5 replies to this topic

[archercr]

I'm using a direct colony suspension, so I streak out a first plate for subculture #1, and store at 4oC and use within 2 weeks.  I make subculture #2 from those colonies to use within 24h.  Why does subculture #1 need to be tossed after 2 weeks?  Thanks!

[Julio-Claudian]

archercr, on Apr 28 2010, 09:30 PM, said:

I'm using a direct colony suspension, so I streak out a first plate for subculture #1, and store at 4oC and use within 2 weeks.  I make subculture #2 from those colonies to use within 24h.  Why does subculture #1 need to be tossed after 2 weeks?  Thanks!

Hi archercr,

From my experience (only two strains actually), some do last longer whilst some just die after 14 days. My strain of B. cepacia lasts only about two weeks but another E. coli is still culturable after a month.

Err, I hope I understand you.

[gebirgsziege]

fundamentals of microbiology: in culture (no matter if liquid or on agar plates) there are usually four phases of growth: lag - log - stationary - death. The length of the phases is depending on the microbs used; and when your bugs reach the death phase, it is difficult (or even impossible) to recover them again.

a rare case to consult wikipedia http://en.wikipedia....acterial_growth

[archercr]

OK. so, even on on an agar plate in the Fridge, they are still growing slowly and can still die?

[gebirgsziege]

The older a colony gets, the more bacteria die. Others will utilise the dead ones for nutrients (kannibalism) and keep on growing, but the older the culture gets, the more dead cells, the more toxic substances around that inhibit the growth of others or even induce death in them (keywords to look up in your text books: quorum sensing, stochastic switch). Some bacteria are more sensitive than others, but for lab exp. usually bacerial cultures in the log phase are used.

[perneseblue]

also, as the bacteria ages, strange things (@recombination) start to happen to the plasmids it contains, especially BACs with sequence repeats. These truncated BACs are smaller giving the bacteria which contains them a shorter growth time, which results in these cell dominating subsequent cultures.