Page 222 - Review of Medical Microbiology and Immunology ( PDFDrive )

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mebooksfree.com mebooksfree.com mebooksfree.com SELF-ASSESSMENT QUESTIONS 211 mebooksfree.com
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CHAPTER 25 Chlamydiae
In exudates, the organism can be identified within epi-
thelial cells by fluorescent-antibody staining or hybridiza-
1. Your patient is a 20-year-old man with a urethral discharge. Gram
tion with a DNA probe. Chlamydial antigens can also be
stain of the pus reveals many neutrophils but no bacteria. You sus-
detected in exudates or urine by enzyme-linked immuno-
pect this infection may be caused by C. trachomatis. Which one of
sorbent assay (ELISA).
the following is the laboratory result that best supports your clini-
Chlamydiae can be grown in cell cultures treated with
cal diagnosis?
cycloheximide, which inhibits host cell but not chlamydial
protein synthesis, thereby enhancing chlamydial replica-
(B) The organism produces beta-hemolytic colonies on blood agar
tion. In culture, C. trachomatis forms inclusions containing (A) Gram stain of the pus reveals small gram-positive rods.
plates when incubated aerobically.
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mebooksfree.com mebooksfree.com mebooksfree.com 2. Regarding chlamydiae, which one of the following is the most mebooksfree.com
glycogen, whereas C. psittaci and C. pneumoniae form
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(C) The organism produces alpha-hemolytic colonies on blood
inclusions that do not contain glycogen. The glycogen-
agar plates when incubated anaerobically.
filled inclusions are visualized by staining with iodine.
(D) Fluorescent-antibody staining of cytoplasmic inclusions in
Exudates from the eyes, respiratory tract, or genital tract
epithelial cells in the exudate.
(E) Fourfold or greater rise in antibody titer against C. trachomatis.
yield positive cultures in about half of cases.
Serologic tests are used to diagnose infections by C. psittaci
accurate?
and C. pneumoniae but are rarely helpful in diagnosing disease
(A) Lifelong immunity usually follows an episode of disease caused
caused by C. trachomatis because the frequency of infection is
by these organisms.
so high that many people already have antibodies.
(B) The reservoir host for the three species of chlamydiae that
cause human infection is humans.
Treatment
and reticulate bodies within cells.
All chlamydiae are susceptible to tetracyclines, such as
(D) They can only replicate within cells because they lack the ribo-
doxycycline, and macrolides, such as erythromycin and (C) Their life cycle consists of elementary bodies outside of cells
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mebooksfree.com mebooksfree.com mebooksfree.com 3. Which one of the following is the drug of choice for sexually trans- mebooksfree.com
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somes to synthesize their proteins.
azithromycin. The drug of choice for C. trachomatis sexu-
(E) The vaccine against C. pneumoniae contains the capsular poly-
ally transmitted diseases is azithromycin. Because the rate
saccharide as the immunogen conjugated to a carrier protein.
of coinfection with gonococci and C. trachomatis is high,
any patient with a diagnosis of gonorrhea should also be
mitted disease (urethritis, cervicitis) caused by C. trachomatis?
treated for C. trachomatis with azithromycin.
(A) Ampicillin
The drug of choice for neonatal inclusion conjunctivitis
(B) Azithromycin
and pneumonia is oral erythromycin. The drug of choice for
(C) Ciprofloxacin
C. psittaci and C. pneumoniae infections and for lympho-
(D) Metronidazole
granuloma venereum is a tetracycline, such as doxycycline.
(E) Rifampin
Prevention
There is no vaccine against any chlamydial disease. The
best preventive measure against C. trachomatis sexually ANSWERS
1. (D)
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transmitted diseases is to limit transmission by safe sex
2. (C)
practices and prompt treatment of both the patient and the
3. (B)
sexual partners, including persons who are asymptomatic.
Sexual contacts should be traced, and those who had con-
tact within 60 days should be treated. Several types of sexu-
ally transmitted diseases are often present simultaneously.
Thus, diagnosis of one requires a search for other causative
Brief summaries of the organisms described in this chapter
agents.
begin on page 666. Please consult these summaries for a rapid
Oral erythromycin given to newborn infants of infected
review of the essential material.
mothers can prevent inclusion conjunctivitis and pneumo-
nitis caused by C. trachomatis. Note that erythromycin
ointment used to prevent neonatal gonococcal conjunctivi-
tis is much less effective against neonatal chlamydial con- PRACTICE QUESTIONS: USMLE &
COURSE EXAMINATIONS
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mebooksfree.com mebooksfree.com mebooksfree.com (National Board) Practice Questions starting on page 713. Also mebooksfree.com
junctivitis. Oral erythromycin should be used.
Questions on the topics discussed in this chapter can be found
Psittacosis in humans is controlled by restricting the
in the Clinical Bacteriology section of Part XIII: USMLE
importation of psittacine birds, treating or destroying sick
birds, and adding tetracycline to bird feed. Domestic flocks
of turkeys and ducks are tested for the presence of
see Part XIV: USMLE (National Board) Practice Examination
starting on page 751.
C. psittaci.
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