MIC database of 1, 407 cephalosporins and oxacephalosporins was utilized to characterize 25 bacterial strains including Gram-positive and Gram-negative bacteria. MIC values were converted to activity rank indices, and distribution patterns of these indices were compared among the bacterial strains. Salmonella enteritidis No. 11 was the most susceptible bacterium, and the activity against this strain was ascribed to the binding of β-lactams to the PBPs without any significant barrier to the approach of β-lactams. Twenty-one strains were assumed to have similar types of PBPs to those of S. enteritidis No. 11 in the binding profile to β-lactams. Comparison of the scatter diagrams of the activity rank indices revealed two different types of resistances arising from β-lactamases (9 strains) and outer membrane permeability and/or active efflux (15 strains). The resistance factor arising from β-lactamase was affected by the nature of the C-3 substituents of β-lactams.