9_3 Bacterial Growth III and control.pptx

Bacterial Growth III Table 5.1  Biological Selection Population is subjected to a limiting environment which results in a differential survival. – Artificial – humans choose what survives or dies – Natural – environment choses Consequences: Change in genetic makeup of popul...

Bacterial Growth III Table 5.1  Biological Selection Population is subjected to a limiting environment which results in a differential survival. – Artificial – humans choose what survives or dies – Natural – environment choses Consequences: Change in genetic makeup of population (allele frequency)  Examples of artificial selection agents Herbicides Pesticides Antibiotics Anti-tumor Anti-viral Salt, temperature, oxygen Character traits – biggest, smallest, tastiest,…  Laboratory Cultivation Selective media – Inhibit the growth of unwanted organisms Allow only sought after organisms to grow Requires some foreknowledge – Examples Thayer-Martin agar – For isolation of Neisseria gonorrhoeae MacConkey agar – selective and differential – For isolation of Gram negative bacteria Mannitol Salt Agar – selective and differential – For isolation of osmotolerant  Laboratory Cultivation Differential media – Contains substance that bacteria change in recognizable way – Example Blood agar – Certain bacteria produce hemolysin to break down RBC » Hemolysis MacConkey agar – Contains pH indicator to identify bacteria that produce acid  Selection: bile salts, dyes inhibits gram + Differential: Fermentation of Lactose + = pink, yellow = - http://www.midlandstech.edu/science/kelleherk/225/labmaterials/sel_diff_media.  Explain it Explain to the person next to you: – Complex and chemically defined media – Selective media and give an example – Differential media and give an example – Can a medium be both selective and differential? Give an example  How tell if have growth? Cells – direct or growth Turbidity Metabolites Culture independent methods  Microscopic Counts of Microbial Cell Numbers Total cell count microscopic cell count: observing and enumerating cells present dried on slides or liquid samples counting chambers with squares etched on a slide for liquid samples (Figure 5.13) Counting chambers allow for precise volume and grids help determine area Figure 5.13  Viable Counting Viable (plate) counts: measurement of living, reproducing population two main ways to perform plate counts: spread-plate method pour-plate method count colonies on plates with 30–300 colonies To obtain the appropriate colony number, the sample to be counted should always be diluted. (Figure 5.15) Figure 5.14 Control of Bacterial Growth  Controlling Growth What is your goal? – No further growth? – Lower levels below infectious dose Remove select pathogens Meet gov regulations – sterilization  Approaches to Control Control mechanisms either physical or chemical – May be a combination of both – Physical methods Heat Irradiation Filtration Mechanical removal – Chemical methods Use a variety of antimicrobial chemicals Chemical depends on circumstances and degree of control required  Control of microbes Principles of control – Sterilization Removal of all microorganisms – Sterile item is absolutely free of microbes, endospores and viruses Can be achieved through filtration, heat, chemicals and irradiation – Disinfection Eliminates most pathogens – Some viable microbes may exist Disinfectants = used on inanimate objects and surfaces Antiseptics = used on living tissues – Pasteurization Brief heat treatment used to reduce organisms that cause food spoilage – Surfaces can also be pasteurized  Pasteurization Brief Heat treatment – Kills heat sensitive organisms – Protect heat sensitive products or items Increase shelf-life or contamination Harshness of treatment determines reduction of microbes Examples for Milk (international dairy association) – 63oC for 30min for Vat Pasteurization – 72oC for 15s High temp short time (HTST) – 96oC for 0.05s Higher heat shorter time (HHST) – 138oC for 2 sec Ultra Pasteurization Microbial Characteristics and Microbial Control https://www.cdc.gov/infectioncontrol/images/ Figure 7.11 Figure-v2.png  Terminology Sterilization: Removal of all microbial life Commercial sterilization: Killing of Clostridium botulinum endospores Disinfection: Removal of pathogens Antisepsis: Removal of pathogens from living tissue Degerming: Removal of microbes from a limited area Sanitization: Lower microbial counts on eating utensils Biocide/Germicide: Kills microbes Bacteriostatic: Inhibiting, not killing, microbes  Bacterial populations die at a constant logarithmic rate. Figure 7.1a  Decimal Reduction Time (DRT) or D-value Minutes to kill 90% of a population at a given temperature Table 7.2  Effectiveness of Antimicrobial Treatment Depends on: – Number of microbes – Environment (organic matter, temperature, biofilms) – Time of exposure – Microbial characteristics Figure 7.1b  Comparison of treatments Czank et al. 2009. Retention of the Immunological Proteins of Pasteurized Human Milk in Relation to Pasteurizer Design and Practice. Pediatric DHM= donorRes. 66: 374-379. human milk  Next Time Enumeration of bacteria Control of bacterial growth