The World of Bacteria. What does a bacterium look like? Internal Structures: cytoplasm nucleoid...
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Transcript of The World of Bacteria. What does a bacterium look like? Internal Structures: cytoplasm nucleoid...
What does a bacterium look like?
Internal Structures:
cytoplasm
nucleoid
ribosomes
Boundaries:
cell membrane
cell wall
capsule
Appendages:
flagellum
pili
Bacteria Identification Criteria
Shapes
Bacilli
Cocci
Sprilli
Growth Patterns
“Prefixes describe pattern”
“strepto…. Means in chains
“staphylo…Means in clusters
Examples:
Streptococcus pneumoniae
The Gram Stain
Christian Gram (1884) develops gram staining process.
Use of two stains: crystal violet and safranine
Stains interact differently with a particular type of cell wall.
Cells will be either Gram positive or Gram negative.
Gram Negative
The Gram-negative cell wall is composed of a thin, inner layer of peptidoglycan and an outer membrane consisting of molecules of phospholipids, lipopolysaccharides (LPS), lipoproteins and sutface proteins. The lipopolysaccharide consists of lipid A and O polysaccharide.
Which is Gram positive?Which is Gram negative?
Gram negative: A group of bacteria that do not retain the crystal violet dye after the differential staining procedure known as Gram staining. They appear pink due to the counterstain, safranin. Gram positive appears purple. The difference between Gram negative and Gram positive bacteria is the cell wall structure, which accounts for the different staining characteristics
Gram Positive Gram Negative
So what is the medical significance of this technique?
The Gram Stain Results:
What are antibiotics?
Antibiotics are strong medicines.Antibiotics only work against infections caused by bacteria. Antibiotics kill bacteria or stop them from growing.Antibiotics should be used wisely.
Antibiotic Producer organism ActivitySite or mode of action
Penicillin Penicillium chrysogenum Gram-positive bacteria Wall synthesis
Cephalosporin Cephalosporium acremonium Broad spectrum Wall synthesis
Bacitracin Bacillus subtilis Gram-positive bacteria Wall synthesis
Polymyxin B Bacillus polymyxa Gram-negative bacteria Cell membrane
Erythromycin Streptomyces erythreus Gram-positive bacteria Protein synthesis
Neomycin Streptomyces fradiae Broad spectrum Protein synthesis
Streptomycin Streptomyces griseus Gram-negative bacteria Protein synthesis
Tetracycline Streptomyces rimosus Broad spectrum Protein synthesis
Vancomycin Streptomyces orientalis Gram-positive bacteria Protein synthesis
Gentamicin Micromonospora purpurea Broad spectrum Protein synthesis
Rifamycin Streptomyces mediterranei Tuberculosis Protein synthesis
Some Clinical Antibiotics
Figure F. Antibiotic-sensitivity testing. Petri dishes were spread-inoculated with Staphylococcus albus (white growth) or Micrococcus luteus (yellow growth) before antibiotic assay "rings" were placed on the agar surface. The coloured disks at the end of each spoke of the rungs are impregnated with different antibiotics. Clockwise from the top (arrow) these are: Novobiocin, Penicillin G, Streptomycin (white disk), Tetracycline, Chloramphenicol, Erythromycin, Fusidic acid (green disk) and Methicillin. Clear zones of suppression of bacterial growth around the individual antibiotic disks are evidence of sensitivity to these antibiotics.The diameter of the clear zone is related to the initial antibiotic concentration (which differs for the antibiotics on the ring), its solubility and its diffusion rate through agar. Standard tests performed on many bacteria by the manufacturers of these assay disks enable the diameter of the clearing zone to be related to the minimum inhibitory concentration (MIC) of each antibiotic for the strain being tested. The MIC can then be compared with the known tissue levels of these antibiotics when they are administered to patients, to assess whether the antibiotics would be effective for treatment of particular pathogens.
Antibiotic Sensitivity
Antibiotic Resistant Bacteria
Bacteria that is not affected by an antibiotic.
Antibiotic resistance is a phenotype. They posses a gene that renders them resistant (genotype).
Antibiotic resistant gene produces enzymes that breakdown the antibiotics.
Antibiotic resistance results from gene action. Bacteria acquire genes conferring resistance in any of three ways.
In spontaneous DNA mutation, bacterial DNA (genetic
material) may mutate (change) spontaneously (indicated by starburst). Drug-resistant tuberculosis arises this way.
In a form of microbial sex called transformation,
one bacterium may take up DNA from another bacterium. Penicillin-resistant gonorrhea results from transformation
How Antibiotic Resistant Bacteria Develophttp://www.fda.gov/fdac/features/795_antibio.html
Most frightening, however, is resistance
acquired from a small circle of DNA called a plasmid, that can flit from one
type of bacterium to another. A single plasmid can provide a slew of different
resistances. In 1968, 12,500 people in Guatemala died in an epidemic of
Shigella diarrhea. The microbe harbored a plasmid carrying resistances to
four antibiotics!
One More Way towards Resistance
What on the plasmid makes the bacteria resistant?
Resistant GenesGenes are located in a circular piece of DNA found
in the bacterial cell called a plasmid.
Bacterial also has chromosomal DNA.