Toxigenic V. cholerae, V. parahaemolyticus, and V. vulnificus in oysters from the Gulf of Mexico and sold in Mexico City.

Oysters can accumulate potentially pathogenic bacteria, such as Vibrio cholerae, V. parahaemolyticus, and V. vulnificus. The aim of this study was to detect the presence of these Vibrio species and their toxigenic variants in oysters from the Gulf of Mexico sold in Mexico City. Oyster samples were studied using traditional culture and molecular polymerase chain reaction analysis. V. cholerae was present in 30.4% of the samples and its toxigenic variant chxA+ in 26.1%. It was isolated only in deshelled oysters, mainly in the dry season. V. parahaemolyticus was present in 95.7% of the samples and the toxigenic variant was found in 17.4%. V. vulnificus was identified in 60.9% of the samples, 38% of which corresponded to the environmental genotype and 21.7% to the clinical genotype, mainly in the cold season. Consumption of the oysters analyzed poses health risks due to the presence of Vibrio species, especially in deshelled oysters.

Heavy metal bioaccumulation in Oreochromis niloticus from Tenango Dam, Puebla, Mexico.

Oreochromis niloticus was used to determine the effects of heavy metals and their concentration in aquatic environments. Its wide distribution, resistance, and economical importance make it a suitable biomonitor. The present study was conducted in the Tenango Dam (Puebla, Mexico) to determine water quality and its impact on O. niloticus, a species that is cultured and commercialized in this area. Five samples were collected over 1 year to evaluate the water's physicochemical parameters (temperature, dissolved oxygen, pH, and hardness) and metal contents (cadmium, chromium, copper, and lead). Metal concentrations, bioconcentration factors, and metallothionein levels were also assessed in O. niloticus livers and muscle tissues. Water and tilapia quality were estimated according to current Mexican guidelines. Results indicated that the water's physicochemical parameters were within acceptable ranges. Metal concentrations, however, suggested that this resource was not suitable for urban use. Moreover, metal levels in fish tissues exceeded the acceptable limits during two periods, rendering it unsuitable for human consumption. The bioconcentration factor indicated that the metals can potentially accumulate in organisms. Furthermore, metallothionein levels in liver and muscle showed a direct correlation with metal concentrations in these tissues. This is the first study to use tilapia as an indicator of contamination in the Tenango Dam, and also the first to describe the presence of metals in this water body.

Quantification of Vibrio species in oysters from the Gulf of Mexico with two procedures based on MPN and PCR.

Oysters can accumulate potentially pathogenic water bacteria. The objective of this study was to compare two procedures to quantify Vibrio species present in oysters to determine the most sensitive method. We analyzed oyster samples from the Gulf of Mexico, commercialized in Mexico City. The samples were inoculated in tubes with alkaline peptone water (APW), based on three tubes and four dilutions (10-1 to 10-4). From these tubes, the first quantification of Vibrio species was performed (most probable number (MPN) from tubes) and bacteria were inoculated by streaking on thiosulfate-citrate-bile salts-sucrose (TCBS) petri dishes. Colonies were isolated for a second quantification (MPN from dishes). Polymerase chain reaction (PCR) was used to determine species with specific primers: ompW for Vibrio cholerae, tlh for Vibrio parahaemolyticus, and VvhA for Vibrio vulnificus. Simultaneously, the sanitary quality of oysters was determined. The quantification of V. parahaemolyticus was significantly higher in APW tubes than in TCBS dishes. Regarding V. vulnificus counts, the differences among both approaches were not significant. In contrast, the MPNs of V. cholerae obtained from dishes were higher than from tubes. The quantification of MPNs through PCR of V. parahaemolyticus and V. vulnificus obtained from APW was sensitive and recommendable for the detection of both species. In contrast, to quantify V. cholerae, it was necessary to isolate colonies on TCBS prior PCR. Culturing in APW at 42 °C could be an alternative to avoid colony isolation. The MPNs of V. cholerae from dishes was associated with the bad sanitary quality of the samples.

[Comparison of techniques for coliform bacteria extraction from sediment of Xochimilco Lake, Mexico]. / Comparación de técnicas para la extracción de bacterias coliformes del sedimento del lago de Xochimilco, México.

