gram pos + neg

Question 1

gram neg vs pos cell wall

Answer 1

gram neg
- have inner + outer membrane
- thin layer of peptidoglycan between which cannot take up the gram stain

gram pos
- lack outer layer
- thick peptidoglycan cell wall which turns purple with a gram stain

Question 2

catalase positive vs negative gram positive cocci

Answer 2

catalase +
- staphylococcus
(catalase positive need particular nutrients, require complex media, preferably supplemented with blood)

catalase -
- streptococcus
- enterococccus

Question 3

which staphylococci is coagulase + vs - ?

Answer 3

coaguase + = staph aureus, staph intermedius

coagulase neg = staph epidermidis

Question 4

alpha haemolytic strep vs beta haemolytic

Answer 4

alpha (green discolouration around colonies)
- strep viridians
- strep pneumoniae

beta (complete clearing around colonies)
- group A-H
- strep pyogenes

Question 5

staph aureus antibiotic in sepsis

Answer 5

flucloxacillin IV

• vancomycin IV in allergy or MRSA

Question 6

coagulase neg staph

Answer 6

(staph epidermidis)

many are flucloxacillin resistant
not as virulent as staph aureus

Question 7

major pathogen in bacterial meningitis

Answer 7

strep pneumoniae

Question 8

where are streptococci commensals?

Answer 8

GI tract - dont cause infection here
- viridans strep live in mouth
- enterococci in bowel

Question 9

name a bacteria that has gamma haemolysis

Answer 9

enterococci

(no-haemolysis)

Question 10

faculative anaerobes

Answer 10

grow aerobically + anaerobically
- do not use oxygen in metabolism
- some capnophilic, some prefer anaerobic conditions for growth

Question 11

haemolysis of strep pyogenes

Answer 11

beta

(Group A beta haemolytic strep)
- pharyngitis, skin

Question 12

bacillia examples

Answer 12

listeria monocytogenes

clostridia (c.diff)

corynebacterium (diphtheroids)
- corynebacterium diphtheriae

Question 13

drug of choice for enterococci

Answer 13

amoxicillin
- vancomycin if amoxicillin resistant

vancomycin resistant enterococcus (VRE)
- linezolid
- daptomycin
- tigecycline

Question 14

gram pos bacillia

Answer 14

C.diff
C.tetani (tetanus)

corynebacterium

bacillus cereus
listeria monocytogenes

Question 15

modes of antibiotic resistance

Answer 15

active efflux - bacteria pushes antibiotic out of the cell

target replication (making Abx less effective)

modified drug target - Abx now ineffective

decreased permeability - alters cell wall structure so cant penetrate

drug inactivating enzymes - bacteria produce enzymes to inactivate the antibiotics

Question 16

mean inhibitory concentration (MIC)

Answer 16

concentration of drug required for kill of 99.9% of organism during 18-24hrs

• conc of drug that allows tube with pathogen to remain clear by visual examination after 18-24hrs

Question 17

beta lactams

Answer 17

Arguably most important drug class
- Allergy is due to a degradation product of beta lactams

Class includes –
o Penicillin
o Flucloxacillin
o Cephalosporins
o Piperacillin/tazobactam
o Carbapenems

Question 18

important causes of gram negative sepsis

Answer 18

E.coli
klebsiella
enterobacter (NOT enterococcus)
pseudomonas aeruginosa

neisseria meningitidis
neisseria gonorrhoea

Question 19

Pathogens that can’t really be seen on gram

Answer 19

myobacterium tuberculosis
chlamydophilia sp
trepnonema pallidum
mycoplasma

Question 20

lipopolysaccharide - gram neg cell wall

Answer 20

• Gram neg cell envelope contains an additional outer membrane composed by phospholipids + lipopolysaccharides which face the external environment
• Highly charged nature of lipopolysaccharides confer an overall negative charge to thegram neg cell wall
• Chemical structure of outer membrane lipopolysaccharides can be unique to specific strains

*Pathogenicity often assoc with lipopolysaccharide layer of gram neg cell envelope

Question 21

coliforms

Answer 21

gram neg, non-spore forming bacilli that are lactose fermenting

e.coli
klebsiella sp
proteus sp
enterobacter sp

Question 22

upper GI organisms vs lower

Answer 22

upper GI - aerobic organsims

lower - anaerobic

Question 23

gentamicin protocol

Answer 23

limit duration
- 72hr duration then IDrequired (24hr if concern re renal function

monitor renal function
prescribe in once only section

Question 24

haemophilus influenza

Answer 24

gram neg coccobacillus
- generally aerobic but can grow as a facultative anaerobe

in vitro growth, requires accessory growth factors
- X factor (hemin)
- V factor (NAD)

-> grows on chocolate agar BUT NOT blood

Question 25

active agent against haemophilus influenza

Answer 25

amoxicillin also doxycycline

Question 26

atypical causes of pneumonia

Answer 26

“non-strep” pneumonia

mycoplasma pneumonia
coxiella burnetti
chlamydophilia psittaci
legionella pneumophillia

Question 27

atypical pneumonia therapy

Answer 27

most respond to doxycycline (tetracycline)
- NOT so much legionella

clarithromycin also works

• quinolones (levofloxacin) if penicillin allergic in severe pneumonia

Question 28

legionella pneumophilia

Answer 28

gram neg bacilli

Lukewarm aerolised water (shower, air conditioning, taps)
o Multiplies within amoebae + ciliated protozoa – small one-celled organisms
 ->These provide nutrients + shelter from adverse environmental conditions, such as extreme temperatures + chemicals like chlorine

o Human immune cells called alveolar macrophages look very similar to protozoa
 ->Legionella invades + grows within alveolar macrophages, mistaking them for their natural host + causing disease

Question 29

who/where is legionella pneumophilia more common

Answer 29

smokers, COPD
Males
immunosuppressed, malignancy
diabetes
dialysis
hottubs