Molecular Basis of Virulence in Staphylococcus aureus Mastitis

INRA, UMR1253, Science et Technologie du Lait et de l'Œuf, Rennes, France.
PLoS ONE (Impact Factor: 3.23). 11/2011; 6(11):e27354. DOI: 10.1371/journal.pone.0027354
Source: PubMed


S. aureus is one of the main pathogens involved in ruminant mastitis worldwide. The severity of staphylococcal infection is highly variable, ranging from subclinical to gangrenous mastitis. This work represents an in-depth characterization of S. aureus mastitis isolates to identify bacterial factors involved in severity of mastitis infection.
We employed genomic, transcriptomic and proteomic approaches to comprehensively compare two clonally related S. aureus strains that reproducibly induce severe (strain O11) and milder (strain O46) mastitis in ewes. Variation in the content of mobile genetic elements, iron acquisition and metabolism, transcriptional regulation and exoprotein production was observed. In particular, O11 produced relatively high levels of exoproteins, including toxins and proteases known to be important in virulence. A characteristic we observed in other S. aureus strains isolated from clinical mastitis cases.
Our data are consistent with a dose-dependant role of some staphylococcal factors in the hypervirulence of strains isolated from severe mastitis. Mobile genetic elements, transcriptional regulators, exoproteins and iron acquisition pathways constitute good targets for further research to define the underlying mechanisms of mastitis severity.

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Available from: Yves Le Loir
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    • "In this regard, in a study comparing subclinical and clinical isolates from S. aureus ovine mastitis, Le Maréchal et al. (2011) found no genotypic, but proteomic and transcriptomic differences. While the strain from ewe subclinical mastitis showed overexpression of genes encoding surface molecules, the strain causing lethal gangrenous mastitis mainly overexpressed genes encoding exoproteins (Le Maréchal et al., 2011). Studies characterizing gene expression of S. aureus from bovine IMI in the presence of host cells have not yet been carried out. "
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    ABSTRACT: Staphylococcus aureus is one of the most prevalent pathogens isolated from bovine mastitis, causing chronic intramammary infections (IMI) that limit profitable dairying. The course of infection is often associated with factors both related to the host and the bacterium. Aims of this study were to select S. aureus isolates from bovine IMI with different genotypic profiles harboring genes involved in adherence and biofilm production, to determine the behavior of these strains in contact with bovine mammary epithelial cells (MAC-T) and the expression of those genes during bacterial-cell early interactions. The genetic diversity of 20 S. aureus strains that were isolated from milk samples taken from cows with persistent-P and non-persistent-NP IMI was high, discriminated into 13 fingerprint groups. The occurrence of genes coding for S. aureus surface proteins (clfA, clfB, fnbA, fnbB, fib, cna) and biofilm formation (icaA, icaD, icaC, bap) and in vitro biofilm-forming ability was not related to strain clinical origin (NP or P). Internalization of S. aureus into MAC-T cells was strain-dependent and internalized bacteria overexpressed adherence and biofilm-forming genes compared with those that remained in the supernatant of co-cultures; particularly those genes encoding FnBPs and IcaD. Strains yielding highest invasion percentages were those able to overexpress fnBP, irrespectively of the presence of other evaluated genes. Strains from NP IMI showed a greater multiplication capacity in vitro compared with strains from P IMI. These results provide new insights about S. aureus differential gene expression of adhesion-internalization factors during early interaction with mammary epithelial cells.
    Full-text · Article · Dec 2015
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    • "Similarly, our findings also differ from the results of more recent DNA microarray or PCR studies that revealed very similar virulence gene expression profiles in isolates with the same sequence type (Jamrozy et al. 2012; Shambat et al. 2012). Our results do agree with those of Munsky et al. (2012) and Le Maréchal et al. (2011) who found variable gene expression in identical environments even when the cells were genetically identical. One explanation of this variability is the possible accumulation of truncations and other nucleotide differences in certain genes. "
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    ABSTRACT: Several studies have shown that protein expression patterns vary in unrelated bacterial strains due to genomic plasticity and gene regulation, resulting in enhanced heterogeneity in the infection potential. However, exoprotein expression patterns of closely related clonal strains have not been well characterized. Here, we used medium-range (pH 4–7) immobilized pH gradient–two-dimensional gel electrophoresis to investigate the exoproteome from closely related Staphylococcus aureus clonal isolates. Interestingly, we found that, under identical in vitro experimental conditions, a number of protein spots were uniquely present in samples from each clonal isolate irregardless of the similarity of the genotype and the same virulence gene profile. Only a few abundant invariant proteins were found among identical genotypic isolates. Our results clearly shown that heterogeneity in the exoproteome was present even among clonally related strains. We suggest that this heterogeneity may contribute to the degree of virulence even within one clonal genotype. The heterogeneity in the exoproteome of closely related S. aureus strains observed in the current study postulates that pre-existing antibodies are not very protective during recurrent infection with the same strain. Therefore, our findings underscore the importance of taking all clonally related strains into account during proteome analyses.
    Full-text · Article · Sep 2015 · Annals of Microbiology
    • "We recently identified an ET-like protein in S. aureus O46, a strain associated to mild ewe mastitis [13] [14]. It showed high similarity with previously described S. aureus ETD in its amino acid primary sequence, including the presence of the typical catalytic site found in the other ET proteins described so far, and was thus named EDT-like. "
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    ABSTRACT: Exfoliative toxins are serine proteases secreted by Staphylococcus aureus that are associated with toxin-mediated staphylococcal syndromes. To date, four different serotypes of exfoliative toxins have been identified and 3 of them (ETA, ETB, and ETD) are linked to human infection. Among these toxins, only the ETD structure remained unknown, limiting our understanding of the structural determinants for the functional differentiation between these toxins. The crystal structure of ETD was determined at 1.95 Å resolution and the structural analysis providing insights into the oligomerization, stability and specificity and enabled a comprehensive structural comparison with ETA and ETB. Despite the highly conserved molecular architecture, significant differences in the composition of the loops and in both the N- and C-terminal α-helices seem to define ETD specificity. Molecular dynamics simulations indicate that these regions defining ET specificity present different degrees of flexibility and may undergo conformational changes upon substrate recognition and binding. DLS and AUC experiments indicated that ETD is monomeric in solution whereas it is present as a dimer in the asymmetric unit indicating that oligomerization is not related to functional differentiation among these toxins. Differential scanning calorimetry and circular dichroism assays demonstrated an endothermic transition centered at 52 °C, and an exothermic aggregation in temperatures up to 64 °C. All these together provide insights about the mode of action of a toxin often secreted in syndromes that are not associated with either ETA or ETB. Copyright © 2015. Published by Elsevier Inc.
    No preview · Article · Aug 2015 · Biochemical and Biophysical Research Communications
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