Figure 3.

AMP-resistant S. aureus are virulent. (a) Haemolytic activity was assessed following isolation on veal blood agar. (b) Carotenoid pigment production was assayed using methanol extraction. Values presented are the mean ± SEM derived from three independent determinations and statistical significance relative to WT was analysed using one-way ANOVA with Fisher's least significant difference test for post hoc analysis (***P < 0.001 or *P < 0.05). To assay in vivo virulence capacity, BALB/c mice were infected intraperitoneally with 0.5–2 × 10⁷ cfu of S. aureus and bacterial cells were enumerated from the (c) spleen, (d) liver and (e) kidney. Values presented are bacterial cfu counts normalized per gram of tissue (cfu/g) from three to four mice per bacterial strain. Boxes show the median and 25th and 75th percentiles, while error bars show the minimum and maximum values. Significant differences in bacterial colonization of AMP-resistant S. aureus strains were determined relative to WT using the Mann–Whitney U-test (*P < 0.05).