Induction of L1 and L2 beta-lactamases of Stenotrophomonas maltophilia

Abstract

Isogenic L1 and L2 gene knockout mutants of Stenotrophomonas maltophilia KJ (KJDeltaL1 and KJDeltaL2, respectively) were constructed by xylE gene replacement. Induction kinetics of the L1 and L2 genes were evaluated by testing catechol 2,3-dioxygenase activity in the mutants. The results suggested that the induction of the L1 and L2 genes was differentially regulated.

FIG. 1.

Induction of C23O activity in S. maltophilia KJΔL1 and KJΔL2. The error bars indicate standard deviations (n = 3). Symbols: ○, mutant KJΔL1; •, mutant KJΔL2. OD₄₅₀, optical density at 450 nm.

FIG. 2.

Induction of C23O activity in S. maltophilia KJΔL1 and KJΔL2 as a function of the inducer concentration. The error bars indicate standard deviations (n = 3). OD₄₅₀, optical density at 450 nm.

FIG. 3.

Induction of C23O activity by various β-lactam antibiotics in S. maltophilia KJΔL1 and KJΔL2. Inducers (shown on the x axis): AMP, ampicillin; CAR, carbenicillin; PIP, piperacillin; CRO, ceftriaxone; FOX, cefoxitin; CFP, cefoperazone; CXM, cefuroxime; CTX, cefotaxime; ATM, aztreonam. The induction ratio of KJΔL2 to KJΔL1 for each inducer is also included. The concentration of each inducer is 50 μg/ml, except that cefoperazone's is 16 μg/ml and aztreonam's is 8 μg/ml. The error bars indicate standard deviations (n = 3). OD₄₅₀, optical density at 450 nm.