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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.

A total of 343 Gram-negative bacteria were isolated and identified from urine specimens of patients with urinary tract infections. All the bacteria were investigated for their production of beta-lactamases by the nitrocefin test. beta-lactamase-producing strains were tested by the Datta method to detect any transfer of beta-lactamase production to a receiving E. coli K12 RN-strain. MICs of six beta-lactamase-stable compounds (ceftazidime, ceftriaxone, cefamandole, cefoxitin, cefotaxime, cefuroxime) were determined against all the beta-lactamase transferring bacteria and their respective transconjugants by a miniaturized dilution broth method. beta-lactamases produced by donors and transconjugants were purified and identified by determination of the isoelectric point by focusing; their hydrolytic activity was assessed by a spectrophotometric method using cytochrome c reduction. A total of 129 bacteria out of 343 produced beta-lactamases and 27 of these transferred the beta-lactamase production by conjugation. The beta-lactamases isolated from donors and transconjugants had the same pl and the same substrate profile. Ceftazidime was more stable to all the beta-lactamases isolated and more active against all the bacteria examined than the other compounds.

The isolation and transferable drug resistance of Escherichia coli from the feces of chickens after oral administration of tetracylcine, chloramphenicol, rifampicin, and amoxicillin were studied. Each antibiotic was administered at two different dosages to four groups of 12 chickens. Treatment was carried out for 3 weeks. Feces were taken weekly and bacteriological examinations performed. E. coli biotypes were identified by fermentation and enzymatic reaction patterns. Antibiotic sensitivity tests were performed on all E. coli isolates. Rapid appearance of E. coli biotypes showing drug-resistance to each antibiotic was observed as soon as 1 week after treatment. Resistance was not detectable a few days after interruption of antibiotic administration. All E. coli strains showing drug resistance to the antibiotic under examination were studied to observe their capacity to transfer antibiotic resistance to E. coli K 12 E 711 F-strain. A high percentage of resistant E. coli strains transferred their antibiotic resistance to E. coli K 12. Transferable drug resistance was demonstrated mainly in tetracycline resistant E. coli.