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R T Marshall

Publications and source records attributed to R T Marshall.

34 records · Page 2Linked to original sources
PubMed1971

Isolation of psychrophilic bacteriophage-host systems from refrigerated food products.

Thirty-eight bacteriophage-host systems were isolated from 22 of 45 refrigerated food products examined under psychrophilic conditions. Isolates were obtained from ground beef, pork sausage, chicken, raw skim milk, and oysters, whereas no isolations were made from liquid egg whites and processed meat products. Thirty of the 38 psychrophilic bacterial hosts were gram-negative rods, and 27 of these were classified within the genus Pseudomonas; three were members of the family Enterobacteriaceae. The remaining eight were gram-positive cocci, which were tentatively classified as Leuconostoc. Plate counts of psychrophilic bacteria were greater than 2.2 x 10(5)/ml (g) in all but one sample which contained phage, whereas phage titers ranged from less than 100 to 6.3 x 10(6) plaque-forming units/ml (g). Phage isolates showed limited host ranges usually attacking only those hosts upon which they were isolated. Of eight phages tested against 13 cultures of known identity, one showed lytic action, and this was against strains of P. fragi.

Animals↗
PubMed1971

Characterization of two psychrophilic Pseudomonas bacteriophages isolated from ground beef.

Characterization studies were performed on two psychrophilic phages which were isolated from ground beef samples. Phage inactivation by exposure to heat, low pH, osmotic shock conditions, and freezing showed that these two isolates were different. One-step growth experiments indicated that one isolate had a burst size five times as large (500) and a latent period two times as long (4 hr) as the other when tested at 7 C. Nucleic acid type was 2-deoxyribonucleic acid for both. Electron micrographs showed one to belong to Bradley's phage group A and the other to phage group C.

Animals↗
PubMed1967

Adsorption of staphylococcal bacteriophage by milk proteins.

Propagation of homologous bacteriophage in a culture of Staphylococcus aureus (1:1 ratio of phage to bacteria) in Trypticase Soy Broth (TSB) and in skim milk indicated more activity of phage in TSB. Early lysis of bacteria in skim milk followed by a pronounced rise in bacterial population suggested that staphylococcal phages were being inactivated by milk. Titration of phages from skim milk, whey, and TSB indicated about 90% adsorption of phages by acid- and heat-precipitable proteins of skim milk, whereas numbers recovered from whey were quite comparable to those recovered from TSB. Reducing the pH from 6.5 to 4.0 increased the percentage of phages recoverable from skim milk from 10 to 56%. Apparently, the changes in electrical charges on the casein micelles at this low pH were responsible for release of many phages from their complex with casein.

Adsorption↗
PubMed1967

Effects of Supplemental Calcium or Calcium-binding Agents on Staphylococcal Bacteriophage Proliferation in Skim Milk.

Additions of 0.0005 N calcium borogluconate to Trypticase Soy Broth (TSB) produced an increase in phage titer about 1 million-fold, whereas its addition to skim milk resulted in about a 100-fold decrease in the maximal titer. Supplemental calcium had a stimulatory influence on bacterial growth in TSB but not in skim milk. Studies were made of the effect of binding of calcium of skim milk on the proliferation of staphylococcal bacteriophage. Sequestering the calcium with 2% phosphate mixture inactivated the phages without affecting the bacterial growth. However, chelation of calcium by 0.012% ethylenediaminetetraacetic acid produced an inhibitory effect on both the phages and the bacteria.

Journal Article↗