem resistance conferred by MΒL is a significant threat to our antibiotic regimen, and the development of MΒL inhibitors is urgently required to restore carbapenem efficacy. Microbial natural products have served as important sources for developing antimicrobial agents targeting pathogenic bacteria since the discovery of antibiotics in the mid-20th century. MΒL inhibitors derived from microbial natural products are still rare compared to those derived from chemical compound libraries. Hydroxyhexylitaconic acids (HHIAs) produced by members of the genus Aspergillus have potent inhibitory activity against clinically relevant IMP-type MBL. HHIAs may be good lead compounds for the development of MBL inhibitors applicable for controlling carbapenem resistance in IMP-type MBL-producing Enterobacterales.

Colistin monotherapy or combination for the treatment of bloodstream infection caused by Klebsiella pneumoniae: a systematic review and meta-analysis.

BACKGROUND: Bloodstream infection of Klebsiella pneumoniae (BSI-KP) were associated with increased mortality. Klebsiella pneumoniae was tested to susceptible to colistin by E-test and broth microdilution method in clinical laboratory. This study aimed to assess the efficacy of colistin versus tigecycline, carbapenem monotherapy and combination in the treatment of BSI-KP. METHODS: Electronic databases such as PubMed, Web of Science and Embase were searched. The last search was in November 24th, 2022, addressing the colistin, carbapenems and tigecycline monotherapy and combination treatments in patients with BSI-KP. The primary outcomes were 30-day or 28-day mortality. OR where available with 95% CI were pooled in random-effects meta-analysis. RESULTS: Following the outlined search strategy, a total of 658 articles were identified from the initial database searching. Six studies, 17 comparisons were included. However, they all were observational design, lacking high-quality randomized controlled trials (RCTs). Moderate or low-quality evidences suggested that colistin monotherapy was associated with an OR = 1.35 (95% CI = 0.62-2.97, P = 0.45, Tau2 = 0.00, I2 = 0%) compared with tigecycline monotherapy, OR = 0.81 (95% CI = 0.27-2.45, P = 0.71, Tau2 = 0.00, I2 = 0%) compared with carbapenem monotherapy. Compared with combination with tigecycline or carbapenem, Colistin monotherapy resulted in OR of 3.07 (95% CI = 1.34-7.04, P = 0.008, Tau2 = 0.00, I2 = 0%) and 0.98 (95%CI = 0.29-3.31, P = 0.98, Tau2 = 0.00, I2 = 0% ), respectively. CONCLUSIONS: Colistin, carbapenem and tigecycline monotherapy showed similar treatment effects in patients who suffered from BSI-KP. Compared with colistin monotherapy, colistin combined tigecycline therapy might play the synergism effects. TRIAL REGISTRATION: retrospectively registered.

Detection of rare carbapenemases in Enterobacterales-comparison of two colorimetric and three CIM-based carbapenemase assays.

