session 8: skin, eye, wounds Flashcards
GAS
-streptococci: divided into 3 groups on the basis of their hemolytic reactions on blood agar plates
Alpha: green zone, partial breakdown of Hb
Beta: clear zone, total breakdown
Gamma: no breakdown of RBC, no change in agar
necrotizing fasciitis ( flesh eating disease)
- caused by S. pyogenes or GAS
- all affected tissue is removed ( degraded) and IV antibiotic started
- aftermath is reconstructive surgery and plastic surgery
Beta hemolytic streptococci
- divided into subgroups dependent on cell wall carbohydrate ( lance filed’s typing)- most disease producing
- S. pyogenes and S. agalactide are the 2 major pathogen (A and B)
- C is several organism
- D is enterococci
- G is several organisms
- also can be sub typed using M. proteins in the cell wall
Streptococcus pyogenes
- Beta hemolytic: important pathogen in skin infections in Group A or GAS
- includes pharyngitis, tonsillitis, impetigo, cellulitis, flesh eating disease
- post infection complications includes acute glomerulonephritis and rheumatic fever: heart tissue and antibody attacks it
streptococcus pyogenes toxins and enzymes
- catalase: breaks down hydrogen peroxide, Staph is positive, Strep is negative
- streptokinase: dissolve blood clots, spreads tissues
- hyaluronidase: breaks down connective tissues
- deoxyribonucleases: degrade DNA: bacteria chew up cell and break down
- proteases: break down proteins ( IgA protease- antibody component by component)
- erthyrogenic toxin: cause scarlet fever, rash, spe toxins: exotoxins which are superantigens, responsible for tissue and muscle breakdown
Erysipelas
- infection in the deeper layer of the skin ( dermal layer)
- can progress to septicaemia and fatal outcome
- can begin as pharyngitis
- treatment is antibiotic: IV penicillin
Toxic shock syndrome
- life-threatening, multi-system effects
- production of a superantigen ( TSST-1 in S. aureus)
- fever, vomiting, sunburn like rash, often involves scalded skin syndrome (SSS) due to exfoliate toxin ( loosen the junction between cells to slough)
- first identified with tampon usage, now common in surgery and IV users
Staphylococcus Sp.
Gram positive cocci in clusters
-non motile, non spore forming and can or not have capsules
3 important species to know:
- S. aureus ( primary pathogen)
- S. epidermis ( opportunistic)
- S. saphrophyticos ( primary pathogen in UT, young women)
S aureus
coagulase positive staphylococci
- aureus means yellow
- produce coagulase ( catalyze fibrinogen to fibrin, soluble to insoluble)
- produce catalase ( breaks down hydrogen peroxide)
- salt tolerant ( survive on surface for a while)
- yellowish colonies
Catalase test
can cause boils and abscesses
- one drop of hydrogen peroxide on a slide, add bacteria and mix
- formation of bubbles=gas ( enzyme is present and breaking down the peroxide, releasing oxygen gas)
Eyelids infection with S. aureus
blepharitis- inflammation of eyelid margins
stye/horaeola- infection of eyelid glands and follicles
Impetigo
often in newborns and young children
- caused by S. aureus and S. pyogenes
- infection of epidermal layer ( facial)
- treatment is topical antibiotics, keeping it clean, it will heal itself
Staphylococcus scalded skin syndrome (SSS)
neonatal or 2 degree to toxic shock syndrome- due to exfoliative toxin and skin lesion
-bacteria attacks the junctions of epidermal cells and cause loosening of skin
psudomonas aeroginosa
in hot tubs!
