Biomedical subjects

R L Buchanan

Publications and source records attributed to R L Buchanan.

At least 19 recordsLinked to original sources

PubMed2006

Determining the microbiological criteria for lot rejection from the performance objective or food safety objective.

The Microbiological Criteria (MC) is a set of parameters used to determine whether a specific lot of food is acceptable or not. These parameters are the microbial test protocol and its sensitivity, the confidence level that an unacceptable lot will be detected, the number of samples to be taken and the number of positive samples that are allowed before rejecting the lot. Determining the microbiological criteria begins with knowledge of the distribution of contamination from samples within a lot, particularly within a lot that is just at the unacceptable level of the microbial hazard. The just unacceptable lot can be defined by the Food Safety Objective (FSO) or Performance Objectives (PO), the small fraction of samples that can exceed these values and the standard deviation of the samples from the lot. With this information, a microbial test protocol is chosen to have a sensitivity level that would detect between approximately 15% and 45% of the samples. A confidence level for the MC and the number of positive samples that would be acceptable (c value which is usually zero) are also chosen. With this information the number of samples (n) required can be calculated. A critical factor in setting the microbiological criteria is the sensitivity of the microbiological test (m value). The sample size (weight) and sampling procedure can affect the standard deviation of the samples, particularly foods with non-homogeneous distribution and low numbers of microorganisms. Sampling, sample preparation and analytical procedures that reduce the variation between the samples will affect the choice of m value and maximum lot mean that meets the MC.

Colony Count, Microbial↗

PubMed2000

Microbial risk assessment: dose-response relations and risk characterization.

Characterizations of the risks associated with foodborne pathogens are dependent on the availability of information on the population's exposure to the biological agents. However, by itself, exposure data are insufficient to assess the public health impact of pathogenic microorganisms. This requires the availability of effective dose-response models. Successful development of models that describe dose-response relations for enteric pathogens is dependent on a sound understanding of the mechanisms of pathogenicity associated with individual pathogens. This includes knowledge of how the various pathogen, host, and food matrix factors influence pathogenicity. Currently, a group of sigmoidal mathematical equations are used to empirically describe dose-response relations. While these have proven to be highly useful, advances in microbial food safety risk assessment will likely require the development of mechanistic models that more effectively consider the range of factors that influence the frequency and severity of foodborne infections in a population.

Animals↗

PubMed2000

Acquisition of microbiological data to enhance food safety.

The routine acquisition and archiving of microbiological data is undertaken for two reasons. The first is the development of historical microbiological profiles of foods, ingredients, or processes in order to determine or verify that microorganisms of concern are being controlled to the level desired. The second reason is data concerning the pathogenicity or virulence of foodborne pathogens and their behavior in foods in order to develop strategies and criteria for assuring microbiological safety. Both types of microbiological data are essential to effective food safety programs. A firm understanding of the uses and limitations of both is essential to correct acquisition, interpretation, and use of such data.

Databases, Factual↗

PubMed1999

Fate of Escherichia coli O157:H7 on fresh-cut apple tissue and its potential for transmission by fruit flies.

Pathogenic Escherichia coli O157:H7, as well as nonpathogenic strains ATCC 11775 and ATCC 23716, grew exponentially in wounds on Golden Delicious apple fruit. The exponential growth occurred over a longer time period on fruit inoculated with a lower concentration of the bacterium than on fruit inoculated with a higher concentration. The bacterium reached the maximum population supported in the wounds regardless of the initial inoculum concentrations. Populations of E. coli O157:H7 in various concentrations of sterilized apple juice and unsterilized cider declined over time and declined more quickly in diluted juice and cider. The decline was greater in the unsterilized cider than in juice, which may have resulted from the interaction of E. coli O157:H7 with natural populations of yeasts that increased with time. Experiments on the transmission of E. coli by fruit flies, collected from a compost pile of decaying apples and peaches, were conducted with strain F-11775, a fluorescent transformant of nonpathogenic E. coli ATCC 11775. Fruit flies were easily contaminated externally and internally with E. coli F-11775 after contact with the bacterium source. The flies transmitted this bacterium to uncontaminated apple wounds, resulting in a high incidence of contaminated wounds. Populations of the bacterium in apple wounds increased significantly during the first 48 h after transmission. Further studies under commercial conditions are necessary to confirm these findings.

