1. Bacterial Skin Infections
Professor Sudheer Kher

2. Learning Objectives Enumerate the microbes causing skin infections.
Describe the
characteristic clinical manifestations
methods of laboratory diagnosis
principles of management
methods of prevention of each of the infections listed.

3. Bacterial Infection of Skin
The Skin
Definition
Skin is largest organ of body. Maintains homeostasis, protects underlying tissues and organs, protects body from mechanical injury, damaging substances, and ultraviolet rays of sun.

4. Recurrent skin infections
Recurrent skin infections should raise suspicion of colonization
Staphylococcal nasal carriage
Resistant strains of bacteria (eg, methicillin-resistant Staphylococcus aureus [MRSA]),
Cancer
Poorly controlled diabetes
Other reasons for immunocompromise (eg, HIV, hepatitis, advanced age, congenital susceptibility).

5. Pyoderma
Pyoderma is a group name for pyococcal dermatoses which are generally purulent. In tropical countries, pyoderma is a common problem, particularly in the summer and the monsoon.
The two important pyogenic organisms are the Staphylococcus aureus and the Streptococcus pyogenes.
Follicular infections are mainly due to staphylococci; while erysipelas and cellulitis are caused by streptococci.
Besides these, other organisms which occasionally come across in pyodermas are Proteus, Pseudomonas and Coliform bacilli.

6. Skin Infections Infection Site Causal Organism Boil Hair follicle
Staphylococcus aureus
Carbuncle
Multiple Hair follicles
Stye
Hair follicle of eye lash
Sycosis barbae
Shaving area
Pemphigus neonatorum
Infant’s skin
Toxic epidermal necrolysis
Erysipelas
Face, sometimes limbs
Streptococcus pyogenes
Acne vulgaris
Face & Back
Propionibacterium acnes

7. S. aureus produces skin infection
I. Direct infection of skin and adjacent tissues
a. Impetigo
b. Ecthyma
c. Folliculitis
d. Furunculosis
e. Carbuncle
f. Sycosis barbae
II. Cutaneous disease due to effect of bacterial toxin
a. Staphylococcal scalded skin syndrome
b. Toxic shock syndrome

8. ß-hemolytic streptococcus produces skin infection
I. Direct infection of skin or subcutaneous
a. Impetigo (non bullous)
b. Ecthyma
c. Erysipelas
d. Cellulitis
e. Necrotizing fascitis
II. Secondary infection
Eczema infection

9. Folliculitis Folliculitis is a bacterial infection of hair follicles.
Folliculitis is usually caused by Staphylococcus aureus but occasionally Pseudomonas aeruginosa (hot-tub folliculitis) or other organisms. Hot-tub folliculitis occurs because of inadequate treatment of water with chlorine or bromine.

11. Folliculitis manifests as superficial pustules or inflammatory nodules surrounding hair follicles.

12. Furuncles and Carbuncles
Furuncles are skin abscesses caused by staphylococcal infection, which involve a hair follicle and surrounding tissue.
Carbuncles are clusters of furuncles connected subcutaneously, causing deeper suppuration and scarring. They are smaller and more superficial than subcutaneous abscesses

13. Furuncles (boils) are tender nodules or pustules caused by staphylococcal infection. Carbuncles are clusters of furuncles that are subcutaneously connected.

14. Carbuncles

15. Treatment of folliculitis
Because most folliculitis is caused by S. aureus, clindamycin 1% lotion or gel may be applied topically bid for 7 to 10 days. Alternatively, benzoyl peroxide 5% wash may be used when showering for 5 to 7 days. Extensive cutaneous involvement may warrant systemic therapy (eg, cephalexin 250 to 500 mg po tid to qid for 10 days).
If these measures do not result in a cure, or folliculitis recurs, pustules are Gram stained and cultured to rule out gram-negative or methicillin-resistant S. aureus (MRSA) etiology, and nares are cultured to rule out nasal staphylococcal carriage. Potassium hydroxide wet mount should be done on a plucked hair to rule out fungal folliculitis.
Treatment for MRSA usually requires two oral antibiotics, and the choice of therapeutic drugs should be based on culture and sensitivity reports.
Hot-tub folliculitis usually resolves without treatment. However, adequate chlorination of the hot tub is necessary to prevent recurrences and to protect others from infection.

16. Hidradenitis suppurativa
Hidradenitis suppurativa is a chronic, scarring inflammation of apocrine glands of the axillae, groin, and around the nipples and anus.

17. Cellulitis
Cellulitis is acute bacterial infection of the skin and subcutaneous tissue most often caused by streptococci or staphylococci.

18. Treatment of cellulitis
Treatment is with antibiotics. For most patients, empiric treatment effective against both group A streptococci and S. aureus is used.
Oral therapy is usually adequate with dicloxacillin 250 mg or cephalexin 500 mg po qid for mild infections. Levofloxacin 500 mg po once/day or moxifloxacin mg po once/day works well for patients who are unlikely to adhere to multiple daily dosing schedules.
For more serious infections, oxacillin or nafcillin 1 g is given IV q 6 h.
Immobilization and elevation of the affected area help reduce edema; cool, wet dressings relieve local discomfort.

