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Microbiology > 21-Staphylococci > Flashcards

21-Staphylococci Flashcards

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Biology 101 flashcards
1
Q

What is the gram reaction of staphylococcus?

A

Gram +

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2
Q

What is the morphology of staph?

A

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.

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3
Q

What is the biological effect of the Protein A virulence factor?

A

inhibits Ab-mediated clearance by binding to the Fc receptor of IgG1, IgG2, and IgG4; leukocyte chemoattractant; anticomplementary

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4
Q

What is the biological effect of the α toxin virulence factor?

A

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

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5
Q

What is the biological effect of the β toxin?

A

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

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6
Q

What is the biological effect of the γ toxin?

A

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)

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7
Q

What is the biological effect of the exfoliative toxins?

A

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).

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8
Q

What is the biological effect of the enterotoxins?

A

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.

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9
Q

What types of enterotoxins are there?

A

Types of Enterotoxin: A (food poisoning), C & D (contaminated milk products), B (staphylococcal pseudomembranous enterocolitis)

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10
Q

What is the biological effect of the TSST-1?

A

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

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11
Q

What is the function of coagulase?

A

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

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12
Q

What is the function of catalase?

A

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.

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13
Q

What is the function of Staphylokinase/Fibrinolysin?

A

dissolves fibrin clots

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14
Q

What is the function of penicillinase?

A

hydrolyzes the β-lactam ring of penicillin thereby rendering the antibiotic ineffective making the organism penicillin resistant.

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15
Q

What is the common reservoir site of S. aureus?

A

found as normal flora on human skin and mucosal surfaces (Nasopharynx); can survive on dry surfaces for long periods of time (due to peptidoglycan)

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16
Q

S. aureus- tramission

A

person-to-person spread through direct contact or exposure to contaminated fomites (ex: bed linens and clothing)

17
Q

S. aureus: What is the clinical presentation of Staphylococcal Scalded Skin Syndrome (SSSS)?

A

disseminated desquamation of epithelium in infants/young children; blisters with clear fluid (no organisms or leukocytes.

18
Q

What is the virulence factor (VF) of SSSS?

A

VF is toxin mediated: Exofoliative Toxin (ETA and ETB)

19
Q

S. aureus: What is the clinical presentation of Bullous Impetigo?

A

localized SSSS, localized cutaneous infection characterized by pus-filled vesicle on a erythematous (redness and inflammation) base in infants/young children.

20
Q

What is the VF of Bullous Impetigo?

A

VF is toxin mediated: Exofoliative Toxin (ETA and ETB)

21
Q

S. aureus: What is the clinical presentation of food poisoning by S. aureus?

A

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)

22
Q

What is the VF of S. aureus food poisoning?

A

VF is toxin mediated: preformed Enterotoxin (heat-stable toxin)

23
Q

S. aureus: What is the clinical presentaiton of enterocolitis?

A

watery diahrrea, abdominal cramping, and fever. Found in people who received broad spectrum antibiotics.

24
Q

What is the VF of enterocolitis?

A

VF is toxin mediated: Enterotoxin A and Leukotoxin LukE/LukD.

25
Q

S. aureus: What is the clinical presentation of Toxic Shock Syndrome (TSS)?

A

ultisystem intoxication characterized by fever, hypotension, and diffuse macular erythematous rash. Think girls and hyperabsorbent tampons.

26
Q

What is the VF of TSS?

A

VF is toxin mediated: TSST-1

27
Q

What are the 5 cutaneous infections of S. Aureus?

A

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)

28
Q

S. aureus: What is the clinical presentation of bacteremia?

A

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.

29
Q

S. aureus: What is the clinical presentation of endocarditis?

A

damage to the endothelial lining of the heart (typically found in the left side of the heart).

30
Q

S. aureus: What is the clinical presentation of pneumonia and empyema?

A

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.

31
Q

S. aureus: What is the clinical presentation of osteomyelitis?

A

destruction of bone, particularly the metaphyseal area of long bones; trauma or surgical procedure

32
Q

S. aureus: What is the clinical presentation of septic arthitis?

A

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.

33
Q

S. epidermidis: What is the clinical presentation of endocarditis?

A
34
Q

S. saprophyticus: What is the clinical presentation of a Urinary Tract Infection (UTI)?

A

dysuria and pyuria; young sexually active women

35
Q

What media do you use to culture S. aureus?

A
36
Q

What is mec A?

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.

37
Q

What is the importance of mec A, clinically?

A

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)

Microbiology (35 decks)

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