2.8. Fungicidal versus fungistatic activity
To determine if exposure to isothiazolinone temporarily or
permanently inhibited spore germination, spores were preincubated
with 50 ppm isothiazolinone for 24 h at 37 C, washed
twice with DI water as described in Section 2.7 and suspended in
RPMI before testing for metabolic activity in the XTT assay.
Following washing, spores were placed on 2% malt extract agar in
a Petri dish and incubated at 27 C for 2 weeks.
3. Results
Complete inhibition of mould growth using two standardized
methods was compared with complete inhibition of metabolic
activity in the XTT assay using isothiazolinone as the model mould
inhibitor. Fig. 1 shows the average of 10 absorbance readings and
standard deviations for mould spores from three test fungi exposed
to two-fold dilutions of isothiazolinone. Absorbance at 490 nm is
indicative of metabolic activity (i.e. mould spore germination). For
all three test fungi, complete inhibition of metabolic activity
occurred at dilutions containing 50 ppm isothiazolinone. Lower
dilutions of isothiazolinone demonstrated decreasing levels of
inhibition. Standard deviation in quantitative results for the XTT
assay increased at concentrations of isothiazolinone that did not
completely inhibit spore germination.
Comparative visual ratings for two standardized laboratory
mould tests using vaccum-treated southern pine specimens are
summarized in Table 1. Even though ASTM D4445 is a 4 week test
and AWPA E24 is an 8 week test, incubation of test specimens was
extended to 12 weeks to evaluate sustained inhibition. Average
ratings and standard deviation for the four-week duration of this
test are shown in bold text in Table 1. Ratings based on visual
evaluations of mould growth can have a high standard deviation
underscoring the importance of replicate specimens. Specimens
treated with 50 ppm isothiazolinone substantially inhibited
mould growth in the D4445 test over the 12-week duration of the
test.
In the AWPA E24 test, specimens treated with 100 ppm isothiazolinone
substantially inhibited mould growth for the 8-week
duration of the test (bold values), but not for 12 weeks. Standard
deviation for each treatment group was lower than that of the
2.8. Fungicidal versus fungistatic activity
To determine if exposure to isothiazolinone temporarily or
permanently inhibited spore germination, spores were preincubated
with 50 ppm isothiazolinone for 24 h at 37 C, washed
twice with DI water as described in Section 2.7 and suspended in
RPMI before testing for metabolic activity in the XTT assay.
Following washing, spores were placed on 2% malt extract agar in
a Petri dish and incubated at 27 C for 2 weeks.
3. Results
Complete inhibition of mould growth using two standardized
methods was compared with complete inhibition of metabolic
activity in the XTT assay using isothiazolinone as the model mould
inhibitor. Fig. 1 shows the average of 10 absorbance readings and
standard deviations for mould spores from three test fungi exposed
to two-fold dilutions of isothiazolinone. Absorbance at 490 nm is
indicative of metabolic activity (i.e. mould spore germination). For
all three test fungi, complete inhibition of metabolic activity
occurred at dilutions containing 50 ppm isothiazolinone. Lower
dilutions of isothiazolinone demonstrated decreasing levels of
inhibition. Standard deviation in quantitative results for the XTT
assay increased at concentrations of isothiazolinone that did not
completely inhibit spore germination.
Comparative visual ratings for two standardized laboratory
mould tests using vaccum-treated southern pine specimens are
summarized in Table 1. Even though ASTM D4445 is a 4 week test
and AWPA E24 is an 8 week test, incubation of test specimens was
extended to 12 weeks to evaluate sustained inhibition. Average
ratings and standard deviation for the four-week duration of this
test are shown in bold text in Table 1. Ratings based on visual
evaluations of mould growth can have a high standard deviation
underscoring the importance of replicate specimens. Specimens
treated with 50 ppm isothiazolinone substantially inhibited
mould growth in the D4445 test over the 12-week duration of the
test.
In the AWPA E24 test, specimens treated with 100 ppm isothiazolinone
substantially inhibited mould growth for the 8-week
duration of the test (bold values), but not for 12 weeks. Standard
deviation for each treatment group was lower than that of the
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