Photobacterium damselae subsp. piscicida

A subspecies of bacteria pathogenic to fish

Photobacterium damselae subsp. piscicida is a Gram-negative, rod-shaped bacterium that is a significant pathogen in marine aquaculture, particularly affecting fish species such as sea bass, sea bream, and turbot. This subspecies is known for causing the disease known as photobacteriosis or pasteurellosis in fish, leading to substantial economic losses in the aquaculture industry.

Taxonomy and Classification

Photobacterium damselae subsp. piscicida belongs to the family Vibrionaceae, which includes other notable genera such as Vibrio and Aliivibrio. The genus Photobacterium is characterized by its bioluminescent properties, although P. damselae subsp. piscicida itself is not bioluminescent.

Morphology and Physiology

Photobacterium damselae subsp. piscicida is a non-motile, facultatively anaerobic bacterium. It is oxidase-positive and catalase-positive, with optimal growth occurring at temperatures between 20°C and 25°C. The bacterium is capable of fermenting glucose and other carbohydrates, producing acid without gas.

Pathogenicity

The pathogenicity of P. damselae subsp. piscicida is primarily due to its ability to produce extracellular toxins and enzymes that damage host tissues. The bacterium invades the host fish through the gills or skin lesions, leading to systemic infection. Clinical signs in infected fish include hemorrhages, ascites, and necrosis of internal organs.

Diagnosis

Diagnosis of photobacteriosis is typically based on clinical signs, histopathological examination, and microbiological culture. The bacterium can be isolated from infected tissues and identified using biochemical tests, such as the API 20E system, which provides a profile of enzymatic activities characteristic of P. damselae subsp. piscicida.

Prevention and Control

Preventive measures in aquaculture include maintaining optimal water quality, reducing stress in fish populations, and implementing biosecurity protocols to prevent the introduction and spread of the pathogen. Vaccination has been explored as a method to protect fish against P. damselae subsp. piscicida, with varying degrees of success.

Research and Developments

Ongoing research is focused on understanding the molecular mechanisms of virulence in P. damselae subsp. piscicida and developing effective vaccines and treatments. Genomic studies have provided insights into the genetic basis of pathogenicity and resistance to environmental stresses.

Also see

• Vibrio
• Aquaculture
• Fish diseases
• Bacterial infections in fish