Spore-Forming Gram-Positive Bacilli: Bacillus & Clostridium Species
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BACILLUS SPECIES
Large aerobic, gram-positive rods arranged in long chains. Bacillus is
saprophytic organisms prevalent in soil, water, and air and on vegetation.
The spores are resistant to environmental changes, and certain chemical
disinfectants, and persist for years in dry earth.
Bacillus anthracis
Pathogenesis:
- Anthrax is a disease of herbivores—goats, sheep, cattle, etc. Humans
become infected by contact with infected animals or their products.
-
In humans, entry of spores through injured skin (cutaneous anthrax) or
mucous membranes (gastrointestinal anthrax), or by inhalation of spores
into the lung (inhalation anthrax).
- The spores germinate in the tissue at the site of entry, and results in formation
of a gelatinous edema and congestion. Bacilli spread via lymphatics to the
bloodstream, and they multiply in the blood and tissues shortly before and
after the animal's death.
- In inhalation anthrax ("woolsorter's disease"), the spores from the dust of
wool, hair, or hides are inhaled, phagocytosed in the lungs, and transported
by the lymphatic drainage to the mediastinal lymph nodes, where
germination occurs. This is followed by toxin production and the
development of hemorrhagic mediastinitis and sepsis, which are fatal.
Clinical Findings
- In humans, 95% of cases are cutaneous anthrax and 5% are inhalation.
Gastrointestinal anthrax is rare.
- Cutaneous anthrax occurs on arms or hands, face and neck. A pruritic papule
Spore-Forming Gram-Positive Bacilli: Bacillus & Clostridium Species
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develops 1–7 days after entry of the organisms or spores. The papule changes
into a vesicle, and a necrotic ulcer develops. The lesions have a characteristic
central black eschar. Lymphangitis and lymphadenopathy and systemic signs
and symptoms of edema, fever, malaise, and headache also occur. After 7–
10 days the eschar is dries, and separates; healing is by granulation and
leaves a scar. In 20% of patients, cutaneous anthrax leads to sepsis,
meningitis and death.
-The incubation period in inhalation anthrax 6 weeks. Clinical
manifestations
are
hemorrhagic
necrosis
and
edema
of
the
mediastinum. Substernal pain. Hemorrhagic pleural; cough is secondary
to the effects on the trachea. Sepsis occurs, and there may be bowel
ulceration, or hemorrhagic meningitis. The fatality rate is high.
Diagnostic Laboratory Tests
- Specimens are fluid or pus from a local lesion, blood, and sputum.
Stained smears from dead animals often show chains of large
gram-positive rods.
- Immunofluorescence staining techniques.
- When grown on blood agar plates, the organisms produce
nonhemolytic gray to white colonies with a rough texture and a
ground-glass appearance. Comma-shaped outgrowths (Medusa
head) may project from the colony.
- An enzyme-linked immunoassay (ELISA) has been developed to
measure antibodies against edema and lethal toxins.
Spore-Forming Gram-Positive Bacilli: Bacillus & Clostridium Species
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Treatment
-
In humans, treatment must be started early. Ciprofloxacin is
recommended;
penicillin
G,
along
with
gentamicin
or
streptomycin, has previously been used to treat anthrax.
- In the setting of potential exposure to B anthracis , prophylaxis
with ciprofloxacin or doxycycline should be continued for 4-8
weeks.
- Some other gram-positive bacilli, such as B cereus, are resistant to
penicillin. Doxycycline, erythromycin, or ciprofloxacin may be
effective alternatives to penicillin.
Epidemiology, Prevention, & Control
- Soil is contaminated with anthrax spores from dead animals. These
spores remain viable for decades. Contact with infected animals or
with their hides, hair, and bristles is the source of infection in
humans.
Control measures include:(1) Disposal of animal carcasses by burning or by deep burial in lime
pits,
(2) Decontamination by autoclaving of animal products
(3) Protective clothing and gloves for handling potentially infected
materials
Spore-Forming Gram-Positive Bacilli: Bacillus & Clostridium Species
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BACILLUS CEREUS
1. Food poisoning caused by Bacillus cereus has two forms:
The emetic type, associated with fried rice, is manifested by nausea,
vomiting, abdominal cramps, and diarrhea and is self-limiting, with
recovery occurring within 24 hours. It begins 1–5 hours after ingestion of
rice and pasta dishes. When large amounts of rice are cooked and allowed
to cool slowly, the B cereus spores germinate and the vegetative cells
produce the toxin.
The diarrheal type, associated with meat dishes and sauces. Has an
incubation period of 1–24 hours and is manifested by:
diarrhea with abdominal pain and cramps. The enterotoxin may be
performed in the food or produced in the intestine.
2.
eye
infections,
severe
keratitis,
endophthalmitis,
and
panophthalmitis. The organisms are introduced into the eye by foreign
bodies associated with trauma.
3. B cereus has also been associated with localized infections and with
systemic infections, including endocarditis, meningitis, osteomyelitis,
and pneumonia; the presence of a medical device or intravenous drug
use predisposes to these infections.