Staphylococci and Related Gram positive Cocci

Question 1

Charactaristics of Staphylococci

Answer 1

Gram +

Cocci arranged in single cells, paits, tetrads, short chains but mostly grape like clusters

non-motile

non-spore forming

Catalase positive

Faculatative anaerobes; except S. Aureus sub species anaerobious, and S. Saccharolyticus. These two are also catalase negative

Question 2

Staphylococci Aureus

Answer 2

Gram + grape clusters

Grows in 24 hours, white cream color, laege coloinies, clearing zone around colonies from beta-hemolysis

Question 3

Staphylococci Aureus Habitat

Answer 3

Found in external environment

Found on skin, and mucous membranes

anterior nares of 20-40% of adults

skinfolds

perineum

Axillae

Vagina

Question 4

Staphylococci Aureus factors predisposing to serious infection

Answer 4

It is an opportunistic pathogen

Defects in leukocyte chemotaxis- Wiskott aldrich syndrome, downs syndrome, job’s syndrome, Chediak-Higashi syndrome, acquires diabetes mellitus, rheumatoid arthritis

Defects in opsonization secondary to congenital or acquired hypogamaglobulinemias

defects in complement

defects in intracellular killing of bacteria after phagocytosis due to inability to activate the membrane bound oxidase system. (Chronic granulomatus disease, lymphoblastic leukemia, acute and chronic mylogenous leukemia)

Skin injuries- burn, surgery, eczema, sprots injuries (contact sports)

Presence of foreign bodies, sutures, IVs, prostetic devices)

infection with other agents, especially influenza or measles

chronic underlying disease- malignancy, alcoholism, heart disease

Use of antibiotics to which S. Aureus is not susceptible

Question 5

Where is S. Aureus part of the normal flora, and what infections can it cause there?

Answer 5

Skin- folliculitis, impetigo, furuncles, carbuncles, post surgical wound infections (can cauee pyoderma)

nose and throat- sinusitus, peritonsilar abcesses, mastoiditis, bronchitis, staphylococcal pneumonia.

GI tract, Urethra, Vagina - enterocolitus, cystitis prostatis, cervicititis, salpingitis, pelvic abcesses

Question 6

Pyoderma

Answer 6

any skin disease that is pyogenic. can be caused by staphylococcal infections or can be automimmune loke in the case of pyoderma gangrenousum.

Question 7

Furuncle

Answer 7

also called a boil

skin disease cause by infection of hair follicles, resulting in localized accumulation of pus, and dead tissue

Red pus filled lumps that are tender, warm, and extremely painful.

A yellow or white point at the center of the lump can be seen when the boil is ready to drain

Question 8

Carbuncle

Answer 8

abcess larger than a boil

usually with one or more openings that is draining pus into the skin

can develope anywhere but are most common in the back and nape of the skin.

Question 9

Toxin mediated infections of S. Aureus

Answer 9

Scalded skin syndrome (neonates and children under age 4)

Toxic-Shock Syndrome

Food Poisoning

Question 10

Staphylococcus Aureus disseminating infections

Answer 10

Pneumonia

Bacteremia

Endocarditis

Osteomyolitis

septic arthritis

septic embolization

metastatic infections

Question 11

Staphylococus Aureus virulance factors

Answer 11

Capsule- prevents ingestions by PMNs

Protein A- binds Fc regions of IgG. interferes with opsonization and ingestion of organism by PMNs

Panton-Valentine Leikocidin (PVL)- enzyme that alters cation permeability of rabbit and human leukocytes, resulting in WBC destruction. (A PVL + strain is more likely to cause infection than a PVL negative strain)

Coagulase-binds to prothrombin and catalyzes the conversion of fibrinogen to fibrin, this coats the bacterial cells with fibrin, makes hem more resistant to opsonizationand phagocytosis.

alpha hemolysin- lyses RBCs. Dermonecrotic, leukocyte toxicity

beta hemolysin- sphingomyelinase, varying lysis of RBCs from different animals due to differences in membran sphingomyelin content. Produces “hot cols lysis” hemolysis enhanced at low temp after 35 C incubation.

delta hemolysin- Produced by 97% of S. Aureus 50-70% of coagulase negative staph. Acts as surfactant that disrupts the cell membrane. interacts with the membrane to form channels that increase in size over time resulting in leakage of cellular contents. Some coagulase-nagative staphylococci produce enough toxin to cause NEC in neonates.

gamma hemolysin- found in some S.Aureus strains. also causes lysis og a variety of cells.

Toxins- exfoliants or epidermolytic toxins. cause staph scalded skin syndrome. Dissolved the mucopolysaccharide matrix of epidermis causing seperation of skin layers. Rare in adults.

Enterotoxins- heat stable molecules responsible for clinical features of stphylococcal food poisoning. Causes vomting with or without diarrhea (2-8 hours). recovery in 24-48 hours. Most common cause of food poisoning in the U.S.

Fibrinolysins - break doen fibrin clots fascilitate spread of infection to other tissues.

Hyaluronidase- hydrolyzes intercellular matrix of acid mucopolysaccharides in tissue acting to spread organisms to adjacent tissue.

Phospholipase C - described in patients with acute respiratory distress syndrome and diseminated intravasculat coagulation. Tissues affected by this enzyme become more susceptible to damage and destruction by bioactive complement components and products during complement activation.

Superantigens - group of toxins knowsn as pyrogenic toxin super antigens.

Question 12

Staphylococcus Aureus Superantigens

Answer 12

Pyrogenic toxin super antigens

toxic shock shock syndorm toxin-1 (TSST-1)

Streptococcal pyrogenic exotoxins (SPE)

streptococcal super antigens

Question 13

Rare Staph Aureus that may be coagulase negative. or positive

Answer 13

S. intermedius

S. hyicus

S. delphini

S. Schleiferi sub specialty coagulans