- gram (-) bacilli; in soil and water
- produce endotoxins and exotoxins
- often opportunistic pathogen ( burn patients)
- difficult to treat ( antibiotic resistant)
- produce blue green irridescent pigment called pyocyanin ( smells like wild strawberries) has pus
- colonizer of lungs in CF
- also cause swimmer’s ear, usually doesn’t cause infections in healthy individuals
warts
a benign tumour
- caused by papilloma virus ( DNA, non-enveloped)
- virus cause proliferation of skin cells “tumour growth”
- transmitted by direct contact: genital warts, plantars warts,
Herpesviruses
Herpes means to crawl or creep
- 8 viruses total
- HSV-1 is cold sores and herpes simplex
HSV 1
- very common, more than 90% infected, most in childhood
- transmitted through oral contact or direct contact
- cause cold sores
- remain latent in ganglia, flare up with stress
- often trigeminal nerve ganglion
Herpes whitlow
occupational hazard of health care workers
Herpes gladitonium
wrestlers
conjunctiva
thin layer of mucous membrane lining the eyelids and covering the surface of the eye
Keratitis
inflammation of cornea, leads to blindness
bacterial keratitis and herpes keratitis
bacterial- more pus due to neutrophils
herpes- scarring of eye surface
C. trachomatis
- ocular: Types A-C, not ever sexually transmitted
- genital: types D-K, LGV
inclusion conjunctivitis: infection in eye with genital chlamydia
opthalmia neonatorum: gonorrhoeae in newborn eye
Staphylococcus epidermis
dominates in skin infection
-diptheroids: coryneobacterium: aerobes on surface
propionibacterium: anaerobes, live under the surface in follicles and glands
some yeasts: madlessezia furfur
skin lesions
vesicle: raised blister with fluid up to 1 cm in diameter
bulla: raised blister with fluid greater than 1 cm
macule: slightly raised flat area with no fluid
pustule: deep pocket of pus up to 1 cm in diameter, very painful
fifth disease, slapped cheek syndrome B-19
- parvovirus B19, DNA, non-enveloped
- mild disease of childhood
- pregnant women get complications- fetal death
- virus includes nucleated RBC destruction, loss in RBC by 30%, abortion for fetus
parasitic disease of the skin
Hookworms: burrow through the skin ( dermatitis)
Leishmania: 2 skin manifestation- cutanous and mucoculanous
Schistosoma: swimmer’s itch
Scabies: tunnel under outer skin layer ( mite)
Myiasis: larva under skin ( common in tropical area)
IV catheter: 4 sources of infections
- microbial contamination at insertion site
- HUB
- contaminated infusate
- hematogenous seeding from a distent site
Abscesses
localized lesion with accumulation of pus anywhere in the body
- result of external infection or internal infection ( after peritonitis)
- often polymicrobial (appendicitis): ‘intra-abdominal abscess”
osteomyelitis
- infection of the bone: by nearby site of infection, like fracture or from circulating microbes
- cause is S. aureus in blood
- cause is polymicrobial ( gram positive or gram negative)- nearby site
surgical infection of upper and lower body
upper body: primarily staph. sp
lower body and abdominal infections: primary faecal flora, gram negative, enterococci
wound abscesses
- localized accumulation of pus
- area of inflammation surrounds the pus and walls it off from surrounding tissue, trying to prevent spread of infection
- difficult to treat with antibiotics since they diffuse poorly in inflamed tissue
- surgical draining is treatment
anaerobic wounds
-common in crushed wounds, puncture wounds
consequences of wounds
- delayed healing
- formation of abscesses
- dissemination or spread of the infection into nearby tissues or the blood lymph
symptoms of bite infection
most common symptoms:
- localized cellulitis
- pain at site of injury
- purulent discharge, often gray and foul smelling
symptoms of bite infection in less than 10% of victims
temperature is above 37.2
regional adenopathy- swollen lymph nodes
puncture wounds most infected
snake bites
- venom causes tissue necrosis where infection can develop
- pseudomonas aeruginosa is the common cause of infections, but can include slamonella, CNS
human bite and clenched fist injuries
- more infected than animal bits
- both aerobic and anaerobic bacteria implicated ( oral flora)
- Eikonella corrodens is an important pathogen
cellulitis
- acute spreading infection of the skin
- involves subcutaneous tissues
- originates from superficial skin lesions or trauma ( boils or ulcers)
- majority of cases caused by S. aureus and S. pyogenes
IVDU
- intravenous drug users
- often get cellulitis or lymphangitis with s. aureus
anaerobic cellulitis
area of traumatized tissue or poor blood circulation
- diabetes very prone to it in feet
- foul smelling exudate, marked swelling and gas
Cat or dog bites can result in an infection of ….
pasteurella multocida, cause lymphangitis and septic shock
Gas gangrene
- caused by Clostridium perfringens ( gram positive spore forming bacilli)
- it’s usually in soil and feces
- usually a result of traumatized tissues with poor blood supply, with anaerobic conditions in wounds ( war wound)
- buttocks and perineum common sites
- organism multiply in subcutaneous tissues and invade deeper tissues, thrive on dead tissues
- produce gas as a by-product of metabolism crackling sound on palpation
- destroys tissue cells and WBC, collagenase, etc.
burns
- infections results from a disruption in the normal homeostasis
- mortality rate with burns are greater than 40% of body surface area is high
- important to maintain blood flow to affected area
- usually both gram positive and negative infections
- cause pseudomonas
-p. aeruginosa commonly infects burn wounds
proplonibacterium acnes
- gram positive, anaerobic, diptheroid bacilus, cause acne
- blocks channels transporting sebum to surface
