The document discusses microbiology of diabetic foot infections, including how to classify and obtain cultures from such infections. It provides recommendations on empiric antibiotic therapy based on infection severity and risk factors. The importance of surgical evaluation and wound care including debridement is also covered.

1. MICROBIOLOGY OF
DIABETIC FOOT
INFECTIONS
Abdullatif Sami Al
Rashed
Clinical Microbiology Resident
King Fahd Hospital of the
University.
Teaching Assistant,
Department of Microbiology,
Imam Abdulrahman Bin Faisal
University, Dammam, Saudi
Arabia.

2. OBJECTIVES
o By the end of this seminar you should
know:
1. How to classify Diabetic Foot Infections
(DFIs).
2. When and How should we obtain cultures
from DFI patients.
3. Best practice for managing of DFIs.

3. CASE STUDY
o A 61-year-old woman known case of diabetes mellitus type II
(DM2) presented in the Emergency Department, with
complaints of pain and swelling in the right second toe with
purulent discharge.
o She was diagnosed with DM2 11 years ago.
o No other associated symptoms.
Other Hx?

4. CASE STUDY
oOn Examination:
o Normal vital signs.
o systemic examinations are unremarkable.
o local Examination:
o Swelling, Redness, and small ulcer with purulent discharge
DDX????

5. What Next?

6. CASE STUDY
 Labs:
Test Result
Hb 11.6 g/dL
WBCs 13.9×109/L
platelets count 447×109/L
CRP 8.51 mg/dL
Blood sugar levels
(fasting)
170 mg
Hb1AC 8.9

7. CASE STUDY
Direct stain

8. CASE STUDY
❓ ❓ ❓

9. AST BY VITEK 2
 MSSA strain.

10. CASE STUDY
Diagnosis:
Diabetic foot infection
Causative Organism:
Staph. aureus (MSSA)

11. WHEN SHOULD I
SUSPECT DFI, AND HOW
SHOULD I CLASSIFY IT?

12. DIABETES IN SAUDI ARABIA
https://www.idf.org/our-network/regions-members/middle-east-and-north-africa/members
saudi-arabia.html

13. 1- The possibility of infection in any foot
wound in diabetics should be considered.
2- Evidence of infection generally includes Classic signs of
inflammation (redness, warmth, swelling, tenderness, or pain) or
purulent secretions, but may also include additional or secondary
signs (e.g, non-purulent secretions, friable or discolored
granulation tissue, undermining of wound edges, foul odor)
IDSA Recommendation Summary

14. 3- Consider factors
that increase the risk
for DFI:
probe-to-bone (PTB) test
an ulceration present for
>30 days and a history of
recurrent foot ulcers
presence of peripheral vascular disease in
the affected limb or loss of protective
sensation
previous lower
extremity amputation
IDSARecommendationSummary

15. 4- A validated classification system, such as the
International Working Group on the Diabetic Foot
(IWGDF) or IDSA, to classify infections and severity of the
cases.
5- Other validated diabetic foot classification schemes
have limited value for infection, as they describe only its
presence or absence.
6- The Diabetic Foot Infection Wound Score may provide
additional quantitative discrimination for research
purposes.
IDSA Recommendation Summary

16. International Working Group on the Diabetic Foot Infectious Diseases Society of America

17. Lipsky BA et al, 2012 Infectious Diseases Society of America clinical practice guideline for the diagnosis and treatment of diabetic foot infections. Clinical infectious diseases. 2012 Jun 15;54(12):e132-73.

18. WHEN AND HOW
SHOULD I OBTAIN
SPECIMEN FOR
CULTURE?

19. Stage Recommendation
Strength of
Recommendation and
Quality of Evidence
For clinically uninfected
wounds No need for collecting a specimen for
culture
Strong
Recommendation, Low
Evidence
For a mild infection in a
patient who has not
recently received
antibiotic therapy
Cultures may be unnecessary
Strong
Recommendation, Low
Evidence
For a deep tissue
infection
A specimen for culture is highly
recommended
(preferably obtained by biopsy or curettage
after the wound has been cleansed and
debrided)
Strong
Recommendation,
Moderate Evidence• N.B:
1. swab specimens should be avoided, especially of inadequately debrided
wounds, as they provide less accurate results.
2. specimens for culture should be collected prior to starting empiric antibiotic
therapy.
IDSA Recommendation Summary

20. Lipsky BA et al, 2012 Infectious Diseases Society of America clinical practice guideline for the diagnosis and treatment of diabetic foot infections. Clinical infectious diseases. 2012 Jun 15;54(12):e132-73.

21. CAUSATIVEPATHOGENS
Oxford Handbook of Infectious Diseases and
Microbiology, 2nd Edition.

22. BACK TO OUR CASE
Should we treat the patient?

23. • No need to start antibiotic therapy
Unaffec
ted
wound
• Start therapy just targeting aerobic gram-
positive cocci (GPC)
Mild/moderat
e infections,
Not received
ABx
• Start broad-spectrum empiric antibiotic
therapy, pending culture results and
antibiotic susceptibility data
Severe
infectio
ns
IDSARecommendation
Summary

24. N.B:
1- Empiric therapy against P. aeruginosa is unnecessary except for
patients with risk factors e.g (high local prevalence of Pseudomonas
infection, warm climate, frequent exposure of the foot to water)
2- Empiric therapy against MRSA should be considered in a patient
with a prior history of MRSA infection; when the local prevalence of
MRSA colonization or infection is high; or if the infection is clinically
severe

25. IDSARecommendation
Summary
If the patient has had a good clinical response
on the empiric therapy, the regimen may be
continued, or even potentially narrowed
“deescalation”
If the patient has not adequately responded to
the empiric regimen, therapy should be
broadened to include all isolated organisms.

