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Biomedical subjects

M P Doyle

Publications and source records attributed to M P Doyle.

At least 37 records · Page 2Linked to original sources
PubMed2001

Survival of salmonellae in pasteurized, refrigerated calcium-fortified orange juice.

Studies were done to determine the survival of salmonellae in orange juice as affected by fortification with calcium. Four brands of commercially pasteurized orange juice fortified with calcium (350 mg/240-ml serving) and nonfortified juice were inoculated separately with three types of inocula: strains of Salmonella Muenchen (inoculum 1), serotypes of human and animal origin (inoculum 2), and isolates from raw produce- and juice-associated outbreaks (inoculum 3). Juice inoculated with populations of 6.6 to 7.0 log10 CFU of Salmonella per ml was held at 4 degrees C for up to 32 days. The number of cells of inoculum 1 that survived in juice fortified with calcium lactate/tricalcium phosphate (CaL/TCP) was significantly lower (P < or = 0.05) (2.80 log10 CFU/ml) than in nonfortified juice (3.50 log10 CFU/ml) after 32 days' storage. Death of salmonellae in inocula 1 and 2 was less in juice fortified with TCP (3.21 and 3.33 log10 CFU/ml, respectively) than in the nonfortified juice (3.75 and 4.15 log10 CFU/ml, respectively). During the 32-day storage period, populations in inocula 1 and 3 showed significantly less inactivation (2.62 and 3.12 log10 CFU/ml, respectively) in juice fortified with calcium citrate (CC) than in nonfortified juice (3.14 and 3.60 log10 CFU/ml, respectively). There were no significant differences in the survival of Salmonella in juice fortified with calcium citrate malate (CCM) and nonfortified juice. Polymerase chain reaction (PCR) typing of randomly selected Salmonella colonies revealed that Salmonella Heidelberg in inoculum 2 and Salmonella Baildon and Salmonella Poona in inoculum 3 were the most prevalent at the end of the 32-day storage period at 4 degrees C, suggesting that serotypes selected for use in inocula differed in tolerance to acidic environments. This study reveals that the form of calcium used to fortify orange juice may affect the survival of Salmonella.

Animals↗
PubMed2000

Selectivity in reactions of allyl diazoacetates as a function of catalyst and ring size from gamma-lactones to macrocyclic lactones.

Catalytic reactions of diazoacetates tethered through zero, one, two, and three ethylene glycol units to an allyl group have been investigated for chemoselectivity, diastereoselectivity, and enantioselectivity. Results from cyclopropanation, carbon-hydrogen insertion, and oxonium ylide generation are compared from reactions of achiral and chiral catalysts of copper(I) and dirhodium(II) carboxylates and carboxamidates. Relative to results from intermolecular reactions of ethyl diazoacetate with allyl ethyl ether, intermolecular reactions show a diversity of selectivities including preference for the opposite configurational arrangement from the one preferred in corresponding intermolecular cyclopropanation reactions. Enantioselectivities for cyclopropanation are dependent on the catalyst ligands in a manner that reflects divergent trajectories of the carbon-carbon double bond to the reacting carbene center. Enantioselectivity increases as a function of ring size with chiral copper catalysts, but the reverse occurs with chiral dirhodium(II) carboxamidates. Mechanistic implications, including those related to the conformation of the reacting metal carbene, offer a new dimension to understanding of enantioselectivity in catalytic asymmetric cyclopropanation reactions.

Allyl Compounds↗
PubMed2000

A new approach to macrocyclization via alkene formation in catalytic diazo decomposition. Synthesis of patulolides A and B.

[reaction: see text] Effective synthetic uses of bisdiazocarbonyl compounds for the selective construction of diverse macrocycles, including the synthesis of patulolides A and B, by catalytic "carbene dimer" formation are reported. Control of stereochemistry and efficient methods for product isomerization or kinetic isomer differentiation have been achieved.

Alkenes↗
PubMed2000

Genomic typing of Escherichia coli O157:H7 by semi-automated fluorescent AFLP analysis.

