Garlic (Allium sativum) has had an important dietary and medicinal role for centuries and has long been
known to have broad antibacterial properties. Streptococcus iniae occurs naturally in marine and estuarine
environments and is one of the major opportunistic pathogenic bacteria in wounded or unhealthy grouper.
The purpose of this study was to investigate the in vitro antibacterial activity of garlic and the effect of
garlic-supplemented diets on growth performance and resistance against S. iniae in orange-spotted grouper
(Epinephelus coioides). The in vitro antibacterial activity of garlic against S. iniae was investigated with the
agar well diffusion, minimum inhibitory concentration and minimum bactericidal concentration methods
and showed a strong inhibitory effect. Fish were fed diets containing 0, 1.3 and 4% of garlic powder for
14 days. The cumulative mortality of the fish fed with the 1.3% garlic diet was significantly (pb0.01) lower
than that of those fedwith the 4% garlic diet and control diet following a challengewith S. iniae and had significantly
(pb0.01) higher percent weight gain and feed efficiency. The results indicate that the inclusion of 1.3% garlic in
the diet of orange-spotted grouper enhances feed efficiency, fish growth and resistance to infection by S. iniae.
© 2012 Elsevier B.V. All rights reserved.