Studies with alpha-ketoglutarate dehydrogenase mutants of Escherichia coli

Summary Two classes of mutant lacking -ketoglutarate dehydrogenase complex activity were detected by biochemical analysis of strains of Escherichia coli requiring succinate for aerobic growth on glucose minimal medium. One class, designated sucA, lacked the -ketoglutarate decarboxylase component (E1) whereas the other class, sucB, lacked the dihydrolipoyl transsuccinylase component (E2). Studies with mixed cell-free extracts showed that the overall dehydrogenase activity could be reconstituted from several pairs of sucA plus sucB mutants but not from mixtures of mutants of the same class. Transduction analysis with phage P1 indicated close linkage between the two genes and their frequencies of cotransduction with gal were similar. The order of the two genes was also established as sucA (E1)-sucB(E2)...gal by reciprocal three-point crosses with several pairs of mutants.     

Morphological, Cultural, Biochemical, and Serological Comparison of Japanese Strains of Vibrio parahemolyticus with Related Cultures Isolated in the United States

Morphological, cultural, biochemical, and serological characteristics of 79 strains of Vibrio parahemolyticus isolated from patients suffering from gastroenteric disease in Japan were compared with 17 suspected V. parahemolyticus cultures isolated from wound infections and 14 nonpathogenic vibrios isolated from an estuarine environment in the United States. These groups were differentiated on the basis of several key reactions which included: the range of growth temperature and salt tolerance; the production of catalase and acetoin; the hydrolysis of starch; the fermentation and utilization as single carbon source of sucrose, cellobiose, and arabinose; and the ability to swarm on 1% agar. The separation of the groups on the basis of cultural and biochemical analyses was confirmed by means of slide agglutinations with specific anti-K antisera. The results of this study strongly suggest that the wound infection isolates are V. parahemolyticus species which are easily distinguished from the nonpathogenic estuarine vibrios.     

Examination of Market Foods for Coliform Organisms

Food specimens (490) in nine categories were examined for total aerobic plate count and numbers and types of coliform organisms, including the enteropathogenic Escherichia coli (EEC). The total counts were compared with various suggested standards, and a limit of 100,000/g appeared to be a realistic goal, except for certain food types with a high level of natural flora. Plate counts in VRB were compared to counts obtained by isolation by enrichment in LST Broth, and the latter method produced a higher percentage of isolations. The presence of E. coli was determined by use of EC Medium incubated at 44.5 +/- 0.1 C. Only 40.4% of the positive EC tubes, however, contained E. coli. It appeared that a limit of 10 coliform organisms per g as a suggested standard could be met with several types of foods. Isolation of EEC was obtained only three times, or in 0.6% of the specimens.