In Vitro Synergistic Activity of Rifampicin Combined with Minimal Effective Antibiotic Concentration (MEAC) of Polymyxin B Against Extensively Drug-Resistant, Carbapenem-, and Polymyxin B-Resistant Klebsiella pneumoniae Clinical Isolates.

We investigated the in vitro antibacterial activity of the combination rifampicin (RIF) + polymyxin B (PB) against extensively drug-resistant (XDR) Klebsiella pneumoniae isolates. We evaluated clinical isolates co-resistant to PB (non-mcr carriers; eptB, mgrB, pmr operon, and ramA mutations) and to carbapenems (KPC, CTX-M, and SHV producers; including KPC + NDM co-producer), belonging to sequence types (ST) ST16, ST11, ST258, ST340, and ST437. We used the standard broth microdilution method to determine RIF and PB minimum inhibitory concentration (MIC) and the checkerboard assay to evaluate the fractional inhibitory concentration index (FICI) of RIF + PB as well as to investigate the lowest concentrations of RIF and PB that combined (RIF + PB) had antibacterial activity. Time-kill assays were performed to evaluate the synergistic effect of the combination against selected isolates. PB MIC (32-256 µg/mL) and RIF MIC (32-1024 µg/mL) were determined. FICI (<0.5) indicated a synergistic effect for all isolates evaluated for the combination RIF + PB. Our results showed that low concentrations of PB (PB minimal effective antibiotic concentration [MEAC], ≤0.25-1 µg/mL) favor RIF (≤0.03-0.125 µg/mL) to reach the bacterial target and exert antibacterial activity against PB-resistant isolates, and the synergistic effect was also observed in time-kill results. The combination of RIF + PB showed in vitro antibacterial activity against XDR, carbapenem-, and PB-resistant K. pneumoniae and could be further studied as a potential combination therapy, with cost-effectiveness and promising efficacy.

Prediction of antimicrobial resistance of Klebsiella pneumoniae from genomic data through machine learning.

Antimicrobials, such as antibiotics or antivirals are medications employed to prevent and treat infectious diseases in humans, animals, and plants. Antimicrobial Resistance occurs when bacteria, viruses, and parasites no longer respond to these medicines. This resistance renders antibiotics and other antimicrobial drugs ineffective, making infections challenging or impossible to treat. This escalation in drug resistance heightens the risk of disease spread, severe illness, disability, and mortality. With datasets now containing hundreds or even thousands of pathogen genomes, machine learning techniques are on the rise for predicting antibiotic resistance in pathogens, prediction based on gene content and genome composition. Aim of this work is to combine and incorporate machine learning methods on bacterial genomic data to predict antimicrobial resistance, we will focus on the case of Klebsiella pneumoniae in order to support clinicians in selecting appropriate therapy.

Coinfection of Klebsiella pneumoniae and Aspergillus in a patient with chronic obstructive pulmonary disease post cardiac arrest: a case report.

INTRODUCTION: Chronic obstructive pulmonary disease is a lung condition characterized by chronic respiratory symptoms (breathlessness, cough, and expectoration). In the advanced stages, patients often report to the Accident & Emergency department due to worsening of symptoms. Because of the repeated exposure to corticosteroids during the management of exacerbations, these patients are susceptible to super additional infections. Pulmonary aspergillosis can be divided into three main categories: invasive pulmonary aspergillosis, allergic bronchopulmonary aspergillosis and chronic pulmonary aspergillosis. Aspergillus overlap syndrome is defined as the presence of more than one form of Aspergillus in a single patient. However, coinfection with Klebsiella and pulmonary aspergillosis overlap syndrome is rare and poses a treatment challenge. As per a pub med search, no such case report has been reported in a case of chronic obstructive pulmonary disease. CASE REPORT: We report the case of a 66-year-old male, Punjabi Hindu by ethnicity, who was a reformed smoker with a known case of COPD. He presented with a history of breathlessness (mMRC grade 4) associated with cough with expectoration and wheezing for 15 days and intermittent episodes of hemoptysis for more than 6 months. The examination revealed tachypnea and wheezing throughout the lung fields. He was initially managed with parenteral steroids and frequent nebulization with bronchodilators. On day 5 of hospitalization, the patient experienced worsening of symptoms and cardiac arrest; he was intubated and return of spontaneous circulation was achieved within 5 minutes of cardio pulmonary resuscitation. Tracheal aspirate and culture revealed Aspergillus fumigatus and Klebsiella pneumoniae respectively. He underwent chest CT, which showed features suggestive of allergic bronchopulmonary aspergillosis and invasive pulmonary aspergillosis. He was found to have elevated ß-D-glucan, galactomannan, and aspergillus IgE and IgG. Severe pneumonia and pulmonary Aspergillus overlap syndrome were managed with antibiotics, steroids, and antifungals. Over the next 15-20 days, his general condition improved. He was discharged after 45 days of hospitalization and continued on oral corticosteroids, antifungals, and inhaled bronchodilators. CONCLUSION: Coinfection with bacteria and fungi worsens the outcome. Clinicians should be aware of the polymicrobial manifestations and various drug interactions involved. Timely diagnosis aids in better management strategies and improved patient outcomes.

