The effect of silver ions and chlorine on the survival of Staphylococcus aureus and Bacillus cereus in dishwater.

This paper investigates the effect of chlorine and silver ion solutions on the survival of Bacillus cereus (vegetative phase) and Staphylococcus aureus in batch cultures, representing dishwater. Dishwater contains organic matter and bacteria and bacterial activities are partly reduced by high pH (11-12) and temperature (55-65 degrees C) in professional and domestic dishwashers. In manual dishwashing, temperature and pH are kept lower (45 degrees C and pH 7), which is less sufficient for the reduction of bacteria. In a broth, organic loaded in order to mimic dishwater, solutions of Ag or hypochlorite were added at 45 degrees C and pH 7 and samples were withdrawn for a period of 40 minutes. 1 ppm Ag+ was required to obtain a 1 to 2 log unit reduction of B. cereus and S. aureus in 10 minutes. An addition of 160 ppm hypochlorite reduced B. cereus and S. aureus by 4 log units in two minutes, whereas 16 ppm of hypochlorite had no effect on the survival of S. aureus. The level of free residual chlorine varied with the COD value of the cultured solutions. We found that both silver and hypochlorite can be used as antibacterial agents in dishwater. The disadvantage with the use of hypochlorite is that the COD value determines the antibacterial effect. Using Ag+ solutions to reduce bacteria has the drawback that they are toxic to water-living organisms and are considered to develop Ag+ resistant bacteria. To reduce the risk of cross-contamination from dishwater to dishware high temperature and detergent with high pH is to be preferred.

Cross-contamination in dishwashers.

Dishwashers are used in central hospital kitchens and ward kitchens to provide clean crockery. Soil recipes based on international standards were tested in order to evaluate the performance of a general dishwasher. In normal use of dishwashers, adherent soils are left on the crockery before cleaning. Different adherent soils, both with and without bacterial contamination, were used to show the effectiveness of the dishwasher to remove this type of soil. It was shown that contamination will occur from the dishwater to crockery with adherent soil. These results demonstrate the importance of cleaning soiled surfaces of crockery mechanically in the dishwashing process. Otherwise cross-contamination, and thereby the spread of infections, may occur.

Minimal-Fouling enzyme electrode for continuous flow measurement of whole blood lactate.

A new membrane system evaluated in an enzyme electrode for monitoring of whole blood lactate under continuous flow conditions has been developed. The membrane confers functional haemocompatibility and has been coupled to an electrode based on amperometric detection of hydrogen peroxide with lactate oxidase interposed between the haemocompatible membrane acting as diffusion barrier and an inner membrane excluding interfering electroactive species. Here, the enzyme electrode is combined with a flow-through measuring chamber and a double lumen catheter permitting continuous sampling and heparinization of blood. The blood contacting membranes have unique haemocompatibility properties and were produced through modification of poly(vinyl chloride), with the nonionic surfactant Pluronic F-68. On-line monitoring of whole blood samples with different amounts of added lactate was carried out to simulate fluctuations in blood lactate levels during extracorporeal monitoring and results were compared with a standard lactate analyser.

On-line calibration of a computerized biosensor system for continuous measurements of glucose and lactate.

An on-line calibration procedure for application in continuous monitoring systems has been developed. Control of the calibration value and recalibration on-line during monitoring is possible without having to disrupt the sample withdrawal. The calibration procedure has been applied and evaluated in a continuous biosensor system based on the detection of oxygen depletion during enzymatic substrate conversion by immobilized oxidases. Evaluation included on-line calibration during continuous measurements of glucose and lactate in bovine blood samples. Calibration of the complete system consisting of a sampling device, a sample handling step, a biocatalytic step, a detection step, and a data processing unit is performed by the on-line addition of a calibration solution to a blank sample which is fed through the system. The calibration cycle is completed within 5.5 min. When recalibration is carried out during monitoring, the calibration solution is added to the sample, instead of to a blank sample, and the increase in outlet singl is registered. The major advantage of this internal standard principle is that the calibration solution is fed through the whole system according to the same path as the sample solution and thus takes into account all parameters influencing the sample. (c) 1995 John Wiley & Sons, Inc.

Differential periodontal temperature measurements in the assessment of periodontal disease activity: an experimental and clinical study.

The difference in surface temperatures between the bottom of periodontal pockets and the attached gingiva adjacent to the openings of the pockets were determined both in monkeys with experimental marginal periodontitis, and clinically in patients with marginal periodontitis. For this purpose a custom-made, temperature-measuring device was developed which enabled immediate recording of temperature differences as well as periodontal pocket depths, bleeding, and attachment levels. The measurements were performed periodically. The differential temperature measurements were correlated to change in periodontal attachment over time. It was shown that differential periodontal temperatures are well correlated to change in periodontal attachment over time. It was furthermore concluded that differential periodontal temperature measurements have the potential of serving as a predictor of activity of marginal periodontitis. However, more extensive data are required to assess the sensitivity and specificity of the method.

Sampling and sample handling--crucial steps in process monitoring and control.

Sampling and sample handling are important considerations in the design of monitoring and control systems for bioreactors. Many factors must be considered in developing strategies for obtaining representative samples, thus ensuring that the status of the bioprocess can be evaluated rapidly, in a reproducible and reliable manner.

Portable system for continuous ex vivo measurements of lactate.

