In the absence of EDTA, none of the bacteriocins showed activity toward the Gram-negative bacteria, as the reduction in CFU was <1 log unit (data not shown). Similarly, when cells were treated with just 20 mM EDTA in

cell buffer (no bacteriocin), the reduction in CFU was typically <1.5 log units (see Fig. 2). Figure 2a illustrates the effects of the bacteriocin–EDTA treatments on the cells of E. coli DH5α. Nisin, gallidermin and CclA inhibited growth in a concentration-dependent manner. At 50 μM, nisin completely inhibited Selleck KU-60019 growth as no viable cells were found on any of the plates (>5.5 log reduction in growth). SubA showed an effect only at high concentrations. There was no reduction of growth when cells were treated with either CbnBM1 or PisA, regardless of the concentration (log reduction <1). The results of the bacteriocin–EDTA

treatments against P. aeruginosa ATCC 14207 are shown in Fig. 2b. CclA exhibited the most drastic effect, with the complete inhibition of growth at concentrations of 12.5 and 25 μM as no viable cells were detected (>5.6 log reduction in growth). Similarly, gallidermin completely inhibited the growth of the bacterium at concentrations of 25 and 50 μM (>5.6 log reduction in growth). Nisin and PisA also reduced growth, with log reductions comparable to each other. CbnBM1 and SubA displayed marginal effects, as inhibition of growth was only observed at higher bacteriocin concentrations. The results of the bacteriocin–EDTA treatments on the growth of S. Typhimurium ATCC 23564 are depicted in Fig. 2c. Only nisin and gallidermin inhibited the growth of the bacterium. Z-VAD-FMK purchase CclA, CbnBM1, PisA and SubA had no effect on growth (log reduction <1). To determine whether EDTA interfered with the antimicrobial activity of SubA (to explain the lack of effect of SubA at low concentrations), an identical set of experiments against a Gram-positive organism (L. lactis ssp. cremoris HP), which is sensitive to SubA, was performed (data not shown). Without EDTA, SubA significantly inhibited the growth of the bacterium (log reduction of 3.3 at 12.5 μM SubA). However,

in the presence of EDTA, SubA had only a marginal effect on growth (log reduction of 1.2 at 12.5 μM SubA), suggesting Metalloexopeptidase that EDTA reduced the killing effect of SubA. In this study, three bacteriocins produced by C. maltaromaticum UAL307 (CclA, CbnBM1 and PisA) were evaluated for activity against Gram-negative bacteria and compared with the activity of the lantibiotics nisin and gallidermin, and the circular bacteriocin SubA. In the absence of EDTA, none of the bacteriocins significantly reduced the growth of E. coli DH5α, P. aeruginosa ATCC 14207 or S. Typhimurium ATCC 23564. However, in combination with EDTA, each bacteriocin displayed a killing effect toward at least one Gram-negative strain in a concentration-dependent manner.