There is a Bergey’s Manual on the shelf below your
lab supply drawer. On page 294 of the
eighth edition (page number may vary according to edition), there is a table
entitled, “Table 8.3. Gram negative
Facultatively Anaerobic Rods.” Use this
table to identify your bacterial colony, based on your observations below. Remember, your organism was oxidase
negative!
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Organism
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Lactose
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Sucrose
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Glucose
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Citrate
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Finally, take some time to practice keying out the API that
were set up from last week’s student specimens. Make sure you are comfortable with these tests!
Bacteria of the Urinary Tract
Except for the lower few millimeters of the urethra, the
urinary tract is sterile. Thus, there
are NO normal flora to be found here.
However, opportunistic and sexually transmitted diseases may be a
problem within the urinary system.
The urinary system consists of the:
- Kidneys
- Ureters
- Bladder
- Urethra
Infections occur when microorganisms (usually bacteria from
the digestive tract) attach to cells lining the urethra and begin to
multiply. If the infection is limited
to the urethra, it is termed urethritis; cystitis is an
inflammation of the bladder, and pyelonephritis is a very serious
inflammation of the kidney(s).
Separate your plates into the two original sets:
- The
early inoculation of urine
- The
late inoculation of urine
Count the number of colonies you observe in each set and
record in the table below. Recall that
you used a calibrated loop, capable of inoculating .01 mL of urine to the
plate, and thus, enabling us to quantify results.
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Blood Agar
Top 1/3 Mid
1/3 Last 1/3
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PEA
Top 1/3 Mid
1/3 Last 1/3
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MacConkey’s
Top 1/3 Mid
1/3 Last 1/3
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Clean Catch Mid-Stream Urine or Voided (‘casual”)
Urine?
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Early
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Late
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What does the colony count of a urine culture indicate to
the clinician? Bearing in mind that
final interpretations of urine cultures must always be evaluated in conjunction
with the clinician’s previous experience and his patient’s clinical history, a
colony count will generally indicate the following:
For a specimen obtained through a suprapubic puncture or a
catheter:
- Any
bacterial colony present is clinically significant
For a specimen obtained as a “clean-catch, mid-stream”
urine:
Probable contamination:
- Bacterial
colony growth present only in upper third of plate
- Numbers
of colonies equal to or less than 100 (< 104 colony forming
units/mL)
Possible UTI-causing organnism:
- Bacterial
colony growth extending 2/3 of the way down the plate
- Number
of CFU/mL equal to 10,000-100,000 (actual colony count not performed)
Probable UTI-causing organism:
- Bacterial
colony growth extending all the way down the plate
- >100,000
CFU/mL (actual colony count not performed)
Specimens that were not collected in the above manner
(voided or “casual”) are inappropriate for culture, a waste of the lab’s time,
and present a great disservice to the patient.
In addition, patients having in-dwelling catheters will often
demonstrate a different population of organisms than those who do not.
The most frequently isolated organism of UTI infections is Escherichia
coli. Other organisms that are
isolated include:
- Proteus
- Enterococcus
- Enterobacter
- Citrobacter
- Klebsiella
- Pseudomonas
- Staphylococcus
saprophyticus
- Staphylococcus
epidermidis
Oral Reports
Each
of you will receive a handout containing a case history followed by a choice of
two etiologic agents. Your assignment
is to:
·
Read through the history carefully
·
Do some research on the disease presented and likely causes
·
Select a likely pathogen from the two choices
·
Describe why this is your selection
·
Devise a plan that will help prove your selection is, in fact, the
cause of the disease
o
Include media selection (basic, selective, differential) and growth
responses for your organism
o
Include biochemical tests that will rule in/rule out etiologic agents
o
Include serodiagnostic tests, when available
·
Do some research on treatment options for your selected pathogen, as it
relates to the site of infection
·
You will turn in a 1-2 page report that includes all of the above
(grammar and spelling do count!)
o
Include a short history
o
Your selection of pathogen and your reason for your selection
o
Your plan for proving your selection (see above)
·
You will present a 3-5 minute presentation of the above (props, such as
posters, transparencies, etc. are fine)
·
Maximum number of points possible:
25
·
Due date: Your scheduled lab
day next week (Tuesday, Wednesday, Thursday)
Take Out Food for the Brain:
True or False: Peptic ulcers are caused by spicy food and
stress.
