Marsh stars in Liverpool.

INTRODUCTION/METHODS After the recognition of contaminating algae on histopathological sections stained by periodic acid Schiff (PAS) and Grocott methods, a detailed audit was undertaken to assess the extent of contamination and its possible source. RESULTS The contaminating organism was a member of the staurastrum genus of Chlorophyta, star shaped organisms commonly found in fresh water marshes. The organisms were seen on sections stained by the diastase-PAS, PAS, or Grocott methods and on cytological preparations between July 2003 and May 2004. It is unlikely that contamination of water baths or concentrated staining solutions was to blame, and a more general contamination of the laboratory water supply is the most likely source. CONCLUSIONS Contaminating organisms may appear on histological and cytological material and their nature and source should be investigated. Although in this instance, confusion with pathologically important organisms was minimal, algae may occasionally cause significant disease.