Isolation and characterization of pneumolysin-negative mutants of Streptococcus pneumoniae

Pneumolysin-negative mutants of Streptococcus pneumoniae were isolated after mutagenesis with ethyl methane sulfonate. Though totally devoid of pneumolysin, these strains produced alpha hemolysis on blood agar when incubated aerobically. It is concluded that the alpha hemolysis typical of pneumococci is unrelated to their pneumolysin content.