That is potential energy.
Unit for x - the change in the spring length:
x = [ m ]
PE s = 1/2 k x²
[ kg m² / s² ] = 1/2 k * [ m² ] /: m²
k = [ kg / s² ]
Answer: The unit for spring constant k is kg/ s²
The effector strain of bacteria is that the bacteria would colonize on the teeth and help prevent the child from developing cavitie