With an infection, it is not unusual to obtain a culture in order to determine
what germs are present as well as what antibiotic will work best to get rid of
it. Regardless of how and where the culture is obtained, the same basic steps
are followed. In this example, we have a patient with a severe ear infection
with pus that has been coming out of her right ear for the past few weeks that
has not responded to antibiotics. A culture is obtained of the pus that is
coming out of the ear with a q-tip swab. This is placed in a tube for transport.
In this second example, we have a patient that has been suffering from high
spiking fevers. Blood is drawn from the patient and into a blood culture bottle.
Once the blood cultures have been obtained, they are placed into a bag for
transport. Both these culture samples are delivered to the microbiology lab where
a technician logs the samples into a computer.
The blood cultures are placed inside an incubator to allow any infection present
to grow further before processing. The ear culture is placed in a holding
bucket along with other samples that has been collected from other patients. The
ear culture swab is moved under a special ventilated hood to prevent
contamination. After labeling, the swab is streaked onto four different algar
plates as well as a slide. Each plate contains a different type of medium or
food which allows for differentiation of what germ may be present as it grows.
A loop further streaks out the specimen on the agar plates. The plates are
inserted into an incubator to allow any germ to grow.
Sometime within the next five days. blood cultures which have been allowed to
incubate are now removed and placed under the hood. Just as with the ear
culture swabs, the blood cultures are applied onto agar plates streaked with
a loop and placed in an incubator to allow for further differentiated growth.
The slides which have been set aside are now brought over to a sink for further
processing. The slides are stained and fixed with special chemicals followed by
rinses. This process is used to Gram stain any organisms present for rough
classification of the infectious organism.
Once the slides have been air-dried, the slides are then examined under the
microscope to visualize any germs present and classified as either gram
positive or gram negative. In this case, gram positive cocci are identified
that resemble Staphylococcus. However to determine whether MRSA is present or
not takes more testing. The next day, the ear
culture and blood culture agar plates which have been placed in the
incubator are removed and carefully examined by a microbiologist. By seeing
within which plates growth has occurred, identification of the infecting organism
can be made and reported. For the ear culture, a diagnosis of Staphylococcus
aureus is made. However the next question is whether this infection is resistant
to any antibiotics or not. The main concern is whether
MRSA is present otherwise known as M R S A. As such, sensitivities will be performed
on the ear culture. The agar plates are taken to a station where a swab of the
organism is diluted inside a test tube.
A detector ensures the proper amount of dilution has occurred. A cartridge
containing a panel of different antibiotics for the germ to be tested
against is then placed with the test tube inside a machine that will then
process the sample.
The next day, the machine will provide a report of what antibiotics the infection
is sensitive and resistant to allowing a physician to provide the best antibiotic
that will kill the germ. For the ear culture, it was found to be MRSA. The
blood culture obtained from our second example did not end up revealing any
infection in the blood. This culture and sensitivity process applies to any
culture obtained from anywhere else in the body.