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COMMON CUTANEOUS BACTERIAL INFECTIONS

PPT Content - Direct Paste Format

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[SLIDE 1] TITLE SLIDE

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[SLIDE 2] OVERVIEW / OUTLINE

1. Impetigo
2. Ecthyma
3. Folliculitis (including Sycosis Barbae)
4. Furunculosis & Carbuncle
5. Cellulitis & Erysipelas
6. Erythrasma
7. Pitted Keratolysis

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SECTION 1 - IMPETIGO

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[SLIDE 3] IMPETIGO - DEFINITION & OVERVIEW

• Superficial bacterial skin infection involving the epidermis
• Most common bacterial skin infection in children
• Two forms: Non-bullous (Impetigo contagiosa) and Bullous impetigo
• Highly contagious; spreads by direct contact

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[SLIDE 4] IMPETIGO - ETIOLOGY

• 50-70% of cases: Staphylococcus aureus (phage group 2; types 71 or 55)
• Remainder: Streptococcus pyogenes (Group A beta-hemolytic) alone or combined
• Bullous impetigo: Exclusively S. aureus - produces exfoliative toxins A & B (cleave desmoglein-1)
• Neonatal impetigo: Group B streptococci; groups C and G rarely isolated
• Streptococci often represent the early pathogen; staphylococci replace as lesion matures

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[SLIDE 5] IMPETIGO - CLINICAL FEATURES

• Discrete thin-walled vesicles → pustules → rupture
• Honey-colored, golden-brown crusts on an erythematous base
• Face (perioral, perinasal), extremities most affected
• Regional lymphadenopathy (especially streptococcal)

• Strikingly large, fragile bullae - predilection for face and perineum
• Rupture → circinate, weepy or crusted lesions ("impetigo circinata")
• Axillae and groins in adults; face and perineum in neonates
• Constitutional symptoms absent initially; neonates at risk for scalded skin syndrome

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[SLIDE 6] IMPETIGO - RISK FACTORS & COMPLICATIONS

• Hot, humid weather; summer months in temperate zones
• Young children; crowded settings (day care, schools)
• Pre-existing skin disease: atopic dermatitis, scabies, pediculosis, insect bites
• Nasal or perineal S. aureus carriage

• Acute Post-Streptococcal Glomerulonephritis (AGN): 2-5% (up to 10-15% with nephritogenic strains)
• Nephritogenic strains: M-types 49, 55, 57, 60, and M-type 2
• Treatment does NOT reduce risk of AGN

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[SLIDE 7] IMPETIGO - DIFFERENTIAL DIAGNOSIS

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[SLIDE 8] IMPETIGO - MANAGEMENT

• Soak off crusts with warm compresses; clean with soap and water
• Apply antibiotic ointment twice daily

• Mupirocin 2% ointment/cream - first-line
• Retapamulin 1% ointment
• Fusidic acid cream
• Reduces risk by 47% vs placebo in high-risk children

• Dicloxacillin or first-generation cephalosporin (cefalexin)
• If MRSA suspected: TMP-SMX, clindamycin, or doxycycline
• Adjust based on culture sensitivities

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[SLIDE 9] IMPETIGO - PREVENTION

• Hand hygiene - frequent, thorough handwashing
• Avoid sharing towels, clothing, sports equipment
• Keep fingernails short and clean
• Cover lesions to prevent spread
• Prophylactic antibiotic ointment to skin trauma sites in high-risk children
• Treat household contacts if recurrent episodes

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SECTION 2 - ECTHYMA

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[SLIDE 10] ECTHYMA - DEFINITION & ETIOLOGY

• Ulcerative pyoderma penetrating through the full epidermis into the dermis
• Described as "impetigo with deeper penetration"

• Primary: Streptococcus pyogenes (Group A beta-hemolytic)
• Secondary: Staphylococcus aureus (especially in IV drug users, HIV patients)
• Predisposing: malnutrition, uncleanliness, trauma, immunosuppression

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[SLIDE 11] ECTHYMA - CLINICAL FEATURES

• Begins as vesicle or vesicopustule on erythematous base
• Enlarges → thick, adherent, "oyster-shell" crust over days
• Removal of crust reveals saucer-shaped ulcer with raised violaceous edges and raw base
• Lower extremities most common; also buttocks
• Local adenopathy may be present
• Heals with scarring (unlike impetigo)
• Rarely progresses to gangrene in debilitated patients
• Vesicles may mimic HSV, especially in atopic dermatitis