Escherichia coli serotype O157:H7 isolates were analyzed using a relatively new DNA fingerprinting method, amplified fragment length polymorphism (AFLP). Total genomic DNA was digested with two restriction endonucleases (EcoRI and MseI), and compatible oligonucleotide adapters were ligated to the ends of the resulting DNA fragments. Subsets of fragments from the total pool of cleaved DNA were then amplified by the polymerase chain reaction (PCR) using selective primers that extended beyond the adapter and restriction site sequences. One of the primers from each set was labeled with a fluorescent dye, which enabled amplified fragments to be detected and sized automatically on an automated DNA sequencer. Three AFLP primer sets generated a total of thirty-seven unique genotypes among the 48 E. coli O157:H7 isolates tested. Prior fingerprinting analysis of large restriction fragments from these same isolates by pulsed-field gel electrophoresis (PFGE) resulted in only 21 unique DNA profiles. Also, AFLP fingerprinting was successful for one DNA sample that was not typable by PFGE, presumably because of template degradation. AFLP analysis, therefore, provided greater genetic resolution and was less sensitive to DNA quality than PFGE. Consequently, this DNA typing technology should be very useful for genetic subtyping of bacterial pathogens in epidemiologic studies.

Animals↗
PubMed2000

Growth supplements for Helicobacter pylori.

The growth response of Helicobacter pylori in broth was determined in the presence of ferrous sulfate, sodium pyruvate, and mucin (porcine stomach). The addition of either ferrous sulfate and sodium pyruvate or mucin to brain heart infusion broth with 7% horse serum (BHI-HS) enhanced the growth of H. pylori. The best growth of strain NB2-1, which was the slowest growing of 10 H. pylori strains evaluated, occurred in the presence of 0.05% ferrous sulfate and 0.05% sodium pyruvate. The addition of 0.3% mucin to BHI-HS reduced the lag time of H. pylori by 48 h and enhanced the growth. On the basis of the results for 10 H. pylori strains, the combination of ferrous sulfate (0.025%), sodium pyruvate (0.025%), and mucin (0.15%) in BHI-HS counteracted the inhibitory effects of the antibiotics used in culture media for selective growth of H. pylori. Results suggest that these supplements may be useful for enhancement of the growth of H. pylori in enrichment media.

Aerobiosis↗
PubMed2000

Fate of Campylobacter jejuni in butter.

An outbreak of Campylobacter enteritis was associated with a restaurant in Louisiana during the summer of 1995. Thirty cases were identified, and four required hospitalization. Campylobacter jejuni was isolated from the patients, and epidemiologic studies revealed illness associated with eating garlic butter served at the restaurant. Three batches of garlic butter prepared by the restaurant associated with the outbreak and a C. jejuni isolate obtained from a patient involved in the outbreak were used for studies to determine the fate of C. jejuni in garlic butter. Studies also were done to determine the efficacy of the heat treatment used by the restaurant to prepare garlic bread to kill C. jejuni. Garlic butter was inoculated with approximately 10(4) and 10(6) CFU/g of C. jejuni and held at 5 or 21 degrees C. Results revealed that the survival of C. jejuni differed greatly, depending on the presence or absence of garlic. At 5 degrees C, C. jejuni populations decreased to an undetectable level (<10 CFU/g) within 3 h for two batches and within 24 h for another batch. In contrast, C. jejuni could survive at 5 degrees C for 13 days in butter with no garlic. At 21 degrees C, C. jejuni populations decreased to an undetectable level within 5 h for two batches and to 50 CFU/g in 5 h for another batch. In contrast, C. jejuni was detected at 500 CFU/g at 28 h after inoculation but was undetectable at 3 days in butter with no garlic held at 21 degrees C. The heating procedure (135 degrees C, 4 min) used to make garlic bread by the implicated restaurant was determined not to be sufficient for killing C. jejuni, with the internal temperature of the buttered bread after heating ranging from 19 to 22 degrees C. This study revealed that C. jejuni can survive for many days in refrigerated butter, but large populations (10(3) to 10(5) CFU/g) are killed within a few hours in butter that contains garlic. Furthermore, the heat treatment used by the restaurant to melt garlic butter in making garlic bread was not adequate to kill C. jejuni.

