Do mutations in one bacterial strain have the same effect in other strains within the same species?
Different strains of the same species have differents genotypes (ie different alleles and therefore express different proteins).So if your protein A in strain 1 has some effect, it could have the same effect in strain 2, but not necessarily.
Indeed lets imagine that protein A interact with protein B in strain 1 to produce an effect. If protein B is absent in strain 2, or different, protein A will have no effect. My point is if you have a mutation in one strain, the same mutation would not necessarily have the same effect (although it is very likely) in an another strain beacause both strain don't express the same proteome.