Molecular and Biochemical Heterogeneity of Class B Carbapenem-Hydrolyzing β-Lactamases in Chryseobacterium meningosepticum

Although the carbapenem-hydrolyzing β-lactamase (CHβL) BlaB-1 is known to be inChryseobacterium meningosepticum NCTC 10585, a second CHβL gene,bla GOB-1 , was cloned from anotherC. meningosepticum clinical isolate (PINT). The G+C content ofbla GOB-1 (36%) indicated the likely chromosomal origin of this gene. Its expression inEscherichia coli DH10B yields a mature CHβL with a pI of 8.7 and a relative molecular mass of 28.2 kDa. InE. coli , GOB-1 conferred resistance to narrow-spectrum cephalosporins and reduced susceptibility to ureidopenicillins, broad-spectrum cephalosporins, and carbapenems. GOB-1 had a broad-spectrum hydrolysis profile including penicillins and cephalosporins (but not aztreonam). The catalytic efficiency for meropenem was higher than for imipenem. GOB-1 had low amino acid identity with the class B CHβLs, sharing 18% with the closest, L-1 fromStenotrophomonas maltophilia , and only 11% with BlaB-1. Most of the conserved amino acids that may be involved in the active site of CHβLs (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 β-lactamases, having 90 to 100% and 86 to 100% amino acid identity, respectively, among 10 unrelatedC. meningosepticum isolates. Each isolate had a GOB-1-like and a BlaB-1-like gene. The same combination of GOB-1-like and BlaB-1-like β-lactamases was not found in two different isolates.C. meningosepticum is a bacterial species with two types of unrelated chromosome-borne class B CHβLs that can be expressed inE. coli and, thus, may represent a clinical threat if spread in gram-negative aerobes.