Activity of Aztreonam/Avibactam and Recently Approved ß-Lactamase Inhibitor Combinations against Enterobacterales and Pseudomonas aeruginosa from Intensive Care Unit and Non-Intensive Care Unit Patients.

We evaluated the activities of aztreonam/avibactam and recently approved ß-lactamase inhibitor combinations (BLICs) to compare the antimicrobial susceptibility patterns of Enterobacterales and Pseudomonas aeruginosa isolated from intensive care unit (ICU) and non-ICU patients. Clinical isolates (1/patient) were consecutively collected from 72 United States medical centres in 2020-2022 and susceptibility tested by broth microdilution. The results for 5421 isolates from ICU patients were analysed and compared to those for 20,649 isolates from non-ICU patients. Isolates from ventilator-associated pneumonia patients were analysed separately. Aztreonam/avibactam inhibited 100.0%/>99.9% Enterobacterales and 100.0%/98.3% of carbapenem-resistant Enterobacterales (CRE) from ICU/non-ICU patients at ≤8 mg/L, respectively. The CRE susceptibility rates were 88.5%/82.9% for ceftazidime/avibactam, 82.1%/81.2% for meropenem/vaborbactam, and 78.2%/72.6% for imipenem/relebactam among ICU/non-ICU isolates. Among the P. aeruginosa isolates from ICU/non-ICU patients, the susceptibility rates were 96.3%/97.6% for ceftazidime/avibactam, 97.2/98.4% for ceftolozane/tazobactam, 97.1%/98.0% for imipenem/relebactam, 77.8%/84.6% for piperacillin/tazobactam, and 76.9%/85.8% for meropenem; aztreonam/avibactam inhibited 78.0%/81.9% of P. aeruginosa at ≤8 mg/L. In summary, lower susceptibility rates were observed among ICU than non-ICU isolates. Aztreonam/avibactam exhibited potent in vitro activity and broad-spectrum activity against Enterobacterales from ICU and non-ICU patients, including CRE and isolates non-susceptible to newer BLICs. Against P. aeruginosa, aztreonam/avibactam showed a spectrum of activity comparable to that of piperacillin/tazobactam, meropenem, and ceftazidime.

Vaborbactam increases meropenem susceptibility in Pseudomonas aeruginosa clinical isolates displaying MexXY and AmpC upregulation.

To evaluate the resistance mechanisms among Pseudomonas aeruginosa clinical isolates exhibiting meropenem (MEM) MIC values higher than meropenem-vaborbactam (MEV). P. aeruginosa clinical isolates collected in US hospitals from 2014 to 2019 were susceptibility tested. Whole-genome and transcriptome sequencing were performed. Results were analyzed for strain typing, acquired ß-lactamases, and mutations in chromosomal genes; gene expression was measured for known ß-lactam resistance contributors. Results were compared to a control group of 10 P. aeruginosa isolates displaying MIC values at 8 mg/L for meropenem ± vaborbactam (MEM = MEV). Out of 88 isolates displaying MEM > MEV, 33 (37.5%) isolates had reproducibly lower MIC values for meropenem-vaborbactam compared to meropenem when retested. The expression of mexX, mexY, mexZ, and ampC was significantly greater among a higher percentage of the MEM > MEV isolates. Furthermore, the association of mexXY and ampC overexpression was detected in 17/33 MEM > MEV isolates and only 1/10 MEM = MEV isolate. In addition, the Pseudomonas-derived cephalosporinase amino acid substitution R79Q was detected among 33.3% of the isolates displaying MEM > MEV, and none of the isolates displayed MEM = MEV. Other resistance mechanisms were not observed or were equally observed in both groups. In rare cases, vaborbactam plays a role in lowering the meropenem MIC values in P. aeruginosa clinical isolates likely due to the inhibition of the AmpC gene that was overexpressed in the presence of upregulation of MexXY with or without alterations in the AmpC gene. IMPORTANCE Pseudomonas aeruginosa isolates are intrinsically resistant to multiple antimicrobial agents and meropenem is an important therapeutic option to treat infections caused by this organism. Meropenem-vaborbactam activity is similar to that of meropenem alone against P. aeruginosa isolates. Isolates belonging to this species that display lower meropenem-vaborbactam compared to meropenem are rare. We initiated this study to understand the resistance mechanisms that could lead to lower meropenem-vaborbactam MIC values when compared to meropenem alone. We documented that isolates displaying lower meropenem-vaborbactam exhibited overexpression of MexXY and AmpC. In addition, isolates displaying the R79Q PDC (AmpC) mutation were more likely to display lower meropenem-vaborbactam when compared to isolates displaying the same MIC values for these agents.

Recent increase in fluconazole-nonsusceptible Candida parapsilosis in a global surveillance with the expansion of the Erg11 Y132F genotype and a rapid detection method for this alteration.

