Oral Presentation 25th International Pathogenic Neisseria Conference 2026

Emergence of cefotaxime resistance in Neisseria meningitidis clonal complex 11 is driven by a novel penA allele and loss of mtrR function (140907)

Van Chi Thai 1 , Amy Pepper 1 , Hisham Osumanu 1 , Nicolie McCluskey 1 2 3 , August Mikucki 1 4 , David Speers 5 , Geoffrey Coombs 2 6 , Shakeel Mowlaboccus 1 6 , Charlene Kahler 1
  1. The Marshall Center for Infectious Diseases Research and Training, School of Biomedical Science, University of Western Australia, Perth
  2. College of Science, Health, Engineering and Education, Murdoch University, Perth, WA, Australia
  3. Lixa Ltd, Nedlands, WA, Australia
  4. The Kids Research Institute Australia, Perth, Western Australia, Australia
  5. Department of Microbiology, Pathwest Laboratory Medicine-WA, Nedlands, Western Australia, Australia
  6. School of Medical, Molecular and Forensic Sciences, Murdoch University, Perth, WA, Australia

Background:
Invasive meningococcal disease (IMD) is a rapidly fatal infection caused by Neisseria meningitidis. Empirical therapy involves penicillin or the third-generation cephalosporins (3GCs), cefotaxime and ceftriaxone. Decreased susceptibility to penicillin (PENDS) is increasingly reported and is associated with mosaic alterations in penicillin-binding protein 2 encoded by penA. Resistance to 3GCs is exceedingly rare, with only 13 cefotaxime-resistant isolates (CEFXR, MIC ≥0.25 μg/mL) reported globally. We describe the first Australian IMD isolate, ExNM672 from clonal complex 11, exhibiting CEFXRCEFTDSPENDS.

Methods:
Antimicrobial susceptibility was determined using ETEST® (BioMérieux). Genomic DNA or PCR amplicons from the CEFXR ExNM672 isolate were naturally transformed into the cefotaxime and penicillin susceptible (CEFXS PENS) MenW clonal complex 11 isolate, ExNM779. Transformants were whole-genome sequenced on the Illumina MiSeq platform. Comparative genomic analyses were performed using PubMLST Genome Comparator and Geneious Prime (v2023.2.1). Gene expression was assessed by RT–qPCR.

Results:
ExNM672 displayed CEFXR (MIC 0.38 μg/mL), decreased susceptibility to ceftriaxone (CEFTDS, MIC 0.125 μg/mL) and PENDS (MIC 0.25 μg/mL). Transformation of CEFXSPENS ExNM779 with genomic DNA from ExNM672 resulted in CEFXRCEFTDSPENDS transformants containing two recombination regions: the dcw cluster containing a novel penA_1281 allele and the mtrR_133 locus. The CEFXRCEFTDSPENDS phenotype was confirmed to be dependent upon both penA1_1281 and mtrR_133 by transformation of amplicons and sequencing of transformants of ExNM779. mtrR_133 contained an in-frame deletion of nine-nucleotides (Δ77–79; T77E78D79) and an N110H substitution in the MtrR ligand binding domain. RT–qPCR of mtrC expression revealed higher expression in ExNM672 relative to CEFTS PENS ExNM779, confirming that MtrR_133 is inactive. PubMLST analysis identified 68 isolates carrying mtrR_133, predominantly European clonal complex 11 strains, suggesting global clonal expansion before the acquisition of penA_1281. A bioinformatic analysis of the other global CEFXR isolates confirmed the co-carriage inactive mtrR alleles.

Conclusion:
CEFXRCEFTDSPENDS is mediated by target modification via mosaic penA alleles and efflux pump derepression due to mtrR inactivation. mtrR inactivation in N. meningitidis predates the acquisition of mosaic penA alleles in this lineage.