Staphylococci Flashcards
Is staphylococcus Gram + or - ?
all are gram +
Is staphylococcus catalase + or - ?
all are catalase +
Does staphylococcus need O2 or not ?
can function with or without O2
What is the outermost layer of the skin ?
epidermis
What are some characteristics of the epidermis ?
- surface layer
- consists of dead flat cells (contain keratin, durable protein) forming a scaly layer
- constantly sloughing/shedding off which makes it hard for bacteria to grow on it
- takes about 1 month to regenerate
What is the middle layer of the skin ?
dermis
What are some characteristics of the dermis ?
- supports epidermis
- contains tiny nerves, blood vessels, and lymphatic vessel penetration
What is the innermost layer of the skin ?
subcutaneous
What are some characteristics of the subcutaneous layer ?
- fatty layer (adipose tissue)
- tubules of sweat glands & hair follicles that go through epidermis and dermis end in this layer
What is sebum ?
oily secretion that the sebaceous glands produce
What is the purpose of sebum ?
- keeps hair and skin soft
- also makes it pliable and water repellant
Through what layers of the skin do hair follicles go through ?
all of them
- can be a passageway for microorganisms to penetrate the skin and reach deeper tissues
What are the conditions needed for acne to develop ?
- excess secretion of sebum-disorder of sebaceous glands
- excess growth of Propionibacterium acnes
What is the importance of normal skin flora ?
- sweat and sebaceous glands are important for the growth of the flora (supplies nutrients like water, AA, and lipids)
- break down lipids producing fatty acid by-products (inhibit growth of potential pathogens)
Define normal flora ?
bacteria that usually is there and/or is expected
What are characteristics of Diphtheroids ?
- Gram + rods
- pleomorphic (change size/shape according to environment)
- low virulence
- Propionibacterium acnes
What are some general characteristics of the micrococcaceae family ?
- aerobic and facultative anaerobic (with or without O2)
- respiration and fermentation metabolism
- gram + cocci, arranged in clumps/clusters
- catalase +
- found on skin and mucous membranes
What are some general characteristics of staphylococci ?
- gram (-) in clumps/clusters
- Catalase +
- Aerobic or facultative anaerobes
- fermenters of carbs
- NaCl (salt) tolerant
What are the 3 skin infections caused by Staphylococcus Aureus (Staph Aureus) ?
- folliculitis
- furuncle
- carbuncle
What is folliculitis ?
small red bumps formed at the site of the involved hair follicle
- pull hair from follicle
- usually small amount of pus and infection clears
What is furuncle ?
a boil, localized skin infection that penetrates into subcutaneous tissue
What is carbuncle ?
painful infection of skin and subcutaneous tissue that manifests as a cluster of boils
- tends to happen in areas with thicker skin like nape of skin, back or thighs
- aka. multiple furuncles grouped together
What is different about Hot tub folliculitis ?
special case of folliculitis not caused by Staph aureus
- caused by inadequate chlorine levels in hot tubs, whirlpools and pools
- caused by pseudomonas aeruginosa
What types of infections can Staph aureus cause ?
- superficial (skin)
- wounds
- deep infections (abscesses) and septicemia
- pneumonia
- food poisoning (intoxication not infection)
- pseudomembranous enterocolitis
- scalded skin syndrome
- toxic shock
- nosocomial infection
Why is food poisoning an intoxication in staph aureus ?
- staph makes an exotoxin and secretes it
- we ingest the toxin and symptoms occur within 2 to 6 hours of ingestion of contaminated food
- symptoms: fever, vomiting, diarrhea
- self-limiting and generally no further treatment
What is pseudomembranous enterocolitis ?
rare complication of prolonged antibiotic therapy
- cuts down intestinal normal flora
- staph aureus overgrows and causes abscesses in bowels
What is scalded skin syndrome ?
staph secretes an exotoxin that causes the skin to peel
- newborns particularly
- in moist & humid areas
What type of environment do Staph toxins tend to like ?
anaerobic environment
In toxic shock syndrome what is the exotoxin secreted ?
TSST-1
What is a nosocomial infection ?
hospital acquired infection (within 72 hrs of admission)
- MRSA (methicillin resistant staphylococcus aureus); hospital and community acquired & usually resistant to antibiotics especially penicillin
What is the primary cause of nosocomial diarrhea ?
Clostridium Difficile (C. Diff)
What is the significance of the capsule in the pathogenesis of staph aureus ?
- protects it from WBC and lets it attach to surfaces
- contributes to organism pathogenicity
What is the significance of the cell wall in the pathogenesis of staph aureus ?
- increased amount of peptidoglycan
- has protein A that binds with antibodies and interferes with phagocytosis by WBC
What is the function of coagulase in staph aureus ?
coagulates blood or plasma
- enzyme
What is the function of hemolysin in staph aureus ?
lyse human and other animal RBC
What is the function of hyaluronidase in staph aureus ?
breaks down hyaluronic acid which binds connective fibers
What is the function of DNase in staph aureus ?
breaks down DNA
What is the function of lipase in staph aureus ?
breaks down lipids in the skin
What is the function of beta lactamase in staph aureus ?
breaks down penicillin’s
- staph are resistant to penicillin therapy
What are the 4 exotoxins with staph aureus ?
- exfoliatins: skin sloughing
- leukocidins: kill WBC
- TSST 1: from toxic shock
- enterotoxins: act in gut and associated with staph food poisoning and pseudomembranous enterocolitis
What does beta hemolytic mean ?
clear zone around the pathogen where the bacteria has completely destroyed the blood
What are some morphology of S. aureus ?
- opaque/white/yellow
- medium to large
- beta hemolytic
What happens in a catalase test ?
want to detect the enzyme catalase using hydrogen peroxide
- Catalase +: when small amount of isolated bacteria is added to hydrogen peroxide bubbles of O2 will happen
What is the importance of a coagulase test with staph ?
used to differentiate staph aureus (+) which does produce the enzyme coagulase, from S. epidermis and S. saprophyticus (-) which don’t produce coagulase
What do the results of a coagulase test mean ?
(+): will clump (s. aureus)
(-): rabbit plasmid will look milky (S. epidermis or saprophyticus)
What is coagulase ?
protein enzyme produced by several microorganisms that enables the conversions of fibrinogen to fibrin
What happens in a bound coagulase test ?
- mix loop of bacterial colony with a drop of human plasma on a slide (bound) and look for clump formation in 10 secs
What happens in a free coagulase test ?
- add broth with Staph to a tube containing rabbit plasma and look for solid mass in tube
- (+):clumping/clotting
What are some characteristics of Staphylococcus intermedius ?
- infrequently seen, can be found in dog bites
- beta hemolytic
What are some characteristics of staphylococcus epidermidis ?
- normal habitat: skin, hair follicles, and mucous membranes
- not pathogenic often but can occasionally
- usually result in invasion of foreign bodies
- catheters changed every 24 hours because this staph can stick to it
- common cause of endocarditis, CSF shunt infections
- some strains more virulent then others
What is the morphology of staphylococcus epidermidis ?
- usually white
- nonhemolytic
- novobiocin sensitive
- round, smooth surface slightly raised, entire edge
What are some characteristics of staphylococcus saprophyticus ?
- can cause urinary tract infections (sexually active young females “honeymooners illness”)
- novobiocin resistant
What is the purpose of selective medium in Mannitol Salt Agar (MSA) ?
says if organism can grow in a high salt concentration
What is the purpose of differential medium in Mannitol Salt Agar (MSA) ?
differentiates between staphs that will ferment mannitol and those that will not
What are the 3 types of normal flora ?
- diphtheroids
- staphylococci
- yeasts
