Microbiology Recall; Gram-Positive Cocci: Staphylococcus

Front 1

What are three medically important gram-positive cocci?

Back 1

1) Staphylococcus
2) Streptococcus
3) Enterococcus

Front 2

What test is positive in Staphylococcus and negative in Streptococcus.

Back 2

Catalase test

Front 3

What is the mechanism of catalase?

Back 3

Converts hydrogen peroxide to water and oxygen:
Catalase inactivates toxic peroxide species, while superoxide dismutase inactivates toxic oxide radicals.

Front 4

What is the difference between staphylococci and streptococci on Gram stain?

Back 4

Staphylococci appear as spherical cocci arranged in irregular grape-like clusters
Streptococci appear as diplococcal pairs or chains rather than as clusters.

Front 5

What are three pathogenic types of Staphylococcus?

Back 5

1) Staphylococcus aureus
2) Staphylococcus epidermidis
3) Staphylococcus saprophyticus

Front 6

Which staphylococci sometimes demonstrate hemolytic properties?

Back 6

S. aureus

Front 7

What type of hemolytic reaction do S. aureus demonstrate?

Back 7

Beta-hemolytic or complete hemolysis characterized by red cell lysis resulting in a clear ring around the colony when cultured on blood agar.

Front 8

What are two tests that can be used to distinguish between strains of Staphylococcus?

Back 8

1) Coagulase Test - to determine if the enzyme is present
2) Mannitol Test - to determine if the organism is able to ferment mannitol

Front 9

What is coagulase?

Back 9

Bacterial enzyme which, when released, activate both prothrombin and the coagulation cascade.

Front 10

What results would you see with the coagulase test for the three pathogenic staphylococci?

Back 10

(+) S. aureus
(-) S. epidermidis
(-) S. saprophyticus

Front 11

What does a coagulase positive test look like?

Back 11

"Clumping" on latex agglutination test.

Front 12

What results would you see with the mannitol test for the three pathogenic staphylococci?

Back 12

(+) S. aureus
(-) S. epidermidis
(-) S. saprophyticus

Front 13

Which of the three pathogenic types of staphylococci are often found in normal flora?

Back 13

S. aureus
S. epidermidis

Front 14

Which of the three pathogenic types of staphylococci produces exotoxin?

Back 14

S. aureus

Front 15

Which of the three pathogenic types of staphylococci is most virulent?

Back 15

S. aureus

Front 16

Which of the three pathogenic types of staphylococci have capsules?

Back 16

S. aureus
S. epidermidis

Front 17

What defense mechanism do encapsulated bacteria utilize?

Back 17

Demonstrate antiphagocytic properties.

Front 18

Do staphylococci contain endotoxin?

Back 18

No, endotoxins are never produced by gram positive bacteria.
Instead of endotoxins, Staphylococcus aureus, like all Gram positive bacteria, stimulate cytokine production by producing surface components including peptidoglycan, teichoic acids, and lipoprotein.

Front 19

What can make Staphylococcus potentially difficult to treat?

Back 19

Staphylococcus, commonly produces Beta-lactamases and/or penicillin binding proteins which result in antibiotic resistance, e.g., methicillin-resistant S. aureus or vancomycin-resistant S. aureus.

Front 20

What is the origin of the word aureus?

Back 20

Aureus comes from the Latin root for gold.

Front 21

What is the relevance of the root of the word aureus?

Back 21

S. aureus colonies appear golden on some media.

Front 22

Does S. aureus grow in the presence of air?

Back 22

Yes, all staphylococci are facultative anaerobes.

Front 23

Where are you most likely to find S. aureus in a healthy, non-infected person?

Back 23

Mucous membranes of anterior nares.

Front 24

What are three major mechanisms that S. aureus uses to cause disease in the host?

Back 24

1) Direct tissue destruction
2) Exotoxin release
3) Promotes immunologic dysfunction

Front 25

What S. aureus proteins contribute to pathogenicity?

Back 25

Protein A, hemolysis, coagulase, leukocidins, penicillinase, superantigens and many enzymes

Front 26

What does protein A bind?

Back 26

The heavy chain constant domain of IgG antibodies.

Front 27

How does protein A binding to IgG antibodies contribute to pathogenicity?

Back 27

Decreases the likelihood of immune system to "see" baceria and therefore decrease opsonization and phagocytosis.

Front 28

What is the result of hemolysins and leukocidins?

Back 28

Destruction of RBC and WBC, respectively

Front 29

What is a specific hemolysin?

Back 29

Alpha toxin

Front 30

How does alpha toxin work on a molecular level?

Back 30

Polymerizes into tubes that pierce membranes resulting in osmotic lysis.

Front 31

What are the clinical implications of alpha toxin?

Back 31

Causes marked necrosis of the skin and hemolysis.

Front 32

What is penicillinase?

