sounds like you are losing your antibiotic cartridge. Perhaps the amount of
Kan. when growing in broth needs to be increased due to a higher cell density
in broth culture (i.e. greater ability to use up the kan faster at least
initially, then once the kan is gone so is your selective pressure.) I have
seen the same effect with mercury resistance.
Good luck.
Lou Passador
Dept. of Microbiology and Immunology
Univ. of Rochester
Rochester NY.
