Quantitative properties of data generated by the examination of Aeromonas salmonicida infected fish by the standard bacteriological loop

The kidneys of 50 Atlantic salmon that had been injected with Aeromonas salmonicida intraperitoneally were examined for the presence of bacteria using two methods. In one method, agar plates inoculated with a loop-full of kidney material were classified into three categories according to the density of growth obtained. The second method involved the plating of serial dilutions of excised kidney material and generated a quantitative estimate of the bacterial load. A highly significant degree of correlation (Spearman's r=0.85) was detected between the data sets generated by the two methods. It is argued that it is legitimate to accept that data generated from the use of a standard loop as a sampling tool can provide a rapid and simple semiquantitative estimate of the bacterial load in the kidney of fish infected with A. salmonicida. The data allowed an estimation of the limit of detection of the loop method as approximately 103 cfu/g.