Klebsiella pneumoniae strain:DT1 | isolate:DT1 Genome sequencing. Klebsiella pneumoniae strain:DT1 | isolate:DT1

Avibactam is a novel broad-range beta lactamase inhibitor active against Ambler class A- (including ESBL and KPC) and some Ambler class D- (e.g. OXA-48) enzymes. We here report on the emergence of ceftazidime-avibactam resistance in clinical multi-resistant, OXA-48 and CTX-M-14-producing K. pneumoniae strain DT12 during ceftazidime-avibactam treatment. Comparative whole genome sequence analysis identified two single nucleotide polymorphisms in the CTX-M-14-encoding gene leading to two amino acid changes (P170S; T264I). Compared to wild type CTX-M-14, expression of CTX-M-14Δ167Δ261 isoform in E. coli Top10 led to a 64- and 16-fold increase in ceftazidime and ceftazidime-avibactam MICs, respectively, functionally linking the observed SNP and elevated MICs. The mutated CTX-M-14 isoform exhibited augmented ceftazidime hydrolytic activity, being a reasonable cause for impaired susceptibility to avibactam inhibition. The P167S exchange in CTX-M was found in association with elevated ceftazidime-avibactam MICs in independent K. pneumoniae isolates, but was not sufficient for full resistance. Apparently, additional, CTX-M-independent mechanisms contribute to ceftazidime-avibactam resistance in K. pneumoniae DT12. This first study on the molecular basis of ceftazidime-avibactam-resistance in K. pneumoniae emerging in vivo underscores the need for continuous monitoring of ceftazidime-avibactam-susceptibility during therapy. Rapid development of CTX-M-14 isoforms exhibiting augmented ceftazidime hydrolytic activity may limit usefulness of ceftazidime-avibactam monotherapies in infections caused by isolates carrying both, blaCTX-M-14 and blaOXA-48.