Bacteria Notes:
Part One: Unity and Diversity
Ways to classify bacteria
Shape and size
Gram positive and Gram negative
Metabolism (include respiration and food source)
A. Size and Shape
· Bacteria were first described by Leeuwenhoek in 1677 after he had invented the compound microscope.
· Bacteria range in size from about 1 to 10 um long by about 0.2 to 0.3 um across (1 um = .001 mm).
Most bacteria come in one of three different shapes:
(1) Rod shaped: Bacillus(i) [filaments or single].
(2) Spherical shaped: Coccus(i) [pairs, chains, groups or single].
(3) Spiral shaped: Spirillum(a) [seldom in colonies]
Some bacteria tend to form groups:
Diplococci are pairs of spherical shaped bacteria
Streptococci are chains of spherical shaped bacteria
Staphylococci are clusters of spherical shaped bacteria
B: Gram positive and Gram negative
The term gram positive or negative, refers to both a staining proccess and specific structure of bacterial cell membranes or wall. The gram staining method is one of the more important techniques in microbiology. Yet one has to realize that this technique is not 100 percent fool proof. Differences in results can be due to type of stains and age of bacteria.
The staining process follows the following protocal:
Heat fix bacteria to slide
Stain with purple dye (crystal violet), rinse with distilled water
Stain with with iodine (marker), rinse with water
Rinse with alchol wash, functions as a decolorization process in which negative lose colour.
Stain with safranin (red stain) which is counter stain for gram negative
In regards to cell membrane structures:
Gram positive bacteria have cell walls composed of peptidoglycan (murein) and teichoic acid. ( basically a sugar based structure combined with amino acids)
Gram negative bacteria also have cell walls composed of a peptidoglycan ( in small amounts) but this layer is surrounded by a lipopolysaccharide outer membrane.
Comparison of Characteristic of Gram + and Gram –
Characteristic
Gram Positive
Gram Negative
Gram Reaction
Stain dark violet or purple
Stain pink
Ratio RNA to DNA
8:1
1:1
Nutritional requirements
More complex
Less complex
Susceptability to penicillin
Marked
Less marked
Susceptability to streptomycin and tetracycline
Much less
Marked
Susceptability to anionic detergents
Marked
Less marked
Resistance to sodium azide
Marked
Less marked
C: Metabolism and Nutrition
Cell Metabolism:
Nutrients are ingested and then:
1. broken down by enzymes within cell
2. further breakdown of material is done to produce energy
· Energy is absorbed by biochemical ADP (adenine di phosphate)
· Energy is released by biochemical ATP ( adenine tri phosphate)
Energy can be produced with or without oxygen
1. Anearobic: are bacteria that do not need oxygen for cell metabolism
2. Areorobic: are bacteria that require oxygen for cell metabolism
3. Facualtative: are bacteria that can metabolize with or without oxygen
Obligate Aerobes are those which must have oxygen
Obligate Anaerobes are bacteria which cannot tolerate oxygen.
There are many types of nutrition found among bacteria:
Autotrophic Nutrition:
1. Some are photosynthetic (use sunlight energy to produce their own food).
2. Some are chemosynthetic (oxidize inorganic compounds to obtain their
energy to produce their own food).
· These organisms are known as Photoautotrophs and Chemoautotrophs in that they manufacture their own food.
Heterotrophic Nutition.
They must obtain their energy and nutrients from other sources.
For example:
· Saprophytic bacteria : digest materials in their environment by releasing powerful digestive enzymes. They then absorb the digested nutrients.
· Parasitic bacteria : rely on other organisms to provide the digested nutrients directly.
Part Two: Interactions
Bacteria can exist everywhere there is life this includes:
in the air
in the water
in the earth
on plants
in organism
· without bacteria, we as humans could not exist
· bacteria are the most primitive form of life because they:
a) grow and reproduce ( as often as one time every 15 minutes)
b) they use nutrients to survive
c) they have simple cell structures
· it is possible to see bacteria through a light or electron microscope
Bacteria are both helpful and harmful
To preserve or stop bacteria metabolism they can be:
chilled
dried out
frozen
heated
Dangerous bacteria are called pathogens because they cause diseases.
to control pathogenic bacteria you can remove bacteria by:
removing all bacteria using extreme heat
wash with antiseptic soaps
use antibiotics
specific immunization for specific bacteria proteins
Some bacteria can become resistant to antibodies by altering protein coat or structure of cell wall.
Bacteria can change into dormant forms called spores, which allow the bacteria to stop metabolism in extremely harsh environments
Useful Bacteria
Most bacteria are not pathogenic — include decomposers, nitrogen
fixing bacteria, vitamin producing bacteria, bacteria used to make
insulin and growth hormone, bacteria used in dry cleaning, tanning,
cheese, yogurt
Essential Bacteria:
Bacteria can be helpful because:
· they help plants absorb nutrients from the soil ( specifically nitrogen)
· they are used to make milk products such as yogurt, cheese and butter
· they can be used to manufacture antibiotics
· they can alter biproducts from sewage treatments into non toxic waste
· they can be used to produce specific gases such as methane
· they are used for fermentation
Escherichia coli Gram – rod shape (bacilli)
Sarcina lutea Gram + round shape (cocci)
Bacillus subtilis Gram + rod shape (bacilli)
Bacillus cereus Gram + rod shape (bacilli)
Serratia marcescens Gram – rod shape (bacilli)
Rhodospirillum rubrum Gram – spiral shape (spirilla)
Harmful Bacteria
Harmful bacteria can cause disease (Pathogenic) by interfering with the host’s normal routine, by destroying cells and tissues, by producing endotoxins and exotoxins, and by eliciting an immune response.
