The Survival of Shigella sonnei in Shredded Cabbage

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.