Page 233 - Review of Medical Microbiology and Immunology ( PDFDrive )

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mebooksfree.com mebooksfree.com mebooksfree.com MacConkey’s agar. It grows better at 25°C than at 37°C; mebooksfree.com
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PART II Clinical Bacteriology
222
made by periodic acid-Schiff (PAS) staining of biopsy
most biochemical test results are positive at 25°C and nega-
specimens of the small bowel in which inclusions are seen
tive at 37°C. Incubation of a stool sample at 4°C for 1 week,
in the macrophages. PAS staining, however, is nonspecific,
and PCR assays, which are more specific, are used to con-
a technique called cold enrichment, increases the frequency
of recovery of the organism. Yersinia enterocolitica can be
firm the diagnosis. First-line treatment typically involves
2 weeks of ceftriaxone, followed by at least 1 year of
reactions.
trimethoprim-sulfamethoxazole.
The laboratory is usually not involved in the diagnosis
of Y. pseudotuberculosis; cultures are rarely performed in
Veillonella distinguished from Y. pseudotuberculosis by biochemical
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cases of mesenteric adenitis, and the organism is rarely
Veillonella parvula is an anaerobic gram-negative diplococ-
recovered from stool specimens. Serologic tests are not
cus that is part of the normal flora of the mouth, colon, and
available in most hospital clinical laboratories.
vagina. It is a rare opportunistic pathogen that causes
Enterocolitis and mesenteric adenitis caused by the
abscesses of the sinuses, tonsils, and brain, usually in mixed
anaerobic infections.
or abscess, either trimethoprim–sulfamethoxazole or cipro-
floxacin is usually effective. There are no preventive mea-
Wolbachia
sures except to guard against contamination of food by the
Wolbachia species are Rickettsia-like bacteria found intra-
excreta of domestic animals.
cellularly within filarial nematodes such as Wuchereria and
Onchocerca (see Chapter 56). Wolbachia release endotoxin-
like molecules that are thought to play a role in the patho-
genesis of Wuchereria and Onchocerca infections. Treatment SELF-ASSESSMENT QUESTIONS
of patients with Wuchereria and Onchocerca infections with
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mebooksfree.com mebooksfree.com mebooksfree.com (A) Its natural habitat is the soil. mebooksfree.com mebooksfree.com
doxycycline to kill Wolbachia results in a significant
decrease in the number of filarial worms in the patient.
1. Regarding Fusobacterium nucleatum, which one of the following is
most accurate?
Wolbachia themselves are not known to cause human dis-
ease but do infect many species of insects worldwide.
(B) It is an anaerobic gram-negative rod with pointed ends.
(C) The drug of choice for infections caused by F. nucleatum is
Yersinia enterocolitica & Yersinia
azithromycin.
pseudotuberculosis
(D) Laboratory diagnosis is based on detecting the ability of the
exotoxin to kill cells in tissue culture.
Yersinia enterocolitica and Yersinia pseudotuberculosis are
gram-negative, oval rods that are larger than Yersinia pestis.
most accurate?
The virulence factors produced by Y. pestis are not made by
(A) It requires both X and V factors to grow on MacConkey’s agar.
these species. These organisms are transmitted to humans
(B) Gram stain of exudate from the lesion shows large gram-
by contamination of food with the excreta of domestic 2. Regarding Haemophilus ducreyi, which one of the following is
positive rods.
mebooksfree.com mebooksfree.com mebooksfree.com 3. Regarding Yersinia enterocolitica, which one of the following is mebooksfree.com
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animals such as dogs, cats, and cattle. Yersinia infections are
(C) Penicillin G is the drug of choice to treat infections caused by
relatively infrequent in the United States, but the number of
H. ducreyi.
documented cases has increased during the past few years,
(D) It causes chancroid, which is characterized by a painful ulcer
perhaps as a result of improved laboratory procedures.
on the genitals.
Yersinia enterocolitica causes enterocolitis that is clini-
cally indistinguishable from that caused by Salmonella or
most accurate?
Shigella. Both Y. enterocolitica and Y. pseudotuberculosis can
(A) It causes mesenteric adenitis, which can mimic appendicitis.
cause mesenteric adenitis that clinically resembles acute
(B) It is a gram-negative diplococcus found primarily within
appendicitis. Mesenteric adenitis is the main finding in
neutrophils.
(C) It is the most common cause of enterocolitis in the United States.
appendectomies in which a normal appendix is found.
(D) Its natural habitat is the human oropharynx, and there is no
Rarely, these organisms are involved in bacteremia or
animal reservoir.
abscesses of the liver or spleen, mainly in persons with
underlying disease. 4. Regarding Ehrlichia chaffeensis, which one of the following is most
accurate?
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Yersinia infection is associated with two autoimmune
mebooksfree.com mebooksfree.com mebooksfree.com (C) Its most common clinical presentation is acute meningitis. mebooksfree.com
(A) It is transmitted primarily by mosquito bite.
diseases: reactive arthritis and Reiter’s syndrome. Other enteric
(B) It forms beta-hemolytic colonies on blood agar.
pathogens such as Salmonella, Shigella, and Campylobacter
also trigger these diseases. Reactive arthritis and Reiter’s
(D) It is endemic on the islands off the coast of Massachusetts (e.g.,
syndrome are described further in Chapter 66.
Nantucket).
Yersinia enterocolitica is usually isolated from stool
(E) It forms an inclusion body called a morula in the cytoplasm of
specimens and forms a lactose-negative colony on
infected cells.
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