P. Mugnier et al., CARBAPENEMS AS INHIBITORS OF OXA-13, A NOVEL, INTEGRON-ENCODED BETA-LACTAMASE IN PSEUDOMONAS-AERUGINOSA, Microbiology, 144, 1998, pp. 1021-1031
A clinical Pseudomonas aeruginosa strain, PAe391, was found to be resi
stant to a number of antibiotics including ticarcillin, piperacillin,
cefsulodin and amikacin, and a disk diffusion assay showed evidence of
pronounced synergy between imipenem and various beta-lactam antibioti
cs. Cloning and nucleotide sequence analysis revealed the dicistronic
arrangement of an aac(6')-lb variant and a novel bla(OXA)-type gene be
tween the intl and qacE Delta 1 genes typical of integrons. In PAe391,
this integron was apparently chromosome-borne. The beta-lactamase, na
med OXA-13, displayed nine amino acid changes with respect to OXA-10:
I in position 10 of OXA-10 to T (I10T), G20S, D55N, N73S, T107S, Y174F
, E229C, S245N and E259A. OXA-13 (pl(app) = 8.0) showed poor catalytic
activity against penicillins as well as cephalosporins, but was effic
ient in hydrolysing some penicillinase-resistant beta-lactams, such as
cefotaxime and aztreonam. It was efficiently inhibited by imipenem (K
-iapp = 11 nM), and formed a stable complex. While the K-iapp value of
meropenem was similar (16 nM), the corresponding complex was less sta
ble.