Antibiotic Susceptibility Testing Flashcards

1
Q

meant to kill off any invading organism

A

bactericidal

-used in immunocompromised patients

-life threatening

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2
Q

prevents further growth of the organism

A

bacteriostatic

-healthy people
-non life threatening diseases

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3
Q

lower dosage

A

bacteriostatic

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4
Q

higher dosage

A

bactericidal

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5
Q

broad spectrum drugs

A

activity against wide range of organisms

-good when we don’t know the organism
downfall= kill more normal flora

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6
Q

narrow spectrum antibiotics

A

limited to target range

best if pathogen known

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7
Q

synergy means

A

2 drugs when given together work better together than on their own

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8
Q

antagonism means

A

if I give you one drug it will counteract another drug

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9
Q

is there an ideal antibiotic?

A

no there is not an antibiotic that fits all

look at cost
site of infection

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10
Q

how long from inception to market does a new drug take

A

over 10 years

-need volunteers to test safe
-resistance happens fast

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11
Q

Average time from hitting market to resistance

A

6 months

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12
Q

most resistance organisms

A

e.coli

superbug- show multi resistance

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13
Q

MDR= multiple drug resistance

A

organism is resistant to 1 agent in 3 or more antibiotic classes

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14
Q

XDR= extra drug resistant

A

resistant in one agent in all but 2 or fewer antibiotic classes

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15
Q

PAN= pan drug resistant

A

resistant to everything
- some e.coli and pseudomonas

-treat with cocktail of drugs

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16
Q

MRSA

A

methicillin resistant staph aureus

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17
Q

VRE

A

vancomycin resistant enterococci

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18
Q

strep pneumo is resistant to

A

penicillin

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19
Q

why so much resistance?

A

antibiotics in agricultural

not finishing antibiotics

laundry detergent, hand sanitizer

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20
Q

what is intrinsic resistance?

A

bacteria is naturally resistant

this is a way we ID some organisms

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21
Q

how does acquired resistance occur?

A

target site modification
plasmids
efflux
enzymes
jumping genes

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22
Q

target site modification

A

target certain site of bacteria and the bacteria changes the site

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23
Q

plasmids

A

extra chromosomal piece of DNA

-resistance gene is found here
-easily transferable from one bacteria to another

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24
Q

efflux

A

antibiotic goes in and organism spits it out

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25
Q

jumping genes

A

transpanozone????

jumps from pieces of DNA to another

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26
Q

things to think about with antibiotic selection

A

resistance, cost, patient population, dosages, location

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27
Q

primary drug

A

first line that has been manufactured in the category
§ From nature, ex. Penicillin
§ Cheaper
§ Less toxic to human
Good treating

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28
Q

secondary drug

A

chemical modifications from primary drugs

-due to resistance of primary drug

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29
Q

tertiary drug

A

alter side chain

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30
Q

farther down the line in modifcations of drugs=

A

higher cost of new drug
more side effects seen in human

treat more poly microbal infections

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31
Q

advantage of more modifications to drugs

A

treat more resistant organisms we are now seeing

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32
Q

standard for inoculum

A

Mc Farland Standards

-sets turbidity standards that allow us to determine the amount of organism present in a broth

-we buy

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33
Q

how to create turbidity

A

barium chloride
sulfuric acid

-now it is given in latex particles

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34
Q

higher you go with Mc Farland standards =

A

more turbidity = more organisms in your broth if matching turbidity standard

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35
Q

most common amount of standard

A

0.5 Mc Farland Standard = 1.5 x 10 ^8 CFU /mL

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36
Q

what is MIC

A

Concentration of antibiotic in mg/mL that prevents the in vitro growth of bacteria

minimum

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37
Q

how is MIC done

A

○ 1 control= broth and organism - makes sure organism is viable ; growth
○ Broth control= Mueller Hinton: make sure broth isn’t contaminated ; no growth
○ Antibiotic control= antibiotic and broth= make sure antibiotic isn’t contaminated ; no growth
○ Incubated 35 degrees 18-35 hours

