CHAPTER 5 CONTROL OF MICROBIAL GROWTH APPOACHES TO CONTROL Physical methods heat treatment irradiation filtration and mechanical removal Chemical methods antimicrobial agents Principles of Control Sterilization the process of removing all microorganisms and virsuse in a product Filtration heat chemicals irradiation A sterile item is free from microbes including endospores and viruses Does not consider prions Disinfection eliminates most all pathogens on in a material Some viable microbes exist Disinfectants chemicals that disinfect animate objects Pasteurization Decontamination Degerming Sanitized Preservation Biocides things that kill life Germicides disinfectants that target bacteria fungi endospores viruses Bactericidal meaning they kill bacteria Antiseptics used to kill bacteria on the skin Uses brief heating to reduce the number of spoilage organisms and kill pathogens Treatment used to kill the number of pathogens considered safe to handle Washing heat disinfectants Decrease number of microbes on skin Implies a substantially reduced number of growth that meets health standards Delaying spoilage of foods by adding growth inhibiting agents Situational Considerations Daily Life o o Hospitals o Microbiology Labs Routine washing and scrubbing with soaps and detergents aid in the mechanical removal of organisms Nosocomial hospital acquired infection High concentrations of disease people with invasive procedures and weak immune systems Aseptic technique the use of specific methods to exclude contaminating microbes fro man environment o Food and Production Facilities Add chemicals to impede or stop microbial growth o Water Treatment Disinfection by products by products of adding chemicals as distinfecting agents that react with naturally occurring items that can cause long term disease Type of Mircoorganism Critical for selecting a microbial agent Bacterial endospores Most resistant form Killed by heat or chemical methods Take a much larger time span to kill Protozoan cysts and oocysts Stages in the life cycle of certain intestinal protozoan pathogens Disinfectant resistant they are excreted in feces and a concern in water treatment Readily destroyed by boiling o Myobacterium species Eaxy cell walls make them resistant to typical microbial agents Stronger more toxic disinfectants muct be used o Pseudomonas o Naked viruses Common environmental organisms that are resistant to chemical disinfectants and in some case seven grow in them Particular concern in hospitals Lake a lipid envelope and therefore are resistant Enveloped viruses are more sensitive to heat and chemicals Numbers of Microorganisms initially present o Time it takes to kill is indicated by the initial population o o o o o o o o o o Decimal reduction time D valve time required to kill 90 of a population of bacteria under specific conditions The temp is indictated by the subscript Environmental Conditions pH temperature fats and other organic material and their prescence certain products like dirt grease etc can impact the degree to which a antimicrobial works Potential Risk of Infection Critical instruments These come into contact with the body tissues Semicritical Instruments Do not penetrate body but come into contact with mucous membranes Mucous membranes pose as a great barrier to microbes like endospores o o o o o o Noncritical instruments Pose little infection risk Ex countertops and stethoscopes Composition of the Item o Many items can be heat sensitive like plastics Moist Heat o Moist heat destroys microorganisms by irreversibly coagulating their proteins o Not an effective mean of sterilization because endospores can stand temperatures higher than 100 Centigrade Boiling o Pasteurization Does not sterlize but reduces the number of microbes in a substance most often food products Kills pathogens without altering food and can increase shelf life High temperature short time utilized by pasteurization protocol raises foods at various high temperatures below boiling pt for brief periods of time Ex milk is 72 degrees every 15 seconds Ultra high temperature method renders the product free of any microbes that can grow at room temperature Rapidly heated to high temperatures and then cooled o Sterilization using pressurized steam Autoclave heats water in an enclosed vessel that achieves temperatures higher than 100 degrees Centigrade As the heated water in the vessel forms steam the steam causes the pressure in the vessel to increase above atm pressure The higher the pressure the higher the temperature that the steam forms Used to terminated heat and moisture tolerant items Flash autoclaving by increasing the temperature things can be sterilized at a faster rate In order to be effective most monitor pressure and allow the steam to penetrate items and displace air Autoclaving tape heat sensitive tape that turns color in the presence of high temperatures In order to ensure autoclaving endospores are also heated and the mixture is then put on a plate to detect growth o The commercial canning process Retort an industrialized autoclave that utilizes steam Designed to destroy Clostridium These cells can germinate and grow in the anaerobic environment of the can Commercially sterile endospores of thermopilic bacteria by be present but can only grow at extremely high temperatures and therefore are no considered dangerous Higher the temp the shorter time to sterilize Higher the population the longer the time to sterilize o Dry Heat Requires longer time and higher temperatures than wet heat in order to be effective Incineration oxidizes the cell components to ashes Flaming heating until a red hot flame appears inoculating loop Hot air ovens oxidize all cell components and irreversibly denature proteins If have fans can circulate heat more effectively and sterilize in a shorter time USING OTHER PHYSICAL METHODS TO REMOVE OR DESTROY MICROBES For materials that are heat sensitive other methods must be utilized in order to create effective sterilization Filtration o Filtration of Fluids Used to sterilize sensitive fluids beer Paper thin membrane filters have microscopic pores that allow fluid to flow through but particles like bacteria cannot Pressure or a vacuum in utilized to increase the filtration time The filters are composed of polycarbonate and cellulose nitrate because absorb little fluid Depth filter trap material within thick filtration material such as cellulose fibers or diatomaceous earth Filtration of Air Have