Topical adjunctive treatment with flagellin augments pulmonary neutrophil responses and reduces bacterial dissemination in multidrug-resistant K. pneumoniae infection.

Objective: Antimicrobial resistance is an emerging problem and multi-drug resistant (MDR) Klebsiella pneumoniae (K. pneumoniae) represents an enormous risk of failing therapy in hospital-acquired pneumonia. The current study aimed to determine the immunomodulatory effect of topical flagellin in addition to antibiotic treatment during respiratory infection evoked by hypervirulent antibiotic-susceptible and antibiotic-resistant K. pneumoniae in mice. Methods: C57BL6 mice were inoculated intranasally with hypervirulent K. pneumoniae (K2:O1) which was either antibiotic-susceptible or multi-drug resistant. Six hours after infection, mice were treated with antibiotics intraperitoneally and flagellin or vehicle intranasally. Mice were sacrificed 24 hours after infection. Samples were analyzed for bacterial loads and for inflammatory and coagulation markers. Results: Flagellin therapy induced neutrophil influx in the lung during antibiotic-treated pneumonia evoked by either antibiotic-susceptible or -resistant K. pneumoniae. The pulmonary neutrophil response was matched by elevated levels of neutrophil-attracting chemokines, neutrophil degranulation products, and local coagulation activation. The combined therapy of effective antibiotics and flagellin did not impact K. pneumoniae outgrowth in the lung, but decreased bacterial counts in distant organs. Neutrophil depletion abrogated the flagellin-mediated effect on bacterial dissemination and local coagulation responses. Conclusion: Topical flagellin administration as an adjunctive to antibiotic treatment augments neutrophil responses during pneumonia evoked by MDR-K. pneumoniae, thereby reducing bacterial dissemination to distant organs.

Artificial intelligence-clinical decision support system for enhanced infectious disease management: Accelerating ceftazidime-avibactam resistance detection in Klebsiella pneumoniae.

BACKGROUND: Effective and rapid diagnostic strategies are required to manage antibiotic resistance in Klebsiella pneumonia (KP). This study aimed to design an artificial intelligence-clinical decision support system (AI-CDSS) using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) and machine learning for the rapid detection of ceftazidime-avibactam (CZA) resistance in KP to improve clinical decision-making processes. METHODS: Out of 107,721 bacterial samples, 675 specimens of KP with suspected multi-drug resistance were selected. These specimens were collected from a tertiary hospital and four secondary hospitals between 2022 and 2023 to evaluate CZA resistance. We used MALDI-TOF MS and machine learning to develop an AI-CDSS with enhanced speed of resistance detection. RESULTS: Machine learning models, especially light gradient boosting machines (LGBM), exhibited an area under the curve (AUC) of 0.95, indicating high accuracy. The predictive models formed the core of our newly developed AI-CDSS, enabling clinical decisions quicker than traditional methods using culture and antibiotic susceptibility testing by a day. CONCLUSIONS: The study confirms that MALDI-TOF MS, integrated with machine learning, can swiftly detect CZA resistance. Incorporating this insight into an AI-CDSS could transform clinical workflows, giving healthcare professionals immediate, crucial insights for shaping treatment plans. This approach promises to be a template for future anti-resistance strategies, emphasizing the vital importance of advanced diagnostics in enhancing public health outcomes.

First report of a bla NDM-producing extensively drug resistant Klebsiella pneumoniae ST437 in Italy.

