lecture 8 - introduction to microobiology Flashcards
WTF is microbiology
Any “living” thing you can see down a microscope
Categorising cells
examples
- Initial binding of Haemophilus influenzae type b to the human nasopharynx is facilitated by Hib pili, filaments expressed on the bacterial surface.
- Mutant strains ofS. pneumoniaethat have lost the ability to form a capsule are readily taken up by white blood cells and do not causedisease
- Mutated forms of C. jejuni do not cause disease as can’t move to infect cells.
staining
gram positive cocci
gram positive bacilli
gram negative bacilli
Microscopic Fungi
What other things can we use for diagnosis?
Variables in bacterial growth
bacterial growth curve
Which bacterial structures can be used as antibiotic targets?
targets vs resistance
What fungal structures can we target with antifungals?
Antimicrobial Resistance
antibiotics
Action of Penicillin
- The bacterial cell wall consists of strands of repeating N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM) subunits.
- The NAM subunits have short peptide chains attached to them. (The proximal alanine is usually L-ala and the distal two are usually D-ala.)
- The PBP binds the peptide side chains and forms the cross-link with the expulsion of one D-Alanine from one peptide side chain.
- The PBP dissociates from the wall once the cross-link has been formed.
- Penicillin is added to the system. It enters the active site of the PBP and reacts with the serine group that is important in its enzymatic activity.
- The beta-lactam ring of penicillin (represented here as the top of the “P”) is irreversibly opened during the reaction with the PBP.
- Penicillin remains covalently linked to the PBP and permanently blocks the active site.
Methicillin-Resistant Staphylococcus aureus (MRSA)
MRSA strains contain Staphylococcal cassette chromosome mec (SCCmec).
This is a mobile genetic element which contains the mecA gene.
The gene mecA encodes for PBP2a – an altered PBP with low affinity for penicillin drugs.
β-lactamase producing Pseudomonas aeruginosa
Enzymes to degrade the β-lactam ring (β-lactamases) can be encoded on transmissible genetic elements (plasmids, integrons, transposons etc.) or the chromosome
There are many ways to be resistant
kosh postulates
If only it was that simple.
Famous exceptions;
Viruses
Prions
H. pylori
Biofilms and synergistic pathogens
Many more
Where are microorganisms found in the normal healthy body?
