E. Cefalì, S. Patanè, A. Arena, G. Saitta, S. Guglielmino,* S. Cappello,* M. Nicolò,* M. Allegrini

INFM and Department of Physics; *Department of Microbiological, Genetic, and Molecular Science, University of Messina, Messina; INFM and Department of Physics, University of Pisa, Pisa, Italy

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Summary: The morphologic and structural variations suffered by cells of a population of Pseudomonas aeruginosa ATCC 27853 under stress conditions were investigated by using scanning near-field optical microscopy. The analysis of the images, supported by microbiological data, showed that the bacteria evolved from the initial distribution of rod-shaped cells of standard size to a population with structural and morphologic modifications. The detection of variations in the optical reflectivity over a subwavelength scale (¾ 100 nm), combined with the concurrently acquired topographical signal, allowed the visualisation of rod-shaped bacteria going towards a lytic process and entire “U”-shaped cells. In the latter cells, which derived from a morphology refolding of rod bacteria, cellular matter seemed to rearrange itself to attain a coccoid stress resistant form, responsible for the residual viability of the population.

Key words: near-field optical microscopy, stress-induced morphology variation

PACS: 07.79.-v, 07.79.Fe, 87.64.Dz