Carbapenemase-producing Klebsiella pneumoniae strains (CP-Kps) have recently been observed to spread rapidly worldwide. New Delhi metallo-ß-lactamase (NDM) producing clones of Klebsiella pneumoniae (K. pneumoniae) cause a significant healthcare burden, particularly in Indian sub-continent, where this clone is circulating widely. However, in Italy, data on the incidence of these new clones is limited, and an ST437 NDM-producing K. pneumoniae strain has not been reported to date. A sacral ulcer infection caused by a K. pneumoniae strain was identified in an 85-year-old Italian male patient with several comorbidities. Antimicrobial susceptibility testing revealed an extensive resistance to a wide range of antimicrobials, including novel agents such as cefiderocol and ceftazidime/avibactam. Genomic analysis identified the pathogen as an ST437 K. pneumoniae strain harboring bla NDM-5, bla OXA-232 and bla CTX-M-15 genes. Following the identification of this first case, several infection control measures were implemented in healthcare settings, including direct precautions and reinforcement of standard cross-transmission control measures. The emergence of pathogenic microbial clones carrying new genetic determinants, particularly in a little city, requires prompt diagnosis and therapeutic protocols. An effective infection control system for the early detection and/or control of the transmission of NDM-producing Enterobacteriaceae is also needed. Further investigations are required to better understand the potential transmission routes and evolution of these clones.

Clinical outcomes and safety of polymyxin B versus tigecycline combination therapy for pneumonia of carbapenem-resistant Klebsiella pneumoniae: a retrospective cohort study.

PURPOSE: Infection by carbapenem-resistant Klebsiella pneumoniae (CRKP) has high mortality. There is no clear optimal therapeutic choice for pneumonia caused by CRKP. The aim of this study was to compare the clinical outcomes and safety of the standard doses of polymyxin B-based regimens vs tigecycline-based regimens and to identify risk factors for mortality. METHODS: This retrospective cohort study included patients with pneumonia caused by CRKP between January 1, 2020 and December 31, 2022. The primary outcomes were 7-day bacterial eradication rate and 14- and 28-day all-cause mortality. The secondary outcome was incidence of acute kidney injury. RESULTS: Seventy-three patients were included in this study, 29 in the polymyxin B-based combination therapy group and 44 in tigecycline-based combination therapy group. There were no significant differences between the two groups in terms of the 7-day bacterial eradication rate (31.03% vs 20.45%, p = 0.409), the 14-day all-cause mortality (37.93% vs 22.73%, p = 0.160), and the incidence of acute kidney injury (14.29% vs 6.82%, p = 0.526). The 28-day all-cause mortality in the polymyxin B-based therapy group was higher than in the tigecycline-based group (75.86% vs 45.45%, p = 0.010). Binary logistic regression analysis revealed that male and previous use of carbapenems were independent factors associated with 28-day all-cause mortality for patients treated with polymyxin B (p < 0.05). CONCLUSIONS: Polymyxin B-based combination therapy at the standard dose should be used with caution for patients with CRKP-induced pneumonia, especially for men who used carbapenems prior to CRKP detection.

Epidemiology, antimicrobial resistance profile and management of carbapenem-resistant Klebsiella pneumoniae among mothers with suspected sepsis in Ethiopia.

