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Biomedical subjects

R E Davis

Publications and source records attributed to R E Davis.

At least 307 records · Page 17Linked to original sources
PubMed1971

Cross-protective antigens of group A streptococci types 3 and 31 and types 46 and 51.

Reciprocal cross-protective antigens have been demonstrated between types 3 and 31 cocci, and one-way cross-protective antigens have been demonstrated between types 46 and 51 cocci. The reciprocal cross-protective antigen of types 3 and 31 is distinct from the specific M protein of either type. In the one-way cross relationship, type 46 cocci contain both type 46 and type 51 M proteins and therefore stimulate protective antibodies against both types. Type 51 cultures contain only the homologous M antigen. These relationships were demonstrated by capillary precipitin tests, indirect bactericidal tests, and in agar-gel diffusion patterns. The practical significance of these relationships in the serological typing of group A streptococci is discussed along with their possible role in immunity to streptococcal infections in man.

Animals↗
PubMed1970

Evidence on possible Mycoplasma etiology of aster yellows disease I. Suppression of symptom development in plants by antibiotics.

Antibiotics suppressed development of aster yellows (AY) disease symptoms in plants of china aster [Callistephus chinensis (L.) Nees.] and annual chrysanthemum (Chrysanthemum carinatum, Schousb.). When inoculated chrysanthemum plants were treated by any of several techniques with tetracycline antibiotics or chloramphenicol, symptoms failed to appear during treatment but appeared 1 to 4 weeks after treatments were terminated. Under continuous administration of chlortetracycline, aster plants with AY symptoms developed symptomless axillary growth, including flowers. Streptomycin, oleandomycin, kanamycin, tylosin, carbomycin, polymyxin, bacitracin, neomycin, sulfanilamide, penicillin, vancomycin, or cycloserine had no discernible effect on development of AY symptoms. Treatment of plants with tetracycline antibiotics before exposure to inoculative (pathogen-transmitting) vectors delayed the appearance of symptoms or prevented AY infection. Remission of AY symptoms in inoculated plants treated with chlortetracycline was correlated with an inhibition of multiplication of AY agent, as measured by bioassay of extracts. The data give additional support to the hypothesis that aster yellows disease is caused by a mycoplasma-like microorganism.

Journal Article↗
PubMed1970

Evidence on Possible Mycoplasma Etiology of Aster Yellows Disease II. Suppression of Aster Yellows in Insect Vectors.

Chlortetracycline or chloramphenicol (but not kanamycin, penicillin, or erythromycin), when administered in hydroponic solution to diseased aster, reduced the availability of the aster yellows (AY) agent to nymphs of Macrosteles fascifrons (Stål). Insects exposed to healthy plants whose roots were immersed in chlortetracycline were able to acquire AY agent from diseased plants the day after removal from the antibiotic-treated plants, but the latent period of the ensuing disease in the insects was prolonged. Chlortetracycline or tylosin tartrate blocked AY infection in nymphs injected with a mixture of antibiotic and the AY agent, but polymyxin, neomycin, vancomycin, penicillin, carbomycin, or chloramphenicol did not. All tetracyclines tested, methacycline, oxytetracycline, and chlortetracycline, produced a dramatic reduction in the ability of infected vectors to transmit AY agent. Tylosin tartrate also reduced transmission when injected into AY-transmitting vectors, but carbomycin, spectinomycin, cycloserine, penicillin, erythromycin, or kanamycin had no such effect. During the first 10 days after injection of tylosin tartrate or oxytetracycline into transmitting vectors, ability of the insects to transmit AY decayed rapidly. Transmission by insects injected with buffer alone, after decreasing the first day after injection, gradually returned to its normal level in less than 1 week. By 2 to 3 weeks after injection with tylosin or oxytetracycline, ability to transmit AY was regained by vectors. The results suggest that tetracycline antibiotics and tylosin tartrate inhibit multiplication of AY agent in the insect. The spectrum of antibiotic activity in the insect is consistent with the hypothesis that AY and other plant yellows diseases are caused by mycoplasma-like organisms.

Journal Article↗
PubMed1970

An automated method for the measurement of folate activity.

A new approach to the estimation of folate activity is described. The system may be used as a semi-automated method or as a fully automated method using the AutoAnalyzer or Mecolab equipment. The methods use a chloramphenicol-resistant strain of L. casei as the test organism, and this eliminates the need for sterilization or aseptic addition. The systems are able to handle extremely large numbers of samples in a relatively short time. Results are similar to those obtained by standard techniques.

Autoanalysis↗
PubMed1970

Automation of the assay of folate in serum and whole blood.

An automated system is described for the microbiological assay of serum and red cell folate concentrations using a chloramphenicol-resistant strain of L. casei. Both serum and whole-blood haemolysates are assayed directly without previous deproteinization. Results by this method are comparable to those obtained by standard manual folate assays. Reproducibility within and between assays is excellent. Special advantages of the method are its simplicity of operation, economy of reagents, and capacity for dealing with large numbers of specimens (80-100 per hour). The latter makes it especially suitable for providing a regional diagnostic service and for population surveys of nutrition.

Autoanalysis↗