The Journal of Medical Microbiology, Vol 37, Issue 4 245-251, Copyright © 1992 by Society for General Microbiology
Evaluation of the PhP system for biochemical-fingerprint typing of strains of Salmonella of serotype Typhimurium
M. Katouli, I. Kuhn, R. Wollin and R. Mollby
Department of Bacteriology, Karolinska Institute, Stockholm, Sweden.
The Phene Plate (PhP) system of biochemical fingerprinting of bacteria is a
computerised typing system, based on quantitative measurements of the
kinetics of several biochemical reactions of bacteria grown in liquid
medium in microtitration plates. For each isolate tested, it yields a
biochemical fingerprint comprising several kinds of quantitative data which
are useful for establishing similarities among strains with a
personal-computer program. In this study, a set of 16 specific substrates
was chosen to differentiate strains of Salmonella of serotype Typhimurium.
The system was evaluated for its typability, reproducibility and
discriminatory power in tests with a collection of 100 epidemiologically
unrelated Typhimurium strains and results were compared with those obtained
by phage typing. At an identity level of 0.980, strains were assigned by
this method to 51 biochemical phenotypes (BPTs), giving a diversity index
of 0.963 and a resolution index of 0.210. In contrast, 24 phage types (PTs)
were identified among these isolates (a diversity index of 0.901). The
combined use of biochemical fingerprinting by the PhP system and phage
typing discriminated 82 phenotypes (a diversity index of 0.994). Stability
of markers in each of the methods was also evaluated after subculture of 20
strains for 21 consecutive days. Only nine biochemical reactions were found
that were subject to small, but measurable, changes for at least one
isolate. These changes slightly decreased the mean similarity coefficients
among strains but the overall BPTs of the strains showed changes in four
strains (20%). In contrast, eight strains (40%) showed changes in their PTs
after this treatment. It is concluded that the PhP system is a highly
discriminatory and reproducible method for typing Typhimurium strains. It
is easy to perform, and may be used alone or in combination with phage
typing in epidemiological studies of Typhimurium strains.
