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Developing a real time sensing system to monitor bacteria in wound dressings.

Farrow MJ, Hunter IS, Connolly P - Biosensors (Basel) (2012)

Bottom Line: It is based on impedance sensors that could be placed at the wound-dressing interface and potentially monitor bacterial growth in real time.Impedance was measured using disposable silver-silver chloride electrodes.The main findings were that the impedance profiles obtained by silver-silver chloride sensors in bacterial suspensions could detect the presence of high cell densities.

View Article: PubMed Central - PubMed

Affiliation: Department of Bioengineering, University of Strathclyde, Wolfson Centre, Glasgow, G4 0NW, UK. malcolm.farrow@strath.ac.uk.

ABSTRACT
Infection control is a key aspect of wound management strategies. Infection results in chemical imbalances and inflammation in the wound and may lead to prolonged healing times and degradation of the wound surface. Frequent changing of wound dressings may result in damage to healing tissues and an increased risk of infection. This paper presents the first results from a monitoring system that is being developed to detect presence and growth of bacteria in real time. It is based on impedance sensors that could be placed at the wound-dressing interface and potentially monitor bacterial growth in real time. As wounds can produce large volumes of exudate, the initial system reported here was developed to test for the presence of bacteria in suspension. Impedance was measured using disposable silver-silver chloride electrodes. The bacteria Staphylococcus aureus were chosen for the study as a species commonly isolated from wounds. The growth of bacteria was confirmed by plate counting methods and the impedance data were analysed for discernible differences in the impedance profiles to distinguish the absence and/or presence of bacteria. The main findings were that the impedance profiles obtained by silver-silver chloride sensors in bacterial suspensions could detect the presence of high cell densities. However, the presence of the silver-silver chloride electrodes tended to inhibit the growth of bacteria. These results indicate that there is potential to create a real time infection monitor for wounds based upon impedance sensing.

No MeSH data available.


Related in: MedlinePlus

An example of the normalised profiles with Ag-AgCl sensors in parallel suspensions: (a) MHB; (b) MHB and low density RN4220 at 16 h; (c) MHB and high density RN4220 at 16 h. Dotted lines indicates the normalised phase angle peak at 16 h.
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biosensors-02-00171-f005: An example of the normalised profiles with Ag-AgCl sensors in parallel suspensions: (a) MHB; (b) MHB and low density RN4220 at 16 h; (c) MHB and high density RN4220 at 16 h. Dotted lines indicates the normalised phase angle peak at 16 h.

Mentions: The normalised phase angle profiles of the lower inoculation density experiments again showed the clearest differences between bacterial cultures and MHB–only vials with sensors present in both to record impedance. In all 24 vials, irrespective of the media type or preparation of the sensor, there were three types of normalised phase angle profiles. The profile for the controls, the MHB-only, contained a peak that increased in magnitude over time and at 16 hours was between 0.79 and 1.58 Hz (Figure 5(a)). These peaks were caused by a reduction in the resistance and capacitance from the background reading. There were two contrasting normalised phase angle profiles for the vials inoculated with low density RN4220 depending on the final cell density reached. The profiles of the low final cell density vials (<1 × 107 CFU∙mL−1) were very similar to the media-only profiles, with magnitudes of the peak above 1.26 and frequencies between 0.79 and 1.58 Hz, and the difference between them could not be distinguished (Figure 5(b)). These profiles occurred in all of the inoculated vials and the final cell numbers were found to be less than 5 × 107 CFU∙mL−1. The second RN4220 phase profile (Figure 5(c)) occurred in vials inoculated with low starting density RN4220 but in these the final cell densities were between 1 × 108 and 1 × 109 CFU∙mL−1. The magnitudes of the peak were below 1.26 and the frequencies of the peaks between 1.58 and 2.00 Hz. This change in the peak was caused by a larger decrease in the resistance and an increase in the capacitance, potentially indicating the increase in metabolites and cell membranes respectively. Therefore it appears that once bacterial cultures reach a sufficient cell density a separate signature trace in the normalised phase angle over frequency occurs and indicates that comparing signature traces could discern between the absence and or/growth of bacteria above certain densities.