The lactate profile in serum was monitored continuously in volunteers under physical exercise on a test bicycle. The assay was operated ex vivo by means of continuous sampling through a coaxial catheter. After dialysis online, lactate was converted by means of lactate oxidase immobilized to porous glass, and the depletion of oxygen was registered by means of a Clark electrode. Good agreement between the continuous monitoring and off-line analyses was found.

Process monitoring by flow-injection immunoassay. Evaluation of a sequential competitive binding assay.

A new variation on the theme of flow-injection binding assays is presented, namely the sequential competitive binding assay, in which the sample containing the native antigen is first introduced into the flow system followed by a pulse of labelled antigen. The flow-injection binding assay was used in monitoring the effluent from column chromatographic separations of proteins. By applying a computer-based evaluation system, concentrations are automatically read and compensation is made for denaturation in the affinity sorbent.

Immunochemically based assays for process control.

Immunoanalysis for process control is reviewed. The development of non-equilibrium immunoassays from a manually operated flow injection system to a completely computerized system for sample analysis as well as calibration and data evaluation is discussed. Several other approaches in using immunochemistry in biosensors for process control are discussed. The fact that reuse of antibodies raises specific demands on their properties is discussed. Even if the area is young, much progress has been achieved and one can foresee an interesting future development of the area.

Continuous monitoring of urea in blood during dialysis.

Urease was immobilized to porous glass and used in combination with a conductivity meter for determining urea in standard solutions as well as in blood from a patient undergoing dialysis. The sampling unit involves a possibility for heparinization at the sampling point and a dialysis step prior to exposure to the enzyme column. The unit operates in a linear mode in the concentration range 5-50 mM. Monitoring of dialysis process gave good correlation with off-line analyses.

Hair cell damage in the inner ear of the guinea pig due to noise in a workshop.

Guinea pigs were exposed to noise in various workshops at a shipyard. The equivalent sound level ranged from 87 to 90 dB(A) and the exposure time was 30 days of 8 hours. The numbers of lost outer hair cells were greater than in control animals, thus establishing a relation between the number of lost hair cells and the total noise dose. A comparison between the results obtained here and results obtained in laboratory experiments shows that although many physical sound parameters may be identical, the effect on the hair cells can be quite different. In particular, the total noise dose is not a parameter which can be directly related to hair cell loss. The most probable explanation for the difference in damage between the laboratory and workshop animals seems to be the rest periods of 16 hours between each of the 8-hour exposure periods.

Hair cell damage in the inner ear of the Guinea pig due to noise in a workshop.

Guinea pigs were exposed to noise in various workshops at a shipyard. The equivalent sound level ranged from 87 to 90 dB(A) and the exposure time was 30 days of 8 hours. The numbers of lost outer hair cells were greater than in control animals, thus establishing a relation between the number of lost hair cells and the total noise dose. A comparison between the results obtained here and results obtained in laboratory experiments shows that although many physical sound parameters may be identical, the effect on the hair cells can be quite different. In particular, the total noise dose is not a parameter which can be directly related to hair cell loss. The most probable explanation for the difference in damage between the laboratory and workshop animals seems to be the rest periods of 16 hours between each of the 8-hour exposure periods.

Comparison between hearing threshold measurements made with and without the aid of an ear speculum.

The hearing threshold levels of a small group of shipyard workers having differing degrees of hearing impairment were measured five times using the following audiometric techniques: fixed-tone Békésy audiometry with MX 41/AR cushions, fixed-tone Békésy audiometry with an ear speculum, and sweep-frequency Békésy audiometry with an ear speculum. From these data the mean standard deviations of the hearing threshold levels for the frequencies 0.5, 1, 2, 3, 4, 5, 6, 7 and 8 kHz were calculated, thus giving a measure of the accuracy of each method. The hearing threshold levels obtained by the three methods are compared, and the merits of data handling, expressing hearing threshold levels in pascals rather than decibels, are also discussed.

Hearing deterioration in shipyard workers. Serial audiometry over a four-year period.

The hearing thresholds of a total of 58 workers aged 20 to 65 years were measured annually over a period of 4 years using Békésy sweep-frequency audiometry. Using these data, accurate values of the yearly rate of change of hearing threshold level were calculated. The rate of change of hearing threshold level due to presbyacusis was obtained from several data sets, and the rate of change of hearing threshold level due to noise was calculated. When the average hearing threshold level over the frequency range 2-8 kHz was considered, it was found to be possible to establish a significant rate of threshold shift caused by exposure to noise for yearly changes as small as approximately 2 dB. In the cases investigated about 30% of the ears showed a significant deterioration in hearing ability due to noise. When comparing the permanent threshold shift caused by noise in groups of younger and older workers, it was found that the younger workers exhibited less threshold shift than expected, whereas the older workers showed a greater threshold shift than expected.

The effect of static middle ear pressures on the hearing threshold.

The effect of static tympanic pressure gradients on hearing sensitivity was studied by introducing relative underpressure of 5, 10 and 15 cmH2O in the middle ear cavity of six normal ears. A self-recording Békésy audiometer was used to measure the hearing threshold shifts during middle ear pressure equilibrations. The threshold loss was most prominent for 0.5 and 1 kHZ and less for 4 kHZ. A threshold gain was shown for 2 and 6 kHZ. Over all test frequencies the threshold shifts were increased with higher relative underpressure in the middle ear cavity. In order to evaluate the hearing impairment caused by noise, it is therefore important to control the middle ear pressure before hearing is tested. A small change in middle ear pressure can be ignored when using the summed hearing thresholds between 2 and 8 kHZ.