Effects of Colistin on Surface Ultrastructure and Nanomechanics of Pseudomonas aeruginosa Cells

Abstract

Chronic lung infections in cystic fibrosis patients are primarily caused by Pseudomonas aeruginosa. Though difficult to counteract effectively, colistin, an antimicrobial peptide, is proving useful. However, the exact mechanism of action of colistin is not fully understood. In this study, atomic force microscopy (AFM) was used to evaluate, in a liquid environment, the changes in P. aeruginosa morphology and nanomechanical properties due to exposure to colistin. The results of this work revealed that after 1 h of colistin exposure the ratio of individual bacteria to those found to be arrested in the process of division changed from 1.9 to 0.4 and the length of the cells decreased significantly. Morphologically, it was observed that the bacterial surface changed from a smooth to a wrinkled phenotype after 3 h exposure to colistin. Nanomechanically, in untreated bacteria, the cantilever indented the bacterial surface significantly more than it did after 1 h of colistin treatment (P-value = 0.015). Concurrently, after 2 h of exposure to colistin, a significant increase in the bacterial spring constant was also observed. These results indicate that the antimicrobial peptide colistin prevents bacterial proliferation by repressing cell division. We also found that treatment with colistin caused an increase in the rigidity of the bacterial cell wall while morphologically the cell surface changed from smooth to wrinkled, perhaps due to loss of lipopolysaccharides (LPS) or surface proteins.

Ultrastructural Analysis of the Rugose Cell Envelope of a Member of the Pasteurellaceae Family

“…Thus, based on these observations, it was concluded that convoluted or irregular surfaces were the result of experimental artifacts. Recently, structural changes in bacterial surface morphology upon challenging bacteria with antibacterial agents have been reported (19)(20)(21)47). As an example, the smooth membrane structure of wild-type E. coli develops blebs and wrinkles after exposure to antimicrobial BP100 and pepR peptides, as revealed by AFM of air-dried bacterial samples (19).…”

“…This membrane dependent mechanism of antibacterial action was observed in Pseudomonas aeruginosa after exposure to colistin, an antibacterial peptide (20). This treatment resulted in an originally smooth surface changing to a wrinkled or rugose phenotype (20). Interestingly, a number of Gram-negative bacteria naturally show convoluted or rugose surfaces (22)(23)(24).…”

“…Bacteria may remodel the outer membrane through the synthesis and modification of the lipid and protein content in response to external stresses, which include changes in ionic strength, osmotic pressure, temperature, and the presence of antimicrobial peptides. Dramatic membrane morphological changes have been observed upon treatment with antibacterial agents or peptides (19)(20)(21). This membrane dependent mechanism of antibacterial action was observed in Pseudomonas aeruginosa after exposure to colistin, an antibacterial peptide (20).…”

“…Dramatic membrane morphological changes have been observed upon treatment with antibacterial agents or peptides (19)(20)(21). This membrane dependent mechanism of antibacterial action was observed in Pseudomonas aeruginosa after exposure to colistin, an antibacterial peptide (20). This treatment resulted in an originally smooth surface changing to a wrinkled or rugose phenotype (20).…”

Nanoinformatics and DNA-Based Computing: Catalyzing Nanomedicine

“…Similarly, nanomechanical approaches study the effect of drugs on Pseudomonas aeruginosa, the causative agent of chronic lung infections in patients affected by cystic fibrosis (19).…”