Atomic force microscopy investigation of phage infection of bacteria

Atomic force microscopy (AFM) was used to study the process of infection of bacterial cells by bacteriophages, for which purpose experimental protocols were elaborated. Three types of bacteriophages were characterized with AFM and transmission electron microscopy (TEM). Bacteriophage interaction with cells was studied for three bacterial hosts: Gram-negative Escherichia coli 057 and Salmonella enteritidis 89 and Gram-positive Bacillus thuringiensis 393. Depending on the phase of lytic cycle, different cell surface changes are observed in AFM images of infected cells in comparison with intact cells: from phage adsorption on the cells and flagella to complete lysis of the cells, accompanied by the release of a large number of newly formed phages. Control experiments (cells without phages and cells with nonspecific phages) did not reveal any surface changes. Penetration of phages inside obligate aerobe Bacillus thuringiensis was shown to be oxygen-dependent and required aeration in laboratory conditions. Our results show great potential of using AFM for numerous fundamental and applied tasks connected with pathogen-host interaction.