Diversity of naturally occurring Ambler class B metallo-β-lactamases in Erythrobacter spp

In silico analysis identified a metallo-β-lactamase (MBL) in Erythrobacter litoralis HTCC2594, sharing 55% amino acid identity with NDM-1. The aim of this work was to characterize the chromosomally encoded MBLs from several Erythrobacter spp. that may represent potential reservoirs of acquired MBLs.

Erythrobacter citreus, Erythrobacter flavus, Erythrobacter longus, Erythrobacter aquimaris and Erythrobacter vulgaris were from the Pasteur Institute collection, France. DNA was extracted and used for shotgun cloning, and β-lactamases were expressed in Escherichia coli. MICs for resulting E. coli recombinant strains were determined by Etest. The deduced amino acid sequences were analysed and compared with BLASTP. Enzymatic activity of bacterial extracts from recombinant E. coli strains was determined by UV spectrophotometry with imipenem (100 μM) as substrate.

Resulting E. coli recombinant strains harboured hypothetical MBL-encoding genes. MICs of β-lactams showed decreased susceptibility to carbapenems only for E. coli (pFLA-1) and E. coli (pLON-1), expressing the MBL from E. flavus and E. longus, respectively. MBLs from different Erythrobacter spp. shared weak amino acid identity, ranging from 45% to75% identity. They differed greatly from that of E. litoralis HTCC2594 (and NDM-1), sharing only 11%-23% identity. Enzymatic activity against imipenem was detectable but weak in all these recombinant E. coli strains, except E. coli (pFLA-1), in which specific activity was significantly higher.

Several chromosomally located MBLs have been identified from Erythrobacter spp. They share weak amino acid identity and are very weakly related to other acquired MBLs (10%-23%).