Developing a real time sensing system to monitor bacteria in wound dressings.

Farrow MJ, Hunter IS, Connolly P - Biosensors (Basel) (2012)

An example of the normalised profiles with Ag-AgCl sensors in parallel suspensions: (a) MHB; (b) MHB and low density RN4220 at 16 h; (c) MHB and high density RN4220 at 16 h. Dotted lines indicates the normalised phase angle peak at 16 h.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4263571&req=5

biosensors-02-00171-f005: An example of the normalised profiles with Ag-AgCl sensors in parallel suspensions: (a) MHB; (b) MHB and low density RN4220 at 16 h; (c) MHB and high density RN4220 at 16 h. Dotted lines indicates the normalised phase angle peak at 16 h.
Mentions: The normalised phase angle profiles of the lower inoculation density experiments again showed the clearest differences between bacterial cultures and MHB–only vials with sensors present in both to record impedance. In all 24 vials, irrespective of the media type or preparation of the sensor, there were three types of normalised phase angle profiles. The profile for the controls, the MHB-only, contained a peak that increased in magnitude over time and at 16 hours was between 0.79 and 1.58 Hz (Figure 5(a)). These peaks were caused by a reduction in the resistance and capacitance from the background reading. There were two contrasting normalised phase angle profiles for the vials inoculated with low density RN4220 depending on the final cell density reached. The profiles of the low final cell density vials (<1 × 107 CFU∙mL−1) were very similar to the media-only profiles, with magnitudes of the peak above 1.26 and frequencies between 0.79 and 1.58 Hz, and the difference between them could not be distinguished (Figure 5(b)). These profiles occurred in all of the inoculated vials and the final cell numbers were found to be less than 5 × 107 CFU∙mL−1. The second RN4220 phase profile (Figure 5(c)) occurred in vials inoculated with low starting density RN4220 but in these the final cell densities were between 1 × 108 and 1 × 109 CFU∙mL−1. The magnitudes of the peak were below 1.26 and the frequencies of the peaks between 1.58 and 2.00 Hz. This change in the peak was caused by a larger decrease in the resistance and an increase in the capacitance, potentially indicating the increase in metabolites and cell membranes respectively. Therefore it appears that once bacterial cultures reach a sufficient cell density a separate signature trace in the normalised phase angle over frequency occurs and indicates that comparing signature traces could discern between the absence and or/growth of bacteria above certain densities.

Bottom Line: It is based on impedance sensors that could be placed at the wound-dressing interface and potentially monitor bacterial growth in real time.Impedance was measured using disposable silver-silver chloride electrodes.The main findings were that the impedance profiles obtained by silver-silver chloride sensors in bacterial suspensions could detect the presence of high cell densities.

View Article: PubMed Central - PubMed

Affiliation: Department of Bioengineering, University of Strathclyde, Wolfson Centre, Glasgow, G4 0NW, UK. malcolm.farrow@strath.ac.uk.

ABSTRACT
Infection control is a key aspect of wound management strategies. Infection results in chemical imbalances and inflammation in the wound and may lead to prolonged healing times and degradation of the wound surface. Frequent changing of wound dressings may result in damage to healing tissues and an increased risk of infection. This paper presents the first results from a monitoring system that is being developed to detect presence and growth of bacteria in real time. It is based on impedance sensors that could be placed at the wound-dressing interface and potentially monitor bacterial growth in real time. As wounds can produce large volumes of exudate, the initial system reported here was developed to test for the presence of bacteria in suspension. Impedance was measured using disposable silver-silver chloride electrodes. The bacteria Staphylococcus aureus were chosen for the study as a species commonly isolated from wounds. The growth of bacteria was confirmed by plate counting methods and the impedance data were analysed for discernible differences in the impedance profiles to distinguish the absence and/or presence of bacteria. The main findings were that the impedance profiles obtained by silver-silver chloride sensors in bacterial suspensions could detect the presence of high cell densities. However, the presence of the silver-silver chloride electrodes tended to inhibit the growth of bacteria. These results indicate that there is potential to create a real time infection monitor for wounds based upon impedance sensing.

No MeSH data available.


Related in: MedlinePlus