A TEM-2 β-lactamase encoded on an active Tn1-like transposon in the genome of a clinical isolate of Stenotrophomonas maltophilia

A constitutively expressed β-lactamase gene from a clinical isolate of Stenotrophomonas maltophilia, J675Ia, has been cloned. Its DNA sequence is almost identical to that of blaTEM2 (one nucleotide change) and the expressed enzyme is a Bush type 2a penicillinase with an amino acid sequence identical to that of TEM-2. The blaTEM gene was present within a novel Tn1/Tn3-type transposon in the genome of isolate J675Ia and the transposon was able to mobilize blaTEM on to the broad host-range conjugative plasmid, R388. When transferred to an Escherichia coli recipient, R388::Tn conferred high-level ampicillin resistance. This represents the first identification of a TEM β-lactamase in S. maltophilia and the first evidence that this important clinical pathogen is able to act as a reservoir for mobile β-lactamase genes in the hospital environment.