Sequence and genome context analysis of a new molecular class D β-lactamase gene from Legionella pneumophila

Legionella pneumophila Philadelphia-1 (ATCC 33152) produces a serine active site beta-lactamase. The chromosomal gene that encodes this enzyme, loxA, has been cloned by PCR using information from the L. pneumophila Philadelphia-1 genome sequencing project. LoxA is a class 2d penicillinase, and its sequence puts it into the molecular class D beta-lactamase family, although phylogenetic analysis shows that LoxA forms a distinct branch in the OXA family along with the LoxA homologue, OXA-29, from Legionella gormanii ATCC 33297(T). Upstream of loxA on the L. pneumophila Philadelphia-1 chromosome is a two-gene locus similar to that found linked to the beta-lactamase genes of Gram-positive bacteria. The unit consists of loxI, encoding a homologue of the Gram-positive beta-lactamase expression regulator, and pbpX, encoding a putative penicillin-binding transpeptidase. Despite the presence of beta-lactamase regulator homologues, we could find no evidence of LoxA induction upon challenge of L. pneumophila Philadelphia-1 with beta-lactams.