Microbiology & Parasitology %

7/28/2019 Microbiology & Parasitology %

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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.

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