1) Drug sensitivity and coagulase type of Staphylococcus aureus isolated at Mahosoto Hospital, Vientiane, Laos in 1993 and at the Ryukyus University Hospital, Okinawa, Japan in 1992 were compared. MIC90 0f erythromycin was 0.4 $ \mu $g/ml in Lao isolates but 100 $ \mu $g/ml or more in Japanese isolates. MICs of tetracycline against 58% of Lao isolates and 25% of Japanese isolates were 12.5 $ \mu $g/ml or more. All Lao isolated were inhibited at 0.8 $ \mu $g/ml or less of cefdinir, whereas only 37% of Japanese isolates. All Lao isolates were inhibited at 6.25 $ \mu $g/ml or less of methicillin, but 63% of Japanese isolates were not inhibited at 100 $ \mu $g/ml of methicillin. The most frequent coagulase type in Lao and Japan was type 5 (54%) and type 2 (53%), respectively. 2) Staphylococcus aureus isolated in Laos was examined for the drug sensitivities and coagulase type. A total of 114 strains examined consisted of 32 isolated in 1995 and 47 isolated in 1996 from the infection focus, and 35 isolated from nasal mucosa of non-infected patients and nurses working in the wards. One strain with coagulase type IV was regarded as methicillinresistant S. aureus (MRSA) depending on the minimum inhibitory concentration of the drugs as >100, 100, 100, >100, and 25 $ \mu $g/ml of methicillin, ampicillin, tetracycline, erythromycin, and cefdinir, respectively. The mec A gene was detected in this strain but not in the others. This is the first report of MRSA from Lao PDR. 3) Thirty-four strains of Vibrio cholerae O1 serotype Ogawa isolated in Laos in 1995 were examined for their biological behavior and cholera toxin productivity. Biotyping indicated that the 34 strains belonged to the EI Tor biotype. Prophage typing identified 31 strains of the Celebes type, including 3 cured Celebes type, and 3 Ubol type. All the strains produced detectable levels of cholerae toxin: 15 isolates produced more than 100 ng/ml, 10 strains between 10 and 100 ng/ml and 9 strains less than 10 ng/ml, determined by using AKI medium in a stationary test tube. The maximum producing was 200 ng/ml. 4) An epidemic Vibrio parahaemolyticus gastroenteritis with several occurred in Vientiane, Laos, an inland country in August and September in 1997. Serotype of the 36 isolates from the patients were all O3:K6. The organisms grew in peptone water supplemented with lO% NaCl. All isolates were positive for Kanagawa phenomenon and tdh gene, but negative for trh gene and urease. Genomic patterns were not completely identical, as determined by pulsefield gel electrophoresis. Although a Kanagawa phenomenon positive V. parahaemolyticus strain was isolated from the suspicious food, a papaya salad containing minced and salted fresh water crab, the serotype was 02:K28, tdh and trh were negative., 5) Reversed passive latex agglutination (RPLA) assay for determining the toxigenicity of Corynebacterium diphtheriae is presented. Rabbit antitoxin antiserum was raised by using commercially available diphtheria toxoid. This antiserum reacted with the diphtheria toxin and it did not cross-react with other extra cellular antigens. Affinity-purified antibodies for latex sensitization were obtained by using HI Trap N-hydroxysuccimmde-activated column. Demonstration of toxin in five of seven clinical isolates was in accordance with the PCR assay and the Vero cell cytotoxicity test. The lowest concentration of diphtheria toxin detectable by the RPLA assay was about 5 ng/ml. The RPLA assay can provide a convenient and reliable method for laboratories involved in the identification of toxinogenic corynebacteria. 6) Etiologic bacteria of 135 cases with diarrheal diseases and the healthy carrier rate in 211 individuals were studied in Laos. Diarrheagenic Escherichia coll, Shigella and Campylobacter were the predominant pathogens isolated. This country does not face the sea, but Vibrio parahaemob′ticus was isolated from 2 cases. Healthy carrier rate of enteropathogenic E. coli as diagnosed by serogroup Class I was 3 times higher than the detection rate in diarrheal patients (10.9% and 3.7%). Healthy carrier rate of Shigella was 4.3%, whereas the detection rate of Shigella in diarrheal patients was 15.4%. The isolation frequencies of enterotoxigenic E.coh and Campylobacter jejuni in the patients and healthy individuals were almost the same. Verotoxin producing E. coli was found in one health individual (Toxin type VT1, O-antigen O111). Rotavirus was detected from 2 adult cases out of 32 examined. 7) The etiological agents of diarrhea in Vientiane, Laos, were studied in the period from October 1996 to August 1997. A total of 880 patients with diarrhea visiting medical facilities were examined for Shigella, Salmonella, diarrheagenic Escherichia coli, Vibrio, Aeromonas, Campylobacter, and rotavirus. Shigella spp., heat-stable enterotoxin (ST)-producing E. coli and serogroup-based enteropathogenic E.coli (EPEC) were found to be the main organisms causing diarrhea in Vientiane, with frequencies of 16.8% (148 of 880), 17.2% (111 of 645), and 11.0% (97 of 880), respectively. Relatively low incidences were observed in the cases of Salmonella spp., (0.6%; 5 of 880), Campylobacter spp. (4.4%;39 of 880), and rotavirus (6.1%; 9 of 148), and no isolates of V. cholerae O1 or O139 or Aeromonas were recovered. The frequencies of isolation of Shigella spp. and heat-labile enterotoxin-producing E.coli were significantly higher in those aged 1 to 5 years than in those younger than 1 year of age and those older than 5 years of age (P, 論文