- Volume 20, Issue 2, 1959

SUMMARY: Small amounts of proflavine were added at intervals of 30 min. to growing cultures of Escherichia coli. Additions during the logarithmic phase gave an increase of resistance of two- or threefold in a high proportion of organisms. Additions in the lag or late logarithmic phase gave no such increase, although the resistance of the organisms themselves was higher in these phases. Whether organisms were able to grow in the presence of proflavine, therefore, depended not only on their resistance but on the conditions in the culture medium. The increase in proflavine resistance, which occurred when drug was added to growing cultures, was not accompanied by increase of cross-resistance to other drugs. The resistance was lost on growth in the absence of drug. For these reasons, the increase is held to be a phenotypic adaptation. There was also an increase in the number of organisms with a high resistance, of the order of that of mutants. These organisms showed cross resistance with other drugs.

Partial synchronization of division was achieved by the temporary cooling of cultures. These synchronized cultures showed cycles of division of about 30 min. They also showed cycles of resistance of c. 20 min. Evidence is presented for the view that the organisms undergo cycles of varying adaptability to proflavine resistance. It is suggested that this variation in adaptability can explain the range of resistance found in an ordinary sensitive culture. It can also explain the effect of proflavine additions in raising the resistance of a high proportion of organisms in a growing culture.

SUMMARY: We attempted to transform proflavine-sensitive strains of Escherichia coli to proflavine resistance by growth in the presence of deoxyribonucleic acid-containing extracts from resistant organisms. Three methods were used to obtain the DNA preparations. Method 1 (Boivin, 1947) did not give active transforming principle, even when a variety of modifications was introduced. Method 2 (McCarty & Avery, 1946) and Method 3 (Mayers & Spizizen, 1954) gave extracts which were active in transformation. With DNA prepared by Method 2, an increase in the number of resistant organisms was found in one of four rough sensitive strains. We concluded that only a small proportion of the organisms of this strain were competent. We were able to increase the proportion of these competent organisms by a method of ‘double replica plating’. According to Method 3, organisms were lysed by sodium dodecylsulphate (Duponol) in presence of citrate, and protein removed by sodium acetate. From the supernatant fluid transforming principle was precipitated by acidified ethanol, and then dissolved in saline. The smooth strain of Escherichia coli used in most of our experiments served as the recipient strain. The transforming principle from resistant organisms was not active alone, but was active in the presence of the protein precipitate. The activity appeared to be lost when the transforming principle was treated with DNAase. No activity was shown by extracts from sensitive organisms. The activation of transforming principle by the protein precipitate is thought to be due to the Duponol carried with it. Duponol appears to inhibit DNAase, so that it might act by preserving transforming DNA from destruction by the enzyme present in the recipient organisms. Our experiments did not always give positive results. Whilst we believe that we have demonstrated transformation in this system, the low reproducibility of our results makes it necessary to repeat and extend.

SUMMARY: Mesophilic strains of the genus Chromobacterium were found to cross-agglutinate extensively, and much of this appears to be due to common rough somatic antigens. The psychrophilic strains also cross-agglutinated to some extent. There was little cross-agglutination between mesophils and psychrophils. Neither mesophils nor psychrophils showed clear-cut antigenic subgroups. Many mesophilic strains, whether isolated from naturally-occurring cases of infection or from water, were found to be virulent for experimental animals. The most virulent were strains from two cases of human infection, which had an LD50 dose for guinea-pigs of c. 5 × 106 viable organisms. The virulent strains did not form a homogeneous antigenic group. Cultures of mesophils contained an endotoxin, but no exotoxin was found. The experimental disease may be an acute, rapidly fatal septicaemia, or a more chronic disease with multiple abscess formation like that found in natural infections; occasionally a local abscess with subsequent recovery was the only result of the injection of cultures.

SUMMARY: The effect of dietary chlortetracycline on the serological type and resistance of the streptococci found in the caeca of chickens has been investigated. In the control birds where only chlortetracycline-sensitive streptococci were present initially, Streptococcus faecium predominated and S. faecalis (mainly the proteolytic variant) was present in small numbers representing three serological types (types H 69 D5, D15 and D76). Administration of chlortetracycline, whether at a low concentration throughout life or intermittently at a high concentration, led to the emergence of a highly-resistant non-proteolytic strain of S. faecalis (type H 69 D5) which became predominant in the antibiotic treated birds. Withdrawal of chlortetracycline was followed by disappearance of type H 69 D5 and the reappearance of types D15 and D76 which were proteolytic. Type D15 remained sensitive to chlortetracycline, but type D76 had become more resistant and eventually became the predominant streptococcus in all the chickens under observation. The serological types of S. faecalis identified in these chickens are also commonly found in the human intestine.

SUMMARY: The passive permeability properties of the plasma-membrane of Staphylococcus aureus (strain Duncan) resemble those of a classical lipid membrane such as that considered by Overton in 1899. In general, solutes carrying more than four water molecules flow across the plasma-membrane only very slowly under an electrochemical gradient. The plasma-membrane is the effective osmotic barrier to small molecular weight solutes and prevents the escape of internal components having a total osmotic concentration corresponding to c. 1 molal sucrose. The protoplast is prevented from swelling by the cell wall which withstands a hydrostatic thrust of some 20 to 30 atmospheres pressure exerted against it by the plasma-membrane in distilled water. The pores in the cell wall, although large enough to permit rapid diffusion of small molecular weight solutes, are too small to allow a dextran of mol. wt. 10,000 to penetrate. The cell wall acts as the osmotic barrier for large molecular weight components, preventing such components in the medium from gaining access to the plasma-membrane surface and preventing such internal components from passing outwards from the surface of the plasma-membrane.

SUMMARY: The compatibility system in Streptomyces fradiae may be characterized as follows. When 108 conidia of each of two freshly isolated auxotrophic mutants are mated on minimal medium, a small number, usually 1 to 10, of ‘primary’ heterokaryotic colonies appear (low-frequency mating, LFM). On the other hand, when ‘secondary parental isolates’ (derived from the conidia produced by ‘primary’ heterokaryons) are mated, the frequency of heterokaryon formation is increased by a factor of several thousand. This high-frequency mating (HFM) is a reasonably stable property, decreasing (or increasing) in a stochastic manner, only after a considerable number of subcultures. A mutational origin is therefore postulated for the HFM and LFM isolates, which must be endowed with variable cultural fitness causing diverse population shifts upon subculture. More effective anastomosis, not increase in residual growth of the ‘secondary parental isolates’, appears to be responsible for HFM. No interspecific crosses were successful, even when an HFM tester stock was used, but heterokaryotic interaction between independently isolated auxotrophic mutants derived from the same line of S. fradiae seemed to increase when an HFM strain was one of the partners.