bacterial infection of the skin and soft tissue joints and bone Flashcards
what bacteria do these risk factors point to? DM neutropenia hot tub exposure IV drug use
DM- s. aureus, group b strep, anaerobes and gram neg bacilli
neutropenia- pseudomonas aeruginosa
hot tub exposure- pseudomonas aeruginosa
IV drug use - MRSA, P. aeruginosa
what do you call an infection that only involves the pores?
the epidermis?
the dermis
the deeper skin structures and muscle?
pores- faruncles, folliculitis and carbunkles
epidermis- erysipelas
dermis- cellulitis
deeper- fasciitis or myositis
Impetigo presentation
- most superficial bacterial skin infection
- caused by s. pyogenes and less s. aureus
- HONEY CRUSTED LESIONS -that start off as vesicles and become pustules that crust over -AROUND MOUTH
- most common bacterial infection
bullous impetigo
- mostly s. aureus
- blisters initially filled with cloudy fluid and rupture resulting in erosions and crusting
- BLISTERS CAUSED BY EXFOLIATIVE TOXIN MADE BY S. AUREUS
ecthyma
- DEEPER FORM OF IMPETIGO with resultant scarring and ulceration- do to lack of treatment or neglect
- cause PUNCHED OUT lesions
- treat with ecthyma and impetigo
treatment for impetigo and ecthyma
- debridement and topical antibiotic with oral antibiotics
what’s a faruncle or boil?
- caused by s. aureus
- deep seated infection of hair follicle
- large, painful, raised nodules that have collection of dead and necrotic tissue
carbuncle?
- caused by s. aureus
- MULTIPLE faruncles/ boils that coalesce and extend into deeper subcutaneous tissue
- patient gets FEVERS AND CHILLS
- often systemic spread- osteomyelitis, endocarditis, bacteremia
what is folliculitis
- it is the infection/ inflammation of a hair follicle caused by many different organisms
erysipelas
- acute infection
- causes inflammation and lymph node enlargement
- CHILLS AND FEVER
- DENOTED BY SHARP BORADER BETWEEN INVOLVED SECTION OF THE SKIN AND UNINVOLVED
- usually preceded by a respiratory or skin infection by s. pyogenes
cellulitis
- skin and subcutaneous tissue
- inflammation and systemic symptoms like fever
- no distinct boarder between infected and noninfected***
- caused by many microbes
what can cellulitis be caused by after
dog/cat bite
normally
salt water exposure
dog/cat bite- pasteurella multocida
normal- s. aureus
saltwater- vibrio vulnificus
paronychia
what is it
acute species
chronic species
- localized superficial infections of the nail folds
- most common infection of the hand
- acutely- can be painful abscess at nailfold- s. aureus
- chronic- there longer than 6 weeks- c. albicans
necrotizing fasciitis
what is it?
treatment?
- caused by s. pyogenes
- acute subcutaneous tissue infection that includes redness and involves deep tissue
- destroys fat and muscle
- cellulitis followed by bullae and gangrene
- leads to organ failure, toxicity and death
- treat with antibiotics and surgical debridement
what kind of bacteria is pseudomonas aeruginosa?
gram neg rod
how do you distinguish between s. aureus and streptococcus pyogenes
s. aureus is catalase pos and pyogenes is neg
- s aureus is in clusters, s. pyogenes is in chains
- both are gram pos cocci
staphylococci breaks down? are they motile or spore forming?
- breaks down H2O2 to H20 and O2
- non flagellate and nonmotile
what is the main way to shed s. aureus?
- nasal shedding
- but can spread without hand washing, environmental surfaces
is s. aureus alpha or beta hemolytic? what can occur to it once it is older or the infection has resolved? what color does it look like under a microscope
it is beta hemo
it can lose its gram positivity
aureus = gold
what are some s. aureus virulence factors?
