Caracterización bioquímica de cepas de coliformes fecales aisladas de alimentos / Biochemical characterizationof fecal coliform strains isolated from food

Se realizó la caracterización bioquímica a 252 cepas de coliformes fecales aisladas de muestras de leche pasteurizada, helados y ostión fresco. El aislamiento se realizó por el método de placa vertida en medio de agar rojo violeta bilis. De las cepas analizadas, el 97,6 %pertenecía al grupo coliformes fecales y y sólo el 2,4 %no pertenecía a este grupo, pero sí a la familia Enterobacteriaceae. El mayor porcentaje de aislamiento correspondió a la especie Escherichia coli (41,5 %), seguida por los géneros Enterobacter (27,6 %), Klebsiella (23,6 %) Citrobacter (7,3 %). Se obtuvieron 86 cepas anaerógenas (34,6 %) de las cuales 26 eran Escherichia coli

Structure and time-dependent behavior of acetylated and non-acetylated forms of a molluscan metallothionein.

Cadmium-induced metallothionein in a mollusc, the oyster Crassostrea virginica, occurs in both blocked and unblocked forms (Roesijadi, G., Kielland, S.L. and Klerks, P. (1989) Arch. Biochem. Biophys. 273, 403-413). The block, which is the sole difference in the structure of the two proteins, was identified as an acetyl group with use of tandem mass spectrometry. The blocked and unblocked proteins carried N-acetylserine and serine, respectively, at the N-terminus and were designated CvNAcMT and CvMT. Only CvNAcMT was detected under basal conditions. Both forms were induced by Cd. Pulse-labeling with [35S]cyteine at specified times during exposure showed that the rate of CvNAcMT synthesis in gills increased rapidly, initially exceeding that of CvMT, then declined to the rate attained by CvMT. Turnover rates for Cd-induced CvMT and CvNAcMT were similar to each other. They appeared to be faster when measured in the absence of Cd in the external medium (k = 0.18 and 0.16/day, respectively), than in its presence (k = 0.03 and 0.06/day, respectively).

[Physico-chemical analysis of Ostreas gigas Thumberg from Xinghua].

This paper presents a comparative physico-chemical analysis of the ancient Ostrea gigas with the medical Ostrea gigas concha, and shows that the protein and amino acid contents in the former are obviously lower than those in the latter, but for the contents of trace elements Mn, Fe, Ni and Pb (with the exception of As), the former appears higher than the latter.

Trace metals in Gulf of Mexico oysters.

Oysters (Crassostrea virginica) from 50 to 69 locations (sites) along the Gulf of Mexico coastline, collected annually in 1986, 1987 and 1988, have been analyzed for 13 trace metals, including most of the metals of concern from an environmental quality perspective. Essentially the entire U.S. Gulf coastline was sampled, from far south Texas to far south Florida. Pooled samples of 20 oysters from three different stations at each site were analyzed by atomic absorption spectrophotometry. The concentrations found were generally less than or equal to literature values from other parts of the world thought to be uncontaminated by anthropogenic trace metal inputs. A few sites did, however, show apparent trace metal pollution and other sites gave anomalous values that cannot readily be explained by either known anthropogenic or natural causes. The range of values for the overall data set (maximum/minimum) varied from 15-fold for Mn to 624-fold for Pb, whereas the coefficient of variation (standard deviation/mean) was generally in the 50-60% range for most metals. Variations were much greater between stations than between years at a given station. Enrichments usually occurred in suites of three to four elements with Ag, Cd, Cu and Zn being the most common suite, thus several strong inter-element correlations were found. There was, however, little correlation between metal levels in oysters and in sediments from the collection sites even when sediment data were rationed to Al (sediment data are not given here). There was likewise little correlation between oyster metal levels and size, sex or reproductive stage of the oysters (data given elsewhere). Geographically, appreciably elevated (greater than 3 times average) metal levels were generally restricted to single sites within bays or estuaries, implying local control. On the other hand, regionally, Ag, Cd and Se levels were somewhat higher in Texas oysters than in those from Florida, whereas the reverse was true for As and Hg. Concentrations were lower than average for several metals in oysters from central Louisiana, especially Ag, Cd and Cu. Thus, the Mississippi River outflow and extensive offshore oil development do not seem to enrich oysters in trace metals.

Accumulation of metals and organochlorines in tissues of the oyster Crassostrea angulata from the Sado Estuary, Portugal.

