title: Atomic force microscopy of bacteria reveals the mechanobiology of pore forming peptide action.
abstract: Time-resolved AFM images revealed that the antimicrobial peptide (AMP) caerin 1.1 caused localised defects in the cell walls of lysed Klebsiella pneumoniae cells, corroborating a pore-forming mechanism of action. The defects continued to grow during the AFM experiment, in corroboration with large holes that were visualised by scanning electron microscopy. Defects in cytoplasmic membranes were visualised by cryo-EM using the same peptide concentration as in the AFM experiments. At three times the minimum inhibitory concentration of caerin, 'pores' were apparent in the outer membrane. The capsule of K. pneumoniae AJ218 was unchanged by exposure to caerin, indicating that the ionic interaction of the positively charged peptide with the negatively charged capsular polysaccharide is not a critical component of AMP interaction with K. pneumoniae AJ218 cells. Further, the presence of a capsule confers no advantage to wild-type over capsule-deficient cells when exposed to the AMP caerin.
authors.affiliation: School of Chemistry, The University of Melbourne, VIC 3010, Australia.
authors.forename: Anna
authors.initials: A
authors.lastname: Mularski
authors.affiliation: Department of Microbiology and Immunology, The Peter Doherty Institute for Infection and Immunity, The University of Melbourne, VIC 3010, Australia.
authors.forename: Jonathan J
authors.initials: JJ
authors.lastname: Wilksch
authors.affiliation: Advanced Microscopy Unit, Bio21 Molecular Science and Biotechnology Institute, The University of Melbourne, VIC 3010, Australia.
authors.forename: Eric
authors.initials: E
authors.lastname: Hanssen
authors.affiliation: Department of Microbiology and Immunology, The Peter Doherty Institute for Infection and Immunity, The University of Melbourne, VIC 3010, Australia.
authors.forename: Richard A
authors.initials: RA
authors.lastname: Strugnell
authors.affiliation: School of Chemistry, The University of Melbourne, VIC 3010, Australia.
authors.forename: Frances
authors.initials: F
authors.lastname: Separovic
mesh_terms: D000595:Amino Acid Sequence; D001419:Bacteria / Q000378:metabolism* / Q000648:ultrastructure; D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism*; D020285:Cryoelectron Microscopy; D018625:Microscopy, Atomic Force; D008855:Microscopy, Electron, Scanning; D008969:Molecular Sequence Data; D010455:Peptides / Q000737:chemistry / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D010455:Peptides
keywords: Antimicrobial peptide; Atomic force microscopy; Caerin; Capsular polysaccharide; Klebsiella pneumoniae; Melittin; Membrane interaction