It has been amply demonstrated, proved, and well documented that the actual prevalent destruction
of various pathogenic/nonpathogenic microorganisms and their subsequent inhibition of the resulting
‘microbial growth’
is invariably and predominantly affected by the following
six cardinal factors, namely :
Population Size
It may be observed that usually an equal fraction of a microbial population gets killed during
each stipulated period (interval); and, therefore, a larger population certainly needs a relatively longer
duration to die than a smaller one. Importantly, the same principle holds good for the
chemical antimicrobial
agents.
Population Composition
Importantly, the overall effectiveness of an
antimicrobial agent exclusively changes with the
prevailing nature of the microorganisms under investigation due to the fact that they differ distinctly in
their susceptibility.
Salient Features :
These are as follows :
(
a) Microbial endospores are found to be much more resistant to a large segment of the antimicrobial
agents in comparison to the vegetative forms.
(
b) Younger cells are invariably more prone to rapid destruction than the corresponding mature
organisms.
(
c) Certain specific species may withstand adverse experimental parameters better than
others.
Example :
Mycobacterium tuberculosis (causative organism for tuberculosis is found to be much
more resistant to antimicrobial agents
vis-a-vis other microorganisms.
Concentration of Antimicrobial Agent
One may observe quite often that the more concentrated a
‘chemical agent’ or ‘intense a physical
agent’
—the more quickly the microorganisms get destroyed. Nevertheless, the ‘agent effectiveness’
is not normally associated with either concentration or intensity directly.
Salient Features
—are as given under :
(1) Spread over a short-range a rather small increase in the concentration of antimicrobial agent
ultimately leads to a definite
exponential rise in its effectiveness ; however, beyond a certain critical
point one may not observe any more increase in the
rate of killing.
(2) Occasionally, an antimicrobial agent is found to be more effective even at much lower concentrations.
Example :
Ethanol 70% (v/v) is more effective in comparison to 95% (v/v), by virtue of the fact
that its (EtOH) activity gets markedly enhanced by the presence of water.
Duration of Exposure
The longer a particular population of microbes is duly exposed to a
microcidal agent, the more
number of microorganisms would be killed. In order to accomplish perfect sterilization, an exposure
duration just sufficient to reduce the ensuing
survival probability to either 10–6 or less must be employed
effectively.
Temperature
It has been noticed that an increase in the temperature at which a particular
chemical agent
invariably exerts its action often increases its activity. Quite often a lower concentration of either a
sterilizing agent or disinfectant may be suitably employed at a higher temperature effectively.
Local Environment
It is, however, pertinent to state here that the population to be controlled is not isolated by surrounded
by several environmental factors which may cause :
•
offer due protection, and• afford destruction.
Examples :
(
a) As heat kills more rapidly at an acidic pH, hence the acidic beverages and food products viz.,
tomatoes
and fruits are much convenient and easy to get pasteurized in comparison to such foods
having higher pHs
e.g., milk.
(
b) Organic matter present in a surface-biofilm would eventually afford due protection of the
biofilm’s microorganisms
; besides, the biofilm together with its associated microorganisms often shallbe difficult to remove efficaciously.