gram positives

Question 1

pathogenesis of toxic shock syndrome

Answer 1

• usually antigen presented via MHCII to specific T cell
• in toxic shock: no APC needed
• toxin allows MHCII to bind to T cell > polyclonal T cell activation

Question 2

Rx for toxic shock

Answer 2

empirical:
fluclox (strep/staph)/ vanc (MRSA) > switch to 3rd gen cef (staph) or penicillin (strep) if identify

+ clinda to cover the eagle effect

Question 3

staph vs strep TSS

Answer 3

staph: 
younger, females
generalised erythroderma and rash more likely to desquamate
N/V/D common
bacteraemia uncommon
TSST1 toxin
mortality low 

strep: 
older, M=F
uncommon n/v/d, no erythroderma 
bacteraemia commmon
strep pyogenic exotoxin A and B
mortality high 30%
coagulopathy + ARDS

Question 4

when are the coagulase negative staphs more pathogenic

Answer 4

when foreign material present e.g. central line

Question 5

examples of coagulase negative staph

Answer 5

staph epi, staph saprophyticus, staph hominis, staph haemolyticus

Question 6

what feature of CoNS is important in how bad the are?

Answer 6

Exopolysaccharide protective biofilm

Question 7

empiric Rx for CoNS

Answer 7

vancomycin! (think about patient Ila)

Question 8

staph aureus exotoxins can cause what 3 clinical pictures

Answer 8

1) SSSS - exfoliatin
2) food poisoning - enterotoxins (A/ B/C1/C2/ D/E)
3) toxic shock - Toxic shock syndrome toxin (TSST-1) - the only superantigen

Question 9

what microbiological makes MRSA different from MSSA

Answer 9

Altered penicillin-binding protein (PBP) - MecA encoding PBP2a

Question 10

what does alpha vs beta haemolytic actually mean for strep? give examples for each.

Answer 10

alpha = partially haemolyses surrounding RBC
- pneumoniae, viridans

beta = fully haemolyses RBC
- pyogenes, agalactiae

Question 11

Lancefield antigen classification: GAS vs GBS vs GDS example each

Answer 11

GAS = strep pyogenes
GBS = strep agalactiae
GDS = enterococcus

Question 12

invasive disease most commonly follows what kind of strep disease?

Answer 12

skin not pharyngitis

Question 13

all the manifestations of GAS!

Answer 13

skin: follicles, cellulitis, erysipelas, nec fasc, impetigo
scarlet fever
tss
pharyngitis

immune: RF, PSGN, ps arthritis, PANDAS

Question 14

GAS tonsillitis vs viral tonsillitis - how to tell?

Answer 14

more likely GAS if:
>4yo
tender tonsillar LN
scarlet fever - blanching, sandpaper-like rash, usually more prominent in skin creases, flushed face/cheeks with peri-oral pallor

Question 15

rheumatic fever tends to occur when post GAS

Answer 15

2-6 weeks (average 3) post GAS pharyngitis

Question 16

transmission rate of maternal GBS

Answer 16

50%

Question 17

early onset vs late onset sepsis GBS

Answer 17

early: <7 days, pneumonia/septicaemia, maternal chemoprophylaxis helps
late: 7-30 days, bacteraemia/meningitis, chemoprophylaxis doesn’t help

Question 18

Rx for the different enterococci

Answer 18

Ampicillin = most active beta lactam 
Vancomycin = ampicillin resistant enterococci 
Teicoplanin = VRE

Question 19

VRE - what makes it resistant?

Answer 19

Alteration of binding site D-alanyl-D-alanine terminus of peptidoglycan precursors

VanA = most common phenotype, higher level resistance, cross-resistance to teicoplannin

VanB = 2nd most common, usually teicoplanin susceptible

Question 20

strep pneumoniae - what protects it from phagocytosis?

Answer 20

polysaccharide encapsulated diplococcus

Question 21

3 very specific immunocompromised states a/w strep pneumoniae

Answer 21

asplenia
sickle cell
nephrotic syndrome

Question 22

compare the two types of strep pneumo vaccines available

Answer 22

Prevenar 13 = CONJUGATE vaccine: Provides T cell immunity, reduces nasopharyngeal colonization by up to 60-70%

Pneumovax 23 = POLYSACCHARIDE vaccine: more capsular types of strep pneumoniae. if higher risk.

Question 23

pathophysiology of clostridium tetani infection

Answer 23

tetanospasmin toxin binds at NMJ > via motor nerve to spinal cord > blocks normal inhibition of antagonistic muscles by cleaving SNARE proteins > contraction and unable to relax!

Question 24

clinical features of tetanus

Answer 24

classic triad:

1) trismus
2) opisthotonus= abnormal posturing with arched back caused by strong muscle spasms
3) risus sardonicus, or “Sardinian grin”: abnormal looking, sustained grin, caused by facial muscle spasm

Laryngeal and respiratory muscle spasm can cause airway obstruction and asphyxiation

sympathetic overactivity

Question 25

Rx for tetanus

Answer 25

if had 3 doses of the vax: give booster if due or if bad wound, >5y since last one (exposure to toxin alone doesn’t give immunity!)

If not/uncertain: vax if clean minor wound; vax + tetanus IG if bad wound

Question 26

what is the new recommendation for boosters for tetanus

Answer 26

10-yearly tetanus boosters are no longer required up until the age of 50, provided that the primary series of 3 vaccinations plus 2 boosters have been given

Question 27

how does clostridium botulinum work?

Answer 27

botulinum toxin inhibits ACh release > blocks neuromuscular transmission

Question 28

classic botulism symptoms vs infant botulism

Answer 28

Classic triad:

i. Symmetrical flaccid ascending paralysis
ii. Clear sensorium
iii. No fever, no paraesthesias

infant:
constipation, poor feeding then the above with resp failure

Question 29

classic risk factor for infant botulism

Answer 29

HONEY

Question 30

which abx in particular are associated with clostridium difficile infection

Answer 30

fluoroquinolones, cephalasporins, clindamycin (lincosamide)

Question 31

treatment of c.diff

Answer 31

metro tds 7-10 days

severe disease vancomycin

Question 32

clinical manifestations of c.diphtheria

Answer 32

1. pharyngeal - bull neck swelling!!
2. cutaneous - gross ulcers
3. neuropathy
4. cardiomyopathy

Question 33

albert stain =

Answer 33

c.diptheria!

Question 34

diphtheria neuropathy - describe

Answer 34

10 days – 3 months: symmetric polyneuropathy with motor deficits with ↓ reflexes, distal to proximal

Question 35

what is the only gram positive bacteria with an ENDO toxin

Answer 35

listeria monocytogenes!

Question 36

Rx for listeria

Answer 36

penicilin - the reason penicillin is included in empiric neonatal sepsis!