Basic Study
Copyright ©The Author(s) 2015. Published by Baishideng Publishing Group Inc. All rights reserved.
World J Clin Infect Dis. Nov 25, 2015; 5(4): 86-93
Published online Nov 25, 2015. doi: 10.5495/wjcid.v5.i4.86
Tuf mRNA rather than 16S rRNA is associated with culturable Staphylococcus aureus
Anne JM Loonen, Petra FG Wolffs, Maikel de Bresser, Maurice Habraken, Cathrien A Bruggeman, Mirjam HA Hermans, Adriaan JC van den Brule
Anne JM Loonen, Maikel de Bresser, Maurice Habraken, Mirjam HA Hermans, Adriaan JC van den Brule, Laboratory for Molecular Diagnostics, Department of Medical Microbiology and Pathology, Jeroen Bosch Hospital, 5200 ME ‘s-Hertogenbosch, The Netherlands
Anne JM Loonen, Maikel de Bresser, Maurice Habraken, Department of Medical Molecular Diagnostics, Fontys University of Applied Sciences, 5600 AH Eindhoven, The Netherlands
Anne JM Loonen, Petra FG Wolffs, Cathrien A Burggeman, Department of Medical Microbiology, CAPHRI, Maastricht University Medical Centre, 6229 HX Maastricht, The Netherlands
Author contributions: Loonen AJM, Wolffs PFG and van den Brule AJC designed the research; Loonen AJM, de Bresser M and Habraken M performed the research; Loonen AJM, Wolffs PFG, Bruggeman CA, Hermans MHA and van den Brule AJC analyzed the data and wrote the paper.
Institutional review board statement: No human subjects were used for this study and therefore no ethical approval was required.
Institutional animal care and use committee statement: No animals were used for this study.
Conflict-of-interest statement: The authors declare that they have no conflict of interest.
Data sharing statement: No additional data are available.
Open-Access: This article is an open-access article which was selected by an in-house editor and fully peer-reviewed by external reviewers. It is distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited and the use is non-commercial. See:
Correspondence to: Adriaan JC van den Brule, PhD, Laboratory for Molecular Diagnostics, Department of Medical Microbiology and Pathology, Jeroen Bosch Hospital, Box 90153, 5200 ME ‘s-Hertogenbosch, The Netherlands.
Telephone: +31-73-5538480 Fax: +31-73-5532136
Received: February 9, 2015
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.

Keywords: Bloodstream infection, Staphylococcus aureus, Viability, mRNA, Polymerase chain reaction, Sepsis, Molecular diagnostics, Blood

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.