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Control of Microbial Growth Chapter 7. Terminology Sepsis refers to microbial contamination. Asepsis is the absence of significant contamination. Antisepsis:

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Presentation on theme: "Control of Microbial Growth Chapter 7. Terminology Sepsis refers to microbial contamination. Asepsis is the absence of significant contamination. Antisepsis:"— Presentation transcript:

1 Control of Microbial Growth Chapter 7

2 Terminology Sepsis refers to microbial contamination. Asepsis is the absence of significant contamination. Antisepsis: Removal of pathogens from living tissue Degerming: Removal of microbes from a limited area Sanitization: Lower microbial counts on eating utensils

3 Terminology contd Decontaminated - item that has been treated to reduce # of disease causing organisms Preservation - delaying spoilage of foods Sterilization, Disinfection, Antiseptic, Bacteriocidal, Bacteriostatic

4 Terms used: Sterilization vs. Disinfection Sterilization: destroying all forms of life Disinfection: destroying pathogens or unwanted organisms Disinfectant vs. Antiseptic Disinfectant: antimicrobial agent used on inanimate objects Antiseptic : antimicrobial agent used on living tissue


6 cidal vs. static Biocide/Germicide: Kills microbes Bacteriostasis: Inhibiting, not killing, microbes Examples: - Bactericidal - kills bacteria - Bacteriostasis (Bacteriostatic)- inhibits bacterial growth - Fungicidal - Fungistatic - Algacidal - Algastatic

7 Methods of control Physical or chemical? – physical control includes heat, irradiation, filtration and mechanical removal – Chemical control involves the use of microbial chemicals – Depends on the situation – degree of control required

8 Methods of control contd Daily life - Cooking - refrigeration - cleaning - soap water mechanical Mechanical and chemical

9 Hospitals – Important to minimize nosocomial infection (hospital acquired infection) due to - weakened patients condition - breaching of intact skin - high concentration of pathogens from patients and workers – Sterile condition Methods of control contd

10 Microbiology lab utilizes – Sterile equipment – Aseptic technique – And possesses workers who takes care of the nature of of microbiologists (GLP) Methods of control contd

11 Foods/food production industry - physical removal - adding chemicals - may result in toxicity - clean surface/ machinery Methods of control contd

12 Selection of Control Method Antimicrobial procedure used for control of microbial growth is based on – Types of microbe – Extent of contamination – Environmental conditions – Potential risk

13 Selection of Control Method contd Types of microorganism - some organisms are more resistant and require stronger measures for control - endospores require chemical treatment for 10 hours - Mycobacteriums waxy cells are resistant to chemicals Mycobacterial cell wall: 1-outer lipids, 2-mycolic acid, 3- polysaccharides (arabinogalactan), 4-peptidoglycan, 5-plasma membrane, 6-lipoarabinomannan (LAM), 7-phosphatidylinositol mannoside, 8-cell wall skeleton

14 Extent of microbial population - larger population take more time to destroy - usually 90% of the population is destroyed in a given period e.g if in 1 st 3 minutes 90% of the population is destroyed, then 90% of the remaining population gets destroyed in the next 3 minutes and so on Selection of Control Method contd


16 Environmental conditions - pH, temperature - presence of - organics: blood - dirt - grease - the potential risk of transmitting infectious agents - critical items - semicritical items - non-critical items Selection of Control Method contd Must be cleaned first, then controlled

17 Critical items have - indirect contact with body tissues - needles, scalpels Semicritical items have contact with - mucous membranes but it does not penetrate endoscopes, endotrachial tubes Selection of Control contd

18 Non-critical items have - indirect contact with unbroken skin - countertops, stethoscopes

19 Methods to Control Microbial Growth Physical Methods Heat Sterilization Dry Heat Incineration Moist Heat BoilingAutoclavingPasteurization Filtration AirLiquid Radiation UV LightIonizing Radiation

20 Physical Microbial Controls: Heat Heat as a microbial control - fast, reliable, inexpensive - does not introduce potential toxic substances Types of heat control include - moist heat - pasteurization - pressurized steam - dry heat

21 Moist heat - causes irreversible coagulation of proteins found in microorganisms - 10 minutes of boiling - most microbes and viruses will be destroyed except endospores and few others which can survives hours of boiling Physical Microbial Controls: Heat contd

22 Pasteurization - reduces number of heat sensitive organisms - widely used in milk and juices increases shelf life and does not alter quality - original pasteurization was 62ºC, 30 mins - now: UHT-shorter time 72ºC, 15 secs Physical Microbial Controls: Heat contd

23 Pressurized steam - pressure cooker or autoclave - higher air pressure increases the temperature at which steam forms - 15 psi (lbs/square inch) at 121ºC for 15 mins -effective to kill endospores Physical Microbial Controls: Heat contd

24 The autoclave: Moist heat and pressure 15psi, 121ºC, 15 minutes Thermal death point (TDP): Lowest temperature at which all cells in a culture get killed in 10 mins Thermal death time (TDT): time to kill all cells in a culture Decimal reduction time (DRT): Minutes to kill 90% of a population at a given temperature

25 The autoclaving machine

26 Temperature of steam and Pressure at sea level

27 The autoclaving machine

28 Dry heat - without moisture e.g. flaming - burns cell constituents - object is oxidized to ash - irreversibly denatures proteins - takes longer (200ºC, 1.5 hrs dry=121ºC, 15 min moist) - advantages are for powders, does not corrode metals and blunt sharps - e.g flasks, tubes, pipettes in microbiological laboratories. Physical Microbial Controls: Heat contd