Animals↗
PubMed2000

Effects of diet on rumen proliferation and fecal shedding of Escherichia coil O157:H7 in calves.

Calves inoculated with Escherichia coli O157:H7 and fed either a high-roughage or high-concentrate diet were evaluated for rumen proliferation and fecal shedding of E. coli O157:H7. Calves fed the high-roughage diet had lower mean rumen volatile fatty acid concentrations and higher rumen pH values than did calves fed the high-concentrate diet. Despite these differences in rumen conditions, the calves fed the high-roughage diet did not have greater rumen populations of E. coli O157: H7 and did not exhibit increased or longer fecal shedding compared with the calves fed the high-concentrate diet. Two calves shedding the highest mean concentrations of E. coli O157:H7 were both fed the high-concentrate diet. There was a significant (P < 0.05) positive correlation between fecal shedding and rumen volatile fatty acid concentration in calves fed a high-concentrate diet. The effects of diet on E. coli O157:H7 proliferation and acid resistance were investigated using an in vitro rumen fermentation system. Rumen fluid collected from steers fed a high-roughage diet, but not from steers fed a high-concentrate diet, supported the proliferation of E. coli O157:H7. Rumen fluid from steers fed a high-concentrate diet rapidly induced acid resistance in E. coli O157:H7. The impact of diet on fecal shedding of E. coli O157:H7 is still unclear and may depend on dietary effects on fermentation in the colon and on diet-induced changes in the resident microflora. However, rapid development of acid tolerance by E. coli O157:H7 in the rumens of calves fed high-concentrate diets, allowing larger populations to survive passage through the acidic abomasum to proliferate in the colon, may be one factor that influences fecal shedding in cattle on feed.

Animal Feed↗
PubMed2000

Fate of Shigella sonnei on parsley and methods of disinfection.

Outbreaks of shigellosis associated with chopped parsley used as a garnish for foods occurred in four states in the United States and in two Canadian provinces in 1998. This prompted a study to determine survival and growth characteristics of Shigella sonnei inoculated onto raw parsley. Two inoculum levels (approximately 10(3) and 10(6) CFU/g) were applied to parsley leaves, portions of which were then chopped. Inoculated whole and chopped parsley leaves were held at 4 degrees C or 21 degrees C for up to 14 days. Initial populations of the organism on chopped parsley receiving high or low levels of inoculum increased by approximately 3 log10 CFU/g, within 1 day at 21 degrees C. Populations of S. sonnei on inoculated chopped or whole parsley leaves held at 4 degrees C decreased by 2.5 to 3.0 log10 CFU/g during a 14-day storage period. The pathogen multiplied, without a lag phase, on inoculated (2.72 log10 CFU/g) chopped parsley held at 21 degrees C, exceeding 6 log10 CFU/g within 24 h. Treatment of inoculated whole parsley leaves with vinegar containing 5.2% (vol/vol) acetic acid or 200 ppm free chlorine for 5 min at 21 degrees C reduced the population of S. sonnei by more than 6 log10 CFU/g, whereas treatment with vinegar containing 7.6% acetic acid or 250 ppm free chlorine reduced initial populations of 7.07 and 7.26 log10 CFU/g, respectively, to undetectable levels (<0.6 log10 CFU/g). These studies revealed that S. sonnei can grow rapidly on chopped parsley held at ambient temperature and remain viable for at least 14 days at 4 degrees C. Treatment of contaminated parsley with vinegar or chlorinated water offers a simple method to reduce markedly or eliminate the pathogen in food-service or home settings.

Acetic Acid↗
PubMed1999

Glutaraldehyde modification of recombinant human hemoglobin alters its hemodynamic properties.