Sixty-eight composite samples of selected tissues (mantle, gills, adductor muscle and other soft parts) of Crassostrea angulata oysters collected in the upper Sado Estuary from May 1985 to May 1987 were analyzed for Fe, Mn, Zn, Cu, Cd, Pb, Ni, Cr, Co, PCB and total DDT. Principal component analysis demonstrated that Cd, Ni, Zn, Cu and Mn were more closely associated with mantle and gills, and their accumulation seemed to be highly influenced by oyster metabolic alterations. In contrast, partitioning of Pb and Cr in C. angulata tissues was largely related to environmental changes. As both biological and environmental factors tend to have major influences at the same period on the accumulation of PCB and DDT, the major factor defining their temporal partition in oysters from this upper estuary could not be clearly discerned. PCB and DDT were principally accumulated in the mantle and visceral mass.

Calcium regulated thin filaments from molluscan catch muscles contain a caldesmon-like regulatory protein.

The thin filaments of the anterior byssus retractor muscle of the edible mussel Mytilus and the transluscent and opaque adductors of the oyster Crassostrea have been isolated and their properties investigated. We find that the thin filaments from all three muscles can activate skeletal muscle myosin ATPase in the presence of calcium but that the activity is inhibited in its absence. The filaments contain a protein which interacts with antibodies to vertebrate smooth muscle caldesmon on immunoblots. The antibodies relieve the inhibition of the thin-filament-activated myosin MgATPase. They can also bundle the thin filaments. We conclude that a caldesmon-like protein is present in molluscan muscle. As in the vertebrate smooth muscle, it could act as part of a control mechanism in addition to the myosin regulatory system. Vertebrate smooth muscle caldesmon can crosslink actin and myosin and it has been suggested that it may in this way contribute to the latch state. A similar interaction may be involved in the catch mechanism in molluscan muscle.

Chelation ion chromatography as a method for trace elemental analysis in complex environmental and biological samples.

The development and evaluation of a new method for the determination of trace transition and rare-earth elements based on the combination of chelation and ion chromatography are described. The new method, chelation ion chromatography (Chelation IC), uses a chelating column to concentrate and separate transition and rare-earth elements from the common alkali and alkaline-earth metals, as well as other matrix components, prior to analysis by ion chromatography. The sample fraction from the chelating column contains only the concentrated analyte ions, thus eliminating interfering matrix components from complex matrices such as seawater and digested biological, botanical, and geological materials. This combination of chelation and ion chromatography provides a technique that makes possible the determination of trace elements in complex matrices that have proven to be difficult or impossible to analyze by ion chromatography or conventional atomic spectroscopy techniques.

Distribution of heavy metals in Gove Harbour, Northern Territory, Australia.

The concentration of four metals in waters and eight metals in oysters and sediments from Gove Harbour, Northern Territory, were determined during the dry season of 1987. The measured concentrations of zinc, cadmium, copper and lead in unfiltered waters were: 1.10-7.28, 0.10-2.20, 0.25-3.45 and 0.15-2.87 micrograms l-1, and zinc, cadmium, copper, lead, aluminium, nickel, manganese and iron in oysters, 60.1-970, 0.14-4.07, 3.77-30.67, ND-0.46, 6.50-1123.0, 0.02-0.44, 0.24-2.04 and 4.28-981.3 micrograms g-1 wet weight, and in sediments, 0.09-22.24, ND-0.45, ND-5.95, ND-2.98, 229.98-16053.5, 0.21-7.70, 13.77-50.24 and 759.5-2659.6 micrograms g-1 dry weight. Concentrations of zinc, aluminium and cadmium were higher in the oysters. The level of cadmium exceeded the National Health and Medical Research Council (NHMRC) recommended limit. In general, levels of these and other metals were higher near a bauxite treatment plant.

Analysis of biological reference materials, prepared by microwave dissolution, using inductively coupled plasma mass spectrometry.

A procedure has been developed for the analysis of biological materials by inductively coupled plasma mass spectrometry (ICP-MS). Fast, efficient and complete sample digestion is achieved by a combined microwave-nitric acid/open beaker-nitric acid-hydrogen peroxide procedure. The ICP-MS analysis is performed with an on-line five-element internal standard to correct for matrix and instrumental drift effects. Results are presented for 24 elements in three biological reference materials (National Institute of Standards and Technology Standard Reference Materials 5277a Liver and 1566 Oyster and International Atomic Energy Agency Certified Reference Material H4 Animal Muscle). For all elements significantly above the detection limit and reagent blank concentrations, good agreement exists between ICP-MS and certified values.

