Genomic Analysis Reveals Streptococcal Diversity

Researchers using a wide range of sophisticated analytic techniques to study the genome of group A streptococci (GAS) have identified the molecular basis for the large variation in infectivity and virulence expressed by different populations of these bacteria.

Investigators at the [U. S.] National Institute of Health's Rocky Mountain Laboratories (Hamilton, MT, USA) obtained 255 different serotype M3 GAS specimens cultured from patients in Ontario, Canada, over 11 years and representing two distinct infection peaks. They used an array of techniques including pulsed-field gel electrophoresis, DNA-DNA microarray, whole-genome polymerase chain reaction (PCR) scanning, prophage genotyping, targeted gene sequencing, and single-nucleotide polymorphism genotyping to establish an index of the genetic diversity of the specimens.

They reported in the July 28, 2004, online edition of the Proceedings of the [U. S.] National Academy of Sciences that variations in gene content were attributable to acquisition or loss of prophages, a molecular process that generates unique combinations of proven or putative virulence genes. The various distinct serotype M3 genotypes that were identified experienced rapid population expansion and caused infections that differed significantly in character and severity. At the molecular level, a four amino acid duplication in the extreme N terminus of M protein was seen to be a factor contributing to an epidemic wave of serotype M3 invasive infections.

"Before the advent of genome sequencing and genome-wide analysis methods, our knowledge of molecular characteristics of pathogenic bacterial infections in distinct populations was extremely limited,” said senior author Dr. James M. Musser, a researcher at the Rocky Mountain Laboratories.

The findings obtained in this study are expected to influence future efforts to develop a vaccine against group A streptococci.


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Rocky Mountain Laboratories