Enterotoxin production by cAMP-deficient mutants of Vibrio cholerae was investigated by the latex agglutination test, CHO cell elongation system, and permeability increasing test. It was revealed that two kinds of permeability-increasing factors were produced by V. cholerae E2 and its cAMP-deficient mutant E2751. They were cholera toxin (CT) and an unknown permeability-increasing factor (PF). PF was separated from CT by DEAE-Sephacel column chromatograhy. Antiserum was prepared against partially purified PF separated by DEAE-Sephacel chromatography and used for the neutralization tests. Neutralization tests with anti CT antiserum and anti PF antiserum showed that CT and PF were entirely different immunplogically. We showed also that though cAMP is not essential for production of CT, it is required for production of this newly found PF.
The present study was undertaken to see whether the virulence of Bacteroides fragilis is enhanced by mixed infection with Escherichia coli. 1. Acceleration of growth of B. fragilis in mixed culture B. fragilis GM7004 (102CFU/ml) inoculated alone into nutrient broth did not grow at 37C for 24hrs. When cultured under the same conditions with 102CFU/ml of E. coli No.94, the bacterial cell population increased to 108CFU/ml or more. This increase was attributed to consumption of the medium-dissolved oxygen by proliferating E. coli and a decreased oxidation-reduction (O-R) potential. B. fragilis GM7004 did not grow in the presence of Pseudomonas aeruginosa E7 and, in this case, O-R potential did not decline though the dissolved oxygen was consumed. Furthermore, O-R potential of both intraperitoneal fluid and serum declined with time when E. coli No.94 was used for the mixed infection with B. fragilis GM7004. 2. Enhancement of virulence of B. fragilis in mixed infection When mice were challenged intraperitoneally with a combination of B. fragilis GM7004 and E. coli No.94 or P. aeruginosa E7, both of which have high superoxide dismutase (SOD) and catalase activities, the virulence of B. fragilis was markedly enhanced in both experiments. On the other hand, the mixed infection with B. fragilis GM7004 and E. coli JC-2 or P. aeruginosa IFO3445, both of which have low SOD and catalase activities, did not enhance the virulence under the same conditions. From the results, it is considered that the pathogenicity of B. fragilis is enhanced in the mixed infection with other species which have the capacity of declining O-R potential in the infected site and high SOD and catalase activities.