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Egon A Ozer

Publications and source records attributed to Egon A Ozer.

4 recordsLinked to original sources
PubMed2026

Transposon insertion sequencing of Pseudomonas aeruginosa identifies multiple intersecting pathways essential for extreme colistin resistance.

Colistin is used to treat antibiotic resistant gram-negative infections, including those caused by Pseudomonas aeruginosa (Pa). Using a diverse collection of clinical isolates, we identified BWH047, a colistin-resistant isolate with an extremely high minimum inhibitory concentration (MIC, 1280 µg/mL). To characterize the genes conditionally essential for colistin resistance in BWH047, we employed transposon insertion sequencing and identified 20 gene candidates. In-frame deletion validated 75% of the candidates and identified genes in several new pathways that contribute to colistin resistance in Pa, including algU and wapH. We also identified several candidate genes from previously reported colistin resistance pathways (e.g., arn, pmrAB). We further investigated the impact of a colistin resistance-associated inner membrane DedA-family undecaprenyl phosphate flippase, which we named DpcA (DedA of Pseudomonas necessary for colistin resistance A). Deletion of dpcA in BWH047 restored sensitivity to colistin (MIC = 0.5 µg/mL) and resulted in several unique changes to the structure of lipopolysaccharide (LPS), including production of decreased amounts of the colistin resistance-conferring 4-amino-4-deoxy-L-arabinose (L-Ara4N) modification on lipid A. This work represents a robust analysis of colistin resistance in Pa and identifies intersecting pathways that contribute to extreme phenotypic resistance.

Pseudomonas aeruginosa↗
PubMed2026

L2 β-lactamase contributes to ceftolozane-tazobactam resistance in Pseudomonas aeruginosa.

The prevalence of non-susceptibility to ceftolozane-tazobactam (C/T) among Pseudomonas aeruginosa remains low, but novel mechanisms of C/T resistance are of concern. Herein, we describe a novel P. aeruginosa genotype associated with high-level C/T resistance (>256/4 µg/mL) in a single patient. Whole-genome sequencing of the isolate was compared to that of a susceptible isolate cultured from the same patient 2 months earlier. Analysis of the sequences revealed two different P. aeruginosa high-risk clones: sequence type (ST)111 followed by ST235. The C/T-resistant ST235 isolate contained five copies of a genetic element composed of an L2 β-lactamase gene (blaL2) and a truncated ampRL2 transcriptional regulator gene, which are commonly found together in Stenotrophomonas maltophilia strains and have not been reported to mediate resistance to C/T. Comparative genomic analysis with other P. aeruginosa isolates failed to identify alternative explanations for the observed C/T resistance. We found that exogenous expression of blaL2 increased C/T minimum inhibitory concentrations (MICs) in genetically distinct P. aeruginosa strains. A screen of our archived isolates identified two P. aeruginosa clinical isolates, PS2045 and PS2046, with one and two copies, respectively, of the genetic element containing blaL2 and truncated ampRL2. Interestingly, disruption of the gene blaL2 but not the truncated ampRL2 in PS2045 led to a decrease in C/T MIC. Thus, we report a novel mechanism of C/T resistance in P. aeruginosa partially mediated by an L2 β-lactamase independently of its canonical regulator, AmpRL2.

bioinformatics↗
PubMed2026

Molecular epidemiology and antimicrobial resistance determinants of Corynebacterium diphtheriae causing infections in Karachi, Pakistan, 2023-2024.

OBJECTIVES: Diphtheria remains endemic in Pakistan, with cases increasing following the COVID-19 pandemic despite ongoing vaccination programs. This study analyzes the genomic diversity, virulence, and antimicrobial resistance patterns of pharyngeal diphtheria strains collected during the Karachi outbreak. METHODS: Corynebacterium diphtheriae isolates from a tertiary care hospital laboratory in Karachi (August 2023-October 2024) were included. Antimicrobial susceptibility testing and whole-genome sequencing of phenotypically confirmed isolates were performed. Phylogenetic and bioinformatics analyses were performed using diphtOscan and AMRFinderPlus tools. RESULTS: A total of 47 pharyngeal C. diphtheriae isolates were included. The median age of patients was 7 years, and the male-to-female ratio was 1.6:1. The tox gene was present in 89.4% of isolates, while only 29% (n = 13/45) demonstrated toxin production. Genomic analysis identified 10 sequence types; ST384 and ST698 were most prevalent. Phenotypically, 34% (n = 16) were resistant to both erythromycin and penicillin, and 49% (n = 23) were multidrug-resistant. The most prevalent resistance genes were sul1 (100%), erm(X) (76.6%), and pbp2m (51.1%). CONCLUSION: Circulation of diverse C. diphtheriae strains with alarming antimicrobial resistance underscores the need for genomic surveillance to evaluate transmission trends. We further highlight the limitations of the Elek test in detecting toxin production and the need for improved diagnostics in low- and middle-income countries.

Antimicrobial resistance↗
PubMed2026

A novel mechanism of ceftolozane-tazobactam resistance in Pseudomonas aeruginosa mediated by L2 β-lactamase.

The prevalance of non-susceptibility to ceftolozane-tazobactam (C/T) among Pseudomonas aeruginosa remains low but novel mechanisms of C/T resistance are of concern. Herein, we describe a novel Pseudomonas aeruginosa genotype associated with high-level C/T resistance (>256/4 μg/mL) in a single patient. Whole genome sequencing of the isolate was compared to that of a susceptible isolate cultured from the same patient two months earlier. Analysis of the sequences revealed two different P. aeruginosa high-risk clones: ST111 followed by ST235. The C/T-resistant ST235 isolate contained five copies of a genetic element comprised of an L2 β-lactamase gene (bla L2) and a truncated ampR L2 transcriptional regulator gene, which are commonly found together in Stenotrophomonas maltophilia strains and have not been reported to mediate resistance to C/T. Comparative genomic analysis with other P. aeruginosa isolates failed to identify alternative explanations for the observed C/T resistance. We found that exogenous expression of bla L2 modestly increased C/T MICs in genetically distinct P. aeruginosa strains. A screen of our archived isolates identified two P. aeruginosa clinical isolates, PS2045 and PS2046, with one and two copies, respectively, of the genetic element containing bla L2 and truncated ampR L2. Interestingly, disruption of the gene bla L2 but not the truncated ampR L2 in PS2045 led to a significant decrease in C/T MIC. Thus, we report a novel mechanism of C/T resistance in P. aeruginosa mediated by an L2 β-lactamase independently of its canonical regulator AmpR L2.

bioinformatics↗