A compound extracted from the leaf of the American
beautyberry re-sensitised methicillin-resistant Staphylococcus aureus (MRSA) to
beta-lactam antibiotics.
Scientists have discovered a compound in the leaves of
a common shrub, Callicarpa americana (American beautyberry),
boosts the activity of the antibiotic oxacillin against antibiotic-resistant
staphylococcus bacteria. The laboratory studies demonstrated that the plant
compound works in combination with oxacillin to overcome methicillin-resistant
Staphylococcus aureus (MRSA)’s resistance to antibiotics.
The American beautyberry is native to the southern US.
According to the researchers, the plant is prolific in the wild and popular in
ornamental landscaping, known for having clusters of bright purple berries that
begin to ripen in the summer that are an important food source for many species
of birds.
“We decided to investigate the chemical properties of
the American beautyberry because it was an important medicinal plant for Native
Americans,” said Cassandra Quave, co-senior author of the study and an
assistant professor in Emory University’s Center for the Study of Human Health
and Emory School of Medicine’s Department of Dermatology. She is also a member
of the Emory Antibiotic Resistance Center and an ethnobotanist – studying how
indigenous people incorporate plants in healing practices to uncover promising
candidates for new drugs.
The team said several Native American tribes relied on
the plant for various medicinal purposes: the leaves were boiled for use in
sweat baths to treat malarial fevers and rheumatism; the boiled roots were used
for treating dizziness, stomach aches and urine retention; and the bark made
into therapies for itchy skin.
In their previous research, Quave and colleagues found
that extracts from the leaves of the beautyberry could inhibit bacterial
growth. Therefore, they elected to test the extracts for efficacy against MRSA.
The team identified that 12(S),16ξ-dihydroxycleroda-3,13-dien-15,16-olide,
a clerodane diterpene isolated from leaves of Callicarpa americana,
slightly inhibited the growth of MRSA. However, when it was tested in
combination with the beta-lactam antibiotic oxacillin (a commonly used
antibiotic which MRSA is resistant to) the two acted synergistically to
overcome MRSA’s resistance to treatment.
The researchers said their next step would be testing
the combination of the beautyberry leaf extract and oxacillin as a therapy for
MRSA in animal models. If those results are promising, the researchers will
synthesise the plant compound in the lab and engineer its chemical structure to
try to further enhance its efficacy as a combination therapy with oxacillin.
“We need to keep filling the drug-discovery pipeline
with innovative solutions, including potential combination therapies, to
address the ongoing and growing problem of antibiotic resistance,” Quave said.
Each year in the US, at least 2.8 million people
contract an antibiotic-resistant infection and more than 35,000 people die,
according to the Centers for Disease Control and Prevention (CDC). Quave
concluded: “Even in the midst of the COVID-19, we can’t forget about the issue
of antibiotic resistance”, noting that many COVID-19 patients are receiving
antibiotics to deal with secondary infections brought on by their weakened
conditions, raising concerns about a later surge in antibiotic-resistant
infections.
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