| Summary: | One hundred and forty-six representative members of the Enterobacteriaceae and related genera were subjected to nimierical taxonomy involving 156 physiological and biochemical tests performed at 30°C in media based on nutrient broth and nutrient agar. The results were analysed and clustered using a series of computer programs. Forty representative strains were selected from the main clusters and subjected to polyacrylamide gel electrophoresis to determine the role of this technique in the classification and identification of bacteria. This involved electrophoresis of soluble cell proteins prepared by growing the bacteria in brain heart infusion broth and centrifuging after 18 to 24 hours while growth was in the logarithmic phase. A thick suspension of each strain was sonicated, while being cooled with ice and water, and the resultant suspension was centrifuged depositing the cell debris and leaving a clear supernatant containing the cell proteins. The protein content of each supernatant was determined and the samples stored at 4°C. The electrophoresis was carried out in a cooled, constant temperature apparatus at 5mA/tube for 2 hours. The gels were scanned in the quartz tubes without staining (using ultraviolet light) in an Unicam SPl800 Densitometer at 280 nm. The resultant electrophoregrams (protein profiles) were digitised onto paper-tape using a voltage interface. The digitised traces were fed into a computer program which standardised, trend analysed, compared and clustered them using two resemblance coefficients based on (i) the taxonomic distance, and (ii) the cosine of the angle subtended by the traces. The results from the polyacrylamide gel electrophoresis were compared with the results from the numerical taxonomy and little success was achieved for classification of individual species, however, the results did demonstrate that the technique could be valuable for identification.
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