Animals↗

PubMed1999

pH-dependent stationary-phase acid resistance response of enterohemorrhagic Escherichia coli in the presence of various acidulants.

The effect of acidulant identity on the pH-dependent stationary-phase acid resistance response of enterohemorrhagic Escherichia coli was studied. Nine strains of E. coli (seven O157:H7, one O111:H-, and one biotype 1 reference strain) were cultured individually for 18 h at 37 degrees C in tryptic soy broth (TSB) plus 1% dextrose and in TSB without dextrose to yield acid resistance induced and noninduced stationary-phase cells, respectively. These cultures were then inoculated into brain heart infusion broth (BHI) supplemented with 0.5% citric, malic, lactic, or acetic acid and adjusted to pH 3.0 with HCl. The BHI tubes were incubated at 37 degrees C for up to 7 h and samples were removed after 0, 2, 5, and 7 h and plated for counting CFU on BHI agar and MacConkey agar (MA). The results were compared to data previously obtained with HCl only. Acid resistance varied substantially among the isolates, being dependent on the strain, the acidulant, and the induction of pH-dependent acid resistance. Hydrochloric acid was consistently the least damaging to cells; lactic acid was the most detrimental. The relative activity of the other acids was strain dependent. Inducing pH-dependent acid resistance increased the already substantial acid tolerance of stationary-phase E. coli. The extent of injury also varied with acid and strain, with as much as a 5-log-cycle differential between BHI agar and MA CFU counts. The accurate determination of the survival of enterohemorrhagic E. coli in acidic foods must take into account the biological variability of the microorganism with respect to its acid resistance and its ability to enhance survival through the induction of physiological stress responses.

Acids, Acyclic↗

PubMed1999

Effects of pH and acid resistance on the radiation resistance of enterohemorrhagic Escherichia coli.

The effects of pH and the induction of pH-dependent stationary-phase acid resistance on the radiation resistance of Escherichia coli were determined for seven enterohemorrhagic strains and one nonenterohemorrhagic strain. The isolates were grown in acidogenic or nonacidogenic media to pH levels of approximately 4.7 and 7.2, respectively. The cells were then transferred to brain heart infusion (BHI) broth adjusted to pH 4.0, 4.5, 5.0, and 5.5 (with HCl) that was preequilibrated to 2 degrees C, and cultures were then irradiated using a 137Cs source. Surviving cells and the extent of injury were determined by plating on BHI and MacConkey agars both immediately after irradiation and after subsequent storage at 2 degrees C for 7 days. Decreasing the pH of the BHI in which E. coli was irradiated had relatively little effect on the microorganism's radiation resistance. Substantial differences in radiation resistance were noted among strains, and induction of acid resistance consistently increased radiation resistance. Comparison of E. coli levels immediately after irradiation and after 7 days of refrigerated storage suggested that irradiation enhanced pH-mediated inactivation of the pathogen. These results demonstrate that prior growth under conditions that induce a pH-dependent stationary phase cross-protects E. coli against radiation inactivation and must be taken into account when determining the microorganism's irradiation D value.

Acids, Acyclic↗

PubMed1999

Contamination of intact apples after immersion in an aqueous environment containing Escherichia coli O157:H7.

The extent and location of Escherichia coli O157:H7 contamination after intact apples were immersed in cold (2 degrees C) 1% peptone water containing approximately 3x10(7) CFU/ml was assessed using four apple varieties, Golden Delicious, McIntosh, Red Delicious, and Braeburn. Room temperature and refrigerated apples were used to determine the effect of temperature differential on E. coli infiltration. The highest levels of E. coli were associated with the outer core region of the apple, followed by the skin. Apples were subsequently treated by immersing them for 1 min in 2,000 mg/liter sodium hypochlorite, followed by a 1-min tapwater rinse. This treatment reduced pathogen levels by 1- to 3-log cycles but did not eliminate the microorganism, particularly from the outer core region. While E. coli was not detected in the inner core of most apples, warm fruit immersed in cold peptone water occasionally internalized the pathogen. The frequency and extent of internalization of the pathogen was less when cold apples were immersed in cold peptone water. Subsequent dye uptake studies with Golden Delicious apples indicated that approximately 6% of warm apples immersed into a cold dye solution accumulated dye via open channels leading from the blossom end into the core region. However, dye uptake did not occur when the dye solution was warmer than the apple.

