Published online Nov 25, 2015. doi: 10.5495/wjcid.v5.i4.86
Peer-review started: February 10, 2015
First decision: March 6, 2015
Revised: May 11, 2015
Accepted: June 9, 2015
Article in press: June 11, 2015
Published online: November 25, 2015
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. cDNA synthesis was performed by using random primers. The presence of S. aureus DNA, rRNA, and mRNA were determined by real-time polymerase chain reaction of the 16S rDNA 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 16S rRNA remained detectable during this whole period. During flucloxacillin treatment S. aureus lost viability from day 3 onwards, while the 16S rRNA-gene and its RNA transcripts remained detectable. DNA and rRNA can be detected in flucloxacillin treated S. aureus cultures that do not further contain culturable bacteria. However, tuf mRNA became undetectable from day 3 onwards. Tuf mRNA 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 16S rDNA and the tuf gene were detected.
CONCLUSION: Tuf mRNA expression is associated with culturable S. aureus and might be used to monitor antibiotic effects.
Core tip: We report our first results from a proof-of-principle study where we show that tuf mRNA expression seems to correlate with active Staphylococcus aureus (S. aureus) infection. The commonly used target, 16S rRNA, seems unsuitable for viability measurements as it can be detected from samples containing unculturable bacteria. This study indicates that tuf mRNA expression is associated with viable S. aureus, as determined by culture.