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Diseases of Aquatic Organisms

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DAO 53:223-229 (2003)  -  doi:10.3354/dao053223

Effect of benzalkonium chloride stress on immune resistance and susceptibility to Lactococcus garvieae in the giant freshwater prawn Macrobrachium rosenbergii

Winton Cheng1, Ching-Hsien Wang2, Jiann-Chu Chen3,*

1Department of Aquaculture, and
2Institute of Tropic Agriculture, National Pingtung University of Science and Technology, Pingtung, Taiwan 912, ROC
3Department of Aquaculture, National Taiwan Ocean University, Keelung, Taiwan 202, ROC
*Corresponding author. Email:

ABSTRACT: Addition of benzalkonium chloride (BKC) at 0, 0.3, 0.6 and 1.0 mg l-1 to tryptic soy broth (TSB) had no effect on growth of Lactococcus garvieae, a bacterial pathogen of the giant freshwater prawn Macrobrachium rosenbergii. However, injection of the cultured cells into prawns at a dose of 4 x 106 colony-forming units (cfu) prawn-1 resulted in significantly higher mortality at 120 h (p <0.05) in prawns injected with cells grown in the absence of BKC than in prawns injected with cells grown in the presence of BKC. In other experiments, prawns were injected with TSB-grown L. garvieae (4 x 106 and 3 x 105 cfu prawn-1) and then held in water containing BKC at 0, 0.3, 0.6 and 1.0 mg l-1. After 120 h, mortality was significantly higher in all the BKC treatments than in the control without BKC. Prawns showed no significant differences in total hemocyte count (THC) or differential hemocyte count (DHC) amongst treatment and control groups. However, 96 h exposure to 0.3 mg l-1 BKC or more resulted in a decrease in phenoloxidase activity and an increase in respiratory burst to levels considered to be cytoxic. In summary, exposure of L. garvieae to BKC at 0.3 mg l-1 or more decreased its virulence to M. rosenbergii, while exposure of M. rosenbergii to BKC at 0.3 mg l-1 or more increased its susceptibility to L. garvieae infection.

KEY WORDS: Macrobrachium rosenbergii · Lactococcus garvieae · Benzalkonium chloride · Challenge · Virulence · Hemocyte count · Phenoloxidase activity · Superoxide anion

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