The physiologic state of Escherichia coli O157:H7 does not affect its detection in two commercial real-time PCR-based tests

Multiplex real-time PCR detection of Escherichia coli O157:H7 is an efficient molecular tool with high sensitivity and specificity for meat safety assurance. The Biocontrol GDS^® and DuPont Qualicon BAX^®-RT rapid detection systems are two commercial tests based on real-time PCR amplification with potential applications for quantification of specific E. coli O157:H7 gene targets in enriched meat samples. However, there are arguments surrounding the use of these tests to predict pre-enrichment concentrations of E. coli O157:H7, as well as arguments pertaining to the influence of non-viable cells causing false positive results. The present study attempts to illustrate the effects of different bacterial physiologic states and the presence of non-viable cells on the ability of these systems to accurately measure contamination levels of E. coli O157:H7 in ground beef. While the PCR threshold cycle (C_T) values of these assays showed a direct correlation with the number of bacteria present in pure cultures, this was not the case for ground beef samples spiked with various levels of injured or healthy cells. Furthermore, comparison of post-enrichment cell densities of bacteria did not correlate with injured or healthy cell numbers inoculated before enrichment process. Ground beef samples spiked with injured or healthy cells at different doses could not be distinguished by C_T values from either assay. In addition, the contribution of nonviable cells in generating positive real-time PCR signals was investigated using both assays on pre-enriched and post-enriched beef samples, but only if inoculated at levels of 10⁶ cells/sample or higher, which are levels not typically seen in ground beef.     

Alicyclobacillus acidoterrestris spores as a target for Cupuaçu (Theobroma grandiflorum) nectar thermal processing: kinetic parameters and experimental methods

The kinetic parameters of thermal inactivation of a spore former, Alicyclobacillus acidoterrestris, in a tropical fruit nectar [25% of Cupua?u (Theobroma grandiflorum) pulp and 15% sugar] were determined by the isothermal method (IM), under batch heating, and by the paired equivalent isothermal exposures (PEIE) method, under non-isothermal continuous conditions. The isothermal experiments were repeated three times, every 4 months, with the same spore suspension kept frozen between experiments. The aging of spores, under frozen storage, seemed to produce a notorious increase in the z-value from experiment to experiment: Experiment 1 (z = 7.8 +/- 2.6 degrees C, D(95 degrees C) = 5.29 +/- 0.96 min), Experiment 2 (z = 22 +/- 5 degrees C, D(95 degrees C) = 5.99 +/- 0.63 min), and Experiment 3 (z =29 +/- 10 degrees C, D(95 degrees C) = 3.82 +/- 0.48 min). The evaluation of the kinetic parameters by the PEIE method was carried out in parallel with Experiment 3, with the same aged spores, and the results (z = 31 +/- 6 degrees C, D(95 degrees C) = 5.5 +/- 1.2 min) were close to the ones obtained in this experiment. From this work, it seems that the PEIE method can also be applied to evaluate the reduction parameters of a spore-forming microorganism, and in a more realistic way, since the continuous system eliminates the errors caused by come-up and cool-down times (CUT and CDT) that are unavoidable in isothermal experiments. Therefore, when designing a thermal process for a continuous system, the PEIE method should be used, or the chances are that the process would be underdesigned, risking that the desired level of spore inactivation would not be achieved. An optimization of the thermal processing conditions was next performed for Cupua?u nectar, considering a 5D reduction in A. acidoterrestris spores. If a pasteurization process is considered, the conditions that ensure safety (9 min at 98 degrees C) only allow a 55% retention of ascorbic acid (AA). If sterilization is considered, 8 s at 115 degrees C will ensure a safe product and retain 98.5% of the original ascorbic acid. Therefore, if A. acidoterrestris is considered as the target microorganism, the nectar should undergo an aseptic high temperature short time principle (HTST) process to achieve a 5D reduction in this acidophilus spore former. However, if the hot-fill-and-hold pasteurization process is preferred, the product should be fortified with ascorbic acid.     

Changes in water content of high plus hydrogel lenses worn on an extended wear basis in a geriatric aphakic population.

