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Biomedical subjects

K W Davies

Publications and source records attributed to K W Davies.

14 recordsLinked to original sources
PubMed2001

Sodium chloride enhances recovery and growth of acid-stressed E. coli O157:H7.

AIMS: Combinations of sodium chloride and acid are frequently used to inhibit growth of spoilage and pathogenic bacteria in food. The influence of differing sodium chloride, lactate and pH values on the growth of stressed and unstressed cells of a non-toxigenic strain of Escherichia coli O157:H7 was studied. METHODS AND RESULTS: At pH 5.5 or 6.0, there was little or no effect on the growth rate in the presence of lactate and/or sodium chloride, but the lag times were longer as the lactate concentration increased. At pH 5.0, in the absence of sodium chloride, increasing the lactate concentration increased the growth rate and the lag time; no growth occurred in the presence of 1.5 g 100 g(-1) lactate. In the presence of 4-6 g 100 g(-1) sodium chloride, growth occurred at 1.5 g 100 g(-1) lactate. The growth rate was similar at all lactate concentrations. CONCLUSION: The results demonstrate that the presence of sodium chloride promoted growth of E. coli O157:H7, especially under stressful conditions of low pH. SIGNIFICANCE AND IMPACT OF THE STUDY: These findings could have implications for the use of acid and sodium chloride as a preservation treatment for the inhibition of E. coli O157:H7 in food.

Colony Count, Microbial↗
PubMed2000

Bacterial thermal death kinetics based on probability distributions: the heat destruction of Clostridium botulinum and Salmonella Bedford.

Despite the long history and excellent record of inactivation models used in thermal processing, there are relatively few approaches that attempt to describe the kinetics commonly observed. There are even fewer examples of models that allow the user to deal with the environmental conditions that influence these kinetics. We describe an approach that assumes a distribution of inactivation times within a population of bacterial cells. The concept allows for alternative interpretations of death kinetics and provides excellent descriptions of data generated with two important foodborne pathogens, Clostridium botulinum and Salmonella Bedford. The Salmonella Bedford data set used is unusual and perhaps unique in that it provides information where more than 50% of the population survival has been measured. These measurements are often overlooked or missed in experimental work but are essential when using a vitalistic approach, enabling calculation of a 50% lethal dose for destruction of bacteria. Use of the normal or Prentice distribution provided better fits to the data than other models commonly used to describe thermal death. There was no obvious bias in the fits even though significant tailing was evident. In addition, the procedure described allows data from all the conditions to be fitted rather than individual independent series. This enables a single equation to be derived that can be judged against the whole domain of the data. Approaches that provide accurate and unbiased descriptions of thermal death are likely to become increasingly important to ensure the safety of more marginal heat processes.

Clostridium botulinum↗
PubMed1999

Survey of serum potassium reference measurements.

We compared the quality of reference measurements for serum potassium in four reference laboratories from three different European countries, using a panel of 60 native patients' samples. The reference methods were based on either ion chromatography (one laboratory) or flame atomic emission spectrometry (three laboratories). Performance specifications for serum potassium measurements were defined as a maximum overall coefficient of variation (CV) of 1.5%, a maximum bias of 0.65% and a maximum total error of 3.0%. The overall imprecision for all laboratories was in the range of 0.7 to 1.3%, and was thus below the proposed specification of 1.5%. However, two laboratories reported 12 and 13 quadruplicates with CVs exceeding this limit. The mean bias (expressed as deviation from the overall mean of all laboratories) for all reference laboratories was < 0.65%. In the lower concentration range, however, one laboratory exceeded this limit. No laboratory measured samples with a total error above 3.0%. From these results, it can be concluded that the reference measurements, and, thus, also the reference methodologies, based on ion chromatography and flame atomic emission spectrometry were equivalent, and able to satisfy current analytical specifications for serum potassium measurements.

Chromatography, Liquid↗
PubMed1998

Quantitative microbiological risk assessment: principles applied to determining the comparative risk of salmonellosis from chicken products.

Ensuring microbiological safety requires identification of realistic hazards and the means of controlling them. The risk assessment framework proposed by Codex Alimentarius allows the impact of raw materials and processes to be appreciated, and the output can be used for risk management and communication. Mathematical models allow numerical information to be processed by a computer and interpreted to give quantitative or comparative risk assessments. In this example, models have been put together according to the Codex. Alimentarius principles, providing a quantitative risk assessment (QRA) of salmonellosis from frozen poultry products. This model-based QRA takes into account three types of information: occurrence and distribution of the agent, sensitivity of populations to infection (e.g., normal or susceptible), and the effect of cooking (in the factory or home) on concentration of the agent and hence risks of infection after product consumption. It only demonstrates the impact of a single-process step (heating) and the effect of changes in population sensitivity, raw material quality, and cooking regime on the final risk. The effects of growth and recontamination are not considered. To aid risk communication, the models have been visualized by means of displays and slider controls on a computer screen because effective communication is essential to encourage manufacturers and their product designers to assess the effect of changes in processing or materials on risk.

Adult↗
PubMed1997

The use of an automated growth analyser to measure recovery times of single heat-injured Salmonella cells.

