Immunoblot fingerprinting of coagulase negative staphylococci.

Coagulase negative staphylococci have become prevalent nosocomial pathogens following the implantation of foreign bodies such as prosthetic valves, cerebrospinal fluid shunts, joint prostheses and central venous catheters. They are also the most common contaminants of blood cultures so that a means of differentiating contamination from a true bacteraemia is important.' Assessment of the clinical importance of an individual blood culture isolate is currently based on the clinical condition of the patient and the presence of similar isolates with identical antibiograms from subsequent blood cultures.2 Unrelated isolates from different patients, however, may have the same antibiogram,3 and retesting the same isolate does not always give reproducible results.4 Baird-Parker5 produced a scheme for differentiating six biotypes ofcoagulase negative Staphylococcus (SI-SVI) and eight biotypes of Micrococcus. Kloss et al used these for species specific groups,6 but the problem remained that isolates of biotype SII (S epidermidis) comprised 75% of all clinically important isolates so that further typing methods were required to subdivide these isolates.7 Results with phage typing have been inadequate both in terms of the number of isolates typable and in the degree of reproducibility.8 Examination of protein profiles obtained by sodium dodecyl sulphate polylacrylamide gel electrophoresis (SDS-PAGE) showed that these were species specific but could not subdivide isolates within the species.9 SDS-PAGE typing with sulphur-35 methionine has been of some value but this is an expensive technique requiring the use of radiolabels and has only been applied to a few isolates.'" Isolates of Staphylococcus aureus have been typed by immunoblotting culture supernatants against human antiserum." In this paper we report the results of immunoblot fingerprinting of isolates of coagulase negative staphylococci. Isolates were examined from 17 unrelated patients with systemic infections to assess the ability of the technique to discriminate between different strains. Multiple isolates were also available from seven patients in whom there was a clinical problem thought to be related to coagulase negative staphylococcus infection. In all cases multiple isolates were obtained from blood cultures, and it was important to decide whether these were several different contaminants or a single predominant pathogenic strain. All isolates were probed by a rabbit hyperimmune antiserum raised against the predominant strain of coagulase negative staphylococcus, Staphylococcus epidermidis, from one of these cases (case 3). Individual isolates from the 17 patients with systemic infections and all isolates from three of the multiply infected systemic cases (cases 5, 6, and 7) were also probed by …