No, the presence / the absence is the normal phrasing. Which presence? Salmonella's presence.
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HSS Would you also say "indicated presence of salmonella," if you would like to emphasize "presence" as opposed to "absence"?I can't really explain this, but I have the sense (instinct?) that when the presense of X is the normal, expected, and desirable condition, the article may optionally be omitted.