Abstract
Isothiocyanates (ITCs) derived from cruciferous plants reveal antibacterial activity, although detailed mechanism is not fully elucidated. Recently it has been reported that ITCs induce the stringent response in Escherichia coli strains. The aim of this work was to determine whether two isothiocyanates, sulforaphane (SFN) and phenethyl isothiocyanate (PEITC), similarly as in E. coli induce stringent response in Bacillus subtilis, model Gram(+) bacterium, and test their potency against a panel of clinical isolates belonging to Gram(+) or Gram(−) groups. Minimal inhibitory concentrations were determined as well as effect of ITCs on membranes integrity, synthesis of DNA, RNA and stringent response alarmones was assessed. SFN and PEITC are effective against B. subtilis and bacterial isolates, namely E. coli, K. pneumonia, S. aureus, S. epidermidis and E. faecalis. Interestingly, in B. subtilis and E. faecalis the inhibition of growth and nucleic acids synthesis is independent of ppGpp accumulation. In bacteria, which do not induce the stringent response in the presence of ITCs, membrane integrity disruption is observed. Thus, ITCs are effective against different pathogenic bacteria and act by at least two mechanisms depending on bacteria species.
Highlights
Over the last few decades infections caused by bacteria resistant to commonly used antibiotics became one of the major health care problems
We reported that the antibacterial activity of ITCs against enterohaemorrhagic E. coli relies on the stringent response induction which is connected with massive production of (p)ppGpp, alarmones responsible for, among others, growth retardation and inhibition of stable RNA synthesis or Shiga toxin-converting phage development[15,16]
We show that SFN and phenethyl isothiocyanate (PEITC) inhibit growth of other bacteria, including clinical isolates of E. coli, K. pneumoniae, S. aureus, S. epidermidis, E. faecalis
Summary
Over the last few decades infections caused by bacteria resistant to commonly used antibiotics became one of the major health care problems. It has been shown that PEITC, SFN, AITC, benzyl isothiocyanate (BITC), PITC and isopropyl isothiocyanate (IPRITC) efficiently inhibited growth of Shiga toxin harboring E. coli strains which was accompanied by an inhibition of the lytic development of Shiga toxin-converting bacteriophage and stx gene expression. These effects were mediated by alarmones of the stringent response[15,16]
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