This document summarizes a presentation on skin and soft tissue infections (SSTIs). SSTIs can be caused by bacteria, fungi, parasites, or viruses. They range from mild to life-threatening. Risk factors include hospitalization, skin injuries, surgery, skin conditions like eczema, obesity, diabetes, and immunosuppression. Classification is based on lesion type, causative agent, and pathogenesis. Clinical manifestations vary and include dermatitis, erythrasma, ringworm, pyoderma, impetigo, and necrotizing infections. Diagnosis involves specimen collection and testing like microscopy, culture, identification and antimicrobial susceptibility. Treatment is guided by test results and prevention focuses on hygiene,

1. SKIN AND SOFT TISSUE INFECTIONS
DEPARTMENT OF MICROBIOLOGY AND IMMUNOLOGY
Presenter: Daniel Mwandu
Facilitator: Dr. Joel Manyahi
Date: 20th Dec, 2023
Venue: Microbiology Lab

2. Presentation Outline
• Introduction
• Risk factor for SSTIs
• Etiology
• Classification
• Clinical manifestation
• Laboratory diagnosis
• Treatment
• Prevention & Control

3. INTRODUCTION
• Skin and soft tissue infections (SSTIs) are clinical
entities of variable presentation, etiology and severity
that involve microbial invasion of the layers of the skin
and underlying soft tissues.
• It can be caused by direct penetration or by
hematogenous spread of pathogens from initial sites
• SSTIs range from mild infections, such as pyoderma,
to serious life-threatening infections, such as
necrotizing fasciitis.

4. Anatomy of the Skin

5. RISK FACTOR FOR SSTIS
• Long hospital stay
• Skin traumatic , Injury and open wounds
• Surgical,
• Skin conditions, such as athlete’s foot or eczema,
• Obesity, Diabetes,
• Immunodeficiency,
• Certain medications.

6. ETIOLOGY
S/no Agent Examples
01 Bacteria Staphylococcus aureus, Pseudomonas aeruginosa,
Enterococcus spp, Escherichia coli, Enterobacter spp,
Klebsiella spp, β-Hemolytic streptococci, Proteus mirabilis,
Coagulase-negative staphylococci, and Serratia spp
02 Fungi Sporothrix schenckii Blastomyces dermatitidis Histoplasma
capsulatum Coccidioides immitis Scopulariopsis spp.
03 Parasites Schistosomes, Strongyloides stercoralis , Wuchereria
bancrofti, Brugia malayi, Onchocerca volvulus, Hookworms
Leishmania spp and Ectoparasite( i.e. ticks, lice, scabies)
04 Viruses Paramyxovirus, Rubella virus, human parvovirus B19,
Enteroviruses, Alphaviruses, poxviridae, HPV,
Herpesviridae(HSV, VZV, CMV, EBV), and Hemorrhagic Fever
Viruses

7. CLASSIFICATION
The skin and soft tissue infections, can be
classified according to
i. The type of skin lesion produced( superficial or
deep)
ii. The causative organism(bacteria, parasites
,fungi or Viruses)
iii. The pathogenesis of the infection such as a
primary entity or secondary to a preexisting
infection or systemic manifestation).

8. Clinical Manifestation
Dermatitis
• It is a general term that describes an inflammation
of the skin.
• It is characterized by areas of redness, swelling,
and sometimes scaling of the skin and pruritus.
• The common infectious causes of dermatitis.
Intertrigo and Superficial Candidiasis

10. Cont..
Erythrasma
• It is a superficial, chronic skin infection
• Usually found in intertriginous areas
• It characterized by Red or brown
hyperpigmented patches of skin
with scaling and central
hypopigmentation.
• It often occurs in men, Obesity, DM
patients, and immunosuppressed.
• Corynebacterium minutissimum, a
skin biota, the causative organism,
produce a lesions with a coral red
fluorescence under a Wood lamp.

12. Cont..
Dermatophytosis
• Dermatophytosis is an infection of the hair, skin,
or nails caused by a dermatophyte
• Three genus Trichophyton, Epidermophyton,
and Microsporum are known causative of
infection, also known as ringworm or tinea
• The classic lesion of a dermatophyte infection is
a circular scaly patch of erythema with a raised
border. The edges are often more inflamed than
the center.

13. Types of ringworms/Tinea

14. Pyoderma

15. Impetigo Erysipelas
cellulitis

16. Bite Infections
• Bites from humans or animals can result to serious
infections with a mixture of aerobic and anaerobic
organisms originated from biting oral cavity and skin biota
of the patient.
• Dog bites are typically polymicrobial and Pasteurella,
Bacteroides spp., Fusobacterium, Prevotella,
staphylococci, etc
• Cat teeth can inflict very deep wounds and have a greater
risk of infection, soft tissue abscess formation, and
infection of underlying bones and joints compared with dog
bites.

17. • Cat bites also progress to
infection more rapidly than dog
bites. Pathogens are similar to
dog with inclusion of Francisella
tularensis
• Human bite pathogens
infections include
Streptococcus anginosus
group, S. aureus, Eikenella
corrodens, Fusobacterium
nucleatum, and Prevotella
melaninogenica.

