Action of and Resistance to drugs and toxic metals by E. Börje Lindström This learning object has been funded by the European Commissions FP6 BioMinE project

Definitions Chemoterapi: - Use of chemical substances against parasites in the host Antibioticum: Substance that is produced by a micro- organism and that: - inhibits growth of a micro-organism (-static) or - kills the micro-organism (-cid)

Producers of antibiotics Actinomycetes - Streptomyces Bacillus - Bacillus Saprophytic fungi - Penicillium, Cephalosporium

Targets for some antibiotics Group WhereTarget Drug I Outside CM On CM Cell wall synth - Penicillin - Bacitracin II Permeability (Osmos) - Nystatin - Polymyxin III Inside CM DNA repication RNA synthesis Protein synthesis Co-factor synthesis - Nalidixic acid - Rifampicin - Streptomycin - Sulfa

Penicillins (b-lactams) CH 2 CO CH CO NH2 Pen G Amp R:

Penicillins (b-lactams), cont NAM – NAG – NAM – NAG – NAM – NAG L-ala D-glu L-lys D-ala NAM – NAG – NAM – NAG – NAM – NAG (D-ala) D-ala L-lys D-glu L-ala Penicillins – block the synthesis Active only on growing cells Lysis of the cell active against both G+ and G- broad spectrum bactericidal Action

Penicillins (b-lactams), cont Side effects on our cells? Allergy? Penicellenic acid  protein Penicilloyl – protein antigen

Streptomycin active against both G+ and G- broad spectrum bactericidal

Streptomycin, cont. Targets (translation): - initiation complex - binding to 30S subunit RpsL-protein Results: - misstranslation - faulty proteins

Streptomycin, cont. Used clinically?-selldom - against TBC Side effects: -dizziness (balance difficulties) - lowering the hearing Note! The 80S ribosome is not effected!

Sulfa drug Sulfa drugs – not antibiotics – produced chemically Growth factor analog Sulfanilamide PABA Folic acid (vitamin) CoF

Sulfa drug, cont. Acts as a competetive inhibitor in synthesis of Folic acid CoF participates in several biosynthetic reactions – aa, purins etc.

Type of resistance no receptors are available 1. Natural, artspecific resistance inactivating enzymes present - Mycoplasma - penicillinase 2. Acquired resistance - sensitive m.o  resistant m.o. Genetic processes: mutation transformation transduction conjugation

Type of resistance, cont. Biochemical mechanisms for acquired resistance: permeability changes of OM or CM- penG, tetracyclin, actinomycin D alternative biosynthesis or increased production - sulfa changed receptor- streptomycin enzym production- penicillinase

Properties of a good antibioticum Broad spectrum Prevent resistant mutants to arise Have no side effects on the human cell Leave the flora of our body intact

Effect on a growing cultur t log OD/VC + drug OD VC log OD/VC + drug t OD VC log OD/VC + drug t OD VC Effect: - static- cid- lytic

Combined usage of antibiotics Antagonism -drugs acting against each other - (-cid) + (-static) - e.g. Penicillin & kloramphenicol/ sulpha Synergism - drugs enhancing their effect - (-cid) + (-cid) - e.g. penicillin + streptomycin

Mercuric resistance Action: -Bind to SH- groups - inhibits synthesis of macro molecules - most sensitiva are transcription and translation Resistance: -usually plasid mediated - both in G+ and G-; S.aureus, Pseudomonads, At. thioxidans - enzymatic reduction; Hg 2+  Hg 0 - Hg 0 less toxic - in organic mercury, C-Hg, Hg is first removed with the enzyme lyas.

Mercuric resistance, cont.

Arsenic resistance Action: -AsO 4 3- ions are transported into the cell via - phosphate-transport system - analog to PO 4 3- ions - inhibits different kinases Resistance: - plasmid mediated - AsO 4 3- is reduced to AsO AsO 2 - is effluxed (transported to the outside)

Arsenic resistance, cont. Genetic: E. coli R773 (plasmid) arsRarsAarsCarsBarsD arsRarsBarsC Chromosome (At. caldus) reductase negative regulator