
Full text loading...
Category: Industrial Microbiology; Clinical Microbiology
Physical Disinfection, Page 1 of 2
< Previous page | Next page > /docserver/preview/fulltext/10.1128/9781555816445/9781555819019_Chap02-1.gif /docserver/preview/fulltext/10.1128/9781555816445/9781555819019_Chap02-2.gifAbstract:
Disinfection is the antimicrobial reduction of the number of viable microorganisms on or in a product or surface to a level previously specified as appropriate for its intended further handling or use. This chapter considers the most widely used methods of physical disinfection, including heat (moist- and dry-heat methods), cold, radiation, and filtration. It discusses heat convection and conduction, with further consideration of radiation (for disinfection). Heat treatment leads to the release of dipicolinic acid and calcium from spores; dipicolinic acid and calcium are considered to play roles in protecting proteins in the inner core from heat damage and are examples of the multiple resistance mechanisms that protect spores from the effects of heat. Electromagnetic radiation is energy transmitted in the form of waves or rays, including X rays and UV and infrared (IR) radiation, which are considered to be within the electromagnetic spectrum. Nonionizing-radiation methods used for disinfection include UV and IR radiation and microwaves. Filtration is one of the oldest and most widely used physical methods for the removal of contaminants from liquids and gases. Filter types can also be classified as screen or depth filters.
Full text loading...
Typical microbial sensitivities to moist-heat disinfection.
Effect of temperature on microbial lethality and Z-value determination.
A pasteurizer for heat treatment of liquids. Courtesy of System Products Ltd.
Moist-heat resistance of microorganisms.
Atomic structure and the source of radiation.
The electromagnetic spectrum. The range of wavelengths is shown on the axis in meters, with the longest wavelengths (radio waves) on the left and shortest (γ rays) on the right.
A representation of a typical UV (low-pressure UV mercury) lamp and the generation of UV radiation.
Simple structure of a magnetron used for the production of microwaves. Voltage applied to a central cathode causes the release of electrons (shown in black), which are forced to circulate by attraction to the anode and the effect of the surrounding magnetic field. Microwaves are released as the circulating electrons lose their energy.
A simple continuous-duty UV disinfection system for liquids. The UV light is encased centrally in a chamber through which the liquid flows.
The theory of filtration. Various types of filtration processes are shown, with larger particles being retained by the filter and smaller particles allowed through the filter. Dead-end (A and B) and cross-flow (C) filters are shown. (A) Simple screen filter; (B) depth screen filter; (C) cross-flow filter.
The microscopic structures of the surfaces of three filter materials. Reproduced with permission of Whatman International Ltd.
Examples of a variety of liquid filter types. Reproduced with permission from the Pall Corporation.
An example of a rigid-walled isolator system, with glove access ports on the front and transfer hatches on either side.
Air pressure in environmentally controlled enclosed areas. (A) Rooms under negative pressure draw air into the room, maintaining microorganisms within the room. Negative pressure is typically used in rooms or cabinets where pathogenic organisms are manipulated. (B) Rooms under positive pressure force air out of the room to reduce the risk of contaminants entering the room. Uses of positive pressure include clean rooms and sterility control isolators.
Biological safety class I, II, and III cabinets. Class I cabinets provide the lowest level of biological control, with all air that leaves the cabinet passing through a HEPA filter. Class III cabinets provide the highest level of control; they are totally enclosed, with access via a glove port, as shown.
Range of filtration methods and reference size exclusion capabilities. Note that the size ranges are shown on a log scale.
Examples of various standards and guidelines for heat disinfection
Wavelengths and energies of types of electromagnetic radiation
Types of UV radiation
IR wavelength range
Typical uses of filtration for liquid and gas applications
Classification of clean rooms based on number of ≥0.5-μm particles detected within a given volume of air
Examples of standards and guidelines for disinfection and sterilization filtration applications