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38
Q

MBC

A

Minimum bactericidal concentration of drug

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39
Q

info about MBC

A

tubes show no turbidity

plated on BAP

look for CFU on actual plate

1st plate that shows 99% reduction of organism= MBC

-higher concentration than MIC

bacteriostatic drugs

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40
Q

kirby bauer principle

A

zone of inhibition is created as a result of antibiotics diffusing away from the disk

read in millimeters

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41
Q

why can’t let bacteria sit more than 15 minutes before plating on Mueller Hinton plate

A

bacteria will double

-almost immediately antibiotic will start working so can’t move disk

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42
Q

method of detection set by

A

CLSI- clinical laboratory standards institute

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43
Q

Muller-Hinton measurements

A

150 millimeters across

depth 4 millimeters

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44
Q

if depth on muller hinton is greater

A

we will get false resistance

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45
Q

if depth is less than normal on a muller hinton plate

A

false susceptibility

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46
Q

how many disks placed on muller hinton

A

12 disks

24 mm apart

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47
Q

pH on muller hinton

A

7.2-7.3 at RT

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48
Q

too low pH on muller hinton=

A

false resistant with amino glycosides

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49
Q

too high pH on muller hinton plate

A

false susceptibility with amino glycosides

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50
Q

what is muller hinton grown in

A

ambient air (O2) not CO2 but depends on organism

CO2 will decrease pH

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51
Q

decrease temp when growing muller hinton

A

false susceptibility

bigger zone sites

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52
Q

only time a muller hinton plate can grow at 35 degrees

A

MRSA

can be incubated at 30, Mec A expressed better at 30 and full 24 hrs

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53
Q

concentrations of what are importatnt in Muller-Honton when testing amino glycosides

A

calcium, magnesium and zinc

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54
Q

when are amino glycoside used

A

for pseudomonas

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55
Q

if concentration is increased =

A

false resistance

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56
Q

if concentration decreased=

A

false susceptibility

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57
Q

drug concentrations -each disk of antibiotics concentration set by

A

FDA

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58
Q

how to store disks

A

refridgerator for up to a week

if not used in a week, store in a frost free freezer at -20

-frost will cause moisture and antibiotics will leak out

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59
Q

before reporting any results we need to do

A

QC on disks and representative organisms

organisms are ATCC

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60
Q

what organisms used for QC

A

○ Always use an E.coli, S. aureus, and pseudomonas
E.coli- gram- , s. aureus, gram +, pseudomonas, non fermenter

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61
Q

when first starting antibiotic panel have to do QC

A

everyday for a month

  • If during the 1 month panel and have less than 3 antibiotics outside accepted readings then can do QC weekly
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62
Q

how read zones on regular muller plate

A

read from back to plate
edge to edge

read above dark surface from back site with reflective light

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63
Q

how to read muller hinton with added choc or blood

A

read from top side with top off

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64
Q

if there is more than 1 organism present on a plate

A

plate to a purity plate

proteus ignore swarming and read outer edges

sulfa- read best defined edge

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65
Q

if 2 or 3 colonies in the zone

A

can’t report out

-purity plate
-hetero resistance -seen in MRSA

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66
Q

what is hetero resistance

A

§ Not every colony in a population expressed resistance to the same degree
§ If see 1 colony in the zone, need to consider entire drug to be resistant

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67
Q

SIR method of reporting based on

A

CLSI

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68
Q

sensitive

A

sensitive to standard dose of drug that is used for the antibiotic

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69
Q

intermediate

A

some things might cause drug to be resistant in vivo
Not first choice of drugs

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70
Q

resistant

A

don’t use this drug

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71
Q

how to determine break points?

