## 2 Results
### MICs vs. Cystic Fibrosis Isolates
\begin{table}
\begin{tabular}{l c c c c} \hline \hline
**Strains** & \multicolumn{3}{c}{**MIC (\(\upmu\)g/mL)**} \\ \cline{2-5} **(Colonial Morphology or Genomovar)** & **1018** & **LL-37** & **1037** & **Polymyxin B** \\ \hline _P. aeruginosa_ PA01 & 16 & 32 & 304 & 2 \\ _P. aeruginosa_ PA14 & 16 & 32 & 304 & 2 \\ _P. aeruginosa_ 3195 (Classic) & 16 & 64 & 304 & 2 \\ _P. aeruginosa_ C2773 (Classic) & 16 & 256 & 152 & 4 \\ _P. aeruginosa_ 1172 (Classic) & 16 & \(>\)128 & 304 & 2 \\ _P. aeruginosa_ 7632 (Classic) & 16 & 256 & 304 & 2 \\ _P. aeruginosa_ 3330 (Classic) & 16 & \(>\)128 & 304 & 2 \\ _P. aeruginosa_ 4020 (Classic) & 16 & \(>\)128 & 304 & 2 \\ _P. aeruginosa_ C4276 (Classic) & 32 & 256 & 608 & 2 \\ _P. aeruginosa_ 2631 (Classic) & 32 & \(>\)256 & 608 & 4 \\ _P. aeruginosa_ C4278 (Mucoid) & 16 & \(>\)256 & 304 & 2 \\ _P. aeruginosa_ 4608 (Mucoid) & 32 & \(>\)128 & 304 & 2 \\ _P. aeruginosa_ 2639 (Mucoid) & 32 & \(>\)128 & 608 & 2 \\ _P. aeruginosa_ 7633 (Entire) & 16 & \(>\)128 & 304 & 2 \\ _P. aeruginosa_ 2955 (Dwarf) & 50 & - \({}^{\rm a}\) & - & - \\ _B. multivorans_ D2661 (Genomovar II) & \(>\)512 & \(>\)512 & \(>\)608 & \(>\)128 \\ _B. cenocepacia_ 4813 (IIIa) & \(>\)256 & \(>\)256 & \(>\)608 & \(>\)128 \\ _B. cenocepacia_ C5424 (IIIa) & 128 & \(>\)256 & \(>\)608 & \(>\)128 \\ _B. cenocepacia_ CEP0055 (IIIb) & 128 & \(>\)512 & \(>\)608 & \(>\)128 \\ _B. cenocepacia_ CEP509 (IIIb) & \(>\)256 & \(>\)512 & \(>\)608 & \(>\)128 \\ _B. stabilis_ C6061(IV) & 64 & \(>\)512 & 304 & \(>\)128 \\ _B. dolosa_ CEP0021(VI) & \(>\)256 & \(>\)512 & \(>\)608 & \(>\)128 \\ _B. ambifaria_ CEP0996 (VII) & 64 & \(>\)512 & \(>\)608 & \(>\)128 \\ \hline \hline \end{tabular} \({}^{\rm a}\) Means not done.  
\end{table} 
Table 1: Peptide 1018 demonstrated weak activity _vs._ planktonically-grown _P. aeruginosa_ cystic fibrosis strains and no activity _vs. B. cepacia_ complex cystic fibrosis isolates. All minimum inhibitory concentration (MIC) assays were performed at least three times. For comparison we included the previously studied _P. aeruginosa_ (non-cystic fibrosis) wild type strains PAO1 and PA14 and _B. cenocepacia_ 4813 [22], as well as showing results for two previously described anti-biofilm peptides (LL-37 [18] and 1037 [21]) and the cationic lipopeptide polymyxin B. Different _Burkholderia_ genomovars denote strains which are phylogenetically differentiable but phenotypically indistinguishable. _Burkholderia multivorans_ (genomovar II), genomovar III (divided into two _recA_ clusters, III-a and III-b, _Burkholderia stabilis_ (genomovar IV), _Burkholderia dolosa_ (genomovar VI), _Burkholderia ambifaria_ (genomovar VII). Consistent with previous studies [22; 32], _Burkholderia_ was confirmed to be intrinsically resistant to antimicrobial peptides and polymycin B by the MIC assays (Table 1). Only peptide 1018 was able to affect any _Burkholderia_ planktonic cells, demonstrating relatively high MICs of 64-128 \(\mu\)g/mL _vs._ five out of the total of 11 known genomovars. Even peptides known to exhibit very potent direct planktonic antimicrobial activity (HHC-10 and HHC-36) [33] were found to be inactive against planktonic cells of _Burkholderia_ strains (MIC \(>256\)\(\mu\)g/mL).