Many cell-free hemoglobin solutions designed as oxygen-carrying therapeutics produce a hypertensive effect in animals. The response is likely due to oxidation of nitric oxide by hemoglobin. Since the site of oxidation may lie outside the vascular compartment, we tested the hypothesis that polymerization of hemoglobin, rHb1.1, by glutaraldehyde would attenuate the hypertensive response. Two products of the cross-linking reaction were isolated, a glutaraldehyde-derivatized monomer (mono-glxrHb) and a glutaraldehyde cross-linked polymer (poly-glxrHb), and evaluated for their effects on systemic hemodynamics in conscious rats. Administration of rHb1.1 caused a mean arterial pressure elevation of approximately 20 mm Hg and an increase in total peripheral resistance of approximately 30%. Administration of mono-glxrHb induced changes in mean arterial pressure and vascular resistance that were significantly diminished relative to those observed with rHb1.1. Poly-glxrHb elicited a mean arterial pressure response that was further reduced compared with that obtained with mono-glxrHb and a change in vascular resistance that was the same as the response to mono-glxrHb. These results suggest that rHb peripheral vasoconstriction elicited by rHb1.1 is significantly attenuated by glutaraldehyde modification of the hemoglobin monomer and that the effect of glutaraldehyde polymerization is likely due to surface modification and/or intramolecular cross-linking, rather than an increase in molecular size.

Animals↗
PubMed1999

Lessons from a large outbreak of Escherichia coli O157:H7 infections: insights into the infectious dose and method of widespread contamination of hamburger patties.

Between November 1992 and February 1993, a large outbreak of Escherichia coli O157:H7 infections occurred in the western USA and was associated with eating ground beef patties at restaurants of one fast-food chain. Restaurants that were epidemiologically linked with cases served patties produced on two consecutive dates; cultures of recalled ground beef patties produced on those dates yielded E. coli O157:H7 strains indistinguishable from those isolated from patients, confirming the vehicle of illness. Seventy-six ground beef patty samples were cultured quantitatively for E. coli O157:H7. The median most probable number of organisms was 1.5 per gram (range, < 0.3-15) or 67.5 organisms per patty (range, < 13.5-675). Correlation of the presence of E. coli O157:H7 with other bacterial indicators yielded a significant association between coliform count and the presence of E. coli O157:H7 (P = 0.04). A meat traceback to investigate possible sources of contamination revealed cattle were probably initially colonized with E. coli O157:H7, and that their slaughter caused surface contamination of meat, which once combined with meat from other sources, resulted in a large number of contaminated ground beef patties. Microbiological testing of meat from lots consumed by persons who became ill was suggestive of an infectious dose for E. coli O157:H7 of fewer than 700 organisms. These findings present a strong argument for enforcing zero tolerance for this organism in processed food and for markedly decreasing contamination of raw ground beef. Process controls that incorporate microbiological testing of meat may assist these efforts.

Animals↗
PubMed1999

Comparison of six dose-response models for use with food-borne pathogens.

Food-related illness in the United States is estimated to affect over six million people per year and cost the economy several billion dollars. These illnesses and costs could be reduced if minimum infectious doses were established and used as the basis of regulations and monitoring. However, standard methodologies for dose-response assessment are not yet formulated for microbial risk assessment. The objective of this study was to compare dose-response models for food-borne pathogens and determine which models were most appropriate for a range of pathogens. The statistical models proposed in the literature and chosen for comparison purposes were log-normal, long-logistic, exponential, beta-Poisson and Weibull-Gamma. These were fit to four data sets also taken from published literature, Shigella flexneri, Shigella dysenteriae, Campylobacter jejuni, and Salmonella typhosa, using the method of maximum likelihood. The Weibull-gamma, the only model with three parameters, was also the only model capable of fitting all the data sets examined using the maximum likelihood estimation for comparisons. Infectious doses were also calculated using each model. Within any given data set, the infectious dose estimated to affect one percent of the population ranged from one order of magnitude to as much as nine orders of magnitude, illustrating the differences in extrapolation of the dose response models. More data are needed to compare models and examine extrapolation from high to low doses for food-borne pathogens.

