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Published on: June 8, 2022
The phenomenon of staphylococcal interbacterial aggregate and net structures (SIAN) in community-associated
Tsai-Wen Wan1, Hiromitsu Mori2, Wei-Chun Hung3
1Department of Epidemiology, Genomics, and Evolution, International Medical Education and Research Center, Niigata, Japan; Clinical Laboratory Sciences and Medical Biotechnology, National Taiwan University College of Medicine, Taipei, Taiwan.
Abstract:
Community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) usually causes skin and soft tissue infections (SSTIs), but occasionally causes invasive infections with a broad range of manifestations. Virulence factors and pathogenesis of CA-MRSA have been investigated in details with genotype ST8/SCCmecIVa (USA300), which first emerged in the United States. However, CA-MRSA evolves rapidly, with different clones dominating in different world regions; their pathogenesis remains unclear. CA-MRSA with genotype ST8/SCCmecIVl (CA-MRSA/J) emerged in 2003 in Japan, spreading widely with a fatal case. We have studied the genetic characteristics of CA-MRSA/J, and during the course of this study, we found that CA-MRSA/J has bacteriophage-like spikes with or without a hexagonal cap (spikes X and Xc). Here, we report that CA-MRSA/J strain NN55 has non-phage-like, one-μm-long/jerky spikes with or without a hexagonal cap (LSX/LSXc), and also that LSX/LSXc forms (staphylococcal) interbacterial aggregate/net structures (SIAN). Regarding the phenomenon of SIAN, NN55 first formed single short spike X, followed by multiple molecules of long and jerky LSX/LSXc, leading to the interbacterial construction of SIAN, in colonies with high cell densities. The LSX/LSXc and SIAN structures have not been reported in S. aureus. NN55 was invasive in a HEp-2 cell assay, exhibiting SIAN. The novel SIAN structures may be foci-skeletons or toxic aggregates in NN55's invasive infections. The phenomenon of SIAN suggests novel staphylococcal cell-surface dynamism, providing a new structure-and-function relationship model and advancing the understanding of CA-MRSA pathogenesis.
Insights
Community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) in Japan forms novel structures called SIAN. These structures may contribute to the invasive nature of this evolving bacterial pathogen.
Area of Science:
- Microbiology
- Bacterial Pathogenesis
- Structural Biology
Background:
- Community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) typically causes skin infections but can lead to invasive disease.
- While USA300 (ST8/SCCmecIVa) is well-studied, other CA-MRSA clones with different pathogenesis are emerging globally.
- CA-MRSA/J (ST8/SCCmecIVl), identified in Japan, has caused fatal invasive infections, necessitating further investigation.
Purpose of the Study:
- To investigate the genetic characteristics and novel structures of CA-MRSA/J.
- To characterize the unique spike structures (LSX/LSXc) and their role in forming staphylococcal interbacterial aggregate/net structures (SIAN).
- To explore the potential contribution of SIAN to the invasiveness of CA-MRSA/J.
Main Methods:
- Genomic analysis of CA-MRSA/J strain NN55.
- Microscopic observation of bacterial colonies to identify and characterize novel spike structures.
- In vitro HEp-2 cell invasion assays to assess the pathogenicity of NN55 and the role of SIAN.
Main Results:
- CA-MRSA/J strain NN55 possesses unique, non-phage-like, long, jerky spikes (LSX/LSXc).
- LSX/LSXc structures facilitate the formation of staphylococcal interbacterial aggregate/net structures (SIAN) in high-density colonies.
- NN55 demonstrated invasiveness in HEp-2 cells, exhibiting SIAN structures, suggesting their role in infection.
Conclusions:
- The novel LSX/LSXc spikes and SIAN structures represent a previously unreported feature in S. aureus.
- SIAN may function as foci-skeletons or toxic aggregates, contributing to the invasive potential of CA-MRSA/J.
- The discovery of SIAN advances the understanding of staphylococcal cell-surface dynamism and CA-MRSA pathogenesis.