PURPOSE: To investigate the water content of hydrogel lenses of relatively high plus power hydrogel lenses after 3 months extended wear and compare values with unused lenses. METHOD: Geriatric aphakic extended wear soft lens patients were fitted with one of four different brands of hydrogel lenses (A) Incanto 78 (Cantor and Nissel, UK), (B) PSL72 (Prospect lenses, UK), (C) ES70 (Ocular Sciences), (D) Proclear (Coopervision). After 3 months continuous wear the lens was removed and water content (WC) was determined at both lens surfaces using an Abbé refractometer. The water content was also measured for 40 unused lenses (+10 to +20D, 10 lenses per brand). RESULTS: One hundred and thirty-two lenses were checked after 3 months extended wear. Mean (+/-S.D.) WC values for front (f) and back (b) surfaces of worn and unworn lenses were, respectively, (A) Worn (n=45): f 73.2(4.13) b 73.8(4.33); unworn f 80.5(0.68) b 81.1 (0.80). (B) Worn (n=37); f 70.5(4.49) b 70.9 (3.89); unworn f 72.5(0.94) b 72.3 (0.89). (C) Worn (n=34); f 68.3(3.18) b 68.4(3.63); unworn f 70.6 (0.48) b 71.1 (0.55). (D) Worn (n=16); f 63.4(3.68) b 63.3(3.19); unworn f 60.9 (1.56) b 61.5 (1.92). There was a significant correlation between WC measured from front and back surfaces (p < 0.01). In worn A-C lenses, front surface WC tended to be lower than back surface WC. For lenses A and C at both surfaces the WC of worn lenses was significantly lower than unworn lenses (p < 0.05). For lens D, mean WC of worn lenses was significantly higher than unworn lenses (p < 0.05). In 80% of B lenses, surface WC of worn lenses were significantly lower than WC of unworn lenses (p < 0.05). There was no relationship between WC and lens power. CONCLUSION: On average, A and C lenses tended to desiccate but D lenses tended to swell as did 20% of B lenses. The front surface of worn lenses measured lower water content than the back surface suggesting the front surface is drier than the back. This apparent difference in water content between the surfaces could be an artefact emanating from differential rates of surface deposition.     

Some practical procedures for the solution of nonlinear finite element equations

Procedures for the solution of incremental finite element equations in practical nonlinear analysis are described and evaluated. The methods discussed are employed in static analysis and in dynamic analysis using implicit time integration. The solution procedures are implemented, and practical guidelines for their use are given.     

Comparison of isolation procedures for essential oils

Summary The influence of the time of distillation on the composition of the essential oils isolated from seed of ajowan, caraway, coriander, and cumin was investigated. The oils were isolated by distillation, as well as by simultaneous distillation-extraction. It was observed that the order of recovery of the oil constituents was determined by their solubility in the distillation water. Hence, the oxygenated compounds, although with higher boiling points, distilled before the hydrocarbons. In comparison, data are included for the oils obtained by solvent extraction from ground seed of the same species. In these cases the proportion of hydro carbons was higher than in the distilled oils. There was also evidence to suggest thatp-cymene in the oils of ajowan and cumin was partly an artefact of distillation.

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Vergleich von Isolierungsverfahren ätherischer ÖleII. Ajowan, Künunel, Koriander und Kreuzkümmel

Zusammenfassung Der Einfluß der Destillationsäuer auf die Zusammensetzung der ätherischen Öle von Ajowan, Kümmel, Koriander und Kreuzkümmel wurde untersucht. Die Öle wurden sowohl durch Destillation als auch durch ein Destillation-Extraktionsverfahren isoliert. Es wurde gezeigt, daß die Reihenfolge der Ölbestandteile während der Destillation bestimmt wurde von ihrer Löslichkeit im Destillationswasser, weshalb die höher siedenden sauerstoffhaltigen Komponenten schneller als die Kohlenwasserstoffe übergehen.Zum Vergleich wurden Angaben aufgenommen für Öle, die mit organischen Lösungsmitteln aus gemahlenen Früchten extrahiert worden waren. In diesen Fällen war die Menge der Kohlenwasserstoffe höher als bei den destillierten Ölen. Es gibt Hinweise dafür, daßp-Cymol in Ajowan- und Kreuzkümmelöl teilweise ein Artefakt der Destillation ist.

