Rapid identification of Legionella pneumophila zinc metalloprotease using chromogenic detection

Strains of Legionella spp. produce extracellular proteases than can be detected using synthetic chromogenic peptides. Chromogenic tri- and tetrapeptides show a high degree of sensitivity, specificity and reagent stability when linked to para-nitroaniline (pNA). For example, SucOMe-Arg-Pro-Tyr.pNa (S-2586) is specifically hydrolysed by proteases of Legionella pneumophila and some other Legionella species. A paper disc method to sample protease directly from agar plates has been used to evaluate chromogenic peptides as reagents for diagnostic purposes. Strains of Legionella spp., Pseudomonas spp. and Enterobacteriaceae were examined, together with a recombinant Escherichia coli strain containing the cloned 38 kDa zinc metalloprotease from L. pneumophila, S-2586 was hydrolysed by 282 out of 283 L. pneumophila strains, and by the recombinant E. coli. Two of the six strains representing other Legionella species, and 22 of the 50 strains from the Pseudomonas group were also positive. No reaction was seen with any of the Enterobacteriaceae strains. Although there was functional homology between proteases from several bacterial groups, the high prevalence of S 2586-hydrolysing proteases within L. pneumophila indicates a potential usefulness for phenotypic identification.