Hi John,
I don't think that there is actual superposition happening in double slit experiments, i.e. the particle used taking both paths until a result is obtained. Rather I think that the moving thing is accompanied by an undetectable disturbance which is able to pass through both slits, and cause a wave interference that then affects the path taken by the particle. Leading to an interference pattern if many individual particles are used.
1. An average bacterium is considerably larger than a particle, even a C60 Buckyball. Estimate: 50um to 750um :.1um(micrometer) is a millionth of a meter. Compared to a Buckyball C60 of 1.1nm 1nm (nanometer) is one billionth of a meter. I think that the imperceptible wave interference (that can affect a particle would likely be too small to affect the path taken by the bacterium. Relative scale is important.
2. You also mention airborne bacteria. The double slit experiments are conducted in an airless environment. How would you prevent air movements influencing the path of the bacteria? The bacteria will require a life supporting environment