Graduate Thesis Or Dissertation
 

Growth, enterotoxin production and energy charge of Staphylococcus aureus under three gaseous environments

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  • The effect of different oxygen atmospheres on growth, energy charge and enterotoxin production of Staphylococcus aureus was investigated. Three atmospheres, air, 5% oxygen in nitrogen and 20% oxygen in nitrogen, were tested on three strains producing enterotoxins A, B and C. Colony forming units (CFU), dry weight, dissolved oxygen, pH, adenosine phosphates and adenylate energy charge and enterotoxin production were measured. The effect of sugars added to the culture media was also studied. A significant difference was observed among the atmospheres in their effect on growth in the earlier hours. Growth was fastest in air for all the strains, followed by 20% and 5% oxygen in nitrogen. Growth response of the strains to the atmospheres were similar among all three strains. Depletion of dissolved oxygen occurred with rapid growth. The pH was alkaline in all cultures by the last hours sampled. A significant difference was also observed among the atmospheres in the effect on enterotoxin production, although this differed among strains. In strains 265-1 and S-6, enterotoxin A and B production, respectively, was faster in air than it was in either 5% or 20% oxygen in nitrogen. This corresponded to the effect on growth rate. The response of strain 361 was distinctively different from the other two strains. In this strain the atmospheres of 5% and 20% oxygen in nitrogen had a stimulatory effect on the rate of production of enterotoxin C. There was a definite pattern of change in energy charge during the growth cycle of S. aureus with apparent difference among three strains. In 265-1, the energy charge increased very rapidly and reached 0.68 at 3 hr of growth; an equivalent level was reached in strains S-6 and 361 at about 8 hr after an initial lag. The time at which enterotoxin production was detectable coincided with a rapid increase in energy charge, except with a lag for strain 361. Added sugars had a slightly stimulatory effect on growth in air and a significantly stimulatory effect on growth in 5% and 20% oxygen in nitrogen. The decreased growth rate observed in 5% and 20% oxygen in nitrogen when cells were grown in the simple NAK medium was relieved in 5% and 20% oxygen in nitrogen when the sugars were added. Sugars repressed enterotoxin production by S. aureus in air. However, the repressive effect of the sugars on enterotoxin production was not observed when the cells were grown in 5% and 20% oxygen in nitrogen. The relationship of energy charge to enterotoxin production should be studied with regard to the effects of media components.
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