Background/Objectives: Bacterial resistance and virulence are challenges in treating bacterial infections, especially in
Klebsiella pneumoniae. Plants of the
Launaea Cass. genus are used traditionally to address a variety of diseases, including infections, but the potential bioactive compounds are unknown. Our goals were to verify the potential contribution of two major polyacetylene glycosides isolated from our previous study, (3
S,6
E,12
E)-6,12-tetradecadiene-8,10-diyne-1-ol 3-
O-
β-D-glucopyranoside (
1) and bidensyneoside A (syn. gymnasterkoreaside A) [(3
R,8
E)-3-hydroxy-8-decene-4,6-diyn-1-yl
β-D-glucopyranoside] (
2), to the anti-infective properties of
Launaea capitata and to develop a dependable HPLC method for their quantification;
Methods: On a panel of
K. pneumoniae clinical isolates, the antibacterial action of
1,
2, and the methanol extract of the whole
L. capitata plant were evaluated by broth microdilution assay, while their antibiofilm action was evaluated by the crystal violet assay. qRT-PCR investigated
luxS,
mrkA,
wzm, and
wbbm genes that encode biofilm formation and quorum sensing (QS). The antibacterial activity of
1 was revealed by employing mice infection. Chromatographic separation was conducted using isocratic elution on a Hypersil BDS C18 column using a photodiode array (PDA) detector;
Results: Compound
1 showed antibacterial activity with MIC values of 16–128 µg/mL. It remarkably reduced strong and moderate biofilm-forming bacterial isolates from 84.21% to 42.1% compared with the extract (68.42%) and
2 (78.95%). Compound
1 also downregulated the QS genes,
luxS,
mrkA,
wzm, and
wbbm, and exhibited in vivo antibacterial action through the enhancement of the histological construction of the liver and spleen, decreased TNF-
α immunoreaction, bacterial burden, and the inflammatory mediators IL-1
β and IL-6. A successful HPLC-PDA approach was developed to separate the binary mixture of
1 and
2 in less than 10 min with high sensitivity, with detection limits down to 0.518 and 0.095 µg/mL for
1 and
2, respectively;
Conclusions: Compound
1 exhibited remarkable antibacterial and antibiofilm properties and may contribute to the anti-infectious traditional uses of
L. capitata, meriting further clinical studies and serving as a reliable quality control biomarker for the plant.
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