|DNA microarrays used to compare strains of Staphylococcus aureus|
Edward R. Winstead
July 23, 2001
Researchers have used DNA microarrays to compare 36 strains of the bacterium Staphylococcus aureus, a human pathogen that can cause life-threatening infections, particularly among hospital patients. The content of the 36 genomes varied widely, and this variation may be relevant to efforts to combat the pathogen, the researchers say.
The DNA microarray used by James M. Musser, of the US National Institute of Allergy and Infectious Diseases, and colleagues contained more than 90 percent of the genome of the strain S. aureus COL. The researchers identified 18 large chromosomal regions that differed significantly among the strains. Ten of these contained genes linked to the bacterium's virulence and its ability to resist antibiotics.
The researchers screened eleven strains that are resistant to methicillin, the antibiotic commonly used to treat S. aureus infections in humans. Methicillin-resistant strains appear to have acquired genes involved in antibiotic resistance directly from other bacterial strains, a biological phenomenon known as horizontal gene transfer.
"It is clear that horizontal gene transfer has played a fundamental role in the evolution of pathogenic S. aureus," the researchers write in Proceedings of the National Academy of Sciences.
Strains of S. aureus that cause toxic shock syndrome were also analyzed. Toxic shock syndrome is a rare blood infection most commonly associated with women who use highly absorbent tampons (although it can affect men and children). Nine of the strains in this study were cultured from women with the illness. The reasons for an epidemic of toxic shock syndrome in the U.S. in the 1970s are unknown, but the microarray analysis suggests that a new virulent strain of S. aureus was not the cause.
"The epidemic of toxic shock syndrome that occurred in the 1970s was caused by a change in the host environment, rather than rapid geographic dissemination of a new hypervirulent strain," the researchers write.
The 36 strains in the study were among the most abundant identified during a survey of 2,077 S. aureus isolates from around the world. Also in the study were strains that cause infectious disease in sheep and cattle.
The research team included Steven R. Gill, of The Institute for Genomic Research (TIGR) in Rockville, Maryland. A pre-publication view of the Staphylococcus aureus COL genome sequence is available at TIGR's Web site.
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