Muhammad Suleman
Kamran Rasool
Fatima Amjad
Aysha Imtiaz
 Control of microbial growth means "Preventing
the growth of microbes"
 Very important in microbiology experiments
 Preventing growth of undesirable
microorganisms
Control
Killing
microorganisms
Preventing their
growth
 Sterilization – a process that destroys all viable microbes, including
viruses & endospores
 Disinfection – a process to destroy vegetative pathogens, not endospores
 Sanitization – any cleansing technique that mechanically removes
microbes
 Degermation – reduces the number of microbes
 Cell Wall
 Cell Membrane
 Proteins
 Nucleic Acid (DNA and RNA)
Physical
Control
Chemical
Control
 Heat
 Cold temperature Treatment
 Desiccation
 Radiation
 Filtration
Thermal death time
Minimum amount of time required to kill microorganisms at a given
temperature
Thermal death point
The lowest temperature at which all microorganisms are killed in 10
minutes
Decimal reduction time.
The time for destruction of 90 percent of the microbial population
 Moist heat – use of hot water or steam
 Vegetative cell with in 2-3 mins
 Bacterial spores 2-3 hours
 Mode of action – denaturation of proteins,
destruction of membranes & DNA
 Autoclave
 Intermittent Sterilization
 Pasteurization
 Boiling
 Dry Heat
 Oxidation of organic molecules
 Denatures proteins (cell destroyed)
 Incineration
Heat treatment from flame or heating coil
Flame of Bunsen burner is 1,870 degrees Celsius.
Furnaces/incinerators burn from 800-6,500 degrees Celsius
 Dry Ovens
 Heat is circulated in an enclosed compartment
 Sterilization requires 150-180 degrees Celsius for 2 to 4 hours (destroys
spores)
 Microbiostatic- Slow growth of microbes
 Refrigeration
 4°C Static, except for psychrotrophs
 short term food preservation
 Freezing
 –20°C or lower (liquid nitrogen -196°C)
 static to many microbes
 long term food preservation (-20°C) or specimen storage (-80 to -196°C)
 used to preserve foods and culture media
 Removal of water
 Stops growth
 Not effective
 Microbes regrow on reintroduction of water
 Removal of microbes by passing through a filter
 Used to sterilize
 heat sensitive liquids
 Air in hospital units
 HEPA Filters in BSL-3
Ionizing
Radiations
Non-Ionizing
Radiations
 Ionizing Radiation
 Highly penetrating
 Break DNA backbone
 used to sterilize food products and medical instruments
 X-rays, gamma Rays
 Non-ionizing Radiation
 less penetrating power
 form T-T Dimers, disrupt DNA structure
 Used to sterilize air and solid surfaces
 UV Rays
 For evaluating the disinfectant or chemical agent
 Dip metal rings into broth cultures of the organisms.
 a disk of filter paper is soaked with a chemical
 placed on an inoculated agar plate
 a clear zone of inhibition indicates effectiveness.
 Halogens
 Phenolics
 Alcohols
 Hydrogen peroxide
 Detergents & soaps
 Heavy metals
 Aldehydes
 Chlorine
 Denaturation of proteins (by disrupting disulfide bonds)
 Calcium hypochlorite : disinfect equipment
 As a gas , maintain low microbial count in water
 Iodine
 Denatures proteins
 Sporicidal
 Degerming agent and disinfectant
 Surface active agent
 Disrupt cell membrane (precipitate proteins)
 Bactericidal, viricidal but not sporicidal
 Best for disinfecting things like pus and saliva
 Triclosan
 added to soaps as antibacterial agent
 Applicable for bacterial and fungi hazardous effects but not sporicidal
 70 % Ethyl alcohol & isopropyl is widely used.
 Act as surfactants
 dissolves membrane lipids
 coagulates proteins of vegetative bacterial cells and fungi
 Evaporates quickly
 Useful in degerming the skin before injections
 Weak solution (3%) to strong solution (25%)
 Produce highly reactive hydroxyl-free radicals
 damage protein & DNA
 interaction with catalase (at injured part)& decomposes to O2 gas
 decomposes to O2 gas – toxic to anaerobes
 Strong solutions are sporicidal
 Detergents
 Quaternary ammonia cations
 Act as surfactant
 Not sporicidal
 Soaps
 Mechanically remove particles containing microbes
 Grease and oils
 Glutaraldehyde & formaldehyde
 Kill microbes by alkylating protein & DNA
 glutaraldehyde in 2% solution (Cidex)
 used as sterilant for heat sensitive instruments
 formaldehyde
 disinfectant, preservative
 toxicity limits use
 Solutions of silver & mercury
 kill vegetative cells in low concentrations by inactivating proteins.
 Bind to the active site of important enzymes
 Oligodynamic action
 Not sporicidal
 Eg. silver nitrate
 Ethylene oxide, propylene oxide, betapropiolactone & chlorine dioxide
 Strong alkylating agents
 Stop DNA-RNA synthesis
 Stop Protein Synthesis
 Disrupt protein structure
 Sporicidal
 Microbes are found everywhere in environment
 Their control is most important
 By killing
 By stopping Growth
 Microbial Death refers to complete loss of reproductive ability of microbes even
under optimum conditions
 Different Methods to control
 Physical Methods
 Chemical Methods
INTERESTING FACT!!!!!
 Deinococcus radiodurans can withstand blasts of radiation 1,000 times greater than
what would kill a human being.