Mutations in ß-Lactamase AmpC Increase Resistance of Pseudomonas aeruginosa Isolates to Antipseudomonal Cephalosporins.
Antimicrob Agents Chemother. 2015 Jul 27;
Authors: Berrazeg M, Jeannot K, Ntsogo Enguéné VY, Broutin I, Loeffert S, Fournier D, Plésiat P
Mutation-dependent overproduction of intrinsic ß-lactamase AmpC is considered as the main cause of resistance of clinical strains of Pseudomonas aeruginosa to antipseudomonal penicillins and cephalosporins. Analysis of 31 AmpC-overproducing clinical isolates exhibiting a greater resistance to ceftazidime than to piperacillin-tazobactam revealed the presence of 17 mutations in the ß-lactamase, combined to various polymorphic amino acid substitutions. When overexpressed in AmpC-deficient P. aeruginosa 4098, the genes coding for 20/23 of these AmpC variants were found to confer a higher (2- to >64-fold) resistance to ceftazidime and ceftolozane-tazobactam than did the gene from reference strain PAO1. The mutations had variable effects on the minimal inhibitory concentrations (MICs) of ticarcillin, piperacillin-tazobactam, aztreonam, and cefepime. Depending on their location in the AmpC structure and their impact on ß-lactam MICs, they could be assigned to 4 distinct groups. Most of the mutations affecting the omega loop, the R2 domain and the C-terminal end of the protein were shared with ESACs (Extended-Spectrum AmpCs) from other Gram-negative species. Interestingly, two new mutations (F121L, P154L) were predicted to enlarge the substrate binding pocket by disrupting the stacking between residues F121 and P154. We also found that the reported ESACs emerged locally in a variety of clones some of which are epidemic, and did not require hypermutability. Taken together, our results show that P. aeruginosa is able adapt to efficacious ß-lactams including the newer cephalosporin ceftolozane through a variety of mutations affecting its intrinsic ß-lactamase, AmpC. Data suggest that the rates of ESAC-producing mutants are ≥ 1.5% in the clinical setting.
PMID: 26248364 [PubMed - as supplied by publisher]