Symbiosis
a close and long-term interaction between two different species
3 types of symbiosis
mutualism (both organisms benefit), commensalism (one benefits and the other is unaffected), and parasitism (one benefits and the other is harmed)
Parasite
organisms that live on or inside another organism, the host, deriving nourishment at the host’s expense
Host
an organism that provides nutrients, shelter, or other resources to another organism
Pathogen
a bacterium, virus, or other microorganism that can cause disease.
Normal Microbiota
the trillions of microorganisms (bacteria, viruses, fungi, and protozoa) that permanently inhabit various body surfaces and systems of healthy individuals.
Conditions that create opportunities for normal microbiota to create disease
Opportunistic Pathogens
Contamination vs infection
Contamination: The presence of harmful microorganisms on or in a surface, object, or body without causing illness.
Infection: The invasion and multiplication of microorganisms in the body that leads to disease symptoms.
4 types of portals through which pathogens invade the body
inhalation (respiratory tract), ingestion (gastrointestinal tract), injection (breaks in the skin or medical procedures), and absorption (through mucous membranes or damaged skin)
Adhesion factors and infection examples
Adhesion factors (adhesins) are structures or molecules that allow microbes to attach to host cells. Examples:
Neisseria gonorrhoeae uses pili to adhere to urogenital epithelium.
E. coli uses fimbriae to attach to intestinal mucosa.
Viruses use spikes
Portals of exit for microbes
Natural body openings or routes by which pathogens leave the host: respiratory droplets, feces, urine, blood, semen/vaginal secretions, saliva, tears, skin flakes, milk.
Infection
The invasion and multiplication of a pathogen in a host, regardless of whether it causes harm.
Disease
A condition in which infection results in noticeable impairment of body function or damage to tissues.
Morbidity
The incidence or prevalence of a disease in a population.
Pathogenicity
The ability of a microbe to cause disease — qualitative.
Virulence
The degree of pathogenicity — how severe a disease the microbe can cause; often linked to virulence factors (capsules, toxins, enzymes, etc.).
Symptoms
Subjective evidence of disease felt by the patient (e.g., pain, fatigue, nausea).
Syndromes
A group of signs and symptoms that together characterize a disease.
Signs
Objective, measurable indicators of disease (e.g., fever, rash, swelling, elevated WBC count).
Etiology
The cause or origin of a disease (infectious agent, genetic factor, environmental exposure).
Koch’s Postulates
- Suspected pathogen must be found in all cases of disease and absent from healthy hosts.
- Pathogen must be isolated and grown in pure culture.
- Cultured pathogen must cause disease when introduced into a healthy susceptible host.
- Same pathogen must be re-isolated from newly diseased host.
Extracellular enzymes and virulence
Extracellular enzymes increase virulence by helping pathogens invade tissues or escape host defenses.
toxins effect on virulence
Toxins directly damage host cells, disrupt physiology, or overstimulate immune responses. They greatly enhance virulence by causing tissue destruction, immune evasion, or systemic effects like shock.
adhesion factors effect on virulence
Adherence factors allow pathogens to anchor to specific host tissues, increasing the likelihood of colonization and infection. Without adhesion, many pathogens cannot establish infection.
