Microbial Diseases and Diversity Flashcards
What do Koch’s postulates prove
that a specific organism causes a specific disease
what are Koch’s postulates
The microorganism must be found in abundance in all cases of the disease and absent from healthy individuals.
The microorganism must be isolated from a diseased individual and grown in pure culture.
The same disease must be produced when the pure culture of the microorganism is inoculated into a healthy susceptible host.
The microorganism must be reisolated from the experimentally infected host and identified as being identical to the original causative agent.
why don’t syphilis and chlamydia fit with Koch’s postulates
they are obligate intracellular parasites and rely on the host for nutrients therefore cannot be grown in vitro
they can be asymptomatic so do not cause sickness or illness
what are the common routes of infection in humans
respiratory system
oral-faecal contamination
contact transmission (fomites)
vector-borne transmission (insects etc)
what bacteria cause stomach ulcers
overview of it
Helicobacter pylori
Gram-negative, motile, oral transmission
pH resistant but unable to grow in these conditions
how does helicobacter infect and allow its own growth
ingestion and flagella propel to mucosa
it produces urease (converts urea to CO2 and ammonia) and lowers the surrounding acidity
makes enzymes to soften the mucous lining
lower acidity allows growth but causes damage and inflammation to host stomach
what are exceptions to Koch’s postulates
microorganisms that are unable to be cultured on artificial media (intracellular parasites)
when 2 or more organisms work in synergy to cause disease (gingivitis)
ethical exceptions
dangerous strains cannot be experimented on
asymptomatic infection
how have Koch’s postulates been refined
advances in technology mean microorganisms can be studied without the need for culture
some hosts are not susceptible to diseases due to genetic resistance
asymptomatic carriers
environmental factors such as diet, stress and exposure can influence development
what features do bacteria, archaea and eukaryotes have in common
plasma membranes and ribosomes
some metabolic pathways
DNA replication
what are major differences between bacteria archaea and eukaryotes
presence of a membrane-enclosed nucleus
presence of peptidoglycan in cell wall
how the membrane lipids are linked
what are the important structural characteristics of bacteria
gram positive/ negative: ability to retain crystal violet due to peptidoglycan layer thickness and the presence or lack of outer membrane
common shapes: cocci (spheres), bacilli (rods) spirilla (spirals)
what are the important structural characteristics of archaea
absence of peptidoglycan (methanogens have pseudopeptidoglycan)
branched chains of lipids with ether (R-O-R) not ester (R-COO-R) linkages
what are the important structural characteristics of eukaryotes
nuclear membrane
firmicutes summary and examples of each type
low GC, Gram-positives
Mycoplasmas (lack a cell wall, small, Gram negative)
Endospore forming:
- Aerobic (bacillus)
-Anaerobic ( clostridium)
Non-spore forming:
- Staphylococcus
actinobacteria summary and example
high GC, Gram-positives
Filamentous branching
streptomyces
