B-183. Regulation of Fatty Acid Modifying Enzyme Activity in Staphylococcus aureus

T. Lu, M. A. McGuire;
Univ. of Idaho, Moscow, ID.

Background: Staphylococcus sp. are the most frequently isolated pathogens from community and hospital acquired infections. Free fatty acids inhibitory to growth are present at the site of many infections. However, many isolates of S. aureus produce fatty acid modifying enzyme (FAME) that attaches free fatty acids to cholesterol, effectively inactivating the inhibitory action of these fatty acids. In previous work, S. aureus global virulence regulators sar and agr affected FAME activity in the early phase of S. aureus growth. We extended the culture length and hypothesized that regulation of FAME activity in S. aureus is affected by sar and agr with possible interactions due to culture conditions. Methods: S. aureus wildtype (RN6390) and its sar- and agr- mutant derivatives were grown in tryptic soy broth at 37ºC at 110 or 250 rpm for 24 h, extended from 8 h in previous work. Every 2 h, growth of the bacterial cultures was followed by assaying optical density at 600 nm and by plating serial dilutions on tryptic soy agar to determine colony forming units. FAME activity produced by these cultures was assayed using a gas chromatographic method measuring the conversion of oleic acid to butyl oleate by culture supernatants. Results: We show that FAME activity did not peak until late stationary phase (20 h) in the wildtype strain. While activity in the mutants increased from 8 to 24 h, it remained low throughout the entire culture period compared to the wildtype. This is contrary to previous work demonstrating FAME activity in the wildtype strain peaked at the beginning of stationary phase (4 h) and in the mutants increased only at the end of incubation (8 h). As previously observed, the sar and agr mutant strains have less FAME activity compared to the wildtype although there was no difference in growth among these strains. Reducing shaking from 250 to 110 rpm decreased FAME activity and growth in these strains. Conclusion: The global regulators agr and sar influence FAME activity, but factors such as other regulators, culture conditions, and media may also play crucial roles in regulating the activity of FAME.