It is possible to use herbarium specimens to screen for antibacterial components in some plants.

The antibacterial activity of herbarium specimens of Combretum erythrophyllum growing in the Pretoria area and originally collected between 92 and 12 years ago were compared with freshly collected leaves. There were no differences in the minimal inhibitory concentration of the different samples with Staphylococcus aureus, Enterococcus faecalis, Escherichia coli and Pseudomonas aeruginosa as test organisms. There were only minor differences in chromatograms separating terpenoids and flavonoids. Light fungal infection indicated by small spots on herbarium leaves generally did not influence the MIC value or the chromatographic profile much, but heavy fungal attack decreased the biological activity of the extracts. Application of the technique to Helichrysum pedunculatum specimens showed that the chemical components apparently did not change over a period of 100 years and the biological activity did not decrease. The examination of herbarium material may be a useful first step to screen plants with stable biologically active components or to establish a scientific base for the use of a plant in traditional medicine.