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Published on: November 4, 2016
Identification and Characterization of Staphylococcus aureus Strains with an Incomplete Hemolytic Phenotype
Haifang Zhang1, Yi Zheng1, Huasheng Gao1
1Department of Clinical Laboratory, The Second Affiliated Hospital of Soochow University Suzhou, China.
Abstract:
Staphylococcus aureus is a common pathogen causing both hospital and community-acquired infections. Hemolysin is one of the important virulence factors for S. aureus and causes the typical β-hemolytic phenotype which is called complete hemolytic phenotype as well. Recently, S. aureus with an incomplete hemolytic phenotype (SIHP) was isolated from clinical samples. To study the microbiologic characteristics of SIHP, the special hemolytic phenotype of SIHP was verified on the sheep blood agar plates supplied by different manufacturers. Expression of hemolysin genes hla, hlb, hlgC, and hld of SIHP was detected by qRT-PCR and it was showed that expression of hlb in SIHP was obviously increased compared to the control S. aureus strains with complete hemolytic phenotype (SCHP), while the expression of hla, hlgC, and hld in SIHP was significantly decreased. In addition, the α-hemolysin encoded by gene hla was decreased obviously in SIHP compared to SCHP by western blot. All 60 SIHP strains were identified to be the methicillin resistant S. aureus (MRSA), and moreover these SIHP strains all contains mecA gene. The virulence gene tst were all present in SIHP, and the intracellular survival ability of SIHP was much greater than that of the gene tst negative S. aureus. We also found that IL-2, IL-6, and IL-17A secreted in the supernatant of SIHP infected macrophages increased significantly compared to tst negative control strains infected ones. MLST analysis showed that all of SIHP strains were classified into ST5 clone. To our knowledge, this study firstly showed that SIHP strains are a kind of methicillin resistant strains which express β-hemolysin highly and possess a potential high virulence, and it was suggested that SIHP should be paid more attention in hospital.
Insights
Newly identified Staphylococcus aureus strains with an incomplete hemolytic phenotype (SIHP) are methicillin-resistant and highly virulent. These SIHP strains exhibit increased beta-hemolysin expression and enhanced intracellular survival, warranting closer attention in healthcare settings.
Area of Science:
- Microbiology
- Infectious Diseases
- Molecular Biology
Background:
- Staphylococcus aureus is a significant pathogen responsible for various infections.
- Hemolysins are key virulence factors in S. aureus, typically causing a complete hemolytic phenotype.
- Staphylococcus aureus with an incomplete hemolytic phenotype (SIHP) has recently been isolated from clinical settings.
Purpose of the Study:
- To investigate the microbiological characteristics of SIHP.
- To compare the hemolysin gene expression and virulence factors of SIHP with control strains.
- To determine the clinical relevance and potential virulence of SIHP.
Main Methods:
- Verification of hemolytic phenotype on sheep blood agar plates.
- Quantitative reverse transcription PCR (qRT-PCR) to detect hemolysin gene expression (hla, hlb, hlgC, hld).
- Western blot analysis for alpha-hemolysin.
- Detection of mecA and tst genes.
- Assessment of intracellular survival and cytokine secretion (IL-2, IL-6, IL-17A) in infected macrophages.
- Multilocus sequence typing (MLST) for clonal analysis.
Main Results:
- SIHP strains showed increased expression of hlb and decreased expression of hla, hlgC, and hld compared to complete hemolytic phenotype strains.
- Alpha-hemolysin levels were significantly reduced in SIHP.
- All 60 SIHP strains were identified as methicillin-resistant Staphylococcus aureus (MRSA) harboring the mecA gene.
- SIHP strains possessed the tst gene, exhibited enhanced intracellular survival, and induced higher levels of IL-2, IL-6, and IL-17A in infected macrophages.
- MLST analysis revealed all SIHP strains belonged to the ST5 clone.
Conclusions:
- SIHP represents a distinct group of methicillin-resistant Staphylococcus aureus strains.
- These strains exhibit high beta-hemolysin expression and possess significant virulence potential.
- The findings suggest SIHP warrants increased attention in hospital environments due to its potential for severe infections.
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