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The three different types (shapes) of bacteria
1. rods: ex. Agents of typhoid fever (slender), anthrax (rectangular), diphtheria (club -shaped)....
2. sphere: ex. Diplococci, agents of gonorrhea, meningitis, streptococci, sarcina (cubelike packet of 8 cocci), stphylococci
3. spiral: ex. Vibrios, spirochetes (syphilis: Treponema pallidum)
- for movement; present in bacillus and spirals but not cocci
- Monotrichous: single flagellum in one pole
- Lophotrichous: more than one flagellum at one pole.
- Amphitrichous: group of flagella at both poles
- Peritrichous: covered; flagella all around
range from 10 micrometer to 20 micrometer; average 15 micrometer in length; about 2 micrometer thick
in order to observe, need to be coated with special dye (silver nitrate)
- bacterial appendages that appear as short flagella
- have no function in mobility; aid in transfer of genetic materials among bacteria; other pili anchor the organisms to surfaces which enhances the ability to cause (establish) disease
Pili are primiraly found in gram negative bacteria such as Neisseria gonorrhoeae
(kidney shaped, gram-)
because pili composed of protein, body's immune system responds to their presence by producing anti-pili antibodies to denature protein in pili (attacks protein in pili)
very sticky, gelatinous structure found in many species of bacteria; layer of polysaccharides and proteins
forms in various species of bacilli and cocci but not spirals
Protects against dehydration and prevent nutrients from nutrient loss by flowing away.
Also, contributes to the establishment of disease because white blood cells cannot perform phagocytosis nor engulf an encapsulated bacteria.
major function of cell wall is to hold cell together and to prevent cell from bursting especially in aqueous solution
- all bacteria except mycoplasma have a cell wall.
- bacterial cell wall is composed of peptidoglycan which is a large molecure of alternating units of two amino-containing carbohydrate: N-acetylglucosamine and N-acetyleneuramic acid joined by amino acids (forming peptide bonds); 60%-90% of cell wall is peptidoglycan
cell wall of gram+ (stained blue/purple) is different than cell wall of gram- (stained red/pink). In gram+, the peptidoglycan is about 25nm with teichoic acid; in contrast, in gram-, the peptidoglycan is 3nm with polysaccharide protein lipids.
gram- cell wall is thinner but more complex with more constituents
most bacteria can be stained with Gram Staining technique; exceptions include TB (needs Acid Fast technique)
Penicillin will prevent newly-produced cells from constructing cell wall leading to destruction of bacterial cell.
(found in human tears and saliva) destroys existing cells by attacking linkage between carbohydrates and peptidoglycan in cell wall
destruction of cell wall leads to destruction of cell
Cell Membrane (Plasma Membrane)
every cell is surrounded by a cell membrane/plasm membrane
- 1. major function is to transport nutrients in and wastes out.
- 2. Also, it is the location for enzymes used in energy production by the cell.
- 3. Also, site for many receptors
about 60% of cell membrane is protein and about 40% is composed of lipid, mainly phospholipids (phospholipid bilayer)
when antimicrobial substances act on cell membrane, bacterial death usually follows; certain detergents, ethyl alcohol and polymyxin dissolve the phospholipid bilayer leading to bacterial cell death.
Some microbiologists combine the following together as the cell envelope:
- cell membrane
- cell wall
- cell capsule (if present)
- (in bacteria) no membrane-bound organelles.
- A gelatinous mass of proteins, carb, lipids, nucleic acids and inorganic ions and dissolved in water. Elastic in structure.
Several types of bodies are found within cytoplasm.
Ribosomes are NOT membrane-bound organelles. Ribosomes are found in every cell. Ribosomes are bodies of protein that function in protein synthesis.
Other bodues include globules of starch (polysaccharide), glycogen, or lipids. Often referred to as Inclusion Bodies
which store nutrients.
- Certain other bodies serve as phosphate depots, commonly known as metachromatic granules; these bodies stain deeply with dyes such as methylene blue; that is, darker than rest of cytoplasm.
- genetic material (chromosome/DNA) found in closed loop (not a membrane-bound organelle) in area called Nucleoid.
