An infection characterized by sudden onset, rapid progression,
and often with severe symptoms
Animal Vector
An animal (nonhuman) that can transmit an infectious
agent to humans
Two types: mechanical and biological
Biological animal vectors: The infectious agent must
incubate in the animal host as part of the agent’s developmental cycle;
eg, the transmission of malaria by infected mosquitoes
Mechanical animal vectors: The infectious agent is physically
transmitted by the animal vector, but the agent does not incubate or grow
in the animal; eg, the transmission of bacteria sticking to the feet of
flies
Carrier
An individual who carries an infectious agent without
manifesting symptoms, yet who can transmit the agent to another individual
Chronic Infection
An infection characterized by delayed onset and slow
progression
Clinical Infection
An infection with obvious observable or detectable symptoms
Commensalism
A symbiotic relationship in which one species benefits,
and the other species is neither helped nor harmed
Communicable Disease
A disease that can be transmitted from one individual
to another
Conjugation
A form of genetic exchange in which a living donor cell
attaches to a recepient cell and DNA is transferred from the donor to the
recipient
In bacteria that conjugate, the donor stain has sex pili.
These are short filamentous structures on the surface of the donor cell.
The sex pili bind to the recipient cell and mediate the tranfer of DNA.
Usually, the recipient does not possess sex pili.
The donor cell contains an F plasmid, a short DNA molecule
that encodes the formation of the sex pili. The F plasmid DNA is transferred
to the recipient during conjugation.
In some strains, the F plasmid has been incorporated
into the donor cell chromosome. In this case, chromosomal genes may be
transferred to the recipient.
Very few bacterial groups can perform conjugation. Examples
include certain strains of Escherichia coli and Salmonella.
Contagious Disease
A communicable disease that is easily spread from one
individual to another
Disease
Any deviation from a condition of good health and well-being
“-emia”
A suffix meaning “presence of an infectious agent”
Examples:
Bacteremia = Presence of infectious bacteria
Viremia = Presence of infectious virus
Fungemia = Presence of infectious fungus
Septicemia = Presence of an infectious agent in the bloodstream
Endemic Disease
A disease condition that is normally found in a certain
percentage of a population
Endotoxin
A type of bacterial toxin having the following properties:
Produced only by gram-negative bacteria
Endotoxins are a component of the gram-negative cell
wall
The action of endotoxin requires the presence of the
bacteria in the host. The endotoxin may be released from the cell wall
as the cells die and disintegrate
Endotoxin is composed of Lipid A: Part of the lipopolysaccharide
layer
Endotoxin is heat-resistant
Mode of action: Irritation/inflammation of epithelium,
GI irritation, capillary/blood vessel inflammation, hemorrhaging
Epidemic Disease
A disease condition present in a greater than usual percentage
of a specific population
Epidemiology
The study of the transmission of disease
Exotoxin
A type of bacterial toxin with the following properties:
May be produced by either gram-positive or gram-negative
bacteria
Is secreted by the bacteria
The action of the exotoxin does not necessarily require
the presence of the bacteria in the host
Most exotoxins are peptide or protein
Most exotoxins are heat sensitive (exception: enterotoxin
of Staphylococcus aureus)
Classes of exotoxins: Neurotoxic, cytotoxic, or enterotoxic
exotoxins
Neurotoxins: Interfere with proper synaptic transmissions
in neurons
Cytotoxins: Inhibit specific cellular activities, such
as protein synthesis
Enterotoxins: Interfere with water reabsorption in the
large intestine; irritiate the lining of the gastrointestinal tract
Fomite
Any inanimate object capable of being an intermediate
in the indirect transmission of an infectious agent
Hemolysis
The lysis or breakdown of erythrocytes by bacteria
Caused by the secretion of bacterial hemolysins
Detected by appearance of colonies on blood agar plates
Types of hemolysis
Beta hemolysis: Complete hemolysis; clear zone around
colonies on blood agar
Alpha hemolysis: Incomplete hemolysis; greenish zone
around colonies on blood agar
Gamma reaction: Absence of a hemolytic reaction; no change
around colonies on blood agar
Infectious Disease
A disease condition caused by the presence or growth
of infectious microorganisms or parasites
“-itis”
A suffix meaning “inflammation of”
Examples:
Pharyngitis = Inflammation of the pharynx
Endocarditis = Inflammation of the heart chambers
Gastroenteritis = Inflammation of the gastointestinal
tract
Localized Infection
An infection that is restricted to a specific location
or region within the body of the host
Mutualism
A symbiotic relationship in which both species benefit
Noncommunicable Disease
A disease that is not transmitted from one individual
to another
Opportunistic Infection
An infection caused by microorganisms that are commonly
found in the host’s environment
This term is often used to refer to infections caused
by organisms in the normal flora
Pandemic
An epidemic affecting a large geographical area; often
on a global scale
Parasitism
A symbiotic relationship in which one species benefits,
and the other species is harmed
Generally, the species that benefits (the parasite) is
much smaller than the species that is harmed (the host)
Pathogenicity
The ability of a microbe to cause disease
This term is often used to describe or compare species
Primary Infection
An infection that develops in an otherwise healthy individual
Reservoir of Infection
The source of an infectious agent
Secondary Infection
An infection that develops in an individual who is already
infected with a different pathogen
Subclinical Infection
An infection with few or no obvious symptoms
Systemic Infection
An infection that has spread to several regions or areas
in the body of the host
Transduction
A form of genetic exchange in which DNA is transferred
from a donor bacterial cell to a recipient cell via a viral (bacteriophage)
intermediate
The donor culture is experimentally infected with the
bacteriophage. During phage replication, a few of the new phage particles
will package some of the donor DNA instead of (or in addition to) the phage
DNA. These particles, consisting of donor DNA packaged into phage capsids,
are called transducing particles.
The recipient culture is experimentally infected with
bacteriophage that had been previously grown on the donor strain cells.
Some of the recipient cells will be infected with transducing particles
(instead of viable phage particles). Donor DNA is transferred by the transducing
particles to these cells.
In random generalized transduction, any of the donor
genes may be transferred to the recipient.
In specialized transduction, only certain donor genes
from a specific chromosomal location are transferred.
Transformation
A form of genetic transfer in which isolated DNA from
a donor bacterial cell culture is transferred to a recipient cell culture.
The DNA is isolated by breaking open the donor cells
and purifying (or partially purifying) the donor DNA. The donor DNA is
mixed with a culture of recipient cells.
The recipient must be able to take the donor DNA into
its cells. This is known as competence for transformation.
Some strains of certain species are naturally competent.
They may take in donor DNA without special treatment. Examples include
Streptococcus pneumoniae, Acinetobacter calcoaceticus, andsome
strains of Bacillus subtilis.
Competence may be induced in certain species that are
not otherwise competent. For example, competence can be induced in Escherichia
coli by treating the cells with Ca2+
Virulence
The degree of pathogenicity in a microorganism
This term is often used to describe or compare strains
within a species