CONTROL OF MICROORGANISMS

- POORNASHRI K G
 DEFINITIONS & TERMS
STERLIZATION – Destruction or complete removal of all viable microorganism
SANITATION – Reduction of microbial population to a safe level.
DISINFECTION – Killing, Destruction or Removal of pathogens.
ASEPSIS – State of complete absence of viable pathogenic microorganisms.
ANTISEPTICS – Agents that are safely applied to inhibit the growth of
microorganisms.
BACTERICIDAL AGENTS – Agents that are designed to kill the bacteria.
FUNGICIDAL – Agents that are designed to kill the fungi.
VIRICIDAL – Agents that are designed to destroy the virus.
BACTERIOSTATIC – Agents that are chemical which inhibit the growth of bacteria.
FUNGISTATIC – Agents that are chemicals which inhibit the growth of fungi.
MICROBIOSTASIS – It refers to inhibition of growth of microorganisms.
 PHYSICAL METHODS

i. HEAT ii. RADIATION iii. FILTERATION

DRY HEAT MOIST HEAT NON-IONIZING IONIZING

❖ DEPTH FILTER
❖ CELLULOSE
❖ RED HEAT ❖ BELOW 100°C ❖ INFRA RED MEMBRANE FILTER
❖ X-RAYS
❖ FLAMING ❖ AT 100°C ❖ ULTRA VIOLET ❖ MICROFILTER
❖ GAMMA RAYS
❖ INCINERATION❖ ABOVE 100°C
❖ HOT AIR OVEN
 i. HEAT
❖ Heating is one of the most popular way of destroying or controlling of
microorganisms.
➢ DRY HEAT
❑ RED HEAT
❖ Holding the articles in flame of Bunsen burner till they become hot. E.g. forceps,
metal needles.
❑ FLAMING
❖ Frequently passing the articles through the flame. E.g. Glass wares.
❑ INCINERATION
❖ Destroying the contaminated material by burning them. E.g. Pathological
materials like sputum, stool, bedding, spoiled bedding.
❑ HOT AIR OVEN
❖ Hot air at 160°C is allowed to circulate between the articles which is used for
sterilization of articles. E.g. Petri dishes, pipettes, conical flasks, syringes,
scissors etc... HOT AIR OVEN
➢ MOIST HEAT
❑ BELOW 100°C
▪ PASTEURIZATION
❖ Pasteurization is the process of control of microorganisms which is applied for
milk & food industry.
❖ 63 °C for 30 minutes (Low Temperature Holding Method)
❖ 72 °C for 20 minutes (High Temperature Holding Method)
▪ VACCINE BATH
❖ Vaccine sterilization by heating in a water bath at 60 °C for one hour.
▪ SERUM BATH
❖ Media containing serum are sterilized by heating in a water bath at 56 °C for
several days.
▪ FRACTIONAL STERLIZATION
❖ The media containing serum is placed in a inspirator and heated at 80 °-85 °C for
30 minutes on 3 successive days.
❖ 1st Day – Vegetative bacteria dies.
❖ 2nd & 3rd Day – Germinal bacterial spores are removed.
❑ AT 100 °C
▪ BOILING
❖ Articles are boiled in water bath at 100 °C for about 10 – 15 minutes.
▪ STEAMING
❖ Articles are steamed at 100 °C for about 90 minutes.
▪ TYNDALIZATION
❖ Steaming at 100 °C for 30 minutes and incubated at 37 °C for about 3
consecutive days.

❑ ABOVE 100 °C
▪ AUTOCLAVING
❖ Steaming occurs at 121 °C with pressure of 15 pounds where the articles
autoclave
are sterilized for about 15 minutes.
E.g. Culture Media, Certain equipment.
 ii. RADIATION
➢ NON – IONIZING RADIATION
❑ INFRARED & UV RAYS:
❖ INFRARED: Used for rapid mass sterilization of prepacked items such as the
syringes, catheters.
❖ UV RAYS: Used for disinfecting the enclosed area such as operation theaters,
labs, entryways and also sterilizing the instruments, glassware.
UV Rays are found to kill many vegetative forms of microorganisms.
➢ IONIZING RADIATION
❑ X-RAYS & GAMMA RAYS:
❖ GAMMA RAYS: Gamma Rays from a cobalt 60 source used in the cold
sterilization of the antibiotics, hormones, plastic disposable supplies such as
syringes etc..
❖ X-RAYS: Bacteria are killed in the X-Ray radiation. It is used as a disinfection
of routine use.
 iii. FILTERATION
❑ DEPTH FILTER
❖ Made up of diatomaceous earth, asbestos or porcelain which entraps the
microorganisms in the fluid.
❑ SINTERED GLASS FILTER
❖ Made up of finely ground glass, the glass granules in the fluid adhere to
one another. Has low absorptive properties.
❑ ASBESTOS FILTER
❖ Made up of asbestos or magnesium silicate & are disc shaped.
❖ Tend to filter the alkaline fluids.
❑ MEMBRANE FILTER
❖ Made up of cellulose, acetate, polycarbonate, polyester or cellulose
nitrate.
❖ Used for water purification & analysis and sterilization & sterility testing.
❑ MICROFILTER
❖ Made up of asbestos which are used to filter the small amount of fluids.
❖ Used for the centrifugation.
 CHEMICAL METHODS
❖ The chemical method of control of microorganisms include the disinfectants, antiseptic,
sanitizer, germicide, bactericide & bacteriostasis.
❖ The primary objective of use of chemicals is to kill or to reduce the microorganisms to a
safety level.
❖ The chemical agents which are used widely in disinfectants and antiseptics are:
Alcohols
Phenols
Aldehydes
Halogens
Heavy metals
Dyes
Detergents
Gaseous agents.
❑ ALCOHOLS
❖ Ethyl alcohol (Ethanol) & isopropyl alcohol are the most frequently used in the disinfectants and antiseptics.
It is used for the disinfection of clinical thermometers.
❖ Alcohols are fungicidal and bactericidal & also it destroys lipid containing viruses.
❖ Methyl alcohol is effective against fungal spores and used for cleaning the cabinets and incubators.

