Investigations on the enzymes and toxins of staphylococci. Relations of pH to growth and production of enzymes

Isolation and characterization of two protease-producing mutants from Staphylococcus aureus

Two mutants with increased protease production were isolated after nitrosoguanidine treatment of Staphylococcus aureus 8325N. The wild type produces low amounts of extracellular proteolytic activity. The enzyme was inducible and could only be detected if casein or preferably skim milk powder was used as inducer. The optimal pH, salt concentration, and media for enzyme production were determined. The mutants differed from the wild type in several phenotypic characters. The pattern of extracellular deoxyribonuclease and alkaline phosphatase differed between the mutants and the wild type. Several carbohydrates such as lactose, galactose, and mannitol were not utilized by the mutants, probably owing to a block in the uptake. Glucose could, however, be utilized by the mutants. Reversion frequency to wild type with regard to carbohydrate utilization was spontaneously high, and all revertants regained the parental pattern irrespective of the carbohydrate used for selection. The results suggest that a single locus may control the excretion of extracellular enzymes and carbohydrate uptake in S. aureus.

Identification of Staphylococcus aureus by simultaneous use of tube coagulase and thermonuclease tests

A simple system is described for efficiently detecting both thermonuclease (heat-stable nuclease) and free coagulase for the routine identification of Staphylococcus aureus in the clinical laboratory. Valid discrepancies between these two tests are rare enough to permit the use of one test as a control of the other.