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MICROBIOLOGY &
PARASITOLOGY
Raymund Christopher R. dela Pea, RN, RM, MAN
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Binary Fission
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PHYSIOLOGY OF BACTERIA
Physiology is study of the functions andvital processes of living organisms.
Areas of interest include: bacterial
reproduction methods, bacterialcolonies, conditions affecting bacterial
growth, and bacterial associations.
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A. Reproduction
B. Bacterial Colony - Sometimes biologists refer to groups of
bacterial cells as colonies. A bacterial colony is the population
of bacteria, growing on a medium, that results from one cell.
C. Conditions Affecting Bacterial Growth - Not all bacterial
colonies grow at the same rate.
Factors controlling the growth rate include:
1. Food - Organisms require food for building cellcomponents and proteins. In addition, food supplies the
necessary energy for cell survival. Microbial activity is limited
when food supplies become exhausted. The amount and type
of food available will have an impact on the type of organisms
that survive and the rate at which they grow.
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a. Organism Classification According to FoodSupply:
(1). Autotrophic bacteria thrive in areas where
organic matter is scarce. Autotrophic bacteria are
"self-nourishing," meaning they are capable ofsurviving in the absence of organic compounds.
Instead of relying on organic compound as a source
of carbon, these organisms use carbon dioxide
(inorganic compound). The carbon is used to buildessential cell materials. Other inorganic compounds,
such as ammonia, dihydrogen, hydrogen sulfide, and
iron containing compounds, provide essential
elements to autotrophic organisms, as well. Algae
and some bacteria are autotrophic.
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(2). Heterotrophic organisms use organic matter for energyand the synthesis of cell materials. Most bacteria are
heterotrophic. Heterotrophic bacteria are categorized according
to the type of organic material upon which they feed.
(a). Strict (obligate) saprophytes are heterotrophic bacteriathat obtain nutritional need from non-living sources. Examples
include:
(aa). Clostridium Tetani - (responsible for lock jaw)
proliferates on dead tissue.
(bb). The causative agent for the food poisoning known as
botulism.
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(b). Strict (obligate) parasites are heterotophicbacteria that only grow on other living organisms.
Most pathogenic bacteria tend to be of this type.
Staph and strept infections are caused by this type of
organism.
(c). Facultative bacteria are those heterotrophs that
live and adapt in food conditions that may vary.
Sometimes they feed on dead tissue, at other timesthey feed on living tissue.
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2. Moisture Requirements -Vegetative cell maintenance and
growth requires water. Food and waste
are transported through the cell wall inwater solutions. In addition, water is a
building material necessary in cell
synthesis. Finally, the necessaryelement of dioxygen is derived from
water.
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3. Oxygen Requirements - Many forms of bacteriarequire the presence of oxygen.
Bacteria are often categorize according to their
oxygen need (some bacteria require it and some do
not). a. Strict (obligate) aerobes are bacteria that only
grow in the presence of oxygen. Micrococcus lutea is
an example of such an organism.
b. Strict (obligate) anaerobes are bacteria that
require a total absence of oxygen. Clostridium
sporogenes is an example of this organism.
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c. Facultative bacteria are those growing inthe absence orpresence of oxygen. Without
the presence of oxygen these bacteria rely
on dioxygen derived from fermentation or
anaerobic glycolysis. In the presence of
oxygen, the same bacteria may rely on the
surrounding atmosphere as a source of
dioxygen for respiration. Escherichia coli (E.Coli) is a facultative organism requiring only
a small amount of dioxygen for growth but
may die when in the presence of excess
dioxygen.
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d. Microaerophillic organisms requirevery little free oxygen to maintain
growth.
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4. Temperature Requirements - As arule, temperature is the most important
factor affecting the growth of
microorganisms. Bacteria can growwithin a range of temperatures.
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a. Maximum temperature is the upper limit at whichreproduction is possible. The rate of bacterial growth
will decline when exposed to high temperature.
Eventually, the bacteria will die if the temperature
becomes too extreme. The maximum temperature willvary from one organism to another. Boiling at one
hundred degrees centigrade for ten to fifteen minutes
will kill bacilli and cocci. Pasteurization, however, will
not kill all organisms. As a method of making dairy
products safe for human consumption, pasteurizationincorporates the use of heat at seventy-two degrees
centigrade for fifteen minutes. This results in killing
pathogenic organisms, such as streptococci,
salmonella, and rickettsia. However, some non-
pathogens , such as lactobacilli, are not killed.
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b. Minimum temperature represents thelowest temperature at which growth occurs.
At low temperatures, cell membranes lose
their structural integrity, resulting in faulty
transportation of nutrients through the cell
wall. The growth rate of bacteria found in
dead human remains becomes slow during
refrigeration.
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c. Optimum temperature is that whichenzyme reactions occur efficiently and
reproduction proceeds at a maximal
rate. The optimum temperature is nearthe normal human body temperature
(37 degrees centigrade) for many, but
not all, bacteria. For example, E coliand the gonococcus require thirty five
degrees centigrade as an optimum.
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d. Classification Organisms may be classifiedaccording to their temperature requirements. This
classification is based on an organism's temperature
range.
(1). Psychrophiles are those organisms that prefer
cold temperatures. Temperatures range from zero to
twenty-five degrees centigrade. An optimum
temperature appears to be around fifteen degreescentigrade. These organisms take part in the
spoilage of refrigerated foods (e.g., milk).
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(2). Mesophiles prefer a moderatetemperature, usually on or about
normal human body temperature.
Temperatures range from twenty-
five to forty degrees centigrade.
Most pathogenic organisms are
considered mesophiles.
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(3). Thermophiles areorganisms that prefer high
temperatures. Their rangebegins around forty-five
degrees centigrade and may
exceed fifty-five degrees. Somespore forming bacteria require
this temperature range.