Β-lactam Agents Research Articles

Clinical manifestations and treatment outcomes for patients with Pseudomonas endocarditis.

To investigate clinical outcomes of patients with Pseudomonas endocarditis and identify factors associated with treatment failure. Adult patients meeting definitive Duke's criteria for Pseudomonas endocarditis at 11 hospitals were identified between May 2000 and February 2024. Failure was defined as death or microbiological failure by day 42. First-line therapy consisted of cefepime, piperacillin/tazobactam, ceftazidime or ceftolozane/tazobactam alone or in combination. Forty-eight patients met inclusion criteria; 29% were persons who inject drugs and 13% were organ transplant recipients. Pseudomonas aeruginosa was the causative species in 98% of cases. Patients who experienced 42 day cure were more likely to be initially managed with first-line β-lactam agents compared with those who experienced clinical failure (97% versus 62%, P = 0.004). Treatment with first-line β-lactams was associated with shorter time to treatment initiation and a lower likelihood of infection due to MDR Pseudomonas spp. In the univariate model, patients who experienced 90 day mortality were more likely to have prosthetic valve endocarditis (57% versus 24%, P = 0.02), an intracardiac complication (36% versus 9%, P = 0.04) and a higher median (IQR) Pitt bacteraemia score [2.5 (2-3.8) versus 1 (0-2), P = 0.048]. Combination therapy did not improve clinical outcomes but did increase the rate of adverse effects resulting in drug discontinuation compared with monotherapy, (21% versus 0%, P = 0.08). This is the largest study of Pseudomonas endocarditis to date. We identified improved clinical outcomes when cefepime, piperacillin/tazobactam, ceftazidime or ceftolozane/tazobactam were used for initial treatment. We did not identify a clinical benefit for combination treatment.

Trends in Empiric Broad-Spectrum Antibiotic Use for Suspected Community-Onset Sepsis in US Hospitals

Little is known about the degree to which suspected sepsis drives broad-spectrum antibiotic use in hospitals, what proportion of antibiotic courses are unnecessarily broad in retrospect, and whether these patterns are changing over time. To describe trends in empiric broad-spectrum antibiotic use for suspected community-onset sepsis. This cross-sectional study used clinical data from adults admitted to 241 US hospitals in the PINC AI Healthcare Database. Eligible participants were aged 18 years or more and were admitted between 2017 and 2021 with suspected community-onset sepsis, defined by a blood culture draw, lactate measurement, and intravenous antibiotic administration on admission. Empiric anti-methicillin-resistant Staphylococcus aureus (MRSA) and/or antipseudomonal β-lactam agent use. Annual rates of empiric anti-MRSA and/or antipseudomonal β-lactam agent use and the proportion that were likely unnecessary in retrospect based on the absence of β-lactam resistant gram-positive or ceftriaxone-resistant gram-negative pathogens from clinical cultures obtained through hospital day 4. Annual trends were calculated using mixed-effects logistic regression models, adjusting for patient and hospital characteristics. Among 6 272 538 hospitalizations (median [IQR] age, 66 [53-78] years; 443 465 male [49.6%]; 106 095 Black [11.9%], 65 763 Hispanic [7.4%], 653 907 White [73.1%]), 894 724 (14.3%) had suspected community-onset sepsis, of whom 582 585 (65.1%) received either empiric anti-MRSA (379 987 [42.5%]) or antipseudomonal β-lactam therapy (513 811 [57.4%]); 311 213 (34.8%) received both. Patients with suspected community-onset sepsis accounted for 1 573 673 of 3 141 300 (50.1%) of total inpatient anti-MRSA antibiotic days and 2 569 518 of 5 211 745 (49.3%) of total antipseudomonal β-lactam days. Between 2017 and 2021, the proportion of patients with suspected sepsis administered anti-MRSA or antipseudomonal therapy increased from 63.0% (82 731 of 131 275 patients) to 66.7% (101 003 of 151 435 patients) (adjusted OR [aOR] per year, 1.03; 95% CI, 1.03-1.04). However, resistant organisms were isolated in only 65 434 cases (7.3%) (30 617 gram-positive [3.4%], 38 844 gram-negative [4.3%]) and the proportion of patients who had any resistant organism decreased from 9.6% to 7.3% (aOR per year, 0.87; 95% CI, 0.87-0.88). Most patients with suspected sepsis treated with empiric anti-MRSA and/or antipseudomonal therapy had no resistant organisms (527 356 of 582 585 patients [90.5%]); this proportion increased from 88.0% in 2017 to 91.6% in 2021 (aOR per year, 1.12; 95% CI, 1.11-1.13). In this cross-sectional study of adults admitted to 241 US hospitals, empiric broad-spectrum antibiotic use for suspected community-onset sepsis accounted for half of all anti-MRSA or antipseudomonal therapy; the use of these types of antibiotics increased between 2017 and 2021 despite resistant organisms being isolated in less than 10% of patients treated with broad-spectrum agents.

