Identification and characterization of surface proteins from Staphylococcus saprophyticus

Staphylococcus saprophyticus Proteomic Analyses Elucidate Differences in the Protein Repertories among Clinical Strains Related to Virulence and Persistence

Staphylococcus saprophyticus is a Gram-positive and coagulase negative cocci that composes the skin microbiota and can act as an opportunistic agent causing urinary tract infections, being more frequent in sexually active young women. The ability of a pathogen to cause infection in the host is associated to its ability to adhere to host cells and to survive host immune defenses. In this work, we presented the comparative proteomic profile of three S. saprophyticus strains. It was possible to characterize differences in the proteome content, specially related to expression of virulence factors. We compiled this data and previous data and we detected one strain (9325) possessing higher production and secretion of proteins related to virulence. Our results show that phenotypic, genotypic, and proteomic differences reflect in the ability to survive during interaction with host cells, since the 9325 strain presented a higher survival rate after macrophage interaction. In counterpart, the 7108 strain that possesses lower content of proteins related to virulence presented higher ability to form biofilm suggesting that this strain can be better adapted to persist in the host and in the environment. Our work describes, for the first time, proteomic flexibility among S. saprophyticus strains, reflecting in virulence and persistence.

The exoproteome profiles of three Staphylococcus saprophyticus strains reveal diversity in protein secretion contents

Staphylococcus saprophyticus is a gram-positive microorganism responsible for urinary tract infections (UTIs). Although some virulence factors are characterized, such as urease, autolysins, adhesins and hemagglutinins, large-scale proteomic studies have not been performed within this species. We performed the characterization of the exoproteome from three S. saprophyticus strains: the reference strain ATCC 15,305, a non-capsular strain 7108 and the 9325 strain containing a thick capsule which were cultured in BHI medium and culture supernatants were analysed by using mass spectrometry approach. We observed a core of 72 secreted proteins. In addition, it was possible to detect diversity in the protein profiles of the exoproteomes. Interestingly, strain 7108 presented no secretion of three antigenic proteins, including the classical SsaA antigen. In addition, the level of antigenic proteins secreted by strain 9325 was higher than in ATCC 15,305. This result was confirmed by Western blot analysis using anti-SsaA polyclonal antibodies, and no production/ secretion of SsaA was detected in strain 7108. Transcriptional data shows that 7108 strain produces transcripts encoding SsaA, suggesting post-transcriptional regulation occurs in this strain. Moreover, when compared with the other strains that were analyzed, it was possible to detect higher levels of proteases secreted by strain 7108 and higher levels of antigenic proteins and transglycosylases secreted by 9325 strain. The results reveal diversity in protein secretion among strains. This research is an important first step towards understanding the variability in S. saprophyticus exoproteome profile and could be significant in explaining differences among strains.

Biochemical characterization of the surface-associated lipase of Staphylococcus saprophyticus

Staphylococcus saprophyticus, an important cause of urinary tract infections, produces a surface-associated lipase, Ssp. In contrast to other lipases, Ssp is a protein that is present in high amounts on the surface of the bacteria and it was shown that it is a true lipase. Characterization of S. saprophyticus lipase (Ssp) showed that it is more similar to Staphylococcus aureus lipase and Staphylococcus epidermidis lipase than to Staphylococcus hyicus lipase and Staphylococcus simulans lipase. Ssp showed an optimum of lipolytic activity at pH 6 and lost its activity at pH>8 or pH<5. The present results show that Ssp activity is dependent on Ca(2+). Consequently, activity increased c. 10-fold in the presence of 2 mM Ca(2+). Optimal activity was reached at 30 degrees C. It was also observed that the enzymatic activity of Ssp depends strongly on the acyl chain length of the substrate molecule.

The surface-associated protein of Staphylococcus saprophyticus is a lipase

Staphylococcus saprophyticus surface-associated protein (Ssp) was the first surface protein described for this organism. Ssp-positive strains display a fuzzy layer of surface-associated material in electron micrographs, whereas Ssp-negative strains appear to be smooth. The physiologic function of Ssp, however, has remained elusive. To clone the associated gene, we determined the N-terminal sequence, as well as an internal amino acid sequence, of the purified protein. We derived two degenerate primers from these peptide sequences, which we used to identify the ssp gene from genomic DNA of S. saprophyticus 7108. The gene was cloned by PCR techniques and was found to be homologous to genes encoding staphylococcal lipases. In keeping with this finding, strains 7108 and 9325, which are Ssp positive, showed lipase activity on tributyrylglycerol agar plates, whereas the Ssp-negative strain CCM883 did not. Association of enzyme activity with the cloned DNA was proven by introducing the gene into Staphylococcus carnosus TM300. When wild-type strain 7108 and an isogenic mutant were analyzed by transmission electron microscopy, strain 7108 exhibited the fuzzy surface layer, whereas the mutant appeared to be smooth. Lipase activity and the surface appendages could be restored by reintroduction of the cloned gene into the mutant. Experiments using immobilized collagen type I did not provide evidence for the involvement of Ssp in adherence to this matrix protein. Our experiments thus provided evidence that Ssp is a surface-associated lipase of S. saprophyticus.

Pathogenesis of infections due to coagulase-negative staphylococci

As a group, the coagulase-negative staphylococci (CoNS) are among the most frequently isolated bacteria in the clinical microbiology laboratory and are becoming increasingly important, especially as causes of hospital-acquired infections. These bacteria are normal inhabitants of human skin and mucous membranes and, therefore, one of the major challenges of daily diagnostic work is to distinguish clinically significant CoNS from contaminant strains. This overview addresses current knowledge of the pathogenesis of infections due to CoNS and particularly focuses on virulence factors of the species Staphylococcus epidermidis. S epidermidis has been identified as a major cause of nosocomial infections, especially in patients with predisposing factors such as indwelling or implanted foreign polymer bodies. Most important in the pathogenesis of foreign-body-associated infections is the ability of these bacteria to colonise the polymer surface by the formation of a thick, multilayered biofilm. Biofilm formation takes place in two phases. The first phase involves the attachment of the bacteria to polymer surfaces that may be either unmodified or coated with host extracellular matrix proteins. In the second phase, the bacteria proliferate and accumulate into multilayered cell clusters that are embedded in an extracellular material. The bacterial factors involved in both phases of biofilm formation are discussed in this review. In addition, the most important aspects of the pathogenic potential of S saprophyticus, S lugdunensis, and S schleiferi are described, although, compared with S epidermidis, much less is known in these species concerning their virulence factors.

Expression of Staphylococcus saprophyticus surface properties is modulated by composition of the atmosphere

Expression of two major surface proteins of Staphylococcus saprophyticus, the haemagglutinin and the Staphylococcus saprophyticus surface-associated protein (Ssp), required carefully defined culture conditions. The Ssp is produced when bacteria are grown on agar, whereas expression of the haemagglutinin requires growth in broth. We sought to identify the environmental signals that are responsible for this modulation. Varying the pH, the osmolarity of the growth medium or the temperature did not influence expression of the proteins. In contrast, growth in an anaerobic atmosphere increased haemagglutination titres and fibronectin binding (both mediated by the haemagglutinin) but suppressed production of the Ssp. As the influence of the CO2 level could be excluded, we conclude that expression of these surface proteins is probably modulated by the O2 content of the atmosphere.