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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 in vitro activity of ceftizoxime compared with other beta-lactamase stable compounds was assessed against recent urinary gram negative isolates. 343 bacterial strains were isolated from patients affected by UTI, identified by standard bacteriological methods and investigated for their production of beta-lactamases by Nitrocefin test. MICs and MBCs of ceftizoxime, ceftriaxone, cefamandole, cefoxitin and cefotaxime were determined by a miniaturized dilution broth method against all beta-lactamase producing bacteria (129 out of 343). Sensitivity of antibiotics to beta-lactamases isolated and semi-purified by ultrasonic disruption and high speed centrifugation was assessed by a spectrophotometric method. In vitro antibacterial activity of each antibiotics was correlated to their sensitivity to isolated beta-lactamases. Ceftizoxime showed lower MIC and MBC values and lower MBC/MIC ratio than the other compounds against all the bacteria including Pseudomonas. Ceftizoxime was not hydrolized by any isolated beta-lactamase.

The in vitro activity of ceftazidime compared with other beta-lactamase stable compounds was assessed against recent Gram-negative isolates. Three hundred forty-three bacterial strains were isolated from patients affected with UTI, identified by standard bacteriological methods and investigated for their production of beta-lactamases by the Nitrocefin test. MICs and MBCs (minimum inhibitory concentrations and minimum bactericidal concentration) of ceftazidime, cefamandole, cefoxitin, cefotaxime and cefuroxime were determined by a miniaturized dilution broth method against all beta-lactamase producing bacteria (129 out of 343). Sensitivity of the antibiotics to beta-lactamases isolated and semipurified by ultrasonic disruption and high-speed centrifugation was assessed by a spectrophotometric method. The in vitro antibacterial activity of each antibiotic was correlated to its sensitivity to isolated beta-lactamases. Ceftazidime showed lower MIC and MBC values and lower MBC/MIC ratios than the other compounds against all the bacteria including Pseudomonas spp. In addition, ceftazidime was not hydrolyzed significantly by any isolated beta-lactamases.