Tuf m RNA rather than 16S r RNA is associated with culturable Staphylococcus aureus

AIM: To study the presence of various nucleic acids targets of Staphylococcus aureus(S. aureus) during bacterial growth and antibiotic induced killing in relation to viability.METHODS: S. aureus was cultured to log phase and spiked in Todd Hewitt(TH) broth and whole blood of healthy human volunteers. Viability of S. aureus after flucloxacillin treatment(0, 1, 3 and 6 d) was assessed by culture on bloodagar plates. DNA and RNA were isolated from 200 μL. c DNA synthesis was performed by using random primers. The presence of S. aureus DNA, r RNA, and m RNA were determined by real-time polymerase chain reaction of the 16 S r DNA and tuf gene(elongation factor Tu).RESULTS: S. aureus spiked in TH broth without antibiotics grew from day 0-6 and DNA(tuf and 16S), and 16 S r RNA remained detectable during this whole period. During flucloxacillin treatment S. aureus lost viability from day 3 onwards, while the 16 S r RNA-gene and its RNA transcripts remained detectable. DNA andr RNA can be detected in flucloxacillin treated S. aureus cultures that do not further contain culturable bacteria.However, tuf m RNA became undetectable from day 3onwards. Tuf m RNA can only be detected from samples with culturable bacteria. When spiking S. aureus in whole blood instead of broth no bacterial growth was seen, neither in the absence nor in the presence of flucloxacillin. Accordingly, no increase in DNA and RNA levels of both 16 S r DNA and the tuf gene were detected. CONCLUSION: Tuf m RNA expression is associated with culturable S. aureus and might be used to monitor antibiotic effects.