International Journal of Aquaculture, 2017, Vol.7, No.18, 122-127
124
Table 3 Detection of antimicrobial activities (diameter of inhibition zone, mm) of aqueous, methanolic and ethanolic extracts of
soursop leaves
Pathogen
Soursop leaves
Control
Aqueous
Methanol
Ethanol
Chloramphenicol
(10 mg/ml)
Chloramphenicol
(20 mg/ml)
Distilled water
Bacillus subtilis
18±0.03
17±0.03
12±0.03
15±0.01
18±0.04
-
Staphylococcus aureus
15±0.01
25±0.01
21±0.02
13±0.01
20±0.01
-
Streptococcus iniae
09±0.02
17±0.02
15±0.03
21±0.02
25±0.02
-
Aeromonas hydrophila
20±0.03
25±0.03
11±0.03
-
-
-
Aspergillus flavus
03±0.01
06±0.01
02±0.01
ND
ND
-
Note: - = No inhibition; ND = Not determined
Table 4 Minimum inhibitory concentration of aqueous, methanolic and ethanolic extracts of soursop leaves
Minimum inhibitory concentration in µg/ml
Method of extraction
Isolates
2000 1000 500 250 125 62.50 31.25 15.63
Aqueous extract
Bacillus subtilis
-
-
-
+ + +
+
+
Staphylococcus aureus
-
-
-
+ + +
+
+
Streptococcus iniae
-
-
-
+ + +
+
+
Aeromonas hydrophila
-
+
+ + + +
+
+
Control
-
-
-
-
-
-
-
-
Ethanolic extract
Bacillus subtilis
-
-
-
+ + +
+
+
Staphylococcus aureus
-
-
-
-
+ +
+
+
Streptococcus iniae
-
-
-
+ + +
+
+
Aeromonas hydrophila
-
+
+ + + +
+
+
Control
-
-
-
-
-
-
-
-
Methanolic extract
Bacillus subtilis
-
-
+ + + +
+
+
Staphylococcus aureus
-
-
+ + + +
+
+
Streptococcus iniae
-
+
+ + + +
+
+
Aeromonas hydrophila
-
-
+ + + +
+
+
Control
-
-
-
-
-
-
-
-
Note: + = indicating growth showed by turbidity of the broth; - = no growth
3 Discussion
The phytochemical screening of the present study revealed the presence of tannins, flavonoids, glucosinolates,
phenol, amino acid and polysterols while saponins was not detected which agreed with the report of Wisdom et al.
(2014) and Anganna and Nursyam (2016) who observed the presence of these metabolites.
The result of this study revealed that microbial loads in the liver, intestine, skin and gills of
C. gariepinus
vary,
with the gills having the highest values of enterobacteriacea and total viable counts. This study were in agreement
with the report of Shalaby et al. (2006) that bacterial loads is greater in the skin and gills than in any part of the
fish, as these parts are the ones constantly exposed to infections.
Also, the result of the present study showed that aqueous, ethanolic and methanolic extracts of soursop leaves had
antimicrobial properties and inhibited the growth of organisms tested. This observation was in accord with the
report of Anganna and Nursyam (2016), Oyedeji et al. (2015) and Haro et al. (2014). The methanolic extracts of
soursop leaves had significantly higher (P<0.05) inhibition zone of diameter compared to aqueous and ethanolic
extracts. Utilization of different types of solvents (aqueous, ethanol and methanol) gives effects to the inhibition
of microbial growth resulting in
B. subtilis
,
S. aureus
,
S. iniae
,
A. hydrophila
and
A. flavus
. The inhibitory effects
of aqueous, ethanolic and methanolic extracts of soursop leaves can be as a result of the active components of
soursop leaves able to enter the cell wall, cell membranes and inhibits cell metabolism. Soursop leaves as
antimicrobial agents for fish culture can be an essentially important in reducing the economic losses for fish
farmer as a result of the world threatens of infectious diseases.
