Antibiotic Susceptibility Testing Flashcards
1
Q
meant to kill off any invading organism
A
bactericidal
-used in immunocompromised patients
-life threatening
2
Q
prevents further growth of the organism
A
bacteriostatic
-healthy people
-non life threatening diseases
3
Q
lower dosage
A
bacteriostatic
4
Q
higher dosage
A
bactericidal
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
6
Q
narrow spectrum antibiotics
A
limited to target range
best if pathogen known
7
Q
synergy means
A
2 drugs when given together work better together than on their own
8
Q
antagonism means
A
if I give you one drug it will counteract another drug
9
Q
is there an ideal antibiotic?
A
no there is not an antibiotic that fits all
look at cost
site of infection
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
11
Q
Average time from hitting market to resistance
A
6 months
12
Q
most resistance organisms
A
e.coli
superbug- show multi resistance
13
Q
MDR= multiple drug resistance
A
organism is resistant to 1 agent in 3 or more antibiotic classes
14
Q
XDR= extra drug resistant
A
resistant in one agent in all but 2 or fewer antibiotic classes
15
Q
PAN= pan drug resistant
A
resistant to everything
- some e.coli and pseudomonas
-treat with cocktail of drugs
16
Q
MRSA
A
methicillin resistant staph aureus
17
Q
VRE
A
vancomycin resistant enterococci
18
Q
strep pneumo is resistant to
A
penicillin
19
Q
why so much resistance?
A
antibiotics in agricultural
not finishing antibiotics
laundry detergent, hand sanitizer
20
Q
what is intrinsic resistance?
A
bacteria is naturally resistant
this is a way we ID some organisms
21
Q
how does acquired resistance occur?
A
target site modification
plasmids
efflux
enzymes
jumping genes
22
Q
target site modification
A
target certain site of bacteria and the bacteria changes the site
23
Q
plasmids
A
extra chromosomal piece of DNA
-resistance gene is found here
-easily transferable from one bacteria to another
24
Q
efflux
A
antibiotic goes in and organism spits it out
25
jumping genes
transpanozone????
jumps from pieces of DNA to another
26
things to think about with antibiotic selection
resistance, cost, patient population, dosages, location
27
primary drug
first line that has been manufactured in the category
§ From nature, ex. Penicillin
§ Cheaper
§ Less toxic to human
Good treating
28
secondary drug
chemical modifications from primary drugs
-due to resistance of primary drug
29
tertiary drug
alter side chain
30
farther down the line in modifcations of drugs=
higher cost of new drug
more side effects seen in human
treat more poly microbal infections
31
advantage of more modifications to drugs
treat more resistant organisms we are now seeing
32
standard for inoculum
Mc Farland Standards
-sets turbidity standards that allow us to determine the amount of organism present in a broth
-we buy
33
how to create turbidity
barium chloride
sulfuric acid
-now it is given in latex particles
34
higher you go with Mc Farland standards =
more turbidity = more organisms in your broth if matching turbidity standard
35
most common amount of standard
0.5 Mc Farland Standard = 1.5 x 10 ^8 CFU /mL
36
what is MIC
Concentration of antibiotic in mg/mL that prevents the in vitro growth of bacteria
minimum
37
how is MIC done
○ 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
38
MBC
Minimum bactericidal concentration of drug
39
info about MBC
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
40
kirby bauer principle
zone of inhibition is created as a result of antibiotics diffusing away from the disk
read in millimeters
41
why can't let bacteria sit more than 15 minutes before plating on Mueller Hinton plate
bacteria will double
-almost immediately antibiotic will start working so can't move disk
42
method of detection set by
CLSI- clinical laboratory standards institute
43
Muller-Hinton measurements
150 millimeters across
depth 4 millimeters
44
if depth on muller hinton is greater
we will get false resistance
45
if depth is less than normal on a muller hinton plate
false susceptibility
46
how many disks placed on muller hinton
12 disks
24 mm apart
47
pH on muller hinton
7.2-7.3 at RT
48
too low pH on muller hinton=
false resistant with amino glycosides
49
too high pH on muller hinton plate
false susceptibility with amino glycosides
50
what is muller hinton grown in
ambient air (O2) not CO2 but depends on organism
CO2 will decrease pH
51
decrease temp when growing muller hinton
false susceptibility
bigger zone sites
52
only time a muller hinton plate can grow at 35 degrees
MRSA
can be incubated at 30, Mec A expressed better at 30 and full 24 hrs
53
concentrations of what are importatnt in Muller-Honton when testing amino glycosides
calcium, magnesium and zinc
54
when are amino glycoside used
for pseudomonas
55
if concentration is increased =
false resistance
56
