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Summary Jawetz Melnick&Adelbergs Medical Microbiology 26/E(MCB); Brucella, Francisella
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Summary Jawetz Melnick&Adelbergs Medical Microbiology 26/E (MCB); Chapter 26
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CHAPTER 181. A 68-year-old woman was seen in the clinic because she had felt feverish and had been experiencing
increasing pain and swelling in her left knee during the past 3 weeks. Four years earlier, a prosthetic joint
had been placed in her left knee. On examination, the knee was swollen, and fluid could be detected.An
aspirate of the fluid was obtained. There were 15,000 polymorphonuclear cells/mL in the fluid. No
organisms were seenon Gram stain. A routine culture was done. On the fourth day of incubation,
colorless colonies smaller than 1 mm in diameter were seen on the blood and chocolate agar plates. The
organism was a tiny gram-negative coccobacillus that was catalase positive and oxidase positive. A urea
slant was inoculated and was positive for urease activity after overnight incubation. The patient was
probably infected with which of the following microorganisms?
Correct:
(D) Brucella species
It causes undulating fever, and can also affect any organ system including joints, thus causing arthritis,
which explains her swollen knee. Since gram staining yielded no organisms, it must mean that the
organism is intacellular like Brucella (since it invades polymorphonuclear cells). Brucella colonies are
also small 0.5 to 0.7 by 0.6 to 1.5 micra.
Incorrect:
(A) Haemophilus influenzae
These infect, mononuclear cells, not polymorphonuclear cells, thus if this is the bacteria, this should be
the one present in high amounts in the infected area.
(B) Haemophilus ducreyi
This causes soft chancre, which does not match the aforementioned symptoms.
(C) Francisella tularensis
Francisella tularensis is biochemically inactive
(E) Staphylococcus aureus
Staphylococcus aureus is not a coccobacilli
2. After the culture (question 1) turned positive, additional history was obtained. Approximately 4 weeks
before the onset of her knee pain, the patient had visited relatives in Israel and traveled to other countries
in the Mediterranean area. She had a particular fondness for one food product that was the probable
vehicle for her infection. The product most likely was
Correct:
(B) Unpasteurized goat’s cheese
2-4 weeks after infection, signs and symptoms due to Brucella infection appear. It is also epidemically
prominent in the mediterranean regions. Unpasteurized milk and cheese from goats is a source of
infection for the bacteria.
Incorrect:
(A) Bananas
Not a vehicle for Brucella
(C) Rare hamburger
, Not a vehicle for Brucella
(E) Green tea
Not a vehicle for Brucella
3. A 55-year-old game warden in Vermont found a dead muskrat on the bank of a stream. He picked up
the animal, thinking it might have been illegally trapped or shot; it was not, and the game warden buried
it. Four days later, he developed a 1.5-cm painful ulcer on the index finger of his right hand, a 1-cm ulcer
on his right forehead, and pain in his right axilla. Physical examination also revealed right axillary
lymphadenopathy. This patient is most likely infected with
Correct:
(E) Francisella tularensis
F. tularensis palaearctica (Type B) occurs mainly in aquatic rodents (beavers, muskrats) in North
America (Vermont is in North America) causes the disease Tularemia, a rare infectious disease that
typically attacks the skin, eyes, lymph nodes and lungs. Ulcers appear at the site of infection, probably
his finger when he held the animal, since it can be transmitted through direct contact. Tularemia is also
characterized by lymphadenopathy.
Incorrect:
(A) Brucella species
Brucella species is transmitted through ingestion of infected goats milk and/ or contact with infected
tissues of cattle, and not through contact with muskrats.
(B) Rickettsia rickettsii
It causes Rocky mountain spotted fever, which is transmitted to humans by the bite of infected tick
species, not muskrats, and while the bacteria does cause rashes, it is not usually associated with skin
ulcers.
(C) Salmonella Typhi
Enteric fevers are severe systemic forms of salmonellosis. Enteric fevers may be preceded by
gastroenteritis, which usually resolves before the onset of systemic disease. The symptoms mentioned
above are not included in the symptoms of enteric fevers, which are include fever, anorexia, headache,
myalgias, and constipation
(D) Haemophilus ducreyi
This causes soft chancre and while it does cause painful ulcers, it is usually on the genitalia. The bacteria
is also transmitted sexually and not through interaction with muskrats.
4. An 18-month-old boy has been playing with a child who develops Haemophilus influenzae meningitis.
The boy’s parents consult his pediatrician, who says she is comfortable that the child will be fine because
he has been fully immunized with the polyribitol ribose phosphate (PRP)–protein conjugate vaccine. For
what reason is it necessary to immunize infants of 2 months to 2 years of age with polysaccharide–
protein conjugate vaccines?
Correct:
(B) Infants 2 months to 2 years of age do not immunologically respond to polysaccharide vaccines that
are not conjugatedto a protein.
Polysaccharide vaccines, such as those developed against prevent infection by inducing an immune
response against specific capsular polysaccharides. These vaccines, however, provided little protective
immunity in infants and young children this is so because the immune system of infants is still
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