Capsaicin: An Important Alkaloid with Potential Against <i>Klebsiella pneumoniae</i>

Background/Objectives: Klebsiella pneumoniae is an important opportunistic pathogen that causes healthcare-associated and community-acquired infections; these include urinary tract infections, bacteremia, pneumonia, and liver abscesses. The rapid spread of multidrug-resistant (MDR) and hy-pervirulent (hvKP) strains of K. pneumoniae, with the ability to adapt to the hospital environment, poses a major challenge for their treatment and control, thereby increasing morbidity and mortality rates globally. In this context, the search for new treatment alternatives is imminent today, with plant-based products being an excellent alternative for use. The aim of this research was to evaluate the antibacterial and an-tibiofilm potential of the alkaloid capsaicin (CAP) against clinical isolates of K. pneumoniae, as well as to explore its possible effect on the cell membrane. Methods/Results: Susceptibility testing using the mi-crodilution method showed antibacterial activity of CAP against all K. pneumoniae isolates tested, with minimum inhibitory concentration (MIC90) values ranging from 28.44 to 1696 &micro;g/mL. Assays to evaluate the effect of CAP against biofilms using the crystal violet technique, showed the ability of CAP to inhibit the formation of biofilms and mature biofilms of K. pneumoniae. Intracellular material leakage experiments (260/280 nm) and Evans blue microscopy showed damage to the cell membrane. Conclusions: This in-dicates that the antibacterial action of CAP could be associated with damage to the integrity of the cell membrane and consequent death of these pathogens. These results serve as a reference for future studies in which the antimicrobial action mechanisms of CAP and its possible synergistic action with other compounds are established.