Introduction to microbiology and bacterial cells

What are the two cellular organism types?

Prokaroytes and eukaryotes

Prokaroyotes

• 1 - 5 um

• Haploid

• Asexual reproduction

• Unicellular

• No true nucleus

• Cell wall

• Bacteria , archae

Eukaroytes

• >10 um

• Diploid

• Sexual reproduction

• Unicellular/multicellular

• True nucleus (some exceptions)

• Fungi (yeasts), algae

Viruses

No cellular structure (genetic material surrounded by protein)

Prions

No nucleic acid (pieces of infectious protein e.g mad cows disease)

Bacteria

• Unicellular

• Huge diversity; size, shape, habitat and metabolism

• Majority are harmless or even beneficial

• Some cause disease and SOME are pharmaceutical contaminats

Name given to bacteria which can cause disease

Pathogenic

How do we name bacteria?

Start with genus then species, write our fill name e.g Escherichia Coli then abbrivate after E. coli

What are the 3 different ways to classify bacteria

• Morphology (cell shape, size, motility, spore forming)

• Metabolism: use of energy/nurtients

• Molecular characteristics: protein, lipid structure sequence of gene encoding 16s RNA

3 different shapes so classify bacteria

Why have we picked the 16s ribosomal RNA gene sequencing for classifcation of bacteria and archae?

• Essential gene-all bacteria have ribosomes

• 16s genes highly conserved (similar in lots of bacteria) but contains hypervariable regions (short section of DNA which are different)

• Therefore BIG variation in the hypervariable regions between species so organisms are easily idenitifed by their sequences (compare to data base)

Bacterial cell structure

What vital component do bacterial cells not contain?

Mitchondria

No mitochondria means what in the cells?

Site of secretion, respiration and environmental response regulators occur on the plasma membrane

Why do bacteria’s ribosomes add up to 70s and not 80s?

Due to svedberg units (density), 50s and 30s subunits make 70s

Where is cytoplasm located?

Between plasma membrane and nucleoid

What does the cytoplasm contains

• Ribosomes

• Inclusion bodies (granules) also known as storage bodies which contain important nutrients (C, P, N, S)

• High conc of dissolved solutes → high osmotic pressure

Bacterial chromosome (nucleoid-genetic material)

• Double-stranded DNA (dsDNA)

• Not enclosed by a nuclear membrane

• Usually single closed circular chromosome

• DNA is supercoild

• 1 copy of each gene

Plasmids (nucleoid- genetic material)

• Extrachromosomal; small circular dsDNA

• Replicate independently of chromosome (multiple copies)

• Encode auxiliary functions e.g antibiotic resistance

Prokaroytic cell wall

• Extremely important structure as it protects bacteria cells from the environment

• Provides rigidity and strength

• Unique to bacteria so it makes an excellent drug target

• Composed of peptidoglycan; cross linked to form a mesh

Peptidoglycan structure

• Sugar back bone joined together by glycosidic bonds

• Every other sugar is linked to a short peptide (chain of amino acids), which crosslink to a peptide on an adjascent glycan backbone

• Strong mesh is formed so NOT a solid barrier

Why is the peptidoglycan structure beneficial?

• Mesh structure = things can pass in/out

• 2 type of bonds make it strong and rigid

• Contains other components that contribute to pathogenicity (ability to cause disease)

• Dynamic structure; constantly being remodelled

Differences in PG structure divide MOST pathogenic bacteria into 2 groups

• Gram positive = stain purple ; Thick PG layer cell wall and x linked to form thick mesh e.g staph

• Gram negative = stain pink ; Thin PG layer surrounded by an outer membrane e.g e coli

Gram-positive cell walls

Gram negative cell wall 1

OUTER MEMBRANE IS MAIN PART

Gram negative cell wall 2

Lipopolysaccharide (endotoxin)

Pathogenic bacteria which are not classified by gram stain

What is a bacterial endospore?

A structure which forms inside a bacteria in response to adverse conditions (nutrients/oxygen)

2 characteristics of bacterial endospores

• Dormant: survive without water and nutrients

• Non reproductive: single endospore forms within a bacteria. Reactivates in response to more favourable conditions

What are bacterial endospores tough against?

What is C.diff?

• Causes hosptial associated diarrhoea

• Obligate anaerobic leading to spore-forming bacteria

• Naturally resistance to many antibiotics

• Can progress causing bloody diarrhoea, inflamed intestine and toxic magacolon leading to death

Capsules and slime layers

P- pili (Fimbriae) and F-pili

• Morphologically and chemically similar

• Hair liked structures composed of protein subunits

P- pili (Fimbriae)

F-pili