15. Skin, Tissue, and Wound Infections

What are the 3 layers of skin & their description?

epidermis: outermost layer

dermis: connective tissue rich in blood, nerve supply, shorter hair follicles, and sebaceous glands

subcutaneous tissue: deeper hair follicles, sweat glands

What are the functions of the skin? (6)

self repairing protection b/w organs & environment

control of body temp

excretion of water & salt

synthesis of chemicals & hormones

contains keratin, which repels water

skin flora defends against pathogens

What are the 4 bacteria that are skin flora?

diptheroids

staph. epidermidis

other coag neg staph

propionibacterium acnes

What are the 3 infections in/around hair follicles? What are they usually caused by?

folliculitis, furunculosis, carbuncles

hair follicle blocked by sebum or minor trauma from friction

What are the 3 bacteria that can cause infections around hair follicles?

S. aureus, pseudomonas aeruginosa (associated w/ swimming pools & hot tub), enterobacteriaceae

What usually causes infections of the keratinized layer of the epidermis?

dermatophyte fungi that cannot penetrate deeper layers of the skin

What are some organisms that can cause ulcerative/nodular lesions at the epidermis & dermis layer?

corynebacterium diptheriae, bacillus anthracis, Nocardia sp, mycobacterium marinum, sporothrix schenkii

Where are anaerobes largely isolated from (regarding subcutaneous infections)? What usually causes non-perineal infections?

perineal, inguinal, and buttock area

mixed facultative aerobes

What can epidermal infections extend to?

subcutaneous tissues & even fascia or muscles

What are some organisms that can be involved w/ fascia/muscle infection?

S. aureus, Group A strep, bacteroides, clostridium, M. tuberculosis, and proteus

What are the 3 sources of wound infections?

Post-operative infections, bite infections, burn infections

What type of sample and which media is best to collect and plate for dermis/epidermis infections?

full-thickness skin biopsy taken at margin of the lesion

blood & chocolate agars

How should needle aspirates from blisters, bullae, and cellulitis be inoculated?

aerobically or CO₂ on blood and MAC @ 35C

What is the most reliable specimen to collect for subcutaneous tissue infection?

base of an ulcer/nodule

deep tissue biopsy w/o touching superficial layers

What should be performed after collection for subcutaneous infections?

gram stain + inoculating aerobically on blood & MAC

What type of tube should be used to collect fascia/muscle infections? And how should it be transported?

blood culture bottles

should be transported anaerobically

For burn patients, what is it important to ascertain?

the number of organisms per gram present in biopsied tissue. >105 cfu/g indicates infection

What must be done to abscesses before undergoing treatment?

must be surgically incised & cleared of pus & debris

What are 95% of S. aureus resistant to?

penicillins & ampicillins