[Detection of hyperproduction of chromosomal beta-lactamase in strains of Escherichia coli, Enterobacter cloacae and Pseudomonas aeruginosa]. / Detección de la hiperproducción de betalactamasa cromosómica en cepas de Escherichia coli, Enterobacter cloacae y Pseudomonas aeruginosa.

ABSTRACT

In order to show up the hyperproduction of chromosomic beta-lactamases in strains of Enterobacteriaceae and Pseudomonas aeruginosa we have tested a variant of a technique proposed by Medeiros et al. It is a qualitative technique and, the modification introduced allows errors of interpretation to be avoided, when the strain is a producer of plasmidic beta-lactamase. It is based on evaluating the amount of beta-lactamase in a culture, measured in time taken for the hydrolysis of nitrocefin, with or without the addition of clavulanic acid. We present the results obtained in 526 selected strains 271 E. coli, 116 E. cloacae and 139 P. aeruginosa. One hundred and twenty for strains hydrolyzed the nitrocefin in the absence of clavulanic acid within 60 seconds. Only 52 (41.94%) of these strains did it when clavulanic acid was present; all of them have been qualified as hyperproducers according to susceptibility to beta-lactam antibiotics and the study and identification of the beta-lactamases by analytic isoelectrofocusing. The hydrolysis was evident before the 15 seconds in the 80% of hyperproducer strains. No false positive results were observed.