I have a couple questions about using antibiotics in culture media to prevent contamination while growing protozoa: 1) Where would be a good place to look for cheap generic antibiotics to use for this purpose? 2) I'm looking for an antibiotic that kills most gram negatives but has no effect on eukaryotic mitochondria. This rules out kanamycin and other aminoglycosides because they act on the 16S ribosomal subunit which is present in mitochondria. If it kills gram positives too that's great. I also value cheapness.