الفهرس 
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Abstract
This investigation was carried out on 57 different clinical samples collected from Faculty
ofMedicine, Cairo University, and Sayed Gala! hospital, El-Azhar University. Out of them, 135
cephradine-resistant bacterial isolates were picked up. The highest activity of cephalosporinase
was exhibited by Salmonella typhi (8), Pseudomonas aeruginosa (10), Staphylococcus aureus (43)
and Escherichia coli (61), on which further studies were carried out.
The optimum conditions for production of cephalosporinase were 37°C for Sal. typhi, Staph. aureus
and E.coli, while it was 25°C for Ps. aeruginosa, and cephradine concentrations of 3.5, 4.0 2.5 and
2.0 mg/ml medium respectively and 50 ml medium in 250 ml flasks gave the best results.
All experimental strains were resistant to streptomycin while susceptible to amikacin, gentamicin,
rifampicin and clavulanic acid. Combinations of sub MICs of these antibiotics with cephradine led
to a decrease in their MICs for all tested strains. Also, the sub MICs of these antibiotics
decreased the activity of the cephalosporinase for the experimental strains.
The cephalosporinases were purified 126.52, 105.4,
113.75 and 106.36 fold in case of Sal. typhi (8), Ps. aeruginosa (10), Staph. aureus (43) and E.
coli (61) respectively using ammonium sulphate, ion exchange chromatography (DEAE-cellulose) and
gel filtration (sephadex G 200) . Their molecular weights and amino acids compositions were also
determined.
The stability of the purfied enzymes was studied. Cephalosporinases of Sal. typhi and E.coli were
stable up to 35°C for 120 min., while these of Ps. aeruginosa and Staph.aureus were stable at 25 and 30°C for 120 min. respectively.
The maximum activity of cephalosporinases of all strains
were at the pH range 6.2 -6.5 . The enzymes were stable when
stored at 4°C for periods of 15, 16, 22 and 6 days for Sal.
typhi, Ps. aeruginosa, Staph. aureus and E. coli respectively.
CaCh stimulated the activity of Ps. aeruginosa
cephalosporinase,while those of the other strains were slightly
stimulated by Mg S04, Fe S04• 7H20 and CaCL2.
Cephalosporinases of all strains were competley or highly
inhibited by sod. azide, KCN, iodine, Cu S04 , Hg CL2 , Ag
N03 , iodoacetic acid, KMn04 and L-cysteine. Amikacin,
rifampicin, chloramphenicol, erythromycin and clindamycin
also had an inhibitory effect on the cephalosporinases of the
tested strains.