Activity of Selected Essential Oils against Candida spp.strains.Evaluation of New Aspects of their Specific Pharmacological Properties,with Special Reference to Lemon Balm

The aim was to investigate the antifungal effectiveness and some of pharmacological properties of essential oils (EOs), which had not yet been thoroughly studied in the planned scope. We first evaluated MIC/MFC of sixteen EOs against C. albicans ATCC 10231. Then, five most active EOs were tested, using 50 clinical Candida spp. strains and additional reference C. albicans ATCC 90028 strain. The time-kill curve, carryover, post-antifungal effects (PAFE), mutant prevention concentrations, the susceptibility of reference strains to the cell wall disrupting agents and tolerance to oxidative stress, were evaluated. For these detailed studies, we chose the following four essential oils. Clove oil, Geranium oil, Lemon balm and Citronella oil, with MICs of 0.097% (v/v), resulted concentration- and time-dependent killing and may be therapeutically safe, because they do not generate resistance. The best one was Lemon balm, which caused most extended PAFE, significantly reduced tolerance to oxidative stress and increased susceptibility to Calcofluor White, Congo Red and SDS. Phytochemical analysis of these four EOs has been performed and compared;looking for the reason that Lemon balm was the best.

Methods for in vitro evaluating antimicrobial activity： A review

In recent years, there has been a growing interest in researching and developing new antimicrobial agents from various sources to combat microbial resistance. Therefore, a greater attention has been paid to antimicrobial activity screening and evaluating methods. Several bioassays such as disk-diffusion, well diffusion and broth or agar dilution are well known and commonly used, but others such as flow cy- tofluorometric and bioluminescent methods are not widely used because they require specified equip- ment and further evaluation for reproducibility and standardization, even if they can provide rapid re- sults of the antimicrobial agent＇s effects and a better understanding of their impact on the viability and cell damage inflicted to the tested microorganism. In this review article, an exhaustive list of in vitro antimicrobial susceptibility testing methods and detailed information on their advantages and limita- tions are reported.

Synergistic effect between cryptotanshinone and antibiotics in oral pathogenic bacteria

Cryptotanshinone (CT), a major tanshinone of medicinal plant Salvia miltiorrhiza Bunge, demonstrated effective in vitro antibacterial activity against all oral bacteria tested in this experiment. The antibacterial activities of CT against oral bacteria were assessed using the checkerboard and time-kill methods to evaluate the synergistic effects of treatment with ampicillin or gentamicin. The CT was determined against oral pathogenic bacteria with MIC and MBC values ranging from 0.5 to 16 and 1 to 64 μg/mL;for am- picillin from 0.0313 to 16 and 0.125 to 32 μg/mL;for gentamicin from 2 to 256 and 4 to 512 μg/mL respectively. The range of MIC50 and MIC90 were 0.0625 - 8 μg/mL and 1 - 64 μg/mL, respectively. The combination effects of CT with antibiotics were synergistic (FIC index < 0.5) against tested oral bacteria except additive, Streptococcus sobrinus, S. criceti, and Actinobacillus actinomycetemcomitans (FIC index < 0.75 - 1.0). The MBCs were shown reducing ≥4 - 8-fold, indicating a synergistic effect as defined by a FBCI of ≤0.5. Furthermore, a time-kill study showed that the growth of the tested bacteria was completely attenuated after 3 - 6 h of treatment with the 1/2 MIC of CT, regardless of whether it was administered alone or with ampicillin or gentamicin. The results suggest that CT could be employed as a natural antibacterial agent against cariogenic and periodontopathogenic bac- teria.

