All strains were obtained from the Institute of
Microbiology, Chinese Academy of Sciences (Beijing, China) and
maintained on MHA slants at 4 C. Cells were prepared by 16-h culture
in MHB at 37 C. A 16-h culture was diluted with MHB to
achieve an inoculum of 1 106 CFU/ml approximately. The number
of cells in the suspensions was determined by duplicate plating
from tenfold serial dilution on MHA and counting the colonies after
incubation at 37 C for 24 h.
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