Genetic and biochemical characterization of GES-16, a new GES-type β-lactamase with carbapenemase activity in Serratia marcescens

摘要

We evaluated the genetic environment ofblaGES-16found in 2 carbapenem-resistantSerratia marcescensclinical isolates recovered from patients hospitalized at a tertiary hospital located in Rio de Janeiro, Brazil. We also compared the kinetics constants for GES-16 and GES-5 against several β-lactams. BothS. marcescensisolates showed identical PFGE pattern and carried the carbapenemase-encoding geneblaGES-16and the extended-spectrum β-lactamase encoding geneblaOXA-10. TheblaGES-16was inserted at the first position of a defective class 1 integron, composed by a fragmented integrase gene that lacked itsattI1recombination site, followed bydfr22,aac(6′)-IIc, andaadA1genes. This integron was located on a 30-kb nonconjugative plasmid. The GES-16 showed 2 amino acid substitutions (Gln38Glu and Gly170Ser) compared to GES-1. Kinetic analysis showed that GES-16 presented hydrolytic activity against all β-lactams tested, except for aztreonam. Imipenem was the carbapenem more efficiently hydrolyzed (highestkcat/Km) by GES-16. The kinetic parameters of GES-16 were similar to those of GES-5. In conclusion, we identified a new GES-type enzyme with carbapenemase activity inS. marcescens. The increasing diversity of such resistance determinants confirms the ongoing evolution of these β-lactamases towards a broader spectrum of activity.