Micro Exam 2 Staph and Strep

Normal flora of the skin

the skin’s environment, shaped by secretions that support certain microbial growth, and inhibits others

what do sebaceous and sweat glands supply?

water, amino acids, and lipids

how does normal flora help regulate skin pH and prevent pathogens?

• normal flora breaks down skin lipids, produces fatty acids which lower pH

• the acidic environment inhibits the growth of potential pathogens

explain how moisture impacts bacterial growth

high moisture levels act as “hot spots” for bacterial growth

what are the 3 groups of normal flora

diphtheroid, staphylococci, yeast

describe diphtheroids

• gram positive

• pleomorphic rods; has lower virulence (disease causing)

describe staphylococci

• gram positive cocci

• coagulase negative staphylococci

describe yeasts

the fungal components of the normal skin flora

what are the 2 conditions required for acne?

• excessive secretion of sebum

• excessive growth of Propionibacterium acnes

describe the pathogenic mechanism of Propionibacteria acnes

• anaerobic

• colonizer hair follicles

• enhanced by oily secretions

• causes follicles to become plugged and inflamed

what are the locations of acne?

• areas where sebaceous glands are well developed

• face, upper chest, back

describe the stages of acne

• plugged hair follicle

• accumulation of skin and sebum, bacteria colonized and releases chemicals into the bloodstream

• immune response occurs to bacterial proliferation, causes mild inflammation and white blood cell recruitment

• marked inflammation and potential scarring

describe the characteristics of family staphylococceae: metabolism, morphology, biochemical, blood breakdown, habitat, clinical role

• aerobic + facultative anaerobic (respiration and fermentation)

• gram positive clumps/clusters

• catalase positive

• skin and mucous membranes

• frequently found as pathogens in humans

what is special about staph aureus?

• only coagulase positive staph

• causes superficial, deep and toxic-mediated illnesses

folliculitis

• small red bumps at site of hair follicle

• contains pus

• clears after hair is pulled

what is hot tub folliculitis caused by?

Pseudomonas aeruginosa, NOT S. aureus

furuncle

• boil

• skin infection that penetrates subcutaneous tissue

• more serious and painful than folliculitis

carbuncle

• cluster of boils

• infection of skin and subcutaneous tissue

• largest, most painful superficial infection

• often occurs in areas with thicker skin

wound infections

occurs when bacteria enters the body through broken skin

deep abscesses and septicemia

infections that spread throughout the blood into organs

when does pneumonia occur

if bacteria reaches lungs

Pseudomembranous Enterocolitis

• rare complication

• normal intestinal flora is reduced

• S. aureus overgrows and causes intestinal abscesses

describe food poisoning: definition, symptoms, onset, treatment

• An INTOXICATION, not an infection. Bacteria secretes an enterotoxin into food

• fever, vomiting, diarrhea

• 2-6 hours after ingestion

• generally self-limiting, no treatment required

scaled skin syndrome

• caused by a secreted exotoxin

• results in peeling of the skin

what is the function of staph aureus cell wall + protein A

protein A binds to antibodies, interferes with phagocytosis, while helps S. aureus evade the immune system

coagulase

coagulates blood or plasma by converting fibrinogen to fibrin

hemolysin

lyses human and animal red blood cells

hyaluronidase

breaks down hyaluronic acid, which binds connective fibers

DNase

breaks down DNA

lipase

breaks down lipids in the skin

Beta-lactamase

breaks down penicillins, making the bacteria resistant to penicillin therapy

TSST-1

exotoxin responsible for Toxic Shock Syndrome

enterotoxins

exotoxins that act in the gut; associated with food poisoning and enterocolitis

what is Methicillin-Resistant Staphylococcus aureus (MRSA)

nosocomial infection that is acquired within 72 hours of being admitted to the hospital

best treatment for MRSA

vancomycin; last resort

what is the major difference between S. aureus and coagulase negative staphylococci?

CNS are less virulent, but they cause opportunistic infections

Staph Epidermidis: Where is it found? What infections are associated? What are the identifying factors? What is the novobiocin result?

• skin, hair follicles, mucous membranes

• infections involving foreign bodies/devices, like catheters

• white, nonhemolytic colonies, catalase positive, coagulase negative, DNAse negative

• sensitive

Staph saprophyticus: What is it associated with? What are the identifying factors? Novobiocin result?

• UTIs, especially in active young females

• white, nonhemolytic colonies, catalase positive, coagulase negative, DNase negative

• resistant

Staph intermedius: What is it associated with? What is the hemolysis pattern?

• dog bites

• beta hemolytic

how is micrococcus different from staphylococcus?

it uses oxidative metabolism NOT fermentative metabolism

what are the identifying characteristics of micrococcus?

coagulase negative, mannitol positive, oxidative

what is the catalase test?

• Differentiates staph positive from negative

• the test with hydrogen peroxide and bubbling

• bubbles = positive, staph

• no bubbles = negative, strep

what is coagulase test

• use this once you know its staph

• decides between S. aureus and CNS

• S aureus, coag +

• CNS, coag -

what indicates a positive coagulase test?

clumping on the sides of the test tube, negative is no clumping

free vs bound coagulase test

free- tube, clot

bound- side, clumping

why is MSA selective

its high salt concentration inhibits most bacteria while allowing staphylococci and micrococcaceae to grow

why is MSA differential

it differentiates organisms based on their ability to ferment mannitol

what color indicates mannitol fermentation on MSA

yellow