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Quantifying the Cytotoxicity of Staphylococcus aureus Against Human Polymorphonuclear Leukocytes
Published on: January 3, 2020
Genomic and transcriptomic differences in community acquired methicillin resistant Staphylococcus aureus USA300 and
Marcus B Jones1, Christopher P Montgomery2, Susan Boyle-Vavra3
1J. Craig Venter Institute, 4120 Capricorn Lane, La Jolla, CA, 92037, USA. mjones@jcvi.org.
Background:
Staphylococcus aureus is a human pathogen responsible for substantial morbidity and mortality through its ability to cause a number of human infections including bacteremia, pneumonia and soft tissue infections. Of great concern is the emergence and dissemination of methicillin-resistant Staphylococcus aureus strains (MRSA) that are resistant to nearly all β-lactams. The emergence of the USA300 MRSA genetic background among community associated S. aureus infections (CA-MRSA) in the USA was followed by the disappearance of USA400 CA-MRSA isolates.
Results:
To gain a greater understanding of the potential fitness advantages and virulence capacity of S. aureus USA300 clones, we performed whole genome sequencing of 15 USA300 and 4 USA400 clinical isolates. A comparison of representative genomes of the USA300 and USA400 pulsotypes indicates a number of differences in mobile genome elements. We examined the in vitro gene expression profiles by microarray hybridization and the in vivo transcriptomes during lung infection in mice of a USA300 and a USA400 MRSA strain by performing complete genome qRT-PCR analysis. The unique presence and increased expression of 6 exotoxins in USA300 (12- to 600-fold) compared to USA400 may contribute to the increased virulence of USA300 clones. Importantly, we also observed the up-regulation of prophage genes in USA300 (compared with USA400) during mouse lung infection (including genes encoded by both prophages ΦSa2usa and ΦSa3usa), suggesting that these prophages may play an important role in vivo by contributing to the elevated virulence characteristic of the USA300 clone.
Conclusions:
We observed differences in the genetic content of USA300 and USA400 strains, as well as significant differences of in vitro and in vivo gene expression of mobile elements in a lung pneumonia model. This is the first study to document the global transcription differences between USA300 and USA400 strains during both in vitro and in vivo growth.
Insights
Methicillin-resistant Staphylococcus aureus (MRSA) USA300 strains exhibit increased virulence due to unique exotoxins and prophage gene expression compared to USA400 strains. This study reveals key genetic and transcriptional differences driving MRSA USA300
Area of Science:
- Microbiology
- Genomics
- Infectious Diseases
Background:
- Staphylococcus aureus is a major human pathogen causing significant illness and death.
- Methicillin-resistant Staphylococcus aureus (MRSA) strains, particularly the USA300 genetic background, have emerged as a significant public health concern.
- The USA300 MRSA clone has largely replaced other community-associated MRSA strains like USA400 in the United States.
Purpose of the Study:
- To investigate the genetic and transcriptional factors contributing to the enhanced virulence of Staphylococcus aureus USA300.
- To compare the genomic content and gene expression profiles of USA300 and USA400 MRSA strains.
- To elucidate the role of mobile genetic elements, exotoxins, and prophages in USA300's fitness and pathogenicity.
Main Methods:
- Whole genome sequencing of 15 USA300 and 4 USA400 clinical isolates.
- Microarray hybridization for in vitro gene expression analysis.
- Quantitative reverse transcription PCR (qRT-PCR) for in vivo transcriptome analysis during a mouse lung infection model.
Main Results:
- Significant differences in mobile genome elements were identified between USA300 and USA400 strains.
- USA300 strains showed unique presence and significantly increased expression (12- to 600-fold) of six exotoxins compared to USA400.
- Up-regulation of prophage genes (ΦSa2usa and ΦSa3usa) in USA300 during in vivo mouse lung infection was observed, suggesting their role in virulence.
Conclusions:
- Genetic content and mobile element expression differ substantially between USA300 and USA400 MRSA strains.
- Increased exotoxin production and prophage gene activity in USA300 contribute to its elevated virulence.
- This study provides the first comprehensive documentation of global transcriptional differences between USA300 and USA400 strains in both in vitro and in vivo settings.
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