Skin, Bone, and Soft Tissue Infections PDF

Skin, Bone, and Soft Tissue Infections Glenn Patriquin MD Visual Dx Skin, Soft Tissue, and Bone Infections Objectives Understand the normal skin flora To become familiar with bacteria which commonly infect skin, soft...

Skin, Bone, and Soft Tissue Infections Glenn Patriquin MD Visual Dx Skin, Soft Tissue, and Bone Infections Objectives Understand the normal skin flora To become familiar with bacteria which commonly infect skin, soft tissues and bones: – Staphylococcus aureus and other species – Streptococcus pyogenes – Anaerobes Identify and understand common diseases of the skin, soft tissues, and bones  Skin - Structure and Function Large, complex organ that protects the body Surface area of 1.5-2 m2 Consists of: – epidermis – dermis – appendages (hair follicles, sweat glands) Acts as a physical barrier against microorganisms Protects from desiccation  Normal Skin Flora Mostly gram-positive bacteria – Staphylococcus spp. – Micrococcus spp. – Corynebacterium spp. (“diphtheroids”) – Cutibacterium (Propionibacterium) acnes Vigorous washing reduces but does not completely eliminate flora Sweat glands and hair follicles help to reestablish bacterial flora  Staphylococcus species Staph: grape-like clusters coccus: spherical Gram-positive cocci - 0.5-1.5 m in diameter Pale to golden-yellow colonies on blood agar All Staphylococci are catalase positive – Break down hydrogen peroxide to water and oxygen All Staphylococcus aureus are coagulase positive – Cause rabbit plasma to coagulate Coagulase reaction + - Catalase reaction  Staphylococcus spp. Classification S. aureus – Coagulase positive Coagulase negative staphylococci: – This refers to all the other Staphylococcus spp – The term is often used to indicate that a Staphylococcal isolate is not S. aureus. S. epidermidis S. saprophyticus Many others …  Staphylococcus aureus - Virulence Factors Coagulase Toxins: – hemolysins – enterotoxins – pyrogenic toxins: A, B, C Exfoliatin Leukocidin Protein A Some isolates are unaffected by common antimicrobials (antimicrobial resistance)   Streptococcus species Strepto: chaining coccus: spherical Gram-positive cocci 0.5-1.5 m in diameter White to grey colonies of various sizes on blood agar – All Streptococci are catalase negative – give no bubbles in hydrogen peroxide. Classified by ability to product hemolysins: – Alpha ()-hemolytic: partial hemolysis of RBCs viridans streptococci, Streptococcus pneumoniae – Beta()-hemolytic: complete hemolysis of RBCs Streptococcus pyogenes, Streptococcus agalactiae – Gamma ()-hemolytic: no hemolysis of RBCs some Streptococcus anginosis   (Gamma) Streptococci: Gram-positive cocci in pairs or chains Haemolysis Colonies S.pneumoniae  Streptococcus pyogenes Group-A streptococci (GAS) from the Lancefield classification Gram-positive bacteria in short chains, 0.5-1.0 m in diameter Expresses -hemolysis – There are other -hemolytic streptococci, which cause similar infections Does not produce catalase or coagulase An aggressive organism!  Aerobic Gram- positive bacteria Catalase test - + Hemolysis Coagulase test α ß - - + Viridans Strep Group A Strep Strep bovis Staphylococcus Staphylococcus Strep Group B Strep Enterococcus epidermidis aureus pneumoniae Group C/G Strep  Anaerobes Bacteria which grow in the absence of oxygen Fusobacterium – facultative (S. aureus, E. coli) – obligate (Bacteroides fragilis, Fusobacterium spp.) Commonly found as normal flora of the bowel and mouth Can infect necrotic (=dead) tissues including skin Anaerobic Jar used to grow anaerobes without oxygen  Anaerobes Gram-positive Gram-negative – Cocci: – Cocci: Peptostreptococcus spp. Veillonella spp. – Bacilli (rods): Cutibacterium acnes, – Bacilli: Clostridium perfringens, C. Bacteroides fragilis tetani, C. difficile Fusobacterium spp. Actinomyces spp.  Skin Rash Lesions - Definitions Vesicle Vesicles: – small, fluid-filled lesions in the epidermis (eg. chicken pox) Bullae: – larger, fluid-filled lesions in Bullae the epidermis (may break) Macules: – flat, reddish lesion from inflammatory infiltrate Macules Jackson-Richards and Pandya; Springer. 2014  Skin Rash Lesions Papules: raised lesion which, when it contains pus, is called pustule Macule Jackson-Richards and Pandya; Springer. 2014  Bacterial Diseases of the Skin Folliculitis: infection of hair follicle (S. aureus) Impetigo: vesicular, later crushed, superficial infection of the skin (S. pyogenes, S. aureus) Cellulitis: acute spreading infection of the skin extending to involve the subcutaneous tissues (S. aureus, S. pyogenes, anaerobes) Erysipelas: distinctive type of superficial cellulitis of the skin with prominent lymphatic involvement (S. pyogenes) Skin Infections Impetigo Erysipelas Folliculitis Cellulitis  Complications of Diseases of the Skin Furuncle: deep inflammatory nodule usually developing from folliculitis (S. aureus) Carbuncle: more extensive than a furuncle with involvement of the subcutaneous fat (S. aureus) Staphylococcal Toxic Shock Syndrome: acute febrile illness with a generalized sunburn-like eruption (S. aureus) Scalded Skin Syndrome: widespread bullae and exfoliation from S. aureus strains producing an exfoliative exotoxin (exfoliatin) Furuncle Carbuncle Staphylococcal Scalded Skin Syndrome Jackson-Richards and Pandya; Springer. 2014; StatPearls Publishing LLC  Soft Tissue Infections Necrotizing fasciitis – “flesh-eating disease” – severe infection involving the subcutaneous soft tissue, particularly the superficial and deep fascia – predisposing conditions: diabetes, abdominal surgery, perineal infection, trauma – organisms: S. pyogenes, C. perfringens, mixed aerobic and anaerobic bacteria (e.g. E. coli + B. fragilis, and other AnO2) – treatment surgical debridement, antibiotics, + immunoglobulins  Gas Gangrene Necrotising Fasciitis Ying et al. 2013. Case Reports in Orthopedics, 942076  Soft Tissue Infections Myositis – infection of skeletal muscle (rare) – S. aureus, S. pyogenes (rare), mixed organisms Gas gangrene – rapidly progressive, life-threatening, toxemic infection of skeletal muscle due to clostridia, esp. C. perfringens  Bone Infections Septic arthritis – infection of joint spaces – hematogenous or contiguous – S. aureus, Streptococcus spp., Gram-negative bacilli Osteomyelitis – infection of the bone – hematogenous or contiguous – S. aureus, S. pyogenes, H. influenzae, Gram-negative bacilli  Diabetic Foot Infection Cellulitis>Deep soft tissue infection >Osteomyelitis (bone infection) Risk factors: – vascular disease (large and small vessel) impedes blood supply and ability to heal, decreases defenses, ulceration – peripheral neuropathy Decreases sensation, awareness of injury – poor foot care – skin breaks not noted  Diabetic Foot Infection Organisms: – skin organisms: S. aureus, Group B Streptococcus, Corynebacterium spp. (diphtheroids) – Gram-negative bacilli (E. coli, K. pneumoniae, Pseudomonas spp.) – Anaerobes, most often in combination with others