Comparison of microbiology

cultures from deep tissue

biopsies compared to

superficial swabs from

infected diabetic ulcers

Steven Brookes-Fazakerley

David Harvey

Simon Platt

Gillian Jackson

Wirral University Hospital NHS Foundation Trust

UK

Comparison of microbiology cultures

from deep tissue biopsies compared to

superficial swabs from infected diabetic

ulcers

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this presentation.

Steven Brookes-Fazakerley

Aim

• To evaluate whether deep tissue biopsy cultures are more accurate & valuable than superficial swab cultures in determining the pathological organisms present in diabetic ulcers

Methods

• Prospective study

• 23 consecutive patients over 9 month period

• All diagnosed & treated in 1 UK hospital

• All patients suffered diabetes mellitus

• All patients suffered an intractable ulcer of the lower limb

• All patients had wound deep tissue biopsy with & superficial wound swab culture

Demographics

• 23 ulcers in 23 patients

• Mean age 58 years (39-86 years)

• 57% involved left lower limb

• 65% (15) male patients

• 65% (15) type 2 diabetics & 35% (8) type 1

• 84% (21) insulin dependent patients

• Median BMI 29.5kg/m2

Ulcer Location

Hallux 22%

1st MT Head 4%

Lesser Toes 31%

Lesser MT Heads 22%

Os calcis 13%

Forefoot & hindfoot

4%

BKA Stump 4%

Organism Superficial Swabs

Cultures Deep Soft Tissue

Culture Bone Culture

Anaerobes 3 9 8

Coagulase negative staphylococci 0 5 3

Diptheroids 1 4 0

S. aureus (not MRSA) 5 9 8

E.coli 1 1 0

Enterococci 5 3 3

Enterobacter 0 1 0

β haemolytic Group B Streptococci 2 2 1

β haemolytic Group C Streptococci 1 1 1

Haemophilus parainfluenzae 0 1 1

Klebsiella spp 0 4 1

Mixed Skin & enteric flora 12 0 0

Morganella morganii 0 2 1

MRSA 1 1 0

Proteus spp 1 3 3

Pseudomonas spp 2 2 2

Serratia spp 1 0 0

Stenotrophomonas maltaphilia 0 1 1

Streptococcus anginosus 0 1 1

Streptococcus mitis 0 1 1

Isolates Grown From Swabs &

Tissue Cultures

Pathogenic Isolates Missed by Swabs

& Cultured Per Tissue Specimen

Patient number Organism

1 S.aureus

2 H.parainfluenzae

4 Klebsiella spp

5 Anaerobes, Enterobacter & S.aureus

7 Proteus spp

10 Anaerobes

11 Anaerobes & S.aureus, S. anginosus

14 S.aureus

15 Klebsiella spp

16 Anaerobes

17 Anaerobes & S.aureus

18 Klebsiella spp

21 Proteus spp

23 Anaerobes & M. morganii

Culture Results

• 74% (17) superficial swabs grew extra organisms (i.e.

bone pathogen & other probable superficial colonisers)

• 13% (3) superficial swabs cultured less organisms than

bone samples (i.e. undercalled the extent of infection)

• 13% (3) superficial swabs cultured different organisms to

bone samples (i.e. incorrect/misleading)

• 52% (12) deep soft tissue & bone cultures were identical

Mean Number Isolates from Swab & Tissue Cultures

Swab Cultures Deep Soft Tissue Bone

1.7 (1-4) 2.3 (1-4) 1.86 (0-4)

Discussion

• Superficial swabs largely isolated enteric

organisms & mixed skin flora

• Superficial swabs failed to identify potential

pathogenic organisms seen in 61% of patients

deep tissue samples

• Bone cultures isolated fewer organisms than

deep soft tissue cultures

Conclusion

• Poor concordance between isolates of

superficial swabs & deep tissue specimens

• Deep tissue specimens from diabetic ulcers

capture more pathogenic organisms

• Superficial swabs are inferior to deep tissue

samples & should not be used to guide antibiotic

treatment

References

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