Step 1: Understanding the Concept:
Power ultrasound (typically \(20\text{--}100\text{ kHz}\)) is an advanced non-thermal preservation technology that inactivates microorganisms through acoustic cavitation.
Cavitation generates highly intense localized shear forces, micro-jets, and shockwaves that mechanically disrupt bacterial cell walls and membranes.
Step 2: Detailed Explanation:
The sensitivity of bacteria to ultrasound-induced mechanical shear forces is highly dependent on their cell wall structure, size, and physical shape:
1. Rod-shaped bacteria (Bacilli) (A): Because of their elongated, cylindrical geometry, they possess a larger surface-area-to-volume ratio and are structurally more asymmetric. This shape makes them highly susceptible to bending stresses, mechanical shear, and shockwaves generated by collapsing cavitation bubbles. Thus, they are more sensitive and easily inactivated.
2. Cocci-shaped bacteria (Spherical) (B): Their spherical shape distributes mechanical pressure symmetrically and uniformly, providing superior structural strength and resistance to shear stress.
3. Spores (C): Bacterial endospores possess highly thick, complex, and protective spore coats, making them extremely resistant to ultrasound inactivation unless combined with high heat and pressure (manothermosonication).
Therefore, rod-shaped bacteria are much more sensitive to ultrasound treatment than spherical cocci or endospores.
Step 3: Final Answer:
Thus, Rod-shaped bacteria are more sensitive to ultra sound inactivation.