Contribution of Panton-Valentine Leukocidin in Community-Associated Methicillin-Resistant Staphylococcus aureus Pathogenesis

Binh An Diep,Li Basuino,Adeline R Whitney,Amy M Palazzolo-Ballance,Liang Chen,Michael Otto,Frank R Deleo,Henry F Chambers,Pierre Tattevin,Barry N Kreiswirth,Kevin R Braughton

doi:10.1371/journal.pone.0003198

Abstract

Community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) strains typically carry genes encoding Panton-Valentine leukocidin (PVL). We used wild-type parental and isogenic PVL-deletion (Δpvl) strains of USA300 (LAC and SF8300) and USA400 (MW2) to test whether PVL alters global gene regulatory networks and contributes to pathogenesis of bacteremia, a hallmark feature of invasive staphylococcal disease. Microarray and proteomic analyses revealed that PVL does not alter gene or protein expression, thereby demonstrating that any contribution of PVL to CA-MRSA pathogenesis is not mediated through interference of global gene regulatory networks. Inasmuch as a direct role for PVL in CA-MRSA pathogenesis remains to be determined, we developed a rabbit bacteremia model of CA-MRSA infection to evaluate the effects of PVL. Following experimental infection of rabbits, an animal species whose granulocytes are more sensitive to the effects of PVL compared with the mouse, we found a contribution of PVL to pathogenesis over the time course of bacteremia. At 24 and 48 hours post infection, PVL appears to play a modest, but measurable role in pathogenesis during the early stages of bacteremic seeding of the kidney, the target organ from which bacteria were not cleared. However, the early survival advantage of this USA300 strain conferred by PVL was lost by 72 hours post infection. These data are consistent with the clinical presentation of rapid-onset, fulminant infection that has been associated with PVL-positive CA-MRSA strains. Taken together, our data indicate a modest and transient positive effect of PVL in the acute phase of bacteremia, thereby providing evidence that PVL contributes to CA-MRSA pathogenesis.

Highlights

The worldwide emergence of community-acquired methicillin resistant Staphylococcus aureus (CA-MRSA) strains has been linked to carriage of genes encoding Panton-Valentine leukocidin (PVL), a two-component leukolytic toxin [1,2,3,4,5,6,7,8,9]
Presence of PVL was associated with up-regulation of staphylococcal protein A (Spa) and other surface proteins and led the investigators to propose a model in which PVL interference with global regulatory networks culminated in overwhelming inflammation and necrosis of the murine lung [14]
Using TaqMan real-time reverse transcriptasePCR, we confirmed that expression of PVL does not alter transcripts encoding accessory gene regulator (AgrA) and Agrregulated virulence factors such as protein A (Spa), a-toxin (Hla), b-hemolysin (HlgABC), serine aspartate repeat protein (SdrD), serine protease (SplA), or clumping factor B (ClfB) (Figure 1A and Table 2)

Summary

Introduction

The worldwide emergence of community-acquired methicillin resistant Staphylococcus aureus (CA-MRSA) strains has been linked to carriage of genes encoding Panton-Valentine leukocidin (PVL), a two-component leukolytic toxin [1,2,3,4,5,6,7,8,9]. Presence of PVL was associated with up-regulation of staphylococcal protein A (Spa) and other surface proteins and led the investigators to propose a model in which PVL interference with global regulatory networks culminated in overwhelming inflammation and necrosis of the murine lung [14]. Such profound effects on global gene expression raise the possibility that the experimental outcomes were due not to PVL, but were consequence of major genetic perturbations [9], perhaps due to pleiotropic mutations that occur with relatively high frequency in laboratory strains [15,16]

Methods

Results

Conclusion