tb chemotherapy & susc

Question 1

First line

Answer 1

Streptomycin (STR)
Isoniazid (INH)
Rifampin (RIF)
Ethambutol (EMB)
Pyrazinamide (PZA)
initial treatment phase recommends treatment with 4 or 5 drugs

Question 2

monoresistant

Answer 2

any one TB drug

Question 3

poly-resistant

Answer 3

any two drugs

but not both Rifampin, and Isoniazid

Question 4

MDR TB

Answer 4

at least isoniazid and rifampin

Question 5

XDR TB

Answer 5

isoniazid and rifampin

and any flouroquinolone and at least 1 of 3 injectable second-line drugs (kanamycin, capreomycin, amikacin)

Question 6

Chemotherapy

Answer 6

follow-up for patients with positive smears is done weekly until two negative smears are obtained
follow up for culture conversion is done on a monthly basis until two sputum cultures are neg

Question 7

INH

Answer 7

inhibits mycolic acid synthase
blocks action of fatty acid synthase
used for prophylaxis
not used for high prevalence of INH-resistance
certain parts of OC INH resistance as high as 21%

Question 8

Rifampin

Answer 8

complexes with RNA polymerase
semi-synthetic
good absorption kills intracellular orgaisms
orange eyes

Question 9

Ethambutol

Answer 9

inhibits mycolic acid synthase
INH-resistant MTB
loss of visual acuity

Question 10

Pyrazinamide

Answer 10

exact target unknown (energy metabolism plasma membrane)
synthetic drug
short course
best for actively multiplying organisms
used during initial phase

Question 11

Drug-resistant TB

Answer 11

treatest with 4 drugs for 6 months

MDR- treatment continued until chest x-ray clears- followed by 12 months additional treatment

Question 12

susceptibility testing

Answer 12

performed on first MTB isolate

if still culture + repeated 2 months

Question 13

followup treatment

Answer 13

smears- weekly until 2 negative smears
sputum cultures monitored mothly until negative
patient monitored monthly for anorexia, nausea
monthly chemistry panel
INH causes mild abnormal liver function

Question 14

DOT

Answer 14

direct observed therapy
ensures patient adherence
all OC cases

Question 15

critical concentration

Answer 15

amount of drug that inhibits growth of most of the cells (95%)

Question 16

Absolute Concentration

Answer 16

standard inoculum is placed on control quadrant and quadrants with graded concentration of the drug
LOWEST CONCENTRATION THAT INHIBITS GROWTH

Question 17

Resistance Ration Method

Answer 17

compares resistance of unknown MTB to a known standard strain
two-fold dilution of drugs
R = MIC Test Strain/ MIC Std. Strain
MIC- lowest conc of drug that prevents visible growth

Question 18

Agar Proportion Method

Answer 18

most commonly used
calculate precise quantitation of the proportion of mutants resistant to a given drug
when 1% of population becomes resistant to critical concentration that drug is not useful for treatment

Question 19

Agar proportion direct

Answer 19

more representative of actual bacterial population
but subject to more variability (contamination)
results only vaiid if MTBC is identified

Question 20

Agar proportion method media

Answer 20

7H10, 7H11 with 4 quadrant
one is drug free
other three have different drugs or different concentrations
0.1 ml seeded onto each quadrant

Question 21

susceptibility interpretation

Answer 21

>500 4+
200-500 3+
100-200 2+
50-100 1+
<50 record number of colonies
atleast one of the control quadratns of the set of should have minimum of 50 colonies

Question 22

BACTEC susceptibility

Answer 22

same principle as conventiaonl agar

growth monitored radiometrically

Question 23

BACTEC SUSC PROCEDURE

Answer 23

inoculum in control is diluted 1:100
rate of growth in control vial is compared to drug
growth index is read daily and delta gi is calculated
final reading when control vial reach GI of 30 or more

Question 24

PZA susceptibility

Answer 24

requires media to be slightly acidic
drug active only at lower ph
modified 7H12 pH = 6.0
gi must reach 200
11% resistant

Question 25

bactec sucs adv.

Answer 25

ideal condition for mtb growth, rapid testsing

automated, direct and indirect

Question 26

bactec susc disadv,

Answer 26

contamination, mixed cultures can yield false resistance

Question 27

MGIT susceptibility

Answer 27

non-radiometic

Question 28

E-test

Answer 28

epsilometer test
MIC- point at which ellipse meets the strip gives you MIC
0.5 McF suspension plated onto 7H10 or 7H11

Question 29

MRD strain in presence of drugs

Answer 29

THRIVE
growth on control quadrant may notoped colonies, but drug quadrant will have profuse growth
vials with drugs may have gi >999

Question 30

Second LIne Drug Susceptibility Testing

Answer 30

considered if
patient has had prior therapy
contact of paitents with MDR-TB
from a country with endemic MDR-TB
isolate resistant to rifampin or other first line-drugs
positive cultue 3 months or more after therapy

Question 31

Luciferase Indirect Quantativie TEst

Answer 31

based on viability of MTB after exposure to a particular drug
vial mycobacteria are vulnerable to infection with mycobacteriophages with firefly luciferase gene
infected cells synthesize & translate mRNA to make luciferase
addition of substrate makes the surviving drug-resistant cells glow

Question 32

Flow cytometry

Answer 32

viable MTB hydrolyze fluorescein diacetate (FDA) and detect fluorescent mycobacteria
does not require multiplication

Question 33

Atypical susceptibility

Answer 33

M. Kansasii, M. szulgai, M. marinum
normally susceptible to rifampin and ehtambutol
M. szulgai & M. kansasii- conventional method m. marinum - Mueller hinton agar enriched with OADC

Question 34

Atypical susceptibility of rapid growers

Answer 34

M. fortuiutm, M. chelonae, M. abscessus are resistant to primary drugs
normally susceptible to aminoglycosides
can cause traumatic infections & have been implicated in infections after surgical procedures
E-test

Question 35

M. fortuitum & M. chelonae resistance

Answer 35

m. chelonae stubborn or resistant to most, m. fortuitum is generally susceptible

Question 36

M. avium complex resistance

Answer 36

resistant to most drugs used for TB

major pathogen in HIV patients, but finding a drug to treat MAC is difficult (considerable mutation)