Typing of methicillin-resistant Staphylococcus aureus in a university hospital setting by using novel software for spa repeat determination and database management

Abstract

The spa gene of Staphylococcus aureus encodes protein A and is used for typing of methicillin-resistant Staphylococcus aureus (MRSA). We used sequence typing of the spa gene repeat region to study the epidemiology of MRSA at a German university hospital. One hundred seven and 84 strains were studied during two periods of 10 and 4 months, respectively. Repeats and spa types were determined by Ridom StaphType, a novel software tool allowing rapid repeat determination, data management and retrieval, and Internet-based assignment of new spa types following automatic quality control of DNA sequence chromatograms. Isolates representative of the most abundant spa types were subjected to multilocus sequence typing and pulsed-field gel electrophoresis. One of two predominant spa types was replaced by a clonally related variant in the second study period. Ten unique spa types, which were equally distributed in both study periods, were recovered. The data show a rapid dynamics of clone circulation in a university hospital setting. spa typing was valuable for tracking of epidemic isolates. The data show that disproval of epidemiologically suggested transmissions of MRSA is one of the main objectives of spa typing in departments with a high incidence of MRSA.

FIG. 1.

Screen shot of the novel Ridom StaphType software featuring a base quality-based sequence editor, a database, and a report generator (not shown) module. This client software synchronizes with an accompanying website to ensure uniform spa code terminology usage.

FIG. 2.

Rank abundance graph demonstrating the frequencies of spa types collected during two study periods.

FIG. 3.

Dendrogram deduced from the cluster analysis of PFGE macrorestriction patterns of spa-1, -3, and -23 strains as determined by the algorithm described by Claus et al. (1). Strains from this study are designated by the letter S followed by a strain number. Additional information was added to spa-1 and -23 strains as follows: 1s, spa-1 and low mupirocin MIC; 1i, spa-1 and high mupirocin MIC; 23i, spa-23 and high mupirocin MIC. As a control, patterns determined previously from diverse other clones at the German reference laboratory for staphylococci were included for cluster analysis (outgroup strains, i.e., 1150/93, Berlin epidemic MRSA; 2378/00, Barnim epidemic MRSA; 635/93, Vienna epidemic MRSA; 134/93, northern German epidemic MRSA; 1000/93, Hannover epidemic MRSA).