The Staphylococcus aureus secretome - TI Pharma

Chapter 3
strain of a patient who suffered from a wound infection induced by this strain (isolate H) one
year before. We found the hlb converting phage FaSa3 in all these isolates, except for isolate
G, as might be expected from the phage dynamics during infection (Goerke et al., 2006;
Goerke et al., 2004). In accordance with this, the phenotype of strain G288 changed from Hlb
positive (G) to Hlb negative (C, D, H, I, J, K) (Table 3). However, the prophage did not
significantly alter the expression of other virulence-associated genes (Figure 1). This might be
mainly due to the fact that RNAIII was not expressed in these isolates under our experimental
conditions (Figure 4) and, accordingly, only a few virulence factors were produced.
Figure 4. Transcription of RNAIII in different clinical S. aureus isolates. RNA was prepared from cells grown in
TSB to an optical density of 10. Serial dilutions of total RNA of clinical isolates and reference strains (RN6390,
COL, Newman) were blotted and crosslinked onto the same positively charged nylon membrane. The membranebound
RNA was hybridized with a digoxigenin labelled RNA probe complementary to RNAIII. Chemiluminescence
signals were detected with a LumiImager (Roche Diagnostics, Mannheim, Germany).
Concluding remarks
In conclusion, our data show that in the species S. aureus, genome plasticity is only one of
several factors involved in exoproteome profile heterogeneity. Expression regulation as well
as protein secretion and modification processes add further dimensions to the heterogeneity of
the virulence potential of S. aureus. Such effects might be further enhanced and fine-tuned by
promoter mutations, differential activities of regulatory molecules and translation regulation
mechanisms. Most probably, the profoundly heterogeneous expression pattern of virulence
genes observed under identical in vitro conditions reflects a very high degree of variability in
vivo. It seems reasonable to suggest that these different virulence protein patterns are linked to
different clinical symptoms in the host. We are currently comparing virulence gene
expression profiles of S. aureus isolates that induced very similar symptoms. In this way, we
hope to identify symptom-/disease-related proteomic signatures that may help in elucidating
specific pathogenic mechanisms. It has been shown that S. aureus carriers mount a very
selective and protective antibody response against superantigens of their colonizing strains
(Holtfreter et al., 2006). Similarly, specific adaptive immune responses might also be raised
against other virulence factors, which vary between strains to a similar extent. These and
other immune mechanisms might explain why S. aureus carriers with bacteremia generally
have a better outcome than non-carriers (Wertheim et al., 2004). Finally, given the extensive
variability of virulence factors and mechanisms in S. aureus, our study has important
implications for vaccine development. The data strongly suggest that the development of
protective vaccines will require a very careful selection and combination of bacterial antigens.
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