Back 32

Secreted form of Beta lactamase.

Front 33

What is the mechanism of action of penicillinase?

Back 33

Inactivates Beta-lactam antibiotics via the disruption of the Beta-lactam portion of the penicillin molecule.

Front 34

What are three proteins made by S. aureus that are specifically used to destroy tissue?

Back 34

1) Hyaluronidase
2) Staphylokinase
3) Lipase

Front 35

How does hyaluronidase work?

Back 35

Breaks down proteoglycans in connective tissue.

Front 36

How does staphylokinase work?

Back 36

Lyses fibrin clots

Front 37

How does lipase work?

Back 37

Catabolism of fats and oils allowing for sebaceous gland colonization.

Front 38

What are superantigen exotoxins?

Back 38

Exotoxin which interact the Vb domain of the T-cell receptor and the major histocompatibility complex (MHC) class II molecules on the surface of antigen-presenting cells directly activating them regardless of antigen specificity.

Front 39

What are two effects of superantigens?

Back 39

1) CD4 T cell and antigen presenting cell proliferation.
2) Substantial increase in the release of CD4 T cell cytokines (IL-1, IL-2, IFN-gamma, and TNF)

Front 40

What are two pyrogenic superantigen exotoxins released by S. aureus?

Back 40

1) Enterotoxin (heat stable)
2) Toxic shock syndrome toxin Exfoliatin is released by S. aureus but is NOT a superantigen.

Front 41

What is the result of the release of exfoliatin exotoxin?

Back 41

Results in scalded skin syndrome where the skin desquamates and sloughs off.

Front 42

What is the pathogenesis of exfoliatin?

Back 42

The toxin attacks the intercellular adhesive layer of the stratum granulosum with resulting desquamation of the epidermis.

Front 43

Which patient population is usually affected?

Back 43

Newborns with recently severed umbilical cords or children with skin infections.

Front 44

Will the skin of a child with scalded skin syndrome contain S. aureus?

Back 44

No, just the exotoxin.

Front 45

What is the result of heat stable enterotoxin release?

Back 45

Gastroenteritis leading to vomiting and diarrhea
Enterotoxin, also a superantigen, is much more stable than S. aureus and may still cause gastroenteritis from cooked foods

Front 46

What is the time course of the enterotoxin mediated gastroenteritis?

Back 46

Rapid onset of acute period of nausea and non-bloody, explosive vomitus from presence of pre-formed enterotoxin.

Front 47

What type of foods facilitates growth of S. aureus?

Back 47

Custards,
Egg salad,
Cream pastry,
Mayonnaise
Potato salad

Front 48

What causes Toxic shock syndrome?

Back 48

1) TSST + S. aureus
2) TSST + streptococci
3) Circulating entertoxin

Front 49

What is the pathogenesis of TSST?

Back 49

Superantigen induced IL-1, IL-2, IFN-gamma, and TNF expression

Front 50

What are the six major symptoms of TSS?

Back 50

1) Fever
2) Nausea and vomiting
3) Watery, non-bloody diarrhea
4) Erythematous rash similar to scarlet fever
5) Epidermolysis of palms and soles
6) Septic shock and organ damage

Front 51

What determines the extent of symptoms in TSS?

Back 51

Presence of the exotoxin rather than the presence of bacteria.

Front 52

What organ systems are directly affected by S. aureus?

Back 52

Skin, heart, lungs, brain, bones, and joints.

Front 53

What five examples of skin infections are caused by S. aureus?

Back 53

1) Folliculitis
2) Abscess
3) Furuncles
4) Carbuncles
5) Wound infection (Impetigo and cellulitis are skin manifestations primarily seen with Group A streptococci)

Front 54

What is folliculitis?

Back 54

An inflammatory reaction in hair follicles

Front 55

What is an abscess?

Back 55

A collection of pus

Front 56

What is a furuncle?

Back 56

Abscess produced by an infected hair follicle deep in the subcutaneous tissue often forming around foreign bodies

Front 57

What is a carbuncle?

Back 57

A much larger, deeper, painful version of a faruncle in which lesions occasionally lead to bacteremia

Front 58

What is a wound infection?

Back 58

Infection at a site of skin trauma, often associated with surgical contamination

Front 59

What is the most severe complication of S. aureus bacteremia on the heart?

Back 59

Acute endocarditis

Front 60

How do patients with S. aureus endocarditis present?

Back 60

Sudden onset of fever, chills, myalgia and evidence of septic emboli.

Front 61

What are the ultimate results of acute endocarditis?

Back 61

Valvular destruction and septic embolization to brain, lung, and spleen, and classic stigmata of endocarditis (Janeway lesions, Roth's spots, Oslers nodes, splinter hemorrhages)

Front 62

What is the most common cause of acute endocarditis from S. aureus?