Food Microbiology↗
PubMed1999

Efficacy of electrolyzed oxidizing water for inactivating Escherichia coli O157:H7, Salmonella enteritidis, and Listeria monocytogenes.

The efficacy of electrolyzed oxidizing water for inactivating Escherichia coli O157:H7, Salmonella enteritidis, and Listeria monocytogenes was evaluated. A five-strain mixture of E. coli O157:H7, S. enteritidis, or L. monocytogenes of approximately 10(8) CFU/ml was inoculated in 9 ml of electrolyzed oxidizing water (treatment) or 9 ml of sterile, deionized water (control) and incubated at 4 or 23 degrees C for 0, 5, 10, and 15 min; at 35 degrees C for 0, 2, 4, and 6 min; or at 45 degrees C for 0, 1, 3, and 5 min. The surviving population of each pathogen at each sampling time was determined on tryptic soy agar. At 4 or 23 degrees C, an exposure time of 5 min reduced the populations of all three pathogens in the treatment samples by approximately 7 log CFU/ml, with complete inactivation by 10 min of exposure. A reduction of >/=7 log CFU/ml in the levels of the three pathogens occurred in the treatment samples incubated for 1 min at 45 degrees C or for 2 min at 35 degrees C. The bacterial counts of all three pathogens in control samples remained the same throughout the incubation at all four temperatures. Results indicate that electrolyzed oxidizing water may be a useful disinfectant, but appropriate applications need to be validated.

Colony Count, Microbial↗
PubMed1999

Microbiological quality and production of botulinal toxin in film-packaged broccoli, carrots, and green beans.

The production of toxin by a 10-strain mixture of proteolytic Clostridium botulinum in fresh produce packaged in polyethylene films with different oxygen permeability was determined. Broccoli florets, shredded carrots, and green beans inoculated with approximately 10(2) C. botulinum spores per g were placed in bags (1.4 kg per bag) composed of four films with different oxygen transmission rates (OTRs). Broccoli was packaged in bags with OTRs of 3 (7,000 cm3/m2/24 h) and 4 (16,000 cm3/m2/24 h), and green beans were packaged in bags with OTRs of 2 (6,000 cm3/m2/24 h) and 4. Broccoli and green beans in bags were compressed and heat-sealed. Shredded carrots were packaged in bags with OTRs of 1 (3,000 cm3/m2/24 h) and 3 and vacuum-sealed. Produce was stored at 4, 13, and 21 degrees C for up to 27 (broccoli) or 28 (carrots and green bean) days and analyzed periodically. At each sampling time, gas composition within the bags, pH of the produce microbial population (total aerobic and anaerobic microorganisms, lactic acid bacteria, psychrotrophic bacteria, yeasts, and molds), and the presence or absence of botulinal toxin were determined. Packaging material affected the quality of vegetables, especially broccoli stored at 4 and 13 degrees C. For example, broccoli was scored as "good" after 22 days at 4 degrees C when it was packaged in film with higher gas permeability (OTR of 4), whereas broccoli appeared to be in "poor" condition when packaged in film with lower gas permeability (OTR of 3). With the exception of lactic acid bacteria, packaging material did not noticeably influence the growth of microorganisms. Lactic acid bacteria grew better in broccoli packaged in bags with an OTR of 3 than in those with an OTR of 4 at all temperatures. Botulinal toxin was detected in broccoli packaged in bags with an OTR of 3 and stored at 13 degrees C for 21 days and in those with an OTR of 4 and 3 and stored at 21 degrees C for 10 days. All toxic samples were visibly spoiled. Toxin was not detected in produce packaged under any other test conditions.

Botulinum Toxins↗
PubMed1999

Fecal shedding and rumen growth of Escherichia coli O157:H7 in fasted calves.

