Sireesha Divyakolu and Dr. Venkataraman Sritharan
Background: Staphylococcus aureus is an important pathogenic bacterium causing both hospital and community acquired infections. Hemolysins are important virulence factors of S. aureus which help in the pathogenesis of diseases. Screening of hemolysins is important in infection control and prevention.
Methods: Aim of the study was to characterize hemolysins of Staphylococcus aureus (n=152) isolated from tertiary hospitals in India, by phenotypic and genotypic methods. Phenotypic characterization of hemolysins of Staphylococcus aureus was done on either sheep or rabbit blood agar plates. Genes encoding hemolysin were amplified with specific primers in a multiplex Polymerase Chain Reaction (PCR) and analyzed by agarose gel electrophoresis.
Results: Genes of all four hemolysins namely hla, hlb, hlg and hld were screened by multiplex PCR. Genotyping revealed that the isolates contained patterns of four, three or two hemolysin genes in multiple combinations. The most common profile comprised of all four hemolysin genes, namely hla, hlb, hlg, hld in a majority of isolates (47.3%, 72/152). Sixty one isolates (40.1%, 61/152) carried three hemolysin genes in three different patterns: 56 (37%) isolates contained hla, hlb, hld genes, second pattern combined 3 genes namely (1.9%) hla, hlg, hld and the third pattern was found in 2 (1.3%) isolates with hlb, hlg, hld. Five (3.28%) isolates in this study had only two hemolysin genes in three different combinations: 2 (1.3%) isolates with hlb:hld, 2 (1.3%) isolates with hla:hld pattern and 1 (0.7%) isolate with hlg:hld pattern. 14 (9.2%) isolates carried only hld gene. Phenotyping showed that all the isolates had α, β and δ activities and high activity of α, β and δ hemolysins were seen in isolates which were obtained from pus, blood and other body fluids. All these sites suffer enormous tissue damage in severe S. aureus infection. The genotype data correlated well with the phenotype analysis.
Conclusions: Four hemolysin genes were detected in all clinical isolates of S. aureus. We could identify the activity of α, β and δ hemolysins on blood agar media. We found out that the isolates displayed varying combination of the four hemolysin genes. These differences in genotype of four genes and the hemolysin activity may indicate a preference mandated by the host tissue or site during the pathogenesis of the disease since each hemolysin has different activity profile. Body fluids in general, pus, blood, sputum in particular carried S. aureus with higher hemolysin activities compared to isolates of specimen from other sites. The results of this study reinforce the importance of hemolysins in S. aureus diseases and suggest that the tissue damages and symptoms are related to the hemolysins activity during pathogenesis.
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