# In Vitro Antibacterialential Activity of Marine Microalgae Extract against _Vibrio harveyi_
## 3 Results
### Co-Culture Antibacterial Assay  
In the co-culture assay, three (3) microalgae species--co-culture assays of _N. oceanica_ (Figure 1a), _T. weissflogii_ (Figure 1b), and _Isochrysis_ sp. (Figure 1d)--demonstrated minimal antibacterial activity by preventing significant (_p_ < 0.05) proliferation of _V. harveyi_ at different time intervals when compared to the control group culture of _V. harveyi_ with no microalgae.  
In the co-culture _V. harveyi_ with _N. oceanica_ (Figure 1a), the concentration of _V. harveyi_ was significantly lower (_p_ < 0.05) at 24 to 48 h incubation as compared to control. However, there was no significant difference (_p_ > 0.05) in _V. harveyi_ concentration at 72, 96, and 120 h incubation.  
For the co-culture _V. harveyi_ with _T. weissflogii_ (Figure 1b), the concentration of _V. harveyi_ was significantly lower (_p_ < 0.05) at 24, 48, and 72 h incubation, followed by no significant difference (_p_ > 0.05) at 96 and 120 h incubation as compared to control.  
Meanwhile, the co-culture _V. harveyi_ with _Isochrysis_ sp in Figure 1d demonstrated a significantly lower (_p_ < 0.05) concentration of _V. harveyi_ at 72, 96, and 120 h, as compared to the control. In comparison to the control, co-culture _V. harveyi_ with _C. gracilis_ (Figure 1c) exhibited no significant difference (_p_ > 0.05) in _V. harveyi_ concentration. In fact, no bibliographic data on the antibacterial activity of _C. gracilis_ described in the prior study is available. The growth of _V. harveyi_ strains increased steadily with time up to 48 h until reaching a plateaued condition and subsequently decreased insignificantly (_p_ > 0.05) at the end of the experiment in the control group culture with no microalgae added.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{3}{*}{**Concentration**} & \multirow{3}{*}{**Extractant**} & \multicolumn{3}{c}{**Diameter of the Inhibition Zone (D) in mm by Marine Microalgae Extract (10\({}^{6}\) Cell/mL)**} \\  & & & \multicolumn{3}{c}{**and Control (Extractant) after 24 h Incubation with _V. harveyi_**} \\ \cline{3-6}  & & \multirow{2}{*}{_N. oceanica_} & _T. weissflogii_ & _C. gracilis_ & _Isochrysis_ sp. &
\begin{tabular}{c} _Control_ \\ _(Extractant)_ \\ \end{tabular} \\ \hline \multirow{3}{*}{\(10^{5}\) CFU/mL} & Ethanol & ++ & ++ & ++ & ++ & – \\  & Methanol & ++ & ++ & ++ & ++ & – \\  & Saline water & ++ & + & ++ & ++ & – \\  & DMSO & ++ & + & + & + & – \\ \hline \multirow{3}{*}{\(10^{6}\) CFU/mL} & Ethanol & +++ & ++ & ++ & ++ & – \\  & Methanol & ++ & ++ & + & ++ & – \\  & Saline water & ++ & + & + & ++ & – \\  & DMSO & + & + & + & + & – \\ \hline \multirow{3}{*}{\(10^{7}\) CFU/mL} & Ethanol & +++ & ++ & + & ++ & – \\  & Methanol & + & + & + & + & – \\  & Saline water & + & + & + & + & – \\  & DMSO & + & + & + & + & – \\ \hline \hline \end{tabular} Note: (–): No activity, (+): D < 6 mm, (++): 6 < D < 8.5 mm, (++): D > 8.5 mm. D: Diameter of the inhibition zone in milimeters.  
\end{table}
Table 1: Antibacterial susceptibility test of the microbial extract against _V. harveyi_.  
Figure 1: _Cont._  
Figure 1: (**a**) _V. harveyi_ concentration was significantly lower (\(p<0.05\)) at 24–48 h incubation in co-culture assay with _N. oceanica_ as compared to control _V. harveyi_ with no microalgae added. (**b**) _V. harveyi_ concentration was significantly lower (\(p<0.05\)) at 24 to 72 h incubation in co-culture assay with _T. weissflogii_ as compared to control _V. harveyi_ with no microalgae added. (**c**) _V. harveyi_ concentration was significantly lower (\(p<0.05\)) at 72 to 120 h incubation in co-culture assay with _Isochrysi_ sp as compared to control _V. harveyi_ with no microalgae added. (**d**) _V. harveyi_ concentration showed no significant difference (\(p>0.05\)) in co-culture assay with _C. gracilis_ as compared to control _V. harveyi_ with no microalgae added. Note: Values are presented as mean \(\pm\)SD. Mean values of _V. harveyi_ within the same time (hours) with different lowercase letters are significantly different (\(p<0.05\)).