Streptolysin S

• leads to β-hemolysis on blood agar

• nonimmunogenic in natural infection

• broad spectrum of potent cytolytic activity

• never fully purified, but est. MW is very low: 2.8 kD

Random transposon mutagenesis of the bacterial chromosome

• transposons are how pathogens spread from chromosome to chromosome

• in the microbio lab, this can mutagenize organisms

• “R-rated experiment where you mate bacteria.” they make sex pili and transfer genetic material

• screen for mutants that have acquired the transposon by administering an antibiotic

GAS sag locus for streptolysin S biosynthesis

• Tn916 transposon led to nonhemolytic strain

• Tn917 transposon led to another nonhemolytic strain

• these two genes were really close to each other, and in fact there are nine genes next to each other, so the whole sequence was termed an operon

• they are now named sagA through sagI

• in fact, targeted mutation of any sag gene led to no hemolysis, but up- or downstream mutations had no effect on hemolytic activity

• so any one sag gene missing led to no hemolysis. that means that losing any one sag is sufficient and necessary for loss of hemolytic capability PDF 16

• wild-type GAS produces a horrible, flesh-eating bacteria PDF 17

• SLS– mutant is much less virulent

Cytolytic effect of SLS on human keratinocytes

• mutant doesn’t injure skin cells

• restoration of gene leads to virulence

Streptolysin S inhibits phagocytosis

• bacterium kills cell before cell kills bacterium

Category: Microbiology Notes