Escherichia coli and Staphylococcus aureus response to sinusoidal mechanical vibrations

Growth regulation in microorganisms has relevance in many areas like pharmaceutical, biomedical, agricultural, food industry etc. Despite nutrients, CO2, glucose, etc. the external environment plays a crucial role in growth regulation. In this study, we report the effect on the growth and size of E. coli (gram-negative) and S. aureus (gram-positive) bacteria subjected to sinusoidal vibrations. The active cultures of the bacterium with optical density O.D. (λ= 610 nm): 1 (≈ 1 × 10 6 cells) were placed on the vibration platform (electrodynamic shaker) and subjected to sinusoidal vibration for 1, 5, 10, and 20 Hz frequency of amplitude 2 mm and 10-minute duration. These cultures were grown in an orbital shaker incubator until they reached the stationary phase. During the growth phases the bacterium yield was measured from O.D. and also estimated from the colony count on agar plate. The bacterial yield shows a linear dependence on vibration frequency. At 20 Hz, enhancement in E. coli and S. aureus occurs from 213 to 455 and 710 to 3500, respectively. SEM revealed the morphological changes. Rod-shaped E. coli shows an increase in length measuring from 1.8 ± 0.3 to 2.2 ± 0.4 µm, and a decrease in diameter, from 0.7 to 0.5 µm. The size of spherical S. aureus bacteria remains unchanged. Vibrational stresses on bacterial cells were modelled using Ansys 14.0 software. From this, it is revealed that, external sinusoidal mechanical vibration within the frequency range (1-20 Hz) is an effective technique to promote cell division and progression in bacterial growth. • Growth enhancement has been found in Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) subjected to sinusoidal mechanical vibration. • Compared to E. coli , the rate of replication and cell division in S. aureus bacteria is maximal. • Elongation in vibration-exposed E. coli is observed. However, no alteration in the morphology of S. aureus is observed in Scanning Electron Microscopy images. • Vibration stress on bacteria has been modelled through Ansys Software.