Gram Postive Organisms

Question 1

Gram postivie cocci are comprised mostly of…

Answer 1

staph and strep

Question 2

Grape like clusters

Answer 2

staph

Question 3

cocci in chains

Answer 3

strep and enterococcus

Question 4

What is the first labratory test we do to differentiate gram positive cocci?

Answer 4

Catalse test

Question 5

Which cocci are catalase positive and which are negative?

Answer 5

Strep is NEGATIVE for catalase
Staph is POSITIVE

Question 6

If your cocci is gram positive and catalase positive, what test do you run next and why?

Answer 6

Coagulase, if its POSITIVE then its staph a, if its negative check novobiocin sensitivity

Question 7

Gram+ cocci, catalase +, coagulase +

Answer 7

staph a

Question 8

Gram + cocci, catalase +, coagulase -

Answer 8

Either staph epidermidis or staph saprophitycus, you would use novobiocin sensitivity to sort them out

Question 9

Which is novobiocin sensitive: staph epidermidis or staph saprophyticus

Answer 9

staph epi

Question 10

If your cocci is catalase negative, then what do you use to tell them apart?

Answer 10

hemolysis

Question 11

Alpha hemolysis is seen with what organisms?

Answer 11

strep pneumo and viridans

Question 12

Beta hemolysis is seen with what organisms?

Answer 12

strep pyogenes and strep agalactiae (GBS)

Question 13

Gram positive cocci that has gamma hemolysis

Answer 13

enterococcus

Question 14

What test would tell you the difference between strep pneumo and viridans?

Answer 14

optochin sensitive and bile solubility

Question 15

How would you tell the difference between strep pyogenes and strep agalactiae

Answer 15

bacitracin sensitivity, GAS is sensitive

Question 16

“green halo”

Answer 16

viridans

Question 17

Gram positive cocci are aerobic or anerobic?

Answer 17

Anerobic

Question 18

Branching gram + robs include…

Answer 18

actinomyces and nocardia

Question 19

What are the nonbranching gram positive rods?

Answer 19

clostridium, corynbacteria (listeria), bacillus

Question 20

What gram positive organisms form spores?

Answer 20

Spore formation is only seen in gram + organisms and these include:
B anthracis, B cereus, C tetani, C botulinin, C diff, c perf

Question 21

What gram positive organisms are urease positive?

Answer 21

staph epi, staph sapro, nocardia

Question 22

What is the advantage to a capsule?

Answer 22

its an antiphagocytic virulence factor

Question 23

What gram positive organisms have a capsule?

Answer 23

strep pneumo, GBS

Question 24

How are encapuslated bacteria dealth with?

Answer 24

Opsonized and then cleared by the spleen

Question 25

Unique protein to surface of Gram + organisms not found on Gram -

Answer 25

Lipoteichoic

Question 26

Lipoteichoic acid induces what immunomodulatory signals?

Answer 26

TNFa and IL-1

Question 27

Binds Fc portion of IgG to evase opsonization

Answer 27

Protein A, produced by Staph A

Question 28

Allows bacteria to invade mucus membranes

Answer 28

IgA protease

Question 29

What gram positive organisms have IgA protease

Answer 29

strep pneumo

Question 30

M protein

Answer 30

allows GAS to evade phagocytosis, is involved in mimicry and is the culprit behind rheumatic fever

Question 31

What gram positive organisms can form biofilms?

Answer 31

Staph epi (think catheters and protheses) S viridans, mutans, and sanguinis ( think dental plaques and infective endocarditis)

Question 32

Yellow sulfur granules

Answer 32

actinomyces

Question 33

Symptoms include fever, sore throat, and development of a grayish-white pseudomembrane on the posterior pharyngeal wall.

Answer 33

Diphtheria caused by Corynebacterium diphtheriae

Question 34

media of choice are cystine-tellurite agar or Löffler medium for growing this organism, yielding black shiny colonies

Answer 34

Corynebacterium diphtheriae, gram positive bacillus

Question 35

club-shaped bacteria with intracellular metachromatic granules grown on tellurite media

Answer 35

Corynebacterium diphtheriae

Question 35

A bacterial virulence factor produced by Clostridium perfringens and Staphylococcus aureus. C. perfringens toxin acts as a phospholipase to degrade cell membranes and tissue. It is the causative agent of gas gangrene and is responsible for the double zone of hemolysis seen on blood agar cultures. S. aureus toxin causes apoptosis through the formation of pores in the cell membrane

Answer 35

alpha toxin

Question 36

Double zone of hemolysis, gas gangrene

Answer 36

alpha toxin from Clostridium perfringens.

