Microorganisms that establish more or less permanent residence but that do not produce disease under normal conditions are called
Normal microbiota, or normal flora.
Microbiota that may be present for several days, weeks, or months and then disappear
Transient microbiota
Is microbiota found throughout the entire body?
No, just localized in certain regions.
What are some factors that determine distribution and composition of the normal microbiota?
Nutrients, physical and chemical factors, the host's defenses, and mechanical factors.
What kind of nutrients can microbes use as an energy source?
It varies, but a microbe will not colonize a body part that cannot supply the appropriate nutrients.
What may nutrients be derived from?
Dead cells, food in the gastrointestinal tract, secretory and excretory products of cells, and substances in body fluids.
What are some physical and chemical factors that affect the growth of microbes and thus the growth and composition of normal microbiota?
Temperature, pH, available oxygen and carbon dioxide, salinity, and sunlight.
What are some of the host's factors that affect normal microbiota?
Age, nutritional status, diet, health status, disability, hospitalization, stress, climate, geography, personal hygiene, living conditions, occupation, and lifestyle.
Once established, the normal microbiota can benefit the host by preventing the overgrowth of harmful organisms. This is called
Microbial antagonism, or competitive exclusion.
How does normal microbiota protect the host from harmful microorganisms?
They compete for nutrients, produce substances harmful to the invading microbes, and affect pH and available oxygen.
What can result when the balance between normal microbiota and pathogenic microbes is upset?
Disease.
The relationship between normal microbiota and the host is called
Symbiosis, the relationship between two organisms in which at least one organism is dependent on the other.
In which symbiotic relationship is one organism unaffected while the other benefits?
Commensalism.
A type of symbiosis that benefits both organisms is called
Mutualism.
Many disease-causing bacteria benefit by deriving nutrients at the expense of the host called
Parasitism.
Some microbes don't cause disease in their normal habitat in a healthy person but may do so in a different environment. This is called
Opportunistic pathogens.
What is an example of commensalism?
Staphylococcus epidermidis bacteria on the skin.
What is an example of mutualism?
E. coli in the large intestine
What is an example of parasitism?
H1N1 virus particles on a host cell.
What is the basic summary of Koch's postulates?
1. The same pathogen must be present in every case of the disease.
2. The pathogen must be isolated from the diseased host and grown in pure culture.
3. The pathogen from the pure culture must cause the disease when it's inoculated into a healthy, susceptible laboratory animal.
4. The pathogen must be isolated from the inoculated animal and must be shown to be the original organism.
What are some exceptions to Koch's postulates?
Some microbes have unique culture requirements, such as rickettsial and viral pathogens which cannot be cultured on artificial media.
Some pathogens can cause several diseases.
Some pathogens cause disease only in humans, such as HIV.
Changes in body functions, such as pain and general discomfort, that are felt by a patient as a result of disease. These are NOT apparent to an observer.
Symptoms
Changes in a body, such as swelling and fever, that can be measured or observed as a result of disease.
Signs
A disease in which an infected person transmits an infectious agent either directly or indirectly, to another person who in turn becomes infected. Chickenpox, measles and influenza are examples.
Communicable disease.
A disease that is very communicable and able to be spread easily and rapidly from one person to another, such as chickenpox.
Contagious disease.
Number of people in a population who develop a disease during a particular time period (rate). It indicates the spread of the disease.
Incidence.
The number of people in a population who develop a disease at a specified time, regardless of when it first appeared. This takes into account both old and new cases.
Prevalence.
A particular disease that occurs occasionally, such as Typhoid fever in the US.
Sporadic disease
A disease constantly present in a population, such as the common cold.
Endemic disease
If many people in a given area acquire a certain disease in a relatively short period, it is called
An epidemic disease.
What disease often reaches epidemic status?
Influenza
An epidemic disease that occurs worldwide
Pandemic disease.
When many immune people are present in a community, what exists?
Herd immunity.
Who benefits from herd immunity?
People who can't be vaccinated.
An infection in which the invading microorganisms are limited to a relatively small area of the body. Some examples are boils or abscesses.
A local infection
Microorganisms or their products are spread throughout the body by the blood or lymph. An example is measles.
Systemic (generalized) infection
Very often, agents of a local infection enter a blood or lymphatic vessel and spread to other specific parts of the body, where they are confined to specific areas of the body. They can arise from infections in teeth, tonsils, or sinuses.
Focal infection
A toxic inflammatory condition arising from the spread of microbes, especially bacteria or their toxins, from a focus of infection.
Sepsis
The presence of bacteria in the blood is called
bacteremia.
What are some predisposing facts that make the body more susceptible to disease?
Gender, inherited traits (sickle cell gene), climate and weather, fatigue, age, lifestyle, nutrition, and chemotherapy.
The general term of any nonliving object involved in the spread of an infection.
Fomite
The passive transport of pathogens on an insect's feet or other body parts, i.e. flies carrying typhoid fever or dysentery.
Mechanical transmission
How does biological transmission occur?
An arthropod bites an infected person or animal and ingests some of the infected blood. The pathogens reproduce in the vector, and the increase in the number of pathogens increases the possibility that they will be transmitted to another host.
Infections patients acquire while receiving treatment for other conditions at a health care facility.
Healthcare-associated infections (HAIs) or nosocomial infections
According to the CDC, how many people are estimated to have at least one HAI?
1 in 25.
In the United States, approximately how many people contract HAIs per year?
2 million.
What are some factors that contribute to HAIs?
1. Microorganisms in the hospital environment.
2. The compromised (weakened) status of the host.
3. The chain of transmission in the hospital.
What are the two most common HAIs?
Urinary tract infection and surgical infections.
What are some means of prevention for HAIs?
1. Reducing the number of pathogens by handwashing, cleaning and disinfecting tubs and instruments, using disposable bandages and intubations.
2. An infection control committee.
What are some factors that affect the emergence of infectious diseases?
New strains, travel, the overuse of antibiotics and pesticides, changes in weather patterns, ecological changes of a region, animal control measures, failures in public health measures.
The study of where and when diseases occur and how they are transmitted in populations is called
Epidemiology