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e.coli-killing infection

Stacy Ferguson sef at med.unc.edu
Sat Nov 25 06:48:40 EST 1995

In article <49196f$ldp at mserv1.dl.ac.uk>,
R Hanemaaijer <R.HANEMAAIJER at novell.pg.tno.nl> wrote:
>Dear netters,
>Help !!
>we have a rather big problem with our E.Coli (both XL-1blue MRF' and 
>JM109). When we grow them, they behave normal untill they reach an 
>OD550 of 0.4. From that moment on in 10 minutes time the OD550 drops 
>to less than 0.1; the medium gets clear with undefined precipitates.
>When we grow them further over-night the culture is full grown (OD550 
>is more than 2.0), but we can not infect them anymore with helper-
>Can the reason be a lytic-phage?, and, if so, does anybody know how 
>can we get rid of them. (We grow M13-phages so we need a F-pilus on 
>the cells) Any suggestions are welcome!!
>Annette van der Goes,
>graduate-student, Leiden.

That does sound rather frustrating. If it is, in fact, a phage contamination
problem, you should be able to figure that out. You might want to ask a 
neighboring lab to grow up some bugs (at least one of the strains you're
having problems with) and give them a tiny bit of your unintended lysate
to titer. If that's it, I suppose you should bleach down your lab and start
all over with brand new bacterial stocks. Getting new stocks would seem to
me to be a heck of a lot easier than trying to clean up your old ones.
They are, after all, common strains.

You may also want to find out if the washing procedures for your 
flasks and stoppers have changed. I recall a similar problem in a 
neighboring lab when i was in grad school. Interestingly, the problem
was traced to a new work study student who was washing the gauze stoppers
for the flasks with some harsh detergent and wasn't rinsing them well.
Turns out that the detergent was somehow working its way into the 
cultures during early log phase and lysing the bugs. It was a pretty
frustrating problem, of course, since a couple people in the lab spent
a great deal of time trying to figure out exactly what was going wrong.
Luckily, the student was finally seen washing the gauze stoppers and 
the problem stopped when they got new gauze and asked the student NOT
to use detergents on them. 



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