Abstract
Staphylococcus schweitzeri belongs to the Staphylococcus aureus-related complex and is mainly found in African wildlife; no infections in humans are reported yet. Hence, its medical importance is controversial. The aim of this work was to assess the virulence of S. schweitzeri in vitro. The capacity of African S. schweitzeri (n = 58) for invasion, intra- and extracellular cytotoxicity, phagolysosomal escape, coagulase activity, biofilm formation and host cell activation was compared with S. aureus representing the most common clonal complexes in Africa (CC15, CC121, CC152). Whole genome sequencing revealed that the S. schweitzeri isolates belonged to five geographical clusters. Isolates from humans were found in two different clades. S. schweitzeri and S. aureus showed a similar host cell invasion (0.9 vs. 1.2 CFU/Vero cell), host cell activation (i.e. expression of pro-inflammatory cytokines, 4.1 vs. 1.7 normalized fold change in gene expression of CCL5; 7.3 vs. 9.9 normalized fold change in gene expression of IL8, A549 cells) and intracellular cytotoxicity (31.5% vs. 25% cell death, A549 cells). The extracellular cytotoxicity (52.9% vs. 28.8% cell death, A549 cells) was higher for S. schweitzeri than for S. aureus. Nearly all tested S. schweitzeri (n = 18/20) were able to escape from phagolysosomes. In conclusion, some S. schweitzeri isolates display virulence phenotypes comparable to African S. aureus. S. schweitzeri might become an emerging zoonotic pathogen within the genus Staphylococcus.
Highlights
Staphylococcus schweitzeri belongs to the Staphylococcus aureus-related complex and is mainly found in African wildlife; no infections in humans are reported yet
A total of 58 isolates from four African countries were included in the study and were confirmed to be S. schweitzeri as all clustered in a neighbor-joining tree based on the cgMLST scheme with the S. schweitzeri type strain (FSA084 = DSM 28300) separately from S. aureus standard strains (Fig. 1)
S. schweitzeri isolates were grouped in five geographical clusters including two from Nigeria
Summary
Staphylococcus schweitzeri belongs to the Staphylococcus aureus-related complex and is mainly found in African wildlife; no infections in humans are reported yet. A first functional study revealed that the S. schweitzeri type strain FSA084T produces α-hemolysin and is cytotoxic to human cell lines (HeLa, HT29)[7]. These preliminary results lead us to the hypothesis that the virulence of S. schweitzeri and S. aureus is equivalent. The aims of this study were (1) to test the virulence of S. schweitzeri in a wide range of in vitro assays on the largest S. schweitzeri collection published so far and (2) to screen systematically clinical samples from humans living in an area where S. schweitzeri is reported frequently in wildlife
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