BACKGROUND: Early detection and proper management of maternal sepsis caused by carbapenem-resistant Klebsiella pneumoniae (CRKP) can significantly reduce severe complications and maternal mortality. This study aimed to describe the epidemiology, antimicrobial resistance profile, and management of carbapenem-resistant K. pneumoniae among sepsis-suspected maternal cases in Ethiopia. METHODS: A prospective cross-sectional study was conducted in five tertiary hospitals from June 2021 to December 2023. Isolation, identification, and antimicrobial susceptibility testing of the isolates were carried out following standard microbiological procedures as stated in the CLSI guidelines. Data on socio-demographics, risk factors, and management strategies were collected with structured questionnaires. Associations between variables were determined using logistic regression analysis in STATA-21. A p-value of less than 0.05 was statistically significant. RESULTS: Of the 5613 total women suspected of having maternal sepsis, 609 (10.8%) of them were infected with K. pneumoniae. The prevalence rates of MDR, XDR, and PDR K. pneumoniae strains were 93.9%, 24.3%, and 10.9%, respectively. The resistance rates for the last-resort antibiotics; amikacin, tigecycline, carbapenem, and third-generation cephalosporin were 16.4%, 29.1%, 31.9%, and 93.0%, respectively. The combination of carbapenem with tigecycline or amikacin therapy was used to manage maternal sepsis caused by cephalosporin-and carbapenem-resistant strains. Sepsis associated risk factors, including septic abortion [AOR = 5.3; 95%CI:2.2-14.4]; extended hospitalization [AOR = 3.7; 95%CI: 1.6-19.4]; dilatation and curettage [AOR = 2.2; 95%CI:1.3-13.4]; cesarean wound infection [AOR = 4.1; 95%CI:2.0-9.2]; indwelling catheterization [AOR = 2.1;95%CI: 1.4-6.2]; ICU admission [AOR = 4.3; 95%CI:2.4-11.2]; post abortion [AOR = 9.8; 95%CI:5.7-16.3], and recurrent UTI [AOR = 3.3; 95%CI: 1.6-13.2] were significantly associated with maternal sepsis caused by K. pneumoniae. CONCLUSIONS: The prevalence of maternal sepsis caused by carbapenem- resistant K. pneumoniae is high and serious attention needs to be given to combat transmission. Therefore, improving awareness, early diagnosis, IPC, integrated maternal surveillance, improved sanitation and efficient antimicrobial stewardship are crucial to combating bacterial maternal sepsis.

Intravenous fosfomycin indications and treatment outcomes in pediatric usage: analysis from a single center in Turkey.

Current data on fosfomycin usage in children are limited. We present data on the clinical use of intravenous (IV) fosfomycin in children. Hospitalized patients who received ≥3 days of IV fosfomycin between April 2021 and March 2023 were analyzed retrospectively. Forty-three episodes of infection in 39 patients were evaluated. The mean age of the patients was 5.35 (10 days to 17.5 years) years, and 54% were male. Infections were hospital-acquired in 79% of the episodes. Indications for fosfomycin were urinary tract infection (35%), bacteremia (32.6%), catheter-related bloodstream infection (16.3%), soft tissue infection (4.7%), sepsis (4.7%), surgical site infection (2.3%), burn infection (2.3%), and pneumonia (2.3%). Klebsiella pneumoniae was identified in 46.5% of the episodes, and a pan-drug or extensive drug resistance was detected in 75% of them. Carbapenem was used before fosfomycin at significantly higher rates in K. pneumoniae episodes (P = .006). Most (88.5%) patients received fosfomycin as a combination therapy. Culture negativity was achieved in 80% of episodes within a median treatment period of 3 (2-22) days, which was significantly shorter in K. pneumoniae episodes (P < .001). Treatment-related side effects were seen in 9.3% of the episodes. Side effects were significant after 3 weeks of treatment (P = .013). The unresponsivity rate to fosfomycin was 23.3%. Nine (21%) of the patients who were followed up in the intensive care units mainly died because of sepsis (56%). IV fosfomycin is an effective agent in treating severe pediatric infections caused by resistant microorganisms. Fosfomycin can be used in various indications and is generally safe for children.

Prevalence and antimicrobial susceptibility pattern of Klebsiella pneumoniae isolated from various clinical specimens at the University of Gondar Comprehensive Specialized Hospital, Northwest Ethiopia.

BACKGROUND: K. pneumoniae become multidrug-resistant (MDR) and commonly poses a serious health threat to patients due to limited therapeutic options. As a result, determining the prevalence and antimicrobial susceptibility patterns of K. pneumoniae isolates from clinical specimens is substantial to patient diagnosis and treatment. METHODS AND MATERIALS: A retrospective cross-sectional study was conducted from July 2021 to July 2022 at the University of Gondar Comprehensive Specialized Hospital, Northwest Ethiopia. Sociodemographic and laboratory data were collected from registered books using a data collection sheet. All types of samples were collected and processed using standard procedures. Identification of K. pneumoniae was done using Gram stain, colony characterization on culture media, anda series of biochemical tests. Antimicrobial susceptibility testing was done by the Kirby Bauer disc diffusion technique. The data were entered using Epi-info version 7 and exported to SPSS version 20 for analysis. RESULTS: Among 2600 clinical specimens, 735 (28.3%) were positive for bacteria, and K. pneumoniae isolates accounted for 147 (20%). Most of them were isolated from neonates and mainly obtained from blood specimens (81.6%). These isolates were 100% resistant to Nalidixic acid, Cefotaxime, and Cefazolin. About 84% and 83.3% of the isolates were also resistant to Ceftriaxone and Tetracycline, respectively. However, they are sensitive to Nitrofurantoin (86.6%), Imipenem (85.7%), Meropenem (79%), and Amikacin (78.3%). The overall proportion of MDR K. pneumoniae isolates accounted for 57.1%. CONCLUSION: The magnitude of MDR K. pneumoniae was very alarming. Therefore, strengthening antimicrobial stewardship programs and antimicrobial surveillance practices is strongly recommended in the study area.

