Overview of Microbiology 1 and 2 Flashcards
What causes infections?
Infections are caused by a range of different microorganisms
- bacteria, fungi, protozoa, helminths, viruses
these organisms could be contaminants
What is the difference between structure of gram positive and negative bacteria? What are other differences?
gram positive
- thick peptidoglycan wall
- no outer membrane = low lipopolysaccharide content
- teichoic acid is present
- no porins
gram negative
- thin peptidoglycan wall
- outer membrane is present = lipopolysaccharides and proteins
- porins are present
Gram positive bacteria stain pink (retain stain) whereas gram negative stain purple (do not retain stain)
Gram positive bacteria are more susceptible to antibiotics than gram negative (are more resistant)
What are the five criteria used to identify an effective antimicrobial agent?
exhibit selective toxicity
have broad spectrum
no hypersensitivity in host
no drug resistance
no harm to normal microbiota
How can genetic material be passed from one bacterium to another?
horizontal gene transfer
- transformation
- transduction
- conjugation
What is the process of transformation?
- DNA is released by the donor bacterium (is dead and degraded) into the environment = lysis
- recipient bacterium takes up DNA from the extracellular environment directly = membrane is made more permeable
- exogenous DNA (genetic material) is incorporated into the cell
- homologous recombination of the recipient and donor cell DNA
the bacteria must be competent
DNA must be at least 500 nucleotides in length
What is the process of transduction?
bacteriophage function as a vector to introduce DNA from the donor bacteria into the recipient bacteria by infection
- bacteriophage infects the donor cell (host cell) = injects its DNA into the cell
- once inside the bacteriophages can follow either the lytic or lysogenic life cycle
- transducing phage with donor DNA infects the recipient cell
- homologous recombination occurs upon infection
lytic - lytic bacteriophages hijack the bacterium’s cell machinery to make more viral particles. this continues until the cell undergoes lysis and releases the bacteriophages. they can then infect the recipient cell
lysogenic - bacteriophage DNA is incorporated into the host’s genome at a specific site and form a protophage then remains dormant until triggered to enter the lytic cycle
What is the process for conjugation?
F-plasmid codes for the formation of the pilus (protein)
pilus extends from the cell surface and attaches to the recipient bacterium = pulls them closer together, forms a mating pair
DNA is transferred across the pilus
- single DNA strand is replicated and transferred
- DNA strand replicates and forms a double stranded molecule which then forms the plasmid
Mating pair is broken at the end of conjugation
Homologous recombination of DNA
if the F-factor is transferred the cell can forms its own pilus and act as a donor
What is the requirements of conjugation?
donor bacterium must have F-plasmid/F-factor (fertility factor)
- they encode for the protein that makes the pilus (cytoplasmic bridge)
recipient bacterium must lack the F-plasmid
donor bacterium must have F-plasmid/F-factor (fertility factor)
- they encode for the protein that makes the pilus (cytoplasmic bridge)
recipient bacterium must lack the F-plasmid
What is normal microbiota?
refers to the microorganisms that reside on the surface and deep layers of skin, in the saliva and oral mucosa, in the conjunctiva, and in the gastrointestinal tracts
What is the function of normal microbiota?
Gut microbiota is essential for (HIMP)
- homeostasis
- intestinal development
- protection against pathogenic challenges
- maturation of the immune system
Gut microbes are involved in metabolic reactions (FBSD)
- fermentation of non-digestable dietary fibre
- biotransformation of conjugated bile acids
- synthesis of some vitamins
- degradation of oxalate-based complexes
What is mutualism?
Mutualism is type of symbiosis that benefits both organisms
What is commensalism?
Commensalism is a relationship occurs when one organism benefits while the other is not much affected, but may indirectly benefit
What is parasitism?
Parasitism: is a relationship where one organism gains while the other suffers
What are challenges to bacterial survival?
Peristalsis
Oxidative stress
- variety of reactive oxygen species, reactive nitrogen species
Antimicrobial peptides components of the innate immune system
- broad class of molecules
Microbe to microbe competition
Niche specificity
What are the problems with antibiotics?
Human gut microbiota can be exposed to anthropogenic antibiotics
- antibiotic therapy can result in severe changes to gut microbiota composition
Rapid evolution and expansion of antibiotic resistance
- rise in antibiotic resistance > development of new antibiotics