Coloring Agents↗

PubMed1998

Inactivation of Escherichia coli O157:H7 in apple juice by irradiation.

Three strains (932, Ent-C9490, and SEA13B88) of Escherichia coli O157:H7 were used to determine the effectiveness of low-dose gamma irradiation for eliminating E. coli O157:H7 from apple juice or cider and to characterize the effect of inducing pH-dependent, stationary-phase acid resistance on radiation resistance. The strains were grown in tryptic soy broth with or without 1% dextrose for 18 h to produce cells that were or were not induced to pH-dependent stationary-phase acid resistance. The bacteria were then transferred to clarified apple juice and irradiated at 2 degrees C with a cesium-137 irradiator. Non-acid-adapted cells had radiation D values (radiation doses needed to decrease a microbial population by 90%) ranging from 0.12 to 0.21 kGy. D values increased to 0.22 to 0.31 kGy for acid-adapted cells. When acid-adapted SEA13B88 cells were tested in five apple juice brands having different levels of suspended solids (absorbances ranging from 0.04 to 2.01 at 550 nm), radiation resistance increased with increasing levels of suspended solids, with D values ranging from 0.26 to 0.35 kGy. Based on these results, a dose of 1.8 kGy should be sufficient to achieve the 5D inactivation of E. coli recommended by the National Advisory Committee for Microbiological Criteria for Foods.

Beverages↗

PubMed1998

Risk assessment: a means for linking HACCP plans and public health.

HACCP plan adoption has greatly enhanced the food industry's ability to systematically design programs to ensure the microbiological safety of foods. Yet, this widening acceptance of the HACCP system has revealed several areas where its application is limited due to reliance on qualitative consideration of hazards and their control. In particular, HACCP planning is limited both conceptually and practically by its inability to quantify the potential combined influence of multiple control-point deviations and to relate the successful operation of a HACCP system to a measurable public-health impact. Recent advances in quantitative microbiological risk assessment appear to offer a means of overcoming these limitations. The integration of HACCP plans with the development of dynamic risk-assessment models offers a means for considering the entire farm-to-table continuum and for relating food-manufacturing operations to public health goals. Such capabilities may be critical to establishing equivalence among HACCP systems.

Food Handling↗

PubMed1997

Development of a quantitative risk assessment model for Salmonella enteritidis in pasteurized liquid eggs.

The performance of hazard analyses and the establishment of critical limits by the food industry are both hampered by the inability to directly relate food processing operations from farm-to-table with their public health impact. Using a 'unit operations' and stochastic simulation approach, data on the frequency of pathogens in raw ingredients, predictive microbiology models for growth and inactivation (thermal and non-thermal), and dose-response models for infectivity were integrated to create a quantitative risk assessment model for a Salmonella enteritidis infection from thermally processed liquid whole eggs made into mayonnaise in the home. The risk assessment indicated pasteurization provides sufficient consumer protection from a high incidence of infected birds and from temperature abuse between the farm and the egg breakers. However scenarios showed how inadequate pasteurization temperatures and/or temperature abuse during storage leads to a hazardous product. This dynamic approach to modeling risk should aid in identification and setting critical control points and assessing the impact of altering food formulations or processes.

Eggs↗

PubMed1997

Expanded models for the non-thermal inactivation of Listeria monocytogenes.

Previously developed four-variable response surface models for describing the effects of temperature, pH/lactic acid, sodium chloride and sodium nitrite on the time to achieve a 4-log, non-thermal inactivation (t4D) of Listeria monocytogenes in aerobic, acidic environments were expanded to five-variable models that distinguish the effects of pH and acidulant concentration. A total of 18 new variable combinations were evaluated and the inactivation kinetics data appended onto a consolidation of two data sets from earlier studies. The consolidated data set, which included 315 inactivation curves representing 209 unique combinations of the five variables, was analysed by response surface analysis. The quadratic model without backward elimination regression was selected for further evaluation. Three additional quadratic models were generated using the concentrations of undissociated lactic and/or nitrous acids as variables in place of percentage lactic acid and sodium nitrite concentration. Comparison of predicted t4D values against literature values for various food systems indicated that the models provide reasonable initial estimates of the inactivation of L. monocytogenes. The models based on the concentration of undissociated lactic and nitrous acids support the hypothesis that antimicrobial activity is associated with this form of the compounds. Evaluation of several examples suggests that these models may be useful for predicting the equivalent of the compounds' "minimal inhibitory concentrations' for accelerating inactivation under various conditions.

