Molecular Characterization of Carbapenem-Nonsusceptible Enterobacterial Isolates Collected during a Prospective Interregional Survey in France and Susceptibility to the Novel Ceftazidime-Avibactam and Aztreonam-Avibactam Combinations

Abstract

An interregional surveillance program was conducted in the northwestern part of France to determine the prevalence of carbapenem-nonsusceptible Enterobacteriaceae (CNSE) isolates and their susceptibility to ceftazidime-avibactam and aztreonam-avibactam combinations. Nonduplicate CNSE clinical isolates were prospectively collected from six hospitals between June 2012 and November 2013. MICs of ceftazidime and aztreonam, alone or combined with a fixed concentration of avibactam (4 μg/ml), and those of carbapenems (comparator agents) were determined. MICs of ertapenem in combination with phenylalanine arginine-naphthylamide dihydrochloride (PAβN) were also determined to assess active efflux. Genes encoding carbapenemases, plasmid-mediated AmpC enzymes, extended-spectrum β-lactamases (ESBLs), and major outer membrane proteins (OMPs) were amplified and sequenced. OMPs were also extracted for SDS-PAGE analysis. Among the 139 CNSE isolates, mainly Enterobacter spp. and Klebsiella pneumoniae, 123 (88.4%) were ertapenem nonsusceptible, 12 (8.6%) exhibited reduced susceptibility to all carbapenems, and 4 Proteeae isolates (2.9%) were resistant to imipenem. Carbapenemase production was detected in only two isolates (producing OXA-48 and IMI-3). In contrast, OMP deficiency, in association with AmpCs and/or ESBLs (mainly CTX-M-9, SHV-12, and CTX-M-15), was largely identified among CNSE isolates. The ceftazidime-avibactam and aztreonam-avibactam combinations exhibited potent activity against CNSE isolates (MIC50/MIC90, 1/1 μg/ml and 0.5/0.5 μg/ml, respectively) compared to that of ceftazidime and aztreonam alone (MIC50/MIC90, 512/512 μg/ml and 128/512 μg/ml, respectively). This study reveals the in vitro activity of ceftazidime-avibactam and aztreonam-avibactam combinations against a large collection of porin-deficient enterobacterial isolates that are representative of the CNSE recovered in the northern part of France.

FIG 1

OMP profiles of representative CNSE isolates compared to wild-type reference strains. OMPs were profiled by SDS-PAGE. Lanes: 1, E. coli porin-deficient strain BH01043; 2, E. coli porin-deficient strain DP02127; 3, E. coli wild-type strain TOP10; 4, E. cloacae porin-deficient strain BH01124; 5, E. cloacae porin-deficient strain AJP01076; 6, E. cloacae wild-type strain ATCC 13047; 7, K. pneumoniae porin-deficient strain AG02123; 8, K. pneumoniae wild-type strain NTUH-K2044. The arrows indicate the positions of the OMPs OmpC and OmpF.