bacterial infections 1 adrian Flashcards
how do pathogenic bacteria survive?
– must remain in close contact with the body and multiply – must survive host defence – must compete against endogenous flor
what do symptoms of infection arise from?
the direct effect of the bacteria eg diarrhoea with salmonela
- the host immune response
how does the host prevent bacteria multiplication?
– bacteria multiplies uncontrollably resulting in death of host
– host removes bacteria (possibly with the help of antibiotics)
– equilibrium reached where both live in balan
what are the different phases of growth?
- Lag phase – very little to no reproduction – maturation – synthesis
- Log phase – number of cells doubles at constant exponential rate
- Stationary phase – population of rate of cell death equals cell growth
- Death phase – population of rate of cell death greater than cell growth
- Dormant – Lack of nutrients for growth
what does selective toxicity require?
- Selective toxicity to microorganism
- Limited / low toxicity to the human or mammalian host
- Relies upon differences between microbial and mammalian cells – structure – function – biochemistry
what are the difference between pro and eukaryotic cells?
- Bacterial cell has a cell wall and plasma membrane the cell wall protects the bacteria from differences in osmotic pressure
and prevents swelling and bursting due to the flow of water into the cell – extra specific targets that mammalian host does not have - Bacterial cells do not have defined nuclei – easy access to DNA as target
- Bacterial cells are relatively simple and do not contain organelles
e.g. mitochondria
– easy access to metabolic processes as targets
the biochem is v different to eukaryotic cells eg vitamin synthesis
what is gram +ve and -ve cell wall staiend with?
+ve= crystal violet-iodine xomplex
-ve= does not reatain gram stain
can you have gra +ve and -ve?
- Some antibacterial agents are active against both Gram positive and Gram negative
bacteria (note, generalisation and is drug/bacterial strain dependant)
– b-lactams (broad spectrum G-ve and many G+ve
what is a simple structure of a gram +ve bacterial cell wall?
- Simple structure – peptidoglycan
outer layer
– no outer membrane
what does peptidoglycan consist of?
parallel sugar backbones composed of
alternating NAG and NAM
what are attached to the NAM through the CA residue?
peptide chains
they are linked together to give extra strength to the cell wall through cross link formation, catalysed by peptidoglycan transpeptidase
what is the structure of gram -ve bacteria cell wall?
- More complex structure
- peptidoglycan linked to outer membrane
(phospholipid/lipopolysaccharide) - Entry to cell via porins found in both
outer and inner membranes - Effective barriers to hydrophilic compounds and large molecules
- More selective uptake
- Uptake of antibiotics effectively through internalisation via porins
what is the structure of a mycolic bacterial cell wall?
- Abnormally thick, viscous and waxy mycolic acid outer layer
– low expression and activity of porin
proteins
– low permeability of cell
– provides intrinsic resistance to antibacterial agents - Similar peptidoglycan cell wall to G+ve/G-ve with additional sugar-based
structure
– Little intrinsic resistance to agents targeting this
what are examples of gram +ve bacteria?
- Gram positive obligate aerobes – Mycobacterium, Chlamydiae
- Gram positive facultative – Cornebacterium, Enterococcus, Staphylococcus, Streptococcus, Listeria
- Gram positive obligate anaerobes – Clostridium
what are examples of gram -ve bacteria?
- Gram negative obligate aerobes
– Legionella, Moraxella, Pseudomonas - Gram negative microaerophilic (lower 02 than atmosphere) – Campylobacter, Helicobacter
- Gram negative facultative – Enterobacteria (Serratia and Enterobacter), Escherichia, Haemophilus, Klebsiella, Neisseria, Proteus, Salmonella, Shigella, Vibrio
- Gram negative obligate anaerobes – Bacteroids
