Lecture 12- Infectious Disease And The GI Tract Flashcards
Bacterial infection factors
*opportunistic vs obligate pathogen;
-opportunistic = may be transmitted without causing disease
-obligate = must cause disease for transmission
*intracellular vs extracellular
*number of infectious units required for enteric pathogens;
Low= shigella dysenteriae (-10 cells)
High= escherichia coli (-100 cells)
*virulence factors= v.cholera only pathogenic if it has integrated bacteriophage DNA to allow toxin production
*damage= direct vs toxin-mediated vs indirect
*exposure= likely to come into contact?
*immuno-compromised host= elderly, very young, HIV
Stages of infectious disease
Exposure- first contact with the pathogen
Incubation period- time between exposure to pathogenic organism + the first appearance of symptoms
Length of incubation period depends on; virulence, portal of entry, infective dose, immune system health, site of infection + pathogen specific factors
Periods- slide 7
Stages of infectious disease
Prodormal period-
- early stage of a disease - when symptoms first appear
-generalised symptoms; malaise, fever, muscle aches
-associated with immune system activation
Gram negative bacterial cell recognition + fever= slide 7
Stages of infectious disease
Illness/acute period;
-infection has developed
Severe stage of infection; pathogen numbers are at their peak
-immune responses limited/developing
-transmission risk at its highest
Stages of infectious disease
Decline;
-immune response/medical intervention results in a killing/removal of the pathogen
Symptoms begin to subside
Immune response peak
Patient doesn’t enter this stage= disease is fatal
Convalescence;
-recovery of patient - tissue and systems are repaired
Length of time based upon; extent of damage, nature of pathogen, site of infection + overall health of patient
The chain of infection
Slides 12-13
Human reservoirs;
Diseases that are transmitted from person to person without intermediaries
- Symptomatic infections; symptoms of infections. Most likely already diagnosed/being treated. Patient contacts/activities are restricted
- Carriers;
Incubatory carriers; transmit the infection before their own symptoms appear
In apparent carriers; never develop the infection but can transmit
Convalescent carriers; still infectious whilst recovering from the infection
Chronic carriers; recovered but are still infectious
Examples of infections; human immunodeficiency virus, smallpox, measles, syphilis, group A streptococcus
Animal reservoirs; AKA Zoonoses
Both domestic, wild animals + insects are included
Direct contact= bite/scratch- rabies
Animal products= sheep wool
Consumption; shellfish
Non-living reservoirs;
Soil, water, food, faeces
^C.tetani, V.cholerae; legionella pneumophila, C. Botulinum + tetani
Barriers to infection + portals of entry
Human body= comprises skin + mucosal epithelia; digestive, respiratory + urinary tracts
Barriers= prevent pathogens from crossing epithelia + colonizing underlying tissues
Surface epithelium= provides mechanical, chemical + microbiological barriers to infection
Portals of entry; same pathogen uses diff routes- slide 19
Bacterial pathogenesis
Bacterial virulence factors play a key role in= colonisation, infection + invasiveness
Slide; 20
Relating bacteria to infection;
Koch’s Postulates; a set of criteria established to identify causative agent of infection
^gene associated with infection should be inactivated
Steps 1-4; slide 21
Origin of modern epidermiology
Epidemiology; study of the distribution + determinants of health-related status and events in specific population
Slides 23-25
Miasma theory; medical theory that disease was caused by noxious forms of air (bad air) from decaying matter
Bacterial biofilms
-aggregates of cells attached to a surface and/or each other, and that are surrounded by an extracellular polymeric matrix
EPS Defining feature with key roles in; structure, antimicrobial protection, retainer water/nutrients, virulence factor, adhesion, genetic transfer + communication
Composition of EPS varies based on species in the biofilm, external conditions; polysaccharides, extracellular DNA + proteins
Some biofilms generate an EPS composed of crystalline minerals; calcium or mg phosphates
5 stages; 26-27
The gastrointestinal tract
Consists of; oral cavity, pharynx, oesophagus, stomach, small intestine, large intestine + anal canal
Accessory organs; teeth, tongue, glandular organs etc
Functions; digestion, adsorption + excretion + immune response
IR= maintains homeostasis
-protects from pathogens we may ingest
-tolerance
-IBS
GI= defence against infections
Typical high-income diet- 200,000 microbes each day
GI tract contains- 100 trillion microorganisms; diff species of bacteria in the colon
Oral infections- tooth decay
Infectious disease of teeth- bacteria may be transferred to others; biofilms form on tooth surface + eventually degrade the structure
Compound by plaque (biofilm) formation;
25+ streptococcus
S.mutans produces an enzyme;
-converts sucrose to a dextran-based polysaccharide
-produces a thick+ sticky substance = plaque
-“secondary colonisers”= can adhere to
S.mutans can ferment carbs to organic acids
-pH < 5.5= allows tooth demineralization
-overtime enamel is broken down= decay
