occurred was recorded as the MIC value. The MIC testing was performed in duplicate. The results of the MIC-test were tested for statistical significance by the Mann–Whitney
U-test. P - 0.05 was considered significant. Ž
The pH was measured in agar plates using a pH-meter Sentron 2001, Sentron, The .
Netherlands supplied with a probe specially designed to measure pH in semisolid samples.
3. Results
All bacteria isolated were Gram-negative and all strains were rod-shaped, except LT 02. All strains were oxidase-positive, except LT 63. A total of 15 strains were
Ž .
Ž .
fermentative Table 2 and 12 strains were non-fermentative Table 3 . Mortality was 100 in the untreated tanks. No larvae were left in the untreated tanks
13 and 17 days after spawning for the first spawning group and for the second spawning
Table 6 Ž
y1
. Ž
MIC values mg ml for the four antibacterial agents with bacteria from both egg groups LT 02–LT 28:
. first egg group, LT 43–LT 70: second egg group tested on Mueller Hinton agar with 25‰ seawater
Strain Chloramphenicol
Florfenicol Fluemequine
Trimethoprimr sulfadiazine
LT 02 4
8 8
2 LT 05
0.5 1
2 1
LT 07 1
1 1
2 LT 08
2 4
8 8
LT 09 16
4 8
8 LT 17
2 2
8 4
LT 18 1
4 8
2 LT 19
2 1
8 4
LT 20 1
2 8
8 LT 21
0.13 1
1 2
LT 22 1
2 8
4 LT 23
2 2
8 4
LT 25 16
16 8
16 LT 28
2 4
8 2
LT 43 16
16 8
16 LT 44
16 16
8 8
LT 51 16
16 8
16 LT 52
2 0.5
8 2
a a
LT 53 1
0.25 LT 54
16 16
8 8
LT 58 2
0.5 8
1 LT 59
16 0.5
8 1
LT 60 0.5
1 8
2 LT 61
1 0.25
2 0.5
LT 62 16
8 2
2 LT 63
16 16
2 16
LT 70 4
0.5 8
2
a
Not measured.
group, respectively, whereas survival of the larvae in the tank with chloramphenicol was approximately 30 at time of settling. The settling took place between 21 and 28 days
after spawning. In general, the numbers of CFU were lower for larvae treated with chloramphenicol
Ž .
than for untreated larvae Fig. 1 . A larger difference in CFU between treated and untreated larvae was found on TCBS agar than on MBA and TSA media. The difference
in the number of CFU between treated and untreated cultures was larger in the second Ž
. egg group than in the first Fig. 1 . In the first egg group, the ratio of CFU between
treated and untreated larvae on TCBS agar was 41 on day 13 after fertilisation. The corresponding ratio was 413 for the second egg group. The same pattern was found for
TSA agar where the ratios were estimated to be 2 for the first egg group and 23 for the second. For MBA dishes, the ratios were 3 and 5 for the first and second egg group,
respectively.
Differences in MIC values were found between strains grown on Mueller Hinton agar Ž
. dissolved in 2 NaCl and Mueller Hinton agar dissolved in 25‰ seawater Table 4 . In
Ž .
Ž .
the cases of fluemequine P s 0.000 and for trimethoprimrsulfadiazine P s 0.013 , the MIC values were significantly higher for both egg groups with 25‰ seawater than
Ž .
Ž .
with 2 NaCl. For chloramphenicol P s 0.16 and florfenicol P s 0.49 , the differ- ences between 2 NaCl and 25‰ seawater were not significant. However, a signifi-
Ž .
cantly higher MIC value was found for chloramphenicol P s 0.021
using 25‰ seawater compared to 2 NaCl in the second egg group.
The pH was measured to be 7.4 in agar plates made with 2 NaCl and 7.2 in agar plates made with 25‰ seawater. The MIC values for each of the individual strains are
listed in Tables 5 and 6.
4. Discussion
