Rapid detection and identification of Streptococcus iniae using a monoclonal antibody-based indirect fluorescent antibody technique

Streptococcus iniae is among the major pathogens of a large number of fish species cultured in fresh and marine recirculating and net pen production systems. The traditional plate culture technique to detect and identify S. iniae is time consuming and may be problematic due to phenotypic variations of S. iniae isolates. The rapid transmission and severe economic impact of this disease necessitates the development of a rapid, reliable, specific, and sensitive technique to detect and identify S. iniae. We developed an indirect fluorescent antibody technique (IFAT) based on a highly specific mononclonal antibody for S. iniae. The IFAT was found to be suitable for the detection and identification of S. iniae from experimentally and naturally infected tilapia (Oreochromis niloticus). The olfactory epithelium of the naris of experimentally and naturally infected tilapia was demonstrated to be a reliable, sensitive, and non-lethal sample site for the detection and identification of S. iniae. This IFAT was validated by the traditional plate culture techniques but found to be considerably less time consuming and problematic. These findings reveal that this IFAT is an improvement in the ability to detect and identify S. iniae in infected and carrier fish.