Antibiotic Treatment of Carbapenem-Resistant Acinetobacter baumannii Infections in View of the Newly Developed β-Lactams: A Narrative Review of the Existing Evidence.

It is estimated that antimicrobial resistance (AMR) is responsible for nearly 5 million human deaths worldwide each year and will reach 10 million by 2050. Carbapenem-resistant Acinetobacter baumannii (CRAB) infections represent the fourth-leading cause of death attributable to antimicrobial resistance globally, but a standardized therapy is still lacking. Among the antibiotics under consideration, Sulbactam/durlobactam seems to be the best candidate to replace current back-bone agents. Cefiderocol could play a pivotal role within combination therapy regimens. Due to toxicity and the pharmacokinetics/pharmacodynamics (PK/PD) limitations, colistin (or polymyxin B) should be used as an alternative agent (when no other options are available). Tigecycline (or minocycline) and fosfomycin could represent suitable partners for both NBLs. Randomized clinical trials (RCTs) are needed to better evaluate the role of NBLs in CRAB infection treatment and to compare the efficacy of tigecycline and fosfomycin as partner antibiotics. Synergism should be tested between NBLs and "old" drugs (rifampicin and trimethoprim/sulfamethoxazole). Huge efforts should be made to accelerate pre-clinical and clinical studies on safer polymyxin candidates with improved lung activity, as well as on the iv rifabutin formulation. In this narrative review, we focused the antibiotic treatment of CRAB infections in view of newly developed β-lactam agents (NBLs).

Comparative In Vitro Activity of Ceftazidime-Avibactam, Imipenem-Relebactam, and Meropenem-Vaborbactam against Carbapenem-Resistant Clinical Isolates of Klebsiella pneumoniae and Pseudomonas aeruginosa.

Co-infection with carbapenem-resistant Klebsiella pneumoniae (CRKP) and Pseudomonas aeruginosa (CRPA) is associated with poor outcomes and historically relied on combination therapy with toxic agents for management. However, several novel β-lactam/β-lactamase inhibitor combination agents have been developed, offering potential monotherapy options. Here, we compare the in vitro activity of ceftazidime-avibactam (CZA), imipenem-relebactam (IRL), and meropenem-vaborbactam (MVB) against both CRKP and CRPA clinical isolates. Minimum inhibitory concentrations (MICs) for each agent were determined using broth microdilution. Carbapenemase gene detection was performed for representative isolates of varying carbapenem resistance phenotypes. IRL demonstrated excellent activity against CRKP and CRPA with susceptibility rates at 95.8% and 91.7%, respectively. While CZA and MVB showed comparable susceptibility to IRL against CRKP (93.8%), susceptibility of CRPA to CZA was modest at 79.2%, whereas most CRPA strains were resistant to MVB. Of the 35 CRKP isolates tested, 91.4% (32/35) carried a blaKPC gene. Only 1 of 37 (2.7%) CRPA isolates tested carried a blaVIM gene, which conferred phenotypic resistance to all three agents. None of the CRKP strains were cross-resistant to all three agents. Source of infection and co-infection did not significantly influence antimicrobial activity for IRL and CZA; none of the CRPA isolates from co-infected patients were susceptible to MVB. Our results suggest that novel β-lactam agents with antipseudomonal activity and stability against carbapenemases, such as IRL and CZA, offer potential monotherapy options for the treatment of co-infection involving both CRKP and CRPA, but not MVB.

Oxidized glutathione reverts carbapenem resistance in blaNDM-1-carrying Escherichia coli.

The emergence of drug-resistant Enterobacteriaceae carrying plasmid-mediated β-lactamase genes has become a significant threat to public health. Organisms in the Enterobacteriaceae family containing New Delhi metallo-β-lactamase‑1 (NDM-1) and its variants, which are capable of hydrolyzing nearly all β-lactam antibacterial agents, including carbapenems, are referred to as superbugs and distributed worldwide. Despite efforts over the past decade, the discovery of an NDM-1 inhibitor that can reach the clinic remains a challenge. Here, we identified oxidized glutathione (GSSG) as a metabolic biomarker for blaNDM-1 using a non-targeted metabolomics approach and demonstrated that GSSG supplementation could restore carbapenem susceptibility in Escherichia coli carrying blaNDM-1 in vitro and in vivo. We showed that exogenous GSSG promotes the bactericidal effects of carbapenems by interfering with intracellular redox homeostasis and inhibiting the expression of NDM-1 in drug-resistant E. coli. This study establishes a metabolomics-based strategy to potentiate metabolism-dependent antibiotic efficacy for the treatment of antibiotic-resistant bacteria.