Nine weaned calves aged from 8 to 12 weeks were fitted with rumen cannulas and were inoculated by cannula with 10(10) CFU of a five-strain mixture of nalidixic acid-resistant Escherichia coli O157:H7. Six calves were fasted for 48 h on days 15 and 16 and days 22 and 23 after inoculation. Samples of rumen contents and feces were obtained daily to enumerate E. coli O157:H7 populations and to determine rumen volatile fatty acid (VFA) concentrations and rumen pH. Fasting resulted in a marked decrease in rumen VFA concentrations from a mean of 135 mmol/liter before the fast to a mean of 35 mmol/liter during the second day of the fast. However, there was no correlation between daily VFA concentration and daily rumen or fecal numbers of E. coli O157:H7 in any of the calves. Fasting generally had no significant effect on the rumen or fecal numbers of E. coli O157:H7. The exception was a single fasted calf that experienced a 3-log(10) CFU/g increase in fecal shedding during and after the first fast. Despite the consistent changes in VFA concentrations in fasted calves, the fluctuations in rumen numbers of E. coli O157:H7 in the rumen of fasted calves were minimal. At the end of the experiment, E. coli O157:H7 was detected in either the rumen or omasum in two of three control calves at necropsy and in either the rumen or reticulum in five of six fasted calves. E. coli O157:H7 was detected in the colon in two of three control calves and in six of six fasted calves at necropsy. These results suggest that in cattle already shedding E. coli O157:H7, feed withdrawal and the associated changes in rumen pH and VFA concentrations have little effect on fecal shedding and rumen proliferation of E. coli O157:H7.

Animals↗
PubMed1999

Antibacterial effect of lactoferricin B on Escherichia coli O157:H7 in ground beef.

The antibacterial activity of lactoferricin B on enterohemorrhagic Escherichia coli O157:H7 in 1% peptone medium and ground beef was studied at 4 and 10 degrees C. In 1% peptone medium, 50 and 100 microg of lactoferricin B per ml reduced E. coli O157:H7 populations by approximately 0.7 and 2.0 log CFU/ml, respectively. Studies comparing the antibacterial effect of lactoferricin B on E. coli O157:H7 in 1% peptone at pH 5.5 and 7.2 did not reveal any significant difference (P > 0.5) at the two pH values. Lactoferricin B (100 microg/g) reduced E. coli O157:H7 population in ground beef by about 0.8 log CFU/g (P < 0.05). No significant difference (P > 0.5) was observed in the total plate count between treatment and control ground beef samples stored at 4 and 10 degrees C. The antibacterial effect of lactoferricin B on E. coli O157:H7 observed in this study is not of sufficient magnitude to merit its use in ground beef for controlling the pathogen.

Animals↗
PubMed1999

Fate of Escherichia coli O157:H7 and Salmonella Enteritidis on currency.

The fate of foodborne pathogens Escherichia coli O157:H7 and Salmonella Enteritidis on coin surfaces was determined at room temperature (25 degrees C). A five-strain mixture of E. coli O157:H7 or Salmonella Enteritidis of approximately 5 x 10(4) CFU was applied to the surfaces of sterile U.S. coins (pennies, nickels, dimes, and quarters) and to the surfaces of two control substrata (Teflon and glass coverslips). During storage at room temperature, E. coli O157:H7 survived for 7, 9, and 11 days on the surfaces of pennies, nickels, and dimes and quarters, respectively. However, the pathogen died off within 4 to 7 days on both the Teflon and glass surfaces. Salmonella Enteritidis survived for 1, 2, 4, and 9 days on the surfaces of pennies, nickels, quarters, and dimes, respectively. Unlike E. coli O157:H7, survival of Salmonella Enteritidis was greatest on both Teflon and glass coverslips, with more than 100 cells per substratum detected at the 17th day of storage. Results indicate that coins could serve as potential vehicles for transmitting both E. coli O157:H7 and Salmonella Enteritidis.

Colony Count, Microbial↗