The action of streptomycin; the metabolic properties of resistant and dependent strains

PYRITHIAMINE ADAPTATION OF STAPHYLOCOCCUS AUREUS I

Das , S. K. (University of Calcutta, Calcutta, India) and G. C. Chatterjee . Pyrithiamine adaptation of Staphylococcus aureus . I. Adaptation and carbohydrate utilization. J. Bacteriol. 83: 1251–1259. 1962.— Staphylococcus aureus has been adapted to pyrithiamine, a thiamine analogue; as a result of this adaptation, the color of the pigment of the organism changes from orange-yellow to lemon-yellow. The adaptation is reversible; the adapted strain will revert after repeated subculture in a medium containing thiamine and no pyrithiamine. Of the major biochemical alterations resulting from adaptation, severe depression in glucose utilization and simultaneous stimulation of acetate utilization have been noticed. The effect of metabolic inhibitors on the utilization of glucose and acetate has also been studied. By measuring the rate of formation of C 14 O 2 from glucose-1-C 14 and glucose-6-C 14 , it has been observed that the reduction in C 14 O 2 formation from glucose-1-C 14 by the adapted organism is much more than that obtained from glucose-6-C 14 , causing thereby a decreased metabolic ratio of these two substrates after such adaptation. Relative to the normal strain, the adapted strain utilizes acetate-C 14 at a much faster rate, both in the formation of C 14 O 2 and also in the incorporation of C 14 into the protein and lipid fractions; the rate of formation of C 14 O 2 from pyruvate-1-C 14 is not greatly altered. It has been postulated that there is a partial blocking of the pentose phosphate cycle, because of the lowered glucose-1-C 14 utilization, and simultaneous stimulation of the tricarboxylic acid cycle; or perhaps the initiation of some other route after pyrithiamine adaptation would account for the great increase in acetate utilization.

The behaviour of a mutant strain of Salmonella typhimurium in experimental mouse typhoid

A streptomycin-resistant mutant of a virulent strain ofSalm. typhimuriumwas less virulent to mice than the parent strain. The difference in virulence was only observed when mice were infected with small numbers of organisms. Although the mutant strain caused fewer deaths than the parent strain it remained capable of establishing persistent infection in the majority of animals.

The significant difference in the behaviour of the two strainsin vivowas that after clearance from the blood multiplication in the tissues began more rapidly with the virulent strain and was progressive, whereas multiplication of the mutant was delayed, was less in degree and was apparently suppressed within a few days of infection.

The mutant strain was apparently identical antigenically with the parent strain, and was equally toxic. The mice dying of infection with this strain did so when the bacterial population had reached a level similar to that in the terminal stage of infection with the virulent strain.

The essential difference between the two strains was the speed and probability of attaining a critical final population. The mutant strain ofSalm. typhimurium, bothin vitroandin vivo, had a slower growth rate than the parent strain. A possible hypothesis to explain the importance of this finding in relation to the outcome of infection has been discussed.

I am indebted to the Medical Research Council for the provision of a grant towards the expenses of this investigation and to Mr T. Norris and Miss Italia S. Alderton for technical assistance.

The effect of x-rays on the rickettsiostatic activity of streptomycin, aureomycin, and penicillin

The effect of x-rays on the rickettsiostatic activity of streptomycin, penicillin and aureomycin in the embryonate egg was investigated. Only a slight reversal of the rickettsiostatic action of 5 mg. of streptomycin occurred in embryonate eggs given 100 r of x-rays at 4 days of incubation, whereas complete reversal occurred in those given 1000 r. Groups of eggs irradiated with intermediate doses of x-rays showed a graded response. The rickettsiostatic activity of 5 mg. (1660 Oxford units/mg.) of penicillin or of 5 mg. of aureomycin was not reversed by doses of x-rays ranging from 100 to 1000 r. 500 r of x-rays reversed the rickettsiostatic activity of 2 mg., 4 mg., 8 mg., or 16 mg. of streptomycin per egg in proportion to the amount of streptomycin injected. The rickettsiostatic activity of 2 mg. of streptomycin was completely reversed and the activity of 16 mg. only partially reversed. Reversal of the rickettsiostatic activity of streptomycin by x-rays was observed when radiation was given up to 6 days after the injection of the antibiotic into 7-day-old embryos. Reversal of the rickettsiostatic activity of 4 mg. of streptomycin could be detected when the antibiotic was injected 3 days after 500 r of x-radiation. Explanations of the observed phenomena are discussed in terms of biochemical and biophysical alterations of the cells of the host.