In vitro development of resistance against antipseudomonal agents: comparison of novel β-lactam/β-lactamase inhibitor combinations and other β-lactam agents.

We subjected seven P. aeruginosa isolates to a 10-day serial passaging against five antipseudomonal agents to evaluate resistance levels post-exposure and putative resistance mechanisms in terminal mutants were analyzed by whole-genome sequencing analysis. Meropenem (mean, 38-fold increase), cefepime (14.4-fold), and piperacillin-tazobactam (52.9-fold) terminal mutants displayed high minimum inhibitory concentration (MIC) values compared to those obtained after exposure to ceftolozane-tazobactam (11.4-fold) and ceftazidime-avibactam (5.7-fold). Fewer isolates developed elevated MIC values for other β-lactams and agents belonging to other classes when exposed to meropenem in comparison to other agents. Alterations in nalC and nalD, involved in the upregulation of the efflux pump system MexAB-OprM, were common and observed more frequently in isolates exposed to ceftazidime-avibactam and meropenem. These alterations, along with ones in mexR and amrR, provided resistance to most β-lactams and levofloxacin but not imipenem. The second most common gene altered was mpl, which is involved in the recycling of the cell wall peptidoglycan. These alterations were mainly noted in isolates exposed to ceftolozane-tazobactam and piperacillin-tazobactam but also in one cefepime-exposed isolate. Alterations in other genes known to be involved in β-lactam resistance (ftsI, oprD, phoP, pepA, and cplA) and multiple genes involved in lipopolysaccharide biosynthesis were also present. The data generated here suggest that there is a difference in the mechanisms selected for high-level resistance between newer β-lactam/β-lactamase inhibitor combinations and older agents. Nevertheless, the isolates exposed to all agents displayed elevated MIC values for other β-lactams (except imipenem) and quinolones tested mainly due to alterations in the MexAB-OprM regulators that extrude these agents.

Clinical and genomic characteristics of IMP-producing Enterobacter cloacae complex and Klebsiella pneumoniae.

Carbapenemase-producing Enterobacterales (CPEs) are one of the top priority antimicrobial-resistant pathogens. Among CPEs, those producing acquired metallo-β-lactamases (MBLs) are considered particularly problematic as few agents are active against them. Imipenemase (IMP) is the most frequently encountered acquired MBL in Japan, but comprehensive assessment of clinical and microbiological features of IMP-producing Enterobacterales infection remains scarce. Here, we retrospectively evaluated 62 patients who were hospitalized at a university hospital in Japan and had IMP-producing Enterobacterales from a clinical culture. The isolates were either Enterobacter cloacae complex or Klebsiella pneumoniae, and most of them were isolated from sputum. The majority of K. pneumoniae, but not E. cloacae complex isolates, were susceptible to aztreonam. Sequence type (ST) 78 and ST517 were prevalent for E. cloacae complex and K. pneumoniae, respectively, and all isolates carried blaIMP-1. Twenty-four of the patients were deemed infected with IMP-producing Enterobacterales. Among the infected patients, therapy varied and largely consisted of conventional β-lactam agents, fluoroquinolones, or combinations. Three (13%), five (21%), and nine (38%) of them died by days 14, 30, and 90, respectively. While incremental mortality over 90 days was observed in association with underlying comorbidities, active conventional treatment options were available for most patients with IMP-producing Enterobacterales infections, distinguishing them from more multidrug-resistant CPE infections associated with globally common MBLs, such as New Delhi metallo-β-lactamase (NDM) and Verona integron-encoded metallo-β-lactamase (VIM).

Sensitizing methicillin-resistant Staphylococcus aureus (MRSA) to cefuroxime: the synergic effect of bicarbonate and the wall teichoic acid inhibitor ticlopidine.

Methicillin-resistant Staphylococcus aureus (MRSA) strains are a major challenge for clinicians due, in part, to their resistance to most β-lactams, the first-line treatment for methicillin-susceptible S. aureus. A phenotype termed "NaHCO3-responsiveness" has been identified, wherein many clinical MRSA isolates are rendered susceptible to standard-of-care β-lactams in the presence of physiologically relevant concentrations of NaHCO3, in vitro and ex vivo; moreover, such "NaHCO3-responsive" isolates can be effectively cleared by β-lactams from target tissues in experimental infective endocarditis (IE). One mechanistic impact of NaHCO3 exposure on NaHCO3-responsive MRSA is to repress WTA synthesis. This NaHCO3 effect mimics the phenotype of tarO-deficient MRSA, including sensitization to the PBP2-targeting β-lactam, cefuroxime (CFX). Herein, we further investigated the impacts of NaHCO3 exposure on CFX susceptibility in the presence and absence of a WTA synthesis inhibitor, ticlopidine (TCP), in a collection of clinical MRSA isolates from skin and soft tissue infections (SSTI) and bloodstream infections (BSI). NaHCO3 and/or TCP enhanced susceptibility to CFX in vitro, by both minimum inhibitor concentration (MIC) and time-kill assays, as well as in an ex vivo simulated endocarditis vegetations (SEV) model, in NaHCO3-responsive MRSA. Furthermore, in experimental IE (presumably in the presence of endogenous NaHCO3), pre-exposure to TCP prior to infection sensitized the NaHCO3-responsive MRSA strain (but not the non-responsive strain) to enhanced clearances by CFX in target tissues. These data support the notion that NaHCO3 is acting similarly to WTA synthesis inhibitors, and that such inhibitors have potential translational applications in the treatment of certain MRSA strains in conjunction with specific β-lactam agents.