We evaluated the rates of fluconazole nonsusceptibility among 1103 Candida parapsilosis isolates collected globally from 2018 to 2021. These rates were <10.3% until 2020 but increased to 15.4% in 2021. Fluconazole-nonsusceptible C. parapsilosis rates were highest in Europe (96/466 isolates; 20.6%) followed by the US (23/386; 6.0%). As the Erg11 Y132F alteration has been a common fluconazole nonsusceptibility mechanism in C. parapsilosis, we developed a PCR assay to detect this mutation. This assay displayed 100% sensitivity and specificity when tested against 56 isolates previously submitted to whole genome sequencing. The Erg11 Y132F alteration was detected in 83.2% of the isolates (104/125) collected during 2018 to 2021 using the PCR assay. The highest rates of the Erg11 Y132F genotype were observed among fluconazole-nonsusceptible isolates from Europe (93.8%), followed by the US (60.9%). An increase in fluconazole-nonsusceptible C. parapsilosis was documented in 2021. Most isolates from Europe and the US carried the Y132F Erg11 alteration that has been reported in various countries.

In Vitro Activity of Tebipenem against Various Resistant Subsets of Escherichia coli Causing Urinary Tract Infections in the United States (2018 to 2020).

This study investigated the activity of an oral carbapenem, tebipenem, against various molecularly characterized subsets of Escherichia coli. A total of 15.0% of E. coli isolates (360/2,035 isolates) met the MIC criteria for screening for ß-lactamases. Most of those isolates (74.7% [269/360 isolates]) carried blaCTX-M. The CTX-M distribution varied (50% to 86%) among Census Regions, as did that of plasmid AmpC genes (up to 41% among E. coli isolates from the New England Region). Tebipenem and intravenous carbapenems showed uniform activity against various E. coli subsets.

The plethora of resistance mechanisms in Pseudomonas aeruginosa: transcriptome analysis reveals a potential role of lipopolysaccharide pathway proteins to novel ß-lactam/ß-lactamase inhibitor combinations.

OBJECTIVES: Whole genome and transcriptome analysis of 213 Pseudomonas aeruginosa isolates resistant to antipseudomonal ß-lactams collected in 30 countries was performed to evaluate resistance mechanisms against these agents. METHODS: Isolates were susceptibility tested by reference broth microdilution. Whole genome and transcriptome sequencing were performed, and data were analysed using open-source tools. A statistical analysis of changes in the expression of >5500 genes was compared to the expression of PAO1. RESULTS: The high-risk clones ST235 and ST111 were the most prevalent among >90 sequence types (STs). Metallo-ß-lactamase (MBLs) genes were detected in 40 isolates. AmpC and MexXY were the most common genes overexpressed in approximately 50% of the 173 isolates that did not carry MBLs. Isolates overexpressing pmrA and pmrB, the norspermidine production genes speD2 and speE2, and the operon arnBCADTEF-ugd were noted among strains resistant to ceftolozane-tazobactam and ceftazidime-avibactam, despite the lack of polymyxin resistance often associated to increased expression of these genes. Overexpression of MuxABC-OpmB, OprG, and OprE proteins were associated with resistance to ceftolozane-tazobactam in addition to the usual genes involved in cephalosporin, monobactam, and carbapenem resistance. Statistical analysis identified discrete mutations in ArmZ, OprD, and AmpC that correlated to antipseudomonal ß-lactam resistance. CONCLUSIONS: P. aeruginosa resistance mechanisms are complex. This analysis suggests the role of multiple genes in resistance to antipseudomonal ß-lactams, including some not commonly described.

Ceftazidime-avibactam activity against a challenge set of carbapenem-resistant Enterobacterales: Ompk36 L3 alterations and ß-lactamases with ceftazidime hydrolytic activity lead to elevated MIC values.

INTRODUCTION: This study examined ceftazidime-avibactam activity against carbapenem-resistant Enterobacterales (CRE) clinical isolates and resistance mechanisms among non-metallo ß-lactamase (MBL) producers displaying ceftazidime-avibactam MIC values at 4 mg/L. METHODS: CRE isolates (286 of 8161 Enterobacterales) collected in Asia-Pacific, Europe and Latin America during 2016 were screened for carbapenemase genes. Selected isolates were susceptibility tested for ceftazidime-avibactam in the presence or absence of phenylalanine-arginyl ß-naphthylamide (PAßN) and polymyxin B nonapeptide (PMBN). Genome sequences were investigated for the integrity of outer membrane protein (OMP) genes and multilocus sequence typing. qRT-PCR assays were conducted to determine expression of acrA, ampC, and OMP genes. RESULTS: Ceftazidime-avibactam inhibited 99.2% of the Enterobacterales, 22 (78.7%) of the 286 CRE and 226 (100%) non-MBL producers. Among carbapenemase producers (85.3%; 244 of 286), the most common gene was blaKPC (76 blaKPC-3 and 46 blaKPC-2), followed by blaOXA-48-like (60 isolates) and blaNDM (37). Ceftazidime-avibactam MIC values at 4 mg/L were noted among 14 Klebsiella pneumoniae (13 carrying blaKPC and 1 blaCTX-M-15) mostly from Italy and Brazil and 1 Klebsiella aerogenes overexpressing ampC. PAßN did not significantly decrease ceftazidime-avibactam results, but adding PMBN did significantly decrease the MIC results for the combination. All K. pneumoniae isolates had a premature stop codon at OmpK35 and most isolates had L3 alterations of OmpK36, low expression of this gene, or OmpC disruption (K. aerogenes). Nine K. pneumoniae isolates belonged to clonal complex 258 and displayed intrahospital clonality. CONCLUSION: Ceftazidime-avibactam is an important addition to the armamentarium against multidrug-resistant organisms, and elevated MIC results for this combination seem to be associated with L3 OmpK36 alterations and ß-lactamases able to hydrolyze ceftazidime.