A CRITICAL-APPRAISAL OF THE PHENE-PLATE BIOCHEMICAL FINGERPRINTING SYSTEM FOR EPIDEMIOLOGIC SUBTYPING OF SALMONELLA-TYPHIMURIUM

The efficacy and reproducibility of the Phene-Plate (PhP) system (Bios ys Inova, Stockholm, Sweden) for biochemical fingerprinting of Salmone lla typhimurium was investigated. Duplicate and replicate assays on 40 epidemiologically related and unrelated strains were performed in two batches of PhP-48 plates. The data were then subjected to various num erical analyses to determine the infra-subspecific relationships of th e isolates, and PhP-types determined by reference to a predetermined i dentity level. Our results show that, (i) presently defined identity l evels are too stringent and delineate PhP-types which are epidemiologi cally unjustified, (ii) tests currently recommended for PhP-typing S. typhimurium may be somewhat unstable and not satisfactory for fingerpr inting purposes, (iii) caution must be exercised when comparing data f rom different batches of PhP-48 plates, and (iv) best results are obta ined when infra-subspecific relationships are determined by visual ass essment of the resulting dendrogram. These data indicate the discrimin atory capacity of the Phene-Plate system to be significantly compromis ed by its reproducibility, although epidemiologically valid data can b e obtained if results are carefully examined.