PLASMID-ENCODED BETA-LACTAMASES RESISTANT TO INHIBITION BY CLAVULANICACID PRODUCED BY CALF FECAL-COLIFORMS

Two new plasmid encoded beta-lactamase enzymes produced by a strain of Escherichia coli and a strain of Citrobacter freundii isolated from c alf faeces have been characterised. Both enzymes were similar to TEM-1 in terms of substrate and inhibition profiles and physical properties but differed from TEM-1 in being far less susceptible to the beta-lac tamase inhibitors clavulanic acid or tazobactam. In each case transfer of the the plasmid E coli K12 rendered it clinically resistant to the combination of amoxycillin and clavulanic acid. The beta-lactamase fr om the E coli had an iso-electric point (pI) of 5.4 and was encoded on a plasmid of 95 Kbp which also mediated resistance to tetracycline, s ulphonamides, apramycin, streptomycin and gentamicin. The beta-lactama se from the C freundii had a pI of 5.2 and was encoded on a 75 Kbp pla smid which also mediated resistance to trimethoprim, chloramphenicol, apramycin, gentamicin and tobramycin.