Susceptibility of Haemophilus influenzae type b to cefaclor and influence of inoculum size

Cefaclor appeared to be an effective antibiotic against both beta-lactamase-positive and beta-lactamase-negative strains of Haemophilus influenzae type b when tested with 10(5) colony-forming units per ml. With inocula in excess of 10(6) colony-forming units per ml, these organisms were neither inhibited nor killed at concentrations of 400 micrograms/ml. This inoculum effect was also demonstrated in time-kill curve studies.