Carbapenem Breakpoints for Acinetobacter baumannii Group: Supporting Clinical Outcome Data from Patients with Bacteremia

Multicenter study on clinical outcomes and poor prognostic factors in patients with Klebsiella pneumoniae bacteremia receiving cefoperazone/sulbactam treatment

BACKGROUND

Infections caused by Klebsiella pneumoniae are common and result in high mortality rates. In vitro studies demonstrated the potency of cefoperazone/sulbactam (CPZ/SUL) against Klebsiella pneumoniae. However, the clinical efficacy of CPZ/SUL for the treatment of K. pneumoniae bacteremia has not been studied.

OBJECTIVES

This study aimed to associate the clinical outcomes of patients with bacteremia with the minimal inhibitory concentrations (MICs) of CPZ/SUL against the causative K. pneumoniae isolates.

METHODS

This multicenter, retrospective study was conducted in Taiwan between July 2017 and April 2021. Patients with K. pneumoniae bacteremia treated with CPZ/SUL were enrolled in this study. CPZ/SUL MICs were determined using the agar dilution method. Data on the patients' clinical outcomes and characteristics were collected and analyzed.

RESULTS

In total, 201 patients were enrolled. Among the causative K. pneumoniae isolates, 180 (89.5%) were susceptible to CPZ/SUL. Most patients (n = 156, 77.6%) had favorable outcomes. The 30-day mortality rate was 11.9% (n = 24). Multivariate risk analyses showed that higher APACHE II score (Odds Ratio [OR], 1.14; Confidence Interval [CI], 1.07-1.21; p < 0.001), metastatic tumors (OR, 5.76; CI, 2.31-14.40; p < 0.001), and causative K. pneumoniae CPZ/SUL MICs > 16 µg/ml (OR, 4.30; CI, 1.50-12.27; p = 0.006) were independently associated with unfavorable outcomes.

CONCLUSION

Patients with K. pneumoniae bacteremia treated with CPZ/SUL at a ratio 1:1 had favorable outcomes when the CPZ/SUL MICs were ≤ 16 µg/ml. Patients with higher APACHE II scores and metastatic tumors had unfavorable outcomes.

Optimal Regimens and Clinical Breakpoint of Avilamycin Against Clostridium perfringens in Swine Based on PK-PD Study

Clostridium perfringens causes significant morbidity and mortality in swine worldwide. Avilamycin showed no cross resistance and good activity for treatment of C. perfringens. The aim of this study was to formulate optimal regimens of avilamycin treatment for C. perfringens infection based on the clinical breakpoint (CBP). The wild-type cutoff value (CO_WT) was defined as 0.25 μg/ml, which was developed based on the minimum inhibitory concentration (MIC) distributions of 120 C. perfringens isolates and calculated using ECOFFinder. Pharmacokinetics–pharmacodynamics (PK-PD) of avilamycin in ileal content were analyzed based on the high-performance liquid chromatography method and WinNonlin software to set up the target of PK/PD index (AUC_0–24h/MIC)_ex based on sigmoid E_max modeling. The PK parameters of AUC_0–24h, C_max, and T_max in the intestinal tract were 428.62 ± 14.23 h μg/mL, 146.30 ± 13.41 μg/ml,, and 4 h, respectively. The target of (AUC_0–24h/MIC)_ex for bactericidal activity in intestinal content was 36.15 h. The PK-PD cutoff value (CO_PD) was defined as 8 μg/ml and calculated by Monte Carlo simulation. The dose regimen designed from the PK-PD study was 5.2 mg/kg mixed feeding and administrated for the treatment of C. perfringens infection. Five respective strains with different MICs were selected as the infection pathogens, and the clinical cutoff value was defined as 0.125 μg/ml based on the relationship between MIC and the possibility of cure (POC) following nonlinear regression analysis, CART, and “Window” approach. The CBP was set to be 0.25 μg/ml and selected by the integrated decision tree recommended by the Clinical Laboratory of Standard Institute. The formulation of the optimal regimens and CBP is good for clinical treatment and to control drug resistance.