Rapid and reliable detection of carbapenemase-producing Enterobacterales (CPE) is crucial for prompt treatment and infection control. Most assays target the primary four enzymes (KPC, OXA-48-like, VIM, and NDM), often missing less common variants (e.g., GES, IMI, OXA-23, and OXA-58). Therefore, assays based on the hydrolysis of carbapenems are recommended in addition to differentiation tests such as PCR or immunochromatographic assays. The aim of this study was to compare the currently Clinical and Laboratory Standards Institute (CLSI)-recommended tests mCIM (modified carbapenem inactivation method) and Carba NP with new colorimetric tests (NitroSpeed-Carba NP) and novel variations of the carbapenem inactivation method (CIM) such as simplified CIM (sCIM) or modified zinc-supplemented CIM (mzCIM). The challenge collection included 205 clinical isolates, 139 CPE vs 66 non-CPE. Among all 205 isolates, the sensitivity/specificity of mCIM was 81.3%/98.5%, Carba NP 76.3%/100%, NitroSpeed-Carba NP 86.3%/78.8%, sCIM 100%/94%, and mzCIM 97.8%/98.5%. For rare carbapenemases (n = 48), the sensitivity of mzCIM (98.3%) and sCIM (100%) was higher than that of mCIM (60.4%), Carba NP (50%), or NitroSpeed-Carba NP (70.2%). Most indeterminate results occurred for mCIM (14.4%), Carba NP (8.2%), and sCIM (6.3%). The detection of rare carbapenemases remains challenging with the currently recommended assays. The CIM-based tests demonstrated superior sensitivity, with sCIM and mzCIM outperforming the currently recommended mCIM and Carba NP, especially among isolates with weakly hydrolyzing carbapenemases (e.g., OXA-23 and OXA-58). Although colorimetric assays provide more rapid results, laboratories have to be aware of the low sensitivity for rare carbapenemases. Both sCIM and the new mzCIM performed well, are cost-effective, and can easily be implemented in any laboratory.IMPORTANCEDetection of so-called rare carbapenemases (e.g., GES, IMI, OXA-23, and OXA-58) in Enterobacterales is challenging, and data on the performance of currently available assays are scarce. This study systematically assessed the performance of currently recommended and novel hydrolysis-based assays on a set of molecularly characterized isolates. It demonstrates that the currently recommended assays mCIM and Carba NP perform well on isolates producing common carbapenemases such as KPC, VIM, NDM, and OXA-48, but have only a moderate sensitivity in the detection of rare carbapenemases. In contrast, the newer CIM-based variants, sCIM and mzCIM, are equally capable of detecting frequent and uncommon carbapenemases. These assays could potentially help to improve our knowledge on the epidemiology of these "rare" enzymes.

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 ß-lactam-ß-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.

Clinical efficacy of cefiderocol-based regimens in patients with carbapenem-resistant Acinetobacter baumannii infections: A systematic review with meta-analysis.

OBJECTIVES: To perform a systematic review with meta-analysis to assess the clinical efficacy of cefiderocol-based regimens for the treatment of carbapenem-resistant Acinetobacter baumannii (CRAB) infections. METHODS: Two authors independently searched PubMed-MEDLINE, Scopus, and Cochrane databases, from inception to 02 July 2023, for randomised controlled trials (RCTs) or observational studies comparing clinical efficacy of cefiderocol-based vs. non-cefiderocol-based regimens in patients with CRAB infections. Data were extracted by the two authors independently, and the quality of included studies was independently assessed using ROB 2.0 or ROBINS-I tools. Primary outcome was mortality rate. Meta-analysis was performed by pooling odds ratios (ORs) retrieved from studies providing adjustment for confounders using a random-effects model with the inverse variance method. Multiple subgroups and sensitivity analyses were conducted to investigate the source of heterogeneity. RESULTS: A total of 530 articles were screened, and 6 studies (1 RCT and 5 observational; N=561; 247 cefiderocol-based vs. 314 non-cefiderocol-based regimens) were included. Cefiderocol did not significantly reduce in-hospital mortality compared to alternative therapies (predominantly colistin-based), but the confidence intervals around the effect estimate included clinically important benefit (N=5; OR 0.64; 95%CI 0.40-1.04; I2=57.5%). When only observational studies providing adjustment for confounders were considered, a lower risk of mortality was found in patients treated with cefiderocol-based regimens (N=4; OR 0.53; 95%CI 0.39-0.71; I2=0.0%). CONCLUSIONS: Cefiderocol-based regimens were associated with a significantly lower risk of mortality in patients with CRAB infections in observational studies providing proper adjustment for confounders.

Identifying Effective Durations of Antibiotic Therapy for the Treatment of Carbapenem-resistant Enterobacterales Bloodstream Infections: A Multicenter Observational Study.

In a propensity-score-weighted cohort of 183 adults with carbapenem-resistant Enterobacterales bacteremia at 24 US hospitals, patients receiving short courses of active therapy (7-10 days, median 9 days) experienced similar odds of recurrent bacteremia or death within 30 days as those receiving prolonged courses of active therapy (14-21 days, median 14 days).

