Chapter 18: Bacterial Diseases

GRAM-POSITIVE BACTERIAL DISEASES

Impetigo

• Superficial nonfollicular infection, due to Staphylococcus aureus or group A Streptococcus, occurs more commonly in children (Fig. 18-1)

• Lesions can begin as erythematous papules that evolve into a vesicle or pustule. The pustules may rupture leaving contagious honey-colored crusts

• Treatment: topical mupirocin

• Bullous impetigo is a toxin-mediated erythroderma (Fig. 18-2) is caused only by Staphylococcus aureus → exotoxin cleaves desmoglein 1 → separation of the epidermis at the granular layer

• Clinical (seen most frequently in newborns)

• Sharply demarcated flaccid bullae without surrounding erythema

• Treatment: dicloxacillin or first-generation cephalosporin, topical mupirocin

Ecthyma

• Differs from impetigo in that the dermis is ulcerated

• Usually caused by group A beta-hemolytic streptococci (GABHS)

• Clinical

  • Thick crusted ulcer that heals slowly and may produce a scar

  • Most commonly affects the lower extremities of children, persons with diabetes, and neglected elderly patient. Often occurs with lymphadenitis

• Histology: ulceration to dermis with bacteria, crusting and an acute inflammatory infiltrate

• Treatment: usually dicloxacillin or first-generation cephalosporin, parental antibiotics may be needed for widespread infection

Bacterial Folliculitis

• Most cases caused by S. aureus (Fig. 18-3)

• Superficial infection: (facial involvement is called Bockhart folliculitis): red papules/pustules, follicularly centered

• Deep infection: (facial involvement = sycosis barbae); erythematous, fluctuant nodules

• Lupoid sycosis: chronic form of sycosis barbae associated with scarring

• Treatment: topical antibiotics, systemic antibiotics may be indicated

Furuncles/Carbuncles

• S. aureus most commonly found (Fig. 18-4)

• Clinical

  • Deep-seated nodules around hair follicle (inflammation involves the subcutis)

  • Multiple furuncles make a carbuncle, evolve from preceding folliculitis

• Treatment: topical mupirocin and dicloxacillin; if large, then also need drainage

Abscess

• Cutaneous abscesses represent a collection of purulent debris in the skin (Fig. 18-5)

• Usually Staphylococcus aureus (including possibly methicillin-resistant strains)

  • Methicillin-resistant S. aureus: altered cell wall transpeptidase (penicillin-binding protein 2a) carried on staph chromosome cassette mecA

    • – transfer by bacterial plasmids

  • Hospital-acquired methicillin-resistant Staphylococcus aureus (MRSA) usually carries mecA types I, II, and III

    • – resistance to clindamycin and macrolides (inducible clindamycin resistance detectable by the “D-zone” test). Community-acquired MRSA commonly carries SCCmec IV

    • – more antibiotic susceptibilities

    • – MRSA usually carries an ...