29 Physical Microbial Controls: Filtration Used for heat sensitive fluids air

30 Fluids – solutions of antibiotics, vitamins, tissue extracts, animal serum, etc. – Depth filters –able to retain microorganisms while allowing fluids to pass through – Membrane Filter - The use of graded pore size 0.2- 0.4µm Physical Microbial Controls: Filtration contd

31 Air - HEPA (High Efficient Particulate Air) filter and laminar air flow are commonly used - filter incoming air and outgoing air respectively - HEPA filter prevents the income of 0.3µm and large size particles to enter. Physical Microbial Controls: Filtration contd

32 Cold sterilization for disposable materials made up of plastics, wool, cotton, etc without altering the material. Radiation damages DNA Ionizing radiation (X-rays, gamma rays, electron beams) Non-ionizing radiation - UV - Microwaves kill by heat not especially antimicrobial Physical Microbial Controls: Radiation


34 Gamma irradiation - penetrate deeply - for heat sensitive materials - causes biological damage to microorganisms - does not alter food flavor (meat) Physical Microbial Controls: Radiation contd

35 UV light – damages the structure and function of nucleic acids – Penetrate poorly- cannot penetrate even into liquid. – Used to disinfect surfaces – Can cause damage to human cells – Germicidal lamps -kill or reduce the number of viable microorganisms to sterilize microbiological laboratories hospital operating rooms, and specific filling rooms in various industries Physical Microbial Controls: Radiation contd

36 Microwave – Kills by heat – Does not affect microorganisms directly Physical Microbial Controls: Radiation contd

37 Physical Methods used to control Microbial growth





42 Chemical Microbial Control Chemical Method Gas sterilantsEthylene oxide Antiseptics and disinfectants Germicidal chemical


44 Grouped according to potency – Sterilants – High-level – Intermediate level – Low level Chemical Microbial Control contd

45 Chemical Control sterilants destroy microorganisms, endospores and viruses used for critical equipment-scalpels

46 chemical control cont'd high level - destroy viruses and vegetative microorganisms (no endospores) - used for semicritical equipment: endoscopes intermediate level - destroy vegetative microorganisms, some viruses - used for non-critical equipment: sthetoscopes low level -destroy fungi, vegetative microorganisms - used for general purpose disinfectants

47 Selecting Germicidal Chemical Germicide: An agent capable of killing pathogens and non- pathogens but not necessarily endospores toxicity to human or environment? - weigh the benefits vs the risks presence of organic material - hypochlotrite is inactivated by the presence of organic matter compatibility -electrical equipment with a liquid?? residue - some have to be rinsed with sterile water cost and availability

48 Selecting germicidal Chemical cont'd storage and stability - may come in concentrated form for ease in storing - those have to be mixed environmental risk - is neutralization necessary before disposal?

49 Classes of Germicidal Chemicals alcohols alcohols aldehydes biguanides ethylene oxide halogens: oxidize proteins

50 Classes of Germicidal Chemicals alcohols - coagulated enzymes and proteins - damage lipid membranes - on-toxic - inexpensive - no residue

51 Classes of Germicidal Chemicals contd aldehydes - inactivate proteins and nucleic acids - toxic to humans Peroxygens - oxidizing agents - hydrogen peroxide - leaves no residue

52 Classes of Germicidal Chemicals contd biguanides - extensive antiseptic use - adheres and persists on skin, mucous membranes - low toxicity Phenolic compounds – Hitorically important – Irritant, unpleasant odor – Destroy cytoplasmic membrane and denatures protein

53 Classes of Germicidal Chemicals contd ethylene oxide - reacts with proteins - gas: penetrable - mutagenic Metal compounds – Interfere protein function – Toxic – pollutants

54 Classes of Germicidal Chemicals contd halogens: oxidize proteins -chlorine -irritating to skin -organic compounds consume free chlorine -iodine -tincture - Iodophore

55 Effect of germicidal activity on Microbes Cytoplasmic membrane Biguanides Phenolics Quats DNA Ethylene oxides Aldehydes Proteins Alcohols Aldehydes Halogens Metals Ozone Peroxygens Phenolics

56 Effect of germicidal activity on Microbes

57 Chemical methods of microbial control Evaluating a disinfectant - Disk diffusion method

58 Preservation of Perishables Extends shelf life – Slow or halts microbial growth thus delaying spoilage

59 Chemical preservatives – Some chemical preservatives are used in non-food items – Food preservatives must be non-toxic to humans Benzoic acid, propionic acids, nitrate are commonly used Nitrate – Inhibits germination of C. botulinum endospores Preservation of Perishables

60 Low temperature storage – Temperature dependent most microorganisms do not reproduce in ordinary refrigerator (0-7ºC) – Freezing ice crystals can cause irreversible damage to many microorganisms (kills up to 50% growth) Freezing stops all growth, but may start to reproduce again once food is thawed

61 Reducing water – Salt/sugar – Draw water out of cell – Less available for microorganisms Drying – Desiccation Removing water such as milk powder Preservation of Perishables Salt cured meat

62 Lyophilization – Freeze drying Freeze food first followed by putting in vacuum Preservation of Perishables

63 Factors that influence effectiveness Number of microbes Environmental influences Time of exposure Microbial characteristics

64 Microbial death curve

65 Limitations: Microbial Characteristics

66 Actions of Microbial Control Agents Alteration of membrane permeability Damage to proteins Damage to nucleic acids

67 Questions???? Sand rich in salts n nitrates preserved mummy

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