Clinical efficacy of ceftazidime/avibactam combination therapy for severe hospital-acquired pulmonary infections caused by carbapenem-resistant and difficult-to-treat Pseudomonas aeruginosa.

OBJECTIVES: This retrospective study aimed to identify the effectiveness of ceftazidime/avibactam (CAZ/AVI) and its optimisation programs for severe hospital-acquired pulmonary infections (sHAPi) caused by carbapenem-resistant and difficult-to-treat Pseudomonas aeruginosa (CRPA and DTR-P. aeruginosa). METHODS: We retrospectively analysed observational data on treatment and outcomes of CAZ/AVI for sHAPi caused by CRPA or DTR-P. aeruginosa. The primary study outcomes were to evaluate the clinical and microbiology efficacy of CAZ/AVI. RESULTS: The cohort consisted of 84 in-patients with sHAPi caused by CRPA (n = 39) and DTR-P. aeruginosa (n = 45) who received at least 72 h of CAZ/AVI therapy. The clinical cure rate was 63.1% in total. There was no significant difference in study outcomes between patients treated with CAZ/AVI monotherapy and those managed with combination regimens. CAZ/AVI as first-line therapy possessed prominent clinical benefits regarding infections caused by DTR-P. aeruginosa. The clinical cure rate was positively relevant with loading dose for CAZ/AVI (odds ratio [OR] 0.03; 95% confidence interval [CI] 0.004-0.19; P < 0.001) and with CAZ/AVI administration by prolonged infusion (odds ratio 0.15; 95% confidence interval 0.03-0.77; P = 0.002). APACHE II score>15 (P = 0.013), septic shock at infection onset (P = 0.001), and CAZ/AVI dose adjustment for renal dysfunction (P = 0.003) were negative predictors of clinical cure. CONCLUSION: CAZ/AVI is a valid alternative for sHAPi caused by CPRA and DTR-P. aeruginosa, even when used alone. Optimisations of the treatment with CAZ/AVI in critically ill patients, including loading dose, adequate maintenance dose and prolonged infusion, were positively associated with potential clinical benefits.

A Retrospective Case-Control Study of Eravacycline for the Treatment of Carbapenem-Resistant Acinetobacter Infections in Patients With Burn Injuries.

Thermal injuries lead to a deficiency in one's natural, protective barrier, resulting in increased susceptibility to pathogens, and often require multiple courses of broad-spectrum antibiotics. Eravacycline (ERA) has shown adequate in vitro activity against multiple multi-drug resistant (MDR) pathogens including Acinetobacter sp. Due to the increasing prevalence of MDR bacteria and the heightened susceptibility of patients with burns to infection, studies are needed to examine the clinical effect of eravacycline in this population. The objective of this retrospective, case-control study was to compare the outcomes of patients with thermal injuries treated with eravacycline versus a matched control for carbapenem-resistant Acinetobacter baumannii (CRAB) infections. Patients with thermal injury admitted to an American Burn Associated-verified burn center from May 1, 2019 to July 31, 2022, who received eravacycline, were randomly matched 4:1 to a historical cohort using a previously established, de-identified dataset of patients treated with colistimethate sodium (CMS) in the same burn center (March 1, 2009 to March 31, 2014), based on % total body surface area (%TBSA), age, and CRAB. A composite favorable outcome was defined as 30-day survival, completion of the course, lack of 14-day recurrence, and lack of acute kidney injury (AKI). Treatment with eravacycline over CMS was not more or less likely to be associated with a favorable response [odds ratio (95% confidence interval), 2.066 (0.456-9.361), P = .347]. Patients treated with CMS had nearly 9-fold higher odds of new-onset AKI versus ERA [8.816 (0.911-85.308), P = .06]. Adverse events were uncommon in the ERA group. There was no difference in mortality.

Cefepime versus carbapenems for treatment of AmpC beta-lactamase-producing Enterobacterales bloodstream infections.