Adequate cefazolin therapy for critically ill patients: can we predict active concentrations from given protein-binding data?

Abstract Objectives Therapeutic drug monitoring of β-lactam antibiotics has become an important tool for treatment of severe infections, especially for critically ill patients who often exhibit altered PK/PD. Therapeutic targets are based on MIC, which refers to the active concentration of the drug. Cefazolin, a β-lactam agent used for treating of MSSA bacteraemia, has a protein binding of approximately 80 %. Therefore, a reliable determination of the active, non-protein-bound concentration is required to ensure optimal therapeutic outcome. Methods From seven critically ill patients who received an initial dose of 2 g cefazolin, followed by a continuous 24 h infusion, a total of 24 serum samples were obtained. The non-protein-bound concentration was directly measured after ultrafiltration and compared to prediction based total concentrations and protein binding values from the literature. For the analysis, a rapid and reliable LC-MS3 based assay was established, offering maximum sensitivity and specificity. Results The measured non-protein-bound concentration varied over a wide range (7.6–118 mg/L), with 22 out of 24 samples exhibiting cefazolin levels above the therapeutic target values (8–16 mg/L). Additionally, the observed protein binding ranged from 29 to 78 % (median 66.8 %), which was significantly lower than that reported in the literature. When comparing the measurements to the predictive performance of total concentrations and protein binding values, poor results were obtained. Conclusions The results show a high variability in plasma protein binding of cefazolin in critically ill patients. Therefore, the “one-dose-fits-all” principle can no longer be considered up to date. For personalised cefazolin therapy based on therapeutic drug monitoring (TDM) it is recommended to determine the active, non-protein-bound drug concentration, as calculations from the total fraction yield poor results.

Genomic features and comparative analysis of a multidrug-resistant Acinetobacter bereziniae strain infecting an animal: a novel emerging one health pathogen?

Acinetobacter bereziniae has recently gained medical notoriety due to its emergence as a multidrug resistance and healthcare-associated pathogen. In this study, we report the whole-genome characterization of an A. bereziniae strain (A321) recovered from an infected semiaquatic turtle, as well as a comparative analysis of A. bereziniae strains circulating at the human-animal-environment interface. Strain A321 displayed a multidrug resistance profile to medically important antimicrobials, which was supported by a wide resistome. The novel Tn5393m transposon and a qnrB19-bearing ColE1-like plasmid were identified in A321 strain. Novel OXA-229-like β-lactamases were detected and expression of OXA-931 demonstrated a 2-64-fold increase in the minimum inhibitory concentration for β-lactam agents. Comparative genomic analysis revealed that most A. bereziniae strains did not carry any antimicrobial resistance genes (ARGs); however, some strains from China, Brazil, and India harbored six or more ARGs. Furthermore, A. bereziniae strains harbored conserved virulence genes. These results add valuable information regarding the spread of ARGs and mobile genetic elements that could be shared not only between A. bereziniae but also by other bacteria of clinical interest. This study also demonstrates that A. bereziniae can spill over from anthropogenic sources into natural environments and subsequently be transmitted to non-human hosts, making this a potential One Health bacteria that require close surveillance.

Structural insights into the molecular mechanism of high-level ceftazidime-avibactam resistance conferred by CMY-185.