Combination of Acacetin with Antibiotics against Methicillin Resistant <i>Staphylococcus aureus</i>Isolated from Clinical Specimens

Methicillin-restitant Staphylococcus aureus (MRSA) is very dangerous bacteria and one of the most feared nosocomial germs. In this study, acacetin was evaluated against 20 clinical isolates of MRSA, either alone or in combination with antibiotics. The acacetin exhibited a good activity against isolates MRSA with MICs/MBCs ranged between 10-80/20-160 μg/mL, for ampicillin 64-1024/128-2048 μg/mL, and for oxacillin 8-32/16-64 μg/mL. The combination of acacetin plus oxacillin or ampicillin was reduced by ≥4-fold against isolates MRSA tested, evidencing a synergistic effect as defined by a FICI of ≤0.5. Furthermore, a time-kill study evaluating the growth of the tested bacteria was completely attenuated after 2-5 h of treatment with the 1/2 MIC of acacetin, regardless of whether it was administered alone or with oxacillin (1/2 MIC) or ampicillin (1/2 MIC). In conclusion, acacetin exerted synergistic effects when administered with oxacillin or ampicillin and the antibacterial activity and resistant regulation of acacetin against clinical isolates of MRSA might be useful in controlling MRSA infections.

In vitro assessment of the synergism between extracts of Cocos nucifera husk and some standard antibiotics

Objective: To evaluate the interactions between the crude extracts of Cocos nucifera(C.nucifera) and six front line antibiotics(ampicillin sodium salt, penicillin G sodium,amoxicillin, chloramphenicol, ciprofloxacin and tetracycline hydrochloride), against some bacterial pathogens linked with human infection.Methods: The pulverized husk of C.nucifera was dissolved in 95% n-hexane and extracted using Soxhlet extraction method and sterile distilled water(aqueous).The antibacterial susceptibility of the crude extracts of C.nucifera was tested against environmental and clinical strains(6) obtained from the South African Bureau of Standards(SABS), Vibrio(6) and Listeria pathogens(6).The agar-well diffusion method was used for screening the extracts for their antibacterial activity.The minimum inhibitory concentration and minimum bactericidal concentration of the extracts were determined.Time-kill assay was used to evaluate bactericidal and/or bacteriostatic activity.The synergistic effect of the crude extracts and antibiotics was assessed and evaluated by adopting the checkerboard methods.Results: With the time-kill assay, the highest bactericidal activity was observed on Vibrio fluvialis EL041 with a-5.6 ± 0.2 log_(10)CFU/mL decrease in cell density as a result of the combination of the extracts and chloramphenicol at two-fold minimum inhibitory concentrations.Synergisms using the time-kill assay constituted about 72%, while indifference constituted about 28%.The checkerboard method revealed synergistic interaction in 67% of the combinations, and indifference in 33%.There was no specificity in the observed synergy to a particular class of antibiotics.Conclusions: This investigation suggests the crude extracts of C.nucifera to be a potential broad spectrum antimicrobial compound.Therefore, further study is needed to isolate the pure compounds from these crude extracts.

Antibacterial activity of the ethyl acetate part of Abrus cantoniensis against Staphylococcus aureus

Objective:The aim of this work was to measure the antibacterial activity(against Escherichia coli and Staphylococcus aureus[S.aureus])of the ethyl acetate part of Abrus cantoniensis and assess their potential as medicines.Methods:The experiment was divided into four groups:negative control group[with Mueller-Hinton broth(MHB)],positive control group(with 75%ethanol),blank group(with MHB)and test group(with the ethyl acetate part of Abrus cantoniensis).The antibacterial activities of the extracts were evaluated by the Oxford cup assay and minimum inhibitory concentration(MIC).Time-kill curve experiments,scanning electron microscopy,the content of DNA,RNA and protein were used to study the antibacterial mechanism of the ethyl acetate extract part on the growth and viability of S.aureus.The study procedures were approved by the Animal Care and Use Committee of Xi’an Jiaotong University(approval No.XJTULAC2016-412)on January 22,2016.Results:The ethyl acetate part of Abrus cantoniensis extract exhibited the highest inhibitory activity against the growth of S.aureus with an inhibition zone diameter of 16.4mm and MIC value of 0.5mg/mL.The general activity range of the ethyl acetate part,determined using a time-killing curve,was found to be 0.5mg/mL to 40mg/mL(MIC to 80
MIC).Changes in the scanning electron microscopy images and of DNA,RNA and proteins of S.aureus indicated possible mechanisms of the inhibitory activity of the ethyl acetate part.Conclusion:The ethyl acetate part of Abrus cantoniensis damaged bacterial cell structures,which results in protoplasm leakage,and eventually bacterial cell death.