[Survival of different strains of Vibrio cholerae on fresh lettuce]

Temperature effect on the survival of Vibrio cholerae in fresh lettuce was studied. Remaining infectivity in leaves experimentally contaminated with different strains of Vibrio cholerae was determined at 4 degrees C and 25 degrees C. The number of colonies in TCBS agar (Vibrio cholerae) and in nutrient agar (Vibrio cholerae and secondary microorganisms) was determined at to (initial time) and at ti (different post-contamination times). The ratio ti/to was calculated in both cases. Different survival features were found among the Vibrio cholerae strains. The CDC-185 was the most sensitive one in the experimental conditions used. At 25 degrees C, Vibrio cholerae grew faster than the secondary microorganisms and perhaps in this way it would survive in nature. At 4 degrees C lettuce leaves contaminated with the CDC-185 and the Peruano strains showed an important overgrowth relative to the secondary microorganisms at the 7th day post-contamination, whereas No O1 and 425 strains were able to inhibit this multiplication. Lettuce leaves were treated with acetic acid 0,05% to determine the inactivation of Vibrio cholerae at low pH. This decontamination treatment was effective, since a reduction of 2 log was obtained in all cases.