Transcript Chapter 19c
Wound Infections • Consequences include: – Delay in healing – May result in localized infection (abscess) – Bacteria or their products may migrate to adjacent tissues or bloodstream Necrotizing Fasciitis • Causative Agent – Streptococcus pyogenes • “flesh eating bacteria” – Dramatic but rare • Small epidemics occur – Generally easily treated • Not a lot of antimicrobial resistance • Signs and symptoms – Nausea, and other flulike symptoms – Intense pain and swelling at infection site – Discoloration and distortion of skin – Skin hot to the touch – Fever, malaise, • Epidemiology – Usually spread through direct contact – Pathogen enters through wound and produces enzymes and toxins that destroy tissue • several cm per hour • may cause organ failure – Severe infections termed invasive • • • • Pneumonia Meningitis Streptococcal toxic shock Death • Prevention – No proven prevention measures – Wounds increase risk – Difficult to diagnose in the early stages because the symptoms are nonspecific and flulike • Treatment – clindamycin and penicillin • treatment must be given early • has little or no effect on bacteria in necrotic tissues • No effect on toxin – Urgent surgery required • Removal of necrotic tissue • Amputation Pseudomonas Infections • Causative agent: – Pseudomonas aeruginosa – G-, aerobic bacillus – Opportunistic pathogen – Major cause of nosocomial infections • Burn and lung infections – Occasional cause of community acquired infections • Contaminated pools and hot tubs • Signs & Symptoms – Change in tissue color • pyocyanin – Chills, fever, skin lesions and shock – Multiple virulence factors • • • • • • • Endotoxin Exoenzyme S Toxin A Elastase Neuramindase Polysaccharide capsule Fimbriae • Epidemiology – Rarely part of the microbiota – Widespread in nature • Found extensively in soil, water and on plants – Introduced in hospitals on shoes, on plants and flowers and on produce – Contaminates soaps, ointments, eye drops, swimming pools and hospital equipment • Prevention – Prevention involves elimination of source – Prompt wound care – Debridement of burns • Removal of eschar followed by application of antibacterial cream like silver sulfadiazine • Treatment – Established infections are extremely difficult to treat • P. aeruginosa is multi-drug resistant • Typically combine aminoglycosides and betalactam drugs • Polymyxin last resort drug Clostridial Myonecrosis • gas gangrene • Causative agent: – Species of Clostridium, most commonly C. perfrigens • Encapsulated; anaerobic, gram + bacillus • Produces endospores • Signs and symptoms – Begins abruptly with rapidly increasing localized pain and swelling – Thin, foul smelling fluid leaks from wound • Fluid is often brownish and frothy – Frothy appearance is due to gas production by infection bacteria – Crepitation – Skin becomes stretched and mottled with black spots • Ishemia and necrosis – Delirium and coma followed by death • Mortality ~ 40% – C. perfringens unable to grow in healthy tissue • Survives well in dead or poorly oxygenated tissue • Releases toxin in tissue – Bacteria produces gas through fermentation • Gas accumulates in tissue contributing to spread • Crepitation Gas-filled spaces produced by C. perfringens. • Bacteria produces neurotoxin • Toxin attacks host cell membrane – Toxin diffuses and kills tissue cells • Other enzymes breakdown dead tissues – Collagenase – Hyaluronidase (spreading factor) – Factors that increase susceptibility to clostridial myonecrosis • Presence of dirt and dead tissue in wound – Spores found in nearly all soil or dusty surface • Poor circulation – encourages poor oxygenation of tissues • Long delays in treatment – Immediate medical attention in severe wound is especially important • Prevention and treatment – Vaccine unavailable – Prompt cleaning and debridement of wound – Surgical removal of dead and damaged tissue • Amputation may be required – Hyperbaric oxygen treatment • Inhibits growth of clostridia – Stops release of toxin – Penicillin or cephalosporin are given to halt bacterial growth • No growth = no toxin production