Chapter 5- control of microbial growthPowerPoint PresentationApproaches to controlDifferent levels of microbial controlFig. per05.01Fig. 27.06Control microbial growthMethodsAntimicrobial agents can be divided into:Table 05.01Selection of an antimicrobial procedureType of microorganismNumbers of microorganismsNumbers of microorganisms initially presentEnvironmental conditionsPotential risk infectionHeatTable 05.02PasteurisationAutoclaving:Autoclave: Pressurized steamFig. 05.03Commercial CanningFig. 05.05Dry heatChemicalsAntimicrobial activity of germicidesSelecting a germicideFig. 05.06Slide 30Slide 31Table 05.04bFiltrationSlide 34Slide 35Filtration of fluidsFiltration of airRadiationElectromagnetic radiationSlide 40UV radiationThymine dimer formation and repairIonizing radiation lethal effectIonizing radiationPreservationChemicalLow temperatureReducing water availabilityChapter 5- control of microbial growthTopics•Approaches to control•Selection of an antimicrobial procedure•Heat•Chemicals•Filtration•Radiation•PreservationApproaches to control•Daily life•Hospital / Laboratory•Food production facilities•IndustriesDifferent levels of microbial controlFigure 5.1Fig. per05.01Red areas showed recovered P aeruginosa following treatment of a person who had it on its burns. this shows how extensively an operating room can become contaminated by a patient and the necessity of a terminal cleaningFig. 27.06Control microbial growth-Growth inhibition (freezing)-killing-Removing from an environment.(washing)Methods •Physical methods–Heat–Irradiation–Filtration–washing•Chemical methods: –antiseptics–DisinfectantAntimicrobial agents can be divided into:•bactericidal- agents that kill •bacteriostatic- agents that inhibit growth.Table 05.01Selection of an antimicrobial procedure•Type of microorganism•Number of microorganisms•Environmental conditions•Potential risks of infectionType of microorganism•Bacterial endospores•Waxy cell wall (ex. Mycobacterium species)•Grow in the presence of disinfectants (ex. Pseudomonas species)•Viruses that lack a lipid envelopeNumbers of microorganisms Figure 5.2Relationship between initial number of microorganisms and the time it takes to kill themNumbers of microorganisms initially present•Decimal reduction time. D value: time required to kill 90% of a population•If 90% bacteria are killed in 3 min , 90% of the remaining will be killed in the next 3 min… It takes 2D to kill a population of 102 bacteria and 10D (30 min) to kill a population of 1010 bacteria•pH•TemperatureTime to kill suspension of M. tuberculosis: with Sodium Hypochlorite–at 50o C 150 sec–at 55o C  55 sec •Organic matterPresence of fat and org. compound (blood…) interfere with heat penetration and chemical disinfectants. Therefore washing surgery tools before sterilizing is imp.Environmental conditionsPotential risk infection•Items used in medicine are categorized according to Potential risk of transmitting infection :•Critical items: direct contact with body tissues :needles scalpel forceps… must be sterilized.•Semi critical items: contact with mucus membranes (Gastrointestinal endoscopes, endotracheal tubes, vaginal specula…) must be free of vegetative bacteria viruses and mycobacteria. If endospores remain it is not a problem. Mucus membranes prevents access of microbes to inner tissues.•Non critical items: pose no risk of infection: Stetoscopes blood pressure cuffs…Come in contact with unbreached skinHeatTable 05.02Pasteurisation•Does not sterilize but reduce nb of heat sensitive microbes without changing taste of food. •HTST method: high temp. short time:•72oC(162oF) for 15 sec (for milk) then rapidly cooled•82oC (180oF) for 20 sec (ice cream)•UHT: Ultra high temp. cream and milk juices in boxes : heat 140-150o C (284-302oF)for a few sec then rapidly cooled (more than pasteurization) Product is asceptically packaged in containers treated with a germicide (H2O2).Autoclaving:•Sterilization using pressurized steam •Vessels: Autoclave, pressure cookers•Principle: Pressure is used to increase temperature of steam. •Water steam temp is 100o C at normal atm pressure. In the autoclave: steam is kept under higher pressure which causes steam temperature to increase. •The autoclave typically uses an operating temperature of 121°C (250oF) at 18 psi. At this temperature, bacterial endospores have a D value = 4 - 5 min, whereas vegetative cells have a D value= 0.1 to 0.5 min. •Generally, the time for sterilization of 1 l solution is 15 min at 121°C.• Bulky objects or large volumes of liquid require more time.Autoclave:Pressurized steamFig. 05.03Commercial Canning•food is sealed and heated so as to kill all living organisms. •Mainly aim at destroying endospores of Clostridium botulinum that produce a very lethal toxin (inhibits acetylcholine). All other bacteria are also killed along. But not endospores of thermophiles but these do not cause problems.Fig. 05.05•Flaming a wire inoculating loop•Oven (160-170°C) (320-340oF)–Good for sterilizing powder, does not corrode metal and does not dull sharp instruments–However, Takes much longer time than moist heat.Dry heat•Potency of germicides•Selecting a germicide•Classes of germicidesChemicalsAntimicrobial activity of germicidesTable 5.3Selecting a germicide•Toxicity•Activity in the presence of organic matter–Chlorox cannot be used in the presence of organic matter Phenolics and QAC can.•Compatibility with the material being treated–electrical instrument s cannot be cleaned with liquid disinfectants. •Residue causing toxicity or corrosion– Chlorox is corrosive for rubber and metals •Cost and availability•Storage and stability•Environmental riskFig. 05.06•Alcohols disinfectant and antiseptics for surface sterilization; limitation evaporates quickly; •Quaternary ammonia compounds (QAC) e.g. benzocalium chloride : disinfectants and antiseptics. Non toxic. Used on inanimate objects and surfaces; preserves non-food substances.•Phenolics : used as antiseptics and disinfectants e.g.: Triclosan in toothpaste . hexachlorophene used for floor disinfection, highly effective against S.aureus •Peroxigens (peroxide) oxidizing agent biodegradable used as antiseptic and disinfectant for juice containers).•Halogens (Chlorine and iodine) disinfect (non-living) objects surface drinking water and