intro to medical microbiology Flashcards
How are bacteria named, use example of E.coli?
- genus first, then species
- underline or italics
- Can abbreviate, so Escherichia coli becomes E. coli
Describe prokaryotes structure (bacteria)
- no nucleus or membrane bound organelles
- single, circular DNA (haploid)
- 70S ribosomes (50S and 30S subunits)
- peptidoglycan cell wall
Describe eukaryotes
- membrane bound nucleus
- chromosomes in nucleus (diploid)
- 80S ribosomes (60S and 40S subunits)
- no cell wall (except plants and fungi)
How are bacteria often classified?
by shape and staining
Describe how shape of bacteria is used to classify them
- ROUND = coccus/cocci
- LONG = bacillus/bacilli
- a few are spiral/branched/comma shaped
What is the difference between gram positive and gram negative bacteria?
GRAM POSITIVE: no outer
membrane
GRAM NEGATIVE: outer membrane
What is the predominant stain used to classify bacteria and what are the results?
- Gram stain
- positive = purple
- negative = pink
Describe Gram positive bacteria?
- thick peptidoglycan layer
- lipoteichoic and teichoic acid
- inner cytoplasmic membrane
Describe Gram negative bacteria?
- outer membrane made of lipopolysaccharide and has protein channels (porins)
- thin peptidoglycan
- inner cytoplasmic membrane
What are the synthetic pathways for peptidoglycan?
- polymerisation of sugars
- elongation of amino acid side-chains
- transpeptidase
Why are the synthetic pathways of peptidoglycan important in medicine?
as all the steps are targeted by important classes of antibiotics
What does each synthetic pathway for peptidoglycan synthesis do?
- POLYMERISATION OF SUGARS: to make the back-bone
- ELONGATION OF AA SIDE CHAINS: to add the peptides
- TRANSPEPTIDASE: to cross-link
Describe the peptidoglycan layer in bacteria?
- SUGARS: glucosamine (NAG) and muramic acid (NAM)
- amino acid peptides, resistant to enzymatic destruction
- cross-linked by transpeptidase enzymes
Describe lipopolysaccharide in gram negative bacteria
- lipid A = long-chain fatty acid anchor (active component)
- core polysaccharide chain
- variable CHO chain (= O antigen)
Why is lipopolysaccharide in gram negative bacteria important?
- major structural component
- effective permeability barrier (including to antimicrobials)
- regulates host immune response
Which patterns of growth can be seen in bacteria?
- MICROSCOPE: in clusters or chains
- SOLIDE CULTURE MEDIUM: colonies are different sizes/shapes
How can bacterial growth be exploited to identify the pathogen?
- patterns of growth
- excrete enzymes, waste products
- different requirements for growth (atmosphere ad nutrients)
What are the 3 possible bacterial atmospheric requirements?
- aerobes
- anaerobes (obligate anaerobes)
- facultative anaerobes
Describe aerobe bacteria?
use oxygen as final electron acceptor (very efficient)
Describe anaerobe (obligate anaerobes) bacteria?
- fermentation, final electron acceptor is organic molecule
- okay when substrates are plentiful
- oxygen usually toxic to them
Describe facultative anaerobe bacteria
can switch between aerobic and anaerobic metabolism
What are some things bacteria can’t make themselves?
- purine and pyrimidines
- amino acid
- vitamins
What are the nutritional requirements for E. coli?
- needs glucose and inorganic salts only
- very easy to grow in lab
What are the nutritional requirements for Treponema pallidum (syphilis)?
- specialised enriched medium
- hard to grow
Describe capsules in bacteria
- polysaccharide coat
- ‘hides’ immunogenic cell wall
- metabolic burden on the bacterium
- grants virulence
- immunity requires antibodies to the capsule
Describe the ribosomes in bacteria
- engines of protein synthesis
- 70S (50S and 30S subunits)
- each contains bacterial RNA and proteins
- the RNA is the target of antibiotics and diagnostic tests
Why do bacteria move?
chemotaxis (moving towards or away from chemical stimuli)
How do bacteria move?
- rotate a flagellum like a propeller
- use a pilus like a grappling hook
- corkscrew motility (spirochete)
How do bacteria stick?
adhesin and receptor bind in a specific/complementary manner
What is docking and anchoring in bacteria?
- DOCKING: non-specific adherence
- ANCHORING: specific adherance
How do bacteria transfer genes?
- transduction
- conjugation
- competence/transformation
What are the mobile genetic elements of bacteria and what do they do?
- plasmids
- transposons
- they code for toxins and antibiotic resistance genes
Describe plasmids
- circular ‘extra-chromosomal’ DNA
- independently replicating
- passed down to offspring
- some transmitted between bacteria
Describe transposons?
- DNA sequences that are able to move location in the genome
- encode transposase and other genes
What are transposons mobile between?
- genomic and plasmid DNA
- plasmids
State the 4 phases of bacterial growth
- lag phase
- exponential phase
- stationary phase
- death phase
Describe the lag phase in bacterial growth
- no increase in cell numbers
- adjustment to new environment
- gene regulation
Describe the exponential phase in bacterial growth
- cell doubling
- slope of the curve = growth rate of organism in that environment
Describe the stationary phase in bacterial growth
- nutrients become depleted
- metabolites build up
- divison stops
- gene regulation
Describe the death phase in bacterial growth
- exhaustion of resources
- toxicity of environment
In which phases of bacterial growth does gene regulation occur?
in the lag phase and stationary phase
What are endotoxins?
lipopolysaccharides found in the cell wall of Gram-negative bacteria
What are the steps to carrying out a gram stain?
- crystal violet
- iodine
- decolourisation with alcohol
- safranin counterstain
What sugars are in the peptidoglycan?
- glucosamine (NAG)
- muramic acid (NAM)
What is the other stain that can be used and in which context is it used?
- Ziehl-Neelsen stain
- for mycobacteria that have thick lipid membrane made of mycolic acids
What are some bacterial growth requirements that are modified in the lab?
- temperature
- pH
- salt content
Give examples of bacteria that lack a cell wall and are not ‘free-living’
- mycoplasma
- chlamydia
What are spores resistant to?
- drying
- temperature
- disinfection
- digestion
Which medically important bacteria make spores?
- bacillus spp
- clostridium
What is gene regulation important for in bacteria?
- conserve energy (prevent unnecessary gene expression)
- Adapt to environmental changes
- coordinated changes in expression of multiple genes
