Section 2: Gram Positive Cocci

Question 1

Staphylococci

Answer 1

• commonly found as normal flora, and are leading cause of wound infections

Question 2

(Staphylocci): Normal Flora

Answer 2

1. Skin: Salt tolerant, grow aerobically
   - LITTLE virulence, unless compromised host
   - fx = competitor against pathogens from colonizing skin
   - produce antimicrobial substances against other G+ (acne)
2. Upper respiratory tract: colonize nasal activity, nasopharynx and pharynx
   - NOT virulent, but are opportunistic
   - 20% of healthy people carry potential S. aureus in nasal cavitiy
3. GI: part of normal Gi flora
   - both upper and lower intestine, higher # in lower, bc flushing of gastric juices through upper intestine

Question 3

(Staphylocci): Morphology

Answer 3

• spherical cells, cocci!
• grapelike clusters bc of cell division pattern
• G+
• non-motile
• non spore forming

Question 4

(Staphylocci): metabolic characteristics

Answer 4

• facultative anaerobes
• catalase positive (hydrogen peroxide -> H2O and O2)
• ferments sugars (glucose, lactose, sucrose)

Question 5

Staphylococcus aureus characteristics

Answer 5

• golden pigment

- coagulase positive (fibrinogen -> fibrin)

Question 6

Staphylococcus aureus virulence factors: protein A

Answer 6

• extracellular surface protein which binds to Fc portion of IgG preventing opsonization by coating bacterium w/ host’s immunoglobin

Question 7

Staphylococcus aureus virulence factors: Exotoxins (4 hemolysins + other toxins)

Answer 7

• Alpha toxin: MOST POTENT membrane-damaging toxin
• Beta toxin: sphingomyelinase that damages membranes rich in this lipid
• delta toxin: small peptide toxin
• gamma toxin: lyses RBC’s
• Leukocidins - endotoxins that destroy WBC’s: kills WBC, preventing phagocytosis, causing release and rupture of lysosomes (that have hydrolytic enzymes) resulting in further tissue damage
• toxic shock syndrome toxin (TSST): superantigen causing massive release of cytokines, causing a drop in Bp and thus kidney failure. Powerful xotoxin stimulateing Tumor Necrosis Factor (TNF) = necrosis; stims interrrleukin = fever,rash; associated with tampon use but affects men and non-menstruating women
• enterotoxin: food = nausea and vomiting; unlike most exotoxins, S aureus enterotoxin is heat stable, and cooking food will not necessarily destroy it
• exfoliatin: exotoxins that destroy material that binds together layers of the skin

Question 8

Staphylococcus aureus virulence factors: Extracellular enzymes

Answer 8

• coagulase: reacts with prothrombin in blood = staphylothrombin = blood clot
• catalase: enzyme that converts H2O2 -> O2 and H2O
• hyaluronidase: enzyme that breaks down proteoglycans in CT
• fibrinolysin (staphylokinase): lyses clots
• penicillinase (B-lactamase)

Question 9

Staphylococcus aureus Pathogenesis

Answer 9

• furuncles (boils) and carbuncles
• impetigo (red sores around the mouth/nose; brown/yellow crusts)
• folliculitis (infection of 1+ hair follicles)
• scalded skin syndrome (peeling epidermis)
• TSS: rash, fever, vomit diarrhea, achey muscles, low BP, rash
• Pneumonia following viral influenza
• osteomyelitis (bone infection): follows trauma, in males under 12
• catheter and shunt infections
• wound infections
• enteritis: inflammation of small intestine via bacterial infection (maybe stomach and LI too)
• MRSA (methicillin resistant S.A): after surgery, long course of antibiotics.

Question 10

Staphylococcus epidermidis

Answer 10

• coagulase negative
• opportunistic pathogen, compromised patients experience infection
• catheters, prosthetic joints, artificial heart valve
• frequent contaminate in blood draws; do 2nd draw to determine if infection

Question 11

Staphylococcus saprolyticus

Answer 11

• coagulase negative

- leading cause (second to e.coli) of urinary tract infections in sexually active females

Question 12

staphylococcus saprolyticus laboratory diagnosis

Answer 12

• staphylococcus saprolycticus (CATALASE POSITIVE) AND streptococcus saprolyticus (CATALASE NEGATIVE) are both G+ cocci and cause similar disease
• Primary pathogen staphylococcus aureus has definitive characteristics:
• • coagulase positive;
• • mannitol fermentation: use MSA (mannitol salt agar) to isolate Staphylococcus sp. (salt tolerant); only S. aureus can ferment mannitol (Thus changes color from red to yellow***)

Question 13

staphylococcus saprolyticus treatment

Answer 13

• staphylococci strains produce penicillinase (B-lactamase)
• methicillin was the choie, but many strains are now resistant (MRSA)
• treat MRSA strains with vancomycin?

Question 14

staphylococcus saprolyticus control

Answer 14

• aseptic procedures

- phage typing for surveillance of nosocomial infections