Semi-quantification of a microbiological method using beta-lactamases in detecting the hydrolysis of beta-lactam antibiotics.

The so-called "double disc" technique of Masuda et al. for detecting the hydrolysis of beta-lactams by beta-lactamases was semi-quantified. This semi-quantification consisted of using beta-lactamase preparations progressively diluted by a factor of ten. The last dilution producing a detectable hydrolysis of the antibiotic was thus noted. By using the species Escherichia coli (potentially cephalosporinase producer) as a model, we studied the possible applications of this method. Due to its great sensitivity it was possible to analyse and appreciate the degradation of some cephalosporins reputedly resistant to beta-lactamases, such as cefoxitin, cefuroxime, cefamandole and cefotaxime. The carboxy-penicillins (carbenicillin and ticarcillin) were the most stable beta-lactams towards the cephalosporinase of E. coli 0002.