ABSTRACT
Shigella flexneri strains were assayed for the ability to synthesize and utilize phenolate and hydroxamate siderophores. The hydroxamate aerobactin was synthesized by all isolates tested, whereas phenolates were only rarely produced. Expression of aerobactin was accompanied by production of a single iron-regulated outer membrane protein (Mr = 74,000). This protein was not produced by a mutant defective in aerobactin utilization and may serve as the aerobactin receptor. Phenolate (enterobactin)-producing strains synthesized three additional outer membrane proteins (Mr = 74,000, 81,000, and 83,000) in response to iron starvation. These proteins are the same apparent size as those produced by Escherichia coli K-12 strains. Ent sequences are apparently present in strains which do not synthesize this compound. Although normally silent, ent genes can be activated in Ent- strains to produce Ent+ variants. These laboratory variants are phenotypically indistinguishable from clinical Ent+ isolates.
Subject(s)
Bacterial Outer Membrane Proteins , Enterobactin/metabolism , Hydroxamic Acids/metabolism , Iron Chelating Agents/metabolism , Receptors, Cell Surface , Serine/analogs & derivatives , Shigella flexneri/metabolism , Biological Transport , Carrier Proteins/biosynthesis , Mutation , Receptors, Immunologic/biosynthesis , Shigella flexneri/geneticsABSTRACT
Yersinia enterocolitica was recovered from 6 of 45 (13%) oyster, 2 of 50 (4%) shrimp and 12 of 58 (21%) blue crab samples. No single method of enrichment (cold mannitol broth or modified Rappaport broth for 7, 21 or 60 days) was most effective for the three types of shellfish examined. The effect of refrigerated storage on Y. enterocolitica depended upon the type of shellfish, condition (raw or boiled), strain of Y. enterocolitica and temperature and time of storage. In general, Y. enterocolitica counts increased in (a) raw oysters stored at 0-2 C for 14-21 days and at 5-7 C for 2-10 days, (b) in boiled shrimp stored at 3-5 C for 7-21 days and (c) in cooked crab meat stored at 5 C for 14 days. Freezing and heating of shrimp and crab meat caused extensive destruction of Y. enterocolitica . Biotypes capable of causing human illness (when inoculated into seafoods) survived and under certain conditions multiplied at refrigeration temperatures. Biochemical characteristics of the isolates from raw shellfish differed from those of clinically significant types.
