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In this study, 176 clinical and environmental Vibrio cholerae strains of different O serotypes isolated in Thailand from 1982 to 1995 were selected and studied for the presence of class 1 integrons, a new group of genetic elements which carry antibiotic resistance genes. Using PCR and DNA sequencing, we found that 44 isolates contained class 1 integrons harboring the aadB , aadA2 , blaP1 , dfrA1 , and dfrA15 gene cassettes, which encode resistance to gentamicin, kanamycin, and tobramycin; streptomycin and spectinomycin; β-lactams; and trimethoprim, respectively. Each cassette array contained only a single antibiotic resistance gene. Although resistance genes in class 1 integrons were found in strains from the same epidemic, as well as in unrelated non-O1, non-O139 strains isolated from children with diarrhea, they were found to encode only some of the antibiotic resistance expressed by the strains. Serotype O139 strains did not contain class 1 integrons. However, the appearance and disappearance of the O139 serotype in the coastal city Samutsakorn in 1992 and 1993 were associated with the emergence of a distinct V. cholerae O1 strain which contained the aadA2 resistance gene cassette. A 150-kb self-transmissible plasmid found in three O1 strains isolated in 1982 contained the aadB gene cassette. Surprisingly, several strains harbored two integrons containing different cassettes. Thus, class 1 integrons containing various resistance gene cassettes are distributed among different V. cholerae O serotypes of mainly clinical origin in Thailand.

Following the emergence of cholera in Lima, Peru, in 1991, isolates of Vibrio cholerae O1 biotype El Tor recovered from patients in various parts of Lima were selected and characterized. Ribotyping and pulsed-field gel electrophoresis (PFGE) revealed four BglI ribotypes and eight NotI PFGE types among 50 V. cholerae O1 strains recovered from patients with cholera in Lima from 1991 to 1995, with certain genotypes appearing to cluster geographically. While differences in ribotype and PFGE type patterns suggest that genetic changes are occurring in the strain responsible for the Latin American cholera epidemic, more frequently than previously reported, 40 (80%) O1 strains showed an identical ribotype pattern and 41 (82%) strains showed closely related PFGE types, types 1, 2, or 3, that differed by less than three restriction fragments. All strains were susceptible to nine antibacterial agents studied. In 1991, more than 95% of the clinical V. cholerae O1 strains were serotype Inaba, whereas from 1992, serotype Ogawa began to predominate, with more than 90% of the isolates being of the Ogawa serotype in 1995. The small differences in genotypes of V. cholerae O1 is remarkable because cholera is highly seasonal in coastal areas of Peru and support the hypothesis that the epidemic strain reemerges from an environmental source. However, the relative high rate of genetic changes within V. cholerae O1 as shown by ribotyping and PFGE should be taken into consideration when typing patterns of V. cholerae O1 associated with cholera in Latin America are evaluated.

Samples (1,318) of enterotoxigenic Escherichia coli (ETEC) isolated in 1994-1995 from children with diarrhea from Nepal, Indonesia, Peru, and Thailand were examined for colonization factor antigen (CFA) and coli surface (CS) antigens. Fifty-five percent of 361 heat-labile and heat-stable (LT-ST), 14% of 620 LT-only, and 48% of 337 ST-only ETEC had CFA/CS antigens. LT-ST ETEC strains were predominantly in the CFA II group, and ST only strains were in the CFA IV group. Additional studies are needed to identify ETEC strains that do not have CFA/CS antigens.

In the present study, 19 strains of Vibrio cholerae O1 biotype El Tor isolated during outbreaks of cholera in Guinea-Bissau in 1987, 1994, and 1995 were characterized to investigate a possible epidemiological relationship among the isolates. On the basis of ribotyping with the restriction enzyme BglI, 5 strains isolated in 1987 showed two closely related ribotypes, while 14 strains isolated in 1994 and 1995 showed the same ribotype that was distinct from the ribotypes of strains isolated in 1987. Southern blot hybridization of BglI-digested genomic DNA with a cholera toxin probe demonstrated that the strains isolated in 1987 showed an identical cholera toxin genotype, whereas O1 strains isolated in 1994 and 1995 showed the same genotype that was distinct from the genotype of strains isolated in 1987. These results were supported by the results of antibiotic susceptibility testing, in which strains isolated in 1987 showed resistance to polymyxin B only, while each of the strains from 1994 and 1995 showed resistance to polymyxin B, trimethoprim-sulfamethoxazole, and the vibriostatic agent O/129. Although our results are based on a limited number of V. cholerae O1 strains, they suggest that the epidemic in Guinea-Bissau in 1994 and 1995 was due to the introduction of a new strain to the country.