Introduction to Bacterial Infections (Pyodermas)😍

Non-Follicular Infections

Impetigo

• Strep > Staph

Bullous Impetigo:

• Bullae (blisters) present

• Common in newborns

• Cause: Only Staphylococcus aureus → Exfoliative toxin

• Crust color: Golden

• Target: Desmoglein 1 (in skin, for bulla)

• Bullae: Superficial, hypopyon (fluid at bottom)

Non-bullous Impetigo (Impetigo Contagiosum):

• Starts as bullae, then ruptures to form crust

• Presentation: Crusted erosions

• Common in toddlers/school-aged children

• Cause:
• Streptococcus (developing nations) >
• Staphylococcus (developed nations)

• Crust color: Honey-colored

• Complication: Post-streptococcal glomerulonephritis (rare)

General Characteristics:

• Mainly on face (common)

Diagnosis:

• Gram stain (Staph & Strep: Gram-positive cocci)

Treatment:

• Mild: Topical antibiotics (Mupirocin, Fusidic acid)

• Severe: Oral antibiotics

Scarlet Fever

• Second disease

• Desquamatous rash
• Sandpaper rash

• S. Pyogenes

• Strawberry tongue

• Pastia lines

• Strawberry, Pasta in a Sandpaper
• For pus patient on second day

 

Erysipelas vs. Cellulitis

• Similarities:
• Tenderness at onset
• Common sites: Legs or forearms
• Systemic symptoms: Fever, malaise
• Swelling present

• Differentiation:
• Erysipelas:
• Group A β Hemolytic Streptococci (Pyogenes)
• Clear, demarcated margin
• Affects superficial dermis & lymphatics
• Million ear sign → Ear pinna involved = Erysipelas
• Cellulitis:
• Strep or Staph
• Diffuse, not clearly demarcated
• Deep subcutaneous infection
• Affects deep dermis to subcutis

• Treatment:
• Both: Oral antibiotics, leg elevation, NSAIDs
• Cellulitis: May need longer therapy

Follicular Infections

• Affect the hair follicle

• Common cause for all follicular infections: Staphylococcus

Types:

1. Superficial Folliculitis (Bockhart's folliculitis)

• Limited to superficial follicle

• Presents: Minute, tender pustules with erythema

• Treatment: Topical antibiotics

2. Deep Folliculitis

• Infection extends deep into follicle

• Can lead to:
1. Sycosis Barbae:
• Not a fungal infection
• Bacterial, painful, pus, crusting
• Distinguish from fungal Tinea Barbae
• Tinea is itchier
2. Dissecting Cellulitis of Scalp 
• if on scalp

• Treatment: Oral antibiotics

• Mnemonic:
• Psycho Barbie (Sycosis Barbae) → With Pus
• Tiny barbie (Tinea Barbae) → Itching

3. Furuncle

• Folliculitis + perifollicular spread
• (erythema, inflammation, tenderness)

• Treatment: Oral antibiotics

Carbuncle

Definition

• Multiple small abscesses coalesce to form a large abscess

Clinical Presentation

• Most common: In diabetics

• Features: Multiple pus points

• Site: Most commonly the nape of the neck

Management

• Drainage with a cruciate incision (to drain all the abscesses)

Toxin-Mediated Infections

Staphylococcal Scalded Skin Syndrome (SSSS)/Ritter disease

• Cause: Staphylococcus (exfoliative toxin ET1)

• Affected: Newborns, infants

• Pathophysiology:
• Starts from staph infection elsewhere
• ET1 binds to Desmoglein 1
• Same as Impetigo
• Intraepidermal split at granular layer
• Oral mucosa spared

• Presentation:
• Exfoliating skin, peeling
• Fever, malaise, possible failure to thrive

• Diagnosis: Nikolsky test positive

• Treatment: Systemic antibiotics

• Mnemonic:
• Toxic staffs exfoliated (Staph → Exfoliative Toxin 1) a newborn on day 1 (desmoglin 1)

Causative Organisms Summary

• Single organism involved summary

Organism	Infections
Staph	• Folliculitis, Furuncles, Carbuncles • Bullous impetigo • SSSS
Strep	• Scarlet fever

• Mnemonic:
• Staphylococcus for follicular;
• Streptococcus for most non-follicular

Corynebacterium Infections

1. Erythrasma

• Cause: Corynebacterium minutissimum

• Sites: Axilla, interdigital web, groins (most common)

• Presentation: Well-demarcated, non-itchy, mildly scaly plaques

• Diagnosis:
• Woods lamp: Coral red fluorescence (due to Corporphyrin 3)

2. Pitted Keratolysis

• Cause: Micrococcus sedentarius (a Corynebacterium)
• Mnemonic: Micro holes (Pitted) in sedentary part

• Predisposing factors: Hyperhidrosis, foot moisture (e.g., swimmers)

• Presentation: Small superficial pits on feet

Virulence factors:

• Capsule: Composed of polypeptide (polyglutamate).

• Bioterrorism agent → Pulmonary anthrax

• Anthrax toxin (Mnemonic: EPL)
• Edema factor: ↑↑ cAMP.
• Protective factor: Facilitates attachment.
• Lethal factor: Causes cell death.

Types of anthrax:

• Cutaneous anthrax
• Hide-Porters disease
• Acquired via skin-to-skin contact.
• Manifests as a malignant pustule (misnomer) with a black eschar.

• Pulmonary anthrax
• Wool sorter's disease
• Causes hemorrhagic mediastinitis.
• Most common form in bioterrorism.

• Intestinal anthrax:
• From consuming undercooked meat.
• Leads to hemorrhagic enteritis.

Diagnosis:

• Serology: Ascoli's ring thermoprecipitin test and ELISA.

• Diagnosis: McFadyean test
• Polychrome Methylene Blue
• Amorphous purplish material around bacilli
• (Capsular material)

• Microscopy: Bamboo stick or box car appearance, and Medusa head appearance.

Culture:

• Blood agar: Frosted glass appearance, comet tail appearance, and beaten egg appearance.

• Penicillin agar: String of pearls appearance.

• Gelatin stab: Inverted fir tree appearance.

• Selective media: PLET media

• Travel in a Boxcar () to anthra () with gf - give string of pearls () and a ring (ascoli’s ring) → watch comet () and eat beaten egg () → when travelling, glass frosted (frosted glass app) → car hit a tree and inverted it (inverted tree app) → hit head (medusa head) → pletho sound (PLET)

 

• Hot Tub Folliculitis:
• Cause: Pseudomonas
• History: Jacuzzi or public pool exposure
• Presentation: Monomorphic papules (especially trunk)

• Ecthyma Gangrenosum:
• Cause: Pseudomonas
• Ek (one) thyma - monas (mono)
• Erythema progressing to skin necrosis
• leading to necrotic crust/eschar
• Affected: Immunocompromised (e.g., HIV, hospitalized)
• Deep infection, leads to scar

General Treatment of Bacterial Infections

• Mild: Topical antibiotics
• Examples: Fusidic acid, Mupirocin, Bacitracin, Retapamulin

• Severe: Oral antibiotics
• Examples: Cloxacillin, Cephalosporins, Erythromycins, Amoxicillin
• (+ Clavulanic acid preferred)

Eschar seen in

• E: Ecthyma Gangrenosum

• S: Scrub typhus, Spider bite

• C: Cutaneous anthrax

NOTE: Ecthyma Types (Distinction):

• Ecthyma Contagiosum: Virus (Parapox → Orf virus)

• Ecthyma Infectiosum: Bacteria (Streptococcus)

• Ecthyma Gangrenosum: Bacteria (Pseudomonas)