The resistance to betalactam antibiotics of lactose-positive and lactose-negative strains of Escherichia coli.

Two groups of Escherichia coli (lactose-positive and lactose-negative strains) were assayed to evaluate the resistance to betalactam antibiotics using disk diffusion technique. 57.66% lactose-positive and 80.82% lactose-negative strains showed the resistance to ampicillin. In lactose-positive E. coli strains 5.00% and in lactose-negative 18.64% strains respectively were resistant to amoxicillin/clavulanic acid.