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

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

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

Demonstration of the collection methods

Filter Paper Pipettes

Images courtesy

of Belfast

City Hospital

RESULTS

0

5

10

15

20

25

30

35

40

Figure 2. pH values of DFU wound fluid containing bacteria Figure 1. Bacteria detected

No

of

DF

Us

wit

h p

rese

nti

ng

ba

cter

ia

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.

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.

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.

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.