MMSC 428 Final Exam Study Guide 2023 with complete solution
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MMSC 428
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MMSC 428
MMSC 428 Final Exam Study Guide 2023 with complete solution
Staphylococcus aureus
-gram positive cocci in cluster
-the most clinically significant staph, important cause of hospital acquired infections
-produces protein A, extracellular enzymes and exotoxins
-facultative anaerobe
-medium si...
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MMSC 428 Final Exam Study Guide 2023 with complete
solution
Staphylococcus aureus
-gram positive cocci in cluster
-the most clinically significant staph, important cause of hospital acquired infections
-produces protein A, extracellular enzymes and exotoxins
-facultative anaerobe
-medium sized B-hemolytic colonies
-halotonic
-mannitol fermentation +
-catalase +
-coagulase +
-serological test for TSST-1 and DNA probes are good for detection
-usually resistant to penicillin and methicillin
staphylococcus aureus clinical manifestations
-furuncle: large, raised suppurative dome shaped abscess (boil) due to infection of
Staph aureus in oil gland or hair follicle
-carbuncle: furuncle lesion progresses deeper and causes more invasive infection in
lower skin, causing systematic symptoms and fever
-impetigo: bullous (>5 mm) pustules filled with fluid surrounded by erythema typically
seen on the face of children
-cellulitis: infection of connective tissue that leads to inflammation
-staphylococcal scalded skin syndrome (SSS): exfoliative dermatitis caused by infection
with staph aureus that releases exfoliatin toxin, leading to red, peeling skin that
resembles 2nd degree burn (infants and neonates mainly)
-toxic shock syndrome (TSS): staph aureus infection releases TSST-1 super antigen
and enterotoxin B to cause systemic symptoms (fever, kidney and liver damage,
vomiting, diarrhea, muscle ache and rash) that can progress to hypotension and shock
(menstrual and nonmenstrual forms)
-intoxication food poisoning: enterotoxins A, D and B contaminate food and leads to
severe projectile vomitting and diarrhea
-nosicomial infections: wound infection, osteomyelitis, biofilm on body implant
-head and neck infections in children
antibiotic resistant staphylococcus aureus
-MRSA (methicillin resistant)
-VISA (vancomycin intermediate)
staphylcoccus lugdunensis
-gram positive staphylococci
-very virulent and clinically significant, causes similar infections to Staph aureus, just
seen less often
-ODC +
-coagulase -
-PYR +
-mannitol -
,-nonhemolytic
-oxacillin resistant
-causes skin abscesses, meningitis, septicemia, septic shock and UTI
-causes very aggressive and fatal infectious endocarditis
staphyloccocus saprophyticus
-gram positive staphylococcci
-coagulase, clumping factor, PYR and ODC -
-nonhemolytic
-common cause of UTI in females, even a small amount in the urine is significant
micrococcus
-gram positive cocci
-used to be grouped with staph but are less clinically significant and lab characteristics
are different
-lysostaphin resistant
-bacitracin sensitive
-glucose fermentation -
-modified oxidase (cytochrome C oxidase) +
staphylcocci characteristics
-gram positive cocci that grow in clusters
-catalase + (good to differentiate from step)
-nonmotile, lack flagella
-facultative anaerobes, prefer aerobic environment
-lysostaphin sensitive
-glucose fermentation +
-modified oxidase +
-bacitracin resistant
-important causes of hospital acquired infections
streptococcus pyogenes (group A streptococcus)
-gram positive cocci in chains
-catalase -
-lancefield group A cell wall antigens
-modified oxidase -
-fastidious, require additional nutrients from blood to be cultured
-B-hemolytic
-streptolysin O causes B-hemolysis in anaerobic conditions
-streptolysin S causes B-hemolysis in aerobic conditions
-PYR +
-small, transparent, dry colonies
-bacitracin sensitive
-produces M protein, hyaluronic acid capsule, pilli, streptodornoase and streptokinase
virulence factors
-treated with penicillins
culture, antigen detection assays or serology are used for diagnosis
streptococcous pyogenes (group A strep) clinical manifestations
-pharyngitis: "strep throat" seen mainly in children from 5-15 with sore throat, malaise,
fever, headache, nausea/ vomitting (adults have M protein antibodies and usually are
, not infected)
-scarlet fever: untreated strep throat causes release of erythrogenic toxins into blood
that breaks own RBCs and causes rash, damage to blood vessels, "strawberry tongue"
(not common in developed countries where people get treated)
-impetigo: dermal infection leads to formation of non-bullous (<5 mm) lesions that leak
and then crust over
-erysipelas: infection of dermis and subcutaneous tissue that leads to erythmatous,
swollen, painful inflamed lesions on the skin (mainly elderly individuals)
-necrotizing fasciitis: life threatening and invasive infection that begins as a skin
infection and rapidly progressing inflammation and necrosis of skin, subcutanous fat
and fascia membrane progress
-purpural fever: infection of neonate that is innoculated with Strep pyogenes from the
vaginal mucosa during birth causing bacteremia, and sepsis (not common anymore)
-streptococcal toxic shock syndrome: initial cold symptoms that progress to flu-like
symptoms and eventually cause a highly fatal pneumonia
-sinusitis with otitis media with effusion (OME): ear infection that is more common in
children due to lateral eustachian tube
streptococcus pyogenes (group A strep) culture
-obtain throat swab
-SBA can be used (normal biota from throat can overpopulate)
-selective strep agar (SSA) is best
post-streptococcal sequealae
immune-mediated conditions that follow infections with streptococcus pyogenes (group
A strep)
-acute glomerulonephritis: infection of the skin leads to type 3 hypersensitivity reaction
when large immune complexes form in blood and get trapped in the glomerulus, body
triggers immune response to clear out immune complexes and damages the kidney
-acute rheumatic fever (ARF): infection of the throat (pharyngitis) is not treated and
body produces antigens against M proteins that cross react with antigens on the heart,
leading to type 1 hypersensitivity reaction that causes progressive valve damage
-both can be treated with penicillin
streptococcus algalactaiae (group B strep)
-gram positive streptococcus
-aerotolerant anaerobe
-group B lancefield cell wall antigens
-CAMP test + (enhanced hemolysis)
-hippurate hydrolysis +
-produces carbohydrate super antigen (similar to endotoxin/ LPS) and sialic acid
capsule
-part of normal biota, found in vaginal mucosa
-fastidious bacteria, requires blood to be cultured
-colonies are small and have small zones of B-hemolysis
-weak virulence
-important cause of perinatal infections (early onset bacteremia and pneumonia, late
onset bacterial meningitis)
-diagnosed using culture or PCR
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