1. Environmental Factors that Influence Microbes Including Antimicrobial Agents

2. Temperature Psychrophile – staphylococcus aureus & Listeria monocytogenes ( food-borne illness) Mesophiles (20 -40°C). Human body is 37°C. Thermophile (45 -80°C). - Thermus aquaticus  Taq polymerase (enzyme) pH, Gases & osmotic pressure

3. Microbial Growth

4. Exponential Growth

5. Growth Curve

6. Control of Microbial Growth

7. Physical, Chemical, vs, Mechanical methods of microbial control

8. Important Terms: Disinfection: – The destruction or removal of vegetative pathogens (not bacterial endospores). Sterilization: – The complete removal or destruction of all viable microorganisms. Used on inanimate objects only Antisepsis: – Chemicals applied to body surfaces to destroy or inhibit vegetative pathogens. Biocide/germicide: –Kills microbes Bacteriostasis: –Inhibiting, not killing, microbes

11. Principles of Effective Disinfection Concentration of disinfectant Organic matter pH Time

12. Figure 7.2 An Autoclave

14. What is Microbial Death? The permanent loss of reproductive capability, even under the optimum growth conditions.

15. How Antimicrobial Agents Work… There are 4 main modes of action: 4 Targets - 1.cell wall synthesis or integrity 2.cell membrane synthesis or integrity 3.protein or nucleic acid synthesis 4.protein structure

16. Cell Wall Interference Purpose of cell wall: Some chemical agents can: – block its synthesis Most common agents prevent cross-linkage of NAM subunits Ex: penicillin – digest the cell wall or – break down it’s surface Ex: detergents and alcohol Bacteria have weakened cell walls and eventually lyse

17. Figure 10.3c-e Bacterial cell wall synthesis and the inhibitory effects of beta-lactams on it. New cross-links inhibited by beta-lactam Previously formed cross-link Methicillin (semisynthetic) Carbapenems Imipenem (semisynthetic) Growth Beta-lactam interferes with the linking enzymes, and NAM subunits remain unattached to their neighbors. However, the cell continues to grow as it adds more NAG and NAM subunits. The cell bursts from osmotic pressure because the integrity of peptidoglycan is not maintained. β-lactam ring Penicillin G (natural) Cephalosporins Cephalothin (natural)

18. Inhibitors of Cell Wall Synthesis Penicillin – Natural penicillins – Semisynthetic penicillins – Extended-spectrum penicillins Polypeptide antibiotics Bacitracin Topical application Against gram-positives Vancomycin Glycopeptide Important "last line" against antibiotic-resistant S. aureus

19. Surfactants on cell membrane

20. Protein or Nucleic Acid synthesis interference Certain drugs/chemicals can bind to the ribosomes in a way that stops peptide bonds from forming. Some agents bind irreversibly to DNA, preventing both transcription and translation, whereas others are mutagenic agents.

21. Inhibition of Protein Synthesis by Antibiotics Figure 20.4

22. Mechanisms of Antimicrobial Action Inhibition of Protein Synthesis – Prokaryotic ribosomes are 70S (30S and 50S) – Eukaryotic ribosomes are 80S (40S and 60S) – Drugs can selectively target translation – Mitochondria of animals and humans contain 70S ribosomes Can be harmful

23. Mechanisms of Antimicrobial Action Inhibition of Nucleic Acid Synthesis – Several drugs block DNA replication or RNA transcription – Drugs often affect both eukaryotic and prokaryotic cells – Not normally used to treat infections – Used primarily in research and perhaps to slow cancer cell replication

24. Protein structure

25. Radiation as a Microbial Control Agent