PURPOSE: Cefepime is recommended for treating infections caused by AmpC beta-lactamase-producing Enterobacterales (AmpC-PE), though supporting evidence is limited. Therefore, this study compared outcomes associated with cefepime versus carbapenem therapy for bloodstream infections (BSIs) caused by AmpC-PE after phenotypic exclusion of ESBL-co-producing isolates. METHODS: This retrospective cohort study compared definite cefepime versus carbapenem treatment for AmpC-PE BSI in hospitalized patients of the University Hospital Basel, Switzerland, between 01/2015 and 07/2020. Primary outcomes included in-hospital death, renal impairment and neurologic adverse events; secondary outcomes included length of hospital stay and recurrent infection. RESULTS: Two hundred and seventy episodes of AmpC-PE BSI were included, 162, 77 and 31 were treated with a carbapenem, cefepime and other antibiotics, respectively. Patients treated with carbapenems were more likely to be transferred to the ICU on admission and more frequently had central venous catheter as a source of infection. In uni- and multivariable analyses, primary and secondary outcomes did not differ between the two treatment groups, except for more frequent occurrence of neurological adverse events among patients treated with carbapenems and shorter length of hospital stay among survivors treated with cefepime. CONCLUSION: After excluding isolates with phenotypic ESBL-co-production, cefepime was not associated with adverse outcomes compared to carbapenems when used to treat BSIs caused by AmpC-PE. Our study provides evidence to support the use of cefepime as a safe treatment strategy for AmpC-PE BSI, particularly in clinically stable patients without initial renal impairment or increased susceptibility to neurological adverse events.

Safety and effectiveness of tigecycline combination therapy in renal transplant patients with infection due to carbapenem-resistant gram-negative bacteria.

Background: Carbapenem-resistant gram-negative bacterial (CRGNB) infections are increasing among kidney transplant recipients, and effective therapeutic options are limited. This study aimed to investigate the efficacy and adverse events associated with combination therapy tigecycline in renal transplant patients with CRGNB infections. Methods: This study retrospectively analyzed 40 Chinese patients with confirmed or suspected CRGNB infections who received tigecycline therapy. The patients' case features and clinical and microbiological data were analyzed. Results: A total of 40 renal transplant recipients received tigecycline therapy for a median duration of 9 (range, 3-25) days. CRGNB isolates were obtained from the organ preservation solution of the donor kidney in 28 patients, with confirmed transmission in 4 patients. Infections were detected in the bloodstream, urinary tract, sputum, and wound. The most prevalent isolates were Klebsiella pneumoniae (75%, 30/40), Acinetobacter baumannii (15%, 6/40), and Escherichia coli (10%, 4/40). A clinical response was observed in 32 (80%) patients. The 28-day all-cause mortality rate was 7.5% (3/40), while the one-year all-cause mortality rate was 2.5% (1/40). While one patient died owing to severe pancreatitis, no serious adverse events related to tigecycline therapy were reported. However, multiple indices of liver function and pancreatitis precursors increased after treatment with tigecycline compared to before treatment. Conclusion: Tigecycline therapy appears to be well tolerated in renal transplant recipients with multidrug-resistant bacterial infections. Nevertheless, attention should be paid to adverse reactions related to tigecycline therapy, especially gastrointestinal reactions, and the related laboratory tests should be closely monitored.

Treatment guidelines for multidrug-resistant Gram-negative microorganisms.

In recent years, new antimicrobials have been introduced in therapeutics, including new beta-lactam-beta-lactamase inhibitor combinations and cefiderocol in response to therapeutic needs in the face of increasing resistance. There are also different treatment guidelines for infections caused by these microorganisms that have been approved by different professional societies, including those of the European Society of Clinical Microbiology and Infectious Diseases (ESCMID), the Infectious Disease Society of America (IDSA) and the Spanish Society of Infectious Diseases and Clinical Microbiology (SEIMC). All of them are based on scientific evidence, but with differences in the weight of expert opinion in their recommendations. Both ESCMID and IDSA include recommendations for the treatment of extended-spectrum beta-lactamase-producing microorganisms. The IDSA is the only one including AmpC producers, all address the treatment of infections caused by carbapenem-resistant Enterobacterales and Acinetobacter baumannii and multidrug-resistant or difficult-to-treat Pseudomonas aeruginosa, and the IDSA and SEIMC include recommendations on the treatment of Stenotrophomonas maltophilia. Future guidelines should integrate new antimicrobials and new innovative management options not covered by current guidelines.

