S. Haruta et al., RESISTANCE TO OXYIMINO BETA-LACTAMS DUE TO A MUTATION OF CHROMOSOMAL BETA-LACTAMASE IN CITROBACTER-FREUNDII, Microbiology and immunology, 42(3), 1998, pp. 165-169
The duplicative mutation of an Ala-Val-Arg sequence at positions 208 t
o 210 in the loop structure of Enterobacter cloacae class C beta-lacta
mase caused substrate specificity extension to oxyimino beta-lactam an
tibiotics and this chromosomal mutation provided bacterial cells with
high resistance to the beta-lactams (M. Nukaga et al, 1995, J. Biol. C
hem, 270, 5729-5735). In order to confirm the universality of this phe
nomenon among other class C beta-lactamases, the duplicative mutation
was applied to a class C beta-lactamase of Citrobacter freundii, which
has 74% homology to the E. cloacae beta-lactamase amino acid sequence
. The counterpart sequence to the Ala-Val-Arg of the E. cloacae enzyme
in C. freundii beta-lactamase was identified to be Pro-Val-His. A Pro
-Val-His sequence was inserted just after the native Pro-Val-His seque
nce at positions 208 to 210 in the C. freundii beta-lactamase. The res
ulting mutant of C. freundii beta-lactamase obtained a striking charac
teristic that we expected, showing substrate specificity extension to
oxyimino beta-lactams. Nearly the same result was obtained with the in
sertion of an Ala-Val-Arg sequence after the native Pro-Val-His sequen
ce. These results indicate that structural modification of this locus
commonly induces modification of the substrate specificity to unfavora
ble substrates for many chromosomal class C beta-lactamases produced b
y Gram-negative bacteria.