ISO 16240:2005 水質 — 水と廃水の遺伝子毒性の決定 — サルモネラ/ミクロソーム試験（エームス試験） | ページ 2

3.1

number of revertants

number of mutants

number of visible mutant colonies per plate at the termination of the test

3.2

dilution level

D

denominator of the dilution coefficient (using the numerator 1) of a mixture of water or wastewater with dilution water (3.16) as integral number

Note 1 to entry: For undiluted water or wastewater, the dilution coefficient is by definition 1:1. The corresponding and smallest possible D value is 1.

3.3

dose-response relationship

reduction of the number of visible mutant colonies per plate with increasing D level

3.4

D_min value

smallest value of D at which, under the conditions of this International Standard, no positive increase in the number of visible mutant colonies per plate is detected

Note 1 to entry: In the case of more than one D_min value (a maximum of four are possible), the highest D value is decisive.

3.5

stock culture

frozen culture for the preservation of the characteristics (e.g. genotype) of Salmonella typhimurium TA 100 and TA 98

3.6

inoculum

part of a thawed stock culture used to inoculate culture medium

3.7

culture medium

aqueous solution of nutrients which are required for the cultivation of the bacteria

3.8

overnight culture

mixture of inoculum and culture medium, incubated for about 18 h at 37 °C ± 1 °C and gentle agitation (e.g. shaken at 100 r/min to 150 r/min)

3.9

plate

solidified mixture of water, agar and other possible constituents (e.g. inorganic salts) in Petri dishes

3.10

softagar

mixture of agar, sodium chloride, histidine, biotin and water

Note 1 to entry: Minimal softagar contains only traces of histidine and is used for the determination of mutants. Maximal softagar contains histidine in excess and is used for the determination of titres.

3.11

S9 fraction

9 000 g supernatant of a tissue homogenate in 0,15 mol/l KCl, obtained from livers of male rats (200 g to 300 g) pretreated with an appropriate substance or substance combination for enzyme induction

3.12

cofactor solution

aqueous solution of chemicals needed for the activity of the enzymes in the S9 fraction

Note 1 to entry: Examples of chemicals needed are NADP, glucose-6-phosphate and inorganic salts.

3.13

S9 mix

mixture of S9 fraction and cofactor solution

3.14

titre determination

method for the determination of the number of bacteria (colony-forming units) in an overnight culture and for the determination of possible bacteriotoxic effects of the test sample

3.15

test sample

sample to be used as test item after all preparative steps (e.g. sterile filtration) have been carried out

3.16

dilution water

sterile water of a conductivity of ≤ 5 µS/cm used for the stepwise dilution of the test sample or used as negative control

3.17

negative control

dilution water (3.16) without test sample

3.18

positive control

known mutagen used to verify the sensitivity of the method or the activity of the S9 mix

Note 1 to entry: The positive controls are dissolved in DMSO prior to use.

3.19

test mixture

mixture of test sample [pure or diluted with dilution water (3.16) ], negative or positive control, bacterial suspension, softagar and S9 mix or buffer

3.20

induction rate

I

difference between the mean value of mutant colonies counted on the plates treated with a dose of the test sample or with a positive control and the mean value of the corresponding plates treated with the negative control using the same strain under identical activation conditions

3.21

background growth

bacterial lawn formed by microcolonies of non-mutated bacteria on a plate with minimal softagar due to the traces of histidine contained in this softagar