Induced Variations in a Penicillin-resistant Staphylococcus

Abstract

SUMMARY: When young cells of a strain of a staphylococcus were exposed to substances noxious to the organism, variations transmissible to progeny were obtained. The variations consisted mainly in a decrease in antibiotic resistance and mouse virulence. Characters of pathogenic strains such as coagulase production, mannitol fermentation and gelatin liquefaction were also abolished.The experiments were carried out in a way that excluded the selection of spontaneous mutants. Adaptation should also be excluded as all variations consisted in a loss or decrease of activities.The variants when first isolated seemed unhealthy, the largest part of their progeny being non-viable and consisting of cells which grew up to a point and lysed without dividing. The results obtained were therefore attributed to a damage of the parent cell caused by the injurious agents used.Antibiotics and other substances noxious to bacteria can induce changes in bacterial cells which are transmissible to progeny for a variable number of generations. The changes have been attributed to a profound disturbance or injury of the parent cell, and in one instance it had been possible to follow, step by step, the evolution of the disturbed cells (Voureka, 1951).The present paper deals with a strain of staphylococcus in the progeny of which decrease of virulence and of resistance to penicillin and to streptomycin were noticed after young growing cells were exposed to injurious agents.New biological characters appeared in a few or in all the colonies grown from the treated cultures. In some cases, the new characters remained unchanged through over 50 passages in normal laboratory media, while in others the variant cell acquired one or more of the characters of the parent. EXPERIMENTALTo exclude, as far as can be done, the possibility that the effects obtained were due to selection of spontaneous mutants endowed with the new characters, the experiments were planned as illustrated schematically in Fig, 1.Freshly isolated cultures derived from one pair of cocci were used in order to have as uniform a population as possible, and the experiments were carried out on a small number of cells so that all the colonies from both the control and the treated bacterial suspension could be examined.The strain selected was a coagulase-positive, phage typable, mouse virulent strain of StaphyZococcus aureus, fermenting mannitol, liquefying gelatin, producing penicillinase and giving a clear-cut zone of haemolysis on horse blood agar; it was resistant to 400 units of penicillin and to 10 units of strepto-

GENETIC NATURE OF STABLE L FORMS OF SALMONELLA PARATYPHI

“…A previous report of heritable mass conversion of a bacterial population by drugs has been published by Voureka (1952). In one of her experiments, staphylococci were incubated in broth containing 20 ,ug/ml chloramphenicol, 50,000 u/ml penicillin, 3 mg/ml H202, 50 u/ml terramycin, or 2.5 mg/ml N-mustard for 24 hr under nongrowing conditions and then plated.…”

The Extracytoplasmic Function Sigma Factor σ S Protects against both Intracellular and Extracytoplasmic Stresses in Staphylococcus aureus

“…Complementation of the S mutation reduced the observed growth impairment significantly, although not completely to wild-type levels. This lack of full complementation is likely attributed to plasmid instability in the presence of DNAdamaging conditions, as suggested by others previously (3,26,49,60,72,75). Further to this, in order to determine whether the role of S was limited to protection against DNA alkylation (as induced by MMS), we next examined the ability of the USA300 S mutant to survive exposure to agents that induce other types of DNA damage.…”

Drug Resistance of Staphylococci II. Joint Elimination and Joint Transduction of the Determinants of Penicillinase Production and Resistance to Macrolide Antibiotics

“…It was reported by Voureka (1952) that virulence and resistance to penicillin (PC) and streptomycin (SM) of a strain of Staphylococcus aureus decreased after an exposure to injurious agents, such as chloramphenicol (CM), tetracycline (TC), nitrogen mustard, etc. Also, the new characters remained unchanged through more than 50 passages in normal laboratory media.…”