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beta-lactamase production was evaluated by chromogenic cephalosporin 87/312 in 116 E. coli isolated from clinical sources. Such test revealed beta-lactamase production in 54 strains out of 116 (46%): MICs of eight beta-lactam antibiotics (Ampicillin, Piperacillin, Cefazoline, Cephaloridine, Cephalexine, Cefuroxime, Cefotaxime, Cefotaxime) were determined using a miniaturized dilution broth method. Cefotaxime and Ceftriaxome and Ceftriaxone showed the highest antibacterial activity. All beta-lactamases produced by E. coli strains under examination were isolated and purified by ultrasonic disruption and high speed centrifugation. Sensitivity of the eight antibiotics to purified beta-lactamases was assessed by a spectrophotometric method that utilizes the velocity of cytochrome c reduction. The sensitivity to beta-lactamases was reflected in the in vitro activity of the antibiotics as assessed by the determination of the MICs.

Thirty-six specimens of feces were taken from as many chicken farms, from which 118 different strains of Enterobacteriaceae were isolated. The resistances of the single isolated bacteria were studied, performing plate sensitivity tests by the Kirby-Bauer method. The capacity of the bacteria under examination to transfer their antibiotic resistances in vitro to a sensitive E. coli strain (E. coli K 12 E 711 F--) was observed. A very high percentage of strains has shown resistance to one or more antibiotics (91%). However a much lesser number of strains were capable of transferring their antibiotic resistances (12.9%). It is suggestive, then, that the animals under examination do not represent an important source of antibiotic resistance diffusion to man.