gram positive bacteria

Question 1

how do gram positive bacteria stain and what colour?

Answer 1

Gram positive bacteria retain the colour of the crystal violet stain in the gram stain (because they have a cell wall composed of a thick layer of peptidoglycan).
They stain purple.

Question 2

how are streptococci classified?

Answer 2

1.Haemolysis
2.Lancefield typing
3. Biochemical properties

Question 3

what is lancefield grouping?

Answer 3

a method of grouping catalyse negative, coagulase negative bacteria based on bacterial carbohydrate cell surface antigens

Question 4

name some important gram positive bacteria

Answer 4

S.aureus, S.epidermis, S.pyogenes, S.pneumoniae, viridans streptococci, C.diphtheriae

Question 5

how are gram positive bacteria spread?

Answer 5

Spread by aerosols, surface-to-surface contact, colonization of prostheses

Question 6

how are gram positive bacteria managed?

Answer 6

Managed with antimicrobials and vaccination

Question 7

clinical case 1-
Pain in shoulder, elevated temperature
MRI scan, disc infection and osteomyelitis C6 &C7,
Blood cultures

Answer 7

Staphylococcus aureus; flucloxacillin 3 months

Question 8

what is coagulase?

Answer 8

enzyme produced by bacteria that clots blood plasma. Fibrin clot formation around bacteria may protect from phagocytosis.

Question 9

what is the most important +ve coagulase?

Answer 9

s. aureus

Question 10

when are coagulase -ve species important?

Answer 10

in opportunistic infections

Question 11

what is the normal habitat of staphylococci?

Answer 11

nose and skin

Question 12

how is staphylococcus aureus spread?

Answer 12

Spread by aerosol and touch
carriers & shedders

Question 13

what are the virulence factors of staphylococcus?

Answer 13

Pore-forming toxins (some strains)
a - haemolysin & Panton-Valentine Leucocidin
Proteases
Exfoliatin
Toxic Shock Syndrome toxin (stimulates cytokine release)
Protein A (surface protein which binds Ig’s in wrong orientation)

Question 14

what is MRSA resistant to?

Answer 14

beta-lactams
gentamicin, erythromycin,
tetracycline

Question 15

S. AUREUS -name some toxic mediated diseases

Answer 15

Scalded skin syndrome
Toxic shock syndrome
Food poisoning

Question 16

S. AUREUS -name some pyogenic diseases

Answer 16

Wound infections
Abscesses (boils, carbuncles)
Impetigo
Septicaemia
Osteomyelitis
Pneumonia
Endocarditis

Question 17

What is the main virulence factor for S.epidermidis ?

Answer 17

ability to form persistent biofilms

Question 18

where does S.epidermidis normally occur?

Answer 18

Infections in debilitated, prostheses (opportunistic)

Question 19

alpha haemolysis

Answer 19

not complete lysis/clearing
still green tinge to it

Question 20

beta haemolysis

Answer 20

complete lysis/clearing

Question 21

what is sero grouping?

Answer 21

grouping based on Carbohydrate cell surface antigens
one method is lance field A-H and K-V

Question 22

describe lance field A-H and K-V

Answer 22

Antiserum to each group added to a suspension of bacteria
clumping indicates recognition

Question 23

what are the two groups of lancefield sero grouping?

Answer 23

group A- S.pyogenes; important pathogen
Group B - S.agalactiae neonatal infections

Question 24

S.pyogenes virulence factors- exported factors

Answer 24

Hyaluronidase - spreading
Streptokinase - breaks down clots
C5a peptidase - reduces chemotaxis

Question 25

S.pyogenes virulence factors- surface factors

Answer 25

Capsule - hyaluronic acid M protein – surface protein (encourages complement degradation)

Question 26

S.pyogenes virulence factors- toxins

Answer 26

Streptolysins O&S - binds cholesterol Erythrogenic toxin - SPeA – exaggerated response

Question 27

name some infections caused by S. pyogenes

Answer 27

Wound infections >> cellulitis, puerperal fever Tonsillitis & pharyngitis Otitis media Impetigo Scarlet fever Complications rheumatic fever glomerulonephritis

Question 28

what is s.pneumoniae?

Answer 28

Normal commensal in oro-pharynx ~ 30% of population

Question 29

causes of s.pneumoniae?

Answer 29

pneumonia, otitis media, sinusitis, meningitis

Question 30

what are the predisposing factors of s.pneumoniae?

Answer 30

impaired mucus trapping (e.g. viral infection) hypogammaglobulinaemia asplenia

Question 31

what are the virulence factors of S.pneumoniae?

Answer 31

Capsule Inflammatory wall constituents teichoic acid (choline) peptidoglycan Cytotoxin

Question 32

what are the virulence factors of S.pneumoniae?- capsule

Answer 32

polysaccharide (84 types), antiphagocytic polyvalent vaccine 23-valent polysaccharide 13-valent conjugate vaccine

Question 33

what are the virulence factors of S.pneumoniae?- inflammatory wall constituents

Answer 33

teichoic acid (choline) peptidoglycan

Question 34

what are the virulence factors of S.pneumoniae?- cytotoxin

Answer 34

pneumolysin

Question 35

what are viridian's group streptococci?

Answer 35

- haemolytic (or non-haemolytic) Some cause dental caries & abscesses

Question 36

when Is viridian's group streptococci important?

Answer 36

Important in infective endocarditits S. sanguinis, S. oralis

Question 37

what causes viridian's group streptococci?

Answer 37

Cause deep organ abscesses (e.g. brain, liver)

Question 38

what are the most virulent-viridian's group streptococci?

Answer 38

the “milleri group” S.intermedius, S.anginosus, S.constellatus

Question 39

gram positive bacilli

Answer 39

Clostridia C. tetani  Tetanus C. botulinum Botulism C. difficile antibiotic associated diarrhea pseudomembranous colitis Listeria monocytogenes Bacillus anthracis Corynebacterium diphtheriae