Tailing-off curve? (and PCR)

This time the contamination issue is resolved. However, the growth curve reveals in another strange way - the curves are tailing off which they're supposed to be level off? What I can figure out in my mind is two possibility - not enough dilution or too short incubation time. Kerry and Peter think it may probably because Salmonella typhimurium are switching their nutrition requirment from protein or sugar to other component, so that they're still keep growing. By the way, Peter finally gave me a green light to prosecute PCR after discussion with Ray. Hmmm...but I didn't realize that the price of primers are the same as (or at least not too far away from) in Taiwan. It's just NZ$ 20...I'd been expecting that it'd be much more expensive in NZ... Anyway, now I'll have to find appropriate primer sequences for identify the species. Today's growth curve setting: 37C, 48 cycles (24 hrs), dilute from 10^-2.