T.J. Atoyebi, 2015

◦ Lecture 7

We all labour against our own cure, for death is the cure of all diseases. —Sir Thomas Browne

T.J. Atoyebi, 2015

Although most microorganisms are beneficial and necessary for human well-being, microbial activities may have undesirable consequences, such as food spoilage and disease.
Therefore it is essential to be able to kill a wide variety of microorganisms or inhibit their growth to minimize their destructive effects.

T.J. Atoyebi, 2015

The goal is twofold:
(1) to destroy pathogens and prevent their transmission,
(2) to reduce or eliminate microorganisms responsible for the contamination of water, food, and other substances.

T.J. Atoyebi, 2015

Control of microorganisms can be achieved by a variety of;
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physical,

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chemical and

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mechanical removal methods.

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T.J. Atoyebi, 2015

1. STERILISATION
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Sterilisation is the process by which all microorganisms present on or in an object are destroyed or removed.

Sterilization involves the destruction or removal of all living microbes, spores, and viruses on an object or in an area.

Vacuum pump suction

T.J. Atoyebi, 2015

Disinfection is the elimination or inhibition of pathogenic microorganisms in or on an object so that they no longer pose a threat.
It is the destruction or removal of vegetative pathogens but not bacterial endospores. Usually used only on inanimate objects.

T.J. Atoyebi, 2015

The process of destroying pathogens is called disinfection. If the object treated is lifeless, such as a tabletop, the chemical agent used is called a disinfectant. However, if the object treated is living, such as a tissue of the human body, the chemical agent used is an antiseptic

T.J. Atoyebi, 2015

An antiseptic is a chemical agent of disinfection that is mild enough to be used on human skin or tissues.

T.J. Atoyebi, 2015

Agents that kill microbes are microbicidal (-cide = “kill”)

or more simply called “germicides.”

If the agent specifically kills bacteria, it is bactericidal; if it kills fungi, it is fungicidal.

T.J. Atoyebi, 2015

Many chemical agents are INHIBITING AGENTS or
MICROBIOSTATIC (-static = “remain in place”);

they reduce microbial numbers or inhibit their growth. Agents can also be; bacteriostatic or fungistatic 4. SANITATION

T.J. Atoyebi, 2015

In sanitization, the microbial population is reduced to levels that are considered safe by public health standards. T.J. Atoyebi, 2015

T.J. Atoyebi, 2015

The four most frequently employed physical agents are; 

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heat, low temperatures, filtration, and radiation. T.J. Atoyebi, 2015

Heat and other physical agents are normally used to control microbial growth and sterilize objects, as can be seen from the continual operation of the autoclave in every
Microbiology laboratory.

Heat is fast, reliable, and relatively inexpensive.
Above the growth range temperature for a microbe;
Enzymes and other proteins as well as nucleic acids are denatured. Heat also drives off water, and because all organisms depend on water, this loss may be fatal.

T.J. Atoyebi, 2015

FILTRATION
Filtration is an excellent way to reduce the microbial population in solutions of heatsensitive material, and sometimes it can be used to sterilize solutions.

Rather than directly destroying contaminating microorganisms, the filter simply removes them.

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T.J. Atoyebi, 2015

RADIATION
Certain types of irradiation are used to control the growth of microorganisms.

These include both ionising and non-ionising radiation.
The most widely used form of non-ionising radiation is ultraviolet (UV) light

T.J. Atoyebi, 2015

CHEMICAL AGENTS
Chemical agents, by contrast,rarely achieve sterilization. Instead, they are expected only to destroy the pathogenic organisms on or in an object or area. T.J. Atoyebi, 2015

Alcohols
Both bacteria and fungi are killed by alcohol treatment, but spores are often resistant.

The use of alcohols is further limited to those materials that can withstand their solvent action.

T.J. Atoyebi, 2015

Halogens
Chlorine is an effective disinfectant as a free gas, and as a component of chlorine releasing compounds such as hypochlorite and chloramines. Chlorine gas, in compressed form, is used in the disinfection of municipal water supplies, swimming pools and the dairy industry.

T.J. Atoyebi, 2015

Surfactants
Surface active agents or surfactants, such as soaps and detergents, have the ability to orientate themselves between two interfaces to bring them into closer contact and facilitate the mechanical removal of dirt and microorganisms.
Cationic detergents such as quaternary ammonium compounds (ammonium chloride) with each hydrogen replaced by an organic group, act by combining with phospholipids to disrupt cell membranes and affect cellular permeability.

ANTIMICROBIAL AGENTS

T.J. Atoyebi, 2015

Major breakthrough in the treatment of infectious diseases was of course the discovery of naturally occurring antimicrobial agents, or antibiotics. These are metabolites produced by certain microorganisms, which inhibit the growth of certain other microorganisms.

An antibiotic is a microbially produced substance
(or a synthetic derivative) that has antimicrobial properties. T.J. Atoyebi, 2015

HOW DO ANTIBIOTICS WORK?

T.J. Atoyebi, 2015

All antibiotics have the common property of interfering in some way with a normal, critical function of the target bacterial cell. The most commonly used antibiotics exert their effect by one of the following methods:
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Inhibition of cell wall synthesis (group I)
Disruption of cell membranes (group II)
Interference with protein synthesis (group III)
Interference with nucleic acid synthesis (group IV)

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T.J. Atoyebi, 2015

The main group which work in this way are the β-lactam antibiotics, so-called because they contain a β-lactam ring in their structure.

Included among this group are the Penicillins and the Cephalosporins.