Phase-out of the BIVR phenomenon. BIVR cells were transferred to antibiotic-free MH agar and the plate was incubated at 37°C for 24 h. Cell suspensions from the plates were inoculated again on antibiotic-free MH agar and incubated for 24 h at 37°C. This serial transfer and culture was continued for 5 consecutive days. The culture was subjected to the BIVR test every day. Only a representative strain from the laboratory stock BIVR, K744 and freshly isolated clinical strains, K725, is presented. 1st to 5th represents the cycle of passage in the antibiotic-free medium.