Concise description of medically important species

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

13. Questions/Suggestions
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