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 β-lactamases, and mutations in chromosomal genes; gene expression was measured for known β-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.

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

OBJECTIVES

Whole genome and transcriptome analysis of 213 Pseudomonas aeruginosa isolates resistant to antipseudomonal β-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-β-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 β-lactam resistance.

CONCLUSIONS

P. aeruginosa resistance mechanisms are complex. This analysis suggests the role of multiple genes in resistance to antipseudomonal β-lactams, including some not commonly described.

Activity of Plazomicin against Enterobacteriaceae Isolates Collected in the United States Including Isolates Carrying Aminoglycoside-Modifying Enzymes Detected by Whole Genome Sequencing

Background

Plazomicin (PLZ) is a next-generation aminoglycoside (AMG) stable against aminoglycoside-modifying enzymes (AME) that completed Phase 3 studies for complicated urinary tract infections and serious infections due to carbapenem-resistant Enterobacteriaceae (ENT). We evaluated the activity of PLZ and AMGs against ENT collected in US hospitals during 2016.

Methods

A total of 2,097 ENT were susceptibility (S) tested by CLSI reference broth microdilution methods. E. coli, Klebsiella spp. Enterobacter spp., and P. mirabilis isolates displaying non-S MICs (CLSI criteria) for gentamicin (GEN), amikacin (AMK), and/or tobramycin (TOB) were submitted to WGS, de novo assembly and screening for AME genes.

Results

Against ENT, PLZ was more active than all 3 clinically available AMGs (Table). PLZ and AMK activities were stable regardless of the infection type; however, differences were observed for GEN and TOB. Bloodstream isolates displayed higher GEN MICs when compared with the other infection sites. TOB activity varied 4-fold, being higher for bloodstream and pneumonia infections and lower for skin/soft tissue and other/unknown specimens. Against 198 isolates carrying 1 or more AME-encoding genes detected among 208 AMG-non-S isolates, the activity of PLZ was 8- to 16-fold greater when compared with the activity of AMK and at least 16-fold higher than the activity of GEN or TOB.

Conclusion

PLZ was active against ENT isolates from US hospitals regardless of infection type. PLZ displayed activity against isolates carrying AME genes that represent 12.0% of selected species. AME-carrying isolates were considerably more resistant to AMK, GEN, and TOB, highlighting the potential value of PLZ to treat infections caused by these organisms.

This project has been funded under BARDA Contract No. HHSO100201000046C.

Disclosures

M. Castanheira, Achaogen: Research Contractor, Research grant; L. M. Deshpande, Achaogen: Research Contractor, Research grant; C. M. Hubler, Achaogen: Research Contractor, Research grant; R. E. Mendes, Achaogen: Research Contractor, Research grant; A. W. Serio, Achaogen: Employee, Salary; K. M. Krause, Achaogen: Employee, Salary; R. K. Flamm, Achaogen: Research Contractor, Research grant