Psychrophilic Bacteria Counts Research Articles

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 × 10 5 /ml (g) in all but one sample which contained phage, whereas phage titers ranged from less than 100 to 6.3 × 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.

Isolation of Psychrophilic Bacteriophage-Host Systems from Refrigerated Food Products 1

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.

Bacteriological Evaluation of Manufacturing-Grade Bulk-Tank Milk1,2

Summary Standard, thermoduric, and psychrophilic counts were made on 701 bulk-tank milk samples of manufacturing grade. These samples were obtained from 267 Iowa producers at all seasons of the year. Plates for standard and thermoduric counts were incubated at 32° C. Direct microscopic clump counts were made on 586 samples. The SPC of 37.7% of the samples exceeded 1,000,000 per milliliter, as compared to 26.5% at this level for the psychrophilic plate count results. Thermoduric counts in excess of 10,000 per milliliter were obtained on 43.6% of the samples. The direct microscopic clump count was considerably less than the SPC on many samples. Of the 245 samples out of 586 comparisons where the results of these two counts failed to agree, all but 16.3% of the samples had high counts of psychrophilic or thermoduric bacteria. Most psychrophilic bacteria stained readily, but many appeared to grow in clumps. The clumps probably were broken up during preparation of dilutions for plating. Thermoduric organisms apparently did not readily take up the stain, although they were not specifically tested.