Identification and Pathology of Lactococcus garvieae Isolated from Cultured and Wild Giant Freshwater Prawns (Macrobrachium rosenbergii de Man) in Thailand

Abstract

Lactococcosis caused by Lactococcus garvieae is an increasing problem in aquaculture. The current study is, to our knowledge, the first record of L. garvieae isolated from giant freshwater prawn (Macrobrachium rosenbergii de Man) in Thailand. These bacteria were isolated from giant freshwater prawns that were either cultured or in their natural environments in Phatthalung and Songkhla, provinces of southern Thailand. Based on conventional and rapid identification systems, as well as genetic and phylogenetic characterizations, the bacteria were identified as L. garvieae. An infectivity trial indicated that all L. garvieae isolates were pathogenic bacteria. Moreover, giant freshwater prawns experimentally infected with L. garvieae KSAAHRC-LA1, by intramuscular injection, exhibited 23.33–86.67% mortality within 10 d and a 10-day LD₅₀ of 1.38 x 10⁷ CFU/ml. Histopathological findings revealed severe damaged hepatopancreatic tubules caused by bacterial infection and hemocytic infiltrations observed in the infected muscle. Haemato-immunological parameters of the giant freshwater prawn infected with L. garvieae indicated depression in the prawn’s immune response.