Studies on bacteriophage and host genes involved in morphogenesis.

Studies on characteristics of Staphylococcus aureus the staphylococcal alpha hemolysin or exotoxin in cell free filtrates, rather than coagulase, correlated with the lethal effects in suckling mice. As observed in these studies alpha hemolysin production was increased by prolonged incubation of S. aureus cultures in the presence of approximately 25% increased carbon dioxide. In normal atmosphere some strains of S. aureaus tested failed to produce alpha hemolysin. Staphylococcal strain differences were observed in hemolysin tube test with human red blood cells. Some S. aureaus strains showed “hot†and “cold†lysis, some only “cold†lysis and some failed to lyse human cells. Staphylococci formed 2 hemolytic bands around S. aureaus colonies on rabbit blood agar after incubation at 37°C for 24 fours. Two to 3 additional bands were formed after refrigeration at 4°C for 24 hours. S. aureaus colonies produced only 1 hemolytic zone on human blood agar. Tube and plate hemolysin test using rabbit red blood cells showed “hot†and “cold†hemolysin activity. Alpha hemolysin was believed to be responsible for “hot†and “cold†hemolysis in tube tests. This “hot-cold†reaction by alpha hemolysin may be related to the “hot†and “cold†hemolytic bands formed around S. aureus colonies when cultured on rabbit blood agar. No immunological difference was established between “hot†and “cold†alpha hemolysins. The presence of “cold†hemolysin in blood agar however does not rule out other unidentified hemolysins. Ultraviolet irradiation and boiling inactivated lethal toxin and hemolysin in a straight line relationship. The “cold†hemolysin however was more resistant to these physical agents than the “hot†hemolysin. Necrosis was produced in sucking mice inoculated with material containing “cold†hemolysin. The necrotic activity correlated the cold hemolysin and is believed to be a new finding. Concentrated alpha hemolysin showed an equivalent 1:1600 minimal hemolytic dose as measure by rabbit red blood cell lysis and an equivalent of 1:2000 minimal lethal dose as measured by intramuscular inoculation of sucking mice. The virulence of S. aureus strain 10 appeared to be related to the number of organisms’ present rather than alpha toxin. Although the virulence of staphylococcus appeared to be related to number of organisms injected into sucking mice, virulence of the other strains tested was associated more specifically with the formation of alpha hemolysin. Other virulence mechanisms should be considered in S. aureaus strains such as strain 10 unless such strains produce toxins in-vivo. Some protection of rabbits was shown when they were inoculated with S. aureus strain 15 mixed and incubated with rabbit or human plasma prior to inoculation. Results were variable in rabbit protection tests which may be explained on differences in the toxic content of cultures due to bacterial variation or due to variation in the different groups of rabbits selected for the test or a combination of both.