Streptolysin S of Streptococcus anginosus exhibits broad-range hemolytic activity

Abstract

Streptococcus anginosus is a commensal of mucous membranes and an emerging human pathogen. Some strains, including the type strain, display a prominent β-hemolytic phenotype. A gene cluster (sag), encoding a variant of streptolysin S (SLS) has recently been identified as the genetic background for β-hemolysin production in S. anginosus. In this study, we further characterized the hemolytic and cytolytic activity of the S. anginosus hemolysin in comparison with other streptococcal hemolysins. The results indicate that SLS of S. anginosus is a broad-range hemolysin able to lyse erythrocytes of different species, including horse, bovine, rabbit and even chicken. The hemolytic activity is temperature dependent, and a down-regulation of the hemolysin expression is induced in the presence of high glucose levels. Survival assays indicate that in contrast to other streptococcal species, S. anginosus does not require SLS for survival in the presence of human granulocytes. Cross-complementation studies using the sagB and sagD genes of Streptococcus pyogenes and Streptococcus dysgalactiae subsp. equisimilis demonstrated functional similarities to the S. anginosus SLS. Nevertheless, distinct differences to other streptolysin S variants were noted and provide further insights into the molecular mechanisms of SLS pathogen host interactions.

Prevalence of Antimicrobial Resistance and Hemolytic Phenotypes in Culturable Arctic Bacteria

“…had mostly hemolytic phenotypes at 15 • C while Bacillus spp. expressed hemolytic activity mainly at 37 • C. Differences in the hemolysins structures and modes of action might explain that some of them have a lytic effect only above certain temperatures, at which the characteristics of erythrocyte membranes change due to increased membrane fluidity (Carr et al, 2001;Asam et al, 2015). Alternatively, the expression of hemolytic genes might be temperature-regulated (as described by Madrid et al, 2002) and could account for the differences observed in our experiments.…”

β-Hemolytic Streptococcus anginosus subsp. anginosus causes streptolysin S-dependent cytotoxicity to human cell culture lines in vitro

“…These results showed that the SLS secreted from β-SAA functions as a cytotoxic factor at least in vitro. However, a recent report described that no difference could be observed between the hemolytic wild-type SAA and the non-hemolytic sagB mutant, at any MOI or time point by the LDH leakage assay for THP-1 and human granulocytes; and hence, concluded that the S. anginosus SLS is a broad-range hemolysin without cytolytic activity [26]. The difference in the experimental design between this previous report and ours were as follows: Firstly, the composition of the co-cultivation medium is different.…”

“…constellatus strain W277 showed the SLS-dependent cytotoxicity in human hepatocellular carcinoma cell HepG2 [12]. However, another group reported that the SLS produced from SAA could not induce the cytotoxicity in the human acute monocytic leukemia cell line THP-1 and human granulocytes [26]. According to another report on the function of LLS, a homolog of SLS secreted from L. monocytogenes, LLS does not contribute to tissue injury and virulence in the host organs of L. monocytogenes [29].…”

“…Secondly, the method for the cytotoxicity assay is also different. The previous report evaluated the cytotoxicity using the LDH leakage method [26]. By this method, the cytotoxicity is detected at a relatively later stage of the cytoplasmic membrane disruption, which enables the leak of the cytoplasmic protein LDH (about 35 kDa of monomer, and the functional tetramer is about 140 kDa).…”

“…However, the cytotoxic potential of the SLS from β-SAA is still inconclusive. The absence of SLSdependent cytotoxicity of β-SAA against the human cell culture line THP-1 and human granulocytes was reported [26]. However, we had reported previously that the culture supernatant of the β-hemolytic S. constellatus subsp.…”