Bacteria - Week 2 Flashcards
Is bacteria a prokaryote or eukaryote?
Prokaryote
Describe the cell wall of a Gram+ bacteria
Thick layer of peptidoglycans containing teichoic acid and lipoteichoic acid (acts as a PAMP). Crystal violet dye stains it purple.
Describe the cell wall of a Gram- bacteria
Thin layer of peptidoglycan. Additional outer layer rich in lipopolysaccharides (antigen that interacts with TLR-4). Crystal violet dye stains it pink.
What does it mean by acid-fast bacteria? Give an example
Characterised by wax-like cell wall that contains mycolic acid.
Gram+ mycobacteria
What is it meant by fastidious bacteria?
Bacteria that will only grow if certain nutrients are present
What shape is a cocci, bacilli and spirilla?
Spherical, rods, helical
Describe the phases of growth you’d see in bacterial numbers when added to a culture medium
lag phase > logarithmic/exponential phase (population doubles at constant rate) > stationary phase > death
What is the term used to describe how bacteria reproduce?
Binary fission - where one bacterial cell divides into two identical daughter cells
Briefly describe the process of transformation
ability to take up DNA fragments from related spp. across cell wall
Describe transduction
transfer of genetic material by infection with bacteriophage
conjugation
bacterial ‘mating’ where DNA is transferred from one bacterium to another by use of a pilus
List Koch’s Postulates
1) microbe must be present in all cases of the disease
2) pathogen can be isolated from diseased host and grown in pure culture
3) pathogen from pure culture causes disease when inoculated into a health, susceptible lab animal
4) pathogen can be re-isolated from new host and shown to be same as originally inoculated pathogen
what is a facultative aerobe?
organism that makes ATP by aerobic resp. when O2 present but can switch to anaerobic resp. if O2 is absent
Obligate aerobe
cannot make ATP in absence of oxygen
obligate anaerobe
dies in presence of o2
Overt/strict pathogen
only associated with human disease - not found in healthy microbial flora
opportunistic pathogen
present in normal gut flora but only causes disease when introduced into unprotected site (e.g. in immunocompromised patients)
facultative pathogen
can grow and survive in environment as well as in host
Give examples of bacterial virulence factors
1) adhesins (pili, outer membrane proteins)
2) flagella
3) toxins
4) capsule
5) type III secreted molecules
What is an endotoxin
part of LPS of cell wall of Gram- bacteria. Heat stable, cell bound. causes general symptoms such as fever, diarrhoea, vomiting. weakly toxic
What is an exotoxin
proteins produced extracellularly by certain Gr+ and Gr- spp. Heat labile, usually highly toxic
enterotoxin
group of exotoxins that acto on small intestine. (C.difficile toxin A)
What is a toxoid?
Inactivated toxin - useful as a vaccine
List various methods of bacterial immune evasion
1) Hide - enter cell and stay intracellular
2) antigenic variation - avoid an established immune response
3) Molecular mimicry - so body recognises it as self
4) modify or block host immune response - e.g. interfere with host’s cell signalling pathways - type III secreted effectors
What is meant by commensal bacteria? Where would you find them?
living in relationship with another organism where one derives benefits from another organism withough hurting or helping it.
Find in normal microbial flora
What factors can affect the human microbiiome?
diet, age, genetics, lifestyle, immune response, microbial co-adaptation, drugs
List some of the positive effects of the gut microbiome
- develop/stimulate immune system
- prevent colonisation of pathogens
- produce beneficial nutrients (e.g. vit. K)
- metabolise natural compounds into more readily available versions
- metabolise xenobiotic substances, destroying toxins
Name a microbe that is present in normal gut flora but that can cause antibiotic-associated diarrhoea in hospitalized patients
Clostridium difficile.
Gr+, anaerobic
What substance in the GI tract keeps vegetative growth of C.diff at bay?
Secondary bile salts
What substance in the GI tract allow C.diff spores to turn into a vegetative state?
Primary bile salts
what is the term used to describe an imbalance of the normal gut microbiota composition
Dysbiosis
What are pre-biotics?
non-digestible food ingredient that beneficially affects the host by selevtively stimulating the growth and/or activity of one or a limited number of bacteria in the colon to improve host’s health
What are probiotics
living, non-pathogenic organisms used as food ingredients to benefit the hosts’ health
