Antimicrobial Activity of Flavonoids against Extended-Spectrum β-Lactamase (ESβL)-Producing Klebsiella pneumoniae

Purpose: In the present study, six flavonoids (5,7-dimethoxyflavanone-4'-O-beta-D-glucopyranoside, 5,7-dimethoxyflavanone- 4'-O-[2 ''-O-(5'''-O-trans-cinnamoyl)-beta-D-apiofuranosyl]-beta-D-glucopyranoside, naringenin-7-O-beta-D-glucopyranoside, 5,7,3'-trihydroxy-flavanone-4'-O-beta-D-glucopyranoside, rutin, and nicotiflorin) isolated from Galium fissurense, Viscum album ssp. album and Cirsium hypoleucum were screened against extended-spectrum beta-lactamase producing multidrug-resistant (trimetoprime-sulphametoxazole, sulbactam-ampicillin, clavulonate-amoxicilin, ceftriaxon, cefepime, imipenem, ceftazidime, tobramicin, gentamicin, ofloxacin, ciprofloxacin) bacteria Klebsiella pneumoniae (ES beta Ls). Methods: We performed susceptibility testing according to the Clinical and Laboratory Standards Institute (CLSI, formerly NCCLS) and used an inhibition endpoint for determination of the minimum inhibition concentrations (MICs). Results: All the flavonoids showed in vitro antimicrobial activity against all the isolated strains of K. pneumoniae similar to the control antibacterial (ofloxacin) at the concentrations of 32 - 64 mu g ml(-1); another control, ampicillin, had no activity. Since, ES beta L-producing strains are known to be resistant to all beta-lactam antibiotics, our results fall notably within the concentration range for antimicrobial activity. Conclusion: To the best of our knowledge, this is the first report of the study of the activity of these flavonoids against (ES beta L)-producing K. pneumoniae and may throw light to the low-toxicity of flavonoids, and their potentials for developing therapies for infections caused by ES beta L-producing bacteria in the future. Further work is under investigation to identify their precise antibacterial mechanism.