Carbapenem-resistant hypervirulent P. aeruginosa coexpressing exoS/exoU in Brazil

Pseudomonas aeruginosa is a ubiquitous organism with high clinical impact due to its intrinsic resistance to many antimicrobial drugs and ability to acquire antibiotic resistance and virulence genes. The type III secretion system (T3SS) is critical in the pathogenesis of this species, where ExoS and ExoU are the main toxins. Strains cocarrying both toxins are considered hypervirulent. However, there is a gap in revealing the coexpression of exoU/exoS. This study characterizes a carbapenem-resistant exoU+/exoS+ P. aeruginosa in Brazil through its expression and genetic context.

Thirty-three P. aeruginosa from Brazil were subjected to antibiotic susceptibility testing and sequencing. The genomes were characterized considering their resistome and virulome, and their phylogeny was established. The expression of exoU/exoS was evaluated by qPCR and the exoU genomic region was analyzed.

A carbapenem-resistant strain presented the exoU+/exoS+ genotype, belonging to serotype O4 and ST4996. Although it did not carry carbapenemases, it presented mutations in the porin OprD. The qPCR assay showed that exoU and exoS are coexpressed at higher levels than control strains, although they share the same promoter and relevant ExoU sites with exoU+/exoS- genomes. Three other Brazilian genomes with this trait were identified, also presenting the exoU gene in the context of the PAPI-2 island.

P. aeruginosa carrying exoS/exoU in Brazil is rare, although they may occur in the clinic associated with carbapenem resistance. Furthermore, although belonging to a different ST, the Brazilian strain PA27N presented exoS/exoU expression levels similar to the hypervirulent P. aeruginosa strains occurring in China.