The emerging problem of intermediate resistance to the glycopeptide antibiotic vancomycin in Staphylococcus aureus isolates has raised concern, since few therapeutic options remain for treatment. The antibiotics kill gram-positive bacteria by interfering with the synthesis of peptidoglycan on the bacterial surface. To identify any cell-surface alterations that correlated with increased resistance, MRSEC researchers Hahm and Sibener, working in conjunction with infectious disease experts Prof. Robert Daum and Dr. Susan Boyle-Vavra of the UC Pritzker Medical School, imaged the bacterial particles with AFM (A).
High-resolution images showed that resistant strains of the bacteria had shallow grooves on their surfaces (B) but that susceptible strains had deeper grooves and often a larger number of surface features (C). While the mechanistic significance of these phenotypic differences are not clear, the use of AFM imaging has provided a new opportunity for identifying and then understanding modes of resistance. Current work is applying this approach to other strains of Staphylococcus aureus to further characterize features that correlate with pathogenicity.
Atomic force microscopy imaging can be used to discern morphological details in the cell wall structure of infectious bacteria, including important phenotypic differences between some mutant strains of drug-resistant as compared to drug-susceptible bacteria. Further development may lead to improved understanding of the mechanism of antibiotic resistance in such organisms.
[Structural and topological differences between a glycopeptide-intermediate resistant clinical strain and vancomycin-susceptible strains of Staphylococcus aureus revealed by atomic force microscopy, Susan Boyle-Vavra, Jongin Hahm, S. J. Sibener, and Robert S. Daum, Antimicrobial Agents and Chemotherapy 44 3456-3460 (2000).]
by Seth B. Darling