EVALUATION OF A POLYMERASE CHAIN REACTION-BASED ASSAY FOR THE DETECTION OF AEROMONAS-SALMONICIDA SS SALMONICIDA IN ATLANTIC SALMON SALMO-SALAR

A PCR-based assay;vas developed to detect Aeromonas salmonicida ss sal monicida (A.s.s.) in infected fish kidney and gills. Samples processed for],CR (polymerase chain reaction) were 100 mi kidney tissue suspens ions and g:ll swabs. The primers and probes employed were derived from sequences of 16S rRNA as well as from plasmid DNA. In order to estima te in vitro sensitivity, various numbers of colony forming units (CFU) of A.s.s. strains were added to kidney and gill samples. A minimum of 20 and 200 CFU were demonstrated in 10 mu l PCR template by the 16S r DNA and the plasmid primers, respectively. The 20 and 200 CFU per 10 m u l PCR template correspond to 10(3) and 10(4) CFU in 100 mi kidney ti ssue suspension. The in vitro specificity testing showed that DNA from A.s.s., A. hydrophila, A, salmonicida ss achromogenes, A. salmonicida ss masoucida, and atypical A. salmonicida were amplified using the 16 S rDNA primers. Only A.s.s. and A. salmonicida ss achromogenes DNA wer e amplified using the plasmid primers. Altogether 25 Atlantic salmon p arr, experimentally challenged by cohabitation, were tested for the pr esence of A.s.s, by PCR and agar cultivation. The rates of recovery we re 13/25 by PCR and 6/25 by agar cultivation. Kidney and gill samples from Atlantic salmon of about 2 kg, obtained at slaughter and consider ed covertly infected with A.s.s., were also tested. A.s.s. was detecte d neither by PCR nor by cultivation. Additionally, kidney samples from feral brood fish were tested. A.s.s, was more frequently, 24/72, dete cted by PCR than with agar cultivation, 6/72.