[Cytometry] Bacterial contamination in Moflo

Rachael Walker rvw24 at cam.ac.uk
Mon May 2 11:48:33 EDT 2011

Dear All

I have been having a recurring bacterial contamination within my MoFlo 
for several months now.  It will be fine for weeks and then it appears 
again.  I regularly leave the machine with ethanol in all the lines for 
the weekend but this doesn't seem to be eliminating the problem.  I have 
changed everything I can think of including all lines, the nozzle 
assembly, sheath filter and autoclaved the sheath tank and the sample 

When I first had this problem I discovered a biofilm looking like rust 
at the top of the nozzle assembly, and when swabbed this showed positive 
for bacteria.  I have changed nozzle assemblies 3 times since then for 
various reasons and I have changed my nozzle as well (which is regularly 
sonicated in detergent).  I put the last nozzle assembly in place about 
6 weeks ago and already it is showing signs of this brown biofilm inside 
it.  Does anyone else see this in their Moflo nozzle assemblies?  The 
only things to have gone through that nozzle assembly are PBS (10x from 
VWR, diluted and autoclaved in house), facs rinse, 70% ethanol and 
cells.  I occasionally run bleach and water through the sample lines.

I managed to run a sorter for nearly 4 years without contaminations and 
now I am plagued with problems.  Are there any dead spaces within the 
machine that I don't know about apart from at the top of the nozzle 

I would be grateful for any advice.

Many thanks


Dr Rachael Walker
Flow Cytometry Core Facility Manager
Wellcome Trust Centre for Stem Cell Research
University of Cambridge
Tennis Court Road

01223 760227

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