Mechanical properties of Salmonella typhimurium and Listeria monocytogenes bacteria

Salmonella typhimurium and Listeria monocytogenes bacteria, which are two important bacteria used for bacterial therapy purposes in order to limit tumor growth, are studied. Mechanical specifications of the bacteria obtained applying nanoindentation with the use of atomic force microscopy (AFM) are reported. The results show that Salmonella typhimurium bacteria have a greater elastic modulus, but smaller adhesion than Listeria monocytogenes bacteria. The elastic modulus of the AFM extension stroke is larger than that of the retraction stroke. The resonant frequencies and amplitudes of the frequency response function of the AFM beam's vertical movements with two bacteria as samples are investigated using the finite element method. The results show that an increase in the elastic modulus of the sample raises the resonant frequency; therefore, the resonant frequency of Salmonella typhimurium bacteria is greater than that of Listeria monocytogenes bacteria. The results obtained by the finite element method and experimental techniques are found to be in good agreement.