The need to separate bacteria from sediment in order to appropriately count them has led to test the efficacy of different techniques. In this research, traditional techniques such as manual shaking, homogenization, ultrasonication, and surfactant are compared. Moreover, the possibility of using a set of enzymes (pancreatine) and an antibiotic (ampicillin) for sediment coliform extraction is proposed. Samples were obtained from Xochimilco Lake in Mexico City. The most probable number of coliform bacteria was determined after applying the appropriate separation procedure. Most of the techniques tested led to numbers similar to those of the control (manual shaking). Only with the use of ampicillin, a greater total coliform concentration was observed (Mann-Whitney, z = 2.09; p = 0.03). It is possible to propose the use of ampicillin as a technique for total coliform extraction; however, it is necessary to consider sensitivity of bacteria to the antibiotic.

Comparación de técnicas para la extracción de bacterias coliformes del sedimento del lago de Xochimilco, México / [Comparison of techniques for coliform bacteria extraction from sediment of Xochimilco Lake, Mexico].

The need to separate bacteria from sediment in order to appropriately count them has led to test the efficacy of different techniques. In this research, traditional techniques such as manual shaking, homogenization, ultrasonication, and surfactant are compared. Moreover, the possibility of using a set of enzymes (pancreatine) and an antibiotic (ampicillin) for sediment coliform extraction is proposed. Samples were obtained from Xochimilco Lake in Mexico City. The most probable number of coliform bacteria was determined after applying the appropriate separation procedure. Most of the techniques tested led to numbers similar to those of the control (manual shaking). Only with the use of ampicillin, a greater total coliform concentration was observed (Mann-Whitney, z = 2.09; p = 0.03). It is possible to propose the use of ampicillin as a technique for total coliform extraction; however, it is necessary to consider sensitivity of bacteria to the antibiotic.

Comparación de técnicas para la extracción de bacterias coliformes del sedimento del lago de Xochimilco, México. / [Comparison of techniques for coliform bacteria extraction from sediment of Xochimilco Lake, Mexico].

The need to separate bacteria from sediment in order to appropriately count them has led to test the efficacy of different techniques. In this research, traditional techniques such as manual shaking, homogenization, ultrasonication, and surfactant are compared. Moreover, the possibility of using a set of enzymes (pancreatine) and an antibiotic (ampicillin) for sediment coliform extraction is proposed. Samples were obtained from Xochimilco Lake in Mexico City. The most probable number of coliform bacteria was determined after applying the appropriate separation procedure. Most of the techniques tested led to numbers similar to those of the control (manual shaking). Only with the use of ampicillin, a greater total coliform concentration was observed (Mann-Whitney, z = 2.09; p = 0.03). It is possible to propose the use of ampicillin as a technique for total coliform extraction; however, it is necessary to consider sensitivity of bacteria to the antibiotic.

Filtration rate, assimilation and assimilation efficiency in Crassostrea virginica (Gmelin) fed with Tetraselmis suecica under cadmium exposure.

Crassostrea virginica is an epibentic filter-feeding bivalve of economical importance in coastal lagoons of the Gulf of Mexico, locations with increasing inputs of heavy metals such as cadmium that have become environmental stressors. In this study, feeding and assimilation of the species were evaluated as physiological indicators of cadmium exposure. For this purpose, the filtration rate (FR), food assimilation (A) and assimilation efficiency (AE) of oysters from the Mandinga Lagoon, Veracruz, Mexico, were examined under sublethal and environmentally realistic cadmium concentrations (95 and 170 micro gCd L(-1)). Semi-static, 12-day bioassays were conducted with organisms placed into individual chambers and fed daily with Tetraselmis suecica. FR was calculated by measuring the depletion in algal density. Caloric contents of food and feces produced were also obtained. Condition Index (CI) and morphometric parameters were evaluated at the beginning and at the end of the assay. Total cadmium concentrations were quantified in water and tissue, and the metal bioconcentration factor (BCF) was calculated. Cadmium exposure significantly reduced FR in oysters (mean value: 0.64 L h(-1) and 0.44 L h(-1)) from control values (1.17 L h(-1)). Extreme values among results demonstrate the existence of a high FR (over 4 L h(-1)) mainly in control oysters, and this was associated with a better physiological condition; a low FR (under 2.5 L h(-1)) indicated metabolic stress as a consequence of Cd exposure. A and AE were significantly modified due to cadmium external levels, and time of exposure. FR and A were linearly related, and both decreased as metal BCF increased. Cadmium bioaccumulation was linearly related with external metal levels. The physiological deterioration of native C. virginica from Mandinga Lagoon was reflected in the alteration of FR, A and AE due to cadmium exposure in concentrations considered sublethal, lowering the feeding and assimilation capability of the organisms. The weight loss and mortality recorded in the oysters exposed to the highest metal concentration, was the final consequence of the overall adverse effect of cadmium exposure.