Luis Materon, Lecture 32, Microbiology, UTPA

Chapter 11 (note: this page is a remnant of the past when I learned to program with HTML 20 years ago)

Physical and Chemical Control of Microorganisms

To reduce contamination, early civilizations used:
salting

smoking

pickling

dried food
sunlight
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strong salts
                  
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filtration

Greeks, Romans and Asians

burned clothes and corpses

stored water in cupper and silver vials

Alexander The Great implemented

boiling of drinking water

burying of the dead

burning sulfur to fumigate homes

application of sulfur as skin ointment

During plague (Yersinia pestis) people used to:

burn the dead

ignite aromatic woods

wear peculiar garments for protection

anoint bodies with herbs

Contaminant

Undesirable or unwanted microorganism at a given place or time
bacterial, algal, fungal cells

bacterial endospores

fungal hyphae, spores

yeasts

protozoa

viruses, etc.

Asepsis

Prevents entry of infectious agents into sterile tissues

Antiseptics

Chemical agents applied directly to body to destroy vegetative pathogens

Iodine for the preparation of skin for surgery

Swabbing an open root cannal with H₂O₂

Wash hands with a germicidal soap

Use of alcohol, etc.

Sterilization

Process that destroys or removes all viable microorganisms including viruses

Reserved for inanimate objects

Sometimes not necessary

Most infectious diseases in humans and animals are caused by non-spore forming microbes

Disinfection

Acts on all microbes except bacterial endospores
Only on inanimate objects otherwise toxic
Removes toxins
2-5% bleach for viruses, iodine solutions for thermometers, boiling food utensils, etc.

Germicides or Microbicides

Act chemically on living tissue

Bactericide (on bacterial cells not in spores)

Fungicide (spores, hyphae, yeasts)

Virucide (inactivate them on tissue)

Sporicide (destroys bacterial spores)

Surfactants

Work as microbicidal agents because they lower the surface tension of cell membranes
Polar molecules with hydrophilic and hydrophobic regions physically bind to lipid layers and penetrate the internal hydrophobic region (leaky spots)

Levels of Resistance to Chemical and Physical Methods

Highest Resistance

Bacterial endospores

Moderate Resistance

Protozoan cysts
Some fungal sexual spores (zygospores)
Some naked viruses
Most resistant viruses

Hepatitis B (DNA enveloped virus)
Poliovirus (RNA naked virus)

Most resistant bacteria

Mycobacterium tuberculosis
Staphylococcus aureus
Pseudomonas spp

Least Resistant

Most bacterial vegetative cells
Fungal spores and hyphae
Enveloped virus
Yeasts
Trophozoites

Factors Affecting Action of Antimicrobial Agents

Number of cells
Nature (if a mixture of bacteria, fungi, virus, etc)
Temperature
pH
Mode of action
Presence of solvents
Presence of organic matter
Inhibitors

Modes of Action of Antimicrobials

Physical and chemical agents target at:

Cell wall

Blockage of synthesis of peptydoglycan
Lisozyme and lysostaphin disrupt bonds in G+
Affected by detergents and alcohol

Cell membrane

Affected by detergents and surfactants

Nucleic acids

Blockage of translation (protein synthesis)
Binding to ribosomes affects translation
Gamma rays, UV radiation
Formaldehyde
Ethylene oxide

Protein function

Denatures
Break bonds
Coagulation (moist heat and strong acids)
Ions of heavy metals