Catalase, superoxide dismutase, and hemolysin in the virulence of Listeria monocytogenes

Six strains of Listeria monocytogenes were examined for catalase, superoxide dismutase (SOD), and listeriolysin O (LLO) activities. The two strains having the lowest catalase activities also possessed the lowest SOD activities. Exogenous hydrogen peroxide was added to suspensions of four L. monocytogenes strains; strains producing the highest catalase levels showed the greatest H$\sb2$O$\sb2$ resistance. Only two strains of L. monocytogenes examined exhibited LLO activity. Various concentrations of NaCl were added to growth media prior to bacterial inoculation. Most strains showed an increase in catalase, SOD, and LLO activities when propagated in media containing 428 mM NaCl (TSBS) followed by a decline in activities at greater NaCl concentrations. Potassium chloride was added to the growth media at identical molar concentrations as NaCl for two L. monocytogenes strains. Stimulation and depression of enzyme activities followed the trends found for cells grown in media containing added NaCl. The catalase and SOD activities were generally higher when cells were grown in media containing NaCl than in media containing equimolar KCl concentrations. The LLO titer for L. monocytogenes 10403S grown in a medium containing 428 mM KCl (TSBK) was approximately 50% higher than when propagated in TSBS. A hemolytic L. monocytogenes strain and a nonhemolytic mutant of this strain grown in media containing either no added salt (TSBW), various concentrations of NaCl, or various concentrations of KCl were injected into ten-day-old chick embryos to relate virulence factor production with pathogenicity. The hemolytic strain gave an LD$\sb{50}$ less than a single cell when grown in many of the aforementioned media while the nonhemolytic strain exhibited a higher LD$\sb{50}$ when propagated in TSBW compared to the other media. The same two strains grown in either TSBW, TSBS, or TSBK were injected into mice. No significant difference (p $<$ 0.05) in virulence was found for cells propagated in any of the growth media. The heat resistance of four strains was examined. No correlation between heat sensitivity and enzyme production could be determined. Cells of one strain grown in media containing the higher NaCl levels tested exhibited enhanced heat lability compared to cells grown in media containing lower NaCl concentrations.U of I OnlyETDs are only available to UIUC Users without author permissio