[Determination of the isoelectric point of beta-lactamases isolated from 67 Klebsiella oxytoca strains and phenotype behaviour against eight beta-lactam antibiotics].

Klebsiella oxytoca is naturally resistant to aminopenicillins and carboxypenicillins by production of a chromosomal beta-lactamase but susceptible to third generation cephalosporins. The third generation cephalosporins activity may be reduced by: overproduction of the chromosomally encoded beta-lactamase or an extended-spectrum beta-lactamase. These activity modification are rarely found in the hospital of Aix-en-Provence (France). The activity modification rate of K. oxytoca resistant by one of these mechanisms between 1986 and 1991 are 3.6% for chromosomally encoded beta-lactamase overproduction and 0.7% for acquisition of an extended-spectrum beta-lactamase. We have determined the isoelectric point (pI) by isoelectrofocusing of the beta-lactamases isolated from 67 K. oxytoca and the activity of 8 beta-lactams has been studied by disk-diffusion. 51 wild strains, 14 overproducing strains (including 2 in vitro mutants) and 2 strains with extended-spectrum beta-lactamase were studied. For every wild strain, we observed only one band except for two strains with two bands (pl 5.4 + 6.3 and pl 5.6 + 7.7). The isoelectric points for the other strains are comprised between pl 5.25 and pl 8.2: 22 pl 7.7; 13 pl 5.25; 4 pl 5.6; 4 pl 6.3; 2 pl 6.6; 2 pl 8.1 and 2 pl 8.2. In the strains with chromosomally encoded beta-lactamase overproduction we observed several bands in each extract and only the major band was considered. The isoelectric point of in vitro mutant strains with beta-lactamase overproduction was the same that the wild strains. We observed 3 pl: 5.25 - 1 pl: 5.6 - 3 pl 6.3 and 5 pl 7.7.(ABSTRACT TRUNCATED AT 250 WORDS)