Download Bacillus cereus

Bacillus
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General Concepts:
The family Bacillaceae, consisting of rod-shaped bacteria that form
endospores, has two principal subdivisions:
1- Anaerobic spore-forming bacteria of the genus Clostridium.
2- Aerobic or facultative anaerobic spore-forming bacteria of the
genus Bacillus.
General Characteristics of Bacillus:
 Rod-shaped, Gram-positive bacteria.
 Endospore-forming aerobic or facultative anaerobic. The spores are
resistant to heat, cold, radiation, desiccation, and disinfectants.
 Are ubiquitous, in soil, water, and airborne thermophilic (< 75°C)
and psychrophilic (>5-8°C), also can flourish at extremes of acidity
& alkalinity (pH 2 to 10).
 Catalase positive (rapidly differentiate from Clostridium).
 Types of Bacillus: Bacillus anthracis , Bacillus cereus, Bacillus
stearothermophilus, Bacillus subtilis, Bacillus larvae.
Bacillus anthracis
Human pathogen isolation also considered zoonosis.
Anthrax: is primarily a disease of herbivores. Humans acquire it as a
result of contact with infected animals or animal products. In humans the
disease takes one of three forms depending on the route of infection
(Transmission):
1- Cutaneous anthrax result from contact human skin with spores or
infected animals & animals products. which accounts for more than
95% of cases worldwide, results from infection through skin
lesions.
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2- Gastrointestinal anthrax result when spores are ingested. usually
in infected meat; and intestinal anthrax is analogous to cutaneous
anthrax but occurs on the intestinal mucosa.
3- Pulmonary anthrax result when inhalation of dust containing
anthrax spores inhaled. It is usually an occupational disease,
such as in persons who handle or sort contaminated wools.
 Gastrointestinal and pulmonary anthrax are both more dangerous
than the cutaneous form because they are usually identified too late
for treatment to be effective.
Virulence factors:
1-Capsule: is antiphagocytic and helps the anthracis to evade the immune
system of the host.
2-The product of exotoxin: This toxin consists of three proteins:
protective antigen (PA), lethal factor (LF) , and edema factor (EF).
Cutaneous Anthrax human: cases are cutaneous infections 95% to 5
days after contact cause 1 small pruritic,  2 non-painful papule at
inoculation site, papule develops into 3 hemorrhagic vesicle & 4
ruptures slow-healing painless 5 ulcer covered with black eschar
surrounded by 6 edema Infection may spread to7 lymphatic / local
adenopathy 8 septicemia may develop mortality in untreated cutaneous
anthrax.
Gastrointestinal (Ingestion) Anthrax: Virtually 100% fatal,
abdominal pain, vomiting of blood, and severe bloody diarrhea.
Inhalation Anthrax: Virtually 100% fatal, pneumonic meningitis may
complicate with cutaneous anthrax and inhalation forms of disease
(pharyngeal anthrax, fever pharyngitis and neck swelling).
Anthrax spores, which are transported to the 1 regional lymph nodes
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where they germinate, multiply, and produce toxin, and characterized
by2 pleural effusions 3 dyspnea, 4 cyanosis,  5 stridor, 6
and shock.
Epidemiology of Bacillus anthracis: The ultimate reservoir of B.
anthracis is contaminated soil, in which spores remain viable for long
periods. Herbivores, the primary hosts, become infected when foraging in
a contaminated region. Enzootic in certain foreign countries (e.g., Turkey,
Iran, Pakistan and Sudan).
Bacillus cereus
- Saprophytic, heat resistant spores.
- Heat and acid stable toxin (Emetic syndrome bacillus).
- Heat labile enterotoxin (Diarrheal disease).
Virulence factor: include : Toxins and Enzymes
TOXINS
1- One emetic toxin(ETE): This toxin is highly resistant to pH(2-11), to
heat, and to proteolytic cleavage.
2- Three different enterotoxins:
 The first enterotoxins (HBL) haemolysin BL is also a hemolysin.
 the second enterotoxin (Nhe) nonhemolytic enterotoxin is not
a hemolysin.
 The third enterotoxin (EntK) is a single component protein that has
not been shown to be involved in food poisoning.
All three enterotoxins are cytotoxic and cell membrane active
toxins that will make holes or channels in membranes.
ENZYMES
Tissue destruction is mediated by cytotoxic enzyme including:
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 Cereolysin.
 Phospholipase C (This enzyme may have a secondary role in
ocular infections).
Bacillus cereus causes two types of food-borne illnesses:
1- One type is characterized by:- nausea and vomiting and abdominal
cramps and has an incubation period of 1 to 6 hours.
This is the "short-incubation" or emetic form of the disease is caused
by a heat-stable emetic toxin(ETE). It resembles Staphylococcus
aureus (staph) food poisoning in its symptoms and incubation period.
2-Second type is manifested primarily by: abdominal cramps and
diarrhea following an incubation period of 8 to 16 hours. Diarrhea may
be a small volume or profuse and watery. This type is referred to as the
"long-incubation" or diarrheal form of the disease, and it resembles
food poisoning caused by Clostridium perfringens. In either type, the
illness usually lasts less than 24 hours after onset. In a few patients
symptoms may last longer. The long-incubation form of illness is
mediated by the heat-labile diarrheagenic enterotoxins (enterotoxin
Nhe and /or hemolytic enterotoxin HBL).
 B. cereus may occasionally produce disease in immune compromised humans (eg, meningitis, endocarditis,
endophthalmitis, conjunctivitis, or acute gastroenteritis).
Epidemiology of Bacillus cereus :
1- Ubiquitous, in soil. People at risk include those who consume food
contaminated with bacterium (e.g., rice, meat ,vegetable).
2-With penetration injuries (e.g., to eye).
3-Receive intravenous injection.
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Bacillus subtilis
This species is commonly found in the upper layers of the soil, and
evidence exists that B. subtilis is a normal gut commensal in humans.
The number of spores found in the human gut was too high to be
attributed solely to consumption through food contamination.
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Diagnosis:
 Cutaneous anthrax is diagnosed on the basis of the characteristic
papule (early) or eschar (later) with extensive surrounding edema.
 History of exposure to animals or their products.

