Evaluation of selected natural sesquiterpenes as sensitizing agents of β-lactam-resistant bacterial strains

AIMS

To evaluate the capacity of fourteen sesquiterpenes to enhance the action of known antibiotics against two β-lactam resistant strains, and to determine a possible mechanism of antibiotic sensitization by assessing their ability to inhibit a β-lactamase enzyme.

METHODS AND RESULTS

The broth microdilution method was used to determine the minimum inhibitory concentration (MIC) of β-lactams cefuroxime (CEFM) and cefepime (CPM) against Staphylococcus aureus 23MR and Escherichia coli 82MR strains in the absence and presence of subinhibitory concentrations of fourteen natural sesquiterpenes. (1R,4R)-4H-1,2,3,4-tetrahydro-1-hydroxycadalen-15-oic acid (5), xerantolide (8), estafiatin (11), and ambrosin (12) exhibited the best sensitizing effects in both strains. These compounds were able to reduce the MIC of CEFM by 2-fold (from 15.0 to 7.5 µg/mL) and CPM by 15-fold (from 0.9 to 0.06 µg/mL) in S. aureus 23MR. For E. coli 82MR, the MIC of CEFM was reduced up to 8-fold (from 120.0 to 15.0 µg/mL). In this strain, the activity of 8 and 11 surpassed that of clavulanic acid (positive reference), which reduced the MIC of CEFM from 120.0 to 60.0 µg/mL. To elucidate a possible mechanism of antibiotic sensitization, molecular docking studies were conducted with β-lactamases. These studies revealed an affinity with the enzymes (energies > -4.93 kcal/mol) by the formation of hydrogen bonds with certain conserved amino acid residues within the active sites. However, the in vitro results indicated only marginal inhibition, with percentages <50%.

CONCLUSIONS

The bioevaluations indicate that nine of fourteen sesquiterpenes enhance the action of CEFM and CPM against the β-lactam resistant strains, and these compounds displayed moderate activity as inhibitors of β-lactamase.

3β-Palmitoyloxy-olean-12-ene analogs from Sapium lateriflorum (Euphorbiaceae): Their cytotoxic and anti-inflammatory properties and docking studies

Ten compounds, including a new anti-inflammatory acyl triterpene, 3β-palmitoyloxy-1β,11α-dihydroxy-olean-12-ene, were isolated from the bioactive organic extract prepared from the leaves of Sapium lateriflorum (syn: S. nitidum). The isolated compounds were screened for their cytotoxic activity against selected human cancer cell lines and did not display significant activity. They were also evaluated as anti-inflammatory agents in mouse models (TPA-induced edema in the ear and in a carrageenan-induced paw edema model). The results indicated that the new compound, 3β-palmitoyloxy-1β,11α-dihydroxy-olean-12-ene, was the compound with major anti-inflammatory activity similar to that of indomethacin, being the hydroxyl at C-11 important for the observed activity. The results of docking studies of the 3β-palmitoyloxy esters of olean-12-ene with NF-κB and with COX-2 receptors were consistent with possible molecular mechanisms of the anti-inflammatory activity.

Antimicrobial Activity of Alternanthera caracasana

The antimicrobial activity of different extracts of Alternanthera caracasana. HBK against 11 bacterial strains and 1 yeast strain was evaluated. The ethyl acetate extract showed antimicrobial activity against Staphylococcus aureus., Staphylococcus epidermidis., Bacillus subtilis., Sarcina lutea., and one strain of Vibrio cholerae.. There was no antimicrobial activity against Candida albicans.. As a bioactive compound, 7-methoxycoumarin was identified.