A set of 20 newly isolated temperate bacteriophages for phage typing of the pathogen Listeria monocytogenes has been investigated by means of electron microscopy and electrophoretic analysis of phage structural proteins. All phages had isometric capsids (60-64 nm diameter), and long contractile or non-contractile tails of 170-320 nm length. They could be classified into 2 morphotypes (Al and Bl) and were assigned to 3 listeriaphage species (4211, 2671, and 2389). Individual protein profiles were generated by SDS-PAGE of viral polypeptides, as well as isoelectric focusing of solubilized phage proteins in immobilized pH gradient gels. The major structural proteins ranged in size from approximately 15 to 38 kD, and showed isoelectric points from pi 4.3 to 6.2. Protein compositions permitted the differentiation of individual phages as well as the recognition and grouping of similar viruses.
Listeria monocytogenes cultures isolated from a variety of seafoods were subjected to phage typing procedures utilizing the French International set of L. monocytogenes bacteriophages. These cultures were also subjected to the activity of newly isolated North American phages to L. monocytogenes. There were 147 serotype 1/2 and 80 serotype 4b L. monocytogenes cultures isolated from 16 varieties of marine products included in this study. L. monocytogenes was most frequently isolated from crab meat, salmon, and shrimp. Bacteriophages to serotype 1/2 isolates most frequently observed as single patterns were 575, 1967, 2685, and 19. Serotype 4b phages observed most frequently were 1317, 2425, and 52 as single phage patterns, and 52/340/110/108/2671/2425/2389 and the new North American phages 90861/910716/93253/90666 as one complete spectrum. The prevalence of L. monocytogenes and their respective phage spectra observed in the 16 varieties of seafoods studied is discussed.
Commercially shredded cabbage distributed at the retail level is usually packaged under vacuum or in a modified atmosphere of nitrogen and carbon dioxide to suppress proliferation of aerobic spoilage microorganisms. The ability of Shigella sonnei to survive and grow in shredded cabbage packaged under these conditions was determined by the 3-tube most probable number procedure. After artificial inoculation with S. sonnei at one of three different levels, the shredded cabbage was packaged aerobically, under vacuum, or under modified atmosphere (30% nitrogen and 70% carbon dioxide) and stored at room temperature (24 ± 2°C) or under refrigeration (0–6°C). For most levels of inoculation, S. sonnei tended to increase or remain relatively high for 1–3 d in cabbage packaged under all three conditions and stored at room temperature. However, after 3 d of storage at this temperature, S. sonnei approached indeterminately low levels. The steady decrease of pH values of shredded cabbage over the storage period may have contributed to the decrease of S. sonnei. Under refrigeration, however, both the S. sonnei levels and the pH values remained relatively constant. The results indicate that S. sonnei can survive and even proliferate in shredded cabbage packaged and stored under a vacuum or modified atmosphere as well as aerobic conditions, thereby posing a potential hazard to the consumer.
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