Factors influencing mortality in intracranial infections caused by carbapenem-resistant Klebsiella Pneumoniae.

It remains that intracranial infection has an alarming mortality and morbidity. Klebsiella pneumoniae (KP) have increasingly been isolated in ventriculitis and meningitis episodes. Intracranial infections caused by carbapenem-resistant Klebsiella pneumoniae (CRKP) account for high mortality. To understand its clinical impact and related risk factors accurately are crucial in the management of bacterial intracranial infection. The retrospective study aimed to delineate the clinical risk of death from intracranial infection and analyze the risk factors. A total of 176 Klebsiella pneumoniae intracranial infectious patients were available to divide into CRKP group and carbapenem-susceptive Klebsiella Pneumoniae (CSKP) group. We performed survival analysis and estimate the time-varying effects of CRKP and CSKP infection on 30-day mortality. Infectious patients caused by CSKP was associated with lower mortality than CRKP group. The risk factors associated with death from intracranial infection caused by Klebsiella pneumoniae included SOFA scores, ventilator therapy, CRKP, and heart failure. Longer hospital stays are independently associated with lower mortality rates. Intracranial infection caused by CRKP was associated with excess mortality. Complex comorbidities mean higher mortality. Active supportive treatment is required for complicated patients with intracranial infections caused by carbapenem-resistant Klebsiella pneumoniae.

Polymyxin combined with Ocimum gratissimum essential oil: one alternative strategy for combating polymyxin-resistant Klebsiella pneumoniae.

Introduction. Multidrug-resistant infections present a critical public health due to scarce treatment options and high mortality. Ocimum gratissimum L. essential oil (O.geo) is a natural resource rich in eugenol known for its antimicrobial activity.Hypothesis/Gap Statement. O.geo may exert effective antimicrobial activity against polymyxin-resistant Klebsiella pneumoniae and, when combined with Polymyxin B (PMB), may exhibit a synergistic effect, enhancing treatment efficacy and reducing antimicrobial resistance.Aim. This study aims to investigate the antimicrobial activity of O.geo against polymyxin-resistant K. pneumoniae using in vitro tests and an in vivo Caenorhabditis elegans model.Methodology. The O.geo was obtained by hydrodistillation followed by gas chromatography. The MIC and antibiofilm activity were determined using broth microdilution. Checkerboard and time-kill assays evaluated the combination of O.geo and polymyxin B (PMB), whereas a protein leakage assay verified its action.Results. Eugenol (39.67%) was a major constituent identified. The MIC of the O.geo alone ranged from 128 to 512 µg ml-1. The fractional inhibitory concentration index (0.28) and time-kill assay showed a synergism. In addition, O.geo and PMB inhibited biofilm formation and increased protein leakage in the plasma membrane. The treatment was tested in vivo using a Caenorhabditis elegans model, and significantly increased survival without toxicity was observed.Conclusion. O.geo could be used as a potential therapeutic alternative to combat infections caused by multidrug-resistant bacteria, especially in combination with PMB.

Pulmonary abscess secondary to epididymitis caused by extended spectrum ß-lactamase-producing hypervirulent Klebsiella pneumoniae: a case report.

