title: Insights into alpha-hemolysin (Hla) evolution and expression among Staphylococcus aureus clones with hospital and community origin.
abstract: BACKGROUND
  Alpha-hemolysin (Hla) is a major virulence factor in the pathogenesis of Staphylococcus aureus infection, being active against a wide range of host cells. Although hla is ubiquitous in S. aureus, its genetic diversity and variation in expression in different genetic backgrounds is not known. We evaluated nucleotide sequence variation and gene expression profiles of hla among representatives of hospital (HA) and community-associated (CA) S. aureus clones.
  
  
  METHODS
  51 methicillin-resistant S. aureus and 22 methicillin-susceptible S. aureus were characterized by PFGE, spa typing, MLST and SCCmec typing. The internal regions of hla and the hla promoter were sequenced and gene expression was assessed by RT-PCR.
  
  
  RESULTS
  Alpha-hemolysin encoding- and promoter sequences were diverse, with 12 and 23 different alleles, respectively. Based on phylogenetic analysis, we suggest that hla may have evolved together with the S. aureus genetic background, except for ST22, ST121, ST59 and ST93. Conversely, the promoter region showed lack of co-evolution with the genetic backgrounds. Four non-synonymous amino acid changes were identified close to important regions of hla activity. Amino acid changes in the RNAIII binding site were not associated to hla expression. Although expression rates of hla were in general strain-specific, we observed CA clones showed significantly higher hla expression (p = 0.003) when compared with HA clones.
  
  
  CONCLUSIONS
  We propose that the hla gene has evolved together with the genetic background. Overall, CA genetic backgrounds showed higher levels of hla expression than HA, and a high strain-to-strain variation of gene expression was detected in closely related strains.
authors.affiliation: Laboratory of Molecular Genetics, Instituto de Tecnologia Química e Biológica (ITQB), Oeiras, Portugal.
authors.forename: Ana
authors.initials: A
authors.lastname: Tavares
authors.affiliation: Dept. of Clinical Microbiology 445, Copenhagen University Hospital, Hvidovre, Denmark.
authors.forename: Jesper B
authors.initials: JB
authors.lastname: Nielsen
authors.affiliation: Dept. of Clinical Microbiology 445, Copenhagen University Hospital, Hvidovre, Denmark.
authors.forename: Kit
authors.initials: K
authors.lastname: Boye
authors.affiliation: Dept. of Clinical Microbiology 445, Copenhagen University Hospital, Hvidovre, Denmark.
authors.forename: Susanne
authors.initials: S
authors.lastname: Rohde
authors.affiliation: Molecular Microbiology of Human Pathogens, ITQB, Oeiras, Portugal.
authors.forename: Ana C
authors.initials: AC
authors.lastname: Paulo
authors.affiliation: Dept. of Clinical Microbiology 445, Copenhagen University Hospital, Hvidovre, Denmark; Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark.
authors.forename: Henrik
authors.initials: H
authors.lastname: Westh
authors.affiliation: Dept. of Clinical Microbiology 445, Copenhagen University Hospital, Hvidovre, Denmark; Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark.
authors.forename: Kristian
authors.initials: K
authors.lastname: Schønning
authors.affiliation: Laboratory of Molecular Genetics, Instituto de Tecnologia Química e Biológica (ITQB), Oeiras, Portugal; Laboratory of Microbiology and Infectious Diseases, The Rockefeller University, New York, New York, United States of America.
authors.forename: Hermínia
authors.initials: H
authors.lastname: de Lencastre
authors.affiliation: Laboratory of Molecular Genetics, Instituto de Tecnologia Química e Biológica (ITQB), Oeiras, Portugal; Laboratory of Bacterial Evolution and Molecular Epidemiology, ITQB, Oeiras, Portugal.
authors.forename: Maria
authors.initials: M
authors.lastname: Miragaia
mesh_terms: D001427:Bacterial Toxins / Q000235:genetics*; D001483:Base Sequence; D017714:Community-Acquired Infections / Q000382:microbiology; D003428:Cross Infection / Q000382:microbiology; D004269:DNA, Bacterial / Q000235:genetics; D006460:Hemolysin Proteins / Q000235:genetics*; D006801:Humans; D016106:Methicillin Resistance / Q000235:genetics; D008826:Microbial Sensitivity Tests; D058885:Multilocus Sequence Typing; D010802:Phylogeny; D020641:Polymorphism, Single Nucleotide / Q000235:genetics; D011401:Promoter Regions, Genetic / Q000235:genetics; D017422:Sequence Analysis, DNA; D013203:Staphylococcal Infections / Q000382:microbiology*; D013211:Staphylococcus aureus / Q000201:enzymology / Q000235:genetics* / Q000472:pathogenicity*; D037521:Virulence Factors / Q000235:genetics
chemical_list: D001427:Bacterial Toxins; D004269:DNA, Bacterial; D006460:Hemolysin Proteins; D037521:Virulence Factors; C021091:staphylococcal alpha-toxin