Smaller molecules of DNA exist apart from the chromosome in separate closed loops called Plasmids
which contain genes but not essential for growth. Many plasmids carry genes for drug resistance caled R-factor
Certain gram+ bacteria are able to produce highly resistant structures (endospores or simply spores).
Members of the genera Bacillus
(gram+) and Clostridium
(gram+; obligate anaerobe) are spore formers. These bacteria grow, mature, and reproduce for several generations as vegetative cells
. Spore formation begins when environment becomes hostile (e.g. lack of nutrients and/or excess wastes).
Endospores may develop at the end of the cell or near the end, or the center -- depending on the species of bacteria.
- Variations in endospore morphology: (1, 4) central endospore; (2, 3, 5) terminal endospore; (6) lateral endospore
- Bacterial spores are probably the most resistant living things compare to other living organisms in a given environment.
- e.g. vegetative bacteria die quickly in water over 80oC but bacterial spores may remain alive in boiling water for 2 hours
- e.g. when placed in 70% ethyly alcohol, spores have survived for 20 years
- e.g. human can barely withstand 500rems of radiation but bacterial spores can survive million rems
- e.g. spores found in intestines of Egyptian mummies alive.
- Four well known serious diseases in humans to be caused by sporeformers:
- Gas Gangrene
Bacterial Reproduction Growth
- No mitosis; no mitotic structures
- Asexual process (binary fission).
- Chromosome duplicates
- Cell elongates
- Plasma membrane pinches inward at center; cell wall pinches in too after thickening to seperate dividing cells
- The interval of time until the completion of the next division; time needed for cell to divide
- E. coli: 20 minutes
- S. aureus: 30 minutes
- M. tuberculosis: 18 hours
- Treponema pallidum: 33 hours
from 1 E. coli
cell at 6am, there will be 67 million by 2:40pm. This may overwhelm body by sheer number. Not all E. coli
are pathogenic; only certain are pathogenic. E. coli
are on large intestine normally.
Bacterial Growth Curve
Lag phase, Log phase, Stationary phase and Decline phase.
- Mesophiles: 20-40 C: Cert. ones can grow at temp substantially below their normal range. At refrigerated food (5 C): Staph, Salmonella, Proteus vulgaris These are not truly Psychrophilic, the term of Psychotrophic is used by some micro.
- Psychrophiles: 0-20 C. They live in ocean depth, in Arctic and Antarctic regions.
- Thermophiles: 40-90 C. Important contaminants in dairy products. No threat to human health.
- Obligate (strict) aerobes: These have to have an absolute requirement for oxygen. Ex. Bacillus and Pseudomonas.
- Obligate anaerobes: Can not multiply if oxygen is present. Some are actually killed by traces of oxygen. Ex. Clostridium.
- Facultative anaerobes: These can utilize oxygen if it is available, but can also grow with out it. Growth is usually rapid if oxygen is present. Ex. E. coli and Saccharomyces
- Facultative aerobes: Prefer anaerobic conditions (but also can grw aerobically). Microaerophilic: These require small amount of oxygen (2% - 10%) but higher can be toxic. Ex. Helicobacter pylori.
- Aerotolerant: These organisms grow in the presence or absence of oxygen. They are insensitive to oxygen. They derive no benefit from oxygen. Ex. Streptococcus pyogenes Capnophilic (capno=smoke): low in oxygen but rich in carbon dioxide. Ex. Neisseria.
- Most bact. Grow at 7.0.
- Acidophiles: Valuable in food and dairy industries. Ex. Lactobacillus and Streptococcus produce the acid that converts milk to buttermilk and cream to sour cream. They pose no threat toto good health when consumed in lg. amounts.
Pattern of nutrition
- Nutrient broth: water, beef extract, and peptone (protein), when agar is added to solidify the medium it is callec nutrient agar.
- Agar is a polysaccharide from marine algae.
- Blood agar: Streptococcus
- Chocolate agar: Neisseria
- Selective media:
- Mannitol Salt Agar: Staphylococcus
- EMB: Eosin Methylene Blue agar: E.coli (gram -)
Differential Media: MacConky agar