β-Lactamases can accumulate stepwise mutations that increase their resistance profiles to the latest β-lactam agents. CMY-185 is a CMY-2-like β-lactamase and was identified in an Escherichia coli clinical strain isolated from a patient who underwent treatment with ceftazidime-avibactam. CMY-185, possessing four amino acid substitutions of A114E, Q120K, V211S, and N346Y relative to CMY-2, confers high-level ceftazidime-avibactam resistance, and accumulation of the substitutions incrementally enhances the level of resistance to this agent. However, the functional role of each substitution and their interplay in enabling ceftazidime-avibactam resistance remains unknown. Through biochemical and structural analysis, we present the molecular basis for the enhanced ceftazidime hydrolysis and impaired avibactam inhibition conferred by CMY-185. The substituted Y346 residue is a major driver of the functional evolution as it rejects primary avibactam binding due to the steric hindrance and augments oxyimino-cephalosporin hydrolysis through a drastic structural change, rotating the side chain of Y346 and then disrupting the H-10 helix structure. The other substituted residues E114 and K120 incrementally contribute to rejection of avibactam inhibition, while S211 stimulates the turnover rate of the oxyimino-cephalosporin hydrolysis. These findings indicate that the N346Y substitution is capable of simultaneously expanding the spectrum of activity against some of the latest β-lactam agents with altered bulky side chains and rejecting the binding of β-lactamase inhibitors. However, substitution of additional residues may be required for CMY enzymes to achieve enhanced affinity or turnover rate of the β-lactam agents leading to clinically relevant levels of resistance.IMPORTANCECeftazidime-avibactam has a broad spectrum of activity against multidrug-resistant Gram-negative bacteria including carbapenem-resistant Enterobacterales including strains with or without production of serine carbapenemases. After its launch, emergence of ceftazidime-avibactam-resistant strains that produce mutated β-lactamases capable of efficiently hydrolyzing ceftazidime or impairing avibactam inhibition are increasingly reported. Furthermore, cross-resistance towards cefiderocol, the latest cephalosporin in clinical use, has been observed in some instances. Here, we clearly demonstrate the functional role of the substituted residues in CMY-185, a four amino-acid variant of CMY-2 identified in a patient treated with ceftazidime-avibactam, for high-level resistance to this agent and low-level resistance to cefiderocol. These findings provide structural insights into how β-lactamases may incrementally alter their structures to escape multiple advanced β-lactam agents.

Characteristics of antibiotic resistance of non-typhoidal Salmonella circulating in the Russian Federation in the period from 2019 to 2022

Introduction. Non-typhoidal Salmonella make a significant contribution to the incidence of enteric infections and are characterized by an increasing proportion of strains resistant to antimicrobial agents (AMA), including the first choice antibiotics (cephalosporins III and fluoroquinolones).
 The purpose of the study is to assess the phenotypic resistance of Salmonella to various classes of AMAs and determine the relationship between the phenotypic resistance, serotype, source of isolation and nature of incidence.
 Materials and methods. We studied 752 representative strains of Salmonella of 2494 strains isolated from various sources (clinical samples, food products, environment) received from 59 regions of Russia in the period from 2019 to 2022. The phenotypic resistance to 22 antibiotics of 11 CLSI classes of AMAs was assessed by broth microdilution method (minimum inhibitory concentration). The diversity of resistance profiles of Salmonella serotypes was compared using the Shannon index.
 Results. The dominant position in terms of isolation frequency is occupied by the serotypes Salmonella Enteritidis, S. Infantis, S. Muenchen, S. Typhimurium, S. Bovismorbificans, which accounted for 64.4% of the studied strains. 543 (72.2%) strains showed resistance to at least one of the tested antibiotics; 193 (25.7%) strains were characterized by multidrug resistance phenotype (MDR). Resistance to AMA classes was characterized by the following distribution: quinolones (61.3%), tetracyclines (28.1%), penicillins (19.1%), β-lactam combination agents (18.6%), folate pathway antagonists (16, 5%), phenicols (10.1%), aminoglycosides (5.6%), cephems (4.7%), monobactams (4.4%), lipopeptides (3.9%). No penem-resistant strains have been identified. The features of Salmonella resistance by AMA classes are shown to depend on the sources of isolation, the Salmonella serotype and the nature of the incidence (outbreak and sporadic).
 Conclusions. Monitoring of phenotypic antibiotic resistance is an important tool for epidemiological surveillance in order to prevent the spread of bacterial resistance to AMAs.

Clinical Features, Genome Epidemiology, and Antimicrobial Resistance Profiles of Aeromonas spp. Causing Human Infections: A Multicenter Prospective Cohort Study.

The genus Aeromonas is increasingly implicated in human infections, but knowledge of its clinical characteristics and antimicrobial resistance profiles has been limited owing to its complex taxonomy. We conducted a multicenter prospective cohort study of patients with Aeromonas infections at hospitals across Japan. Patients were eligible for inclusion if they had an Aeromonas spp. strain in a clinical culture and were considered infected at the culture site. Clinical data were collected, and isolates underwent susceptibility testing and whole-genome sequencing. A total of 144 patients were included. Hepatobiliary infection accounted for a majority of infections (73% [105 of 144]), which mostly occurred in elderly patients with comorbid conditions, including hepatobiliary complications. The all-cause 30-day mortality rate was 10.0% (95% confidence interval, 4.9%-14.8%). By whole-genome sequencing, 141 strains (98%) belonged to 4 Aeromonas species-A caviae, A hydrophila, A veronii, and A dhakensis-with significant intraspecies diversity. A caviae was predominant in all infection sites except skin and soft tissue, for which A hydrophila was the prevailing species. The genes encoding chromosomally mediated class B, C, and D β-lactamases were harbored by 92%-100% of the isolates in a species-specific manner, but they often lacked association with resistance phenotypes. The activity of cefepime was reliable. All isolates of A hydrophila and A dhakensis carried an mcr-3-like colistin resistance gene and showed reduced susceptibility to colistin. Hepatobiliary tract was the most common infection site of Aeromonas spp., with A caviae being the dominant causative species. The resistance genotype and phenotype were often incongruent for β-lactam agents.