A

regression analysis

SIR are breakpoints

○ Test hundreds of different organisms using standard dose that should go on each disk
○ Plot MIC against zone size = determine where we should establish the break points

72
Q

how to do a manual muller-hinton

A

cut plate in half and lawn upper half, rotate and repeat 2 more times

rim edges

73
Q

e testing known as

A

gradient disk method

elliptical pattern

74
Q

advantage of E testing

A

we can get MIC

used in life threatening organisms

75
Q

disadvantage of E testing

A

can’t test 12 antibiotics

expensive to do

76
Q

where the drug intercepts the drug pattern-

A

MIC amount of drug can be used

77
Q

screen for beta lactamase enzyme which can break down the ring

A

cefainse disk

has nitrocefin on it

resistant means can’t use beta lactam drugs
-can occur in multiple different ways

78
Q

antibiotic on _____ disk

A

nitrocefin

groups of drugs known as sulfasporein

79
Q

only time we do the disk is when

A

the organism is capable of producing enzymes

ex. H.flu, moraxella, neisseria gonorrhea

80
Q

only test we do on H. influenza

A

beta lactamase

81
Q

moraxella

A

used to be 100% penicillin sensitive

now 98% penicillin resistant

82
Q

neisseria gonorrhea

A

some places do it with beta strep group A

-beta strep group A considered universally susceptible to penicillin

83
Q

no beta lactamase on

A

MRSA

-confirm through a different method

84
Q

majority of times beta lactam drugs inhibit

A

cell wall synthase of organism

-sites where enzymes are referred to penicillin binding proteins (PBP)

when drug binds to protein stops the cell wall synthase

85
Q

3 modes of resistance

A

-production of beta lactamase

-altered binding protein sites

-efflux

86
Q

first method used to screen for MRSA

A

Oxacillin

could see heteroresistance

87
Q

instead of using oxacillin we want to now test with

A

cefoxitin

-helps mec a be better expressed

88
Q

1st step in finding MRSA

A

resistant to cefoxitin

89
Q

once MRSA is ID as having resistance to cefoxitin and oxacillin what is done

A

PBP2a latex test

90
Q

recommended for detecting MRSA

A

1- Recommended that do not read susceptibility testing for a full 24 hours
2- Tested at 30 degrees
3-Add 2-4% sodium chloride to all plates used for MRSA testing

91
Q

resistance with cefoxitin means

A

no penicillin drugs can be used

92
Q

after testing with cefoxitin it gets sent to

A

PCR to look for Mec A gene

93
Q

1 drawback with testing with cefoxitin

A

not accurate results with spinal fluid

Spinal fluid should be sent for PCR testing

94
Q

PCR can not look for presence of

A

Mec C gene

95
Q

if organism is not a MRSA can still use

A

penicillin, methicillin, oxacillin

96
Q

screening tool for MRSA

A

chromogenic agar

-typically cefoxitin with color changing substrate
-DO NOT use colonies on this agar for susceptibility testing

97
Q

most resistance to vanco is because

A

altered binding sites
some have beta lactamase that can confer resistance to vanco

glycopeptide

98
Q

VISA

A

vancomycin intermediate S.aureus

4-8

retest before reporting out

99
Q

VRSA

A

vancomycin resistant s.aureus

> 16 ug/mL

CDC reportable

must retest before reporting out

100
Q

beta lactamase inhibitor

A

Group of drugs similar to beta lactam drug and bind to a beta lactamase enzyme to stop the action of the enzyme

bactericidal actions as well

101
Q

examples of beta lactamase inhibitor

A
  • Clavulanic acid
  • Sulbactam
  • Tazobactam
  • Avibactam
  • Ampicillin/ sulbactam
  • Ticarcillin/ clavulanic acid
  • Piperacillin/ tazobactam

DONT work with MRSA

102
Q

know if beta lactamase inhibitors work

A
  • Zone size >5mm from original zone size, the beta lactamase inhibitor will work
103
Q

inducible resistance

A

to clindamycin

gram + cocci

if organism has been exposed to erythromycin this can cause it to be resistant to clindamycin

104
Q

if resistant from onset

A

no inducible resistance

NO D test

105
Q

if resistant to erythromycin and suspectible to clindamycin MUST

A

perform D test

flatten side of D pointed toward erythro.

