- Volume 62, Issue 3, 1970

SUMMARY: Plasmids containing the genetic determinants for resistance to tetracyclines (Tc), streptomycin (Sm) and sulphonamide (Su), colicine production (Col) and α-haemolysin production (Hly) were transferred from four wild strains of Escherichia coli to E. coli K12 by conjugation brought about by F factor. Linkage was demonstrated between F and Tc and between Sm and Su. No linkage was noted between Col, Hly, F and Tc, and Sm and Su, which were transmitted as four independent units in no predetermined order. F and Tc were eliminated together during acridine orange and sodium lauryl sulphate treatment; the other characters were not eliminated. After mating for prolonged periods, F and Tc were most frequently found in the recipients. Recipients of other characters in the absence of F and Tc did not transmit them.

SUMMARY: Strains of Escherichia coli were isolated whose resistance to ampicillin (Ap), tetracyclines (Tc) or streptomycin and sulphonamides (SmSu) or whose production of colicine (Col) or α-haemolysin (Hly) could not be transmitted to E. coli k 12 F−. Determinants controlling these characters (except Ap), could be mobilized in some of them after infection with transfer factors. Of 60 strains of E. coli isolated from the faeces of healthy pigs, cattle and human beings and selected because they did not possess R factors and did not produce colicine, α-haemolysin, porcine enterotoxin (Ent) or K 88 antigen (transmissible characteristics), 20 (33%) contained transfer factors that could mobilize determinants from one or more of nine determinant donor strains; 8 contained at least two transfer factors, one fi − and the other fi +. The nine determinant donor strains contained Tc, SmSu, Col or Hly determinants; some were wild strains and others were obtained from interrupted mating experiments in which E. coli k 12 F− was the recipient strain. The ability of a transfer factor to mobilize a determinant was not simply a function of the transfer factor and the determinant but was strain-dependent. Positive results were obtained most frequently when transfer was between strains of k 12. Transfer factors that could mobilize determinants in determinant donor strains were found in all except one of 78 porcine enterotoxigenic strains of E. coli selected because they did not possess R factors or transmissible colicine. Nearly all of them produced α-haemolysin and over half of them K 88 antigen. On the evidence available, the high incidence of transfer factors in these strains suggests that enterotoxin production in all of them was controlled by transmissible plasmids and that the genetic determinants controlling α-haemolysin production in some of them might be chromosomal. The linkage between Ent and the factor responsible for its transfer was not always close. Despite a previous statement to the contrary (Smith & Halls, 1968), this transfer factor was fi − both fi − and fi + factors could transfer Hly. No close association between the plasmids controlling the five characteristics Neo (neomycin resistance), Ent, Col, Hly and K 88 was apparent in mating experiments using as donor a porcine strain of E. coli carrying all five transmissible plasmids. Transfer factors were found in 15 of 21 human enteropathogenic strains and in one of five sheep enteropathogenic strains; none of these 26 strains possessed characteristics known to be transmissible.

SUMMARY: During surveys of the prevalence of trypanosomiasis, 37 isolates of trypanosomes of the subgenus Trypanozoon were collected over a period of five years from a herd of cattle kept on a farm in an area in Nigeria where human and animal trypanosomiasis is endemic. Thirty-three were typical isolates of Trypanosoma brucei but four were unusual in several respects and their identity was uncertain.

The antigenic relationships of the trypanosomes were determined by agglutination tests using antisera to the predominant variant antigens of each isolate. Comparisons of groups of isolates obtained in two of the surveys showed that some of the animals in the herd were infected with antigenically related trypanosomes. Four isolates obtained in one survey had antigens in common and probably belonged to one trypanosome strain, while 26 isolates obtained in another survey seemed to have been derived from three different strains. At least ten animals examined in the latter survey were infected with two strains of Trypanosoma brucei at the same time. Comparisons of trypanosomes obtained in successive surveys showed that one isolate was very closely related to four isolates obtained from different animals two years later. Agglutination and neutralization tests, and a study of variant antigen production by clones prepared from the first isolate and one of the later group of four isolates, established the antigenic similarity of these trypanosomes and provided direct evidence of the long-term antigenic stability of a trypanosome strain under field conditions. Apart from this notable exception, there was little antigenic relationship among the trypanosomes isolated from year to year and at least seven antigenically distinct strains of T. brucei were isolated from the herd in the five-year observation period.

SUMMARY: Differences in phage type between plum and cherry strains of Pseudomonas morsprunorum were stable during passage through the homologous and heterologous hosts. In experiments controlled by phage typing reisolates from lesions, both strains were specific for the homologous plant when inoculated into leaves at low concentrations (< 105/ml.) but not at high concentrations (> 106/ml.). No specificity was observed in wound inoculations of branches made during the winter.

