Antibiotics
Antifolates include sulfamethoxazole and trimethroprim. They target gram positive and gram negative bacteria. They are bacteriostatic and inhibit folate synthesis at two different steps. Thereby, metabolities and pyrimidines/purines for DNA synthesis isn't produced
How does Bacteria develop antibiotic resistance? How is DNAP5 linked to this?
Through mutations in bacteria due to stress (e.g., UV light, antibiotics). Where specifically one mutation generation system = SOS (10-50 genes).
There are 2 main proteins involved: RecA regulator and LexA repressor. RecA binds to ssDNA gets activated and becomes a protease, cleaves the lexA from operator and we get expression of the SOS genes, such as DNAP5. DNAP5 lacks the 3' to 5', meaning that it can't go back and fix missing nucleotides. Hence, on subsequent replication rounds the mutation is solidified. Hence can become resistance to antibiotics.
What is the main function of CHIPS?
S.aureus secretes CHIPS which blocks the activation of the two strong chemoattractants (C5a and formylated peptides) by binding to theor receptors, thereby eliminating the migration of neutrophils to the site of infections
What are the possible modes of Transmission?
Faecal-oral
Gastric-oral
Oral-oral
Alginate: 12 gene operon that is a polymer of mannuronic acid
Psl: 12 gene operon that is composed of mannose, rhamnose and glucose
Pel: 7 gene operon that comprises of galactosamin and acetyl-galactosamine
What type of antibiotic is only useful against gram + bacteria?
Glycopeptides e.g. vancomycin
What is the process of transformation?
Transformation is a process of how antibiotic resistance is transmitted between cells. It involves the stable uptake of "free" DNA. This is done through making bacterial cells competent by using CaCl, which basically roughs up the bacterial cell membrane, allowing them to take up external pieces of DNA. This DNA will be stably recombined into the host genome.
What complex and protein together can contribute to the evasion of opsonisation? Describe.
SCIN and SAK
SCIN complex binds to and stabilises C3 convertase (C2aC4b, C3bBb), thereby preventing the deposition of C3b on the surface of bacterial cells
SAK is a plasminogen activator and produces plasmin by binding to C3b and IgG degrading them.
What does the VacA gene sequence that causes the highest virulence look like?
S1M1
In cystic fibrosis what is the function of the CFTR channel? What happens when it becomes mutated?
CFTR regulates chloride ion transport across epithelial, its absence or dysfunction leads to no transport of Cl- into the mucus = reabsorption of H2O = mucus layer is thick and sticky. This affects mucocillary appartus which is important for removing potential pathogenic microbes. Hencce, this mucus layer is now susceptible to colonisation.
Which antibiotic irreversibly interacts with the ribosome and affects protein synthesis?
Aminoglycosides
What are the other two ways that antibiotic resistance can be transferred between cells? Describe.
Conjugation and transduction.
Conjugation involves a type IV secretion system (that can encode for things to secrete) in a cell that is F+ and R+. One strand of DNA is nicked and leaves the cell via pilus that joins with another cell. This cell is F- and R-. The synthesis of this strand of DNA now makes the cell R+ and F+
Transduction is the transfer of bacterial genes by viruses phage. The phage attaches and infects bacteria via phage tail fibres with its phage head being where the genetic material is located. The phage injects its genetic material into the cell, which hijacks the replication machinary of the cells. As the phage is making more of its components, sometimes it can misincorporate pieces of the bacterial genome into its phage head. On subsequent rounds of infection the phage can introduce that DNA into a new recipent bacterial cell and through stable recombination this piece of DNA is incorporated into the bacterias genome.
What are the two main types of superantigens and their roles?
Toxic shock syndrome toxin (TSST-1) and staphylococcal enterotoxin.
They bind to the macrophages then the T cells via the beta chain, independent of their antigen recognition region. Now there is prolonged interaction between the macrophages and T cells and you can increase of cytokine release = cytokine storm. Also get leakage of endothelial cells, leading to toxic shock syndrome
What two components that regulate the expression of the urea cluster and its functions? When is it turned 'on'?
ArsS and ArsR
This is turned on when H+ levels are high:
A transmembrane protein (ArsS) undergoes a conformational change and in an ATP dependent way it is phosphorylated on a conserved histidine in its C terminus. Once the kinase has been phosphorylated, the P group is passed onto a regulatory protein (ArsR), which is phosphorylated at a conserved aspartate residue in its N terminus. The protein undergoes a conformational change, becomes a transcription factor and binds the promotor sequence of those urease genes (A/B, E/F/G/H, I).
