L15 Applied Microbiology

一、Controlling Food Spoilage

Methods of preservation 保存

1. Filtration
2. Low Temperature
3. High Temperature
4. Pasteurization
5. Dehydration
6. Radiation
7. Others

1. High Hydrostatic Pressure (HHP)

Applies pressures from 100-800 milliPascals (MPs)

• highly detrimental to cell membranes
• effective at eliminating eukaryotic microbes
• not as effective at elimination of Gram-positive microbes

2. Packaging

Modified atmosphere packaging (MAP)

• shrink wrap materials and vacuum technology control atmosphere
  • impermeable to gasses
  • high CO2 content packaging
  • high O2 content packaging produces superoxide radicals that inhibit microbial growth

Chemical-Based Preservation

Microbial Product-Based Inhibition

Bacteriocins 细菌素

Bacteriocins are proteinaceous toxins produced by bacteria to inhibit the growth of similar or closely related bacterial strain(s).

Bacteriophages

• sprayed onto ready-to-eat meats prior to packaging

二、Water Purification and Sanitary Analysis

Sanitary Analysis of Waters 水质卫生分析

Based on detecting indicator organisms

• indicate fecal contamination of water supplies
• indicate possible contamination by human pathogens

1. “Ideal” Indicator Organism

Suitable for analysis of all types of water

Present whenever enteric pathogens are present

Survives longer than hardiest enteric pathogen

Does not reproduce in contaminated water

Detected by highly specific test

• test easy to do and sensitive

Harmless to humans

Its level in water reflects degree of fecal pollution

Two Commonly Used Indicators

1. Conforms (Escherichia, Enterobacter, Klebsiella, etc.)

2. Fecal Streptococci

   • increasingly used to test brackish and marine water

2. Multiple-tube Fermentation Test

MPN: most probable number

3. Other Tests for Indicator Organisms

1. Membrane filtration technique
2. Presence-absence (P-A) test
3. Defined substrate tests 定义基板测试
4. Molecular analysis
   • flow cytometry
   • FISH
   • quantitative PCRs
   • microarrays

Wastewater Treatment

Decreases organic matter and number of microorganisms

Has lead to major reduction in spread of pathogens

1. Wastewater Treatment Processes

Primary treatment

• removes solid material and forms sludge

Secondary treatment

• dissolved organic matter transformed into microbial biomass and carbon dioxide

Tertiary treatment

• removal of nitrogen and phosphorus that may promote eutrophication
• removes heavy metals, biodegradable organics, and remaining microbes, including microbes

Measuring Water Quality

Testing for water quality is often a measurement of carbon (organic matter) removal

• total organic carbon (TOC) levels

  • oxidation of carbon to CO2, then measuring by infrared methods

• chemical oxygen demand (COD) test

  • similar to TOC testing, but will not measure lignin levels

• biochemical oxygen demand (BOD) test

  • measures carbon oxidized by microbes in 5 days at 20° C