This study examined the effect of diabetic foot ulcer (DFU) wound fluid pH on the presence of bacteria. Wound fluid was collected from 55 patients with DFUs and tested for pH and bacteria. A variety of bacteria were found, most commonly Staphylococcus and Streptococcus species. Higher pH wound fluid (>7.5) was associated with some bacterial species while others were found more often at neutral pH (<7.5). DFUs with clinical signs of infection had significantly higher pH than non-infected wounds. The results suggest that wound fluid pH, especially values over 7.2, could help identify silent infections and inform treatment decisions.

1. THE EFFECTS OF DIABETIC FOOT
ULCER (DFU) WOUND FLUID pH
ON DFU BACTERIA
Carla McArdle1, Katie Lagan1, Sarah Spence2 and David McDowell2
1 Centre for Health and Rehabilitation Technologies (CHaRT), School of Health
Sciences, University of Ulster, Northern Ireland
2 School of Health Sciences, University of Ulster, Northern Ireland

2.  15-20% of people with diabetes will develop diabetic foot ulcers
(DFUs) at some point in their lifetime (Diabetes UK, 2012).
 DFUs pose high risks of microbial infection which can often lead to
systemic infection and/or amputation.
 Diabetes is the most common cause of lower limb amputation
(Amputee Statistical Database UK, 2007).
 The study aims to determine if the pH of wound fluid affects the
presence/absence of bacteria, and ultimately the presence of
infection.
Introduction

3.  Ethical approval and research governance was granted to collect wound fluid from 55
patients (48 males) with DFUs attending Belfast Health and Social Care trust (BHSCT)
clinics.
 The average duration of the DFUs was 6.5 months and the average size was 4.7cm2
 Wound fluid was aseptically collected onto filter paper or by pipette aspiration.
 Wound fluid pH was determined using a micro-electrode pH meter.
 Wound fluid bacteria were recovered by enrichment in TSB for 24hrs @ 37oC and plating
on selective agar plates including; MacConkey Agar (Staphylococcus spp, Enterobacter
spp), Chromocult Agar (E. Coli, Coliforms), Baird Parker Agar (Staphylococcus spp),
Columbia Blood Agar (Streptococcus spp).
Methodology

4. Demonstration of the collection methods
Filter Paper Pipettes
Images
courtesy
of
Belfast
City
Hospital

5. RESULTS
0
5
10
15
20
25
30
35
40
Figure 2. pH values of DFU wound fluid containing bacteriaFigure 1. Bacteria detected
NoofDFUswithpresentingbacteria
6.5
8.0
7.5
7.0
8.5
6.0
pH
DFUs presented with a varied range of bacteria with the most common bacteria found being Staphylococcus
and Streptococcus spp. Figure 1 displays the bacteria that were detected and the number of DFUs each
bacterial species presented in.
The median pH values varied with some bacteria being detected more frequently at slightly alkaline values
(>pH7.5) and others at more neutral values (<pH7.5). For example the median pH value that
Staphylococcus spp. presented at was <pH7.2 in comparison to Pseudomonas spp. whose median value was
>pH 7.6.

6. RESULTS
Figure 3. Wound fluid pH and the presence/absence of clinical signs of
DFU infection
9.0
8.5
8.0
7.5
7.0
6.5
6.0
Absent Present
pH
DFUs which had no visual signs of infection had a relatively wide range of pH values
however those that presented with clinical signs and thus deemed clinically infected had an
pH value in an alkaline state.

7. Discussion and Conclusion
 The varied range of bacterial species and pH values detected indicates the ability of
bacteria to survive over a relatively wide range of pH values.
 Comparison of DFU pH values with clinical assessment of infection suggested that the
pH of infected DFUs is higher than non-infected wounds. This suggests that the
observation of pH values greater than 7.2 may signal ‘silent infection’ warranting
further monitoring and/or treatment.
 As visual signs of infection are limited or absent in DFUs, such instrumental
determination of wound pH may be valuable in assessing wound status.
 This study demonstrates that the collection of wound fluid is an easy, non-invasive
method that has the potential to become an integral part of clinicians’ daily practice,
aiding in clinical decision making in the diagnosis of DFU infections.

8. References and Acknowledgements
 Amputee Statistical Database for the United Kingdom, 2007. Lower Limb Amputations
 Diabetes UK. Diabetes in the UK 2011/12. Key Statistics on Diabetes. London: Diabetes
UK. 2011.
Author Carla McArdle would like to sincerely thank Jill Cundell (local collaborator) and
Mr Louis Lau (principal investigator) from the Belfast City Hospital, Belfast, NI for their
involvement in the research study.
Carla McArdle would also like to thank Department and Employment and Learning
(DEL) and the College of Podiatry for providing her with funding in order to present her
research at the EWMA-GNEAUPP conference.