There are references in the literature to several plants which may have antimicrobial activity. Some of the plants are unlikely to be found growing in UK (unless perhaps as house plants). Many of the bacteria mentioned are not suitable for use in school laboratories, but you may record activity against laboratory organisms.

Raspberry juice cordial has a long been used in Australia for the prevention and treatment of gastroenteritis in livestock, cage birds and humans. The antimicrobial properties of raspberry juice cordial, raspberry juice, raspberry leaf extract and a commercial brand of raspberry leaf tea were investigated against five human pathogenic bacteria and two fungi. Raspberry cordial and juice were found to significantly reduce the growth of several species of bacteria, including Salmonella, Shigella and E. coli, but demonstrated no antifungal activity. No antimicrobial activity was detected in the leaf extract or tea.

Essential oils distilled from members of the genus Lavandula have been used both cosmetically and therapeutically for centuries with the most commonly used species being L. angustifolia, L. latifolia, L. stoechas and L. x intermedia though there are many claims about the biological activity of these oils much of this has not been substantiated by scientific or clinical evidence. Among the claims made for lavender oil are that is it antibacterial and antifungal.

Certain constituents in brewed coffee exhibited antibacterial activities against a strain of Legionella pneumophila. The constituents showing antibacterial activities were found only in extracts made with cold or hot water. It was shown that the antibacterial substances were protocatechuic acid (3,4-dihydroxy benzoic acid), chlorogenic acid, and caffeic acid.

The crude methanolic extracts of Hygrophila stricta and Peperomia pellucida were fractionated into petrol, dichloromethane, ethyl acetate and butanol. All the crude extracts and the fractions exhibited a very good level of broad spectrum antibacterial activity. The fractions were more active than the crude extracts. The petrol fraction of H. stricta and the butanol fraction of P. pellucida were particularly good. No activity was noticed for the fungi tested.

The antibacterial activity of compounds obtained from licorice was measured against upper airway respiratory tract bacteria such as Streptococcus pyogenes, Haemophilus influenzae and Moraxella catarrhalis. Among the tested compounds, licoricidin exhibited the highest activity against all tested microorganisms. Three coumarin derivatives, glycerol, glycerin and glycycoumarin also showed antibacterial activity.

The potential presence of naturally occurring antimicrobials in petals of Camellia japonica L., a member of the tea family, was investigated against food borne pathogens in microbiological media and food. Petals of the Camellia flower (C. japonica L.) were extracted with methanol and fractionated into basic, acidic, and neutral fractions. The acidic fraction (equivalent to 1.0 g of raw sample per disk) produced an inhibitory zone of 14 to 19 mm (diameter) in a disk assay against the pathogens Salmonella typhimurium DT104, Escherichia coli O157:H7, Listeria monocytogenes, and Staphylococcus aureus on agar plates. Milk was used as a model food system. Aqueous extract at a concentration of 100 mg/ml was bacteriostatic against all the food borne pathogens in the milk stored at 25ºC for up to 4 days.

Antimicrobial activity of Verbascum macrurum Ten. (Scrophulariaceae). Extracts made from leaves with ethanol/water gave the most activity.

Antibacterial activity of the essential oil from Aristolochia indica (a shrubby, twining plant indigenous to India). The essential oil of Aristolochia indica, containing beta-caryophyllene and alpha-humulene as major constituents, was found to show a moderate antibacterial activity.

Extracts of various herbs and spices (for example sage, thyme, clove, garlic) have been shown to have antimicrobial activity.

Some mosses and lichens also contain antimicrobial compounds.