Frontiers in Cellular and Infection Microbiology (Nov 2016)
Identification and Characterization of Staphylococcus aureus Strains with an Incomplete Hemolytic Phenotype
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, Staphylococcus aureus with an incomplete hemolytic phenotype (SIHP) was isolated from clinical samples. To study the microbiologic characteristics of SIHP, SIHP was inoculated on the sheep blood agar plates supplied by different manufacturers to compare their hemolytic phenotype. Expression of hemolysin genes hla, hlb, hlgC and hld of SIHP was detected by qRT-PCR. In addition, the alpha-hemolysin encoded by gene hla was analyzed by western blot. At the same time, the antimicrobial susceptibility of SIHP was tested using the broth dilution method. The main antibiotic resistance gene mecA and virulence genes tst were detected by PCR in SIHP strains. Furthermore, the virulence of SIHP strains was detected through comparing their intracellular survival in macrophage. The cytokines and chemokines secreted by macrophage were measured by flow cytometry. Finally, the genotyping of SIHP was performed by multilocus sequence typing (MLST) analysis. The results showed that the incomplete hemolytic phenotype of SIHP could be observed on the sheep blood agar plates from different suppliers. The relative mRNA expression of hlb in SIHP was obviously increased compared to the control Staphylococcus aureus strains, while the expression of hla, hlgC and hld in SIHP was significantly decreased. In addition, it was shown that the alpha-hemolysin of SIHP was less than that of control strains as well. All sixty SIHP strains were identified to be the methicillin resistant Staphylococcus 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 Staphylococcus 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
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