06 Gram Positive Organisms

Question 1

Catalase test

Answer 1

Bubble = positive = Staphylococcus

No bubble = neg = Streptococcus

Question 2

Coagulase

Answer 2

Clotting = positive = S. aureus

No clotting = negative = S. saprophyticus / S. epidermidis

Question 3

Susceptibility test

Answer 3

Disk diffusion test (Kirby-Bauer method)

S. saprophyticus = novobiocin resistant

Question 4

Mannitol test

Answer 4

High salt content
Growth and yellow in color = positive = S. aureus
No growth and no yellow color = neg = not S. aureus

Question 5

Staph culture

Answer 5

grey-yellow = hemolytic in media = S. aureus
grey-white= non-hemolytic in media = S. epidermidis
grey = non-hemolytic in media = S. saprophyticus

Question 6

Antigenic structures (Staph)

Answer 6

Peptidoglycan: IL1 -> complement system, PMN, neutrophil
Teichoic acid: antigenic but nonvirulent
Capsules: inhibits phagocytosis; conjugate vaccines (capsule + carrier protein)
(MSCRAMM) Protein A: adhesin to Fc of IgG, decreases opsonization and phagocytosis
(MSCRAMM) Clumping factor: adhesin fo coagulase -> fibrinogen and platelets; aggregates bacteria
Coagulase: bind with prothrombin -> fibrin on bacterial cell wall; hides bacteria

Question 7

Enzymes (Staph)

Answer 7

1. Catalase: H2O2 -> H2O + O2
2. Coagulase: clotting
3. Hyaluronidase: spreading factor, degrades ECM/CT
4. Staphylokinase: forms plasmin -> fibrinolysis -> bacteria can enter
5. Beta lactamase: antibiotic resistance
6. Proteinases and Lipases
7. Hemolysin (alpha, beta, delta, gamma)
8. PVL + gamma hemolysin: lyse WBC; seen in MRSA; bacteriophage mediated
9. Exfoliative toxin: dissolves mucopolysaccharide in skin; toxin a (heat stable), toxin b (heat labile)
10. TSST1: binds with MHC II, TSS
11. Enterotoxin: resistant to gut enzymes, heat stable, pathogenicity islands in bacteriophages

Question 8

Pathogenesis (Staph)

Answer 8

Fomites
Normal microbiota
Food poisoning
Furuncle

Question 9

Clinical manifestations (Staph)

Answer 9

1. Skin and soft tissue
2. Direct Organ Dissemination (hematogenous spread)
3. Toxin release (food poisoning, TSS, SSSS [neonates], blood and catheter infections)

Question 10

Classification (Strep)

Answer 10

1. Hemolysis patterns (B = complete lysis, yellow; a = partial/incomplete lysis, dark and green; Gamma = no lysis)
2. Specific antigens: A (S. pyogenes) B (S. agalactiae),D (Enterococcus), no group (S. pneumoniae/S. viridans)
3. Capsular polysaccharides
4. Biochemical tests (bile esculin, sodium hippurate, CAMP factor production, susceptibility to chemical reagents)

Question 11

Bile-esculin test

Answer 11

For group D strep
Black = pos = Enterococcus
No black = neg = Viridans

Question 12

Sodium Hippurate test

Answer 12

for group B (S. agalactiae)
precipitation/purple = pos = S. agalactiae
no precipitation/purple = neg = group a/b

Question 13

Group A Strep antigenic structure

Answer 13

M protein: prevents phagocytosis, inhibits complement activation, mediates bacterial attachment, can cross react with connective cardiac tissue -> rheumatic heart disease

Question 14

Group a strep toxins and enzymes

Answer 14

1. Streptokinase: escape blood clots. treats pulmonary emboli and coronary artery thrombosis
2. Deoxyribonuclease (streptodornase): positive antibody after infection
3. Streptococcal pyrogenic exotoxins: scarlet fever, STSS
4. Hemolysins: streptolysin s (not antigenic) O (antigenic)

Question 15

Local invasion/exotoxin release of strep

Answer 15

erysipela (superficial)
cellulitis (deep)
necrotizing fasciitis (Strep w M protein, cannot be phagocytosed)
puerperal fever (after fever)
bacteremia (bacteria in blood)/sepsis

Question 16

Local infections of strep

Answer 16

strep sore throat (red tonsils)

streptococcal pyoderma

Question 17

Systemic invasion of strep

Answer 17

Strep Shock Syndrome (soft tissue infection -> bacteremia, M type 1 and 3, pyrogenic toxin a and b)
Scarlet Fever (pharyngitis, pyrogenic toxin a-c)

Question 18

Post streptococcal diseases

Answer 18

Acute glomerulonephritis
Rheumatic fever (M protein vs heart tissue = deformed valves and aschoff bodies)

Question 19

Morphology (Bacilus)

