Development of a reverse line blot hybridization method for detection of some streptococcal/lactococcal species, the causative agents of zoonotic streptococosis/lactococosis in farmed fish

Streptococcosis/lactococcosis is the cause of high morbidity and mortality in aquaculture sector and to date a number of species of Streptococcus and Lactococcus genera including S. iniae, S. agalactiae, S. dysagalactiae, S. parauberis, S. feacalis, L. garvieae and L. lactis have been discriminated as the cause of disease in aquatic animals. Despite the use of diagnostic molecular methods for each of these bacterial species, no data is available on a suitable, rapid and simple simultaneous detection tool for these pathogens. This paper describes a simultaneous detection method which is PCR based on a reverse line blot [RLB] for rapid detection and differentiation of four species of genera of Streptococcus and Lactococcus genera consisting of S. iniae, S. agalactiae, S. parauberis and L. garvieae the most important agents of the disease in fish. A reverse line blot [RLB] assay was developed for the simultaneously identification of four species of Streptococcus/lactococcusconsisting of S. iniae, S. parauberis, S. agalactiaeand Lactococcusgarvieae. The assay employs one set of primer pair for specific amplification of the 16S rRNA gene. These were designed based on the nucleotide sequences of 16S rRNA gene sharing a homology region with Streptococcus spp. and Lactococcus spp. DNA was extracted from the pure bacterial colonies and amplified. A membrane was prepared with specific oligonucleotide for each bacterial species. PCR products were then hybridized to a membrane. The amplification resulted in PCR product of 241 bp in length. No cross-reactions were observed between any of the tested bacterial species, and mixed DNAs from these four bacterial species were correctly identified. This RLB method is a suitable technique for a simultaneous detection of these species of bacterial fish pathogens that are some of the main causes of streptococcal/lactococcal infections in both freshwater and marine aquatic animals, and so we recommend its use for integrated epidemiological monitoring of streptococcosis/lactococcis in aquaculture industry.