mellonella, thereby enhancing the host defense against B. cenocepacia infection. As shown in Fig. 4c, at 10 h postinfection, the four immune-related genes were
either inactive (uninfected larvae treated with DHA) or expressed at very low levels (infected larvae with and without DHA treatment). However, at 21 h postinfection, the mRNAs of gallerimycin, IMPI and lysozyme were found to be induced either in the infected larvae-treated or untreated with DHA. Nevertheless, the total amount of mRNA encoding gallerimycin reached its highest value in the DHA-treated larvae (120-fold). The housekeeping gene actin was used as a reference for relative quantification of mRNA (Fig. 4c). The antimicrobial property of essential SB203580 LCUFAs and their derivatives has been recognized for many years (Desbois & Smith, 2010). In the present study, we have investigated for the first time the in vitro antimicrobial properties of eight different LCUFAs against B. cenocepacia, an emerging pathogen in patients with CF. We observed that of the LCUFAs tested, only three fatty acids have anti-Burkholderia activity,
namely petroselinic acid, DHA and nervonic acid. The differences in growth inhibition most likely correlates with the geometry and position of the carbon-carbon double bonds as well as the carbon chain lengths of the LCUFAs tested (Huang et al., 2010). DHA showed the highest level of growth inhibition, albeit with moderate efficacy (millimolar concentrations) BI 2536 in vivo (Fig. 1). This is consistent with previous published studies that indicate that DHA exhibits a broad spectrum of in vitro antibacterial activity against various Gram-positive and Gram-negative pathogenic bacteria (Shin et al., 2007; Martinez
et al., 2009). The mechanism of action of DHA against B. cenocepacia K56-2 is not known. Possibly, as described Mirabegron for other LCUFAs, DHA primarily affects the integrity of the bacterial plasma membrane, thereby leading to cell damage and cell death (Desbois & Smith, 2010). There are, however, some differences in DHA activity between cell types, whereby DHA has a higher antimicrobial activity against Gram-positive bacteria, which again, probably is a result of structural differences in the cell wall and/or plasma membrane (Shin et al., 2007). To further extend and confirm the in vitro anti-Burkholderia activity of DHA, a panel of 19 isolates representing all 17 Bcc species was tested. Our results indicated that all Bcc isolates were inhibited by 50 mM DHA, although significant differences in the levels of growth inhibition were observed across all species (Fig. 3). No obvious link was observed between DHA and antibiotic or biocide resistance as previously published (Nzula et al., 2002; Rose et al., 2009). The clinical isolate B. cenocepacia J2315 was found to be more susceptible to DHA than other B. cenocepacia strains, yet J2315 was the strain most resistance to meropenem (Nzula et al., 2002). Conversely, strain B.