26. Antibiotic Selection Overview: Questions
Should be Considered
Is there a
clinical
evidence
of
infection?
YES
Is there high
risk of MRSA?
Include Anti-
MRSA therapy
in empiric
regimen
Has patient
received
antibiotics in
the past
month?
If YES include
agents active
against GNB
If NO, agents
against just
aerobic GPC
may be
sufficient
‐ Are there
risk factors for
Pseudomonas
infection?
If YES include
agents active
against
Pseudomonas
If NO,
antipseudom
onal
treatments
rarely neededNO
Do not treat
with
antibiotics

27. Lipsky BA et al, 2012 Infectious Diseases Society of America clinical practice guideline for the diagnosis and treatment of diabetic foot infections. Clinical infectious diseases. 2012 Jun 15;54(12):e132-73.

28. LipskyBAetal,2012InfectiousDiseasesSocietyofAmericaclinicalpracticeguidelineforthediagnosisandtreatmentofdiabeticfootinfections.Clinicalinfectiousdiseases.2012Jun15;54(12):e132-73.

29. https://www.moh.gov.sa/en/CC
C/healthp/regulations/Docume
nts/National%20Antimicrobial%2
0%20Guidelines.pdf

30. Lipsky BA et al, 2012 Infectious Diseases Society of America clinical practice guideline for the diagnosis and treatment of diabetic foot infections. Clinical infectious diseases. 2012 Jun 15;54(12):e132-73.

31. DEFINITIVE THERAPY
Should be based on the results of an appropriately obtained
culture and sensitivity testing of a wound specimen as well
as the patient’s clinical response to the empiric regimen.
If the cultures yield organisms that are commonly
considered to be contaminants (eg, CoNS, GPB) :
may be true pathogens in a DFI.
Because these organisms are often resistant to the
prescribed antibiotic, the clinician must decide if the
preponderance of clinical and microbiologic evidence
suggests they are pathogens that require targeted therapy.

32. SHOULD WE
CONSIDER
SURGICAL
INTERVENTION??

33. N.B:
1- The absence of fever or leukocytosis should not discourage the
clinician from considering surgical exploration of a DFI.
IDSARecommendation
Summary
1.Assessment by a surgeon for all patients with a moderate or severe DFI is
recommended
1.Urgent surgical intervention for infections accompanied by gas in the
deeper tissues, an abscess, or necrotizing fasciitis, and for wounds with
substantial nonviable tissue or extensive bone or joint involvement
1.Consider involving a vascular surgeon early for revascularization whenever
ischemia complicates a DFI, especially in any patient with a critically ischemic
limb.

34. WOUND CARE
Debridement:
1. Debridement involves removing necrotic or nonviable
tissue, slough, or foreign material from the wound, as
well as trimming any surrounding hyperkeratosis
(callus).
2. This process also removes colonizing bacteria, aids
granulation tissue formation and reepithelialization,
reduces pressure at callused sites, facilitates the
collection of appropriate specimens for culture, and
permits examination for the presence of deep tissue
(especially bone)
The goal is to enable wound healing and to
remove a reservoir of potential pathogens

35. WOUND CARE
Wound Dressings
The choice of dressing should be based on the size, depth,
and nature of the ulcer (eg, dry, exudative, purulent)
The principal function of a wound dressing is to help
achieve an optimal healing environment.
Available data do not advocate using topical antimicrobials
for most clinically uninfected wounds (cadexomeriodine and
silver-based dressings)

36. DIABETIC FOOT
OSTEOMYELITIS (DFO)
DFO Should be suspected in any infected, deep, or large foot
ulcer, especially one that is chronic or overlies a bony
prominence.
Imaging should be considered (plain radiographs and MRI)
The most definitive way to diagnose DFO is by the
combined findings on bone culture and histology
Surgical intervention, including
amputation with antibiotics is the
treatment choice

37. DIABETIC FOOT
OSTEOMYELITIS
Antibiotic therapy:
No data support the superiority of any specific antibiotic agent
or treatment strategy, route, or duration of therapy.
It is important to consider the presence and amount of any
residual dead or infected bone and the state of the soft
tissues.:
When a radical resection leaves no remaining infected tissue,
only a short duration of antibiotic therapy is needed (2-5 days)
 if infected bone remains despite surgery, prolonged treatment
is advisable. (4weeks)

38. REFERENCES
Lipsky BA, Berendt AR, Cornia PB, Pile JC, Peters EJ, Armstrong DG, Deery HG, Embil JM, Joseph
WS, Karchmer AW, Pinzur MS. 2012 Infectious Diseases Society of America clinical practice
guideline for the diagnosis and treatment of diabetic foot infections. Clinical infectious
diseases. 2012;54(12):e132-73.
Lipsky BA, Aragón‐Sánchez J, Diggle M, Embil J, Kono S, Lavery L, Senneville É, Urbančič‐Rovan
V, Van Asten S, Peters EJ, International Working Group on the Diabetic Foot (IWGDF). IWGDF
guidance on the diagnosis and management of foot infections in persons with diabetes.
Diabetes/metabolism research and reviews. 2016;32:45-74.
https://www.idf.org/our-network/regions-members/middle-east-and-north-
africa/members/46-saudi-arabia.html
Oxford Handbook of Infectious Diseases and Microbiology, 2nd Edition.