Synergistic effects of polymyxin and vancomycin combinations on carbapenem- and polymyxin-resistant Klebsiella pneumoniae and their molecular characteristics.

IMPORTANCE: This study provides insights into the mechanisms of polymyxin resistance in K. pneumoniae clinical isolates and demonstrates potential strategies of polymyxin and vancomycin combinations for combating this resistance. We also identified possible mechanisms that might be associated with the treatment of these combinations against carbapenem- and polymyxin-resistant K. pneumoniae clinical isolates. The findings have significant implications for the development of alternative therapies and the effective management of infections caused by these pathogens.

The efficacy of mesenchymal stem cell treatment and colistin-fosfomycin combination on colistin-resistant Acinetobacter baumannii sepsis model.

INTRODUCTION: This study examines the role of mesenchymal stem cells (MSCs) in an experimental sepsis model developed with colistin-resistant Acinetobacter baumannii (CRAB). MATERIALS AND METHODS: BALB-c mice were divided into treatment groups (MSC, MSC + colistin (C)-fosfomycin (F), and C-F and control groups (positive and negative)). CRAB was administered to mice through intraperitoneal injection. Three hours later, C, F, and MSC were given intraperitoneally to the treatment groups. Colistin administration was repeated every 12 h, F administration was done every 4 h, and the second dose of MSC was administered after 48 h. Mice were sacrificed at 24 and 72 h. The bacterial load was determined as colony-forming units per gram (cfu/g). Histopathological examination was conducted on the left lung, liver, and both kidneys. IL-6 and C-reactive protein (CRP) levels in mouse sera were determined by enzyme-linked immunosorbent assay. RESULTS: Among the treatment groups, the C-F group had the lowest colony count in the lung (1.24 ± 1.66 cfu/g) and liver (1.03 ± 1.08 cfu/g). The highest bacterial clearance was observed at 72 h compared to 24 h in the MSC-treated groups (p = 0.008). The MSC + C-F group showed the lowest histopathological score in the liver and kidney (p = 0.009). In the negative control group, the IL-6 level at the 24th hour was the lowest (p < 0.001). Among the treatment groups, the CRP level was the lowest in the MSC + C-F group at 24 and 72 h. CONCLUSION: In a CRAB sepsis model, adding MSCs to a colistin-fosfomycin treatment may be beneficial in terms of reducing bacterial loads and preventing histopathological damage.

Chemical composition and antibacterial activity of bee venom against multi-drug resistant pathogens.

Bee venom with an antimicrobial effect is a powerful natural product. One of the most important areas where new antimicrobials are needed is in the prevention and control of multi-drug resistant pathogens. Today, antibacterial products used to treat multi-drug resistant pathogen infections in hospitals and healthcare facilities are insufficient to prevent colonisation and spread, and new products are needed. The aim of the study is to investigate the antibacterial effect of the bee venom (BV), a natural substance, on the species of Methicillin resistant Staphylococcus aureus, Vancomycin resistant Enterococcus faecalis, Carbapenem resistant Escherichia coli, Carbapenem resistant Klebsiella pneumoniae and Carbapenem resistant Acinetobacter baumannii. As a result of this study, it was found that MIC90 and MBC90 values ranged from 6.25 µg/mL - 12.5 µg/mL and numbers of bacteria decreased by 4-6 logs within 1-24 h for multi-drug resistant pathogens. In particular, Vancomycin resistant Enterococcus faecalis isolate decreased 6 log cfu/mL at 50 µg/mL and 100 µg/mL concentrations in the first hour. The effective bacterial inhibition rate of bee venom suggests that it could be a potential antibacterial agent for multi-drug resistant pathogens.Contribution: The treatment options of antibiotic-resistant pathogens are a major problem in both veterinary and human medicine fields. We have detected a high antibacterial effect against these agents in this bee venom study, which is a natural product. Apitherapy is a fashionable treatment method all over the world and is used in many areas of health. Bee venom is also a product that can be used as a drug or disinfectant raw material and can fill the natural product gap that can be used against resistant bacteria.