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[SLIDE 12] ECTHYMA - DIFFERENTIAL DIAGNOSIS

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[SLIDE 13] ECTHYMA - MANAGEMENT

• Soak crust with warm compresses; remove carefully
• Clean with soap and water

• Mupirocin ointment twice daily
• Retapamulin or bacitracin ointment - alternatives

• Dicloxacillin or first-generation cephalosporin (oral)
• Adjust per culture and sensitivity
• TMP-SMX or clindamycin if MRSA suspected

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SECTION 3 - FOLLICULITIS

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[SLIDE 14] FOLLICULITIS - DEFINITION & ETIOLOGY

• Superficial or deep infection/inflammation of hair follicles

• Most common: Staphylococcus aureus
• Gram-negative folliculitis: After prolonged antibiotic use for acne (Klebsiella, Enterobacter, Proteus)
• Hot tub folliculitis: Pseudomonas aeruginosa
• Pityrosporum folliculitis: Malassezia spp. (not bacterial, but clinically mimics)
• MRSA increasingly implicated

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[SLIDE 15] FOLLICULITIS - CLINICAL FEATURES

• Thin-walled yellowish-white pustules at follicular orifices
• Develops in crops, heals in a few days
• Extremities, scalp, face (perioral)

• Any hair-bearing area: trunk, extremities, beard, axillae, pubis, thighs
• Pubic folliculitis may be sexually transmitted

• Chronic perifollicular pustular infection of the bearded region
• Papules and pustules pierced by hairs; burning/itching
• Upper lip near nose is a characteristic early site
• Atrophic scarring may result in severe cases
• Associated blepharitis and conjunctivitis in severe cases

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[SLIDE 16] FOLLICULITIS - DIFFERENTIAL DIAGNOSIS

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[SLIDE 17] FOLLICULITIS - MANAGEMENT

• Mupirocin 2% ointment
• Topical clindamycin or retapamulin
• Benzoyl peroxide washes (5-10%)
• Chlorhexidine 4% wash
• Dilute sodium hypochlorite baths (bleach baths: ½ cup/40-gallon tub)
• Aluminum chloride anhydrous (Drysol) - effective for chronic buttock folliculitis

• First-generation cephalosporin or dicloxacillin
• If MRSA suspected: TMP-SMX, clindamycin, doxycycline, minocycline, or linezolid
• Base on culture and sensitivity

• Mupirocin to anterior nares daily for 5 days; repeat monthly

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SECTION 4 - FURUNCULOSIS & CARBUNCLE

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[SLIDE 18] FURUNCULOSIS & CARBUNCLE - DEFINITION & ETIOLOGY

• Acute, round, tender, circumscribed, perifollicular abscess ending in central suppuration
• Deep S. aureus infection of hair follicle and surrounding tissue

• Two or more confluent furuncles with separate heads
• Deeper, more severe; associated with systemic features

• Staphylococcus aureus - principal organism
• MRSA increasingly common (community-acquired MRSA)
• Nasal/perineal carrier state is the most important reservoir

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[SLIDE 19] FURUNCULOSIS - CLINICAL FEATURES & RISK FACTORS

• Sites of predilection: nape, axillae, buttocks, face (upper lip, nose - DANGER AREA)
• Begin in hair follicles → central necrosis → spontaneous rupture with purulent/necrotic discharge
• Pain, warmth, tenderness, induration
• Carbuncles: constitutional symptoms common (fever, malaise)

• Diabetes mellitus
• Alcoholism / malnutrition
• Blood dyscrasias; neutrophil dysfunction disorders
• Immunosuppression (HIV/AIDS, steroids, isotretinoin therapy)
• Renal dialysis patients
• Atopic dermatitis (promotes S. aureus carrier state)

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[SLIDE 20] FURUNCULOSIS - DIFFERENTIAL DIAGNOSIS

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[SLIDE 21] FURUNCULOSIS - MANAGEMENT

• Incision & Drainage (I&D) - definitive for fluctuant abscess
• Warm compresses for early non-fluctuant lesions
• Avoid I&D for lesions on upper lip, nose, external ear canal (sinus/CNS risk)

• RCT evidence: clindamycin OR TMP-SMX after I&D improves cure rates even for abscesses <5 cm
• MSSA: dicloxacillin, first-gen cephalosporin, clindamycin
• MRSA/resistant: TMP-SMX, doxycycline, minocycline, clindamycin, linezolid
• Carbuncles or facial furuncles: IV antibiotics may be required

