Pathogens in Perspective Flashcards
What are environmental pathogens?
Microorganisms that normally spend substantial part of their lifecycle outside human hosts
BUT when introduced to humans cause disease with measurable frequency
What are some examples of Pathogenic Bacteria?
Staphylococcus aureus
Clostridium tetani
Yersinia pestis
Campylobacter jejuni
E.Coli O157:H7
Vibrio cholerae
Leptospira interrogans
Borrelia burgdorferi
What are some examples of classes of Protozoans?
Amoebae
= Entamoeba histolytics
Ciliates
= Balantidum coli
Flagellates
= Giardia lamblia
Apicomplexans
= Cryptosporidium parvum
= Plasmodium vivax
What are some examples of viral pathogens?
Gastroenteritis causing:
= Rotavirus
= Adenovirus
= Norwalk
Non Gastroenteritis causing:
= Polio
= Enteroviruses 68-71
= Hepatitis A + E
Environmental zoonotic viruses
= Ebola
= West Nile Fever
+ SARS-CoV-2
What are some examples of fungal pathogens?
Candida albicans
Asperigillus fumioatus + flavus
Cryptococcus neoformans
Histoplasma capsulatum
What is the resident flora ?
= the ‘norm’
= includes bacteria, fungi, protozoa, viruses, helminthes and arthropods
= most bacteria in large intestine
= internal organs, tissues + fluids are microbe-free
= unique to an individual
= large metabolic potential (microbial gene pool very large)
Microbial antagonism
= bacterial flora benefit host by preventing overgrowth of harmful microbes
What is the Gut microflora? How does it change over time?
Pre-birth = gut thought to be sterile
After birth = acquire commensal bacteria from environment
(breaking of foetal membranes, handling, feeding)
= commensal bacteria dominate
(changes can lead to disease e.g. IBD)
= density of bacteria depends on location
(e.g. less in stomach compared to intestine and colon)
= most diversity in colon
(mostly anaerobic, with aerobic less abundant)
What are some functions of intestinal bacteria?
Protective functions
= pathogen displacement
= nutrient competition
= receptor competition
= production of anti-microbial factors
Structural functions
= barrier fortification
= induction of IgA
= apical tightening of tight junctions
= immune system development
Metabolic functions
= control IEC differentiation + proliferation
= metabolise dietary carcinogens
= synthesise vitamens
= ion absorption
= salvage of energy
= ferment non-digestible dietary residue and endogenous epithelial-derived mucus
What are some factors influencing intestinal flora?
Delivery method at birth
Antibiotics
Oral contraceptives
Radiation / Chemotherapy
Corticosteroids
Sugar in diet
Bactericidal chemicals in drinking water
Pesticides in food
Alcohol
Heavy metals
H.pylori
Gastrointestinal pH
Stress
How does the human microbiota change with age?
As age increases, gut microbial community significantly changes
(new strains, increase in diversity)
Process of early development of the microbiota is hight unstable and idiosyncratic (structural or behavioural)
Microbiota also differs among children from different countries
Vaginal vs C-section also makes a difference
(returns to normal after about 6 weeks)
What are the different classes of pathogen? How is the severity of an infection determined?
True pathogens
= capable of causing disease in healthy persons with normal immune defences
= very few microbes are always pathogenic
= e.g. influenza, plague bacillus, malarial protozoan
Opportunistic pathogens
= cause disease when the host’s defences are compromised or when they grow in part of body not natural
= more microbes are potentially pathogenic
= e.g. Pseudomas sp, Candida albicans
Severity of disease depends on:
= virulence
(virulence factor = characteristic or structure that contributes to ability of microbe to cause disease)
What are the 5 modes of transmission?
Person to person transmission
= sexually transmitted diseases
= respiratory infections
Foodborne transmission
= insufficient cooking
= poor sanitation
Waterborne transmission (environmental)
= drinking water / swimming
= faecal-oral route
Airbone transmission (environmental)
= aerosols
= wastewater treatment plants, land application
Vector-borne transmission (environmental)
= bite of an animal host
What are some portals to entry?
= characteristic route a microbe follows to enter tissues of body
Skin
= nicks, abrasions, punctures, incisions
GI tract
= food, drink
Respiratory tract
= oral and nasal cavities
Urogenital tract
= sexual, displaced organs
Transplacental entry
What is the Infectious Dose (ID)?
= minmum number of microbes required for infection to proceed
= microbes with small IDs have greater virulence
= varies between genus, species and strain
How do microbes attach to the host?
Adhesion
= microbes gain stable foothold at portal of entry
= dependent on binding between specific molecules on host and pathogen
e.g. fimbriae, flagella, adhesive slimes or capsules, pili