[Molecular epidemiological characterization of hypervirulent carbapenem-resistant Klebsiella pneumoniae in a hospital in Henan Province from 2020 to 2022].

Objective: The study investigated the clinical distribution, antimicrobial resistance and epidemiologic characteristics of hypervirulent Carbapenem-resistant Klebsiella pneumoniae (hv-CRKP) in a hospital in Henan Province to provide a scientific basis for antibiotic use and nosocomial infection prevention and control. Methods: A retrospective analysis of the clinical data from the cases was carried out in this study. Clinical data of patients infected with the CRKP strain isolated from the clinical microbiology laboratory of Henan Provincial Hospital of Traditional Chinese Medicine from January 2020 to December 2022 were retrospectively analyzed. A string test, virulence gene screening, serum killing, and a G. mellonella infection model were used to screen hv-CRKP isolates. The clinical characteristics of hv-CRKP and the drug resistance rate of hv-CRKP to twenty-five antibiotics were analyzed using WHONET 5.6. Carbapenemase phenotypic characterization of the hv-CRKP was performed by colloidal gold immunochromatographic assay, and Carbapenemase genotyping, multi-locus sequence typing (MLST) and capsular serotyping of hv-CRKP isolates were performed by PCR and Sanger sequencing. Results: A total of non-duplicate 264 CRKP clinical isolates were detected in the hospital from 2020 to 2022, and 23 hv-CRKP isolates were detected, so the corresponding detection rate of hv-CRKP was 8.71% (23/264). The hv-CRKP isolates in this study were mainly from the intensive care unit (10/23) and neurosurgery department (8/23), and the main sources of hv-CRKP isolates were sputum (10/23) and bronchoalveolar lavage fluid (6/23). The hv-CRKP isolates in this study were highly resistant to ß-lactam antibiotics, fluoroquinolones and aminoglycosides, and were only susceptible to colistin, tigecycline and ceftazidime/avibactam. The detection rate of the blaKPC-2 among 23 hv-CRKP isolates was 91.30% (21/23) and none of the class B and class D carbapenemases were detected. Results of MLST and capsular serotypes showed that ST11 type hv-CRKP was the dominant strain in the hospital, accounting for 56.52% (13/23), and K64 (9/13) and KL47 (4/13) were the major capsular serotypes. Conclusion: The hv-CRKP isolates from the hospital are mainly from lower respiratory tract specimens from patients admitted to the intensive care department and the drug resistance is relatively severe. The predominant strains with certain polymorphisms are mainly composed of the KPC-2-producing ST11-K64 and ST11-KL47 hv-CRKP isolates in the hospital.

Induced Heteroresistance in Carbapenem-Resistant Acinetobacter baumannii (CRAB) via Exposure to Human Pleural Fluid (HPF) and Its Impact on Cefiderocol Susceptibility.

