Environmental Pathogens Lecture 1 Flashcards
Define a pathogen
A biological agent that causes disease or illness in a host. Can be bacteria, fungi, protozoan or viruses.
What is an environmental pathogen?
Microorganisms that normally spend a substantial amount of their lifecycle outside of human hosts, but when introduced to humans cause disease with measurable frequency.
Give some examples of bacteria
Staphylococcus aureus- from the skin, an opportunistic pathogen. e.g., MRSA
Campylobacter jejune- found in chicken farms, causes gastroenteritis.
Legionella pneumophilia- causes Legionnaires- found in AC units, taps, showers. Can be free living or an intracellular pathogen (protozoan and alveolar macrophages).
Borrelia burgdorferi- causes Lyme disease- tick borne and temperature effects their population
Normal Resident Flora
- microbes that engage in mutual/commensal associations (indigenous flora and microbiota).
- Includes bacteria, fungi, protozoa and viruses. Most areas of the body in contact with the environment harbour microbes.
- Bacterial flora provide a benefit by preventing overgrowth of harmful microbes–microbial antagonism
What is microbial antagonism?
- Resident flora (bacteria) prevent overgrowth of other harmful microbes
How much bacteria colonises the human body?
- 10^14 microbial cells are associated with the human body, 80% of which have been cultured.
What is the Gut microbiota?
Gut microbiota are the microorganisms, including bacteria and archaea, that live in the digestive tracts.
- Breaking of foetal membrane exposes the infant.
- Post gut is transformed and acquisition is random not predetermined
- Host provides bacteria with nutrients
Describe the changing gut microbiota with age
Birth: delivery and mode of feeding affects composition of the gut. E.coli colonises in first 14 hours
Early childhood- new strains outcompete old ones, rapid increase in diversity. Shifts in response to diet, illness, hormones
Adult microbiota- Highly distinct, changes slower
Elderly- substantially different than your
Few microbes are pathogenic
Factoring influencing intestinal flora
Delivery method at birth, antibiotics, diet, stress, contraceptives, bactericidal chemicals in drinking water, heavy metals
Define infection
a condition in which pathogenic microbes penetrate host defences, enter tissues and multiply causing disease
Define Disease
Any deviation from health, disruption of a tissue or organ.
Define pathogenicity
An organisms ability to cause disease
Define virulence
A measure of the degree of disease that a pathogen causes
Define ‘true pathogens’ and give examples
Capable of causing disease in healthy person with normal immune defences- influenza virus, malaria
Define opportunistic pathogens and give examples
Cause disease when hosts defences are compromised or grow in a part of the body not natural to them.
E.g., Pseudomonas and Candida albicans
Name the 5 modes of transmission of pathogens
Person to person- direct contact, STIs, respiratory infections (coughing/sneezing)
Waterborne transmission*- drinking water/swimming (ingestion), faecal oral route (contamination of water)
Foodborne transmission*- insufficient cooking, ingestion of raw/unwashed food, poor sanitation or hygiene. 6million cases/year US
Airborne transmission*- Aerosols, wastewater treatment plants, sludge, showers e.g., Legionella
Vector borne transmission*- bite of an animal host- Malaria, African sleeping sickness, Yellow fever
*denotes environmental routes
Portals of entry of microbes
Skin- abrasions GI tract- food/drink Respiratory tract Urogenital (sexual) Transplacental
Define Infectious Dose (ID)
- Minimum number of microbes required for an infection to proceed.
- Microbes with smaller ID have greater virulence
- Varies between species, genus and strain
- Cholera ID: 10^8 cells, Measles 1 virus,
Describe the 3 stages of infection
- Attaching to the host via adhesion- dependent on binding between specific molecules on the host and pathogen. e.g., fimbrae, flagella, slimes/capsules, pills.
- Surviving host defences- initial response from host comes from phagocytes.
- Antiphagocytic factors are used to avoid this.
- Species of Staphylococcus and Streptococcus produce leukocidins- toxic to WBCs.
- Slime layer/capsule makes phagocytosis difficult
- Ability to survive intracellular phagocytosis Legionella pneumophilia. - Causing disease- Virulence factors e.g., exoenzymes digest epithelial tissues and promote invasion of pathogens, toxigenicity- ability to produce toxins at site of multiplication (endotoxin-LPS, exotoxins secreted by gram +ve and -ve).
- Antiphagocytic factors
Describe the four phases of infectious disease
- Incubation period- time from initial contact to appearance of symptoms (several hours-several years).
- Prodromal stage: mild symptoms, unspecific, feelings of discomfort.
- Period of invasion: multiplication high level, specific symptoms
- Convascelent period: a person begins to respond to infection, symptoms decline.
Define localised infection
Microbes enter the body and remain confined to a specific tissue
Define systemic infection
Infection spreads to several sites and tissue fluids usually in the bloodstream
Define focal infection
When infectious agents break loose from a local infection and is carried to other tissues
Define mixed infection
Several microbes grow simultaneously at the infection site-poly microbial
