listeria and salmonella

[shahbaz]

i was testing a food sample for the presence of the food poisoning bacteria listeria and salmonella. however i was only going to incubate the samples for 48hours but the samples were left in for 72hours instead!! i was wondering that will this increase in time difference have had had an effect on the presence of the pathogens since none was detected on the tuna sample?

[factor-fiction]

Is this a cleverly disguised homework question?
There's a site here which may be a starting point but I'm sure there's loads of info on the web.http://www.laboratorytalk.com/news/app/app119. html
This site suggests 24-48 hours is good and traditionally samples are left for 5-7 days, so I'm not sure another 24 hours is significant. Have you got any text books on this?.

[theprof]

As factor30 implies, this is pretty fundamental stuff and you should know the answer yourself.

Check your course notes.