Re: TSA plates for environmental monitoring
Hi Laura
Prior to weekend store the plates in refrigerator and again incubate the plates (after week end) in optimum temperature. During the refrigerated conditions bacteria will live but growth will not occur.
Regards
S. Subramaniam
While this can be a good idea, make sure that you validate doing so, as the thermal shock of moving from 35 degrees to 2 degrees can kill some bacterial cells, leaving you no viable colony to subculture and identify. If your microflora is predominantly Bacillus species then you should be OK, however if they are Staphs and Micrococci then you may have a problem.
In my experience the instruction for 5 days is a
minimum incubation time, so incubate for seven days inside a polythene bag to preserve humidity (bag will not become microaerophillic there is more than enough oxygen in plate head space). Perform an interim count at 48 to 72 hours, marking the interim count on the plate base, in case you get a swarmer which obscures underlying colonies. Other methods I have seen is an initial incubation period at 35 degrees for 48 hours followed by bacterial count, then a reincubation at 24 degrees (in a polythene bag) for a further five days to enumerate moulds, yeasts and other ambient growers.
Both work fine, but again you need to validate against your microflora and I would suggest a suitable test panel (USP/EP/JP panels are generally acceptable and I think they are now harmoniized which makes a pleasant change)
Hope this helps,
Jimmy