[Multifactorial analysis of the phenotypes for beta-lactams of 1044 Escherichia coli strains]

1,044 E. coli strains were randomly collected by the beginning of 1992. Their susceptibility for seven beta-lactam antibiotics: amoxycillin, augmentin, ticarcillin, claventin, cephalothin, cefoxitin and cefotaxime, was studied routinely by the agar diffusion method. The datas were analyzed by the CERIB multifactorial analysis package which yields to homogeneous populations. This analysis showed four well defined populations: 1) 588 strains (56.4%) susceptible to all antibiotics; 2) 410 strains (39.3%) present a penicillinase phenotype; 3) 11 strains (1.05%) are cephalosporinase producer; 4) 7 strains (0.67%) were identified as producing an extended-spectrum beta-lactamase. The remaining strains: 28 (2.68%) had a reduced susceptibility to all antibiotics, which suggests the combination of few resistance mechanisms or other hypothesis.