A new approach to the study of recovery times of single heat-injured Salmonella cells is described. It comprises the generation of a standard heat-injured culture, serial dilution of this culture to near extinction, inoculation of the serial dilutions across many microtitre plates and measurement of the subsequent recovery and growth using an automated turbidometric analyser. Lag times for individual cells were estimated from turbidity data using a model that accurately extrapolated the growth curve back to the starting inoculum level. Lag times were compared using a number of different commercially available pre-enrichment media. The most typical result was a very broad distribution of lag times at the single cell inoculum level, with many values in excess of 20 h. Even at an inoculum level 10-fold higher, lag times for some injured cells were estimated to be > 10 h. More significantly, it was found that some media recovered more injured cells than others and vice versa. Between the worst and best media there were as many as 3 log10 cycles difference in the number of cells recoverable. No trends were apparent linking choice of medium with performance. The implications of these findings, in relation to traditional and rapid methodology, are discussed.

Automation↗
PubMed1994

An example of the stages in the development of a predictive mathematical model for microbial growth: the effects of NaCl, pH and temperature on the growth of Aeromonas hydrophila.

The stages involved in developing a predictive model are illustrated using data describing the effects of temperature (3-20 degrees C), NaCl concentration (0.5-4.5% w/v) and pH (4.6-7.0) on the aerobic growth of Aeromonas hydrophila (cocktail of 6 strains). Optical density measurements using micro-titre plates were used as an initial screen, to determine the appropriate sampling times for viable counts to be made and to determine the approximate boundaries for growth. Growth curves were generated from viable counts and fitted using a modified Gompertz equation. Quadratic response surface equations were fitted to the log of lag and generation times, in response to the variables of temperature, NaCl and pH (in terms of hydrogen ion concentration). The effects of various combinations of these controlling factors are described. Comparisons between predicted growth rates and lag times from our response surface equations and other models for growth of A. hydrophila, developed with viable count data and optical density measurements, are made, together with comparisons with data from the literature on the growth of this bacterium in foods.

Aeromonas hydrophila↗
PubMed1993

A comparison of Agiolax and lactulose in elderly patients with chronic constipation.

In a double-blind crossover study the efficacies of Agiolax, a combination of fibre and senna pod, and lactulose were compared in 77 long-stay elderly patients with chronic constipation. Mean daily bowel frequency, stool consistency and ease of evacuation were significantly greater with Agiolax than lactulose. The recommended dose was exceeded more frequently with lactulose than Agiolax (chi 2 = 8.38, p < 0.01). Adverse effects were not different for the 2 treatments. In long-stay elderly patients with chronic constipation Agiolax and lactulose were well tolerated, but Agiolax proved a more effective treatment.

Aged↗
PubMed1992

Dental caries in 12-year-old children in Salford, UK: changes over 28 years.

A sample of 111 12-year-old children in Salford, UK was examined in 1988, and the findings compared with those of a survey carried out in 1960 of 12-year-old children in the same city. Between 1960 and 1988, the mean DMFT of the boys fell from 6.04 to 2.34 and that of the girls from 6.54 to 3.40. All types of teeth were affected by caries in 1960 but in 1988 none of the canines and mandibular lateral incisors were affected. In 1960 the permanent first molars contributed 57% of the boys' and 54% of the girls' total DMFT while in 1988 they contributed 87% of the boys' and 73% of the girls' DMFT. Jackson's Treatment Index showed that the dental services were making a greater impact in 1988; for the boys it rose from 29.5 to 63.2 and for the girls from 27.8 to 62.3.

Child↗
PubMed1992

A classification of residential neighbourhoods (ACORN) in relation to dental health and dental health behaviours.

Five-year-old children in two district health authorities in the North Western Region of England were examined during 1989-90. Questionnaires were issued to parents to determine whether dental health and related behaviours were associated with socio-economic status. Parents of 1858 children in Salford (response rate = 78 per cent) and 1691 in Trafford (response rate = 81 per cent) returned the questionnaires. Their replies were analysed by dividing the children into a hierarchy according to a classification of residential neighbourhood (ACORN). Significantly fewer in the highest of three Divisions in both districts had suffered from toothache and had undergone a general anaesthetic to have teeth extracted. They were also more likely to have had their teeth brushed with toothpaste by their first birthday and to have visited the dentist by their second. Because ACORN had detected these differences in dental health related behaviour it was possible to identify localities towards which dental health promotion activities can be directed.

Carbonated Beverages↗
PubMed1990

Dental health education: training of homecarers of mentally handicapped adults.

A seven week induction course for homecarers of mentally handicapped adults, organised by the Social Services Department in Salford, UK, includes a dental health education session of one and a half hours. The session is divided into three parts; an illustrated discussion, a demonstration of tooth-brushing and a practical component session where carers are divided into pairs and carry out oral hygiene measures for each other. The effectiveness of the session has been assessed using a questionnaire. This was completed by 33 carers who attended the session and 31 carers who had not. Many members of both groups knew about the shape and colour of healthy gums and what plaque was. However significantly fewer of the control group knew that gum disease resulted from a lack of toothbrushing, what to do with bleeding gums and the amount of toothpaste to use on the toothbrush.

Female↗