19. Cutaneous Abscess
A cutaneous abscess is a localized collection of pus in the skin and may occur on any skin surface.

20. Erysipelas
Erysipelas is a type of superficial cellulitis with dermal lymphatic involvement.
Erysipelas is characterized clinically by shiny, raised, indurated, and tender plaque-like lesions with distinct margins.
Erysipelas is most often caused by group A (or rarely group C or G) β-hemolytic streptococci and occurs most frequently on the legs and face.
Other causes - Staphylococcus aureus (including methicillin-resistant S. aureus [MRSA]), Klebsiella pneumoniae, Haemophilus influenzae, Escherichia coli.
It is commonly accompanied by high fever, chills, and malaise. Erysipelas may be recurrent and may result in chronic lymphedema.

21. Erysipelas is characterized by shiny, raised, indurated, and tender plaque-like lesions with distinct margins. It is most often caused by β-hemolytic streptococci and occurs most frequently on the legs and face.

22. Erythrasma
Erythrasma is an intertriginous infection with Corynebacterium minutissimum.
Most common among patients with diabetes and among people living in the tropics.

23. Impetigo and Ecthyma
Impetigo is a superficial skin infection with crusting or bullae caused by streptococci, staphylococci, or both.
Ecthyma is an ulcerative form of impetigo.

24. Impetigo (Non-Bullous) Impetigo (Bullous)
Bullous impetigo is a superficial skin infection that manifests as clusters of vesicles or pustules that enlarge rapidly to form bullae. The bullae burst and expose larger bases, which become covered with honey-colored varnish or crust.
Non-bullous impetigo is a superficial skin infection that manifests as clusters of vesicles or pustules that rupture and develop a honey-colored crust.

25. Ecthyma gangrenosum is a bacterial skin infection (caused by Pseudomonas aeruginosa) that usually occurs in people with a compromised immune system.
Ecthyma is a skin infection similar to impetigo, but more deeply invasive. Usually caused by a streptococcus infection, ecthyma goes through the outer layer (epidermis) to the deeper layer (dermis) of skin, possibly causing scars.

26. Necrotizing Subcutaneous Infection (Necrotizing Fasciitis)
Typically caused by a mixture of aerobic and anaerobic organisms that cause necrosis of subcutaneous tissue, usually including the fascia.
This infection most commonly affects the extremities and perineum. Affected tissues become red, hot, and swollen, resembling severe cellulitis.
Without timely treatment, the area becomes gangrenous. Patients are acutely ill. Diagnosis is by history and examination and is supported by evidence of overwhelming infection.
Treatment involves antibiotics and surgical debridement. Prognosis is poor without early, aggressive treatment.

27. Necrotising fasciitis

28. Treatment
Surgical debridement
Antibiotics
Amputation if necessary

29. Bacterial Infection of Skin Lab. Diagnosis
Specimen collection.
Skin biopsy
Skin swab
Pus swab
Nasal / skin swab

30. Lab. Diagnosis Suspected organisms
Impetigo: Group A Streptococcus, Staphylococcus aureus
Folliculitis: Staphylococcus aureus, Pseudomonas aeruginosa
Furuncles: Staphylococcus aureus
Carbuncles: Staphylococcus aureus
Cellulitis: Group A Streptococcus, Staphylococcus aureus, Hemophilus influenzae
Erysipelas: Group A Streptococcus
Necrotizing fasciitis: Group A Streptococcus, Clostridium perfringens and other species, Bacteroides fragilis, the anaerobes, Enterobacteriaceae, Pseudomonas aeruginosa

31. Principles of therapy of pyoderma
Good personal hygiene
Management of predisposing factors
Local
Attend to traumas, Pressure, Sweating, Bites
Treat pre-existing dermatosis
Investigate carrier sites: Nose, Axilla, Perineum
Systemic
Treatment of disease like DM
Nutritional deficiency
Immunodeficiency

32. Principles of therapy of pyoderma
Local therapy
Cleaning with soap-water and weak KMN04 solution
Removal of crusts with KMN04 solution
Application of antibacterial cream
Systemic therapy
Antibiotics

33. Recurrent staphylococcal infection
Persistent nasal carriage
Abnormal neutrophilic chemotaxis
Deficient intracellular killing
Immunodeficient status
D.M.

34. Staph. carriage elimination
Nasal & perineal care
Rifampicin 600 mg/d 7-10 days
Clindamycin 150 mg/d 3 months
Topical mupirocin
Replacement of microflora with a less pathogenic stains of S.aurus (strain 502)

35. Antibiotic Resistance Profiles of MRSA
100% B-lactam antibiotics
94% resistant to clindamycin and erythromycin
89% resistant to ciprofloxacin
56% resistant to trimethoprimsulfamethoxazole
33% resistant to tetracycline
3% resistant to rifampin
3% resistant to fusidic acid
2% resistant to mupirocin