Toxicidad y teratogénesis por arsénico en aguas en el pez cebra (Danio rerio) / Toxicity and teratogenesis by arsenic in water in the zebra fish (Danio rerio)

El objetivo del trabajo fue estudiar los daños teratogénicos y la inducción de micronúcleos en células branquiales de peces cebra (Danio rerio) por presencia de arsénico en las aguas. Fueron mantenidos en aguas bicarbonatadas cálcicas magnésicas de un pozo de referencia y del pozo 'Zimapán 5', del Municipio Zimapán, Estado de Hidalgo, México. Este último, con un contenido de arsénico que varía de 0,395-0,630 mg/L. Para el estudio de genotoxi-cidad se evaluaron durante 180 días en 3 tratamientos: agua del pozo de referencia (control negativo, sin As), agua del pozo de referencia adicionada con 5,0 mg As (V)/L (control positivo), y en agua del pozo 'Zimapán 5', colocándose 65 especimenes por tratamiento. Después de 30 días hubo una disminución de As en el agua del control positivo de 1092,65 ppb (36,42 ppb/día) mientras en pescados hubo un incremento de 523,81 ppb (17,46 ppb/día). Para el agua del pozo 'Zimapán 5' hubo una disminución de 211,40 ppb (7,04 ppb/día), y en pescados hubo un incremento de 74,73 ppb (2,49 ppb/día). Este resultado pone de manifiesto el alto grado de bioacumulación de As en el pez, que en relación al control negativo muestra que es 2,54 veces mayor. En relación a la frecuencia de inducción de micronú-cleos en células branquiales, al final de los 180 días en el control negativo hubo una generación espontánea de 0,8 micronúcleos/1000 células, en el control positivo hubo una frecuencia de inducción de micronúcleos 163,5 veces mayor que en el control negativo, mientras que en los peces expuestos al agua del pozo 'Zimapán 5' fue 56,25 veces mayor con respecto al mismo. Estos resultados demuestran la genotoxicidad del As en Danio rerio. Para el estudio de teratogénesis, se colocó una hembra y un macho en apareamiento en las mismas condiciones de los tratamientos, obteniendo que a mayor concentra-ción de As en el agua mayor porcentaje de huevos no viables, menor porcentaje de huevos viables y de eclosión, mayor porcentaje de alevines recién eclosionados y juveniles con malformaciones, y menor porcentaje de juveniles sobrevivientes (AU)

The objective of this work was study the teratogenic damages and the induction of micronuclei in gill cells of zebra fish (Danio rerio). They was maintained in calcium-magnesium bicarbonated waters from a reference well and 'Zimapán 5' well, the latter with an arsenic (As) content ranging from 0.395 to 0.630 m/L. For the genotoxicity study the specimens were studied during 180 days in 3 separated lots; in reference well water (negative control), in reference water to which was added 5 mg/L As (V) (positive control); and in water from 'Zimapán 5' well, with specimens by treatment. In waters an As concentration diminution was observed with time, whereas in fish there was an increase. After 30 days there was an As diminution in water from positive control of 1092.65 ppb (36.42 ppb/day) whereas in fish it had increased to 523.81 ppb (17.46 ppb/day). For the water from 'Zimapán 5' well there was a diminution of 211.40 ppb (7.04 ppb/day), and in fish there was an increase of 74.73 ppb (2.49 ppb/day). This result indices the grade high of bioaccumulation of As in fish, in relation with negative control is 2.54 major. In relation to micronucleus frequency in gill cells, at the end of 180 days in the negative control there was a spontaneous generation of 0.8 micronuclei/1000 cells, in the positive control there was a micronucleus frequency 163.5 times greater than in negative control, whereas for the fish exposed to 'Zimapán 5' well water the micronucleus frequency was 56.25 times greater than with the negative control. Taken together these results demonstrate the genotoxicity to Danio rerio of As in the well water (AU)

Antimicrobial activity of three Mexican Gnaphalium species.

The antibacterial activity of the hexane, ethyl acetate and methanol extracts of the flowers, leaves and stems of Gnaphalium oxyphyllum var. oxyphyllum, G. liebmannii var. monticola and G. viscosum was investigated. The hexane extracts showed in all cases the higher inhibitions, G. oxyphyllum flower extract exhibiting the wider spectrum of activity.

Behavior of enterotoxigenic strains of Staphylococcus aureus in milk fermented with a yogurt starter culture.

The ability of a yogurt starter culture formed by Streptococcus salivarius subsp. thermophilus and Lactobacillus delbrueckii subsp bulgaricus to inhibit the growth of four enterotoxin type A and B producers Staphylococcus aureus strains (ATCC 6538, S6, FRI-100 and a strain isolated from milk) during fermentation of milk and subsequent storage was investigated. Sterile skim milk was inoculated with about 10(6) CFU/ml of S. aureus and with about 10(6) CFU of starter culture, and incubated at 42 degrees C during 8 h, followed by refrigeration at 4 degrees C. Samples were taken every 2 h during fermentation and every 2 days during storage. Viable count of lactic acid bacteria and S. aureus as well as pH, acidity, thermostable deoxyribonuclease (TNase) and staphylococcal enterotoxin A (SEA) production were evaluated. Behavior of four strains was similar; S. aureus survived the 8 h fermentation with LAB, and its population began to decrease from the first day of storage, being completely inhibited at 9-10 days. TNase and SEA production were positive in all samples taken along the study. It was demonstrated that enterotoxigenic strains of S. aureus were able to survive the fermentation of milk with a yogurt starter culture and they were inhibited after several days during storage of the fermented product, contrary to the general belief which considered it very difficult due to the low pH. Even though S. aureus was inhibited, TNase and SEA were demonstrable along the storage. Therefore, fermented milks may play an important role in the transmission of this organism.

[Survival of Listeria monocytogenes in milk fermented with a starter culture for making yogurt]. / Sobrevivencia de Listeria monocytogenes en leche fermentada con un cultivo iniciador para elaborar yogur.

The purpose of this research was to determine the survival of Listeria monocytogenes in sterile skim milk during the fermentation with a yogurt starter culture and during storage at refrigeration temperature. Sterile skim milk was inoculated with 10(3), 10(5) and 10(7) cfu/ml of L. monocytogenes and with 10(6) cfu of lactic acid bacteria. Inoculated milks were fermented for 8 h at 42 degrees C, followed by refrigeration at 4 degrees C. Samples were taken at 2 h intervals during fermentation and at 2 days intervals during storage. Acidity and pH were measured, as well as viable count of lactic acid bacteria and pathogen. L. monocytogenes survived 8h, 10 days and 32 days in the fermented milk, when the inocula were 10(3), 10(5) and 10(7) cfu/ml, respectively. Inhibition of the pathogen was associated with a decrease of pH below 4.0 and increase in acidity. It was demonstrated that this pathogen is able to survive several weeks in milk fermented with a starter culture, contrary to the general belief which considered it very difficult due to the low pH. Therefore fermented milks may play an important role in the transmission of these bacteria.