Characterization of Antimicrobial Resistance Mechanisms and Virulence Determinants in Colistin- and Carbapenem-Resistant Pseudomonas aeruginosa

Antibiotics like colistin can save patients infected with carbapenem-resistant Pseudomonas aeruginosa. However, patients can succumb to such infections even if they undergo colistin therapy. This prompted us to investigate the probable antimicrobial resistance mechanisms and virulence determinants involved in colistin- and carbapenem-resistant P. aeruginosa (CCRPA). Of the 448 P. aeruginosa clinical strains, 19 isolates were resistant to both colistin and carbapenem. Carbapenemases and efflux pump encoding genes were assessed by multiplex PCR and qPCR, respectively. blaVIM was detected among six CCRPA isolates and blaIMP in one strain. The expression levels of pmrA and phoP, as well as pmrB genes and their association with colistin resistance, were assessed by qPCR and semi-quantitate PCR, respectively. pmrA and phoP genes were significantly enhanced in three and nine CCRPA isolates, respectively. We also phenotypically evaluated biofilms, pyocyanin, and alginate production among CCRPA strains. Alginate production was observed in 15 isolates, followed by biofilm (n = 8) and pyocyanin (n = 5). Our results highlighted the coexistence of colistin and carbapenem resistance and biofilm formation among clinical isolates of CCRPA. Further studies are required to trace the source and the origin of colistin and carbapenem resistance in this specific environment.