if concentration decreased=
false susceptibility
57
drug concentrations -each disk of antibiotics concentration set by
FDA
58
how to store disks
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
59
before reporting any results we need to do
QC on disks and representative organisms
organisms are ATCC
60
what organisms used for QC
○ Always use an E.coli, S. aureus, and pseudomonas
E.coli- gram- , s. aureus, gram +, pseudomonas, non fermenter
61
when first starting antibiotic panel have to do QC
everyday for a month
- If during the 1 month panel and have less than 3 antibiotics outside accepted readings then can do QC weekly
62
how read zones on regular muller plate
read from back to plate
edge to edge
read above dark surface from back site with reflective light
63
how to read muller hinton with added choc or blood
read from top side with top off
64
if there is more than 1 organism present on a plate
plate to a purity plate
proteus ignore swarming and read outer edges
sulfa- read best defined edge
65
if 2 or 3 colonies in the zone
can't report out
-purity plate
-hetero resistance -seen in MRSA
66
what is hetero resistance
§ 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
67
SIR method of reporting based on
CLSI
68
sensitive
sensitive to standard dose of drug that is used for the antibiotic
69
intermediate
some things might cause drug to be resistant in vivo
Not first choice of drugs
70
resistant
don't use this drug
71
how to determine break points?
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
how to do a manual muller-hinton
cut plate in half and lawn upper half, rotate and repeat 2 more times
rim edges
73
e testing known as
gradient disk method
elliptical pattern
74
advantage of E testing
we can get MIC
used in life threatening organisms
75
disadvantage of E testing
can't test 12 antibiotics
expensive to do
76
where the drug intercepts the drug pattern-
MIC amount of drug can be used
77
screen for beta lactamase enzyme which can break down the ring
cefainse disk
has nitrocefin on it
resistant means can't use beta lactam drugs
-can occur in multiple different ways
78
antibiotic on _____ disk
nitrocefin
groups of drugs known as sulfasporein
79
only time we do the disk is when
the organism is capable of producing enzymes
ex. H.flu, moraxella, neisseria gonorrhea
80
only test we do on H. influenza
beta lactamase
81
moraxella
used to be 100% penicillin sensitive
now 98% penicillin resistant
82
neisseria gonorrhea
some places do it with beta strep group A
-beta strep group A considered universally susceptible to penicillin
83
no beta lactamase on
MRSA
-confirm through a different method
84
majority of times beta lactam drugs inhibit
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
3 modes of resistance
-production of beta lactamase
-altered binding protein sites
-efflux
86
first method used to screen for MRSA
Oxacillin
could see heteroresistance
87
instead of using oxacillin we want to now test with
cefoxitin
-helps mec a be better expressed
88
1st step in finding MRSA
resistant to cefoxitin
89
once MRSA is ID as having resistance to cefoxitin and oxacillin what is done
PBP2a latex test
90
recommended for detecting MRSA
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
resistance with cefoxitin means
no penicillin drugs can be used
92
after testing with cefoxitin it gets sent to
PCR to look for Mec A gene
93
1 drawback with testing with cefoxitin
not accurate results with spinal fluid
Spinal fluid should be sent for PCR testing
94
PCR can not look for presence of
Mec C gene
95
if organism is not a MRSA can still use
penicillin, methicillin, oxacillin
96
screening tool for MRSA
chromogenic agar
-typically cefoxitin with color changing substrate
-DO NOT use colonies on this agar for susceptibility testing
97
most resistance to vanco is because
altered binding sites
some have beta lactamase that can confer resistance to vanco
glycopeptide
98
VISA
vancomycin intermediate S.aureus
4-8
retest before reporting out
99
VRSA
vancomycin resistant s.aureus
>16 ug/mL
CDC reportable
must retest before reporting out
100
beta lactamase inhibitor
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
examples of beta lactamase inhibitor
* Clavulanic acid
* Sulbactam
* Tazobactam
* Avibactam
* Ampicillin/ sulbactam
* Ticarcillin/ clavulanic acid
* Piperacillin/ tazobactam
DONT work with MRSA
102
know if beta lactamase inhibitors work
* Zone size >5mm from original zone size, the beta lactamase inhibitor will work
103
inducible resistance
to clindamycin
gram + cocci
if organism has been exposed to erythromycin this can cause it to be resistant to clindamycin
104
if resistant from onset
no inducible resistance
NO D test
105
if resistant to erythromycin and suspectible to clindamycin MUST
perform D test
flatten side of D pointed toward erythro.
