o Wounds are infected by microbes from fingers air object causing wound normal flora attach to exposed Wound Infections Chapter 24 Wounds can be classified as o o o o o incised incision knife other sharp object surgical wound infections large healthcare cost puncture small sharp object laceration tissue is torn contusion crushed tissue by impact burn a k a thermal burns are initially sterile Wound Infections underlying tissue parts fibrin fibrinogen collagen o wound abscess localized collection of pus surrounded by body tissue abscess helps localize infection to prevent spread in body to resolve abscess must rupture to a body surface or be surgically drained Common Bacterial Wound Infections Consequences of wound infection o o o Staphylococcal Wound Infections o o o delay in healing formation of abscess localized damage spread of bacteria or their products to tissues and bloodstream systemic damage staphylococci are the leading cause of wound infections commonly in nose on skin two species account for most human infections S aureus S epidermidis pyogenic produce pus inflammation swelling pain redness fever if infection has spread some strains cause toxic shock syndrome o o o o Staphylococci common skin organisms are Gram aerobic anaerobic salt tolerant sweat o some impt Staphylococcus aureus virulence factors Coagulase Clumping factor A Protein A note that all three helps bacteria colonize fibrin and plastics in wound also coats S aureus surfaces binds coats antibody Fc to Staph cell envelope protect hide coat bacteria from immune cells therefore immunity to Staph infections weak Staphylococcal Wound Infections Staphylococcus epidermidis o is bound tightly to S aureus surfaces where it stimulates formation of blood fibrin from fibrinogen fibrin coating little or no invasivness normally stays on skin surface but through a wound can colonize in dwelling devices e g catheters biofilm protects from phagocytosis and antibiotics cells from biofilms carried into bloodstream can subacute bacterial endocarditis or multiple tissue abscesses generally in immuno compromised Prevention of infection cleanse wound remove dirt and crushed tissue close promptly pre surgical antibiotics o o lowers infection rate extensive precautions in hospitals Treatment can be very challenging due to widespread antibioticR lactamaseR penicillins such as methicillin vancomycin teicoplanin but vancomycinR VISA strain appeared in 1997 newer drugs linezolid synercid and daptomycin are effective several more being tested o Group A Streptococcal Infections a k a flesh eating primary pathogen is o Streptococcus pyogenes common cause of wound infections not alot of antimicrobial resistance can generally be treated but if invasive can cause rapidly deteriorating disease and death Severe S pyogenes infections are invasive pneumonia meningitis Puerperal childbirth Fever Necrotizing fasciitis fascia fibrous tissue underlying the skin and surrounding muscles and organs Streptococcal toxic shock Two extracellular products important for virulence Pyrogenic exotoxin A a superantigen streptococcal toxic shock Exotoxin B tissue degrading protease helps invasion Flesh eating infections recorded for centuries usually sporadic but cause public alarm USA 2002 9 000 cases invasive S pyogenes infections 1080 deaths 135 from necrotizing fasciitis Epidemiology Treatment urgent surgery sometimes amputation due to rapid spread of toxin Penicillin still usually effective o must be given early o o o little or no effect on bacteria in necrotic tissues no effect on toxin surgery may still be necessary o Pseudomonas aeruginosa Infections Pseudomonas aeruginosa generally aerobic but can grow anaerobically produces numerous water soluble pigments combinations of pigments tissues often green opportunistic pathogen major cause of nosocomial infections lungs and wounds wounds esp burns widespread in nature especially soil water plants o enters hospitals on shoes ornamental plants and flowers produc Pseudomonas persist in dampness or standing water contaminates soaps cosmetics contact lens solution swimming pools hospital equipment etc change in tissue color chills fever skin lesions and shock due to bacteria in bloodstream Symptoms Prevention Treatment eliminate sources of bacteria prompt wound care remove dead tissue from burns and apply o o silver sulfadiazine Silverex etc topical sulfonamide silver antibacterial established infections very difficult to treat o P aeruginosa is multi drug resistant high dose IV antibiotics o Tetanus Early symptoms Later symptoms restlessness irritability difficulty swallowing contraction of jaw muscles convulsions particularly in children increased muscle involvement and pain difficulty breathing death Clostridium tetani Pathogenesis o o o o o o o pneumonia regurgitation of stomach contents into lungs anaerobic Gram positive spore former spherical endospores at tip of rod instead of oval centered spores of other Clostridium pathogens swarming growth on laboratory media endospores very common in dust and soil not invasive colonization usually confined to wound toxin does the damage Tetanus toxin tetanospasmin toxin two protein chains heavy chain binds receptors on motor neurons lighter chain taken up through endocytosis Tetanospasmin blocks inhibition of motor neurons causing spastic paralysis uncontrolled muscle contraction usually begins in the jaw spreads through nervous system very painful frequently fatal Epidemiology C tetani found in dirt dust and GI tract of humans and other animals from food carrying C tetani spores soil or fecal contamination infections in anaerobic locations o o puncture wounds stepping on a nail body piercing tattooing animal bites dirty needles incisions surgical infections a few dozen cases in US annually 25 mortality much more common in poor countries neonatal tetanus Prevention immunization tetanospasmin toxoid developed in 1924 widely used for WWII wounded DPT combination vaccine with diphtheria and pertussis Treatment metronidazole IV to kill multiplying bacteria but not spores thoroughly clean wound and remove dead tissue debridement aerobic tetanus immune globulin TIG antitoxin antibodies to inactivate tetanospasmin if not bound to neurons