The Occurrence and Characterization of Class I, II, and III Integrons Among Carbapenemase-Producing Clinical Strains of Acinetobacter baumannii in Tehran, Iran

Background: Acinetobacter baumannii has emerged as a critical pathogen with high morbidity and mortality in long-term hospitalized patients who stay in intensive care units. Carbapenemases and integrons are two critical DNA elements that contribute to the emergence of multidrug-resistant (MDR) A. baumannii. Objectives: The current study aimed at characterization and molecular detection of class 1, 2, and 3 integrons among carbapenemase-producing A. baumannii strains recovered from a clinical setting in Tehran, Iran. Methods: A total of 65 non-replicated clinical strains were considered in this study. Class 1, 2, and 3 carbapenemase genes and clonal relatedness of the isolates were investigated by PCR assay. Results: The prevalence of carbapenemases was as follows: blaOXA23 (92.31%), blaVIM (69.23%), and blaNDM (1.54%). In addition, PCR sequencing confirmed the presence of gene cassette arrays consisting of aacA4-catB8-aadA1 (12/46, 26.09%), aadB-aadA1 (26.09%, 12/46), arr2-cm1A5 (30.43%, 14/46), and dfrA1-aadA1 (7.39%, 8/46) in class 1 integron and dfrA1-sat2 (52.94%, 9/17), and sat2-aadA1 (47.06%, 8/17) in class 2 integron. Sequence-based typing of both blaOXA-51-like and ampC revealed the following distribution of three different clone types among isolates: clonal complex (CC) 10 (46.15%, 30/65), CC2 (40%, 26/65), and CC3 (13.85%, 9/65). Statistical analysis showed that the presence of the intI1, blaOXA23, blaVIM, or blaNDM genes can significantly increase the acquiring MDR phenotypes in A. baumannii isolates. Conclusions: High prevalence of carbapenemase-producing A. baumannii harboring integrons is alarming public health. It seems that class 1 integron can be served as a predictive biomarker for the presence of MDR phenotypes in the clinical setting. However, integrons do not carry carbapenemases in these strains.

In Vitro Synergy of Colistin in Combination with Meropenem or Tigecycline against Carbapenem-Resistant Acinetobacter baumannii

Acinetobacter baumannii is currently classified as one of six pathogens that contribute to increased patient mortality. Thus, exploratory studies navigating alternative treatment strategies are of supreme interest. Herein, we completed minimum inhibitory concentration (MIC) testing, and time-kill analyses (TKA) on 50 carbapenem-resistant Acinetobacterbaumannii isolates including 28 colistin-resistant isolates. Upon testing of MEM or TGC in the presence of sub-inhibitory COL against the 50 isolates, there was a median 2-fold reduction in MEM and TGC MICs. In the TKAs, the COL+MEM combination was synergistic in 45 (90%) isolates and bactericidal in 43 (86%) isolates at 24 hours, whereas the COL+TGC combination TKAs demonstrated synergy in 32 (64%) isolates and bactericidal activity was shown in 28 (56%) isolates. Additionally, sulbactam (SUL) and TGC were added to the COL+MEM dual therapy regimen to assess the possible utility of a triple therapy regimen against five non-responsive isolates. The COL+MEM+SUL and COL+MEM+TGC regimens effectively restored synergy in (5/5) 100% of the isolates. The results of this study demonstrate the potential utility of COL combinations in the treatment of carbapenem-resistant isolates.

Cefiderocol: A Novel Siderophore Cephalosporin against Multidrug-Resistant Gram-Negative Pathogens

Cefiderocol (CFDC), (formerly S-649266), is a novel injectable siderophore cephalosporin developed by Shionogi & Co., Ltd., with potent in vitro activity against Gram-negative pathogens including multidrug-resistant (MDR) Enterobacteriaceae and non-fermenting organisms, such as Pseudomonas aeruginosa, Acinetobacter baumannii, Burkholderia cepacia, and Stenotrophomonas maltophilia. Characterized by its siderophore catechol-moiety, CFDC uses a "trojan-horse approach" to navigate through the bacterial periplasmic space, thus evading various beta-lactam degrading enzymes and other mechanisms of resistance present in Gram-negative bacteria. More specifically in carbapenem-resistant Enterobacteriaceae, CFDC has been shown to have activity against extended spectrum beta-lactamases (ESBLs), such as CTX-type, SHV-type, and TEM-type, as well as the Ambler classes of beta-lactamases, including class A (KPC), class B (NDM, IMP, and VIM), class C (AmpC), and class D (OXA, OXA-24, OXA-48, and OXA-48-like). In addition to the strong activity that CFDC has been shown to have against MDR P. aeruginosa, it has also displayed activity against the OXA-23, OXA-24, and OXA-51, beta-lactamases commonly found in MDR A. baumannii. Cefiderocol was recently approved by the US Food and Drug Administration (FDA) for use in complicated urinary tract infections (cUTI), including pyelonephritis, for use in patients 18 years or older with limited or no alternative options for treatment, and is currently being evaluated in a phase III trial for use in nosocomial pneumonia caused by Gram-negative pathogens. The unique features and enhanced activity of CFDC suggest that it is likely to serve as a viable therapeutic option in the treatment of MDR Gram-negative infections. The purpose of this review is to provide an overview of previously published literature explaining CFDC's pharmacology, pharmacokinetic / pharmacodynamic (PK / PD) properties, microbiologic activity, resistance mechanisms, safety parameters, dosing and administration, clinical data, and potential place in therapy.

