Control of Microbial Growth

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Chapter 7

• Control of Microbial Growth

Siti Sarah Jumali 06-4832123 www.slideshare.net/sa
rah_jumali
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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

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Terminology contd

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

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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

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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

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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

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Methods of control contd

• Daily life
• - Cooking
• - refrigeration
• - cleaning
• - soap water

mechanical
Mechanical and chemical
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Methods of control contd

• 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

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Methods of control contd

• Microbiology lab utilizes
• Sterile equipment
• Aseptic technique
• And possesses workers who takes care of the
  nature of of microbiologists (GLP)

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Methods of control contd

• Foods/food production industry
• - physical removal
• - adding chemicals
• - may result in toxicity
• - clean surface/ machinery

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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

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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
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Selection of Control Method contd

• 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 1st 3 minutes 90 of the population
  is destroyed, then 90 of the remaining
  population gets destroyed in the next 3 minutes
  and so on

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Selection of Control Method contd

• Environmental conditions
• - pH, temperature
• - presence of
• - organics blood
• - dirt
• - grease
• - the potential risk of transmitting infectious
  agents
• - critical items
• - semicritical items
• - non-critical items

Must be cleaned first, then controlled
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Selection of Control contd

• 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

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Selection of Control contd

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

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Methods to Control Microbial Growth
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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

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Physical Microbial Controls Heat contd

• 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

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Physical Microbial Controls Heat contd

• 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

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Physical Microbial Controls Heat contd

• 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

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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

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The autoclaving machine
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Temperature of steam and Pressure at sea level
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The autoclaving machine
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Physical Microbial Controls Heat contd

• Dry heat
• - without moisture e.g. flaming
• - burns cell constituents
• - object is oxidized to ash
• - irreversibly denatures proteins
• - takes longer (200ºC, 1.5 hrs dry121ºC, 15 min
  moist)
• - advantages are for powders, does not corrode
  metals and blunt sharps
• - e.g flasks, tubes, pipettes in microbiological
  laboratories.

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Physical Microbial Controls Filtration

• Used for heat sensitive fluids
• air

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Physical Microbial Controls Filtration contd

• 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

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Physical Microbial Controls Filtration contd

• 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.

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Physical Microbial Controls Radiation

• 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

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Physical Microbial Controls Radiation contd

• Gamma irradiation
• - penetrate deeply
• - for heat sensitive materials
• - causes biological damage to microorganisms
• - does not alter food flavor (meat)

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Physical Microbial Controls Radiation contd

• 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

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Physical Microbial Controls Radiation contd

• Microwave
• Kills by heat
• Does not affect microorganisms directly

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Physical Methods used to control Microbial growth
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Chemical Microbial Control
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Chemical Microbial Control contd

• Grouped according to potency
• Sterilants
• High-level
• Intermediate level
• Low level

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Chemical Control

• sterilants
• destroy microorganisms, endospores and viruses
• used for critical equipment-scalpels

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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

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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

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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?

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Classes of Germicidal Chemicals

• alcohols alcohols
• aldehydes
• biguanides
• ethylene oxide 
• halogens oxidize proteins

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Classes of Germicidal Chemicals

• alcohols
• - coagulated enzymes and proteins
• - damage lipid membranes
• - on-toxic
• - inexpensive
• - no residue

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Classes of Germicidal Chemicals contd

• aldehydes
• - inactivate proteins and nucleic acids
• - toxic to humans
• Peroxygens
• - oxidizing agents
• - hydrogen peroxide
• - leaves no residue

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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

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Classes of Germicidal Chemicals contd

• ethylene oxide 
• - reacts with proteins
• - gas penetrable 
• - mutagenic
• Metal compounds
• Interfere protein function
• Toxic
• pollutants

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Classes of Germicidal Chemicals contd

• halogens oxidize proteins
• -chlorine
• -irritating to skin
• -organic compounds consume free chlorine
• -iodine
• -tincture
• - Iodophore

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Effect of germicidal activity on Microbes
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Effect of germicidal activity on Microbes
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Chemical methods of microbial control

• Evaluating a disinfectant
• - Disk diffusion method

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Preservation of Perishables

• Extends shelf life
• Slow or halts microbial growth thus delaying
  spoilage

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Preservation of Perishables

• 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

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Preservation of Perishables

• 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

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Preservation of Perishables

• Reducing water
• Salt/sugar
• Draw water out of cell
• Less available for microorganisms
• Drying
• Desiccation
• Removing water such as milk powder

Salt cured meat
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Preservation of Perishables

• Lyophilization
• Freeze drying
• Freeze food first
• followed by putting in vacuum

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Factors that influence effectiveness

• Number of microbes
• Environmental influences
• Time of exposure
• Microbial characteristics

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Microbial death curve
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Limitations Microbial Characteristics
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Actions of Microbial Control Agents

• Alteration of membrane permeability
• Damage to proteins
• Damage to nucleic acids

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