Autumn inoculation of cherry leaf scars with cherry strains resulted in severe disease, with a dose response type of relationship between inoculum concentration and infection. Plum strains were ineffective through cherry leaf scars and inhibited infection by cherry strains when present in the same inoculum. The inhibitory effect was not observed with plum strains killed by heat or streptomycin, or with plum strains inoculated live in the presence of bacteriostatic levels of streptomycin.

SUMMARY: A gene specifying triosephosphate isomerase (tpi) has been located between rha and glpK on the Escherichia coli chromosome. Very recently a gene specifying fructose-6-phosphate kinase (pfk) has been located in this same area and we have found that the tpi and pfk are highly cotransducible. This finding provides the first indication of any close chromosomal association between genes specifying glycolytic enzymes.

SUMMARY: A gene specifying ribokinase has been located on the Escherichia coli chromosome close to the reported position of an uncharacterized ribose*- negative mutation. This uncharacterized mutant has been shown to lack ribose permease and thus the genes for two enzymes of ribose catabolism are close together on the chromosome.

SUMMARY: When staphylococci, resistant to 4 μg. tetracycline/ml., were grown in nutrient media at subinhibitory levels of the drug, phenotypical resistance increased until the cocci grew with 160 μg. tetracycline/ml. Resistance increased most rapidly at the highest concentration of tetracycline which did not significantly inhibit growth. Increase in resistance was also obtained by pre-incubation with β-apo-5-oxy-tetracycline. Increase in resistance could be prevented by chloramphenicol and actinomycin D, but not by nalidixic acid. When a highly resistant culture was transferred to tetracycline-free medium, phenotypical resistance decreased gradually; after four transfers on nutrient agar it returned entirely to the original level.

SUMMARY: Resistance of Staphylococcus aureus m to tetracycline was due to an extrachromosomal genetic unit (plasmid) that could be eliminated by growth at 44°. The susceptible (eliminated) strain actively concentrated tetracycline from the nutrient medium by an energy-dependent transport system. The resistant culture accumulated the drug to a much lesser degree than the susceptible culture, both according to the E 380 of the bacterial extract and to its radioactivity after incubation with tritiated tetracycline. Accumulation of tetracycline was low and independent of the external concentration until this reached a level corresponding approximately to the minimal inhibitory concentration.

Pre-incubation with tetracycline at low concentrations decreased ability to accumulate the drug. This pre-incubation effect was not prevented by nalidixic acid but was by actinomycin D.

SUMMARY: At low concentrations (0·03 to 3 μg./109 cells), purified prymnesium toxin lysed penicillin and lysozyme-EDTA spheroplasts of Escherichia coli and Pseudomonas fluorescens and protoplasts of Micrococcus lysodeikticus and Bacillus subtilis. Intact E. coli and P. fluorescens were unaffected by the toxin (3·3 μg./ml.), but E. coli b was lysed by prymnesium toxin in the presence of EDTA. The activities of selected detergents against spheroplasts and EDTA-treated E. coli b were compared with the action of prymnesium toxin.

SUMMARY: Mutants refractory to colicin E2, previous phenotypic symbol RefII, have now been divided into two major phenotypic groups. CetC mutants in distinction to CetB mutants show increased sensitivity to u.v. and to a detergent (DOC). CetC mutants may also show other properties, including abortive growth of bacteriophage λ and defective division. CetB mutants are refractory to E 2 at 30° but largely sensitive at 37°. CetC mutants are also refractory at 30° but may be either sensitive or completely refractory at 37°. In contrast to Rec− mutants, CetC strains are not sensitive to gamma rays but two mutants show enhanced DNA breakdown after u.v. irradiation. CetC mutants seem defective in a specific membrane component which renders them insensitive to E2 and alteration of which can affect several aspects of DNA metabolism.

SUMMARY: A cetB locus, determining E2 refractivity at low temperature, has been mapped at minute 89 on the Escherichia coli k 12 chromosome and is 94 % linked to the hsp loci. A second locus, cetA, which controls expression of cetB in some way, was found to be 70 % co-transducible with and to the right of thr. Both cetB and cetC, another locus which determines E2 refractivity, are 21 % co-transducible with serB and the cetC locus therefore also probably lies close to hsp. Mutations of the cetC locus appear to be pleiotropic and the additional characteristics of these mutants, u.v. sensitivity, detergent sensitivity, recombination deficiency, filament formation, and abortive λ growth, are all fully co-transducible with E 2-refractivity. In addition, u.v.-resistant revertants of CetC mutants simultaneously revert to all wild-type characteristics including E 2 sensitivity. The nature of the recombination deficiency of some CetC mutants has been examined and both episomal and chromosomal gene transfer to the mutants found to be normal. P1 transduction frequencies with CetC mutants are, however, also normal and it is suggested that the mutants may be deficient in some recombination step unique to Hfr × F− crosses.