FIG 5.

Fatty acid composition of S. aureus membranes is a determinant of daptomycin bactericidal activity. (A) Percentages in total area of each class of fatty acids present in the membrane whether or not bacteria were tolerant. An asterisk (*) represents a statistically significant difference between fatty acid percentages, regardless of whether bacterial cells are susceptible or tolerant to daptomycin (P < 0.05). (B) Correlation between the fatty acid percentages and the susceptibility of the strains (defined below). The results shown here consider the susceptibilities of the four strains independently of the phase of growth. Each bar represents the percentage values for each type of fatty acid. *, SFA and iso BCFA percentages were statistically different between the four strains (P < 0.05); **, anteiso BCFA percentages were statistically not different between the two strains (P < 0.05). For both (panels A and B), the results shown consider all the data obtained, independently of the strain and the growth phase. In order to classify the different experiments, we considered that bacteria were susceptible to daptomycin when the log reduction in bacterial counts was positive (a decrease in bacterial populations), and, a contrario, that bacteria were tolerant when the log reduction in bacterial counts was negative (an increase in bacterial counts) or zero.