Introduction

Atomic force microscopy (AFM) was used as a novel approach to achieve enhanced characterization of the three-dimensional fine structure and topology of cocci from Staphylococcus aureus. To gain insight into the mechanism of resistance to vancomycin in recently emerging glycopeptide-intermediate S. aureus (GISA), strains were examined that were either susceptible or resistant to glycopeptides and/or methicillin. The surfaces of cocci of a vancomycin-susceptible control strain, RN4220, contained a single circumferential ring located at the equatorial plane corresponding to the septal plane of division. A single ring was also present on cocci of a methicillin-resistant (MR) vancomycin-susceptible control strain. In contrast, the cocci of an MR-GISA clinical isolate had two nearly parallel circumferential rings separated by a gap of intervening cell wall material. Similar to the GISA strain, cocci of a vancomycin-susceptible revertant strain derived from strain NJ had two nearly parallel rings.

When grown in the presence of a sub-inhibitory concentration of vancomycin, cocci of all three vancomycin-susceptible strains were induced to produce additional ring-like structures in addition to the primary ring or rings present in the untreated strain. In contrast, cocci of the GISA strain did not produce an additional (third) ring when grown in the presence of vancomycin. The topological feature that best distinguished the vancomycin-susceptible strains from the GISA isolate was a shallower depth of the groove that formed the circumferential ring of the vancomycin-susceptible strains. Also, the depth of the rings increased considerably when cells were grown in the presence of vancomycin in all strains tested. AFM has therefore allowed us to discriminate between cocci of vancomycin-susceptible strains and those of a typical GISA strain. This study demonstrates the utility of using AFM to visualize bacterial cell surface topology and in studying the effects of cell wall active agents on bacterial cells.

* This research is the result of a new collaborative effort involving researchers in both the Biological Sciences (BSD) and Physical Sciences (PSD) Divisions of UC:

	Department of Pediatrics: Dr. Susan Boyle-Vavra and Prof. Robert S. Daum
	Dept. of Chemistry & The James Franck Institute: Dr. Jongin Hahm and Prof. Steven J. Sibener The biological imaging is part of the doctoral dissertation of J. Hahm

Recent Results

For a graphic showing results for the New Jersey strain, click here.

For a graphic showing results for the RN4220 strain, click here.

References

86. "Structural and topological differences between a glycopeptide-intermediate resistant clinical strain and vancomycin-susceptible strains of Staphylococcus aureus revealed by atomic force microscopy"

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