1. Bacillus and Corynebacterium
Aman Ullah
B.Sc. Med. Lab. Technology
M. Phil. Microbiology
Certificate in Health Professional Education
Lecturer, Department of Medical Lab. Technology
Institute of Paramedical Sciences,
Khyber Medical University, Peshawar, Pakistan
2. Bacillus
Bacillus anthracis and Bacillus cereus
Bacillus anthracis
Disease
B. anthracis causes anthrax
common in animals but rare in humans
Human disease occurs in three main forms:
cutaneous, pulmonary, and gastrointestinal
3. Important Properties
B. anthracis is a large gram-positive rod with
square ends, frequently found in chains
Its antiphagocytic capsule is composed of D-
glutamate
It is nonmotile, whereas other members of the
genus are motile
4. Transmission
Spores of the organism persist in soil for years
Humans are most often infected cutaneously at
the time of trauma to the skin, which allows the
spores on animal products, such as hides,
bristles, and wool, to enter
Spores can also be inhaled into the respiratory
tract
Gastrointestinal anthrax occurs when
contaminated meat is ingested
5. Pathogenesis
Pathogenesis is based primarily on the production of two
exotoxins, collectively known as anthrax toxin
The two exotoxins, edema factor and lethal factor
Edema factor, an exotoxin, is an adenylate cyclase that causes
an increase in the intracellular concentration of cyclic AMP
This causes an outpouring of fluid from the cell into the
extracellular space, which manifests as edema
Lethal factor is a protease that cleaves the phosphokinase that
activates the mitogen-activated protein kinase (MAPK) signal
transduction pathway
This pathway controls the growth of human cells, and cleavage
of the phosphokinase inhibits cell growth
6. Clinical Findings
The typical lesion of cutaneous anthrax is a painless
ulcer with a black eschar (crust, scab), local edema is
striking, the lesion is called a malignant pustule
Pulmonary (inhalation) anthrax, also known as
"woolsorter's disease," begins with nonspecific
respiratory tract symptoms resembling influenza,
especially a dry cough and substernal pressure. This
rapidly progresses to hemorrhagic mediastinitis, bloody
pleural effusions, septic shock, and death
The symptoms of gastrointestinal anthrax include
vomiting, abdominal pain, and bloody diarrhea
7. Laboratory Diagnosis
Smears show large, gram-positive rods in chains
Culture and sensitivity C/S
Serological diagnosis
8. Bacillus cereus
Disease
B. cereus causes food poisoning
Transmission
Spores on grains such as rice survive steaming and rapid frying. The
spores germinate when rice is kept warm for many hours
Pathogenesis
B. cereus produces two enterotoxins
One of the enterotoxins adds adenosine diphosphate ribose, a
process called ADP-ribosylation, to a G protein, which stimulates
adenylate cyclase and leads to an increased concentration of cyclic
adenosine monophosphate (AMP) within the enterocyte
Other enterotoxin is a superantigen
9. Clinical Findings
There are two syndromes:
One has a short incubation period (4 hours) and
consists primarily of nausea and vomiting
Other has a long incubation period (18 hours)
and features watery, nonbloody diarrhea
Laboratory Diagnosis
This is not usually done
10. Corynebacterium diphtheriae
C. diphtheriae is found on the skin, and in the nose,
throat, and nasopharynx of carriers and patients with
diphtheria
Transmission: By respiratory droplets
Pathogenicity: Diphtheria is caused by the local and
systemic effects of a single exotoxin that inhibits
eukaryotic protein synthesis
This toxin inactivates eukaryotic polypeptide chain
elongation factor EF-2 by ADP-ribosylation, thus
terminating protein synthesis
11. Corynebacterium diphtheriae
Disease: Diphtheria
Clinical Manifestation: This life-threatening disease
begins as a local infection, usually of the throat
The infection produces a distinctive thick, grayish,
adherent exudate (called a pseudomembrane) that is
composed of cell debris from the mucosa, and
inflammatory products
The exudate coats the throat and may extend into
the nasal passages or respiratory tract where it
sometimes obstructs the airways, leading to
suffocation
12. Corynebacterium diphtheriae
Generalized symptoms are due to dissemination
of the toxin
Although all human cells are sensitive to
diphtheria toxin, major clinical effects involve the
heart (myocarditis may lead to congestive heart
failure and permanent heart damage) and
peripheral nerves
Lab diagnosis can be done by staining smear or
C/S