Aerobiosis↗

PubMed1996

Culturing enterohemorrhagic Escherichia coli in the presence and absence of glucose as a simple means of evaluating the acid tolerance of stationary-phase cells.

Prior growth of seven enterohemorrhagic and one nonenterohemorrhagic strains of Escherichia coli in tryptic soy broth with (TSB+G) and without (TSB-G) 1% glucose was evaluated for its effect on acid tolerance. The final pHs of 18-h TSB+G and TSB-G cultures were 4.6 to 5.2 and 6.9 to 7.0, respectively. Cells were then transferred to brain heart infusion broth adjusted to pH 2.5 or 3.0 with HCl, incubated at 37 degrees C for up to 7 h, and assayed periodically for viable populations with brain heart infusion and MacConkey agars. All enterohemorrhagic strains were acid resistant (< 0.5 log decline after 7 h) when initially cultured in TSB+G, but substantial differences in acid tolerance were observed among strains cultured in TSB-G (log declines ranged from < 0.3 to > 3.8). The results indicated that prior growth in a medium with and without a fermentable carbohydrate is a convenient way to studying the induction of acid tolerance, that acid inactivation is preceded by a period of acid injury, and that pH-independent and pH-dependent stationary-phase acid tolerance phenotypes may exist among strains of enterohemorrhagic E. coli.

Acids↗

PubMed1995

Expanded response surface model for predicting the effects of temperatures, pH, sodium chloride contents and sodium nitrite concentrations on the growth rate of Yersinia enterocolitica.

The previously reported data set for the low temperature (5, 12 and 19 degrees C) of Yersinia enterocolitica was expanded to include higher abusive temperature (28, 37 and 42 degrees C). In addition to temperature, the data set included the effects and interactions of pH (4.5-8.5), sodium chloride (0.5-5%) and sodium nitrite (0-200 micrograms ml-1) on the aerobic growth of Y. enterocolitica in brain heart infusion broth. Growth curves were modeled by fitting viable count data to the Gompertz equation. Quadratic models of natural logarithm transformations of the Gompertz B and M values and the derived values for lag phase durations and generation times were obtained using response surface analyses. Predictions based on the models for B and M values were comparable to predictions based on the derived values. These revised models provide an expanded means for rapidly estimating how the bacterium is likely to respond to any combination of the four variables within the specified ranges.

Aerobiosis↗

PubMed1994

Expansion of response surface models for the growth of Escherichia coli O157:H7 to include sodium nitrite as a variable.

The previously published (Buchanan et al., 1993a) response surface models for estimating the aerobic and anaerobic growth of Escherichia coli O157:H7 as a function of temperature, initial pH, and sodium chloride content have been expanded to include sodium nitrite as a further variable. A fractional factorial design was employed to quantitate the effect of NaNO2 in conjunction with the four other variables by culturing a three-strain mixture in brain heart infusion broth. The activity of NaNO2 was strongly pH-dependent, with inhibition being significant at pH values < or = 5.5 and enhanced by lowering the incubation temperature. The effects of the variables on Escherichia coli O157:H7 growth kinetics were modeled by response surface analysis using quadratic and cubic polynomial models of the natural logarithm transformation of both the Gompertz B and M parameters (Gompertz parameters) and the lag phase duration (LPD) and generation time (GT) values (kinetics parameters) calculated for individual growth curves. All models provided reasonable estimates for most variable combinations; however, comparisons of predicted versus observed values indicated that overall the most useful models were the cubic models based on LPD and GT values. Although additional validation of the models is required, comparisons of predicted times to a 1000-fold increase in population density against those calculated from previously published growth studies indicate that the models are an effective means for acquiring 'first estimates' of the growth characteristics of E. coli O157:H7.

