Characterization and identification of SFDC-1, a novel AmpC-type beta-lactamase in Serratia fonticola

The clinical and environmental infections caused by AmpC beta-lactamases have been increasingly reported recently. In this study, we characterize the novel chromosome-encoded AmpC beta-lactamase SFDC-1 identified in Serratia fonticola strain R28, which was isolated from a rabbit raised on a farm in southern China. SFDC-1 shared the highest amino acid identity of 79.6% with the functionally characterized AmpC beta-lactamase gene bla(YRC-1), although it had highly homologous functionally uncharacterized relatives in the same species from different sources, including some of the clinical significance. The cloned bla(SFDC-1) exhibited resistance to a broad spectrum of beta-lactam antibiotics, including most cephalosporins with the highest resistance to ampicillin, cefazolin and ceftazidime, with increased MIC levels >= 128-fold compared with the control strains. The purified SFDC-1 showed catalytic activities against beta-lactams with the highest catalytic activity to cefazolin. The genetic context of bla(SFDC-1) and its relatives was conserved in the chromosome, and no mobile genetic elements were found surrounding them.