The evaluation of novel chromogenic substrates for the detection of lipolytic activity in clinical isolates of Staphylococcus aureus and MRSA from two European study groups

Eight novel chromogenic substrates were evaluated for their efficacy in detecting lipase activity in clinical isolates of Staphylococcus aureus from the United Kingdom and Malta. All isolates metabolized the chromogenic lipase substrates 5-(4-hydroxy-3,5-dimethoxyphenylmethylene)-2-thioxothia-zolidin-4-one-3-ethanoic acid (SRA)-propionate, SRA-butyrate, SRA-octanoate and 2-[2-(4-hydroxy-3,5-dimethoxyphenyl)-vinyl]-3-methy-benzothiazolium salt (SB(Z)TM)-acetate. Over 90% of the isolates metabolized the lipase substrates SRA-decanoate and SRA-laurate. However, only 0.6% of UK isolates and 2% of Maltese isolates metabolized the lipase substrate SRA-myristate; none of the isolates tested metabolized SB(Z)TM-butyrate. Traditional Tween 80 assays showed that over 73% of the UK methicillin-resistant Staphylococcus aureus (MRSA) isolates and 83% of the UK methicillin-sensitive Staphylococcus aureus (MSSA) isolates demonstrated lipolytic activity. In contrast, Maltese isolates showed lipase activity in 94% and 88% of the MRSA and MSSA strains, respectively. Lipases in MRSA and MSSA demonstrated substrate specificity whose activity appeared dependent upon hydrocarbon chain length of the chromogen. These novel chromogens can be used for lipase enzyme detection and have application for full characterization of numerous S. aureus lipases.