Molecular and biochemical heterogeneity of class B carbapenem-hydrolyzing beta-lactamases in Chryseobacterium meningosepticum

Although the carbapenem-hydrolyzing beta-lactamase (CH beta L) BlaB-1 is kn own to be in Chryseobacterium meningosepticum NCTC 10585, a second CH beta L gene, bla(GOB-1) was cloned from another C, meningosepticum clinical isol ate (PINT). The G+C content of bla(GOB-1) (36%) indicated the likely chromo somal origin of this gene. Its expression in Escherichia coli DH10B yields a mature CH beta L with a pI of 8.7 and a relative molecular mass of 28.2 k Da, In E, coli, GOB-1 conferred resistance to narrow-spectrum cephalosporin s and reduced susceptibility to ureidopenicillins, broad-spectrum cephalosp orins, and carbapenems, GOB-1 had a broad-spectrum hydrolysis profile inclu ding penicillins and cephalosporins (but not aztreonam), The catalytic effi ciency for meropenem was higher than for imipenem, GOB-1 had low amino acid identity with the class B CH beta Ls, sharing 18% with the closest, L-1 fr om Stenotrophomonas maltophilia, and only 11% with BlaB-1, h-Post of the co nserved amino acids that may be involved in the active site of CH beta Ls ( His-101, Asp-103, His-162, and His-225) were identified in GOB-1, Sequence heterogeneity was found for GOB-1-like and BlaB-1-like beta-lactamases, hav ing 90 to 100% and 86 to 100% amino acid identity, respectively, among 10 u nrelated C. meningosepticum isolates. Each isolate had a GOB-1-like and a B laB-1-like gene. The same combination of GOB-1-like and BlaB-1-like beta-la ctamases was not found in two different isolates. C. meningosepticum is a b acterial species with two types of unrelated chromosome-borne class E CH be ta Ls that can be expressed in E, coil and, thus, may represent a clinical threat if spread in gram-negative aerobes.