BACKGROUND: Pulmonary abscesses resulting from epididymitis caused by extended spectrum ß-lactamase-producing hypervirulent Klebsiella pneumoniae (ESBL-hvKp) in a nondiabetic patient are extremely uncommon. The infection caused by this disseminated drug-resistant bacteria, which is generally considered an intractable case, poses a potential challenge in clinical practice. CASE PRESENTATION: In this case report, we present the clinical course of a 71-year-old male patient with epididymitis, who subsequently developed cough and dyspnea following anti-infection treatment. Imaging examinations revealed severe pneumonia and pulmonary abscess. The infection of ESBL-hvKp in the epididymis led to bacteremia and subsequent lung lesions. Due to poor response to anti-infection therapy, the patient required an extended duration of anti-infection treatment and ultimately chosed to discontinue treatment. CONCLUSIONS: Acute epididymitis caused by ESBL-hvKP infection can result in the spread of the infection through the bloodstream, leading to severe pneumonia and lung abscess. Given the critical condition of the patient, even with active anti-infection treatment, there is a risk of treatment failure or potentially fatal outcomes.

Characterization of a KPC-84 harboring Klebsiella pneumoniae ST11 clinical isolate with ceftazidime-avibactam resistance.

A novel KPC variant, KPC-84, identified in a Klebsiella pneumoniae isolate from China, exhibits a threonine (T) to proline (P) amino acid substitution at Ambler position 243(T243P), altering from the KPC-2 sequence. Cloning and expression of blaKPC-84 in Escherichia coli, with subsequent MIC assessments, revealed increased resistance to ceftazidime-avibactam and significantly reduced carbapenemase activity compared to KPC-2. Kinetic measurements showed that KPC-84 exhibited sligthly higher hydrolysis of ceftazidime and reduced affinity for avibactam compared to KPC-2. This study emphasizes the emerging diversity of KPC variants with ceftazidime-avibactam resistance, underscoring the complexity of addressing carbapenem-resistant Klebsiella pneumoniae infections.

Antibacterial effect of phage cocktails and phage-antibiotic synergy against pathogenic Klebsiella pneumoniae.

The global rise of antibiotic resistance has renewed interest in phage therapy, as an alternative to antibiotics to eliminate multidrug-resistant (MDR) bacterial pathogens. However, optimizing the broad-spectrum efficacy of phage therapy remains a challenge. In this study, we addressed this issue by employing strategies to improve antimicrobial efficacy of phage therapy against MDR Klebsiella pneumoniae strains, which are notorious for their resistance to conventional antibiotics. This includes the selection of broad host range phages, optimization of phage formulation, and combinations with last-resort antibiotics. Our findings unveil that having a broad host range was a dominant trait of isolated phages, and increasing phage numbers in combination with antibiotics significantly enhanced the suppression of bacterial growth. The decreased incidence of bacterial infection was explained by a reduction in pathogen density and emergence of bacterial resistance. Furthermore, phage-antibiotic synergy (PAS) demonstrated considerable broad-spectrum antibacterial potential against different clades of clinical MDR K. pneumoniae pathogens. The improved treatment outcomes of optimized PAS were also evident in a murine model, where mice receiving optimized PAS therapy demonstrated a reduced bacterial burden in mouse tissues. Taken together, these findings offer an important development in optimizing PAS therapy and its efficacy in the elimination of MDR K. pneumoniae pathogens. IMPORTANCE: The worldwide spread of antimicrobial resistance (AMR) has posed a great challenge to global public health. Phage therapy has become a promising alternative against difficult-to-treat pathogens. One important goal of this study was to optimize the therapeutic efficiency of phage-antibiotic combinations, known as phage-antibiotic synergy (PAS). Through comprehensive analysis of the phenotypic and genotypic characteristics of a large number of CRKp-specific phages, we developed a systematic model for phage cocktail combinations. Crucially, our finding demonstrated that PAS treatments not only enhance the bactericidal effects of colistin and tigecycline against multidrug-resistant (MDR) K. pneumoniae strains in in vitro and in vivo context but also provide a robust response when antibiotics fail. Overall, the optimized PAS therapy demonstrates considerable potential in combating diverse K. pneumoniae pathogens, highlighting its relevance as a strategy to mitigate antibiotic resistance threats effectively.

Role of volume and inoculum in MIC assessment: a study with meropenem and Klebsiella pneumoniae.