106
what gene causes clindamycin inducible resistance
erm gene and NOW msr gene
place antibiotics 15-20 mm apart
D+= resistant to both
done on S.aureus or CNS
107
VRE
vancomycin resistant enterococci
108
VRE genes resistant
* Van A, Van B, Van C, Van E, Van G
○ Most common A and B
confer via a plasmid
109
van c
intrinsic resistance, we don't need to worry about
○ E.gallinarium
○ E.flavescens
○ E.casseliflavens
110
most common VRE seen in lab
* E.faecium
* E.faecalis
* Don't have to be VRE, just most common to be
111
VRE requires patient to be isolated in a hospital because
lives in gut and if have stool on hand can be easily transferred patient to patient
112
how to detect VRE?
vanco plates good screens
6mg of vanco on ??
if organism grows= vanco resistant
done for epidemiology purposes
113
gentamicin belongs to
amino glycosides
114
enterococci are intrinsically resistant to
small amounts of amino glycosides
115
some enterococci can be treated with
combing a cell wall agent with aminoglycoside
synergistic affect
used on VRE
116
Now some enterococci have plasmids that are conferring resistance
to high levels of amino glycosides
now synergistic relationship can't be used
117
if resistance to gentamicin
500 mg/mL considered high level resistance and can't use synergistic drugs
118
esbl
extended spectrum beta lactamase
-gram - organisms
resistance goes to cephalosporins
119
first 2 noted ESBLs
klebsiella and e.coli
-now go into enterobacterace
120
if organism is reported ESBL need to report R to
cephalosporins, aztreonam, and all penicillin
121
different enzymes that cause ESBL
* TEM-1
* SHV-1
* CTX-M
* OXA
122
how to determine if ESBL
indicator drugs
ceftazidime and cefotaxime
if resistance to any one of indicator drugs = pair with beta lactamase indicator
123
if increase of at least 5 mm or more in zone size=
ESBL
-after confirmed need to use carbapenems
124
SPICE (space) organisms INDUCED resistance to
Amp C gene
chromosomal beta-lactamase genes
gram -
most organisms have AMP C gene that is not expressed
125
if organism has a not expressed Amp C gene and come in contact with ______ gene will be expressed
cephalosporins
this is due to Amp C gene
126
enzymes known as _________ that confer resistance to carbapenem drugs
carbapenmases
-plasmid mediated enzymes
known as KPC or CRE
127
KPC
klebsiella pneumonia carbapenmases
128
CRE
carbapenem resistance enterobactace
now
129
CRE resistant to
* Penicillin's
* Cephalosporins
* Aztreonam
* Carbapenems
130
if you have a CRE what drug is used to treat
tigecycline
polymyxin B -was off the list because neprho toxin- can't use on kidney patient
131
how to determine CRE
look for indicator drugs
○ Imipenem
○ Meropenem
○ Ertapenem - majority use this
132
what CRE indicator drug is best
ertapenem
better results than other 2, express carbapenmase enzyme
133
main class of beta lactamase enzyme
class b= metallo-B-lactamase
134
metallo-B-lactamase enzyme requires
metal ion to hydrolyze beta lactam ring
metal used: magnesium and zinc
135
New metallo beta lactamase enzyme found
new delhi- class B
not inhibited by beta lactamase inhibitors
inhibited by EDTA
136
test for carbpenmases
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
inhibitors of cell wall synthesis
mode of action
