Figure 1.
Species-selective antibacterial peptide-PNAs in axenic and two-species mixed culture.
E. coli (dark grey), K. pneumoniae (white) and S. Typhimurium (light grey). All cultures were incubated for 16 hrs. A) axenic cultures of the species were treated with E. coli- specific Ec1000 at 3.2 µM, K. pneumoniae-specific Kp0001 at 3.2 µM and S. Typhimurium-specific Se0001 at 2.0 µM. Asterisks indicate species-selective growth inhibition of E. coli, K. pneumoniae and S. Typhimurium respectively. B) Two-species mixed cultures treated with peptide-PNAs as above. The control cultures show the relative proportion of the two species without treatment, the two treatments to the left of the control represent the same mixed culture treated with a peptide-PNA. Black arrows indicate non species-selective growth inhibition of S. Typhimurium by Ec1000. Error bars are standard error for biological replicates (n = 3).
Table 1.
Properties of peptide-PNAs used in this study.
Table 2.
PNA binding site analysis in target species.
Figure 2.
Species-selective antibacterial peptide-PNAs in three-species mixed culture.
B. subtilis (dark grey), K. pneumoniae (white) and S. Typhimurium (light grey) in mixed culture were separately treated with Ec108 at 3.5 µM, Kp0001 or Se0001 at 4.5 µM or by combined treatment of Kp0001 and Se0001 both at 4.5 µM. All cultures were incubated for 16 hrs. Selective inhibition of either K. pneumoniae or S. Typhimurium individually or together, achieved with the peptide-PNAs, could not theoretically be achieved with any combination of the twenty known antimicrobial compounds tested in this study. Error bars as above.
Figure 3.
S. Typhimurium-selective growth inhibition.
Peptide-PNA Se0002 was designed to target the −5 to +5 region of the translational initiation region (TIR) of ftsZ in S. Typhimurium. Se0002 has 2 base pair mismatches in the TIR of ftsZ in E. coli. (A) Growth curve analysis of Se0002 in pure culture. E. coli growth in the presence of 1.25 µM Se0002 (solid line) was identical to that of untreated controls (not shown). S. Typhimurium growth was inhibited in the presence of 1.25 µM of Se0002 (dotted line) relative to the untreated control (dashed line). Growth in the treated samples after 10 hrs was not due to resistance (see text for details). (B) Mixed cultures of GFP-labeled S. Typhimurium AC02 and DsRed-labeled E. coli AC01 were treated with 1.25 µM Se0002; and imaged by fluorescence microscopy after 6 hrs of incubation. The filamentous growth phenotype was only observed in S. Typhimurium AC02 and is consistent with silencing of ftsZ expression.
Table 3.
Bacterial strains used in this study.