Screening of Chinese medicinal plants for inhibition against clinical isolates of methicillin-resistant Staphylococcus aureus (MRSA)

Synergistic antibacterial and antibiotic effects of bisbenzylisoquinoline alkaloids on clinical isolates of methicillin-resistant Staphylococcus aureus (MRSA)

The antibacterial activity of two bisbenzylisoquinoline alkaloids, tetrandrine (Tet) and demethyltetrandrine (d-Tet), alone and in combination with the antibiotics ampicillin (AMP), azithromycin (AZM), cefazolin (CFZ) and levofloxacin (LEV) against 10 clinical isolates of staphylococcal chromosomal cassette mec (SCCmec) III type methicillin-resistant Staphylococcus aureus (MRSA) was studied. Susceptibility to each agent alone was tested using a broth microdilution method. The chequerboard and time-kill tests were used for the combined evaluations. The minimal inhibitory concentrations/minimal bactericidal concentrations (MICs/MBCs, μg/mL) ranges alone were 64-128/256-1,024 for both Tet and d-Tet. Significant synergies against 90% of the isolates were observed for the Tet/CFZ combination, with their MICs being reduced by 75-94% [fractional inhibitory concentration indices (FICIs) ranged from 0.188 to 0.625], respectively. An additive bactericidal result was also observed for the Tet (d-Tet)/CFZ combination in the time-kill experiments. These results demonstrated that Tet and d-Tet enhanced the in vitro inhibitory efficacy of CFZ. Their potential for combinatory therapy of patients infected with MRSA warrants further pharmacological investigation.

In vitro synergistic interaction of 5-O-methylglovanon and ampicillin against ampicillin resistant Staphylococcus aureus and Staphylococcus epidermidis isolates

5-O-methylglovanon (5-O-MG) is a bioactive compound that was first isolated and characterized from Glycosmis plants. In this study, we found that chemically synthesized 5-O-MG has antimicrobial ability against eleven clinical ampicillin resistant Staphylococcus aureus and S. epidermidis isolates. The MICs of 5-O-MG against the S. aureus and S. epidermidis isolates were 12.5-50 μg/mL and 25-50 μg/mL, respectively. In combination with ampicillin, a synergistic interaction between 5-O-MG and ampicillin against the eleven resistant Staphylococcus isolates was observed, with fractional inhibitory concentration indices of 0.03-0125. Moreover, the anti-staphylococcal activity of 5-O-MG in combination with ampicillin was comparable with that of clavulanic acid in combination with ampicillin. The drug combination had no antagonistic effects when tested against any of the strains. Time-killing assays confirmed the synergy between 5-O-MG and ampicillin (p < 0.01). The combination of these two agents yielded greater than a 2 log(10) cfu/mL decrease in comparison with 5-O-MG or ampicillin alone. These findings suggest that 5-O-MG is a promising compound with the potential for future anti-staphylococcal drug development.

Antifungal, antibacterial and antimycobacterial activity of Entada abysinnica Steudel ex A. Rich (Fabaceae) methanol extract

The purpose of the study was to investigate the antifungal, antibacterial and antimycobacterial properties of methanol extract of Entada abysinnica steudel ex. A. Rich (Fabaceae) leaves used by herbalists from the Lake Victoria region, Kenya. The extract was tested against four strains of mycobacteria (Mycobacterium tuberculosis, Mycobacterium kansasii, Mycobacterium fortuitum, and Mycobacterium smegmatis) using BACTEC Mycobacteria Growth Indicator Tube (MGIT) 960 system and the proportional method. Standard procedures were used to determine the zones of inhibition, minimum inhibitory concentrations (MICs) and minimum bactericidal/fungicidal concentrations (MBCs/MFCs) for Candida albicans, Salmonella typhi, Staphylococcus aureus, Pseudomonas aeruginosa, Escherichia coli, and Klebsiella pneumoniae. The extract showed activity against some mycobacteria strains, especially M. tuberculosis. It also showed strong antimicrobial activity (zones of inhibition were between 9.00 and 14.10 mm) against C. albicans, Sa. typhi, and St. aureus. The extract gave a better zone of inhibition against C. albicans than fluconazole whose zone of inhibition was 13.00 mm. The MICs and MBCs for C. albicans and Sa. typhi were good. The crude extracts were also analyzed for the presence of phytochemicals. Phytochemical screening indicated that the extract most abundantly contained tannins, saponins, and flavonoids. The data suggest that the methanolic leaves extract of E. abysinnica could be a rich source of antimicrobial agents, especially antifungals. The results further show that there is some merit in the use of the plant in alternative medical practices. However, bioassays of isolated compounds are underway and will be reported during subsequent communications.