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[SLIDE 22] FURUNCULOSIS - PREVENTION

• Daily 4% chlorhexidine wash (axillae, groin, perianal) for 1 week
• Bleach baths (sodium hypochlorite 0.005%) - 3x/week
• Launder bedding and clothing daily (initially)
• Frequent handwashing; avoid sharing personal items
• Mupirocin to anterior nares twice daily (patient and family)
• Rifampin 10 days + dicloxacillin (MSSA) or TMP-SMX (MRSA) for carriage eradication
• Low-dose clindamycin for 3 months for recurrent furunculosis
• Treat atopic dermatitis; don't share moisturizer containers

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SECTION 5 - CELLULITIS & ERYSIPELAS

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[SLIDE 23] CELLULITIS & ERYSIPELAS - DEFINITION

• Infection of the deep dermis and subcutaneous tissue
• Presents with erythema, edema, warmth, and pain (Celsus's 4 cardinal signs)
• Ill-defined borders; unilateral lower extremity most common

• Variant involving predominantly superficial lymphatic vessels
• Sharply demarcated ("raised palpable edge"), bright red, edematous plaques
• More superficial; fever more common

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[SLIDE 24] CELLULITIS - ETIOLOGY & MICROBIOLOGY

• Streptococcus pyogenes (Group A beta-hemolytic) - historically classic for erysipelas
• Staphylococcus aureus (including community-acquired MRSA)
• Groups B, C, G streptococci

• Bite wounds: Pasteurella spp., Eikenella, Capnocytophaga canimorsus (polymicrobial)
• Aquatic trauma: Aeromonas, Vibrio vulnificus, Mycobacterium marinum
• Immunocompromised/diabetics: Gram-negative organisms, Pseudomonas, fungi
• Portal of entry found in up to 62% of cases (toe web infections most common)

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[SLIDE 25] CELLULITIS - CLINICAL FEATURES

• Spreading ill-defined erythema, edema, warmth, pain
• Lower extremity most common in adults; face in children
• Almost always unilateral (bilateral = consider alternative diagnosis)
• Lymphangitis (linear streaking), tender lymphadenopathy
• "Skip areas" of spared skin; peau d'orange skin
• Bulla formation, superficial necrosis in severe cases

• Painful, warm erythema with well-defined, raised borders
• Leg 76-90%, then face and upper extremity
• Salmon-red color; surface may look like orange peel
• Fever, chills, and malaise more common

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[SLIDE 26] CELLULITIS - DIAGNOSIS & INVESTIGATIONS

• History and physical examination
• Misdiagnosis rate >30% in acute care settings
• Dermatology consultation improves diagnostic accuracy

• Asymmetry (unilateral): 3 pts
• Leukocytosis ≥10,000/μL: 1 pt
• Tachycardia ≥90 bpm: 1 pt
• Age ≥70 years: 2 pts
• Score 0-2: NPV >83% | Score ≥5: PPV >82%

• CBC: leukocytosis in 34-50%
• ESR/CRP elevated in >75%
• Blood cultures: positive in only ~5% (reserve for high-risk patients)
• Skin swabs/needle aspiration: low yield; not routinely recommended (IDSA 2014)
• Abscess/pustule cultures: recommended

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[SLIDE 27] CELLULITIS - DIFFERENTIAL DIAGNOSIS

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[SLIDE 28] CELLULITIS - MANAGEMENT

• Penicillin V or amoxicillin-clavulanate
• Cephalexin (first-gen cephalosporin) - preferred
• Dicloxacillin

• TMP-SMX (trimethoprim-sulfamethoxazole)
• Clindamycin
• Doxycycline

• Cefazolin or ceftriaxone - standard
• Nafcillin / oxacillin - for MSSA
• Vancomycin - MRSA / severe / penicillin allergy
• Piperacillin-tazobactam or imipenem if polymicrobial suspected

• Elevate affected limb
• Mark the advancing border with pen to monitor response
• Serial photography in inpatients

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[SLIDE 29] CELLULITIS - PREVENTION OF RECURRENCE

• Treat underlying predisposing factors (tinea pedis, lymphedema, leg edema)
• Compression stockings for lymphedema / chronic edema
• Maintain skin integrity - moisturize, avoid trauma
• Secondary prophylaxis (recurrent cellulitis ≥3 episodes/year):
  • Penicillin V 250 mg twice daily (IDSA recommended)
  • Erythromycin if penicillin allergic
• Weight management (obesity is a risk factor)
• Optimize glycemic control in diabetics

