have throughout life, generally a mutualistic relationship.
inhabit for a few hours or days, can have a mutualistic,
commensalistic, or parasitic relationship
What are opportunistic pathogens?
� Introduction of normal microbiota into an unusual site in the
body� Immune suppression� Long-term antimicrobial
treatment or other changes that modify interactionsor abundance
of normal microbiota
Examples of resident microbes that can cause infection or can become oprtunistic
Bacteroides � normally found in gut.
Actinomyces � found in upper respiratory tract.
Sites where pathogens are maintained as a source of infection
Three types of reservoirs
�Animal reservoir�Human carriers�Nonliving reservoir
(contaminated food, water, objects)
Portals of entry
�Skin�Mucous membranes�Placenta�Entry via the
parenteral route circumvents the usual portals (via stab, cut, needle, etc)
Diseases spread from animal hosts to humans.
What is the definition of disease?
Also referred to as morbidity is any change from a state of
health.Occurs when the pathogen multiplies sufficiently to adversely
What are the stages of disease?
Incubation Period, Prodromal Period, Illness, Decline, Convalecence.
What is the difference between a sign and a symptom ?
Symptoms: Subjective characteristics of disease felt only by the
patient (ex: nausea, dizziness, fatigue)Signs: Objective
manifestations of disease observed or measured by others (ex: rash,
What are virulence factors?
Factors that enable bacteria to invade the body andcause disease.
What are extracellular factors?
Enzymes secreted out of cell.
Secreted by the pathogen to dissolve structural chemicals in the
body and avoid body defenses
Degree of pathogenicity (this does NOT tell you how severethe
disease is; some virulent organism do not cause severe illnesses)
How easy it is to give it to another person.
is the ability of a microorganism to cause disease
Chemicals that harm tissues or trigger host immune responses that
cause damage�Two types�Exotoxins�secreted by
bacteria�Endotoxins�Gram negative cell wall component (Lipid A:
causes fever, inflammation, diarrhea)
�Prevent phagocytosis from taking place
�Factors prevent phagocytosis by the host's phagocytic
cells�Capsule: Composed of chemicals not recognized as foreign,
�slippery� and difficult for phagocytes to engulf�Antiphagocytic
chemicals: Prevent fusion of lysosome and phagocytic
vesicles�Leukocidins directly destroy phagocytic white blood cells
How can diseases be transmitted?
�Communicable: transferred from another infected host
(flu)�Noncommunicable: not transferred from another host (tetanus)
What is a nosocomial disease?
HAIs are infections that are the result of hospital care
The study of the cause of disease
The normal growth of resident microbes outcompetes the growth of
other microbes�Use nutrients, take up space, release toxic waste
products that keep pathogens from becoming established
�Any non-living source of disease�Examples: Contaminated soil,
water, and food can be reservoirs of infection
Why are humans considered a dead-�?end host for many zoonotic disease?
Because you can't give it to another human.
How can pathogens adhere to a host to cause disease? Bacteria
have adhesinsfound on fimbriae, flagella, and glycocalyces
How can pathogens adhere to a host to cause disease? Viruses
glycoprotein ligands on surface of capsid or envelope
How can pathogens adhere to a host to cause disease? Protozoans
How can pathogens adhere to a host to cause disease?
Helminths (parasitic worms):
How can diseases be transmitted?
�Contact transmission�Vehicle transmission�Vector transmission
Direct contact transmission
�Usually involves body contact between hosts
�Indirect contact transmission
�Pathogens are spread from host to host by fomites
are any inanimate object.. cup
�Spread of pathogens in droplets of mucus by exhaling, coughing, and sneezing
When pathogens travel more than 1 meter via an aerosol
Commonly spreads gastrointestinal disease
Spread of pathogens on inadequately processed, cooked, or
�Blood, urine, saliva can carry pathogens�Prevent contact with
conjunctiva or breaks in the skin or mucous membranes
animals that carry pathogens
Two types of arthropod vectors:
�Arachnids (mites, ticks)�Insects (fleas, kissing bug, etc.)
transmit pathogens and serve as host for some stage of the pathogen's
passively transmit pathogens present on their body to new hosts (ex:
Pathogen acquired from the health care environment
Pathogen arises from normal microbiota due to factors within the
health care setting
Means �doctor induced� and is the result of modern medical procedures
(surgery, catheters, etc.)
Use of antimicrobial drugs reduces competition from some resident
microbiota �other microbes may thrive