106
Q

what gene causes clindamycin inducible resistance

A

erm gene and NOW msr gene

place antibiotics 15-20 mm apart

D+= resistant to both

done on S.aureus or CNS

107
Q

VRE

A

vancomycin resistant enterococci

108
Q

VRE genes resistant

A
  • Van A, Van B, Van C, Van E, Van G
    ○ Most common A and B

confer via a plasmid

109
Q

van c

A

intrinsic resistance, we don’t need to worry about

○ E.gallinarium
○ E.flavescens
○ E.casseliflavens

110
Q

most common VRE seen in lab

A
  • E.faecium
  • E.faecalis
  • Don’t have to be VRE, just most common to be
111
Q

VRE requires patient to be isolated in a hospital because

A

lives in gut and if have stool on hand can be easily transferred patient to patient

112
Q

how to detect VRE?

A

vanco plates good screens

6mg of vanco on ??

if organism grows= vanco resistant

done for epidemiology purposes

113
Q

gentamicin belongs to

A

amino glycosides

114
Q

enterococci are intrinsically resistant to

A

small amounts of amino glycosides

115
Q

some enterococci can be treated with

A

combing a cell wall agent with aminoglycoside

synergistic affect

used on VRE

116
Q

Now some enterococci have plasmids that are conferring resistance

A

to high levels of amino glycosides

now synergistic relationship can’t be used

117
Q

if resistance to gentamicin

A

500 mg/mL considered high level resistance and can’t use synergistic drugs

118
Q

esbl

A

extended spectrum beta lactamase

-gram - organisms

resistance goes to cephalosporins

119
Q

first 2 noted ESBLs

A

klebsiella and e.coli

-now go into enterobacterace

120
Q

if organism is reported ESBL need to report R to

A

cephalosporins, aztreonam, and all penicillin

121
Q

different enzymes that cause ESBL

A
  • TEM-1
    • SHV-1
    • CTX-M
    • OXA
122
Q

how to determine if ESBL

A

indicator drugs

ceftazidime and cefotaxime

if resistance to any one of indicator drugs = pair with beta lactamase indicator

123
Q

if increase of at least 5 mm or more in zone size=

A

ESBL

-after confirmed need to use carbapenems

124
Q

SPICE (space) organisms INDUCED resistance to

A

Amp C gene

chromosomal beta-lactamase genes

gram -

most organisms have AMP C gene that is not expressed

125
Q

if organism has a not expressed Amp C gene and come in contact with ______ gene will be expressed

A

cephalosporins

this is due to Amp C gene

126
Q

enzymes known as _________ that confer resistance to carbapenem drugs

A

carbapenmases

-plasmid mediated enzymes

known as KPC or CRE

127
Q

KPC

A

klebsiella pneumonia carbapenmases

128
Q

CRE

A

carbapenem resistance enterobactace

now

129
Q

CRE resistant to

A
  • Penicillin’s
  • Cephalosporins
  • Aztreonam
  • Carbapenems
130
Q

if you have a CRE what drug is used to treat

A

tigecycline
polymyxin B -was off the list because neprho toxin- can’t use on kidney patient