If you answered
‘true,’ then you have not heard about Helicobacter pylori, an only
recently “discovered” and renamed bacterium (of course, if you asked the
bacterium, it would tell you it didn’t know it was missing!) that is purported
to be the causative agent of 80% of all stomach ulcers and 90% of all duodenal
ulcers (the remainder are thought to be
due to long-term use of nonsteroidal anti-inflammatory agents such as aspirin
and ibuprofen, and, rarely, some stomach or pancreatic cancerous tumors).
H. pylori is an interesting bacterium in that it has made a very
harsh environment downright homey. Half
a gallon of gastric juice sloshes through the stomach each day. Gastric juice contains potent digestive
enzymes and concentrated hydrochloric acid—not exactly milk and cookies for
one’s celiac guests. A thick layer of
mucus protects the stomach from its own gastric juices self-digesting it away. The spiral H. pylori burrows into
this mucus and fights off any stomach acid that comes its way through an enzyme
it produces called urease. Urease
converts urea (also found abundantly within the stomach) into bicarbonate and
ammonia, which are strong bases.
Furthermore, the
host’s own immune responses (T cells, other white blood cells, and their
arsenal of infection fighting chemicals) are impotent in destroying H.
pylori, because they cannot get through the stomach lining very
easily. But, they don’t give up, and
that makes the problem much worse. As
the immune response grows, the dead and dying granulocytes spill superoxide
radicals onto the cells lining the stomach.
Extra nutrients are sent to reinforce the greatly weakened white blood
cells, and H. pylori ravishes the bounty, gorging on supplies meant for
the host’s army. It is only a matter of
time before this cycle of immune defenses gone awry and the resulting
population explosion of H. pylori initiates gastritis. Gastritis often develops into peptic ulcer
disease. In some instances, these
developments are precursors to deadly cancers.
Transmission is thought
to be fecal-oral, through contaminated food and water. H. pylori is also thought to be
transmitted orally (e.g., through kissing), as it has been found in saliva.
Diagnosis is made
through blood, breath, and tissue tests.
Blood tests are indirect serodiagnostic procedures; breath tests look
for products of the characteristic urease; and tissue tests use stains of
sections of the stomach’s cells to demonstrate the bacterium’s presence.
Treatment consists of
a two week course of “triple therapy,” a cocktail of two antibiotics and acid
suppressor/stomach lining shielder.
This therapy has been shown to prevent ulcer recurrence in greater than
90% of infected individuals.
H. pylori infection is very common.
Within the United States, most people over the age of 50 are infected
with it. Because of better food
preservation techniques in the last 40 years, only about 20% of people under
the age of 40 are thought to be infected.
Outside of the United States, the numbers are higher. So, why don’t more people have ulcers, if
the rate of infection is so high? The
reason is because H. pylori does not cause ulcers in every person it
infects. Why this is so is not fully
understood yet.
Would you consider H.
pylori to be “normal flora” of the stomach, or should anybody found to be
infected undergo treatment? You tell
me.
H. pylori, greatly magnified. Note spiral shape.
A silver stain (Warthin Starry) of
HP (black wiggly things) on gastric mucus-secreting epithelial cells (x1000).
This picture is notorious because it is a slide of one of the investigator’s
stomach biopsy (Dr. Marshall) taken 8 days after he drank a culture of H.
pylori. The experiment was published in 1985 (Marshall BJ, Armstrong JA,
McGechie DB, Glancy RJ., Attempt to fulfill Koch's postulates for pyloric Campylobacter.
Med J Aust 1985; 142: 436-439).
Take Home Thought
When opportunity knocks, sometimes the door’s for the bacteria.
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