The World of Bacteria

What does a bacterium look like?

Internal Structures:

cytoplasm

nucleoid

ribosomes

Boundaries:

cell membrane

cell wall

capsule

Appendages:

flagellum

pili

Shapes of Bacteria

Bacteria Identification Criteria

Shapes

Bacilli

Cocci

Sprilli

Growth Patterns

“Prefixes describe pattern”

“strepto…. Means in chains

“staphylo…Means in clusters

Examples:

Streptococcus pneumoniae

Bacterial Growth Patterns:Streptococcus

Bacterial Growth Patterns:Staphylococcus

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.

How else are bacteria identified? Another criterion? Composition and Construction

of the Cell Wall

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.

Gram Staining Process

What color are gram positive? What color are gram negative?

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.

Binary Fission: Asexual Reproduction