The document explains methods to determine the oxygen requirements of bacteria, particularly microaerophiles, by growing them in varying oxygen environments. It discusses the importance of conditions such as using a candle jar to simulate reduced oxygen environments for specific bacteria, including their growth limitations at atmospheric oxygen levels. Additionally, it describes a newer anaerobic system that uses a gas-generating sachet to create ideal growth conditions for anaerobes.

1. BY SREEREMYA.S

2.  An excellent way to determine the oxygen
needs of your bacterium is to grow it in
different oxygen environments---
atmospheric oxygen of 22%, no oxygen at all
(GasPak jar), and reduced oxygen at less than
10% (candle jar)--and compare the qualitiy
and quantity of
growth.

3.  The candle jar at right has 3-5% CO2 and 8-
10% O2 (0.3% and 21% in the atmosphere,
respectively). This is a handy way to
determine if you have an aerobe which is
microaerophilic, since they grow optimally
under reduced (but present) oxygen
conditions as in the candle jar.

5.  Many microaerophilic bacteria will grow
poorly at 22% O2, whereas some will not
grow at all (e.g. Neisseria gonorrhoea).
Possibly the by-products of aerobic
respiration, superoxide radicals and hydrogen
peroxide, make it difficult for the
microaerophiles to do well in 22% O2.

6.  Some microaerophiles are actually
capnophilic (requiring elevated CO2 levels to
grow). Strict aerobes may not grow well in a
candle jar, depending on the species. The
Gram + genus Bacillus and Gram – genus
Pseudomonas include aerobic bacillus-shaped
bacteria.

8.  The newer anaerobic system (seen at right)
consists of a plastic container (for the agar plates
and a paper gas generating sachet. The sachet
contains ascorbic acid and activated carbon
which reacts on exposure to air, when removed
from the enclosed envelope. Oxygen is rapidly
absorbed and CO2 is produced. When the paper
sachet is placed in a sealed plastic pouch, this
reaction will create ideal atmospheric conditions
for the growth of anaerobes—anaerobic within
2.5 hours.

9.  Because a GasPak jar looks the same, whether
it has oxygen inside or not, an indicator strip,
containing methylene, is included in the jar.
 Methylene blue is blue when oxidized,
colorless when reduced. The carbon within
the pouch reacts with free oxygen in the jar,
producing 10- 15% CO2.