Human Microbiota Intro (9) Flashcards
What are micro-organisms that cause disease called?
Virulent/pathogenic
Akaryote
Without a nucleus
Prokaryote
Genetic material in a single DNA chain, not enclosed in a nucleus (bacteria)
Eukaryote
Distinct nucleus (protocists, fungi, plants, animals)
Koch’s postulates
Robert Koch’s criteria used to decide if microorganism caused a disease
Koch’s postulate for genes
Genes encode virulence factors
- The gene encoding the trait of interest should be present and transcribed/translated in a virulent strain and be silent in a strain that does not cause disease; disruption of the gene in a virulent strain should result in the formation of a strain that is incapable of casing disease;
Problems with Koch’s postulates
- Difficulty of isolation the causative agent
- Impossible to grow some pathogens in artificial culture
- Ethical objections
- Animal models not sufficient/don’t behave same as humans
What are Viruses?
Obligate intracellular parasites
What are viruses comprised of?
Nucleic acid (DNA/RNA) core wrapped in a protein coat (capsomeres), some have a lipid envelope
Why are retroviruses unusual?
The virion carries an RNA copy of the genome but upon infection a host cell cDNA copy of virus genome is made using reverse transcriptase
Bacteriophage
Attacks bacteria
Bacterial shapes
Round, rod-shaped, icosahedral, brick-shaped, bullet-shaped
Viroids
Naked, infectious RNA molecules - plants suffer
Prions
Causes spongiform encephalopathies e.g. BSE/CZJ
Microfungi
Eukaryotic
What are most microfungi’s cell wall made of?
Chitin (polymer of N-acetyl glucosamine)
Where else is chitin found?
Exoskeleton of arthropods e.g. insects
Moulds
Fungi that grow in mats of tiny filaments (hyphae), form mats (mycelia), can be subdivided into separate compartments by cross walls (septa), multicellular organisms related to mushrooms
What genus is most common fungi?
Cladosporium
Yeast
Unicellular fungi e.g. Saccharomyces cerevisiae
What diseases do moulds form?
Superficial infections e.g. ringworm and athlete’s foot
What diseases do yeast form?
Thrush by Candida albicans
Protista
Unicellular eukaryotes, many free-living, some cause serious infections, can infect any human tissue
How are protista spread?
- Produce cysts to survive outside the body
- Insects
- Sex
Classes of protista
- Apicomplxa (sporozoa)
- Flagellate protista
- Ciliate protista
- Amoebae
Examples of infections caused by protists
Toxoplasmosis, amoebic meningitis, malaria, trypanosomiasis, leishmaniasis (Kala-Azar), amoebic dysentery, diarrhoea
Protista and vaginal infections
Caused by Trichomonas vaginalis, causes foul-smelling vaginal discharge, men can be asymptomatic carrier/balantis
Bacteria
Lack a membrane-bound nucleus/prokaryotes, small minority cause disease
Common shape of bacteria
Round/cocci or rod-shaped/bacilli, few are comma-shaped/spiral
Gram reaction
Ability to retain crystal violet-iodine dye complex when treated with acetone/alcohol
Gram +ve bacteria
30-40 layers of peptidoglycan
Gram -ve bacteria
Outer contains lipopolysaccharide, lipid A on surface acts as endotoxin > gram-negative shock
How are bacteria motile?
Flagella
What are fimbriae?
Hair-like structures that aid adhesion (gram -ve)
What are pili?
Tubes the join two cells together during conjugation to exchange genetic material (gram -ve)
What is a capsule?
Protects bacterium, even within phagocytes, preventing death
Why do some bacteria produce slime?
Helps stick to surface
What are endospores?
Resist a range of hazardous environments and protect against heat, radiation and desiccation (only few species have)
Spread of infection
- Droplet
- Faecal-oral
- Sexually
- Direct inoculation
- Animals
- Zoonoses (infection through animals being a reservoir)
- Fomites
- Intoxication
Examples of diseases acquired through drinking water
Typhoid, cholera, dysentery, hepatitis A and poliomyelitis
Virulence factors
Traits used to complete the cycle of infection
