Activity of ceftazidime-avibactam against Escherichia coli isolates from U.S. veterans (2011) in relation to co-resistance and sequence type 131 (ST131) H30 and H30Rx status.

Escherichia coli ST131, with its multidrug-resistance-associated H30R1 and H30Rx clonal subsets within the H30R subclone, causes most antimicrobial-resistant E. coli infections. The activity of ceftazidime-avibactam (CZA) against ST131 strains is undefined. We determined CZA MICs for 595 E. coli clinical isolates from 24 Veterans Affairs Medical Centers (2010-2011). Resistance status and MICs were compared with study resistance category (fluoroquinolone-susceptible, fluoroquinolone-resistant, and extended-spectrum beta-lactamase (ESBL)-producing); ST131, H30R1, and H30Rx status; blaCTX-M-15-like genotype; and MICs for piperacillin-tazobactam, levofloxacin, gentamicin, ceftazidime, and meropenem. Proportion resistant ranged from zero (CZA, meropenem) to 61% (levofloxacin). MICs generally increased by resistance category (from fluoroquinolone-susceptible through fluoroquinolone-resistant to ESBL), clonal subgroup (from non-ST131-H30 through H30R1 to H30Rx), and blaCTX-M-15-like status. CZA MICs were slightly but significantly greater in association with resistance (or elevated MICs) to each comparator yet remained in the susceptible range. CZA was reliably active and outperformed noncarbapenem comparators, so it should prove useful as a carbapenem-sparing alternative.