Trouble-shooting
Guide: If you have a contamination problem, select what you
believe to be the organism
from the short descriptions
below and click on the image to go to a more detailed
page.
Bacteria
Bacterial contamination is
usually manifest by a sudden change in pH, cloudiness in the
medium, sometimes with a slight whiteish film on the cell
surface of plates, dishes, or on the bottom of bottles of
medium that typically dissipates when the vessel is moved.
Under low power (100x) spaces between cells will appear
granular or you may see very small black dots. In some cases
under higher magnification (400x) cocci or "rods" may be
distinguished and there may be motibility of the bacteria.
Bacteria can usually be distinguished from media components
such as serum protein by the regular particulate morphology
of the organism versus an irregular shape in the case of
serum protein cryoprecipitates.
Fungus (Mold) Fungi (molds)
show up as thin filamentous mycelia and sometimes as denser
clumps of spores. Fungi are usually very slow growing but in
advanced stages of contamination often overtake a culture as
a fuzzy growth (either whiteish or black) that can be seen
without a microscope.
Mycoplasma
Mycoplasmas cannot be
detected by the naked eye or even by typical light
microscopy. Therefore, mycoplasma contamination must be
detected by alternative testing
methods. The image provided
here is of a mycoplasma "colony" after being propagated on
special agar. The colony has a typical "fried egg"
appearance.
Yeast
Yeasts appear as round or
ovoid particles that are smaller than mammalian cells and
are mostly seen as "budding" from other yeast particles in
chains of two, three, or more. In advanced stages, they can
appear as multi-branched chains of particles.