18. Cont..
Diabetic Foot Infections
• It is a very common in DM patients;
• It is risk factors including peripheral neuropathy,
traumatic feet, and kidney dysfunction.
• it can manifest to cellulitis, soft tissue
ulceration and gangrene
• Ulcerative lesions and gangrene may be is a
result of mixed infections of gram positive and
negative bacteria and both aerobes anaerobic
bacteria.
.

19. Necrotizing Soft Tissue Infection
• A necrotizing soft tissue infection is a serious,
life-threatening condition. It can destroy skin,
muscle, and other soft tissues.
• Subtypes of necrotizing infection (infectious
gangrene) include
i. Type I caused by polymicrobial
ii. Type II, monomicrobial usually S. pyogenes
iii. Gas gangrene (type III), caused by Clostridium
spp. and marine vibrios

20. Common viral infection of skin

21. Laboratory diagnosis
Specimen collection:
-Proper container
-Proper transport media
-Proper storage
conditions
Collection technique:
-deep pus swab
-needle Aspirate
Near skin swab
Diagnosis technique:
-Macroscopic
-Microscopic
-Culture and
sensitivity
Successful
diagnosis

22. Sample
• A variety of diagnostic methods may be helpful
in determining the cause of skin and soft tissue
infections.
• Swabs of surface wounds or skin are likely to
yield colonizing or contaminating bacteria.
• Therefore deep aspirates or biopsies are
recommended.
• Other specimen are Blood for culture (if systemic
infection is suspected) and Fluid aspirates from
infected lesion for culture

24. Specimen collection;
• Collect the specimen using a sterile cotton-wool
swab if aspirate is not possible
• Pus from an abscess is best collected during
abscess incision and drainage.
• Pus from a wound should be collected before an
antiseptic dressing is applied
• Swabs should be well soaked in pus to collect
adequate pus.
24

25. 25

26. Storage and transportation;
• If pus swab use Amies transport
medium.
• If aspirate transfer the fluid to a
sterile, leak-proof container.
• cooked meat medium (or
thioglycollate broth) when anaerobic
pathogen are suspected

27. Macroscopic examination
• Observing the presence of granules and
branching filaments suggestive of infections
with actinomycetes or fungi.
• Color- white-yellow, brown, green
• Smell eg foul smelling for Anaerobic infections
• a Wood lamp, for suspicion of dermatophytes
(Microsporum) will fluoresce yellow-green.

28. Microscopic examination
• Gram stain
• For fungi suspicion ,a wet mount with 10% to
20% potassium hydroxide solution. Also
Calcofluor white (CW) stain may also be used.
• if mycobacterial disease is suspected, ZN or FM
• To identify Nocardia species, a modified acid-
fast stain can be performed,

29. Culture
• Bacteria culture by using BA and CA, and MCA;
• For anaerobic organisms, an anaerobic transport
and growth media should be used to maximize
recovery.
• For fungal(Candida spp.) on Sabouraud dextrose
agar(SDA).
• For mycobacteria spp, Lowenstein-Jensen and
Middlebrook media could be used
• For viruses, cell culture to observe CPE.

30. Identification
• A Gram stain provides the morphologic
• Growth characteristics and colonies
appearance in culture media,
• Convention Biochemical tests and API 20E can
help identify the organism,
• An automated MALDI-TOF MS has recently
been adapted in many laboratories.

31. Other techniques. These include
• Urine antigen detection (e.g., for systemic fungi);
• serum antibody tests for bacteria, viruses, and
parasites;
• Immunological assay(ELISA)
• Molecular techniques(PCR) for the detection of
a great variety of bacteria, fungi, and viruses.

32. Antimicrobial susceptibility testing
• Antimicrobial susceptibility testing is
subsequently performed on isolates based on
Standards updated guidelines eg CLSI and
EUCAST.
• Also molecular techniquies can be used for
detection the mecA gene confer for methicillin
resistance (e.g., in S. aureus) and the vanA and
vanB genes conferring vancomycin resistance
(e.g., in Enterococcus).
• Also MALDI-TOF MS can be used

34. Treatment,
• Treatment should be guided by AST results
• For bacteria wound dressing with mupirocin
(topical)
• For severe bacteria infection, Topically or orally
administered erythromycin or clindamycin and
amoxicillin-clavulanic are useful
• Superficial mycoses use topical antifungal
agents such as clotrimazole. Oral antifungal
agents such as fluconazole,

35. Prevention and control
Improve personal hygiene
 Hand washing
Wash lesions with soap and water
Remove crust
Vaccination to immunocompromised such as
namely on conjugated vaccines against
pneumococcus, H influenzae and N meningitidis,

36. References
• Jawetz, Medical Microbiology, 28th Edition.
• Textbook of Diagnostic Microbiology-sixth Edition (2018)
By Connie R. Mahon, Donald C. Lehman.
• Monica Cheersburgh 2nd Edition.
• Tanzania Standard Treatment Guideline, 2021
• Published Articles.