Akiyoshi Utsunomiya

Major Enteropathogenic Bacteria Isolated from Diarrheal Patients in Bolivia: A Hospital‐Based Study

A total of 1,234 fecal samples from diarrhea cases were examined for etiological bacterial agents at medical facilities in La Paz and Sucre, Bolivia. Eighty strains of Shigella spp., 39 strains of Salmonella spp., 29 strains of Vibrio cholerae, and 222 strains of enteropathogenic Escherichia coli (139 EPEC, 55 ETEC, 29 EIEC, and 1 EHEC) were isolated. With regard to the serovars of Shigella, S. flexneri 2a, 3a, and 1b were predominant. In the case of Salmonella, S. enteritidis was the most common, followed by S. typhi, S. poona, and S. paratyphi B. Out of 29 cholera strains, 25 belonged to biovar El Tor, serovar Ogawa while the remaining 4 were serovar Inaba. Among 55 strains of ETEC serotypes, 5 showed ST producers but none showed LT producers. Likewise, among 55 strains of enterohemorrhagic serotypes, only one strain (O157:H7) produced verocytotoxin (VT 2). The results of drug sensitivity tests revealed the predominance of Shigella, EPEC, and ETEC strains resistant to aminobenzil‐penicillin (ABPC) and trimethoprim. Since diarrheal patients in Bolivia are treated mainly with ABPC or sulfamethoxazole/trimethoprim (SXT) and rarely with gentamicin, kanamycin, or other drugs, it is possible that ABPC‐ and SXT‐resistant strains will increase and persist in the near future.

Immunogenicity of Vibrio cholerae O1 Fimbriae in Animal and Human Cholera

Parenteral immunization with either formalin‐fixed whole cells of the fimbriate Bgd17 strain or purified fimbriae protected against Vibrio cholerae O1 infection in rabbits, independent of biotype and serotype. Parenteral immunization of adult rabbits with purified fimbriae prior to V. cholerae O1 challenge resulted in a reduction of 2 to 3 orders of magnitude in the number of bacteria recovered from the small intestines of immunized rabbits in comparison to non‐immunized controls. IgG and IgA antibodies against fimbrillin of V. cholerae O1 were detected in the convalescent sera of patients with cholera; however, little fimbrial antigen was detected in the commercially available cholera vaccines when examined by polyclonal and monoclonal antibodies against fimbriae. These data suggest that fimbrial hemagglutinin is a major adhesin of V. cholerae O1 and that parenteral immunization with fimbriae generates a specific immune response in the gut that may serve as one means of mitigating subsequent V. cholerae O1 gut infection.

Studies on Novel Pili from Shigella flexneri

Pili were detected using electron microscopy in clinical isolates of Shigella flexneri which had been continuously subcultivated in liquid media. Morphologically, the pili appeared as thin, flexible, cylindrical structures of up to 2–5 μm in length and about 3–5 nm in diameter. Two strains showed mannose‐resistant (MR) hemagglutination to fresh fowl erythrocytes (type 4), and one to tannic acid‐treated horse erythrocyte (type 3) pili. These pili are novel and different from the mannose‐sensitive (MS) type 1 pili described by Duguid and Gillies.

Expression of Fimbriae and Hemagglutination Activity in Shigella boydii

This report describes the presence of type 1 fimbriae on Shigella boydii 5 which agglutinate guinea pig erythrocytes and feature mannose‐sensitive adherence. Morphologically, the fimbriae were thin, rigid cylinders 2–5 μm in length and 3–5 nm in diameter, and the organella retained axial holes. This is the first study to have revealed the existence of type 1 fimbriae on S. boydii.

Detection and Quantitative Assessment of a Vibrio cholerae O1 Species in Several Foods by a Novel Enzyme Immunoassay

A selected antibody enzyme immunoassay (SAEIA) for the general detection of Vibrio cholerae O1 species has been developed using the immunological reagents of a rabbit antiserum specific for V. cholerae O1 classical Inaba 569B and immobilized cell fragments of V. cholerae O1 E1 Tor 85P6, and β‐D‐galactosidase‐labeled goat anti‐rabbit immunoglobulin G as tracer. The SAEIA was specific for V. cholerae O1 species and showed low cross‐reaction values to other microorganism species tested including Vibrio parahaemolyticus. The detection limit of the SAEIA was 4,500 cells per assay for all the 13 strains of V. cholerae O1 examined. Quantitative comparison on the growth of the E1 Tor 85P4 in several foods cultured for 24 hr were studied using the SAEIA. Preceding the experiments, little inhibition of every food homogenate for the measurement of the SAEIA was first demonstrated and then the homogenate was directly used for an assay sample. The interaction of the growth of Escherichia coli to that of V. cholerae O1 in a food was also found to be little under the mixed culturing of both bacteria using the SAEIA.