Also is confirmed by observation of characteristic encapsulated
bacilli in polychrome methylene blue-stained smears of blood,
exudate, lymph and cerebrospinal fluid.
 Culture.

ELISA for capsule antigens anthrax is (95% sensitivity).
Control:
 Anthrax: Control in animals is essential for control in humans. In
endemic areas, animals that die suddenly should be handled
cautiously and livestock should be vaccinated annually. A human
vaccine is available for individuals in high-risk occupations.
 Vaccine (controversial)
 Laboratory workers
 Employees of mills handling goat hair
 Active duty military members
 Food poisoning is controlled by
 Adequate cooking.
 Avoidance of recontamination of cooked food, and proper
storage (efficient refrigeration).
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Treatment:
 Anthrax is readily treated with antibiotics (e.g., penicillin,
tetracycline, chloramphenicol, gentamicin, or erythromycin).
 Treatment is with non-ß-lactam antibiotics for Gram-positive
bacteria.
Antimicrobial Susceptibility of Bacillus spp Isolates
DRUG
ORGANISM
Bacillus cereus
Imipenem, Vancomycin, Ramoplanin,Teicoplanin,
Chloramphenicol, Clindamycin, Gentamicin, Trovafloxacin,
Levofloxacin, Ciprofloxacin, Norfloxacin, Ofloxacin, Sparfloxacin.
Non - B. cereus
Penicillin, Mezlocillin, Oxacillin, Cefazolin, Cefotaxime, Imipenem,
Vancomycin, Chloramphenicol, Clindamycin, Ciprofloxacin.
Spores may be:
1. Central.
2. Sub-terminal,(eg. Clostridium perfringens).
3. Oval and terminal, resembling a tennis racket.
4. Spherical and terminal, giving a drumstick appearance (Clostridium
tetani)
Medical Importance of Bacterial Spores
Important features of Spores
Medical Implications
Spores are highly resistant to heating;
spores are not killed by boiling
(100OC) but are killed at 121OC.
Medical supplies must be heated to 121oC
for at least 15 minutes to be sterilized.
Spores are highly resistant to many
chemicals, including most
disinfectants.
Only solution designated as sporicidal will
kill spores.
Spores can survive for many years in
soil and other inanimate objects.
Wound contaminated with soils can be
infected with spores and cause diseases
such as tetanus, gas gangrene.
Spores do not exhibit measurable
metabolic activity.
Antibiotics are ineffective against spores.
Spores formed only when nutrients
are insufficient.
Spores are not found at the site of infection
because nutrients are not limiting.
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Bacillus
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References:
1- Jawetz, Melnick, & Adelberg’s.( 2013). Medical Microbiology (Twenty-Sixth Edition).
2- Ray, C.G., ed. (2004). Sherris Medical Microbiology (4th ed.). McGraw Hill.
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