Infections caused by Carbapenem-resistant Acinetobacter baumannii (CRAB) isolates, such as hospital-acquired pneumonia (HAP), bacteremia, and skin and soft tissue infections, among others, are particularly challenging to treat. Cefiderocol, a chlorocatechol-substituted siderophore antibiotic, was approved by the U.S. Food and Drug Administration (FDA) in 2019 and prescribed for the treatment of CRAB infections. Despite the initial positive treatment outcomes with this antimicrobial, recent studies reported a higher-than-average all-cause mortality rate in patients treated with cefiderocol compared to the best available therapy. The cause(s) behind these outcomes remains unconfirmed. A plausible hypothesis is heteroresistance, a phenotype characterized by the survival of a small proportion of cells in a population that is seemingly isogenic. Recent results have demonstrated that the addition of human fluids to CRAB cultures leads to cefiderocol heteroresistance. Here, we describe the molecular and phenotypic analyses of CRAB heteroresistant bacterial subpopulations to better understand the nature of the less-than-expected successful outcomes after cefiderocol treatment. Isolation of heteroresistant variants of the CRAB strain AMA40 was carried out in cultures supplemented with cefiderocol and human pleural fluid (HPF). Two AMA40 variants, AMA40 IHC1 and IHC2, were resistant to cefiderocol. To identify mutations and gene expression changes associated with cefiderocol heteroresistance, we subjected these variants to whole genome sequencing and global transcriptional analysis. We then assessed the impact of these mutations on the pharmacodynamic activity of cefiderocol via susceptibility testing, EDTA and boronic acid inhibition analysis, biofilm formation, and static time-kill assays. Heteroresistant variants AMA40 IHC1 and AMA40 IHC2 have 53 chromosomal mutations, of which 40 are common to both strains. None of the mutations occurred in genes associated with high affinity iron-uptake systems or ß-lactam resistance. However, transcriptional analyses demonstrated significant modifications in levels of expression of genes associated with iron-uptake systems or ß-lactam resistance. The blaNDM-1 and blaADC-2, as well as various iron-uptake system genes, were expressed at higher levels than the parental strain. On the other hand, the carO and ompA genes' expression was reduced. One of the mutations common to both heteroresistant strains was mapped within ppiA, a gene associated with iron homeostasis in other species. Static time-kill assays demonstrated that supplementing cation-adjusted Mueller-Hinton broth with human serum albumin (HAS), the main protein component of HPF, considerably reduced cefiderocol killing activity for all three strains tested. Notably, collateral resistance to amikacin was observed in both variants. We conclude that exposing CRAB to fluids with high HSA concentrations facilitates the rise of heteroresistance associated with point mutations and transcriptional upregulation of genes coding for ß-lactamases and biofilm formation. The findings from this study hold significant implications for understanding the emergence of CRAB resistance mechanisms against cefiderocol treatment. This understanding is vital for the development of treatment guidelines that can effectively address the challenges posed by CRAB infections.

Clinical, biological and genome-wide comparison of carbapenem-resistant Klebsiella pneumoniae with susceptibility transformation to polymyxin B during therapy.

OBJECTIVES: The emergence of carbapenem-resistant Klebsiella pneumoniae (CRKP) is a major clinical concern, and polymyxin B (PMB) is a 'last resort' antibiotic for its treatment. Understanding the effects of drug susceptibility transformation in CRKP-infected patients undergoing PMB treatment would be beneficial to optimize PMB treatment strategies. METHODS: We retrospectively collected data from patients infected with CRKP and treated with PMB from January 2018 to December 2020. CRKPs were collected before and after PMB therapy, and patients were classified into the 'transformation' group (TG) and 'non-transformation' group (NTG) by the shift of susceptibility to PMB. We compared clinical characteristics between these groups, and further analysed the phenotypic and genome variation of CRKP after PMB susceptibility transformation. RESULTS: A total of 160 patients (37 in the TG and 123 in the NTG) were included in this study. The duration of PMB treatment before PMB-resistant K. pneumoniae (PRKP) appearance in TG was even longer than the whole duration of PMB treatment in NTG (8 [8] vs. 7 [6] days; p 0.0496). Compared with isogenic PMB-susceptible K. pneumoniae (PSKP), most PRKP strains had missense mutations in mgrB (12 isolates), yciC (10 isolates) and pmrB (7 isolates). The competition index of 82.4% (28/34) of PRKP/PSKP pairs was <67.6% (23/34), and 73.5% (25/34) of PRKP strains showed a higher 7-day lethality in Galleria mellonella and a greater ability to resist complement-dependent killing than their corresponding PSKP, respectively. CONCLUSION: Low dose with longer PMB treatment durations may be associated with the emergence of polymyxin resistance. The evolution of PRKP is predominantly mediated by an accumulation of mutations, including those in mgrB, yciC, and pmrB. Lastly, PRKP exhibited reduced growth and increased virulence compared with parental PSKP.