· An endotoxin is a toxin within the bacterium that is only released when the bacterium dies and it breaks down.
· An exotoxin is a toxin released by living bacteria.
Koch’s Postulates: –
used to prove that an organism is responsible for a particular disease.
1. must be shown that the organism in question is always present in
the diseased hosts.
2. microbe must be isolated from the host and grown in a pure
culture.
3. microbe from pure culture must be capable of producing the
disease symptoms in a new healthy host.
4. microbes isolated from the newly infected host must be grown in a
pure culture and compared to the original micro-organism.
Examples:
a) Respiratory Tract: Strep throat, Rheumatic fever, Scarlet fever;
Pneumonia, Whooping cough, Diphtheria, Tuberculosis…
b) Skin: Staph (pimples and boils), Leprosy, Gas gangrene…
c) Nervous System: Tetanus, Botulism, Meningitis…
d) Digestive System: Typhoid fever, Cholera, Dysentery; (food
poisoning) Salmonella, Botulism, Staph…
e) Venereal Diseases: Gonorrhea, Syphilis…
Infection by bacteria
There are three lines of defence through which bacteria must
penetrate:
a) through the strong epidermal tissue (skin).. .in wounds, pores,
openings.
b) phagocytic white blood cells which engulf foreign materials including bacteria.
c) antibodies produced by other white blood cells.
Active Immunity –
– is slow acting (because the body is taking time to produce antibodies against the infection); but long lasting (because the body produces “memory cells” which “remember” how to produce these specific antibodies again).
Normally produced by actual initial infection (chicken pox), or by using a vaccine (polio, smallpox). The vaccine consists of either weakened (attenuated) bacteria, dead bacteria, or artificial products which resemble the actual foreign invader (antigen).
Passive Immunity
This is fast acting (because the person is injected with antiserum containing the necessary antibodies or antitoxin); but short-lived (because the person does not actually produce the antibodies – hence no memory cells for the future!). The protein antibodies are often provided from the blood of a larger animal such
as a horse! (Tetanus, Rabies). New techniques have been designed so that bacteria can produce specific antibodies. Newborns initially have Passive Immunity through the passage of antibodies across the placenta, and in the Mother’s milk. In some cases, injection of Toxoids stimulate the production of natural antitoxins.
Antibiotics a biological substance which will kill or slow (inhibit) the growth
of an organism.
e.g. Penicillin, Tetracycline, Bacitracin, Ampicillin,
Erythromycin…
a) must be bacteria-specific.
b) some people are allergic to certain antibiotics.
c) some could kill off useful bacteria.
d) may reduce the competitive pressure and allow
harmful bacteria to survive.
e) may cause resistant strains to develop.
Other biocides include: Sulfur Drugs, antitoxins, various
bacteriocides, disinfectants…
Part Three: Changes with time
Reproduction
1. Bacteria reproduce mostly asexually by a process called BinaryFission. In this method, the circular ring of DNA replicates, and then the cell divides into two daughter cells — each with its own DNA.
2. Some bacteria can also undergo sexual reproduction by a process called Conjugation. In this method, the “male” is connected to the “female” by a tube called a Pilus. The DNA from the “male” then travels through the tube to the “female”. Here, it recombines with the “female” DNA and the “female” bacterium then divides.
Some bacteria can be Transformed into a different cell by absorbing fragments of DNA of other cells. In another method of producing recombined bacterial DNA, bacteriophages (viruses) carry portions of the bacterial DNA from one cell to another. This process is called Transduction.
4. When environmental conditions are not favourable, some bacteria are capable of forming highly resistant thick-walled Endospores until conditions once again return to normal.
Part Four Form and Function
Cell Structure:
A bacteria cell has the following structures:
Nuclear material in the form of DNA to pass on genetic information
Cell membrane: which controls the flow of material in and out of a cell
Ribosome: which assist in making cell proteins
Cell wall
Flagella
Endospores
Response to Stimulus:
Bacteria Lab Questions:
1. Why must you always use sterile technique when working with
bacteria?
2. What does “pathogenic” mean?
3. What is an “inoculum”?
4. List three general rules for handling bacteria.
5. When is the Pour Plate Method of culturing bacteria used?
6. Why must you be careful in regulating the temperature of the melted agar in the Pour Plate Method?
7. In procedure 7 in each of the labs, why did you have to flame the mouths of the test tubes?
8. What is the reason for using the streak plate method?
9. What is the reason for using the Pour plate method?