- capsule (antiphagocytic), biofilm (to adhere to surface of foreign bodies like valves and catheters), peptidoglycan (endotoxin like activity), teichoic acid (for adhesion) and protein A (inhibits antibody mediated clearance via binding Igg Fc domain- basically binds the part that the phagocyte is supposed to bind, not the pathogen)
- Toxins- cytotoxin (alpha thru gamma- toxic to many cells), exfoliative toxins,
- has hydrolases that hydrolyze host tissue to aid in spread of the bacteria throughout the body
what are the two forms of exfoliative toxins
ETA and ETB
- serine proteases that break down desmosomes (intraepidermal junctions)
- MEDIATE STAPH SCALDED SKIN SYNDROME
Protein A
inhibits antibody mediated clearance via binding Igg Fc domain- basically binds the part that the phagocyte is supposed to bind, not the pathogen
what is the main enterotoxin that is found in s. aureus? what’s it associated with
enterotoxin A- insensitive to heat and gastric enzymes
associated with food poisoning
Hyaluronidase
fibrinolysin
lipases
nucleases
- hydrolyzes hyaluronic acid in connective tissue to spread bacteria thru body
breaks down fibrin
hydrolyzes lipase
hydrolyzes DNA
**pathogenesis of s. aureus?
- staph binds cell via teichoic acid
- it then secretes alpha toxin that pokes holes in cell so that the bacteria can enter
- once inside, the bacteria secretes protein A to sop up the antibody at the Fc region and prevent it from binding and eliminating the bacteria
- capsule serves as an antiphagocytic agent as well
what is scalded skin syndrome?
- s. aureus infection
- usually in babies that got it from mom
- looks like scalded skin and can only culture in nasal area even though it starts in the nose and spreads systemically on skin
- TOXIN MEDIATED
what actually causes the scalded skin
the exfoliative enzymes ETA and ETB
*why is staph aureus not culturable from skin?
because it’s a toxin mediated disease
don’t get leukocytes either- does not cause inflammation, just blistering
how do eta and etb work?
- they are serine proteases that attack desmosomes, DESMOGLEIN-1 that is responsible for linking together the intercellular bridges in the stratum granulosum of the epidermis
- protective antibodies result to fight of the infection eventually
what does staph aureus induced scalded skin syndrome present ?
- first presents as just an infection of the conjunctiva, nasopharynx or umbilicus
- the reaches exfoliate phase (in second day) where you break in in bulla and then they break easily with manual pressure = NIKOLSKY SIGN - resembles scalded skin
- 3-5 days: skin desquamates leaving normal skin in 7-10 days
how do you manage scalded skin syndrome
fluid replace, antibiotics (vanco and oxacillin)
diagnosis of SSSS
presentation of skin biopsy in nasal area
-histology reveals a CLEAVAGE PLANE in the upper epidermis
How are staphylococci generally able to establish infection in immunocompetant people
- it can do so when it enters with a foreign body
MRSA
- methicillin resistant staphalococcus aureus- mostly a skin infection that can go systemic
- has beta lactamases (usually by plasmid exchange) that resist beta lactam of PCN
- as a result we started treating with semisynthetic PCN resistant to B lactamase like methicillin and oxacillin and nafcillin BUT
- MRSA- has Mec A gene that codes for a PCN biding protein that is on the peptidoglycan and has a low affinity for methicillin and other synthetic PCN and cephalosporins
treatment for MRSA?
vanco
what do you prescribe for s. aureus with beta lactamases?
penicillinase-resistant PCN like nafcillin and oxacillin
what is osteomyelitis
- bone pain, fever, swelling and malaise
- almost always associated with bacterial infection
what are some risk factors for osteomyelitis
- DM, bone surgery, untreated tissue infections near bone, kidney dialysis, sickle cell, foreign body
=anything that might impair blood flow to the bone
what is osteomyelitis mostly caused by
s. aureus
what is septic arthritis
painful, erythematous joint with purulent material obtained on tapping
usually in large joints- shoulder, hip elbow
THE MOST COMMON REASON WHY KIDS AND ADULTS RECEIVE INTRAARTICULAR INJECTIONS OF WHO HAVE MEHANICALLY ABNORMAL JOINTS
what is the most common cause of septic arthritis? in sexually active individuals?
s. aureus
N. gonorrhea -mostly in women and present as grey/white lesions on skin
what are these virulence factors associated with exfoliative toxin enterotoxin a tsst-1 lipopolysaccharide capsule
exfoliative toxin- ssss enterotoxin a- food poisoning tsst-1- toxic shock syndrome lipopolysaccharide- endoxin that's gram neg capsule- general s. aureus infection
what is important when diagnosing SSSS, what should you remember?
- it is not going to be detected at lesions of the skin and there will be no leukocytes present