Exotoxin A
Type III secreted exotoxins - S, T, U, Y
Name the 3 antibiotics that are bacteriostatic.
Macrolides
Tetracyclines
sulfonamides +/- trimethoprim
What are the genes involved in Methicillin Antibiotic Resistance and how are they regulated?
MecR1 is a transmembrane domain protein, it has a B-lactam sensor in the N-terminus and a protease in the C-terminus. The C-terminus cleaves MecI, a transcriptional regulator which can then bind to the promoter sequence of the MecA gene. MecA encodes PBPa2 (altered penicillin binding protein). This allows bacteria to synthesize the cell walls by cross-linking the peptide chains from D-alanine to D-lysine using the PBP2a.
BlaR1 is also a transmembrane protein which detects the antibiotics in the N-terminus and has protease activity in the C-terminus. It cleaves BlaI, a transcriptional regulator which can bind to the promoter sequence of the BlaZ gene. BlaZ encodes a B-lactamase which can break down the B-lactam ring in B-lactam antibiotics such as Methicillin.
BlaR1 can also cleave MecI for the regulation of MecA genes.
Which virulence factor released by S. aureus affects the stratum granulosum of the epidermis?
exfoliative toxins - affects the Dsg-1 (more specifically EC3 and EC4) between keratinocytes.
Describe the ways in which H. pylori causes inflammation.
H. pylori can bind to pattern recognition receptors e.g. TLRs such as TLR 2 (peptidoglycan), TLR 4 (LPS), TLR 5 (flagella). As well as this, HP- NAP is released which crosses gastric epithelia into lamina propria and makes endothelium stickier for immune cell entry.
What are the 2 functions of the type III secreted toxins released by P. aeruginosa?
1. ADP-ribosyl transferase activity.
2. Rho GTPase activity.
Which antibiotic is useful against serious respiratory infections?
Monobactams
Describe the pathway that is involved with a bacteria becoming vacomycin resistant.
In the presence of vancomycin, vancomycin binds to the N terminus of the VanS sensor (a transmembrane kinase). This will undergo a conformational change, brining its ATP binding site closer to a conserved histidine that is found in the C terminus. This conserved histidine will become phosphorylated. The phosphate group will then interact with VanR (a gene regulator protein), where the phosphate group is transferred to a conserved aspartate residue in the N terminus of the VanR gene protein. This protein undergoes a conformational change and binds to the promoter sequence. VanH now produces pyruvate, which produces lactate. VanA product will ligate the D-lactate to D-alanine preventing vancomycin from binding to these aa side chains. VanX/Y encodes peptidases that continually break down these D-alanine, D-alanine residues, thereby maximising that D-lactate is incorporated into the aa side chains
Name the antimicrobials (AMPs) that are attracted to S. aureus and why they are attracted, as well as how S. aureus overcomes this attraction.
Defensins and cathelicidins (AMPs) are + charged and are attracted to the - charge of the cell wall (contributed to by lipotechoic and techoic acids. S. aureus overcomes this by neutralising the charge of the acids through inserting D-alanine through the Dlt-operon. This neutralisation, decreases the electrostatic attraction and therefore S. aureus protects itself from AMPs.
Explain the CagA protein, its origin, and how it contributes to Gastric Cancer.
CagA is located on the terminal end of a large pathogenic island inherited via horizontal gene transfer.
CagA is transferred into host cells via a type 4 secretion system (also found on the large pathogenic island) which acts as a molecular syringe.
CagA harbours EPIYA motif and is phosphorylated in host cytoplasm on tyrosine residues by host kinases. It can then bind to the N-terminus of SHP2 to activate it.
SHP2 activates Ras, Raf, Mek, Erk pathway which is involved with cell growth.
Therefore, in the inflammatory environment, CagA contributes to continued cell proliferation and growth of mutated cells which contributes to cancer formation.
Describe how P. aeruginosa controls the expression of genes related to virulence and biofilm formation
The LasI-LasR and RhlI-RhlR system regulate expression of genes involved in virulence and biofilm formation.
LasR encodes a cognate receptor and LasI encodes a synthase that produces C-12 HSL that binds LasR which then enables the expression of LasI (auto-induction loop) as well as virulence genes and those involved in biofilm formation.
RhlR encodes a cognate receptor and RhlI encodes a synthesis that produces C-4 HSL that binds RhlR that then enables the expression of RhlI and genes involved in virulence and biofilm formation.