FIG 6.

HPLC analysis to detect tyrosine, p-HPA, and p-cresol in spent culture media. The concentrations of tyrosine, p-HPA, and p-cresol in late-exponential-growth cultures of C. difficile strain 630Δerm were determined by HPLC. Minimal medium was supplemented with 0.4 mg/ml tyrosine or 2 mg/ml p-HPA. Statistical analysis using linear regression was undertaken (i) to determine whether there was a significant increase in p-HPA and p-cresol production in media containing tyrosine (in black) and (ii) to determine whether there were any significant differences in the amount of p-HPA in the 2 mg/ml supplemented media compared to the amount of p-HPA produced in growth media containing tyrosine (in gray) (*, P < 0.05; ***, P < 0.001).