Submitted to: Veterinary Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/12/2010
Publication Date: 8/26/2010
Publication URL: http://hdl.handle.net/10113/49071
Citation: Evans, J.J., Pasnik, D.J., Klesius, P.H. 2010. A commercial rapid optical immunoassay detects Streptococcus agalactiae from aquatic cultures and clinical specimens. Veterinary Microbiology. Vol. 144(3-4):422-428. Interpretive Summary: Streptococcus agalactiae, group B Streptococcus (GBS) has been found in numerous animal species and causes a variety of diseases. Recently, Evans et al., (2008ab) reported a genetic relationship between human and fish GBS. Given this similarity, it may be possible that a human GBS identification test kit, BioStar STREPT B Optical ImmunoAssay (OIA), could be used to non-lethally monitored and identify GBS from aquatic species in the wild, aquacultural settings, and public display aquaria at the onset of disease. Our results demonstrate the utility of the STREPT B OIA to identify GBS directly from non lethally obtained swabs of clinically infected fish.
Technical Abstract: The BioStar STREPT B Optical ImmunoAssay (OIA) (BioStar® OIA® Strep B Assay Kit; Biostar Incorporation; Louisville, CO, USA) was used to identify 32 known group B streptococcus (GBS) isolates of fish, dolphin, bovine, and human origin. Thirteen non-GBS isolates from fish and other animals were tested as negative controls. Three groups of six Nile tilapia (Oreochromis niloticus) (mean weight of 40.60 ± 1.70 g) each were inoculated intraperitoneally with either 106 colony forming units (cfu) GBS /fish, 106 cfu S. iniae /fish or 100 µL of tryptic soy broth (TSB) and observed for disease signs and mortality for seven days. The nares and brain of all fish were swabbed and subjected to the STREPT B OIA for detection of GBS antigen immediately after swabbing (0 hours) or 24, 48 and 72 hours post swabbing and compared to conventional culture on trypticase soy agar with 5% sheep blood (commonly known as direct TSA). This commercial assay gave 100% analytical specificity of known aquatic animal non-GBS isolates and no cross reactivity. The STREPT B OIA method demonstrated a diagnostic sensitivity of 75 % and a diagnostic specificity of 69.2 % compared to direct TSA. The percent agreement between the OIA and culture method was 100%. GBS antigen could be retrieved by OIA following 72-hour storage of swabs. These results demonstrate the utility of the STREPT B OIA to identify GBS from culture and directly from swabs of clinically infected fish. Keywords: Streptococcus agalactiae, GBS, fish, BioStar STREPT B Optical ImmunoAssay (OIA)