@article{mbs:/content/journal/micro/10.1099/00221287-37-2-157, author = "May, J. W. and Houghton, R. H. and Perret, C. J.", title = "The Effect of Growth at Elevated Temperatures on Some Heritable Properties of Staphylococcus aureus", journal= "Microbiology", year = "1964", volume = "37", number = "2", pages = "157-169", doi = "https://doi.org/10.1099/00221287-37-2-157", url = "https://www.microbiologyresearch.org/content/journal/micro/10.1099/00221287-37-2-157", publisher = "Microbiology Society", issn = "1465-2080", type = "Journal Article", abstract = "SUMMARY: Populations of a predominantly tetracycline-resistant, penicillinase-positive strain of Staphylococcus aureus grown at 43.44° gave rise to progressively increasing proportions of tetracycline-sensitive and penicillinase-negative cocci. The losses did not appear until after the elapse of a number of generations at the elevated temperature, and then apparently proceeded independently, tetracycline resistance being lost more rapidly than the ability to produce penicillinase. Tetracycline-sensitive and penicillinase-negative variants were extremely stable and the growth rates at 44° of the parent strain and the tetracycline-sensitive variants were indistinguishable. Screening for numerous other ‘marker’ properties revealed no changes under the test conditions. The evidence suggests that tetracycline resistance and penicillinase-forming ability probably depend on the presence of two different plasmids in the cocci; that the replication-rates of the plasmids at elevated temperature are less than that of the cocci; and that the plasmids, once lost, are not spontaneously resynthesized nor, at least for that conferring tetracycline resistance, regained by infection. However, such a hypothesis raises the question of how equilibrium, particularly between the tetracycline-resistant and sensitive cocci, is maintained in a population growing at 37° and observed to change in one direction but never in the reverse direction.", }