Control of Microbial Growth Tim Ho University of Alberta, Canada * The materials are mostly based on Dr. Brian Lanoil’s Microb Part III

Objectives 1.Know 3 methods of microbial control 2.Know the strategies on how drugs control the growth of microorganisms. 3.Understand how do bacteria become resistant to antibiotics. 2 Physical agents Mechanical removal methods Chemical agents

3 Antibiotic resistance It is always the serious problem Plasmid transfer, the horizontal gene transfer, is the main cause of resistance Nosocomial infection: an infection occurs in a hospital environment Image: Reacher M H et al. BMJ 2000;320:

4 Image: Bacterial mechanisms of Antibiotic resistance Exclusion: active efflux from the cell Enzymatic inactivation: enzyme is produced to inactivate antibiotic molecule Modification of antibiotic or target

5 3 Sources of resistance genes Bacterial chromosomes: - Spontaneous mutations cause drug target sites change Plasmids: - R plasmids: resistance - can be transferred to other cells by horizontal gene transfer - Can carry multiple genes Mobile genetic elements: -Transposons, integrons - can be freely exchanged between bacteria

6 Horizontal gene transfer in bacterial cell 1.Transformation: transfer of free DNA from environment 2.Conjugation: require contact 3.Transduction: transfer gene by viral delivery Image:

7 How to prevent drug resistance Drug should be given in high concentration Give two or more drugs at the same time Use drugs ONLY when necessary Future solutions: develop new drugs, use bacteriophages to treat bacterial disease… WHY: make sure the drug kill all bacteria otherwise it is high possibility that few resistant bacteria remain in body and starts to grow.