Intro to bacteria

Page 1

Size

Prokaryote - most common escherichia coli 1.5um

Eukaryote- e.g. RBC 8 um

Microplasma - cell with no cell wall 0.4 um

The smaller the size

Large SA:V ratio

Nutrient transport faster

Higher growth rate . Allows the organism to evolve faster and so adapt to new environments

Prokaryote cell - See image

Cell wall

Cell membrane - selectively permeable , regulates passage of molecules in and out of bacteria

Nuclear region

Ribosomes made up of rRNA and protein

Capsules

Cytoplasm - containing enzymes, regulatory proteins and protein synthesis machinery

Protein functions in plasma membrane

Transport of nutrients

Energy generation

Secretion

Synthesis or peptidogylcan

Regulatory proteins

Cell wall

Provides shape and rigidity

Gram staining - divides bacteria into two groups

gram positive - peptidoglycan layer retains crystal violet-iodine complex

gram negative - liposaccharide layer washes away upon alcohol removing crystal violet-iodine complex

lipopolysaccharide membrane has a section which acts as a pyrogenic endotoxin

Peptidoglycan backbone is a polymer of two sugar derivatives each backbone linked by peptide bridge

Enzymes involved in forming peptidoglycan cross links are targets of antibiotics such as penicillin

Acid fast organisms

Peptidoglycan and lipids in the cell wall

Don't stain well with gram stain

Slow growing

Mycolic acids in cell wall.

Impedes entry of molecules

Protects from acids, alkalis and digestion in phagocytes

Responsible for inflammatory response in lungs

Mycoplasmas

Pleomorphic o cell wall

Smallest replicating organisms

No cell wall

Penicillin has no effect

Parasitic or saprophytic

Require external supply of cholesterol, amino acids and fatty acids

Cell surface structures

Flagella

-Function is motility

-Rigid structures

-Composed of flagellin (protein subunits)

-Chemotaxis (movement of bacteria towards nutrients)

-Stereotyping

-Molecular typing

Fimbriae and pili

-Hairlike structures of bacterial cells

-Attachment to surfaces-- environmental, virulence

-Sexual reproduction-- allow transfer of plasmids and so antibiotic resistance

Outer membrane proteins

Porin proteins form pores on bacterial cell surface allowing nutrients from outside into periplasmic space

Proteins that -specifically bind

-scavenge for nutrients

-enhance adhesion to/ interaction with target cells and surfaces

Capsules and slime layers

True capsule is a discrete detectable layer of polysaccharide outside cell wall

A slime layer is a less discrete structure or matrix which embeds cells

Give adherence of bacteria to particular surfaces - may be specific or non specific

Taxonomy

Two names, genus and species

Classification

Phenotype

-Shape

---coccus

---spirillum

---bacillus

-Stain

---Gram positive

---Gram negative

---Acid-Fast

-Oxygen requirements

---Aerobic 20% o2

---microaerophillic-- 4/5% o2

---anaerobic 0%

-Culture properties

-Colonial morphology

-Biochemistry reactions

genotype

-DNA based

---GC content

---Genome hybridisation i.e. %hybridised

-Phylogenetic analyses

-MLST

-Whole genome

-rRNA sequences