Chapter 9 Lecture 4
Filters continued
We use filters not only for heat sensitive materials, but Healthcare workers use filtration to prevent airborne contamination of microbes
Surgical masks to prevent exhaled microbes from contaminating the environment
Cotton plugs are place in culture vessels to prevent contaminations by airborne microbes
High-efficiency particulate air filters (HEPA) are mounted on air ducts of some hospital rooms with airborne diseases like TB and then we can put pts in rooms who are immunocompromised like a burn pt or an AIDS patient
Osmotic Pressure
A type of microbial control using the ancient method of high concentrations of salt or sugar in foods to stop or inhibit the growth of microbes
Remember what osmosis is? It is the movement of water across a semipermeable membrane from an area of higher water concentration to an area of lower water concentration
Cells in hypertonic solution of salt or sugar lose water, and the cell shrinks.
By removing the water from the cell, the cell can’t complete cellular metabolism (the enzymes in the cell can only function in aqueous environments)
This is how we preserve honey, jerky, jams, jellies, salted fish and some types of pickles.
Radiation
Is a physical method to control microbial growth. The shorter the wavelength of an electromagnetic wave, the more energy it carries.
Shorter wavelength radiation is more suitable for microbial control
When discussing radiation we describe it as ionizing or nonionizing
Electron beams, gamma rays and some X-rays all have wavelengths shorter than 1 nm(ionizing). They are considered ionizing because when they strike molecules, they have enough energy to expel electrons from atoms, creating an ion.
These ions disrupt hydrogen bonding, oxidize (crumble, corrode) double covalent bonds and create hydroxyl radicals and these ions will denature other molecules, like DNA which in turn causes fatal mutation and the death of a cell.
Electron beams effective at killing microbes but do not penetrate well
Gamma rays penetrate well but require hours to kill microbes,
Irradiation with gamma rays kills not only microbes, but also the larvae and eggs of insects; it also kills the cells of fruits and vegetables preventing microbial spoilage and overripening which makes it effective for sterilization – good at penetrating and causing widespread/extensive damage
X rays require long time to kill microbes
Not practical for microbial control
Nonionizing Radiation
Its wavelength is greater than 1nm, so it does not have enough energy to force electrons out of orbit which makes it nonionizing.
It does though, have enough energy to EXCITE electrons causing them to make new covalent bonds.
These covalent bonds will have an affect on the 3-D structure of proteins and nucleic acids.
UV light, visible light, infrared radiation, and radio waves are nonionizing radiation. Out of all these, UV light has enough energy to to be a practical antimicrobial agent, but it does not penetrate well
This makes nonionizing radiation suitable for disinfecting air, transparent fluids, and surfaces of objects
Chemical Methods of Microbial Control
Physical agents can be and are sometimes used for disinfection, antisepsis, and preservation, more often, we see chemical agents being used for the same purposes
Chemical agents will effect microbes’ cell walls, cytoplasmic membrane, proteins, and DNA
You will learn that just like physical agents. The effect of a chemical agent will vary with temperature, length of exposure, and the amount of contaminating organic matter in the environment. The effect also depends on the pH, concentration, and freshness of the chemical
Chemical agents destroy or stop the growth of enveloped viruses and the vegetative cells of bacteria, fungi, and protozoa
Phenol and Phenolics
Joseph Lister used phenol (carbonic acid) to reduce infection during surgery
Phenolics are made up of phenol molecules that have been chemically modified by an addition of reactive atoms
Chlorinated phenolics have one or more atoms of chlorine added which enhances antimicrobial action and they have less odor than just phenol
Natural oils like pine and clove oils are phenolics and can be used as antiseptics
Denature proteins and disrupt cell membranes in a wide variety of pathogens.
They are effective even in the presence of vomit, pus, saliva, and feces and the remain active on surfaces for a long period of time
Because they remain active on surfaces for a long time, they are used in health care settings, labs and households.
Negative effects of phenolics- bad odor, irritate skin on some people