Lecture 12- Infectious Disease And The GI Tract Flashcards
(24 cards)
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
The Chain of Infection (How Infections Spread)
🔗 There are 6 links in the chain:
*Infectious Agent
Bacteria, viruses, fungi, parasites (germs that cause disease)
*Reservoir (Where germs live)
Humans, animals, food, water, soil, faeces
*Portal of Exit (How germs leave)
Coughing, sneezing, blood, urine, poo, wounds, etc.
*Mode of Transmission (How germs spread)
Direct (touch, fluids)
Indirect (contaminated objects, water, phones)
*Portal of Entry (How germs enter a new person)
Cuts, mucosa, GI tract, urinary tract, lungs, sexual contact, medical devices
*Susceptible Host (Person who gets infected)
Very young/old, chronic illness, malnourished, immunosuppressed
🛑 How to Break the Chain of Infection
✅ At each link, we can take actions to stop spread:
*Infectious Agent
Diagnose & treat early, Use correct antibiotics (antimicrobial stewardship)
*Reservoir
Clean/disinfect surfaces, Safe food & water, Control pests
*Portal of Exit
Cover coughs/sneezes, Dispose of waste safely, Hand hygiene
*Mode of Transmission
Wash hands regularly, Use PPE (gloves, masks), Sterilize equipment
*Portal of Entry
First aid: clean and cover wounds, Remove contaminated medical tubes, good hygiene
*Susceptible Host
Vaccinate, treat underlying conditions, patient education
Isolate if needed
Break even ONE link in the chain → infection stops spreading
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- skin, inhalation + ingestion
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
1) Suspected pathogen should be found in abundance in infected organism.
2) Pathogen should be isolated (from infected organism) and grown in pure culture.
3) Isolated microorganism should cause disease when introduced into a healthy organism.
4) Microorganism should be reisolated from the (now) diseased host.
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, retain 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
Immune response = 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 food 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