Aerobiosis↗

PubMed1994

Response surface model of the effect of pH, sodium chloride and sodium nitrite on growth of Yersinia enterocolitica at low temperatures.

A fractional factorial design was used to measure the effects and interactions of temperature (5, 12, 19 degrees C), pH (4.5-8.5), sodium chloride (0.5-5%) and sodium nitrite (0-200 micrograms/ml) on the aerobic growth of Y. enterocolitica in brain heart infusion broth. Growth curves were modeled by fitting plate count data to the Gompertz equation. Quadratic models of natural logarithm transformations of the Gompertz B and M values and the derived values for lag phase durations and generation times were obtained using response surface analysis. Predictions based on the models for B and M values were comparable to predictions based on the derived values. These models provide a means for rapidly estimating how the bacterium is likely to respond to any combination of the four variables within the specified ranges.

Cold Temperature↗

PubMed1994

Model for the combined effects of temperature, initial pH, sodium chloride and sodium nitrite concentrations on anaerobic growth of Shigella flexneri.

A fractional factorial design was used to measure the effects and interactions of temperature (12-37 degrees C), initial pH (5.5-7.5), NaCl (0.5-4.0%) and NaNO2 (0-1000 ppm) on the anaerobic growth kinetics of Shigella flexneri in Brain-Heart Infusion broth. Anaerobic conditions were established by flushing the culture flasks with N2. A total of 375 cultures representing 124 variable combinations were analyzed, with growth curves being generated using the Gompertz equation. Growth rates decreased with decreasing temperature, decreasing pH and increasing NaCl level. NaNO2 in combination with low temperature, low pH and high NaCl content effectively inhibited S. flexneri. Response surface analysis was used to obtain models for estimating the growth of S. flexneri in terms of temperature, initial pH, and NaCl and NaNO2 concentrations. A third-order equation using the natural logarithm transformations for the Gompertz B and M terms gave reasonable estimates of bacterial growth in response to any combination of the variables studied within the specified ranges.

Anaerobiosis↗

PubMed1994

Comparison of the Tecra VIA kit, Oxoid BCET-RPLA kit and CHO cell culture assay for the detection of Bacillus cereus diarrhoeal enterotoxin.

Two commercial serological kits (Oxoid BCET-RPLA and Tecra VIA) and a Chinese hamster ovary (CHO) cell cytotonicity assay for the detection of Bacillus cereus diarrhoeal enterotoxin were compared. Eleven B. cereus strains and one enterotoxigenic B. thuringiensis strain were evaluated. Both kits and the CHO cell assay yielded positive toxin responses for cell-free culture filtrates from eight out of 11 diarrhoeal enterotoxigenic strains. An emetic enterotoxin producing strain was negative with all three assays. Two B. cereus strains were negative using the BCET-RPLA kit, but positive with the Tecra VIA kit and CHO cell assay. The BCET-RPLA indicated significant levels of enterotoxin after samples were boiled, whereas the CHO cell and Tecra assays were negative. Overall, the cell culture assay was the most sensitive. However, the Tecra VIA kit provided similar results and was better suited for the rapid detection of B. cereus diarrhoeal enterotoxin.

Animals↗

PubMed1993

Defective glia in the Drosophila brain degeneration mutant drop-dead.

To understand better the cellular basis of late-onset neuronal degeneration, we have examined the brain of the drop-dead mutant of Drosophila. This mutant carries an X-chromosomal recessive mutation that causes severe behavioral defects and brain degeneration, manifested a few days after emergence of the adult. Analysis of genetically mosaic flies has indicated that the focus of the drop-dead mutant phenotype is in the brain and that the gene product is non-cell autonomous. We examined the adult drop-dead mutant brain prior to onset of symptoms and found that many glial cells have stunted processes, whereas neuronal morphology is essentially normal. Adult mutant glial cells resemble immature glia found at an earlier stage of normal brain development. These observations suggest that defective glia in the drop-dead brain may disrupt adult nervous system function, contributing to progressive brain degeneration and death. The normal drop-dead gene product may prevent brain degeneration by providing a necessary glial function.

Animals↗