131
Q

how to determine CRE

A

look for indicator drugs

○ Imipenem
○ Meropenem
○ Ertapenem - majority use this

132
Q

what CRE indicator drug is best

A

ertapenem

better results than other 2, express carbapenmase enzyme

133
Q

main class of beta lactamase enzyme

A

class b= metallo-B-lactamase

134
Q

metallo-B-lactamase enzyme requires

A

metal ion to hydrolyze beta lactam ring

metal used: magnesium and zinc

135
Q

New metallo beta lactamase enzyme found

A

new delhi- class B

not inhibited by beta lactamase inhibitors

inhibited by EDTA

136
Q

test for carbpenmases

A

Detect presence of class A,B,C,D but doesn’t say which class it is

do this test if ID as CRE

look for chromogenic changes

137
Q

inhibitors of cell wall synthesis

A

mode of action

don’t allow cell walls to be made by bacteria

138
Q

majority of beta lactam drugs are

A

bactericidal

oldest group of antibiotics

side chains easily manipulated

efficacy against gram - and +

139
Q

natural penicillin

A

○ Penicillin G- given shot
○ Penicillin V- oral

140
Q

semi-synthetic penicillin

A

○ Methicillin
○ Oxacillin
○ Nafcillin
○ Ampicillin
Amoxicillin

141
Q

newest generation of penicillin

A

piperacillin

142
Q

where do cephalosporins come from

A

acremonium

-contain a beta lactam ring

143
Q

what generation of cephalosporins can cross the blood brain barrier

A

3rd generation

up to 5th now

144
Q

cephalosporins better at what gram

145
Q

cephalosporins inhibitor of

A

cell wall synthesis

146
Q

monobactams only used for

A

gram - organisms

inhibitor of cell wall synthesis

includes aztreonam

147
Q

carbapenems are inhibitors of

A

cell wall synthesis

ertapenem
Meropenem
Imipenem

148
Q

carbapenems efficacy against

A

gram + and gram -

DOES not work against VRE or MRSA

149
Q

glycopeptides inhibitors of

150
Q

main glycopeptides

A

vancomycin

no beta lactam ring
nephro toxic
only gram +
IV best way to administer

151
Q

glycopeptides can’t penetrate

A

cell wall of gram - organisms

152
Q

how does vanco resistance happen

A

efflux technique

153
Q

choice of treatment for MRSA

A

vancomycin

154
Q

inhibitors of cell membrane synthesis are more toxic to

A

humans

disrupt formation of cell membrane or alter membrane and things leak out

topical agents typically

155
Q

bacitracin

A

topical agent
ID beta strep group A

156
Q

polymyxin

A

topical agent
taken off the market because extremely nephro toxic

now back

157
Q

how does inhibitors of protein synthesis work

A

binding to 30S or 50S ribosomal units

used for gram + or -

158
Q

aminoglycosides

A

inhibitor of protein synthesis

gentamycin -crosses most often
Kanamycin
Tobramycin
Amikacin
Streptomycin-secondary drug for myco

159
Q

aminoglycosides mainly used on

A

gram -

less toxic against gram +

nephro and odo toxic

160
Q

what values need to be run on people with aminoglycosides

A

bun and creatinine

monitor kidney

161
Q

can’t use on pregnant women

A

tetracycline

binds calcium and cause discoloration of fetal and adult teeth- permanent

162
Q

tetracycline new generation

A

tigecyclines

-last resort

163
Q

what kind of organisms is tetracycline best for

A

intracellular

chlamydia

164
Q

macrolides

A

inhibitor of protein synthesis

erhyomycin- if allergic to penicillin
azithromycin-strep Z pack
chloramphenicol- cause aplastic anemia

165
Q

drug of choice for haemophilus influ

A

chloramphenicol

166
Q

inhibitors of folic acid synthesis

A

sulfa drugs -work by inhibiting folic acid pathway

used for UTI
concentrate urinary tract

167
Q

nucleic acid synthesis

A

inhibit enzymes needed for DNA or RNA synthesis

fluoroquinolones
against gram - and anaerobic

riframpin- used for TB

168
Q

staph saprophyticus intrinsic resistance to

A

novobiocin

169
Q

leuconostoc intrinsic resistance to

A

vancomycin

170
Q

listeria intrinsic resistance to

A

ceftriaxone

171
Q

enterococcus gallinarium intrinsic resistance to

A

vancomycin

172
Q

proteus intrinsic resistance to

A

tetracycline

173
Q

klebsiella intrinsic resistance to

A

ampicillin, ticarcillin and carbenicillin

174
Q

serratia intrinsic resistance to

A

Ampicillin, erythromycin, and Cephalothin

175
Q

always recheck before reporting out

A

MRSA, VISA, VRSA, beta strep group A, erythromycin R and clindamycin S