Principales características y diagnóstico de los grupos patógenos de Escherichia coli / Principal characteristics and diagnosis of the pathogenic groups of Escherichia coli

Escherichia coli colonizes the human intestinal tract within hours of birth and is considered a non-pathogenic member of the normal intestinal flora. However, there are six pathogenic groups that may produce diarrhea: enterotoxigenic (ETEC), enterohemorrhagic (EHEC), enteroinvasive (EIEC), enteropathogenic (EPEC), enteroaggregative (EAEC) and diffusely adherent (DAEC) groups. E. coli can be isolated and classified using traditional methods, by identifying its biochemical or serum characteristics. The pathogenic mechanisms may be studied in cell cultures and animal model assays, as well as more up to date molecular biology methods for study and diagnosis. The latter have proven that genes are involved in pathogenesis. The objective of the present work is to draw attention to the importance of E. coli as a pathogenic organism. This microorganism is an etiologic agent of sporadic cases of diarrhea, hemorrhagic colitis, dysentery, and hemolytic uremic syndromes and outbreaks. Diarrheic E. coli manifestations occur mainly among infants, and deep knowledge and understanding of this microorganism are crucial to better epidemiologic surveillance.

Brote causado por Escherichia coli en Chalco, México / Outbreak caused by Escherichia coli in Chalco, Mexico

OBJECTIVE: To identify the etiologic agent responsible for a disease outbreak following an overflow of sewage water in Valle de Chalco, Mexico. MATERIAL AND METHODS: A retrospective cross-sectional study was carried out. Rectal samples were collected from the population of Chalco valley, who suffered from diarrhea and vomiting during a natural disaster that took place on May 31, 2000. The Instituto de Diagnóstico y Referencia Epidemiológicos (Epidemic Reference and Diagnosis Institute, InDRE, Ministry of Health), received 1521 rectal swab samples from diarrhea cases, to test for E. coli strains. Statistical analysis was performed to find a difference of proportions between cases and non-cases (chi-squared test). ETEC, EIEC, EPEC and EHEC pathogenic E. coli groups were hybridized by colony blot. RESULTS: Strains isolated were ETEC (62.2), EIEC (0.84), EPEC (0.84), and EHEC non-O157:H7 (0.08); there was no hybridization in 36.02 of E. coli strains. Other isolated microorganisms were Salmonella spp (0.45) and Shigella spp (0.06). CONCLUSIONS: Enterotoxigenic E. coli was the most likely etiologic agent. Sanitary control strategies should be targeted to preventing outbreaks caused by this pathogenic agent.

Vibrio cholerae 01 fenotipos y genotipos México / Vibrio cholerae 01 phenotypes and genotypes Mexico

Se caracterizaron 26922 cepas de Vibrio cholerae aisladas en México de 1991 a 1993, el patrón fenotípico demostró que 100 por ciento pertenece al biovar El Tor y fueron sensibles a los antibióticos, excepto a la furazolidona, la estreptomicina y el sulfixosasol probados en 1993. Se empleó como marcadores epidemiológicos al 97 por ciento de las cepas que fueorn resistentes. Se observó un cambio drástico en la frecuencia de los serotipo Inaba; en 1991 el 99.5 por ciento de las cepas fueron Inaba mientras que para 1992, el 95.0 por ciento fueron del serotipo Ogawa, fueron toxigénicas, y las no 01 dieron negativa la prueba de ELISA, PCR y los cultivos celulares para investigar toxina colérica. Los ribotipos correspondieron en su mayoría al patrón 5, un lote pequeño a la 6a y dos al ribotipo 12. En este estudio se buscó el ribotipo 2, que se ha relacionado con las cepas aisladas del Golfo de México entre las cepas hemolíticas, pero hasta ahora no se ha identificado ninguna cepa con dicho patrón. Para estudios fenotípicos y genotípicos en apoyo al análisis epidemilógico de la enfermedad, es conveniente continuar haciendo el cultivo en una fracción de las muestras para recuperar cepas puras, aunque se utilicen pruebas rápidas para el diagnóstico de cólera