Expression of δ-toxin by Staphylococcus aureus mediates escape from phago-endosomes of human epithelial and endothelial cells in the presence of β-toxin.
ABSTRACT Staphylococcus aureus is able to invade non-professional phagocytes by interaction of staphylococcal adhesins with extracellular proteins of mammalian cells and eventually resides in acidified phago-endosomes. Some staphylococcal strains have been shown to subsequently escape from this compartment. A functional agr quorum-sensing system is needed for phagosomal escape. However, the nature of this agr dependency as well as the toxins involved in disruption of the phagosomal membrane are unknown. Using a novel technique to detect vesicular escape of S. aureus, we identified staphylococcal virulence factors involved in phagosomal escape. Here we show that a synergistic activity of the cytolytic peptide, staphylococcal δ-toxin and the sphingomyelinase β-toxin enable the phagosomal escape of staphylococci in human epithelial as well as in endothelial cells. The agr dependency of this process can be directly explained by the location of the structural gene for δ-toxin within the agr effector RNAIII.
[show abstract] [hide abstract]
ABSTRACT: The mechanisms governing the epidemiology dynamics and success determinants of a specific healthcare-associated methicillin-resistant S. aureus (HA-MRSA) clone in hospital settings are still unclear. Important epidemiological changes have occurred in Europe since 2000 that have been related to the appearance of the ST22-IV clone. Between 2006 and 2010, we observed the establishment of the ST22-IV clone displacing the predominant Italian clone, ST228-I, in a large Italian university hospital. To investigate the factors associated with a successful spread of epidemic MRSA clones we studied the biofilm production, the competitive behavior in co-culture, the capacity of invasion of the A549 cells, and the susceptibility to infection in a murine model of acute pneumonia of the two major HA-MRSA clones, ST22-IV and ST228-I. We showed that persistence of ST22-IV is associated with its increased biofilm production and capacity to inhibit the growth of ST228-I in co-culture. Compared to ST228-I, ST22-IV had a significantly higher capacity to invade the A549 cells and a higher virulence in a murine model of acute lung infection causing severe inflammation and determining death in all the mice within 60 hours. On the contrary, ST228-I was associated with mice survival and clearance of the infection. ST22-IV, compared with ST228-I, caused a higher number of persistent, long lasting bacteremia. These data suggest that ST22-IV could have exploited its capacity to i) increase its biofilm production over time, ii) maintain its growth kinetics in the presence of a competitor and iii) be particularly invasive and virulent both in vitro and in vivo, to replace other well-established MRSA clones, becoming the predominant European clone.PLoS ONE 01/2012; 7(8):e43153. · 4.09 Impact Factor
Article: Staphylococcus aureus elaborates the leukotoxin LukAB to mediate escape from within human neutrophils.[show abstract] [hide abstract]
ABSTRACT: Methicillin-resistant Staphylococcus aureus (MRSA) of the pulsed-field type USA300 are primarily responsible for the current community-associated epidemic of MRSA infections in the USA. The success of USA300 is partly attributed to the ability of the pathogen to avoid destruction by human neutrophils (polymorphonuclear leukocytes or PMNs), which are crucial to the host immune response to S. aureus infection. In this work, we investigated the contribution of bi-component pore-forming toxins to the ability of USA300 to withstand attack from primary human PMNs. We demonstrate that in vitro growth conditions influence the expression, production, and availability of leukotoxins by USA300, which in turn impact the cytotoxic potential of this clone towards PMNs. Interestingly, we also found that upon exposure to PMNs, USA300 preferentially activates the promoter of the lukAB operon, which encodes for the recently identified leukocidin AB (LukAB). LukAB elaborated by extracellular S. aureus forms pores in the plasma membrane of PMNs leading to PMN lysis, highlighting a contribution of LukAB to USA300 virulence. We now show that LukAB also facilitates the escape of bacteria engulfed within PMNs, in turn enabling the replication and outgrowth of S. aureus. Together, these results suggest that upon encountering PMNs S. aureus induces the production of LukAB, which serves as an extra- and intra-cellular weapon to protect the bacterium from destruction by human PMNs.Infection and immunity 03/2013; · 4.21 Impact Factor