Objectives Understand the basic principles of antimicrobial chemotherapy Overview of the following as major bacterial targets for antibiotics: Examples of antibiotics that interfere with these targets and understand why they are selectively toxic Describe why use of antibiotics selects for antibiotic resistance and to illustrate this with three specific examples of the resistance mechanisms used by bacteria Sequence of events involved in the establishment of infection List the common site of entry Outline key bacterial factors involved in production of tissue damage Outline the concept of virulence factors Define the term primary pathogen and contrast with opportunist pathogen

“A bacterium, virus, or other microorganism that can cause disease”

Successful Pathogens Opportunistic Pathogens ‘cheating!!’ Causes diseases when host defenses are impaired Primary Pathogens Cause disease in the absence of immune defects

1.Colonisation – adhesion and nutrient acquisition 2.Invasion of tissues 3.Avoidance of host defences 4.Tissue Damage Bacterial Disease Processes

First interaction of bacteria is normally on a mucosal surface, however, physiological mechanisms will flush away the bacteria To overcome the flushing mechanism, bacteria must adhere to the surfaces Adhesion involves specific adhesins (fimbriae) and receptors (extracellular matrix proteins such as collagen on the host cell) Nutrients – Bacteria requires IRON but free iron levels in the tissue cannot support its growth, therefore bacteria express high affinity iron uptake systems Colonisation

Invasion Bacteria needs to penetrate into, through or between host cells to spread to other sites They produce extracellular substances which facilitate invasion called invasins

How does the body get rid of bacteria? 1. Contact between phagocyte and microbial cell 2. Engulfment 3. Phagosome formation 4. Phagosome-lysosome fusion 5. Killing and digestion 4 ways that bacteria use to avoid getting killed Avoidance of host defences

Resists the complement proteins Avoids the actions of antibody Avoids phagocytosis Modulate cytokine response Lipopolysaccharide (LPS) (Endotoxin) Capsule Fimbrae Flagella Envelope proteins

Direct effects of bacterial toxins Indirect effects of bacterial toxins Induction of autoimmune response Tissue Damage

EXOTOXINSENDOTOXINS Made by Gram +ve and -veMade by Gram -ve ProteinLipopolysaccharide CytoplasmicOuter Membrane Secreted by living bacteriaReleased on cell lysis Heat labileHeat stable

Antibiotic Therapy Selective toxicity -Kill bacteria pathogen rather than the host cell Achieve an inhibitory concentration at the site of infection -Deliver enough antibiotics to stop bacteria growing Penetrate bacterial cell to reach the particular target Overcome resistance mechanisms

Common sites of entry MOUTH Peptococcus Peptostreptococcus Actinomyces SKIN/SOFT TISSUE S. Aureus S. Pyogenes S. Epidermidis Pastuerella BONE + JOINT S. Aureus S. Epidermidis Streptococci N. Gonorrhoeae Gram –ve rods ABDOMEN E. Coli Proteus Klebsiella Enterococcus Bacteroides sp. URINARY TRACT E. Coli Proteus Klebsiella Enterococcus Staph. Saprophyticus UPPER RESP. S. Pneumoniae H. Influenzae M. Catarrhalis S. Pyogenes LOWER RESPIRATORY (COMMUNITY) S. Pneumoniae H. Influenzae K. Pneumoniae Legionella Pneumophilia Mycoplasma Chlamydia LOWER RESPIRATORY (HOSP) K. Pneumoniae P. Aeruginosa Enterobacter sp. Serratia sp. S. Aureus MENINGITIS S. Pneumoniae N. Meningitidis H. Influenza Group B Strep E. Coli Listeria

Prokaryotes vs. Eukaryotes Cell WallProtein synthesisNucleic acid syn. Bacteria ✓ 70S RibosomesBinary fission Host Cell ✗ 80S RibosomesMitosis and Meiosis

Inhibitors of cell wall synthesis Inhibitors protein synthesis Inhibitors of nucleic acid synthesis

Glycopeptides Eg. Vancomycin Beta-lactams Eg. Penicillin, Cephalosporins, Carbapanems, Monobactoms Inhibitors of cell wall synthesis

NAGNAMPPC 55 lipid L- lysine Glycopeptides Binds on to D-ala-D-ala residues and prevents incorportion of new subunits to form the bacteria well wall Molecular structure of bacterial cell wall

Beta-lactam Antibiotics O R S COOH N O R S N R Cephalosporins Monobactams R N OSO 3 O Carbapenems O R C COOH N R Penicillins

Penicillin-binding-proteins are enzymes involved in the cross-linking of bacterial cell wall components Beta-lactam antibiotics bind to penicillin-binding- proteins (PBP) to prevent the bacteria from constructing a cell wall Beta-lactam Outer membrane Cytoplasmic membrane PBP Beta-lactamase Porins

Inhibitors of protein synthesis Aminoglycosides Tetracyclines Chloramphenicol Antibiotics target the smaller, 70S ribosomes in bacteria

Nucleic Acid synthesis Inhibition of precursor synthesis Eg. Sulphonamides, Trimethoprim Inhibitors of DNA replication Eg. Quinolones Inhibitors of RNA polymerase Eg. Rifamycins

Folate required to synthesise purines and pyrimidines Bacteria make their folate Humans obtain in diet Sulphonamides + Trimethoprim blocks the same pathway but inhibits different enzymes Inhibition of precursor synthesis Pteridine + PABA Dihydropteroic acid Tetrahydrofolic acid DNA synthesis DHPS DHFR Dihydrofolic acid

RNA polymerase enzyme that converts DNA to mRNA is different in eukaryotes and prokaryotes Rifamycins bind specifically to the prokaryotic RNA polymerase to inhibit transcription Inhibitors of RNA polymerase

1.