Characterization of transcription within sdr region of Staphylococcus aureus

Abstract

Staphylococcus aureus is an opportunistic pathogen responsible for various infections in humans and animals. It causes localized and systemic infections, such as abscesses, impetigo, cellulitis, sepsis, endocarditis, bone infections, and meningitis. S. aureus virulence factors responsible for the initial contact with host cells (MSCRAMMs-microbial surface components recognizing adhesive matrix molecules) include three Sdr proteins. The presence of particular sdr genes is correlated with putative tissue specificity. The transcriptional organization of the sdr region remains unclear. We tested expression of the sdrC, sdrD, or sdrE genes in various in vitro conditions, as well as after contact with human blood. In this work, we present data suggesting a separation of the sdr region into three transcriptional units, based on their differential reactions to the environment. Differential reaction of the sdrD transcript to environmental conditions and blood suggests dissimilar functions of the sdr genes. SdrE has been previously proposed to play role in bone infections, whilst our results can indicate that sdrD plays a role in the interactions between the pathogen and human immune system, serum or specifically reacts to nutrients/other factors present in human blood.

Fig. 1

Analysis of sdr locus organization. Fragment of genomic sequence of S. aureus strain USA300 with marked putative promoter −35 and −10 sequences of sdrC, sdrD, and sdrE (boxed) and a rho independent terminator (bold) in the intergenic region between sdrC and sdrD. Because of the length of the putative reading frames, for protein coding sequences of sdrC, sdrD, and sdrE genes only the start and stop codon are shown with dots marked inbetween (bold italic, boxed)

Fig. 2

Expression of sdrC, sdrD, and sdrE genes during growth at 37°C. Expression of studied genes was calibrated to gyrA level and normalized to expression in early log (EL) growth phase. EL early logarithmic, ML mid logarithmic, LL late logarithmic, and S stationary growth phase. Error bars 1 standard deviation

Fig. 3

Influence of low and high growth temperature on expression of sdrC, sdrD, and sdrE genes. Expression of studied genes was calibrated to gyrA level and normalized to expression in early log (EL) growth phase. EL early logarithmic, ML mid logarithmic, LL late logarithmic, and S stationary growth phase. Error bars 1 standard deviation

Fig. 4

Effect of in vitro growth conditions on the expression of sdr genes. a Influence of osmotic stress on the expression of sdrC, sdrD, and sdrE genes. b Influence of divalent ions on expression of sdrC, sdrD, and sdrE genes. Expression of studied genes was calibrated to gyrA level and normalized to expression in early log (EL) growth phase. Error bars 1 standard deviation

Fig. 5

Influence of human blood on expression of sdrC, sdrD, and sdrE genes. Expression of studied genes was calibrated to gyrA level and normalized to expression at time 0. Error bars 1 standard deviation