21-Staphylococci Flashcards
What is the gram reaction of staphylococcus?
Gram +
What is the morphology of staph?
cocci that grows in a pattern that resembles a cluster of grapes and whose colonies will gradually turn yellow. Many Staphylococci are covered with a polysaccharide capsule and most produce a slime layer (loose-bound, water-soluble film) to at least some degree.
What is the biological effect of the Protein A virulence factor?
inhibits Ab-mediated clearance by binding to the Fc receptor of IgG1, IgG2, and IgG4; leukocyte chemoattractant; anticomplementary
What is the biological effect of the α toxin virulence factor?
disrupts the smooth muscle in blood vessels by integrating in the hydrophobic regions of the host cell membrane (forms pores –> rapid efflux –> lysis) and is toxic to many types of cells including: RBC’s, leukocytes, hepatocytes, and platelets
What is the biological effect of the β toxin?
aka sphingomyelinase, specificity for sphingomyelin and lysophospatidlycholine (catalyzes the hydrolysis of membrane phospholipids) and is toxic to a variety of cells: RBC’s, fibroblasts, leukocytes, and macrophages
What is the biological effect of the γ toxin?
causes pore formation with subsequent ↑ permeability to cations and osmotic instability; as a result it causes the lysing of neutrophils, macrophages, and RBC’s (hemolysis)
What is the biological effect of the exfoliative toxins?
serine proteases that split the intercellular bridges in the stratum granulosum epidermis; not involved with cytolysis or inflammation. Staphylococcal scalded skin syndrome (SSSS) is a range diseases caused by exfoliative toxins. The forms of the toxin are ETA (heat stable and chromosomal) and ETB (heat liable and plasmid mediated).
What is the biological effect of the enterotoxins?
Superantigens (stimulate proliferation of T cells and release of cytokines); stimulate release of inflammatory mediators in mast cells (emesis; blowing chunks), increasing intestinal peristalsis and fluid loss (diahrrea), as well as nausea and vomiting.
What types of enterotoxins are there?
Types of Enterotoxin: A (food poisoning), C & D (contaminated milk products), B (staphylococcal pseudomembranous enterocolitis)
What is the biological effect of the TSST-1?
Superantigen (stimulates proliferation of T cells and release of cytokines); produces leakage or cellular destruction of endothelial cells as a result this causes hypovolemic shock leading to multi-organ failure
What is the function of coagulase?
converts fibrinogen to insoluble fibrin and causes the staphylococci to clump; the fibrin layer around the staphylococcal abscess localizes the infection and protects the organism from phagocytosis
What is the function of catalase?
catabolizes hydrogen peroxide into water and oxygen gas; is used when phagocytes release an oxidative burst with toxic metabolites (ex: hydrogen peroxide and superoxide). Therefore its more for protection than it is causing disease.
What is the function of Staphylokinase/Fibrinolysin?
dissolves fibrin clots
What is the function of penicillinase?
hydrolyzes the β-lactam ring of penicillin thereby rendering the antibiotic ineffective making the organism penicillin resistant.
What is the common reservoir site of S. aureus?
found as normal flora on human skin and mucosal surfaces (Nasopharynx); can survive on dry surfaces for long periods of time (due to peptidoglycan)
S. aureus- tramission
person-to-person spread through direct contact or exposure to contaminated fomites (ex: bed linens and clothing)
S. aureus: What is the clinical presentation of Staphylococcal Scalded Skin Syndrome (SSSS)?
disseminated desquamation of epithelium in infants/young children; blisters with clear fluid (no organisms or leukocytes.
What is the virulence factor (VF) of SSSS?
VF is toxin mediated: Exofoliative Toxin (ETA and ETB)
S. aureus: What is the clinical presentation of Bullous Impetigo?
localized SSSS, localized cutaneous infection characterized by pus-filled vesicle on a erythematous (redness and inflammation) base in infants/young children.
What is the VF of Bullous Impetigo?
VF is toxin mediated: Exofoliative Toxin (ETA and ETB)
S. aureus: What is the clinical presentation of food poisoning by S. aureus?
intoxication (disease caused by bacterial toxin present in food rather than directly from the organism); rapid onset (< 4hrs) of severe vomiting, diahrrea and abdominal cramping, resolution is within 24hrs.
Contamination of food by human carrier (processed meat, custard filled pie, potato salad, and ice cream; Picnic’s)
What is the VF of S. aureus food poisoning?
VF is toxin mediated: preformed Enterotoxin (heat-stable toxin)
S. aureus: What is the clinical presentaiton of enterocolitis?
watery diahrrea, abdominal cramping, and fever. Found in people who received broad spectrum antibiotics.
What is the VF of enterocolitis?
VF is toxin mediated: Enterotoxin A and Leukotoxin LukE/LukD.
S. aureus: What is the clinical presentation of Toxic Shock Syndrome (TSS)?
ultisystem intoxication characterized by fever, hypotension, and diffuse macular erythematous rash. Think girls and hyperabsorbent tampons.
What is the VF of TSS?
VF is toxin mediated: TSST-1
What are the 5 cutaneous infections of S. Aureus?
o Impetigo- localized cutaneous infection with pus filled vesicles; young children found on face and hands
o Folliculitis- impetigo involving hair follicle’s; base of eyelid (Stye)
o Furuncles (boils)- large, painful, pus-filled cutaneous nodules
o Carbuncles – furuncles merge and extend to the deeper subcutaneous tissue; systemic disease (bacteremia, fever and chills)
o Wound Infections- erythema and pus at the site of a traumatic or surgical wound; infections with foreign bodies (stitches, splinter, or dirt)
S. aureus: What is the clinical presentation of bacteremia?
spread of infection into the blood from a focus of infection; acquired in hospital after surgical procedure or result from the continued use of a contaminated IV catheter.
S. aureus: What is the clinical presentation of endocarditis?
damage to the endothelial lining of the heart (typically found in the left side of the heart).
S. aureus: What is the clinical presentation of pneumonia and empyema?
aspiration of oral secretions or the hematogenous spread of the organism from a distant site causing consolidation and abscess formation in the lungs; seen in very young, elderly, and patients with pulmonary disease; severe form of necrotizing pneumonia w/ septic shock.
S. aureus: What is the clinical presentation of osteomyelitis?
destruction of bone, particularly the metaphyseal area of long bones; trauma or surgical procedure
S. aureus: What is the clinical presentation of septic arthitis?
painful erythematous joint with collection of purulent material in the joint space; young children or adults receiving intraarticular injections or who have mechanically abnormal joints.
S. epidermidis: What is the clinical presentation of endocarditis?
S. saprophyticus: What is the clinical presentation of a Urinary Tract Infection (UTI)?
dysuria and pyuria; young sexually active women
What media do you use to culture S. aureus?
What is mec A?
• The mecA gene codes for a different penicillin-binding protein (PBP2’) which retains enzymatic activity and allows it to build peptidoglycan in the presence of methicillin and nafcillin.
What is the importance of mec A, clinically?
This has resulted in the development of MRSA, which is more difficult to treat.
• Methicillin Resistant Staphlycoccus Aureus (MRSA) is always treated with Vancomycin (antibiotic)
