Microbes

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Transcription

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occurs in the nucleus

DNA--->mRNA

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Translation

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occurs in the ribosome

mRNA to protein

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Bacterial DNA #1 Chromosome

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- circular, double stranded

- free in cytoplasm

- occupies half volume of cell

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Bacterial DNA #2 Plasmid

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-Extra Chromosomal self replacing unit

- contain 2% genetic info of bacterium

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Mutations

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1. spontaneous errors by DNA polymerase

2. Mutagens

3. genetic engineering

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Type of Mutation 1: Conjugations

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– Two live bacteria; unidirectional transfer fromdonor to recipient

• F+ donor cell has a F plasmid(F(ertility) factor)

• F- recipient cell lacks F factor– F+ forms bridge with F-–

Replication and passage of one single-strand ofF plasmid DNA through bridge. Secondstrand is synthesized in both.

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Transductions

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- requires viruses

- defective particles from dead donor carry bacterial DNA to live recipient

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Transformations

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• Acquisition of naked DNA from surroundingenvironmentIntegrate new DNA fragment into chromosome

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Genetic Engineering

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- Manipulation of DNA in a lab

- can change genetic makeup of a cell or organism

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Physical Methods to control Microbes

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1. Dry heat

2. Low temperatures

3. Ultraviolet radiation

4. Drying

5. Filtration (heat sensitive solution passed through filter

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Chemical methods to control microbes

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1. alcohol

2. soaps

3. phenols (block lipid formation)

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Cephalosporins

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-antibiotics

- primarily against gram bacteria

- Block formation of peptidoglycan cross linking inbacterial cell wall

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Microbial Load

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– Usually low

– Load can be high, as long as not pathogenic– Shelf life: length of time a particular food maybe stored

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Important characteristics of food spoilage

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1. ph range

2. temperature

3. water content

4. physical structure

5. oxygen availability

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Meat

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• High nutrient supply for microbes to thrive

– Cannot be pasteurized

– Meat processing has many opportunities forcontamination

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Seafood

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- microbes adapted to grow in cold environments

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Dairy

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• Key characteristics of milk

– Neutral pH

– Extremely nutritious fluid

- Inside of udder is sterile!!Acquisition of microbes from duct leading toudder

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Pasteurization

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• Purpose: eliminate pathogenic bacteria and lowertotal number of bacteria to decrease chances of spoilage; dairy and fruitjuices

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Osmotic Pressure

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- large quantities of salt or sugar

- water flows out of microbes via osmosis

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chemical preservatives

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- • Organic acids damage microbial membranes andinterfere with the uptake of certain essential organic substances.

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Targets of antibiotics

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1. cell wall

2. nucleic acid

3. DNA (translation)