Synergism and efficacy of some naturally occurring D-amino acids against clinically relevant bacterial and fungal species

Amino acids are predominantly synthesized and used in their L-enantiomeric form in all three kingdoms of life. However, bacteria produce diverse D-amino acids that are involved in the synthesis and cross-linking of peptidoglycan. Several studies reported possible antimicrobial activities of selected D-amino acids against Escherichia coli. The present study was undertaken to investigate the antibacterial and antifungal susceptibility patterns and growth inhibitory effects of certain D-amino acids, including D-alanine, D-lysine, D-serine, and D-proline. Our findings indicate that D-lysine is the most potent antibacterial and antifungal, among the examined D-amino acids, followed by D-alanine, whereas D-serine and D-proline had insignificant antimicrobial activities. Gram positive bacteria were more susceptible to the antibacterial effects of D-amino acids than Gram negative bacteria. Growth kinetic studies revealed that D-lysine and D-alanine resulted in extended lag phases, suggesting that the D-amino acids successfully influenced the microorganisms' ability to use nutrients efficiently and disrupted their normal biological functions. Additionally, synergism was evident between D-alanine and D-lysine when combined with either Ampicillin or Amphotericin B. These results suggest a new avenue for D-amino acids' potential as naturally occurring antimicrobial reagents for the treatment and prevention of microbial growth in food and agriculture applications

Antimicrobial activity of some medicinal plants against different Candida species

The anticandidal activity of nineteen Jordanian plant extracts [Capparis spinosa L., Artemisia herba-alba Asso, Echinops polyceras Boiss., Gundelia tournefortii L., Varthemia iphionoides Boiss. and Blanche, Eruca sativa Mill., Euphorbia macroclada L., Hypericum trequetrifolium Turra, Achillea santolina L., Mentha longifolia Host, Origanum syriacum L., Phlomis brahchydo [Boiss.] Zohary, Teucrium polium L., Anagyris foetida L., Trigonella foenum-graecum L., Thea sinensis L., Hibiscus sabdariffa L., Lepidium sativum L., Pimpinella anisum L.] were tested against Candida albicans ATCC 10231, Candida glabrata ATCC 1615 and Candida krusei ATCC 6258] in addition to some other clinical isolates of these species. Fluoconazole was used as a reference standard to determine the sensitivity of the strains. The minimum inhibitory concentration ranged from 3.1 to 25 mg ml[-1]. Most of the extracts exhibited anticandidal effect. Although the in vitro obtained findings are promising, the extracts need further studies to be standardized for in vivo therapeutic applications

Effect of chemosensitizers on minimum inhibitory concentrations of fluconazole in candida albicans

To evaluate the effect of chemosensitizers on the in vitro activity of fluconazole against Candida albicans strains. Using Clinical Laboratory Standard Institute method, antifungal activity of fluconazole was determined alone and in combination with 16 chemosensitizers that included verapamil, reserpine, quinine, quinidine, gemfibrozil, lansoprazole, tamoxifen, diltiazem, desipramine, nicardipine, cyclosporine, chlorpromazine, prochlorperazine, promethazine, thioridazine, and trifluoperazine. Further studies were done using double combinations of selected chemosensitizers with fluconazole [28 combinations]. For testing combinations, half of the minimum inhibitory concentration [MIC] of each agent was selected in order to avoid the effect of the drug alone. One reference strain [ATCC90028] and one clinical isolate of C. albicans were used for testing the in vitro activity. Broth dilution method was used to determine the MICs of fluconazole and chemosensitizers. Of the 16 chemosensitizers tested, 3 exhibited in vitro activity by increasing fluconazole susceptibility to 7-fold. The MICs of the reference strain and clinical isolate for fluconazole were 5.5 and 0.55 MU g/ml, respectively, and these were reduced to 0.76 MU g/ml by gemfibrozil, 0.83 MU g/ml by quinine, and 0.76 MU g/ml by chlorpromazine in the reference strain, with MIC reduction to 0.08 MU g/ml by all three chemosensitizers in the clinical isolate. Some double combinations reduced the MIC of fluconazole to 10- to 100-fold, even when the chemosensitizers were not effective alone. The most effective double combinations were those of chlorpromazine with either reserpine or nicardipine

Comparison of the antimicrobial activity of two different extracts of Jordanian plants: a preliminary study

Aqueous and ethanolic extracts of three Jordanian plants [Rosmarinus officinalis, Mentha arvensis and Thymus capitatus] were studied for their antimicrobial activity against Staphylococcus aureus, Bacillus subtilis, Escherichia coli, C and ida albicans, C and ida tropicalis and Trichosporon cutaneum. The antimicrobial activity was detected using filter paper disc diffusion method. The ethanolic extract of R. officinalis and T. capitatus inhibited the growth of all microorganisms used, while their aqueous extracts were active against S. aureus, B. subtilis and E. coli. Aqueous and ethanolic extracts of arvensis inhibited the growth of S. aureus, B. subtilis and E. coli