OBJECTIVES: Pharmacodynamic parameters evaluated under conditions that simulate an infection site volume and microbial load might reveal hidden risks of resistance selection and subsequent treatment failure. The study aimed to investigate the predictive potential of MICs determined at various conditions on the antimicrobial effect and emergence of resistance. METHODS: We assessed meropenem MICs (microdilution: 0.2 mL, 5 × 105 cfu/mL; macrodilution: 2 mL, 5 × 105 cfu/mL), MICHVs (220 mL, 5 × 105 cfu/mL), MICHIs (0.2 mL, 5 × 107 cfu/mL) and MICHVIs (220 mL, 5 × 107 cfu/mL) for five Klebsiella pneumoniae strains and analysed these values alongside the results of experiments in a dynamic in vitro model. A clinically relevant meropenem dosing regimen was simulated and the starting bacterial inocula were 106 and 108 cfu/mL. RESULTS: The effectiveness of meropenem agreed with MICHVs for the 106 cfu/mL inoculum and with MICHIs or MICHVIs for the 108 cfu/mL inoculum. Strains characterized as resistant according to these values grew during meropenem exposure, and resistant mutants were selected. CONCLUSIONS: Our results suggest that MICHV-based parameters may be suitable for predicting antibacterial effects and the risk of resistance development when the inoculum is 106 cfu/mL, while MICHI- or MICHVI-based parameters are suitable for these purposes when the inoculum is 108 cfu/mL. Also, the correlation between resistance selection and the MICHI-based parameter was as high as one that corresponds with a mutant prevention concentration (MPC)-based parameter; this suggests that the MPC can be replaced by the more easily determined alternative parameter MICHI.

Biliary pharmacokinetic/pharmacodynamic analysis of continuous infusion meropenem/vaborbactam in a case series of orthotopic liver transplant recipients.

OBJECTIVE: To analyse the biliary pharmacokinetics/pharmacodynamics (PK/PD) of continuous infusion (CI) meropenem-vaborbactam (MEM-VBM) in a case series of orthotopic liver transplant (OLT) recipients being treated for Klebsiella pneumoniae carbapenemase-producing Klebsiella pneumoniae (KPC-Kp) related biliary tract infections (BTIs) or as preemptive therapy of KPC-Kp rectal colonization. METHODS: Critical OLT recipients receiving CI MEM-VBM (2 g/2 g q8h over 8 h) because of KPC-Kp related BTIs or as preemptive therapy of KPC-Kp rectal colonization, having Kehr's tube positioned and undergoing simultaneous therapeutic drug monitoring of MEM and VBM in plasma and bile were retrospectively assessed. Bile-to-plasma ratio of free steady-state concentrations (fCss) of MEM and VBM was used for assessing biliary penetration. Optimal joint MEM-VBM PK/PD target attainment was defined as MEM fCss/MIC ratio >4 coupled with VBM free area under time-concentration curve (fAUC)/threshold concentration (CT) ratio >24. RESULTS: Overall, four critical OLT recipients were included. Median bile-to-plasma ratio was 0.32 for MEM (range 0.21-0.79) and 0.40 for VBM (range 0.20-0.77). Biliary MEM-VBM joint PK/PD target attainment was optimal in 3/4 OLT recipients and quasi-optimal in the other one. CONCLUSIONS: The 1:1 proportion between MEM and VBM concentrations was maintained unchanged in the bile, allowing us to assume that the efficacy of MEM-VBM may be appropriate even in the treatment of BTIs. CI administration was an effective strategy for attaining aggressive biliary joint PK/PD targets against pathogens with an MIC up to 2 mg/L.

Emergence of silent NDM-1 carbapenemase gene in carbapenem-susceptible Klebsiella pneumoniae: Clinical implications and epidemiological insights.

The global dissemination of carbapenemase genes, particularly blaNDM-1, poses a significant threat to public health. While research has mainly focused on strains with phenotypic resistance, the impact of silent resistance genes has been largely overlooked. This study documents the first instance of silent blaNDM-1 in a cluster of clonally related carbapenem-susceptible K. pneumoniae strains from a single patient. Despite initial effectiveness of carbapenem therapy, the patient experienced four recurrent lung infections over five months, indicating persistent K. pneumoniae infection. Genomic sequencing revealed all strains harbored blaNDM-1 on the epidemic IncX3 plasmid. A deletion within the upstream promoter region (PISAba125) of blaNDM-1 hindered its expression, resulting in phenotypic susceptibility to carbapenems. However, in vitro bactericidal assays and a mouse infection model showed that K. pneumoniae strains with silent blaNDM-1 exhibited significant tolerance to carbapenem-mediated killing. These findings demonstrate that silent blaNDM-1 can mediate both phenotypic susceptibility and antibiotic tolerance. In silico analysis of 1986 blaNDM sequences showed that 1956 (98.5%) retained the original promoter PISAba125. Given that previous genomic sequencing typically targets carbapenem-resistant strains, accurately assessing the prevalence of silent blaNDM remains challenging. This study highlights the hidden threat of silent resistance genes to clinical antimicrobial therapy and calls for enhanced clinical awareness and laboratory detection.