❑ PHENOLS
❖ Phenols are obtained from the distillation of coal at temperatures between the 170 °C and 270 °C.
❖ The bactericidal effect of phenols is due to their ability to damage the cell membrane and inactive
membrane bound oxidases and dehydrogenases, thereby causing the lysis & death of microorganisms.
❖ Phenols such as cresols, xylenols & other orthophenylphenol are used as disinfectants in labs & hospitals.

❑ ALDEHYDES
❖ Aldehydes are the class of chemicals with the general formula (RCHO) of aldehydes, a several of low
molecular weight compounds are antimicrobial.
❖ Two of the most effective alcohols are formaldehyde and glutaraldehyde. Both are highly sporicidal.
i. Glutaraldehyde: effective against Tubercle bacilli. ii. Ortho-phthalaldehyde: effective against endospores.
iii. Peracetic acid: effective against Staphylococcus aureus.
❑ HALOGENS
❖ Among the halogens (fluorine, chlorine, bromine, iodine & astatine), the chlorine and iodine
have the antimicrobial property.
❖ IODINE: Used as a skin disinfectant as it has a bactericidal property with moderate action
against spores. It is effective against tubercle bacteria.
❖ CHLORINE: Used as disinfectants as they are highly bactericidal and virucidal. Organic
chloramines are used as antiseptic for dressing the wounds.

❑ HEAVY METAL
❖ The ions of heavy metals such as mercury, silver, arsenic, zinc and copper were used as
germicides.
▪ COPPER SULPHATE: Effective algicide and used in lakes & swimming pools.
▪ MERCURIC CHLORIDE: Bacteriostatic and used for inactivation & preservation process.
▪ SILVER NITRATE: 1% of silver nitrate is often added to the eyes of infants to prevent
ophthalmic gonorrhea.
▪ SILVER SULFADIAZINE: Used on the skin burns.
❑ DYES
❖ Aniline and Acridine Dyes are extensively used as skin & wound antiseptics. They are active
against the Gram positive and Gram negative bacteria.
❖ Sodium azide dye is used as disinfectants.

❑ DETERGENTS
❖ Anionic Detergents have antimicrobial property. They are used as disinfectants.
❖ Cationic Detergents such as Benzalkonium kill the most of bacteria and endospores. They are
often used as disinfectants for food utensils and small instruments and as skin antiseptics.

❑ GASEOUS AGENTS
❖ ETHYLENE OXIDE (EtO): It is both microbial and sporicidal which kills by combining with cell
proteins. Many heat sensitive items such as plastic petri dishes, syringes, catheters, sutures and
heart lung machines are sterilized by means of EtO.
❖ BETAPROPIOLACTONE (BPL): It is employed as a sterilizing gas. In liquid forms it is used to
sterilize the vaccines and sera. It kills microorganisms more readily than the EtO.
❖ HYDROGEN PEROXIDE: Vapour phase of hydrogen peroxide has been used to decontaminate
biological safety cabinets.
 ANTIMICROBIAL AGENTS
❖ An antimicrobial is an agent that kills microorganisms or stops the growth of
microorganisms.
❖ Antimicrobial medicines can be grouped according to the microorganisms they act upon.
E.g. Antifungals are used against the fungi.
❖ The use of antimicrobial medicines to treat infection is known as antimicrobial
chemotherapy, while the use of antimicrobial medicines to prevent infection is known as the
antimicrobial propylaxis.

❑ BIOCHEMICAL ACTION OF ANTIMICROBIAL AGENTS

❖ Antimicrobial agents interfere with specific processes that are essential for growth or
division.
❖ Based on the mode of action, the antimicrobials are classified into:
▪ Inhibitors of bacterial & fungal cell walls – Penicillin & cephalosporins inhibit the Gram
positive and Gram negative bacteria.
▪ Inhibitors of cytoplasmic membranes – Polymyxin B & E cause disorganization of
membrane permeability, so that nucleic acid leaks out & the cell dies.
▪ Inhibitors of Nucleic Acid synthesis: Certain antibiotics can interfere with the nucleic acid
synthesis.
▪ Inhibitors of Nucleotide Synthesis:
➢ Flucytosine inhibits the yeast species.
➢ Adenosine arabinoside inhibits the viruses.
➢ Acyclovir is nucleoside analog that inhibits herpes viruses.
➢ Zidovudine inhibits Human Immunodeficiency diseases.
➢ Rifamycin inhibit the DNA directed RNA polymerase.
➢ Ciprofloxin interact with DNA gyrase and possess the antimicrobial property.
➢ Aminoglycosides act by binding to specific ribosomal units.
➢ Chloramphenicol is a bacteriostatic agent that inhibits peptide bond formation.
➢ Erythromycin inhibits Mycoplasma. Chlamydia, Legionella by peptidyl transferase reaction.
▪ Inhibitors of Ribosome Function:
➢ A number of antibacterial agents act by inhibiting ribosome function. Amimoglycosides act by
binding to specific ribosomal subunits.
➢ Isoniazid a mycocidal nicotinamide derivative that inhibits Mycobacterium. It affects synthesis of
lipids.
SOME
ANTIMICROBIALS
&
ITS MODE OF
ACTION