Effects of inoculum size and incubation time on broth microdilution susceptibility testing of lactic acid bacteria

Inoculum size and incubation time were varied during broth microdilution testing of the susceptibilities of 35 strains of lactic acid bacteria to six antibiotics. An increase in either parameter resulted in elevated MICs for all species. An inoculum of 3 x 10(5) CFU/ml is recommended to assess the antibiotic susceptibilities of these bacteria by using broth microdilution.