Antibacterial and synergistic activity of a new 8-hydroxyquinoline derivative against methicillin-resistant Staphylococcus aureus

Aim: To evaluate the antibacterial and synergistic effect of a new 8-hydroxyquinoline derivative (PH176) against MRSA. Materials & methods: PH176 activity was determined by broth microdilution against 38 Staphylococcus aureus clinical isolates. The antibacterial and synergistic effects with oxacillin and nitroxoline were evaluated by time-kill assays to five MRSA isolates. Toxicity was evaluated by in vitro and ex vivo models. Results: The MIC₅₀ and MIC₉₀ of PH176 were 16 and 32 μg/ml, respectively. The PH176 and nitroxoline led to a reduction in colony count for four isolates and the combination of PH176 and oxacillin acted synergically for three isolates. Furthermore, PH176 was determined to be noncytotoxic/nonirritant. Conclusion: These results demonstrate that PH176 has revealed promising results to be a potential candidate to treat MRSA infections.

The calculation of positive ancl negative spin densities in aromatic free radicals

A simple method of calculating the unpaired π electron spin density is proposed which equates the unpaired spin density to the difference between a density of n-1 electrons of a spin and a density of n electrons of β spin. The α spin density is found from an SCF-Pariser-Parr type calculation for 2(n+l) electrons in n + 1 closed shells and the β spin density from a calculation on 2n electrons in n, closed shells. Positive and negative spin densities are found which are in excellent agreement with experiment. These results are compared to spin densities calculated by other methods, and an improvement is noted in the representative cases considered.