Re: what does this mean?

In short they are saying that the E. coli bacteria are somewhat acid resistant in the first place.  But their ability to survive acidic conditions is more limited in the presence of oxygen and enhanced when placed in an oxygen reduced environment.

Then they tested the effectiveness of various acids held at a pH of 3.2 with oxygen removed to see how much of the bacteria were killed in the cultures after 24 hours at a specific temperature.  They found sulfite was the most effective acid in killing the E.coli while malic acid was the least effective.