Answer 19

Saprophytic
B anthracis: - hemolysis, nonmotile
B cereus: + hemolysis, motile, food poisoning
B subtilis: contaminant

Question 20

B anthracis virulence factors

Answer 20

Capsule: virulence, antiphagocytic
Toxin: PA (protective antigen), LF (lethal factor), EF (edema factor), PA+LF (lethal toxin causing necrosis and death), PA+EF

Question 21

B anthracis clinical pathology

Answer 21

Papules with necrotic ulcer, edema, eschar formation, inflammation
Cutaneous anthrax (spores on skin), inhalation (bioterrorism), gastric

Question 22

Types of B cereus

Answer 22

Emetic (nausea, vomiting, occasional diarrhea, found in sporulates of rise)
Diarrheal (no vomiting)
Eye infection
Localized infections

Question 23

Clostridium morphology

Answer 23

Saprophytic
C botulinum
C tetani
C perfringes

Question 24

Spore forming species

Answer 24

Bacillus (anthracis, cereus, subtilis)

Clostridium (botulinum, tetani, perfringes, difficile)

Question 25

C botulinum characteristics

Answer 25

Causes flaccid paralysis Spores are resistant to heat, decreased in high pH Toxin: light chain lyses SNARE proteins + heavy chain

Question 26

Types of botulism

Answer 26

Adult: eat neurotoxin | Infant/child: eat spores and it germinates in the gut

Question 27

C tetani characteristics

Answer 27

Found in soil and feces Flagellar antigen Tetanospasmin (neurotoxin): spastic paralysis, non invasive, A and B units

Question 28

C tetani clinical findings

Answer 28

``` Difficulty swallowing Vocal cord spasm Opisthotonos (back arching) Risus sardonicus (sardonic smile) Trismus (lockjaw) ```

Question 29

C tetani prevention

Answer 29

Active immunization (toxoid antigen -> antibodies) Prophylaxis with antitoxin Wound care Penicillin

Question 30

C perfringes toxin

Answer 30

``` Clostridium perfringes enterotoxin Intense diarrhea Incubation period: 7-30 h Hypersecretion in small intestines Self-limiting Test: stormy fermentation (coagulates the milk) ```

Question 31

C perfringes invasive toxin

Answer 31

a toxin: lecithinase (skin lecithin, platelet aggregation makes anaerobic environment)

Question 32

C perfringes pathology

Answer 32

Gas gangrene (clostridial myonecrosis) COH ferments and produces gas -> cackling sounds -> distention of tissues -> compromised blood supply Crepitation (cracking skin from gas)

Question 33

C difficile characteristics

Answer 33

``` Antibiotic associated diarrhea Psudomembranous colitis (type a = enterotoxin = watery and bloody diarrhea; type b = cytotoxin = plaques and micro-abscesses in intestine) ```

Question 34

Non-spore forming species

Answer 34

Corynebacterium diptheriae | Listeria monocytogenes

Question 35

C diptheriae characteristics

Answer 35

``` Metachromic granules (beaded appearance) Potassium tellurite growth (black) Loeffler media (white) Invasive Toxic (toxigenicity found in bacteriophage) ```

Question 36

Diptheria

Answer 36

Bull neck (swollen lymphs from lymphatic edema) Toxin produces necrotic epithelium Psudeomembrane and bacteria grows inside nectrotic tissue

Question 37

L monocytogenes morphology

Answer 37

``` Facultative anaerobe with short rods Tumbling motility Can survive in low temp, pH, and high salt Catale + Esculin + ```

Question 38

L monocytogenes virulence factors

Answer 38

Intracellular organism = cell-mediated immunity Antigenic structure: O somatic antigen / H flagellar antigen Factors: Adhesin proteins (Ami, fbp a, flagellin proteins), surface proteins (for entrance; internalin a/b, actin a), listerolysin O, iron, filopodia

Question 39

L monocytogenes pathophysio

Answer 39

adhesion (adhesin proteins) -> surface proteins for entering -> pH decreases inside vacuole due to listeriolysin O -> filopods+actin propel to another cell

Question 40

B anthracis pathophysio

Answer 40

PA binds to surface receptors -> LF+EF enter cell -> EF = edema, LF = death

Question 41

C botulinum pathophysio

Answer 41

Botulinum toxin goes to gut -> absorbed to blood -> goes to neuron -> light chain of toxin lyses SNARE SNAP protein -> no release of neurotransmitter -> flaccid paralysis

Question 42

L monocytogenes clinical findings

Answer 42

Gastroenteritis Granulomatous infanseptica (neonatal sepsis, pustular lesions, granuloma in organs, death on delivery) Listeria meningoencephalitis

Question 43

Actinomycetes characteristics

Answer 43

Aerobic Chains with branches Long cell wall with mycolic acid