A study of the antimicrobial activity of selected synthetic and naturally occurring quinolines

The antimicrobial activities of 60 naturally occurring and synthetic quinolines were studied. The quinolines were organised into seven structural subgroups and, using an in-house microtitre assay, were tested against a range of Gram-positive and Gram-negative bacteria, including a hospital isolate of meticillin-resistant Staphylococcus aureus (MRSA). The quinolines exhibiting good bioactivity [i.e. low minimum inhibitory concentration (MIC)] against two S. aureus strains were then assessed for their antimicrobial activity against a range of eight clinically isolated MRSA strains. The study showed that 30 of the tested compounds displayed antimicrobial activity, mostly against Gram-positive bacteria. The effects of substituent groups on the bioactivity of these quinolines have also been discussed. The quinoline 4-hydroxy-3-iodo-quinol-2-one (11) exhibited significant antimicrobial activity, being active against the MRSA clinical isolates with MIC values comparable with the antibiotic vancomycin used in the treatment of MRSA infections. In particular, 4-hydroxy-3-iodo-quinol-2-one (11) showed MIC values of 0.097 μg/mL against an Irish hospital MRSA-1 strain and 0.049 μg/mL against a distinct MRSA strain as well as a non-typeable MRSA strain.