Question 37

The___________________produced by Clostridium perfringens is a lecithinase that degrades cell membrane phospholipids. Degeneration of membrane phospholipids leads to cell lysis and myonecrosis, resulting in gas gangrene with bullous lesions and crepitus. Additionally, the lecithinase activity of this toxin causes hemolysis, which characteristically manifests as a double zone of hemolysis on blood agar.

Answer 37

alpha toxin

Question 38

Double zone of hemolysis

Answer 38

alpha toxin

Question 39

alpha toxin is produced by

Answer 39

Clostridium perfringens and staph a

Question 40

a protease that cleaves SNARE proteins, which are required for neurotransmitter release.

Answer 40

Tetanospasmin produced by Clostridium tetani

Question 41

Infective endocarditis, think what organisms?

Answer 41

strep viridans staph aureus staph epi

Question 42

This organisms causes infective endocarditis with prothsetic heart valves or previously damaged native valves.

Answer 42

Viridans strep, presents subacutely

Question 43

the most common pathogen that causes acute infective endocarditis

Answer 43

staph aureus

Question 44

Infective enocarditis after the dentist

Answer 44

strep viridans

Question 45

Virulence factor that allows staph epi to form biofilms on prothetics

Answer 45

exopolysaccharides

Question 46

Staphylococcal scalded skin syndrome

Answer 46

A blistering skin disorder caused by exfoliative toxins produced by S. aureus following a local infection (e.g., pharyngitis, bullous impetigo). Typically affects children < 6 years. Fever and diffuse, tender erythema occur, followed by extensive flaccid intraepidermal blisters and sloughing off of the superficial layer of skin to reveal moist, red tissue underneath, giving the area a "scalded” appearance. Mucous membranes are typically spared.

Question 47

A pathogen is isolated from the patient's cerebrospinal fluid that does not grow on regular blood agar plate but produces colonies when co-cultured with Staphylococcus aureus.

Answer 47

Haemophilus influenzae. It requires factors X (hematin) and V (NAD) for growth, which are not found in regular sheep blood agar. Staphylococcus aureus produces NAD and lyses erythrocytes in the agar, which releases hematin into the surrounding growth medium and allows Haemophilus to grow within the hemolytic zone of S. aureus. This is known as the satellite phenomenon or satellitism.

Question 48

The most important virulence factor of Streptococcus pneumoniae is its ...

Answer 48

The most important virulence factor of Streptococcus pneumoniae is its polysaccharide capsule, which acts by masking subcapsular antigens. The capsule prevents opsonization (inhibits binding of antibodies and complement activity), which protects bacteria from phagocytosis (e.g., by macrophages in the spleen).

Question 49

The media commonly used to culture C. diphtheriae are ______________________ and _________________________

Answer 49

Tellurite agar and Löffler medium

Question 50

How do we differentiate GBS and GAS?

Answer 50

Since both S. agalactiae and S. pyogenes are catalase-negative, coagulase-negative, beta-hemolytic, capsulated cocci that can form mucoid colonies, the susceptibility to bacitracin can be used to differentiate the two species. Additionally, we can use the Hippurate test and pyrrolidonyl arylamidase (PYR) test. It will be negative for GBS and positive for GAS.

Question 51

pyrrolidonyl arylamidase (PYR) test: positive or negative for GBS

Answer 51

Negative

Question 52

What types of infections can strep pyogenes cause?

Answer 52

S. pyogenes can cause pharyngitis, tonsillitis, scarlet fever, a broad spectrum of skin and soft tissue infections (e.g., impetigo, erysipelas, cellulitis, necrotizing fasciitis), toxic shock syndrome, and certain postinfectious immunological phenomena (e.g., PSGN, rheumatic fever).

Question 53

Bile solubility is a characteristic of what gram positive cocci?

Answer 53

Streptococcus pneumoniae.

Question 54

The sloughing of epidermis when lateral pressure is applied to the skin. Suggests detachment of the epidermis from the dermis. Characteristic of pemphigus vulgaris, staphylococcal scalded skin syndrome, Stevens-Johnson syndrome, toxic epidermal necrolysis, and certain forms of epidermolysis bullosa.

Answer 54

Nikolsky sign

Question 55

What gram positive organism excretes a toxin that cleaves desmoglein-1

Answer 55

staph a, it secretes an exfoliative toxin that can lead to ssss. Desmoglein-1 is a desmosomal protein located in the granular layer of the epidermis and responsible for attaching the keratinocytes to one another. Loss of the cell-to-cell attachments results in intraepidermal fissure formation, which presents as fragile, flaccid blisters. Bullous impetigo is also caused by staphylococcal exfoliative toxins but remains localized, in contrast to SSSS.