We normally add a very low concentration of antibiotics like Penicillin, Streptomycin, Chloramphenicol or Tetracycline or a mixture of them in the culture plate to avoid bacterial growth in the mammalian cell culture medium in a dose dependent manner. If a bit higher concentration is added is it going to affect the mammalian cell viability and growth in the culture? Do lack of functional complement proteins in the serum (due to heat inactivation) has anything to do with the toxicity (if any) of the mammalian cells to the antibiotics ?