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SECTION 6 - ERYTHRASMA

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[SLIDE 30] ERYTHRASMA - DEFINITION & ETIOLOGY

• Superficial bacterial infection of the skin characterized by well-defined reddish-brown patches in intertriginous areas

• Corynebacterium minutissimum - gram-positive diphtheroid rod
• Produces coproporphyrin III → characteristic fluorescence
• Produces two serine proteases

• More common in tropical climates
• Males > Females
• Predisposed: obesity, diabetes, immunosuppression (HIV)
• In immunocompromised: may cause bacteremia, cellulitis, costochondral abscess

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[SLIDE 31] ERYTHRASMA - CLINICAL FEATURES

• Web spaces of toes (4th-5th most common): white hyperkeratotic macerated plaque
• Genitocrural area, axillae, inframammary region: reddish-brown, finely scaled, "cigarette paper" thin patches
• Intergluteal cleft, perianal skin
• Lesions are well-demarcated with uniform appearance (unlike tinea which has central clearing)

• Usually asymptomatic
• Genitocrural form: may itch and burn

• Wood's lamp: Coral-red fluorescence (coproporphyrin III)
• Wash area before exam to avoid false-negative

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[SLIDE 32] ERYTHRASMA - DIFFERENTIAL DIAGNOSIS

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[SLIDE 33] ERYTHRASMA - MANAGEMENT

• Topical erythromycin solution or gel - first-line
• Topical clindamycin
• Fusidic acid cream
• Whitfield's ointment (alternative)

• Erythromycin 250 mg four times daily for 14 days - effective
• Clarithromycin 1 g single dose - equally effective, better compliance
• Tetracyclines: alternative option

• Keep intertriginous areas dry
• Lose weight; control diabetes
• Absorbent powders; loose-fitting clothing

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SECTION 7 - PITTED KERATOLYSIS

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[SLIDE 34] PITTED KERATOLYSIS - DEFINITION & ETIOLOGY

• Bacterial infection of the plantar stratum corneum characterized by small crateriform pits on pressure-bearing areas of feet

• Kytococcus sedentarius (formerly Micrococcus sedentarius) - primary organism
• Dermatophilus congolensis and Corynebacterium spp. also implicated
• Produces two serine proteases that degrade keratin
• Male:Female ratio approximately 8:1
• Tropical climates >> temperate climates

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[SLIDE 35] PITTED KERATOLYSIS - CLINICAL FEATURES

• Shallow, discrete, round pits 1-3 mm in diameter (some >0.7 mm)
• Located on pressure-bearing areas: ball of foot, heel, plantar surface of toes
• Pits coalesce → large defect with serpiginous borders
• Web spaces also involved (may be the only site)
• Usually asymptomatic but:
  • Malodorous (2/3 of patients) - characteristic fetid odor
  • Sliminess - feet stick to socks (70%)
  • Pain, burning, irritation (1/3 of patients)
• Histology: keratin pits lined by cocci and filamentous bacteria

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[SLIDE 36] PITTED KERATOLYSIS - DIFFERENTIAL DIAGNOSIS

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[SLIDE 37] PITTED KERATOLYSIS - MANAGEMENT

• Topical erythromycin - first-line
• Topical clindamycin
• Topical mupirocin

• Miconazole or clotrimazole cream
• Whitfield's ointment

• 5% benzoyl peroxide gel
• 10-20% aluminum chloride solution (anti-hyperhidrosis)
• Botulinum toxin injection if associated hyperhidrosis

• Keep feet dry; change socks frequently
• Breathable footwear; avoid occlusive shoes
• Absorbent foot powders

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[SLIDE 38] COMPARATIVE SUMMARY TABLE

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[SLIDE 39] KEY REFERENCES

1. Andrews' Diseases of the Skin: Clinical Dermatology, James WD et al., Elsevier, 12e (9780323547536)
2. Fitzpatrick's Dermatology, Kang S et al., McGraw-Hill, 9e (9780071837781) - Chapters 150, 151
3. IDSA Clinical Practice Guidelines for Skin and Soft-Tissue Infections, Stevens DL et al., Clin Infect Dis, 2014
4. Jacka J et al., "Systematic Review of Cellulitis Guidelines: Non-Pharmacological Management in Preventing Recurrence," Australas J Dermatol, 2025 (PMID 40530782)
5. Dermatology 2-Volume Set, Bolognia JL et al., 5e (9780702082252)

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