Physical and Chemical Control of Microorganisms I. Terms II. Factors which determine the effectiveness of control methods III. Methods of physical control IV. Chemical agents

Terms 1) “Control” -- Limiting exposure to _______________________ agents  Microorganisms are part of our environment  Infection can be controlled by limiting exposure to infectious agents 2) _______________ -- Removal or destruction of all _________________ microorganisms. “sterile” 3) Disinfection -- Removal or destruction of pathogens from ________________________ areas. “disinfectant” 4) Antisepsis -- Removal or destruction of vegetative forms from _______ _____________. “antiseptic” Note: Antiseptics and disinfectants do the same thing, but in different environments

Terms (continued) 5) Sanitization -- any cleansing technique that mechanically removes microorganisms. Usually soaps

More terms 6) “-cide” refers to ______________. “Bacteriocide” kills bacteria, “fungicide” kills fungi, etc. 6) “-cide” refers to ______________. “Bacteriocide” kills bacteria, “fungicide” kills fungi, etc. 7) “-static” means ‘to stand still’. Refers to an agent which prevents _______________ but doesn’t kill. “Bacteriostatic” or “fungistatic” or “virustatic” agent 7) “-static” means ‘to stand still’. Refers to an agent which prevents _______________ but doesn’t kill. “Bacteriostatic” or “fungistatic” or “virustatic” agent

Factors which determine the effectiveness of a control method 1. The number of microorganisms # of ________ cells Time (min.) “Death curve” Note log scale on y axis (each increment is 10X reduction in numbers)

Decimal reduction time (DRT) -- Time for a _____ reduction in population size. Here DRT = ______ If the goal is to reduce numbers to 10 2 then the size of the initial population will determine how long it will take, in this case, ____________ minutes Time (min.)

Factors which determine the effectiveness of a control method (cont.) # of viable cells Time (min.) Vege- tative cells __________________ Spore formers vs. non-spore formers

Factors which determine effectiveness of a control agent (cont.) Temperature and _______ of the environment Temperature and _______ of the environment ___________________ of the agent ___________________ of the agent Mode of action of the agent Mode of action of the agent  Microbistatic vs. microbicidal  Cellular target Presence of ________________ compounds or inhibitors of the control agent Presence of ________________ compounds or inhibitors of the control agent

Methods of Physical Control: Heat _________ heat  Hot water, boiling water, steam  60° - 135° C  Denatures proteins, nucleic acids __________ heat  Ovens  160° - >1000° C  Denatures, oxidizes At lower temperatures, moist heat is __________ effective than dry heat

Moist heat methods I. Boiling water -- ________ min. boiling kills all vegetative cells II. Pasteurization -- Heating to temp. below boiling to kill specific pathogens and increase shelf-time  Batch method -- 63°-66° for 30 min.  ___________ method ° for 15 sec. Results in killing of most viruses and 97-99% reduction in veg. stages of bacteria and fungi  UHT (Ultra High Temp) ° 1-2 ___________. Milk can last up to 3 months unrefrigerated Primary pathogen targets of pasteurization: ______________, Listeria, Mycobacterium, Campylobacter, Brucella

Moist heat methods (cont.) III. Steam under pressure  Highest temp. of moist heat at sea level -- _________° C  If ____________ increased, higher temps. can be reached Autoclaving Commonly: _______° C at 15 PSI ________ min. at this temp. is very effective

Effects on cellular proteins Text, Fig. 11.4

Physical methods: radiation

____________ -- knocks electrons off atoms --> ions e.g. gamma rays, x-rays  Damages DNA and proteins by breaking bonds -- Fig  Exposure hazard to humans  Penetrates ___________ and liquids  Used in fruits & vegetables, now meats Non-ionizing -- excites atoms but doesn’t ionize e.g. ____________, sunlight e.g. ____________, sunlight  Damages DNA by creating T-T dimers -- Fig. 11.8,  Relatively safe to use  Doesn’t penetrate solids or liquids well  ______________ sterilization, water treatment

Text, Fig. 11.8

Text, Fig

Other physical control methods Sonication -- Disruption using ___________ waves Filtration Text, Fig

Chemical control agents I. Many kinds but most function by:  Disrupting __________________  Altering ________________ and/or nucleic acid structure II. Effectiveness is determined by:  Concentration  Contact time

Major groups ________________ ________________ Phenol and its derivatives Phenol and its derivatives Alcohols Alcohols Hydrogen peroxide Hydrogen peroxide Detergents Detergents Heavy ___________ Heavy ___________

Halogens Mainly _______________, also iodine and fluorine Mainly _______________, also iodine and fluorine Iodine “iodophors” most common iodine compound used in hospitals: Betadine, Povidone, etc. Less ____________ than free iodine due to slow release of free iodine. Iodine “iodophors” most common iodine compound used in hospitals: Betadine, Povidone, etc. Less ____________ than free iodine due to slow release of free iodine. 3 Chlorine forms: 3 Chlorine forms: Cl 2 (chlorine gas) OCl (hypochlorite -- common ‘bleach’) NH 2 Cl (chloramines) In solution, these compounds combine with water to form hypochlorous acid (HOCl). This is the active form which destroys by ____________ Effective against: bacteria, fungi, spores, viruses Limitations:  ineffective at _____________ pH  ______________: light and O 2 cause breakdown

Phenols OH phenol OH CH 3 p-cresol (lysol) OH Cl OH Cl CH 2 Cl Cl Cl Cl Hexachlorophene (phisohex) Phenolics affect protein function and/or disrupt membranes

Alcohols Ethanol -- 70% to 95% Ethanol -- 70% to 95% Isopropanol -- more microbicidal but also more __________ Isopropanol -- more microbicidal but also more __________ Destroy cell membranes, can coagulate proteins

Hydrogen peroxide (H 2 O 2 ) Forms _______________ free radicals (e.g. superoxides, hydroxyl radicals: see last lecture) which are toxic to all cells Also breaks down to H 2 O and O 2, therefore is strongly effective against _____________.

Detergents All solubilize membranes and disrupt proteins Text, Fig. 11.3

Detergents (cont.) Two types: ___________ (charged) and non-ionic Non-ionic and anionic detergents (like soaps) are not very microbicidal, although they may be very effective in sanitization. _____________ detergents (like benzalkonium chloride) are the most effective ionic detergents.

Heavy metals Mainly only mercury and silver preparations are used now. Merthiolate, mercurochrome, silver nitrate, etc. Form ions which complex with cell components, stopping growth Disadvantages:  _________________  Microbes can develop ___________________