Evaluation of a computer-assisted method of analysing SDS-PAGE protein profiles in tracing a hospital outbreak of Serratia marcescens

Sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) profiles of bacterial proteins have been successfully used for taxonomical purposes. More recently this technique has been applied to epidemiological investigations in respect of various micro-organisms including Neisseria meningitidis, Staphylococcus aureus and Clostridium difficile. The main limitations of the methods so far described are lack of standardisation in extraction and separation as well as in the analysis of results. Although reproducibility in the same laboratory has been shown to be satisfactory, comparison of results among laboratories is still difficult. Moreover, assessment of differences and/or similarities among chromatograms or autoradiographs showing many bands depends upon qualitative descriptions. Interpretation of densitometric scannings is laborious and time-consuming. In this paper we present our experience of a completely standardised, fully computer-controlled procedure for SDS-PAGE (AMBIS System) in analysing 35S-methionine-labelled total proteins. The methodology proved very useful in monitoring a hospital outbreak of Serratia marcescens. It allowed us to make quantitative comparison in a shorter time as well as to handle easily a great amount of data and usefully integrate it with those obtained with other systems such as serotyping. Furthermore, when the two systems are used together, more precise information can be gained. In this epidemic, serotyping indicated the presence of two groups which would have been missed by PAGE analysis alone. Electrophoretotyping, however, focused on similarities of cellular proteins among the epidemic strains. This allowed us to distinguish them from epidemiologically unrelated strains of the same serogroup.(ABSTRACT TRUNCATED AT 250 WORDS)