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
Dental abscess; result of infection extending into the pulp of the tooth
Pulp can become necrotic
-associated with tooth decay; breaks down the enamel allowing bacterial access to the dentin + underlying pulp
Severe throbbing pain; tooth tender to touch
Without treatment= dental abscess persist, pain may subside as the nerves die; abscess may burst
Treatment= root canal treatment/ tooth removal; antibiotics
Not treated= infection can spread inside + outside of the mouth
Periodontal disease
Chronic bacterial infection affecting the gums + bone supporting the teeth
Gingivitis (inflammation) -> periodontitis (gums recede- teeth become loose + may fall out)
Host response makes infection worse; gingival inflammation -> temp increases -> increased flow in gingival crevicular fluid (GCF)
- break down of GCF; contains iron + tissues; more nutrients for bacteria
-continuous cycle until tooth loss
Oral thrush- Candida Albicans
Fungal infection; overgrowth of the mucous membranes in the mouth- C.albicans
Commensal member of the human microbiome;
50% have C.albicans in oral cavities
Newborns >64% get colonised during passage through birth control
Overgrowth of C.albicans usually associated with immune system suppression
Opportunistic pathogen- risk factors
-elderly/newborns, chemotherapy, HIV/AIDS, antibiotics + steroids
The human stomach
Function; temp storage, mechanical digestion (muscular contractions) + chemical digestion (gastric acid secretion)
Gastric acid= digestive fluid secreted by gastric gland cell, comprises of; hydrochloric acid, gastric lipase, pepsin (breaks down proteins into peptides/amino acids)
Lowers stomach pH to 1-2; intolerable of microbial life
Helicobacter pylori
Gram negative, spirochete + highly motile
Associated with; gastritis, ulcers + gastric cancers
Adapted to survive in stomach acid;
-secretes urease= breaks down urea into ammonia + bicarbonate
-produces a cloud of increased pH around the bacterial cells
-cells = survive stomach acid
Virulence factors= VacA- cytotoxin; exotoxins, LPSA- endotoxin
^ = localised tissue destruction + ulceration
-can also infect the duodenum
- found in 80% of patients with the infection -> leads to duodenal ulcers
Slide 39-41
H.pylori- detection + treatment
Detection;
Urea breath test- using carbon isotopes
Blood/stool test for H.pylori antibodies
Treatment;
Antibiotics + proton pump inhibitors
Amoxicillin, clarithromycin + metronidazole
PPIs= reduce stomach acid production -> allows ulcers to heal
Antibiotic = 1 week treatment, tested again for H.pylori after 4 weeks
Emerging infectious disease
Either newly recognised in a population/ exist but are rapidly increasing in incidence/geographic age
Contributing factors; population growth, increase immunocompromised patients, travel, climate change, AMR + breakdown in living conditions
Examples; COVID-19, HIV, Mpox
ESKAPE Pathogens
6 extremely virulent + highly antibiotic-resistant bacteria pathogens
Gram + and Gram - = evade/escape commonly used antibiotics; increasing multi-drug resistance MDR
Staphylococcus aureus- food poisoning
Eating good contaminated with toxins produced by S.aureus= food contam during handling process
Enterotoxin= super antigen -> diarrhoea + vomiting
30 mins-8hrs = after consumption
Symptoms= fever, abdominal cramping, diarrhoea, headache
^ resolve in 24hrs