Back 62

IV drug use

Front 63

In IVDUs, which heart valves are likely to be affected S. aureus endocarditis?

Back 63

Right heart valves, usually tricuspid valve.
IV injections go into the vein and veins drrain back to the right side of the heart.

Front 64

What effect does S. aureus have on the lungs?

Back 64

Severe, necrotizing pneumonia

Front 65

Who is most likely to be affected with necrotizing pneumonia?

Back 65

Middle aged adults living in the community following viral influenza infection.

Front 66

What is the clinical course of pneumonia?

Back 66

Acute fever and chills with lobar consolidation of lung with potential cavitation secondary to destruction of the lung parynchema

Front 67

What are likely sequelae of cavitations?

Back 67

Effusions and empyema

Front 68

What effect does S. aureus have on the brain?

Back 68

Meningitis, cerebritis, and brain abscess

Front 69

How do patients with meningitis present?

Back 69

High fever, nucal rigidity, headache, change in mental status (obtundation), focal neurologic sign or coma.

Front 70

What effect does S. aureus have on the bones?

Back 70

Acute and chronic osteomyelitis infection.

Front 71

Who is most likely to have osteomyelitis?

Back 71

Males under 12

Front 72

How do patients with osteomyelitis present?

Back 72

Asymmetrical, swollen, warm tissue over bone; systemic fever and shakes secondary to bacteremia

Front 73

What effect does S. aureus have on the Joints?

Back 73

Septic arthritis secondary to synovial membrane invasion.

Front 74

Is septic arthritis a medical emergency?

Back 74

Yes, pus can rapidly cause irreparable cartilage damage.

Front 75

What is the most common overall cause of septic arthritis?

Back 75

S. aureus

Front 76

Who is most likely to be affected by S. aureus induced septic arthritis?

Back 76

Young and old (pediatric age group and adults over 50)

Front 77

What is the most common cause of septic arthritis in the middle age population?

Back 77

N. gonorrhea

Front 78

How do patients with S. aureus septic arthritis present?

Back 78

Acutely painful, swollen, red-hot joint.

Front 79

How would you diagnose septic arthritis?

Back 79

Yellowish fluid on arthrocentesis with >100,000 neutrophils along with positive gram stain or culture.

Front 80

How would you treat septic arthritis?

Back 80

1) Drain the joint
2) Antimicrobial therapy

Front 81

Why are most S. areus types resistant to Penicillin G?

Back 81

Presence of penicillinase-encoding plasmids and transposons, commonly found in community and hospital acquired strains.

Front 82

What is MRSA?

Back 82

Methicillin-Resistant Staphylococcus Areus, which carries Beta-lactam enzymes used for peptidoglycan synthesis that are insensitive to the antibiotic effects of methicillin

Front 83

Where do MRSA types of infections usually develop?

Back 83

Hospitals or nursing homes where broad spectrum antibiotics are used.

Front 84

How is MRSA transmitted between patient?

Back 84

Usually via hand contact from health care workers.

Front 85

How can transmittion of MRSA between patients be prevented?

Back 85

Frequent proper hand washing?

Front 86

What is the gold standard treatment for severe MRSA infection?

Back 86

Vancomycin, although resistance has developed.

Front 87

What is S. epidermidis?

Back 87

A coagulase negative organism found as normal flora on the skin.

Front 88

Does S. epidermidis have a low or high virulence compared to S. aureus?

Back 88

Low

Front 89

Does S. epidermidis have an increased or decreased liklihood of drug resistance when compared to S. aureus and why?

Back 89

More frequent than S. aureus because it is innately more resistant.

Front 90

What population groups are frequently infected with S. epidermidis?

Back 90

1) Patients with Foley catheters, IV lines or any indwelling lines
2) Patients with prosthetic devices or damage heart valves
3) Immunocompromised patients

Front 91

What gives S. epidermidis a predilection for prosthetic devices?

Back 91

Formation of biofilms on implanted surfaces resulting in adherence of the polysaccharide capsule

Front 92

How do you determine if S. epidermidis bacteremia is of a blood-origin or from contamination?

Back 92

Sterilely draw more than one blood sample from two different sites 15 minutes apart.

Front 93

What is S. saprophyticus?

Back 93

A coagulase negative organism which causes urinary tract infection and cystitis.

Front 94

Where is S. saprophyticus found?

Back 94

Normal flora of the vagina

Front 95

What test can be performed to help distinguish S. saprophyticus from other staphylococci?

Back 95

Novobiocin (antibiotic) sensitivity.

Front 96

What results would you see with the novobiocin sensitivity test for the three pathogenic staphylococci?

Back 96

S. saprophyticus is (+), or resistant, demonstrating growth
S. aureus and S. epidermidis are (-), or sensitive, demonstrating no growth.

Front 97

Who is most likely to be infected with S. saprophyticus?

Back 97

Young healthy sexually-active females