Control of Microbial Growth

1
Control of Microbial Growth

• Chapter 7

2
History

• Humans vs. Microbes
• infections
• diseases
• plagues
• epidemics
• pandemics

3
Nursery Rhyme
Ring- a - ring of rosies Pocketful of
posies Achoo ! Achoo ! We all fall down.
4
Bubonic Plague or the Black Death

• Epidemic swept thru Europe in the Middle Ages
  (13th and 14th centuries)
• 40 million people were killed
• About 1/3 of the population of the continent
• Etiological agent
• Yersinia pestis Gram (-) rod
• 2 Vectors
• Rat
• Flea

5
Yersinia pestis - Gram (-) bacillus Vectors -
Rat and Flea
6
Bubonic Plague Infection

• 1. Flea bite with Yersinia pestis
• 2. Bacteria multiply in the bloodstream
• Bacteremia
• 3. Bacteria localize in lymph nodes, especially
  axillary and groin areas

7
4. Hemorrhaging occurs in lymph nodes, resulting
in black and blue swellings or Buboes (hence
the name Bubonic Plague or Black Death)
8
Bubonic Plague Infection

• 5. If untreated, about 50 Mortality Rate
• 6. If bacteria spread to the lungs, it becomes
  Pneumonic Plague and is now highly contagious
  (Almost a 99 Mortality Rate)

9
Nursery Rhyme
Ring - a - ring of rosies, A pocketful of
posies Achoo ! Achoo ! We all fall down.
10
I wouldnt touch it with a 10
pole
11
Humans vs. Microbes

• 1. Most of History, microbes have been winning
  the battle
• 2. In the last 100 yrs or so the battle has swung
  in our favor
• Why?
• Because of our increasing knowledge of how to
  Control Microbial Growth

12
Smallpox
Variola virus Eradicated in
1977 (Somalia)
13
Methods to Control Microbial Growth

• 1. Physical
• 2. Chemical

14
Terms used

• Sterilization vs. Disinfection
• Sterilization
• destroying all forms of life
• Disinfection
• destroying pathogens or unwanted organisms

15

• Disinfectant vs. Antiseptic
• Disinfectant
• antimicrobial agent used on inanimate objects
• Antiseptic
• antimicrobial agent used on living tissue

16
cidal vs. static

• Bactericidal - kills bacteria
• Bacteristatic - inhibits bacterial growth
• Fungicidal
• Fungistatic
• Algacidal
• Algastatic

17
Factors that effect Antimicrobial Activity

• 1. Temp
• 2. Time
• 3. Concentration of Antimicrobial agent
• 4. Type of Microbe
• 5. Activity of Microbe
• 6. Presence of organic matter

18
Targets of Antimicrobial Agents

• 1. Cell membrane
• 2. Enzymes Proteins
• 3. DNA RNA

19
Physical Methods of Microbial Control

• 1. Heat
• works by denaturing enzymes and proteins
• A. Thermal Death Point (TDP)
• lowest temp. at which all microorganism in a
  liquid culture are killed in 10 minutes
• B. Thermal Death Time (TDT)
• minimum length of time in which all
  microorganisms in a liquid culture are killed at
  a given temperature

20
Moist Heat

• 1. Boiling Water
• kills vegetative bacterial cells, Fungi and many
  viruses
• not effective for endospores and some viruses
• Hepititis (20 min)
• Some spores may survive boiling water for up to
  20 hrs

21
Moist Heat

• 2. Autoclave (Steam under pressure)
• preferred method of sterilization
• Water boils at 100 C
• Increasing the pressure raises the Temp.
• 15 lbs./ per sq. inch (psi) ------gt 121 C
• 121 C for 15 min.

22
Kilit Ampule

• Spores of Bacillus stearothermophilus
• fermentable sugar
• pH indicator
• basic - red
• acid - yellow

23
Dry Heat

• 1. Direct Flaming
• Inoculating Loop and Needle 100 effective
• 2. Incineration
• disposable wastes (paper cups, bags, dressings)
• 3. Hot Air Sterilization
• Oven ( 170 C for 2 hours)
• used on substances that would be damaged by moist
  heat sterilization
• gauzes, dressings or powders

24
Filtration

• Removes microorganisms from solutions that might
  be damaged by heat
• culture media
• enzymes
• vaccines
• antibiotics

25
Radiation

• 1. Ionizing Radiation
• gamma rays x-rays
• penetrates most substances
• Used on substances that could be damaged by heat
• plastic petri dishes
• plastic syringes
• catheters
• surgical gloves

26
Radiation

• 2. Non-Ionizing Radiation
• UV Light
• does not penetrate plastic, glass or
  proteinaceous matter
• Used to reduce microbial populations
• hospital rooms
• nurseries
• operating rooms

Thymine Dimers
27
Pasteurization

• Disinfection - not sterilization (removes
  unwanted organisms)
• Mycobacterium tuberculosis
• 63 C for 30 minutes
• 72 C for 15 seconds (HTST)
• Thermodurics
• able to survive high temps.

28
Methods used to control Microbial Growth

• 1. Heat
• Moist Heat
• Boiling Water
• Steam Heat (Autoclave)
• Dry Heat
• Direct Flaming
• Incineration
• Hot Air Sterilization (Oven)
• 2. Filtration
• 3. Radiation
• Ionizing Radiation
• Non-Ionizing Radiation
• 4. Pasteurization (Heat)

29
(No Transcript)