Antibacterial and synergy of a flavanonol rhamnoside with antibiotics against clinical isolates of methicillin-resistant Staphylococcus aureus (MRSA)

The in vitro antibacterial activity of taxifolin-7-O-α-L-rhamnopyranoside (TR) and its synergy with four conventional antibiotics (ampicillin (AMP), levofloxacin (LEV), ceftazidime (CAZ) and azithromycin (AZM)) against ten clinical isolates of methicillin-resistant staphylococcus aureus (MRSA) were evaluated, respectively. Individual MICs and MBCs were determined by microdilution methods following the CLSI guidelines. Anti-MRSA synergy effects were measured using the chequerboard and time-kill curve tests. MICs/MBCs (μg/ml) ranges were 32-64/64-128 for TR alone against all 10 MRSA isolates. Chequerboard method showed that significant synergies were observed for the TR/CAZ and TR/LEV combinations with FICI ranged 0.187-0.375 and 0.25-0.5, respectively. Some synergy and additivity effects were also observed for TR/AMP and TR/AZM combinations. In the time-kill dynamic confirmation test, synergy results kept by the TR/CAZ combination (2.186 log₁₀ cfu/ml increase in killing), but the TR/LEV combination changed to additivity (1.839 log₁₀ cfu/ml increase in killing). These results demonstrated that TR enhanced the efficacy of CAZ and LEV in vitro, which had potential for combinatory therapy of patients infected with MRSA.

Antibacterial effect (in vitro) of Moringa oleifera and Annona muricata against Gram positive and Gram negative bacteria

Antibacterial effects of aqueous and ethanolic extracts of seeds of moringa (Moringa oleifera) and pods of soursop (Annona muricata) in the concentration of 1:5 and 1:10 in volumes 50, 100, 150 and 200 µL were examined against Staphylococcus aureus, Vibrio cholerae, Escherichia coli (isolated from the organism and the aquatic environment) and Salmonella Enteritidis. Antibacterial activity (inhibition halo > 13 mm) against S. aureus, V. cholerae and E. coli isolated from the whiteleg shrimp, Litopenaeus vannmaei, was detected in aqueous and ethanolic extracts of moringa. E. coli isolated from tilapiafish, Oreochromis niloticus, was sensitive to the ethanolic extract of moringa. The aqueous extracts of soursop showed an antibacterial effect against S. aureus and V. cholerae, but the antibacterial activity by the ethanol extracts of this plant was not demonstrated.

Synergistic effects between aminoethyl-chitosans and beta-lactams against methicillin-resistant Staphylococcus aureus (MRSA)

Two kinds of aminoethyl-chitosans (AEC), AEC90 and AEC50, which had degrees of deacetylation of 90% and 50%, respectively, were prepared and their synergistic effects in combination with beta-lactams including ampicillin, penicillin, and oxacillin against two standard methicillin-resistant Staphylococcus aureus (MRSA) strains and twelve clinical isolated MRSA strains were investigated. When AECs and beta-lactams were combined, synergistic effects were observed with fractional inhibitory concentration (FIC) indices of 0.252-0.508, and the MICs of beta-lactams in the presence of AECs were dramatically reduced.

Betulin-derived compounds as inhibitors of alphavirus replication

This paper describes inhibition of Semliki Forest virus (SFV) replication by synthetic derivatives of naturally occurring triterpenoid betulin (1). Chemical modifications were made to OH groups at C-3 and C-28 and to the C-20-C-29 double bond. A set of heterocyclic betulin derivatives was also assayed. A free or acetylated OH group at C-3 was identified as an important structural contributor for anti-SFV activity, 3,28-di-O-acetylbetulin (4) being the most potent derivative (IC50 value 9.1 microM). Betulinic acid (13), 28-O-tetrahydropyranylbetulin (17), and a triazolidine derivative (41) were also shown to inhibit Sindbis virus, with IC50 values of 0.5, 1.9, and 6.1 microM, respectively. The latter three compounds also had significant synergistic effects against SFV when combined with 3'-amino-3'-deoxyadenosine. In contrast to previous work on other viruses, the antiviral activity of 13 was mapped to take place in virus replication phase. The efficacy was also shown to be independent of external guanosine supplementation.