Bacterial Cultivation and Antibiotic Resistance

Bacterial strains and plasmids used in these studies are described in Table 1. Escherichia coli, used for vector propagation, was grown in Luria-Bertani (LB) broth (Difco) containing 50 μg/ml kanamycin sulfate (Amresco, Solon, OH). S. pyogenes strains were grown in Bacto Todd Hewitt Broth (Becton, Dickinson and Company, Sparks, MD) supplemented with 2% Bacto yeast extract (THY medium) at 37°C or Brain Heart Infusion media (BHI) (Himedia Laboratories, India) at 37°C with the addition of the appropriate antibiotics (Sigma); growth was determined by monitoring the absorbance at 600 nm. Strain SF370SmR is a streptomycin resistant derivative of strain SF370, containing a spontaneous mutation in the rpsL gene [19 ]. No differences between SF370 and the streptomycin resistant derivative were observed with respect to growth rate or in the various biological assays employed [19 ]. Chemically defined media (CDM) was prepared as described in the literature [20 (link)].