Combining in vitro protein detection and in vivo antibody detection identifies potential vaccine targets against Staphylococcus aureus during osteomyelitis

P Martijn Den Reijer,Mehri Tavakol,Willem J B Van Wamel,Susan V Snijders,Antoni P A Hendrickx,Marjan Sandker

doi:10.1007/s00430-016-0476-8

P Martijn Den Reijer, Mehri Tavakol + Show 4 more

Open Access

https://doi.org/10.1007/s00430-016-0476-8

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Abstract

Currently, little is known about the in vivo human immune response against Staphylococcus aureus during a biofilm-associated infection, such as osteomyelitis, and how this relates to protein production in biofilms in vitro. Therefore, we characterized IgG responses in 10 patients with chronic osteomyelitis against 50 proteins of S. aureus, analyzed the presence of these proteins in biofilms of the infecting isolates on polystyrene (PS) and human bone in vitro, and explored the relation between in vivo and in vitro data. IgG levels against 15 different proteins were significantly increased in patients compared to healthy controls. Using a novel competitive Luminex-based assay, eight of these proteins [alpha toxin, Staphylococcus aureus formyl peptide receptor-like 1 inhibitor (FlipR), glucosaminidase, iron-responsive surface determinants A and H, the putative ABC transporter SACOL0688, staphylococcal complement inhibitor (SCIN), and serine–aspartate repeat-containing protein E (SdrE)] were also detected in a majority of the infecting isolates during biofilm formation in vitro. However, 4 other proteins were detected in only a minority of isolates in vitro while, vice versa, 7 proteins were detected in multiple isolates in vitro but not associated with significantly increased IgG levels in patients. Detection of proteins was largely confirmed using a transcriptomic approach. Our data provide further insights into potential therapeutic targets, such as for vaccination, to reduce S. aureus virulence and biofilm formation. At the same time, our data suggest that either in vitro or immunological in vivo data alone should be interpreted cautiously and that combined studies are necessary to identify potential targets.

Highlights

Staphylococcus aureus is the most common causative organism of osteomyelitis [1,2,3], which is defined as an infection of the bone and is associated with significant morbidity [1, 4, 5]
Ten patients who were diagnosed with chronic osteomyelitis caused by S. aureus, confirmed by deep bone culture, were included in this study
IgG levels against 14 diverse virulence factors, such as alpha toxin, the surface protein iron-responsive surface determinant A (IsdA), and the housekeeping protein glucosaminidase, were significantly increased in osteomyelitis patients compared to healthy controls

Summary

Introduction

Staphylococcus aureus is the most common causative organism of osteomyelitis [1,2,3], which is defined as an infection of the bone and is associated with significant morbidity [1, 4, 5]. Osteomyelitis is associated with the formation of bacterial biofilms [3, 6], which are defined as complex communities of bacteria enclosed in a polymer matrix that differ significantly in their gene. Biofilm formation is believed to increase resistance against antibiotics and the host immune system, which further complicates the treatment of such infections [3, 8, 9]. Together with the increasing incidence of resistant S. aureus isolates [10, 11], the difficult treatment of osteomyelitis underscores the need for alternative treatment strategies. One such strategy is the development of a vaccine [12]. Clinically evaluated vaccines might have failed because these were based on single antigens, while the awareness is currently increasing that multiple virulence factors of S. aureus should be targeted to undermine bacterial virulence [12, 13]

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