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
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.
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.
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
9.
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.
11.
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.
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
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
23.
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
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
33.
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.
Editor's Notes
The skin, skin structures, and normal microbiota play a significant role in protecting the host against microbial invasion and disease. ■ Virulence factors of disease-producing organisms (e.g., toxins) can enable the organisms to evade host defense mechanisms, which can result in severe manifestations of infection. ■ A compromised immune system can lead to more severe or unusual manifestations of infection and can allow normally innocuous organisms to be pathogenic. ■ The occurrence of disease in a host is a function of the underlying host’s immunity and virulence of the pathogen. ■ The method and site of collection, quality of the clinical specimen, and clinical context are all important factors to consider when distinguishing between colonization and infection. ■ Proper specimen collection and laboratory processing of specimens are factors critical to the success of making a microbiological diagnosis of infection
Bacteria, viruses, fungi, and parasites are all important causes of skin and soft tissue infections.
S. aureus and S. pyogenes are important causes of pyoderma.
Intertrigo (intertriginous dermatitis) is an inflammatory cutaneous condition that occurs in body areas subjected to heat, moisture, and friction, which work together to cause maceration and skin breakdown. Infectious agents enhance this process. Intertrigo usually occurs in the skin folds of infants and obese adults and often can be found in the axillae, in perineum (e.g., diaper rash), beneath the breasts, and in abdominal folds. The most common organism present in these areas is Candida, although S. aureus and coliforms also can play a role
A and B Axilla of a 65-year-old White man with erythrasma showing a well-demarcated erythematous plaque with fine scale (A). Wood lamp examination of the area showed characteristic bright coral red fluorescence (B).
C and D A well-demarcated, red-brown plaque with fine scale in the antecubital fossa of an obese Hispanic woman (C). Wood lamp examination revealed bright coral red fluorescence (D).
Transmitted by human contact, sharing of clothesi ans coms, also zoonotic.
Erysipelas
The impairment of host defenses seen in diabetic patients can also allow weakly virulent organisms, such as coagulase-negative staphylococci and diphtheroids, to be pathogens in the skin.
For example, if pustules or vesicles are present, the roof or crust should be removed with a sterile blade, and any pus or exudate should be Gram stained and cultured
Anaerobic culture
When an anaerobic infection is suspected (specimen is often foul-smelling), or the Gram smear shows an ‘anaerobic mixed flora’, inoculate a second blood agar plate and incubate it anaerobically (see subunit 7.4) for up to 48 hours. The anaerobic blood agar plate may be made selective by adding neomycin to it (see No. 16).
At a final neomycin concentration of 50–70 g/ml, the majority of facultative anaerobic Gram negative rods will be inhibited.