Question

Which of the following is a gram positive pathogenic bacteria ?

• A. Yersinia ruckeri
• B. Aeromonas hydrophila
• C. Streptococcus iniae
• D. Flavobacterium columnare

Hint:

While the majority of fish bacterial pathogens are Gram-negative rods (like Aeromonas, Yersinia, Flavobacterium), Streptococcus is the classic Gram-positive coccus pathogen in aquaculture.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Bacterial pathogens of aquatic organisms are classified primarily based on their Gram-staining characteristics, cell morphology, and biochemical properties.
Most fish pathogens are Gram-negative, but there are some highly significant Gram-positive exceptions.

Step 2: Detailed Explanation:
Let us examine the Gram reaction and characteristics of each listed bacterial pathogen:
1. Streptococcus iniae (C): A highly virulent, spherical (coccus) bacterium that forms chains. It is Gram-positive. It is a major cause of streptococcosis in wild and cultured finfishes globally, leading to meningoencephalitis, exophthalmia ("pop-eye"), and high mortalities. Thus, (C) is correct.
2. Yersinia ruckeri (A): A Gram-negative, rod-shaped bacterium that causes Enteric Redmouth Disease (ERM) in salmonids.
3. Aeromonas hydrophila (B): A Gram-negative, rod-shaped, motile bacterium that causes Motile Aeromonas Septicemia (MAS) in freshwater fishes.
4. Flavobacterium columnare (D): A Gram-negative, long, thin rod-shaped bacterium that causes columnaris disease, characterized by yellowish, saddle-back lesions.

Step 4: Final Answer:
Therefore, Streptococcus iniae is a Gram-positive pathogenic bacteria.