Resumen: Enviromental strain of Vibrio cholera of San Luis Potosi, Mexico, do not contain functional ctxAB genes but express multiple antibiotic resistance traits

Abstract

The main pathogenic factor of Vibrio cholerae O1 and O139 serotypes, causative agents of cholera, is the production of cholera toxin (CTX) encoded by the phage CTXphi. Other plasmids or integrons capable of horizontal transmission and encoding antimicrobial resistence are frequently found in O1/O139 and environmental non-O1/O139 strains. The last have are belived to constitute reservoirs for pathogenic determinants responsible of the cyclic cholera outbreaks. To identify probable reservoirs of transmissible pathogenic determinants, we analyzed the presence of ctxAB genes and the patterns of antibiotic resistance in environmental isolates of V. cholerae obtained in the state of San Luis Potosi, Mexico. Methods and results: The main sources of V. cholerae were local urban sewage waters (36.4%) and fresh waters together with derived edible products (34.4%). More than 40 different serotypes were identified, but none corresponded to the O1 or O139. Fourteen biochemical patterns were found clustered into four closely related groups. By PCR analysis two isolates obtained from marine products showed the presence of ctxAB amplification bands about 52 bp smaller than those obtained with O1 reference strains. No CTX production was detected in these two environmental strains suggesting the existence of a deletion involving the ctxA gene. A high frequence of resistance was observed against amoxicillin / clavulanic acid (73.7%), and erythromycin (30.9%); and intermediate frequence was observed against cefazolin (12.6%), cefapime (13.7%), tetracycline (8.3%) and trimethoprim / sulfamethoxazol (7.4%). Nine isolates displayed strong resistance against four to seven different antibiotics indicating the presence of chromosomal and extrachomosomal determints of antibiotic resistance. Conclusion: Enviromental V. cholerae in San Luis Potosi do not contain funtional ctxAB genes; however, transmissible elements containing antibiotic multiresistance determinants are relatively frequent.