Page 209 - Review of Medical Microbiology and Immunology ( PDFDrive )

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mebooksfree.com mebooksfree.com mebooksfree.com Other Mycoplasmas mebooksfree.com mebooksfree.com
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PART II Clinical Bacteriology
198
Legionella pneumophila [Legionnaires’ disease], Chlamydia
pneumoniae, Chlamydia psittaci [psittacosis], Coxiella bur-
Mycoplasma hominis has been implicated as an infrequent
netii [Q fever], and viruses such as such as influenza virus
cause of pelvic inflammatory disease. Ureaplasma urealyti-
and adenovirus. The term atypical means that a causative
cum may cause approximately 20% of cases of nongonococ-
bacterium cannot be isolated on routine media in the diag-
cal urethritis. Ureaplasmas can be distinguished from
nostic laboratory or that the disease does not resemble
pneumococcal pneumonia.) The onset of Mycoplasma
which degrades urea to ammonia and carbon dioxide.
pneumonia is gradual, usually beginning with a nonpro-
ductive cough, sore throat, or earache. Small amounts of mycoplasmas by their ability to produce the enzyme urease,
mebooksfree.com mebooksfree.com mebooksfree.com (A) Amoxicillin is the drug of choice for pneumonia caused by this mebooksfree.com
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whitish, nonbloody sputum are produced. Constitutional
SELF-ASSESSMENT QUESTIONS
symptoms of fever, headache, malaise, and myalgias are
pronounced. The paucity of findings on chest examination
1. Mycoplasma pneumoniae is an important cause of atypical pneu-
is in marked contrast to the prominence of the infiltrates
monia. Regarding this organism, which one of the following is the
seen on the patient’s chest X-ray. The disease resolves spon-
most accurate?
taneously in 10 to 14 days. In addition to pneumonia, M.
pneumoniae also causes bronchitis.
organism.
(B) Antibody in a patient’s serum will agglutinate human red blood
The extrapulmonary manifestations include Stevens-
cells at 4°C, but not at 37°C.
Johnson syndrome, erythema multiforme, Raynaud’s phe-
(C) Gram stain of the sputum reveals small gram-negative rods.
nomenon, cardiac arrhythmias, arthralgias, hemolytic
(D) It is an obligate intracellular parasite that can only grow within
anemia, and neurologic manifestations such as Guillain-
human cells in the clinical laboratory.
Barré syndrome.
(E) People with cystic fibrosis are predisposed to pneumonia
caused by this organism.
Laboratory Diagnosis
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2. Which one of the following is the drug of choice for atypical pneu-
monia caused by M. pneumoniae?
Diagnosis is usually not made by culturing sputum sam-
(A) Amoxicillin
ples; it takes at least 1 week for colonies to appear on special
(B) Azithromycin
media. Culture on regular media reveals only normal flora.
(C) Ceftriaxone
Currently, a polymerase chain reaction (PCR) assay that
(D) Gentamicin
detects M. pneumoniae specific nucleic acids in sputum or
(E) Vancomycin
in respiratory secretions is the best diagnostic procedure.
Serologic testing for the presence of antibodies in the
patient’s serum may also be useful. A cold-agglutinin titer
of 1:128 or higher is indicative of recent infection. Cold
agglutinins are IgM autoantibodies against type O red
2. (B)
blood cells that agglutinate these cells at 4°C but not at
37°C. However, only half of patients with Mycoplasma 1. (B)
mebooksfree.com mebooksfree.com mebooksfree.com begin on page 665. Please consult these summaries for a rapid mebooksfree.com
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pneumonia will be positive for cold agglutinins. The test is
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SUMMARIES OF ORGANISMS
nonspecific; false-positive results occur in influenza virus
Brief summaries of the organisms described in this chapter
and adenovirus infections. The diagnosis of M. pneu-
moniae infection can be confirmed by a fourfold or greater
review of the essential material.
rise in specific antibody titer in either a complement fixa-
tion or an ELISA test.
PRACTICE QUESTIONS: USMLE &
Treatment
COURSE EXAMINATIONS
The treatment of choice is either a macrolide, such as
erythromycin or azithromycin, or a tetracycline, such as
in the Clinical Bacteriology section of Part XIII: USMLE
doxycycline. The fluoroquinolone levofloxacin is also effec-
(National Board) Practice Questions starting on page 713. Also
tive. These drugs can shorten the duration of symptoms,
see Part XIV: USMLE (National Board) Practice Examination
although, as mentioned earlier, the disease resolves sponta- Questions on the topics discussed in this chapter can be found
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starting on page 751.
neously. Penicillins and cephalosporins are inactive
because the organism has no cell wall.
Prevention
There is no vaccine or other specific preventive measure.
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