Assessment of mortality-related risk factors and effective antimicrobial regimens for treatment of bloodstream infections caused by carbapenem-resistant Pseudomonas aeruginosa in patients with hematological diseases.

Background: Infections caused by carbapenem-resistant Pseudomonas aeruginosa (CRPA) are related to higher mortality. The objective of this study was to explore clinical outcomes of CRPA bacteremia, identify risk factors and also, compare the efficacy of traditional and novel antibiotic regimens. Methods: This retrospective study was conducted at a blood diseases hospital in China. The study included hematological patients who were diagnosed with CRPA bacteremia between January 2014 and August 2022. The primary endpoint was all-cause mortality at day 30. Secondary endpoints included 7-day and 30-day clinical cure. Multivariable Cox regression analysis was employed to identify mortality-related risk factors. Results: 100 patients infected with CRPA bacteremia were included and 29 patients accepted allogenic-hematopoietic stem cell transplantation. 24 received ceftazidime-avibactam (CAZ-AVI)-based therapy and 76 received other traditional antibiotics. 30-day mortality was 21.0%. Multivariable cox regression analysis showed neutropenia >7 days after bloodstream infections (BSI) (P=0.030, HR: 4.068, 95%CI: 1.146~14.434), higher Pitt bacteremia score (P<0.001, HR:1.824, 95%CI: 1.322~2.517), higher Charlson comorbidity index (P=0.01, HR: 1.613, 95%CI: 1.124~2.315) and bacteremia due to multidrug-resistant Pseudomonas aeruginosa (MDR-PA) (P=0.024, HR:3.086, 95%CI: 1.163~8.197) were identified as independent risk factors of 30-day mortality. After controlling for confounders, an additional multivariable cox regression analysis revealed definitive regimens containing CAZ-AVI were associated with lower mortality in CRPA bacteremia (P=0.016, HR: 0.150, 95%CI: 0.032~0.702), as well as in MDR-PA bacteremia (P=0.019, HR: 0.119, 95%CI: 0.020~0.709). Conclusions: For patients with hematological diseases and CRPA bacteremia, 30-day mortality rate was 21.0% (21/100). Neutropenia >7 days after BSI, higher Pitt bacteremia score, higher Charlson comorbidity index and bacteremia due to MDR-PA increased 30-day mortality. CAZ-AVI-based regimens were effective alternatives for bacteremia due to CRPA or MDR-PA.

Cefepime vs carbapenems for treating third-generation cephalosporin-resistant AmpC ß-lactamase-hyperproducing Enterobacterales bloodstream infections: a multicenter retrospective study.

OBJECTIVES: AmpC ß-lactamase-hyperproducing Enterobacterales (ABLHE) bloodstream infections (BSI) are emerging and leading to therapeutic challenges worldwide. Prescriptions of carbapenems may lead to the emergence of resistance. This study aimed to compare cefepime with carbapenems for the treatment of third-generation cephalosporin-resistant ABLHE BSI. METHODS: This retrospective multicenter study included patients with ABLHE BSI from two tertiary hospitals in France, between July 2017 and July 2022. Non-AmpC-producing Enterobacterales, extended-spectrum ß-lactamase, and carbapenemase-producing Enterobacterales were excluded. Cefepime was prescribed only in case of minimal inhibitory concentration ≤1 mg/l. The primary outcome was 30-day in-hospital mortality from the date of index blood culture. Secondary outcomes were infection recurrence and treatment toxicity. An inverse probability of treatment weighting approach was used to balance the baseline characteristics between the two groups. RESULTS: We analyzed 164 BSI, which included 77 in the cefepime group and 87 in the carbapenem group. In the weighted cohort, the 30-day mortality rates were similar between the cefepime group (23.3%) and the carbapenem group (19.6%) with a relative risk of 1.19 (95% confidence interval, 0.61-2.33 P = 0.614). No significant difference in recurrence or toxicity was found between the two groups. CONCLUSION: This study adds evidence in favor of the use of cefepime for treating third-generation cephalosporin-resistant ABLHE BSI in case of minimal inhibitory concentration ≤ 1 mg/l, which could spare carbapenems.