The Controversial Effect of Antibiotics on Methicillin-Sensitive S. aureus: A Comparative In Vitro Study.

Methicillin-sensitive Staphylococcus (S.) aureus (MSSA) bacteremia remains a global challenge, despite the availability of antibiotics. Primary treatments include β-lactam agents such as cefazolin and flucloxacillin. Ongoing discussions have focused on the potential synergistic effects of combining these agents with rifampicin or fosfomycin to combat infections associated with biofilm formation. Managing staphylococcal infections is challenging due to antibacterial resistance, biofilms, and S. aureus's ability to invade and replicate within host cells. Intracellular invasion shields the bacteria from antibacterial agents and the immune system, often leading to incomplete bacterial clearance and chronic infections. Additionally, S. aureus can assume a dormant phenotype, known as the small colony variant (SCV), further complicating eradication and promoting persistence. This study investigated the impact of antibiotic combinations on the persistence of S. aureus 6850 and its stable small colony variant (SCV strain JB1) focusing on intracellular survival and biofilm formation. The results from the wild-type strain 6850 demonstrate that β-lactams combined with RIF effectively eliminated biofilms and intracellular bacteria but tend to select for SCVs in planktonic culture and host cells. Higher antibiotic concentrations were associated with an increase in the zeta potential of S. aureus, suggesting reduced membrane permeability to antimicrobials. When using the stable SCV mutant strain JB1, antibiotic combinations with rifampicin successfully cleared planktonic bacteria and biofilms but failed to eradicate intracellular bacteria. Given these findings, it is reasonable to report that β-lactams combined with rifampicin represent the optimal treatment for MSSA bacteremia. However, caution is warranted when employing this treatment over an extended period, as it may elevate the risk of selecting for small colony variants (SCVs) and, consequently, promoting bacterial persistence.

Plasmid-encoded VCC-1 β-lactamase in a clinical isolate of Aeromonas caviae.

Vibrio cholerae carbapenemase (VCC-1) is a chromosomal encoded class A carbapenemase thus far reported in environmental Vibrio cholerae isolates. Here, we report the first isolation of a blaVCC-1 -carrying Aeromonas caviae from a clinical sample in Israel. The isolate was resistant to all β-lactam agents, including carbapenems. The blaVCC-1 was located on a large plasmid. GC content suggests that the origin of the blaVCC-1 gene is neither Aeromonas nor Vibrio spp. but an unknown progenitor.

Assessment of cefiderocol disk diffusion versus broth microdilution results when tested against Acinetobacter baumannii complex clinical isolates.

The aim of this study was to evaluate the correlation between inhibitory zones and minimum inhibitory concentrations (MICs) when testing cefiderocol against Acinetobacter baumannii complex using disk diffusion and the broth microdilution (BMD) method according to the Clinical and Laboratory Standards Institute (CLSI) and European Committee on Antimicrobial Susceptibility Testing (EUCAST) criteria. Four-hundred and sixty-eight non-duplicated A. baumannii complex clinical isolates were collected from 56 hospitals of the China Antimicrobial Surveillance Network from 2019 to 2021. BMD using iron-depleted cation-adjusted Mueller-Hinton broth (ID-CAMHB) and standard disk diffusion methods were performed according to CLSI guidelines. Results were interpreted according to the CLSI and EUCAST breakpoints. Categorical agreement (CA), minor error (mE), major error (ME), and very major error (VME) were calculated for disk diffusion methods. The susceptibilities of all A. baumannii complex isolates by BMD were 98.7% (CLSI) and 97.6% (EUCAST). For all A. baumannii complex isolates, CA was 98.1% (CLSI) and 97.0% (EUCAST), with 0.9% (CLSI) and 1.9% (EUCAST) of VME, respectively. For the carbapenem-susceptible A. baumannii complex, the CA was 100%, with no mE or VME using both CLSI and EUCAST breakpoints. For carbapenem-resistant A. baumannii complex, CA was 97.5% (CLSI) and 96.2% (EUCAST), with 1.1% (CLSI) and 2.5% (EUCAST) of VME, respectively. Regarding the difficult-to-treat resistance A. baumannii complex isolates, CA was 97.6% (CLSI) and 95.7% (EUCAST), with 1.2% (CLSI) and 3.1% (EUCAST) of VME, respectively. Cefiderocol disk diffusion was difficult to assess in this study. Very few isolates were resistant to cefiderocol by BMD using CLSI breakpoint, and these were categorized as susceptible with the disk diffusion test. This study did, however, show that the main proportion of A. baumannii isolates were susceptible to cefiderocol by BMD, including carbapenem-resistant A. baumannii. IMPORTANCE Carbapenem-resistant Acinetobacter baumannii is a major global health concern due to its high prevalence and limited treatment options. Cefiderocol is the only novel Food and Drug Administration (FDA)-approved β-lactam agent for the salvage treatment of carbapenem-resistant A. baumannii infection. Currently, a commercial automated susceptibility testing panel of cefiderocol is unavailable. Both the preparation of iron-depleted cation-adjusted Mueller-Hinton broth and the performance of broth microdilution are cumbersome in routine microbiology laboratories. A disk diffusion method is convenient for cefiderocol antimicrobial susceptibility testing, but limited data are available specifically for A. baumannii clinical isolates. Moreover, the Clinical and Laboratory Standards Institute published revisions to the A. baumannii cefiderocol disk diffusion breakpoints in 2022. Hence, we evaluated the performance of cefiderocol disk diffusion compared with the reference BMD against A. baumannii clinical isolates, especially those with cefiderocol zone diameters ≤ 14 mm.

