The pseudomonas aeruginosa isolates in my mac plates are very dry. Can u plz suggest me a method to make them grow again normally. Will taking more culture from the old plate(dry) and streaking it in a new Mac plate help the bacteria to grow normally ?
If not then please suggest any other method
Dear Arnav,
Restreaking from an old dry colony may allow you to recover your strain, but there are two issues you need to keep in mind.
First, colonies stored on agar plates (or even slants) will often pick up contamination which may not be obvious when you re-streak onto fresh medium, and you need to be mindful that the colonies that appear show the correct colony morphology expected for your strain, otherwise you may pick a contaminant and start work with that. For this reason, I'd suggest using a pseudomonas-selective growth medium (Pseudomonas selective agar - PSA - or King's A or B agar) rather than Mac agar which is normally used for for enteric bacteria.
Second, bacteria growing in a colony on a plate, even for a few days, have the chance to accumulate mutations during every replication cycle - and over a few days, bacteria can go through many generations. This means that strains poorly adapted to growth on agar may mutate and new lineages selected which may have lost important phenotypes you are interested in. We work with Pseudomonas fluorescens SBW25 and a particular mutant known as the Wrinkly Spreader. In a 3-day colony of WS, more than 50% of the cells are revertants (wild-type-like), and if you are not careful, re-streaking from an old plate may result in the propagation or testing of mutated lineages rather than of the expected strain.
The appropriate manner to keep bacterial stocks for long time is at -80°C as a glycerol stock (we use 30% over-night culture plus 70% of 50% (v/v) sterile glycerol; a normal freezer is not cold enough). If you are using spore-formers, these can be stored reasonably well on plates or in slants at room temperature once the spores have developed.
Andrew
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