Abstract
Stenotrophomonas maltophilia
is a nosocomial pathogen with an intrinsic broad-spectrum resistance to
β
-lactam compounds and other antibacterial agents. It produces two chromosomal
β
-lactamases:
a clavulanic acid-sensitive class A (L2) and a tetrameric carbapenemase (L1 or BlaS). We screened 40
S. maltophilia
multidrug-resistant clinical isolates recovered between 1995 and 1998 in the Varese
Hospital (Italy) for the presence of the metallo-
β
-lactamase. The isolates were investigated by phenotypic profiling (enzymatic activity and antibiotic resistance pattern) and molecular methods
such as PCR and pulsed-field gel electrophoresis (PFGE) to reveal intraspecies diversity. For the tested
S. maltophilia
strains, we showed that the
β
-lactamase production could be induced
by the presence of imipenem (50
μ
g/ml) in the culture media. Addition of 1 mM dipicolinic acid completely inhibited the hydrolysis of imipenem but decreased that nitrocefin in a strain-dependent
manner. Full activity of crude extract towards imipenem could be restored by addition of 1 mM ZnCl
2
. Finally, the gene encoding the carbapenem-hydrolyzing
β
-lactamase from
S. maltophilia
ULA-511 and 39/95, a clinical strain, were isolated and sequenced. These two strains have a different profile of multidrug resistance. The two metallo-
β
-lactamases were found to be isologous.
The difference of sensitivity of these two strains was associated to the level of production of the metallo-
β
-lactamase.