Figure 3: Bacterial identification and demonstration of susceptibility to selected antibiotics following a 6-hour culture. After first preparing a 0.5 McFarland in Fastidious Broth and then diluting bacterial isolates out, antibiotics were added to the wells giving the final concentrations indicated. (a) Dilutions of GBS strain 12386 (confirmed to be susceptible to penicillin by disk diffusion), in the presence of 0, 0.06, 0.12, or 0.25 μg/mL penicillin. (b) E. faecalis was diluted out in Fastidious Broth in the presence (4 μg/mL) or absence of vancomycin. Enterococcus faecalis ATCC strain 29212 was confirmed to be susceptible to vancomycin by disk diffusion. (c) N. gonorrhoeae was prepared and diluted out, as above, in 0, 0.5, or 1 μg/mL penicillin. Strain 1279, a clinical isolate of N. gonorrhoeae, was shown to be susceptible to penicillin by disk diffusion. Each test was performed in triplicate and data shown are representative of three individual experiments. Again, bacterial concentrations were confirmed by CFUs following plating on agar for 24–48 hours.