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Part I: Chem. Mikrobiol. Technol. Lebensm. (in press)     

Oxidation of pyrite in coal to magnetite

When bituminous coal is heated in an inert atmosphere (He) containing small amounts of oxygen at 393–455 °C, pyrite (FeS₂) in coal is partially converted to magnetite (Fe₃0₄). The maximum amount of Fe₃0₄ formed during the time of heating corresponds to 5–20% of the total pyrite present, depending on the coal sample. The magnetite forms as an outer crust on the pyrite grains. The fact that the magnetic properties of the pyrite grains are substantially increased by the magnetite crust suggests that pyrite can be separated from coal by use of a low magnetic field. In a laboratory test, 75% removal is obtained by means of a 500 Oe magnet on three samples, and 60% on a fourth sample.     

Flour mill stream blending affects sugar snap cookie and Japanese sponge cake quality and oxidative cross-linking potential of soft white wheat

The purpose of this research was to study the functional differences between straight grade (75% extraction rate) and patent (60% extraction rate) flour blends from 28 genetically pure soft white and club wheat grain lots, as evidenced by variation in sugar snap cookie and Japanese sponge cake quality. Functional differences were examined relative to arabinoxylan content, protein content, and oxidative cross-linking potential of flour slurries. Oxidative cross-linking measurements were obtained on flour slurries with a low shear Bostwick consistometer and considered endogenous oxidative cross-linking potential (water alone) or enhanced oxidative cross-linking potential (with added hydrogen peroxide-peroxidase). A 2-way ANOVA indicated that flour blend was the greater source of variation compared to grain lot for all response variables except water-extractable arabinoxylan content. Patent flours produced larger sugar snap cookies and Japanese sponge cakes, and contained significantly less total and water-unextractable arabinoxylans, protein, and ash than did straight grade flours. Patent flours produced more viscous slurries for endogenous and enhanced cross-linking measurements compared to the straight grade flours. The functional differences between patent and straight grade flours appear to be related to the particular mill streams that were utilized in the formulation of the 2 flour blends and compositional differences among those streams.     

Biotechnology of Wheat Quality

Wheat gluten proteins are largely responsible for the visco-elastic properties that allow doughs to be processed into bread and various other food products including cakes, biscuits (cookies), pasta and noodles. Detailed biochemical and biophysical studies are revealing details of the molecular structures and interactions of the individual gluten proteins, and their roles in determining the functional properties of gluten. In particular, one group of gluten proteins, the high molecular weight (HMW) subunits of glutenin, have been studied in detail because of their role in determining the strength (elasticity) of doughs. The development of robust transformation systems for bread wheat is now allowing the role of the HMW subunits to be explored experimentally, by manipulating their amount and composition in transgenic plants. Such studies should lead to improvement of the processing properties of wheat for traditional end uses and the development of novel end uses in food processing or as raw material for other industries. © 1997 SCI.     

Characterization of O157:H7 and other Escherichia coli isolates recovered from cattle hides, feces, and carcasses

In a previous study, the seasonal prevalence was reported for stx+ Escherichia coli O157:H7 in feces and on hides and carcasses of cattle at processing. Overall, 1,697 O157:H7 isolates have now been characterized for the incidence of (i) eae(O157), hlyA, stx1, and stx2 in the recovered isolates and (ii) presumptive rough and presumptive nonmotile isolates. Seven O157:H7 isolates (0.4%) lacked stx genes, although they carried eae and hlyA. All but one of the isolates carried both eae and hlyA. Approximately two-thirds of the isolates (64% when one isolate per sample was considered) carried both stx1 and stx2. E. coli O157:H7 cells that harbored both stx1 and stx2 were more often recovered from hides in the fall (79% of the fall hide isolates) and winter (84% of the winter hide isolates) than in the spring (53%) and summer (59%). Isolates recovered from preevisceration carcasses showed a similar but not statistically significant trend. Twenty-three of the 25 O157:H7 isolates carrying stx1 but not stx2 were recovered during summer. Fifteen presumptive rough and 117 presumptive nonmotile stx+ O157:H7 isolates were recovered. Ten (67%) of the presumptive rough isolates were recovered during summer. Ninety-five of the presumptive nonmotile isolates (81%) were recovered during fall. Forty-eight percent of the false-positive isolates (175 of 363) tentatively identified as O157:H7 were O157+ H7- and lacked eae(O157), hlyA, and stx. These data suggest that in beef processing samples (i) there are minor seasonal variations in the prevalence of stx genes among E. coli O157:H7 isolates, (ii) presumptive rough and presumptive nonmotile stx+ O157:H7 isolates are present, (iii) E. coli O157:H7 isolates lacking stx genes may be rare, and (iv) O157+ H7- isolates lacking stx genes can result in many false-positive results.