The rapid global expansion of multidrug (MDR) and extensively drug-resistant (XDR)
bacteria reflects the urgent need of a novel course in antibiotic therapy to tackle
infectious diseases such as tuberculosis [1]. Considering the rising numbers of multidrug resistance especially in mycobacteria including the Mycobacterium tuberculosis complex, they are one of the critical global health concerns [2]. Efflux pumps (EP) present one of the key strategies of bacteria to protect themselves
against antimicrobials [3]. We investigated specific isolated flavonoids from Scutellaria species for their antimicrobial activity against the non-pathogenic surrogate models
for Mycobacterium tuberculosis, i. e. Mycobacterium smegmatis mc2 155, Mycobacterium aurum ATCC 23366 and Mycobacterium bovis BCG ATCC 35734. The MICs of the plant compounds against the studied strains were
determined using microbroth dilution and SPOTi- assays [5].
Prior to efflux assays, all compounds tested at sub inhibitory concentrations, were
evaluated for their synergistic effects with ethidium bromide (EtBr) and rifampicin
against M. smegmatis strain. M. smegmatis and M. aurum were further assessed for accumulation of EtBr in the presence and absence of the
plant compounds as putative efflux pump inhibitors (EPIs) including the reference
inhibitors verapamil (VP) and chlorpromazine (CPZ) by detecting efflux activity through
a fluorometric method. Based on the results obtained from our experiments, skullcapflavone
II exerts potent antimycobacterial activity against M. aurum (MIC = 7.8 mg / L) and M. bovis BCG (MIC = 31.25 mg / L) and considerably increases the susceptibility of M. smegmatis to ethidium bromide (MF = 128) and rifampicin (MF = 4).