Determination of phosphorus in biological material using electrothermal atomisation atomic absorption spectrometry with a molybdenum tube atomiser.

Phosphorus has been determined by electrothermal atomisation atomic absorption spectrometry with a molybdenum tube atomiser. The effects of interferents on the phosphorus signal have been investigated. Chemical interferences were eliminated by high-temperature pyrolysis. The detection limit for the molybdenum tube system was 2.3 ng (corresponding to 2.3 micrograms ml-1 when 1 microliter was injected into the atomiser) and the characteristic mass was 1.9 ng of phosphorus. A calibration graph method combined with high-temperature pyrolysis has been evaluated through the determination of phosphorus in biological materials. The sensitivity, accuracy and precision of the method were superior to or nearly equal to those of graphite furnace atomic absorption spectrometry. The advantages of the high-temperature pyrolysis method are its simplicity and low cost.

Determination of iodine in oyster tissue by isotope dilution laser resonance ionization mass spectrometry.

The technique of laser resonance ionization mass spectrometry has been combined with isotope dilution analysis to determine iodine in oyster tissue. The long-lived radioisotope, 129I, was used to spike the samples. Samples were equilibrated with the 129I, wet ashed under controlled conditions, and iodine separated by coprecipitation with silver chloride. The analyte was dried as silver ammonium iodide upon a tantalum filament from which iodine was thermally desorbed in the resonance ionization mass spectrometry instrument. A single-color, two-photon resonant plus one-photon ionization scheme was used to form positive iodine ions. Long-lived iodine signals were achieved from 100 ng of iodine. The precision of 127I/129I measurement has been evaluated by replicate determinations of the spike, the spike calibration samples, and the oyster tissue samples and was 1.0%. Measurement precision among samples was 1.9% for the spike calibration and 1.4% for the oyster tissue. The concentration of iodine determined in SRM 1566a, Oyster Tissue, was 4.44 micrograms/g with an estimate of the overall uncertainty for the analysis of +/- 0.12 microgram/g.

Simultaneous determination of butyltin and phenyltin compounds in oysters by capillary gas chromatography.

A method is described for the simultaneous determination of butyl- and phenyltin compounds in oyster samples. The organotin compounds were extracted (as chlorides) from oyster homogenates with hydrochloric acid and benzene in the presence of 0.05% tropolone. These compounds were converted into pentyl derivatives with pentyl Grignard reagent and then analysed by capillary gas chromatography with a flame photometric detector equipped with a 393-nm filter. The recoveries of six organotin compounds added to oyster samples ranged from 71 to 74%. The detection limits of butyl- and phenyltin compounds were in the 5-9 pg range as tin. We detected significant amounts of three organotin compounds (di- and tributyltin and triphenyltin) in oyster samples.

Zinc from oyster tissue as causative factor in mouse deaths in official bioassay for paralytic shellfish poison.

Toxicity (extreme weakness, body temperature drop, cyanosis, some slow deaths) in test mice, upon intraperitoneal injection of standard-method paralytic shellfish poison (PSP) extracts of some PSP-free oysters, is consistent with the relatively high levels of zinc in these extracts. As a rough guideline, the threshold for a toxic response corresponds to a drained tissue zinc level of over 900 micrograms/g. The identification of zinc as the substance responsible has been supported by inducing toxicity in control extracts by spiking with nontoxic levels of zinc, and by eliminating toxicity from toxic extracts by chemical removal (precipitation, ion exchange) of metals.

The rapid decomposition of biological materials by using a microwave acid digestion bomb.

A microwave acid decomposition technique was evaluated for decomposing biological standard reference materials (NBS oyster tissue and bovine liver) for trace metal analyses. Dissolution consisted of HNO3 decomposition in a closed Teflon bomb. A microwave oven was used as the heat source. Complete decomposition times were less than 1 min. Resulting solutions were analyzed by atomic absorption spectrophotometry for Cd, Cu, Fe, Pb, and Zn. Recoveries were estimated by comparison with National Bureau of Standards certified values. The precision and accuracy of the results ranged from 1 to 13% and 93 to 106%, respectively.