LukMF' is the major secreted leukocidin of bovine Staphylococcus aureus and is produced in vivo during bovine mastitis.

Manouk Vrieling,Glenn F Van Wigcheren,Eveline M Boerhout,Tanja G Mols-Vorstermans,Lindert Benedictus,Jos A G Van Strijp,Carla J C De Haas,Kok P M Van Kessel,Piet C Aerts,Victor P M G Rutten,Piet J.M Nuijten,Ad P Koets,Kirsten J Koymans,Ineke J J M Daemen

doi:10.1038/srep37759

Abstract

Staphylococcus aureus is a major human and animal pathogen and a common cause of mastitis in cattle. S. aureus secretes several leukocidins that target bovine neutrophils, crucial effector cells in the defence against bacterial pathogens. In this study, we investigated the role of staphylococcal leukocidins in the pathogenesis of bovine S. aureus disease. We show that LukAB, in contrast to the γ-hemolysins, LukED, and LukMF′, was unable to kill bovine neutrophils, and identified CXCR2 as a bovine receptor for HlgAB and LukED. Furthermore, we assessed functional leukocidin secretion by bovine mastitis isolates and observed that, although leukocidin production was strain dependent, LukMF′ was most abundantly secreted and the major toxin killing bovine neutrophils. To determine the role of LukMF′ in bovine mastitis, cattle were challenged with high (S1444) or intermediate (S1449, S1463) LukMF′-producing isolates. Only animals infected with S1444 developed severe clinical symptoms. Importantly, LukM was produced in vivo during the course of infection and levels in milk were associated with the severity of mastitis. Altogether, these findings underline the importance of LukMF′ as a virulence factor and support the development of therapeutic approaches targeting LukMF′ to control S. aureus mastitis in cattle.

Highlights

Neutrophil recruitment is key to limit S. aureus infections[12]
First we assessed the ability of the different leukocidins to permeabilise bovine neutrophils
Pore formation was induced by LukMF′,LukED and both γ-hemolysins (HlgAB and HlgCB) (Fig. 1a), but whereas LukAB permeabilised human neutrophils, bovine neutrophils were unaffected by the toxin (Fig. 1b) and, putative bovine receptor orthologues of LukAB were not further investigated

Summary

Introduction

Several leukocidins have been shown to successfully target and kill bovine neutrophils[13], their expression by bovine mastitis isolates and their role in the pathogenesis of bovine S. aureus mastitis is unknown. For the bovine mastitis isolate S1444, it was shown that S. aureus employs LukMF′to kill bovine neutrophils at a distance, thereby preventing phagocytosis[21]. While LukMF′and HlgCB have been shown to target both human and bovine orthologues of the same receptors[21,25], the bovine targets of HlgAB, LukED, and LukAB have not been described. Bovine mastitis isolates of S. aureus can potentially secrete five different leukocidin pairs, of which four have been described to target bovine neutrophils, i.e. LukMF′,LukED, HlgAB, and HlgCB13,21,25. First we assessed the toxic activity of LukAB on bovine neutrophils and identified the bovine target receptor orthologues of HlgAB and LukED. We studied the role of LukMF′in vivo in an experimental intramammary S. aureus infection model

Methods

Results

Conclusion