Defining standard and high dosages for β-lactam agents administered by intermittent, prolonged or continuous infusion: a PK/PD simulation study.

The new definitions of antimicrobial susceptibility categories proposed by EUCAST in 2020 require the definition of standard and high dosages of antibiotic. For injectable β-lactams, standard and high dosages have been proposed for short-infusion regimens only. To evaluate dosages for β-lactams administered by prolonged infusion (PI) and continuous infusion (CI). Monte Carlo simulations were performed for seven injectable β-lactams: aztreonam, cefepime, cefotaxime, cefoxitin, ceftazidime, piperacillin and temocillin. Various dosage regimens based on short infusion, PI or CI were simulated in virtual patients. Pharmacokinetic (PK) profiles and PTAs were obtained based on reference population PK models, as well as PK/pharmacodynamic targets and MIC breakpoints proposed by EUCAST. Alternative dosage regimens associated with PTA values similar to those of recommended dosages up to the breakpoints were considered acceptable. Adequate PTAs were confirmed for most EUCAST short-infusion dosage regimens. A total of 9 standard and 14 high dosages based on PI (3 to 4 h) or CI were identified as alternatives. For cefepime and aztreonam, only PI and CI regimens could achieve acceptable PTAs for infections caused by Pseudomonas spp.: 2 g q8h as PI of 4 h or 6 g/24 h CI for cefepime; 2 g q6h as PI of 3 h or 6 g/24 h CI for aztreonam. These alternative standard and high dosage regimens are expected to provide antibiotic exposure compatible with new EUCAST definitions of susceptibility categories and associated MIC breakpoints. However, further clinical evaluation is necessary.

In vitro activity of cefiderocol against Pseudomonas aeruginosa demonstrating evolved resistance to novel β-lactam/β-lactamase inhibitors.

Cefiderocol demonstrates excellent activity against MDR Pseudomonas aeruginosa; however, the activity against isolates from patients previously treated with β-lactam agents is unknown. We aimed to determine the activity of cefiderocol against P. aeruginosa collected before and after treatment with traditional β-lactams and new β-lactam/β-lactamase inhibitors. Cefiderocol MICs were determined in triplicate in iron-depleted cation-adjusted Mueller-Hinton broth and compared with β-lactam MICs tested by standard methods. All isolates underwent WGS analysis to identify mutations associated with resistance. One hundred and seventy-eight P. aeruginosa isolates were evaluated; 48% (86/178) were non-susceptible to ceftazidime/avibactam, ceftolozane/tazobactam and/or imipenem/relebactam. The cefiderocol MIC50 and MIC90 were 0.12 and 1 mg/L, respectively. Median cefiderocol MICs did not vary against isolates classified as MDR, XDR, or those non-susceptible to ceftazidime/avibactam, ceftolozane/tazobactam and/or imipenem/relebactam when compared with non-MDR isolates. Against isolates collected from patients previously treated with ceftolozane/tazobactam, cefiderocol MICs were increased 4-fold compared with baseline. Cross-resistance to cefiderocol was identified in 21% (3/14) of patients who developed treatment-emergent resistance to ceftolozane/tazobactam. Overall, 6% (11/178) of isolates demonstrated cefiderocol MICs ≥2 mg/L, which were disproportionately collected from patients previously treated with ceftolozane/tazobactam (73%; 8/11). Isolates with reduced cefiderocol susceptibility harboured mutations in ampC, tonB-dependent receptors, the response regulator pirR and ftsI. Cefiderocol demonstrates excellent in vitro activity against P. aeruginosa isolates exposed to other novel β-lactam agents; however, some exceptions were identified. Cross-resistance between cefiderocol and ceftolozane/tazobactam was evident, but not with ceftazidime/avibactam or imipenem/relebactam. Reduced cefiderocol susceptibility was mediated by mutations in ampC and tonB-dependent receptors.

