Global changes in Staphylococcus aureus gene expression in Human blood by Malachowa et al., 2011

Staphylococcus aureus is one of the leading causes of bloodstream infections worldwide, however, the mechanisms employed by the bacterium to survive in human blood, and therefore cause infection is poorly understood.

Thus, to better understand the relationship between the bacterium and the human blood, the authors have analyzed the transcriptome of the bacterium after ex vivo exposure to human blood and serum.  Additionally, they have assessed the percentage of survival of the bacterium in the human blood.

With this approach they have find:

1. After 120 minutes of exposure to human blood there were still a significant number of bacteria alive in the blood (approximately 35%).

2. Transcriptional analysis have revealed that the bacterium suffer extensive alterations in its metabolism probably as a  way to adapt in such particular conditions:

2.1. secondary  metabolites biosynthesis, nucleotide, amino acid as well as co-enzyme transport and metabolism were found up-regulated

2.2. global regulators such as accessory gene regulator (agr) and  staphylococcal accessory regulator (sar) were found down-regulated

2.3. virulence and defense factors such as gamma hemolysin genes (hlgA, hlgC and  hlgB) were up-regulated concomitantly with saeRS that is though to be the gamma hemolysin regulator.

3. Having in account the gamma hemolysin genes are important virulence factors and that these genes were differentially expressed after contact with human blood or serum  it suggested  it expected that hlg genes contribute to the bacterium survival and evasion in human blood.

To better understand the role of hlg genes in evasion, a mutant strain for this operon has been created.  Survival experiments have shown that the mutant strain presented reduced survival in blood, although the effect was not very strong.

Hence, hlg has shown to be involved in S. aureus survival in human blood, although with a modest contribution.

Reference of the article summarized above:

Malachowa N, Whitney AR, Kobayashi SD, Sturdevant DE, Kennedy AD, Braughton KR, Shabb DW, Diep BA, Chambers HF, Otto M, DeLeo FR. (2011) “Global changes in Staphylococcus aureus gene expression in human blood”. PLosOne 6(4): e18617.

RM: AF 1383

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