Tomatidine and analog FC04–100 possess bactericidal activities against Listeria, Bacillus and Staphylococcus spp

Abstract

BackgroundTomatidine (TO) is a plant steroidal alkaloid that possesses an antibacterial activity against the small colony variants (SCVs) of Staphylococcus aureus. We report here the spectrum of activity of TO against other species of the Bacillales and the improved antibacterial activity of a chemically-modified TO derivative (FC04–100) against Listeria monocytogenes and antibiotic multi-resistant S. aureus (MRSA), two notoriously difficult-to-kill microorganisms.MethodsBacillus and Listeria SCVs were isolated using a gentamicin selection pressure. Minimal inhibitory concentrations (MICs) of TO and FC04–100 were determined by a broth microdilution technique. The bactericidal activity of TO and FC04–100 used alone or in combination with an aminoglycoside against planktonic bacteria was determined in broth or against bacteria embedded in pre-formed biofilms by using the Calgary Biofilm Device. Killing of intracellular SCVs was determined in a model with polarized pulmonary cells.ResultsTO showed a bactericidal activity against SCVs of Staphylococcus aureus, Bacillus cereus, B. subtilis and Listeria monocytogenes with MICs of 0.03–0.12 μg/mL. The combination of an aminoglycoside and TO generated an antibacterial synergy against their normal phenotype. In contrast to TO, which has no relevant activity by itself against Bacillales of the normal phenotype (MIC > 64 μg/mL), the TO analog FC04–100 showed a MIC of 8–32 μg/mL. Furthermore, FC04–100 showed a strong bactericidal activity against L. monocytogenes SCVs in kill kinetics experiments, while TO did not. The addition of FC04–100 (4 μg/mL) to a cefalexin:kanamycin (3:2) combination improved the activity of the combination by 32 fold against cefalexin and kanamycin-resistant MRSA strains. In combination with gentamicin, FC04–100 also exhibited a strong bactericidal activity against biofilm-embedded S. aureus. Also, FC04–100 and TO showed comparable intracellular killing of S. aureus SCVs.ConclusionsChemical modifications of TO allowed improvement of its antibacterial activity against prototypical S. aureus and of its bactericidal activity against L. monocytogenes. Antibacterial activities against such prominent pathogens could be useful to prevent Listeria contamination in the food chain or as treatment for MRSA infections.

Tomatidine Is a Lead Antibiotic Molecule That Targets Staphylococcus aureus ATP Synthase Subunit C

“…The mutant descriptions and MICs of TO, FC04-100 stereoisomers (FcM, FC04-100 major stereoisomer; Fcm, FC04-100 minor stereoisomer), and gentamicin are reported in Table 1. Note that we previously reported the MICs of the FC04-100 mixture of stereoisomers to be 8 to 16 and 0.5 to 2 g/ml for prototypic S. aureus and SCVs, respectively (13,37). Table 1 shows that FcM is the most potent component of the FC04-100 mixture.…”

“…Like bedaquiline, which is highly selective for the mycobacterial ATP synthase (9,10), TO selectively targets species of the Bacillales, namely, Staphylococcus, Listeria, and Bacillus spp. (11)(12)(13). Staphylococcus aureus and methicillin-resistant S. aureus (MRSA) are often associated with recurrent and difficult-to-treat hospital-or community-acquired infections (14,15) and are among the bacterial threats identified by the CDC that require immediate attention (16).…”

“…Our laboratory extensively documented the very potent (in the nanomolar range) and selective antibacterial activities of TO against SCVs of Staphylococcus, Bacillus, and Listeria spp. (11)(12)(13)37). We also investigated several structural analogs of TO in order to better understand its structure-activity relationship (37) and identified a promising TO derivative possessing a diamino group replacing the 3␤-hydroxyl group of TO (FC04-100) ( Fig.…”

“…1). In addition to its anti-SCV activity, FC04-100 interestingly gained antibacterial activity against prototypical strains (13). The mode of action of TO and its analogs was clearly associated with the respiratory chain, but their molecular target was unknown until now.…”

Tomatidine, a natural steroidal alkaloid shows antiviral activity towards chikungunya virus in vitro

“…Tomatidine is a steroidal alkaloid derived from the stem and leaves of unripe, green tomatoes. It has been described to exhibit a variety of health-beneficial biological activities, including anti-metastatic activity 14 , anti-inflammatory activity 15 , anti-microbial activity [16][17][18] , and was shown to have a protective effect against age-related muscle atrophy 19 . Tomatidine was also found to exhibit antiviral activity towards the plant viruses Sunnhemp Rosette and Tobacco mosaic virus 20 .…”