ABSTRACT
The antibacterial effectiveness of three selected disinfectants (household bleach, phenol and ethanol) was determined using agar well diffusion method. Phenol coefficient was used to compare the effectiveness of the disinfectants against phenol under experimental conditions. The test organisms include Staphylococcus aureus and Pseudomonas aeruginosa isolated from both clinical and environmental samples. The undiluted concentrations of the disisnfectants showed varying zones of inhibition against the test organisms, on Staphylococcus aureus it ranged from 41.00±2.83mm (bleach) to 46.50±4.95mm (phenol), and on Pseudomonas aeruginosa it ranged from 40.00±0.00mm (bleach) to 43.50±2.12mm (phenol). No activity was observed with the absolute ethanol. The diluted concentrations of the other disinfectants also showed varying zones of inhibition, On Staphylococcus aureus the mean zone diameter range from 10.00±0.00mm with 38%v/v bleach to 43.50±2.12mm with 75%v/v phenol. Pseudomonas aeruginosa exhibited inhibitions with zone diameter as low as 15.00±0.00mm with 28.5%v/v bleach to as high as 41.00±1.41mm with 75%v/v of phenol. The phenol coefficient test also showed varying results with bleach being the most efficient on the test organisms. The result qualifies these chemical solutions a good disinfectant hence their use externally as a sterilizing agent should be encouraged to avoid contraction of related infections caused by these test organisms.
TABLE OF CONTENTS
Title page
i
Certification
ii
Dedication
iii
Acknowledgement
iv
Table of contents v
List of tables viii
List of figures
ix
Abstract
x
CHAPTER
ONE
1.0 Introduction
1
1.1 Aim of study
3
1.2 Objectives of the study 3
CHAPTER
TWO
2.0 Literature review
4
2.1 Brief history of disinfectants
7
2.2 Disinfecting agents
8
2.2.1 Alcohols
8
2.2.2 Halogens
9
2.2.3 Phenols and Phenolics
10
2.3 Factors affecting the efficacy of
disinfection and sterilization
11
2.3.1 Number and location of
Microorganisms
11
2.3.2 Innate Resistance of
Microorganisms
11
2.3.3 Concentration and potency of
disinfectants
12
2.3.4 Physical and chemical factors
13
2.3.5 Organic and inorganic matter
14
2.3.6 Duration of exposure
14
2.3.7 Biofilms
15
2.4 Test organisms
16
CHAPTER
THREE
3.0 Materials and methods
18
3.1 Source of microorganisms 18
3.3.0 Confirmatory test for isolates
18
3.3.1 Gram staining
18
3.3.2 Catalase test
18
3.3.3 Coagulase test
19
3.3.4 Oxidase test
19
3.4 Test organism suspension
20
3.5 Inoculation of the test organisms 20
3.6 Preparation of the disinfectants
20
3.7 Efficacy testing 20
3.7.1 Pouring of the disinfectant and
incubation
21
3.8 Determination of the phenol
coefficient of the disinfectants
21
CHAPTER
FOUR
4.0 Results
22
CHAPTER
FIVE
5.0 Discussion and conclusion
29
5.1 Discussion
29
5.2 Conclusion
31
References
32
Appendix
LIST OF TABLES
Table 1: Morphological and Biochemical
characteristics of the test isolates 24
Table 2: Phenol coefficient test of the
disinfectants against the test organisms 28
LIST OF FIGURES
Fig. 1: Zone of
inhibition of the diluted concentrations of the test disinfectants on S. aureus 25
Fig. 2: Zone of inhibition of the diluted
concentrations of the test disinfectants on P.
aeruginosa 26
Fig. 3: Zone of
inhibition of the undiluted concentrations of the disinfectants on the test
organisms 27
CHAPTER ONE
1.0 INTRODUCTION
The
term control of microorganisms refers to the reduction in number or activity of
the total microbial load. The principal reasons for controlling micro organisms
are as follows; to prevent transmission of diseases and infection, to prevent
contamination by the growth of undesirable microorganisms, to prevent deterioration
and spoilage of materials by microorganisms(Pelezar et al., 2006; Willey et al.,
2008). The control directed at destroying harmful microorganisms is called disinfection.