In Vitro Susceptibility to Ceftazidime-Avibactam and Comparator Antimicrobial Agents of Carbapenem-Resistant Enterobacterales Isolates.

The emergence of carbapenem-resistant Enterobacterales (CRE) has been recognized as a significant concern globally. Ceftazidime/avibactam (CZA) is a novel β-lactam/β-lactamase inhibitor that has demonstrated activity against isolates producing class A, C, and D β-lactamases. Here-in, we evaluated the in vitro activity of CZA and comparator antimicrobial agents against 858 CRE isolates, arising from the Southeast Asian region, collected from a large tertiary hospital in Singapore. These CRE isolates mainly comprised Klebsiella pneumoniae (50.5%), Escherichia coli (29.4%), and Enterobacter cloacae complex (17.1%). Susceptibility rates to levofloxacin, imipenem, meropenem, doripenem, aztreonam, piperacillin/tazobactam, cefepime, tigecycline, and polymyxin B were low. CZA was the most active β-lactam agent against 68.9% of the studied isolates, while amikacin was the most active agent among all comparator antibiotics (80% susceptibility). More than half of the studied isolates (51.4%) identified were Klebsiella pneumoniae carbapenemase (KPC)-2 producers, 25.9% were New Delhi metallo-β-lactamase (NDM) producers, and Oxacillinase (OXA)-48-like producers made up 10.7%. CZA was the most active β-lactam agent against KPC-2, OXA-48-like, and Imipenemase (IMI) producers (99.3% susceptible; MIC50/90: ≤1/2 mg/L). CZA had excellent activity against the non-carbapenemase-producing CRE (91.4% susceptible; MIC50/90: ≤1/8 mg/L). Expectedly, CZA had no activity against the metallo-β-lactamases (MBL)-producing CRE (NDM- and Imipenemase MBL (IMP) producers; 27.2% isolates), and the carbapenemase co-producing CRE (NDM + KPC, NDM + OXA-48-like, NDM + IMP; 3.0% isolates). CZA is a promising addition to our limited armamentarium against CRE infections, given the reasonably high susceptibility rates against these CRE isolates. Careful stewardship and rational dosing regimens are required to preserve CZA's utility against CRE infections.

In vitro activities of ceftazidime–avibactam, ceftolozane–tazobactam, meropenem–vaborbactam and other comparators against Pseudomonas aeruginosa isolates with discrepant resistance to carbapenems: Data from the Antimicrobial Testing Leadership and Surveillance (ATLAS) program, 2012–2021

In this study, we aimed to investigate the in vitro susceptibility and β-lactamase-encoding genes of Pseudomonas aeruginosa isolates with discrepant resistance to various carbapenems. We obtained data on P. aeruginosa isolates from the Antimicrobial Testing Leadership and Surveillance program from 2012 to 2021. Minimum inhibitory concentrations of P. aeruginosa isolates were determined using the broth microdilution method. β-lactamase-encoding genes were identified using multiplex polymerase chain reaction assays. Among the P. aeruginosa isolates tested, the percentages of isolates resistant to imipenem, meropenem, and doripenem were 26.9% (14,447/53,617), 20.5 (14,098/68,897), and 17.5% (3,660/20,946), respectively. Imipenem-resistant P. aeruginosa isolates were more susceptible to all tested antimicrobial agents (except colistin) than the meropenem- or doripenem-resistant P. aeruginosa isolates. Carbapenemase genes were detected in 14.3% (2,020/14,098) of meropenem-resistant P. aeruginosa isolates. Imipenem-resistant meropenem-susceptible P. aeruginosa isolates had higher susceptibility profiles, fewer carbapenemase genes (0.3% [5/1,858] vs. 4.1% [10/242]; p < 0.05), and a lower risk of being classified as multidrug-resistant than the imipenem-susceptible meropenem-resistant isolates (16.1% [299/1,858] vs. .73.6% [178/242]; p < 0.05). Among all β-lactam combination agents, ceftazidime-avibactam and ceftolozane-tazobactam had higher susceptibility rates than meropenem-vaborbactam for meropenem-resistant P. aeruginosa (61.8% and 55.5% vs. 30.2%; p<0.05). In conclusion, discrepancy in the resistance of different P. aeruginosa isolates to various carbapenems suggests their different underlying resistance mechanisms. These findings can be useful for effective resistance trend monitoring and accurate antimicrobial treatment in the future.