| dc.description.abstract | Background: Fish farming is always challenging due to serious Streptococcus
agalactiae (group B streptococcus; GBS) infections. In detail, there are three
serotypes Ia, Ib and III which are the main cause of fish disease by the GBS strain.
Objective: In this study, the objective is to identify pathogenic bacteria and
determine the LD50 value result in GBS serotypes Ia (GBS-Ia), GBS serotypes Ib
(GBS-Ib), and GBS serotypes III (GBS-III).
Methods: The experiment was designed to identify GBS serotypes causing
diseases by virulent test. In dead fish samples, pathogenic bacteria can be
distinguished when going through the culture process and isolation, to verify the
accuracy by PCR. Next, the Reed & Muench(1938) method was applied to
determine LD50 values which caused the 50% mortality by injecting GBS-Ia, GBS Ib, and GBS-III to tilapia (Oreochromis niloticus) .
Results: The virulent tests resulted in 100% mortality caused by GBS-Ib and GBS
III, while the results of GBS-Ia just reached 20%. The determined LD50 of
serotypes Ib and serotypes III were 105.7 CFU/ml and 105.04 CFU/ml respectively.
That means the GBS-Ib had higher virulence than GBS-III based on the LD50 value
and timeline of infection. Infectious fish demonstrated erratic swimming, loss of
appetite, depigmentation on the body, operculum areas, caudal fin erosion, and
hemorrhages eyes in the external sign of fish. In internal signs, most fish organs
were hemorrhages. To confirm the bacterial isolation, multiplex PCR was used to
identify the correct serotypes.
Conclusion: Three serotypes of Streptococcus agalactiae (group B streptococcus;
GBS) are different in biochemical characteristics and in some cases LD50 value
may not calculate. The findings expand the information on GBS-specific serotypes
and support previous literature on different serotypes for a deeper explanation of
these serotypes in detail. | en_US |