don't allow cell walls to be made by bacteria
138
majority of beta lactam drugs are
bactericidal
oldest group of antibiotics
side chains easily manipulated
efficacy against gram - and +
139
natural penicillin
○ Penicillin G- given shot
○ Penicillin V- oral
140
semi-synthetic penicillin
○ Methicillin
○ Oxacillin
○ Nafcillin
○ Ampicillin
Amoxicillin
141
newest generation of penicillin
piperacillin
142
where do cephalosporins come from
acremonium
-contain a beta lactam ring
143
what generation of cephalosporins can cross the blood brain barrier
3rd generation
up to 5th now
144
cephalosporins better at what gram
positive
145
cephalosporins inhibitor of
cell wall synthesis
146
monobactams only used for
gram - organisms
inhibitor of cell wall synthesis
includes aztreonam
147
carbapenems are inhibitors of
cell wall synthesis
ertapenem
Meropenem
Imipenem
148
carbapenems efficacy against
gram + and gram -
DOES not work against VRE or MRSA
149
glycopeptides inhibitors of
cell wall
150
main glycopeptides
vancomycin
no beta lactam ring
nephro toxic
only gram +
IV best way to administer
151
glycopeptides can't penetrate
cell wall of gram - organisms
152
how does vanco resistance happen
efflux technique
153
choice of treatment for MRSA
vancomycin
154
inhibitors of cell membrane synthesis are more toxic to
humans
disrupt formation of cell membrane or alter membrane and things leak out
topical agents typically
155
bacitracin
topical agent
ID beta strep group A
156
polymyxin
topical agent
taken off the market because extremely nephro toxic
now back
157
how does inhibitors of protein synthesis work
binding to 30S or 50S ribosomal units
used for gram + or -
158
aminoglycosides
inhibitor of protein synthesis
gentamycin -crosses most often
Kanamycin
Tobramycin
Amikacin
Streptomycin-secondary drug for myco
159
aminoglycosides mainly used on
gram -
less toxic against gram +
nephro and odo toxic
160
what values need to be run on people with aminoglycosides
bun and creatinine
monitor kidney
161
can't use on pregnant women
tetracycline
binds calcium and cause discoloration of fetal and adult teeth- permanent
162
tetracycline new generation
tigecyclines
-last resort
163
what kind of organisms is tetracycline best for
intracellular
chlamydia
164
macrolides
inhibitor of protein synthesis
erhyomycin- if allergic to penicillin
azithromycin-strep Z pack
chloramphenicol- cause aplastic anemia
165
drug of choice for haemophilus influ
chloramphenicol
166
inhibitors of folic acid synthesis
sulfa drugs -work by inhibiting folic acid pathway
used for UTI
concentrate urinary tract
167
nucleic acid synthesis
inhibit enzymes needed for DNA or RNA synthesis
fluoroquinolones
against gram - and anaerobic
riframpin- used for TB
168
staph saprophyticus intrinsic resistance to
novobiocin
169
leuconostoc intrinsic resistance to
vancomycin
170
listeria intrinsic resistance to
ceftriaxone
171
enterococcus gallinarium intrinsic resistance to
vancomycin
172
proteus intrinsic resistance to
tetracycline
173
klebsiella intrinsic resistance to
ampicillin, ticarcillin and carbenicillin
174
serratia intrinsic resistance to
Ampicillin, erythromycin, and Cephalothin
175
always recheck before reporting out
MRSA, VISA, VRSA, beta strep group A, erythromycin R and clindamycin S
