Pine conk extracts weaken bacteria’s antibiotic defence

Researchers at Tallinn University of Technology have found that extracts from the pine conk mushroom, which is common in Estonian forests, act against the bacterium that causes Lyme disease and three gram-negative bacteria often linked to hospital infections, ERR reported.

Lyme disease, caused by Borrelia burgdorferi, can be treated with antibiotics, but some patients continue to experience symptoms after treatment ends. Researchers cite the bacteria’s ability to form biofilms, strong protective layers that help them survive exposure to medicines, as one possible reason.

The study also examined Klebsiella pneumoniae, Acinetobacter baumannii and Enterobacter cloacae. These bacteria can cause respiratory, urinary tract and bloodstream infections and are significant pathogens in hospitals.

Gram-negative bacteria are more difficult to affect with many antibacterial substances because of their cell structure. Tallinn University of Technology chemists have for years searched for antibacterial bioactive compounds in plants found in Estonia and used in folk medicine. Earlier studies identified such compounds in ribwort plantain and greater burdock.

For the latest study, the researchers turned to fungi. Maria Kulp, the study’s lead author and head of the university’s analytical chemistry research group, said the team chose the pine conk, Fomitopsis pinicola, because the medicinal mushroom contains various bioactive compounds, while its potential antibacterial, antioxidant and especially anti-Borrelia burgdorferi effects have not been sufficiently studied.

The researchers grew the mushroom’s mycelium in a laboratory to obtain material with a consistent composition that would not depend on where it was collected. They then prepared water and ethanol extracts and tested their effects on the Lyme disease bacterium and the three problematic hospital bacteria.

Laboratory tests showed that the extracts slowed the growth of all the bacteria studied, reduced their viability and, in some cases, destroyed them completely. The extracts also inhibited the formation of biofilms and reduced their extent.

Because biofilms make bacteria considerably more resistant to medicines, weakening them is considered an important direction in the development of new antimicrobial treatments.

The researchers also examined the extracts’ antioxidant properties and their effects on healthy cells. The tests showed a dose-dependent ability to neutralise cell-damaging free radicals, while most of the extracts had low cytotoxicity. Human cells generally tolerated them well.