It usually refers to the destruction of vegetative (non-endospore forming)
pathogens.
The
term most commonly applies to the use of a disinfectant to free an inert
surface or substance. When this treatment is directed at living tissue, it is
called antisepsis, and the chemical is then called antiseptic. Therefore, in
practice the same chemical might be called a disinfectant for one use and
antiseptic for another (Tortora et al.,
2004; Ryan and Ray 2004). According to W.H.O and Brooks et al., disinfectants are toxic not only for microbial pathogens
but for host cells as well and because of this, they can only be used to
inactivate microorganisms in the inanimate environment or to a limited extent,
on skin surfaces but cannot be administered systemically.
Antiseptics
are biocides or products that destroy or inhibit the growth of microorganisms
in or on living tissue (e.g. health care personnel hand washes and surgical
scrubs); and disinfectants are similar but generally are products or biocides
that are used on inanimate objects or surfaces. Disinfectants can be
sporostatic but are not necessarily sporicidal (Johnston et al., 2002).
A
wide variety of active chemical agents (or “biocides”) are found in antiseptics
and disinfectants. Depending on the chemical nature of disinfectants and
antiseptics they can be categorized into several groups. They are alcohols,
phenolics, halogens, Quaternary
Ammonium
Compounds (QACs) and aldehydes. The mode of action of disinfectants and
antiseptics differ greatly according to the chemical substance present. The
choice of the disinfectant to be used depends on a particular situation. Some
disinfectants have a wide spectrum (kill nearly all microorganisms), whilst
others kill a smaller range of disease-causing organisms, but are preferred for
other properties (they may be non-corrosive, non-toxic, or inexpensive)
(Pelczar et.al., 1993).
The
content of many chemical agents can be expressed by more than one notation. In
dilutions, a small volume of the liquid chemical (solute) is diluted in a large
volume of solvent to achieve a certain ratio. In general, solutions of low
dilution or high percentage have more of the active chemical (are more concentrated)
and tend to be more biocide, but expense and potential toxicity can necessitate
using the minimum strength that is effective (Talaro, 2003).
The
effectiveness of a given disinfectant can be evaluated using the Phenol
co-efficient test which is the best known disinfectant screening test in which
the potency of a disinfectant is compared with that of phenol. The
basic principle now widely accepted is that, the antimicrobial efficiency of a
disinfectant or an antiseptic is examined at three stages of testing (Pelczar et al., 1993).
The
first stage concerns laboratory tests in which it is verified whether a
chemical compound or a preparation possesses antimicrobial activity. For these
preliminary screening tests, suspension tests are considered. In the second
stage of tests, disinfection procedures and not disinfectants are examined. It
is determined under which conditions and at which use-dilution for a given application
the preparation is active: the tests simulate real-life situations; such tests are
carrier tests for the disinfection of materials by submersion and surface
disinfection tests. The last stage takes place in the field, and comprises the
in-situ tests which examine whether, after a normal
period
of use, germs are still killed by the disinfectant solution.
1.1 AIM OF THE STUDY
The
aim of the study was to compare the efficacy of three used disinfectant,
bleach, phenol and ethanol on two bacterial isolates, Pseudomonas aeruginosa and
Staphylococcus aureus; to know if the disinfectants have any antimicrobial activity
against the test microorganisms; and to know the susceptibility of the test gram
positive and gram negative bacteria to the test disinfectants.
1.2 OBJECTIVE OF THE
STUDY
The
objectives of the study were;
·
To isolate the test
organisms
·
To evaluate the
potentiality of the different disinfectants on the test organism
·
To determine the Phenol
Coefficient of the disinfectants
·
To compare the
effectivity of the different disinfectants using the test organisms
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