The Bla2 beta-lactamase from the live-vaccine strain of Francisella tularensis encodes a functional protein that is only active against penicillin-class beta-lactam antibiotics

Abstract

Francisella tularensis ssp. tularensis is a category A select agent and the causal organism for the zoonotic disease tularemia. The vast majority of F. tularensis isolates are beta-lactamase-positive. beta-lactamase production is widely believed to be responsible for the inefficacy of beta-lactams in the treatment of tularemia. In this study, we report the cloning and characterization of the two chromosomally encoded F. tularensis ssp. holarctica live-vaccine strain (LVS) beta-lactamases. The two LVS beta-lactamases were homologous to F. tularensis Schu S4 open reading frames FTT0681c and FTT0611c and have been named bla1 (LVS) and bla2 (LVS), respectively. Recombinant expression in Escherichia coli suggested that bla1 (LVS) did not encode a functional beta-lactamase, whereas bla2 (LVS) encoded a functional beta-lactamase that hydrolyzed penicillins but was inactive against third-generation cephalosporins, including cefprozil. As both LVS and Schu S4 were susceptible to cefprozil, we developed three new shuttle vectors based on selection for the production of the Bla(shv-2) extended-spectrum beta-lactamase with cefprozil. The resulting shuttle vectors were suitable for recombinant gene expression and complementation studies in LVS and Schu S4.