A Comparative Investigation of Streptococcus Agalactiae Isolates from Fish and Cattle

Abstract

Streptococcus agalactiae is the causative bacterium of streptococcosis and causes severe economic losses in wild and cultured fish and cattle, worldwide. In fish, infection can result in septicemia with hemorrhages on the body surface and in the external and internal organs. Streptococcus agalactiae may be isolated from brain, nares, head kidney and eye of infected fish. Streptococcus agalactiae also causes bovine mastitis and the organism can be isolated from milk samples. Streptococcus agalactiae is classified as Lancefield’s group B Streptococcus (GBS). There are also nine GBS capsular polysaccharide serotypes. Despite the significance of the disease, only limited information is available on the identification and characterization of the S. agalactiae isolates from fish and cattle. In the present study, GBS isolates from fish (n = 36), bottlenose dolphin (n=1) and cattle GBS isolates (n=10) were found to have a number of common phenotypic characteristics of the S. agalactiae reference strains (n=4). However, the phenotypic characteristics of these GBS isolates were different from the reference strains of Streptococcus dysgalactiae (n=2), Streptococcus phocae (n=1), Streptococcus iniae (n=1) and Lactococcus garvieae (n=1). The results showed that GBS isolates of fish and cattle origins could be distinguished from each other by capsular serotype, CAMP factor, D-lactose and D-trehalose fermentation, growth pattern in fluid medium and whole cell fatty acid profiles. Studies were performed to determine the pathogenicity of cattle isolates for Nile tilapia (Oreochromis niloticus) and channel catfish (Ictalurus punctatus). The cattle isolates were found not to be infectious for either fish species. No diseases signs or isolation of GBS cattle isolates from the brain or head kidney of fish at 24 and 48 hour post-injection were noted. Fish isolates were evaluated to determine whether a single clone or multi-clones of S. agalactiae were responsible for streptococcal disease in mullet and seabream during the Kuwait Bay, Kuwait epidemic by amplified fragment length polymorphism (AFLP). The results indicated that the infection was not caused by a single clone of S. agalactiae. The results suggest that five GBS S. agalactiae clones were involved in the epidemic that affected primarily mullet and seabream.