Streptococcosis is a disease with major health and economic impacts on the tilapia industry worldwide (Mian et al. 2009). In 1997, more than US$150 million of annual losses representing treatment, morbidity and mortality were recorded and this value increased to US$250 million by 2008 (Klesius, Shoemaker & Evans 2008). In Colombia, Streptococcus agalactiae (Lancefield group B streptococci; GBS) is the main bacterial pathogen of tilapia (Jiménez et al. 2007), causing heavy but not yet quantified losses.
