Activity of several Helycrisum species extracts against clinical isolates of human Gram-positive pathogens.

Gram-positive bacteria like Streptococcus agalactiae, Methicillin-resistant Staphylococcus aureus (MRSA), S.epidermidis (MRSE) and glycopeptyde resistant Enterococcus faecalis are becoming common causes of several types of severe infections, both in the community and in the hospital settings. Because of this scenario and the therapeutic limitations descending from the acquisition of multiple-resistance by these organisms, the need for new classes of antibacterial compounds has become urgent and many compounds, naturally occurring in several plants, are receiving sustained attention regarding their potential use as antimicrobial agents. Several Helicrisum species are considered medicinal plants (1) and posses a documented antibacterial activity (2). In this work the potential antimicrobial activity of Helycrisum siculum (Spreng.) Boiss, H. litoreum Guss., H. scandens Guss. and H. hyblaeum Brullo (3) have been investigated. H. litoreum Guss. and H. scandens Guss where tested as total extracts while 3 and 5 fraction groups obtained respectively from H. siculum (Spreng.) Boiss (HEE-3.1, HEE-3.2, HEE-3.4) and H. hyblaeum Brullo (HEB-2.1 HEB-2.5, HEB-2.6, HEB-2.7, HEB-2.8), were evaluated. The antimicrobial activity of all materials were preliminary analyzed on a few Gram-positive (S.aureus ATCC-29213, S.epidermidis ATCC-35984) and Gram-negative organisms (Escherichia coli ATCC-25922) and a clear antimicrobial activity against Gram-positive strains of the two total extracts from H. litoreum Guss. and H. scandens Gus and of 4 out of the 8 fraction groups was found. No activity against Gram-negative organisms was detected. After these preliminary results, minimal inhibitory concentrations (MICs) of the extracts and the active fractions were determined by standard methods (4) on 14 strains previously isolated from human specimens and identified according to standard procedures (5). The strains tested included: 4 S.aureus (2 MRSA, 1 MSSA and the ATCC strain), 3 S. epidermidis (2 MRSE, 1MSSE), 4 E. faecium (3 strains were resistant to glicopeptydes) and 3 S.agalactiae strains. Table 1, showing the MIC values obtained, indicates that each Helycrisum species analyzed is endowed with a specific antibacterial activity. A very narrow distribution of MIC values for each extract or fraction groups was observed, and, interestingly enough, this feature was constant, regardless of the species analyzed or the patterns of resistance to antimicrobial drugs possessed by the strains. Our results indicate that these Helycrisum species can be considered for further bio-guided procedures aimed at isolating new compounds potentially active against important Gram-positive human pathogens.