The stock antibiotic solution consisted of 0.02 g each
of tetracycline, streptomycin and penicillin, dissolved in
10 ml sterile, distilled water, filter-sterilized through a 0.2 mm
filter (Nalgene Disposable Filterware, Nalge Nunc International
Rochester, NY); from this, 1 ml was added per litre of
medium.