Resistance Genes and Mortality in Carbapenem-resistant Klebsiella pneumoniae Bacteremias: Effects of the COVID-19 Pandemic

Background: Emerging carbapenem-resistant Klebsiella pneumoniae (K. pneumoniae) (CRKP) bacteremias are presenting significant public health risks due to limited treatment options and increased mortality. K. pneumoniae isolates exhibit carbapenem resistance rates that vary from 25% to 50% throughout the European continent, including our country. Aims: To assess the characteristics of CRKP bacteremia, a condition that has recently demonstrated an increasing prevalence in our center. We sought to ascertain the resistance rates of isolated strains to antibiotics other than carbapenems, identify the responsible carbapenemase genes, evaluate the efficacy of antibiotics, determine mortality rates, explore clonality among strains, and investigate the influence of the COVID-19 pandemic on all these factors. Study Design: Retrospective observational study. Methods: This study included patients aged 18 and older who had experienced meropenem-resistant K. pneumoniae bacteremia. Meropenem resistance was confirmed by employing the Kirby-Bauer disk diffusion method. Meropenem minimum inhibitory concentration (MIC) levels were determined using the gradient test, while colistin MIC levels were ascertained using the disk elution technique. Carbapenemase genes were evaluated via colony polymerase chain reaction (PCR), and clonality analysis was performed using the arbitrarily primed PCR technique. Results: The study comprised 230 patients, with a mean age of 63.1 ± 15.9 years, of whom 58.7% were male. Oxacillinase-48 (OXA-48) was detected in 74.8% of the patients, New Delhi metallo-beta-lactamase (NDM) in 12.6%, OXA-48 + NDM in 7.8%, and KPC in 4.8%. The 14-day and 30-day mortality rates were 57% and 69.6%, respectively. Multivariate analysis of the 30-day mortality revealed several crucial factors, including bacteremia development in the intensive care unit, the occurrence of bacteremia during the COVID-19 pandemic, polymicrobial bacteremia, the use of indwelling intravenous catheters, a platelet count of ≤ 140,000/µl, procalcitonin levels of ≥ 6 µg/l, and a Charlson comorbidity score ≥ 3. Notably, the OXA-48 and KPC genes were upregulated significantly during the COVID-19 pandemic, while the NDM gene groups were downregulated. Additionally, both 14-day and 30-day mortality rates increased significantly. Conclusion: In this study, the most prevalent carbapenemase gene was OXA-48; however, there has been a recent increase in KPC genes. No dominant epidemic strain was identified through clonality analysis. The clustering rate was 68% before the pandemic, increasing to 85.7% during the pandemic. The significance of infection control measures is underscored by the rise in both clustering and mortality rates during the COVID-19 pandemic.

Molecular characterization of NDM and OXA-48-like-producing Klebsiella pneumoniae ST16 and hypervirulent ST337 clone among two patients; a case report.

Carbapenem-resistant Klebsiella pneumoniae (CRKP) infections are a major public health problem, requiring the use of last-resort antibiotics such as colistin. However, there is concern regarding the emergence of isolates resistant to this agent. The report describes two patients with urinary tract infection (UTI) and ventilator-associated pneumonia (VAP) infection caused by CRKP strains. The first case was a 23-year-old male with UTI caused by a strain of ST16 co-harboring blaCTX-M, blaTEM, blaSHV, blaNDM, blaOXA-48-like genes. The second case was a 39-year-old woman with VAP due to hypervirulent ST337-K2 co-harboring blaSHV, blaNDM, blaOXA-48-like, iucA, rmpA2 and rmpA. The patients' general condition improved after combination therapy with colistin (plus meropenem and rifampin, respectively) and both of them recovered and were discharged from the hospital. This study highlights the necessary prevention and control steps to prevent the further spread of CRKP strains should be a priority in our hospital.