Page 148 - Review of Medical Microbiology and Immunology ( PDFDrive )

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CHAPTER 17 Gram-Positive Rods
Lethal factor is a protease that cleaves the phosphoki-
six doses of vaccine over an 18-month period are given.
nase that activates the mitogen-activated protein kinase
(MAPK) signal transduction pathway. This pathway con-
Annual boosters are also given to maintain protection.
Incinerating animals that die of anthrax, rather than
trols the growth of human cells, and cleavage of the phos-
burying them, will prevent the soil from becoming con-
phokinase inhibits cell growth. Protective antigen forms
pores in the human cell membrane that allows edema fac-
tor and lethal factor to enter the cell. The name protective
2. Bacillus cereus
antigen refers to the fact that antibody against this protein
protects against disease. taminated with spores.
Disease
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Clinical Findings
Bacillus cereus causes food poisoning.
The typical lesion of cutaneous anthrax is a painless ulcer
with a black eschar (crust, scab) (see Figure 17–1). Local
edema is striking. The lesion is called a malignant pustule.
Spores on grains such as rice survive steaming and rapid
Untreated cases progress to bacteremia and death.
frying. The spores germinate when rice is kept warm for
Pulmonary (inhalation) anthrax, also known as
many hours (e.g., reheated fried rice). The portal of entry
“wool-sorter’s disease,” begins with nonspecific respira-
is the gastrointestinal tract.
tory tract symptoms resembling influenza, especially a
dry cough and substernal pressure. This rapidly pro-
gresses to hemorrhagic mediastinitis, bloody pleural
Bacillus cereus produces two enterotoxins. The mode of
effusions, septic shock, and death. Although the lungs
action of one of the enterotoxins is the same as that of chol-
are infected, the classic features and X-ray picture of Pathogenesis
era toxin (i.e., it adds adenosine diphosphate ribose, a
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pneumonia are not present. Mediastinal widening seen
process called ADP-ribosylation, to a G protein, which
on chest X-ray is an important diagnostic criterion.
stimulates adenylate cyclase and leads to an increased con-
Hemorrhagic mediastinitis and hemorrhagic meningitis
are severe life-threatening complications. The symptoms
of action of the other enterotoxin resembles that of staphy-
of gastrointestinal anthrax include vomiting, abdominal
lococcal enterotoxin (i.e., it is a superantigen).
pain, and bloody diarrhea.
Clinical Findings
Laboratory Diagnosis
There are two syndromes. (1) One syndrome has a short
Smears show large, gram-positive rods in chains (see
Figure 17–2). Spores are usually not seen in smears of
sea and vomiting, similar to staphylococcal food poisoning.
exudate because spores form when nutrients are insufficient,
(2) The other has a long incubation period (18 hours) and
and nutrients are plentiful in infected tissue. Nonhemolytic
features watery, nonbloody diarrhea, resembling clostridial
colonies form on blood agar aerobically. In case of a bio- incubation period (4 hours) and consists primarily of nau-
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gastroenteritis.
terror attack, rapid diagnosis can be performed in special
laboratories using polymerase chain reaction (PCR)–
Laboratory Diagnosis
based assays. Another rapid diagnostic procedure is the
direct fluorescent antibody test that detects antigens of
the organism in the lesion. Serologic tests, such as an
enzyme-linked immunosorbent assay (ELISA) test for
Treatment
antibodies, require acute and convalescent serum samples
Only symptomatic treatment is given.
and can only be used to make a diagnosis retrospectively.
Prevention
Treatment
Ciprofloxacin is the drug of choice. Doxycycline is an alter-
be kept warm for long periods.
native drug. No resistant strains have been isolated
clinically. There is no specific means of prevention. Rice should not
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CLOSTRIDIUM
Prevention
Ciprofloxacin or doxycycline was used as prophylaxis in
those exposed during the outbreak in the United States
tetani, Clostridium botulinum, Clostridium perfringens
in 2001. People at high risk can be immunized with cell-
(which causes either gas gangrene or food poisoning),
and Clostridium difficile. All clostridia are anaerobic,
free vaccine containing purified protective antigen as
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