Search

Colistin resistance is caused by different lipopolysaccharide (LPS) modifications, and we propose to evaluate the effect on the innate immune response ofin vivoandin vitrocolistin resistance acquisition. We used 2 pairs of isogenic strains: (1)Escherichia coliATCC25922, susceptible to colistin and its isogenic transconjugant-carryingmcr-1 gene; and (2) OXA-48, CTX-M-15K. pneumoniaesusceptible to colistin (CS-Kp) isolated from a urinary infection and its colistin-resistant variant (CR-Kp) from the same patient after prolonged treatment with colistin. No mutation of described genes for colistin resistance (pmrA, pmrB, mgrB. phoP/QandcrrAB) were found in the CR-Kp genome; however, LPS modifications were characterized by negative-ion MALDI-TOF. The strains were co-cultured with human monocytes to determine their survival after phagocytosis and induction to apoptosis. Also, monocytes were stimulated with bacterial LPS to study cytokine and immunecheckpoint production. The addition of 4-amino-4-deoxy-l-arabinose (Ara4N) to lipid A of CR-Kp accounted for the colistin resistance. CR-Kp survived significantly longer inside human monocytes after being phagocytosed compared with the CS-Kp strain, whereas no significant differences were observed for theE. coliisogenic strains. In addition, LPS from CR-Kp induced both higher apoptosis in monocytes and higher levels of cytokine and immune checkpoint production than LPS from CS-Kp. This effect was strictly the opposite forE. coli. Our data reveal a variable impact of colistin resistance on the innate immune system, depending on the responsible mechanism. Adding Ara4N to LPS increases bacterial survival after phagocytosis and elicits a higher inflammatory response than its colistin-susceptible counterpart.