Lectures 13&14: Pathogenicity of Microorganisms Flashcards
Parasites are organisms that
- Live on or within a host organism and are metabolically dependent on the host
- are any organism that cause disease
The host is
larger organism that supports the survival and growth of a smaller organism
Infection
- A parasite growing and multiplying within/on a host
- may or may not result in overt infectious disease
Pathogen
- Any parasite organism causing infectious disease
Primary (frank) pathogen
Causes disease by direct interaction with healthy host
Opportunistic pathogen
May be part of normal flora and causes disease when it has gained access to other tissue sites or host is immunocomprimised
Pathogenicity
ability to cause disease
Chain of events for a successful infection
- agent identitiy
- virulence of agent
- means of exposure to agent
- dose of agent
- susceptibility of host to agen
infections passed from animal to human are termed
zoonoses
What does animate mean
from other humans or animals
what does inanimate mean
from water, soil, and food
Natural enviromental location in which the pathogen resides
Reservoir (can be animate or inanimate)
organisms that spread disease from one host to another
vector
infectious disease
infection with viruses, bacteria, fungi, protozoa, and helminths
Objective changes in body that can be directly observed
Signs
subjective changes experienced by patient
symptoms
Set of characteristic signs and symtpoms
disease syndrome
Incubation period
period after pathogen entry, before signs and symptoms
Prodromal stage
- Onset of signs and symptoms
- not clear enough for diagnosis
Period of illness
- disease is most severe, signs and symptoms
Convalescence
Signs and symptoms begin to disappear
Course of infectious disease
- Incubation period
- Prodromal stage
- Period of illness
- Convalescence
A pathogen must contact a host and survive within it to cause a disease. To survive, it needs
- A suitable environment
- A source of nutrients
- in competition with eukaryotic host cells
- Protection from harmful elements
- virulence factors allow a pathogen to oucompete host cells and resist their defenses
Some survival strategies for pathogens once in the host are
- Adhesins
- Enzymes
- Toxins
- Invasins
- Autoinducers
Virulence factors determine the
degree to which a pathogen causes damage, invasion, infectivity
What is virulence
degree or intensity of pathogenicity
Virulence is determined in part by pathogen’s ability to
- survive outside of host
- more dependent on host (cannot survive outside of host)= less virulent
*
- more dependent on host (cannot survive outside of host)= less virulent
What does pathogenicity islands mean
- Major virulence factors on large segments on chromosomal or plasmid DNA
- Increase bacterial virulence
- absent in nonpathogenic members
- common sequence characteristics
- insertion-like seqquences for mobility
- G + C content different from bacterial genome
- several open reading frames
- Can be spread through horizontal transfer of virulence genes to bacteria
What is the first step in disease
- entrance and attachment
- Portal of entry
- Skin, respiratory, gastrointestinal, urogenital systems, or conjunctiva of eye, parental route (break in barrier defenses)
- Vector borne, sexual contact, blood transfusion, or organ transplant
- Adherence
- medated by special molecules called adhesins
- Colonization
- A site of microbial reproduction on or within host
- does not necessarily result in tissue invasion or damage
- Portal of entry
What are the adherence structures of microbes
- Pili or fimbriae (adhesion molecules on bacterium’s cell surface) bind complementary receptor sies on host cell surface