Acinetobacter Pneumonia: Improving Outcomes With Early Identification and Appropriate Therapy

In an era of increasing antimicrobial resistance, Acinetobacter distinguishes itself as one of the most resistant Gram-negative bacteria responsible for significant morbidity and mortality. New solutions are needed to combat the detrimental effects of increasing rates of antimicrobial resistance. Using empiric broad-spectrum antibiotics in patients deemed at risk for infections caused by multidrug-resistant pathogens may protect against attributable mortality, but this temporary solution furthers the risk of antimicrobial resistance. In this article we will review relevant strategies to aid with early identification and appropriate treatment of Acinetobacter pneumonia while preserving antibiotic susceptibility.

A Human Biofilm-Disrupting Monoclonal Antibody Potentiates Antibiotic Efficacy in Rodent Models of both Staphylococcus aureus and Acinetobacter baumannii Infections

Many serious bacterial infections are antibiotic refractory due to biofilm formation. A key structural component of biofilm is extracellular DNA, which is stabilized by bacterial proteins, including those from the DNABII family. TRL1068 is a high-affinity human monoclonal antibody against a DNABII epitope conserved across both Gram-positive and Gram-negative bacterial species. In the present study, the efficacy of TRL1068 for the disruption of biofilm was demonstrated in vitro in the absence of antibiotics by scanning electron microscopy. The in vivo efficacy of this antibody was investigated in a well-characterized catheter-induced aortic valve infective endocarditis model in rats infected with a methicillin-resistant Staphylococcus aureus (MRSA) strain with the ability to form thick biofilms, obtained from the blood of a patient with persistent clinical infection. Animals were treated with vancomycin alone or in combination with TRL1068. MRSA burdens in cardiac vegetations and within intracardiac catheters, kidneys, spleen, and liver showed significant reductions in the combination arm versus vancomycin alone (P < 0.001). A trend toward mortality reduction was also observed (P = 0.09). In parallel, the in vivo efficacy of TRL1068 against a multidrug-resistant clinical Acinetobacter baumannii isolate was explored by using an established mouse model of skin and soft tissue catheter-related biofilm infection. Catheter segments infected with A. baumannii were implanted subcutaneously into mice; animals were treated with imipenem alone or in combination with TRL1068. The combination showed a significant reduction of catheter-adherent bacteria versus the antibiotic alone (P < 0.001). TRL1068 shows excellent promise as an adjunct to standard-of-care antibiotics for a broad range of difficult-to-treat bacterial infections.

Multicenter Study of the Relationship between Carbapenem MIC Values and Clinical Outcome of Patients with Acinetobacter Bacteremia

The Clinical and Laboratory Standards Institute (CLSI) and the European Committee on Antimicrobial Susceptibility Testing (EUCAST) offer different recommendations for carbapenem MIC susceptibility breakpoints for Acinetobacter species. In addition, the clinical efficacy of the intermediate category remains uncertain. This study was designed to determine the optimal predictive breakpoints based on the survival of patients with Acinetobacter bacteremia treated with a carbapenem. We analyzed the 30-day mortality rates of 224 adults who received initial carbapenem monotherapy for the treatment of Acinetobacter bacteremia at 4 medical centers over a 5-year period, according to the carbapenem MICs of the initial isolates. The 30-day mortality was about 2-fold greater in patients whose isolates had carbapenem MICs of ≥8 mg/liter than in those with isolates with MICs of ≤4 mg/liter. The differences were significant by bivariate analysis (53.1% [60/113] versus 25.2% [28/111], respectively; P < 0.001) and on survival analysis by the log rank test (P < 0.001). Classification and regression tree analysis revealed a split between MICs of 4 and 8 mg/liter and predicted the same difference in mortality, with a P value of <0.001. Carbapenem treatment for Acinetobacter bacteremia caused by isolates with carbapenem MICs of ≥8 mg/liter was an independent predictor of 30-day mortality (odds ratio, 4.218; 95% confidence interval, 2.213 to 8.039; P < 0.001). This study revealed that patients with Acinetobacter bacteremia treated with a carbapenem had a more favorable outcome when the carbapenem MICs of their isolates were ≤4 mg/liter than those with MICs of ≥8 mg/liter.