Mircobio #2

• Bacteria are prokaryotic cells

• Eukaryotic cells include; fungi, plant cells, protozoa and metazoa

• prokaryotic cells are very small (appox. 0.2-2.0 micrometers)

  • They have no nuclear membrane

  • No membrane bound organelles

  • No cytoskeleton

  • Simple flagella

  • Cell walls are complex

  • plasma membrane usually WITHOUT sterols and carbohydrates (CHOs)

  • Smaller ribosome

  • Simple circular chromosomes

  • Cell division is by binary fission (check bio 11 notes for image ref)

  • No sexual reproduction

• Eukaryotic cells are small (10-100 micrometers)

  • True nucleus

  • Orangelles with membranes

  • cytoskeleton 

  • Complex flagella

  • Cell walls are simple, if present

  • Plasma membrane with sterols and carbohydrates 

  • Cell division: mitosis

  • Sexual reproduction

Naming Bacteria 

• Based on genetic interrelatedness

• Two names: one is the genus and the other the species

• Convention: 

  • Genus capitalized, species lower case

  • Genus and species are in italics

  • I.e. Salmonella typhi, Staphylococcus sp.

Bacterial structure

• Membrane 

• Chromosomal DNA

• Capsule 

• Extrachromosomal DNA

• Flagellae

• Fimbriae

• Cell wall

Plasma membrane

• Phospholipid bilayer with proteins

• Synthesis and secretion of enzymes and toxins

• Active transport of molecules into cytoplasm

• Energy is produced in the plasma membrane (no mitochondria)

• Different from human cells (p.m. has cholesterol)

• Different from fungal cells (p.m has ergosterol)

Cytoplasm

• Nucleotide: area with DNA, no membrane

• Plasmids, not all bacteria have plasmid; they can survive without. 

  • It can give them antibiotic resistance 

• Ribosomes

  • Protein synthesis

  • 2 subunits (70s)

• Inclusions 

  • Nutrients in vacuoles

Chromosonal DNA VS Extrachromosomal DNA

• Chromosonal DNA

  • n=1 in most bacteria

  • Double stranded

  • Circular 

  • In area call NUCLEOTIDE

• Extrachromosonal DNA: PLASMIDS

  • small 

  • Circular

  • Usually are not essential for survival 

  • Often provide selective advantage

    • I.e. antibiotic resistance

Capsule

• In some bacteria 

• Important for survival in host

• Poorly antigenic (Ts and Bs can’t ‘see’ them easily)

• Antiphagocytic (APCs has trouble ‘eating’ them)

• Can promote adherence to other bacteria

Flagellae

• External 

• Ropelike propellers

• Made of flagellin

• Anchored to membrane by hook

• Allows bacteria to swim

  • Towards food and away from poisons

Fimbrae 

• External 

• Hairlike

• Made of pilin

• Smaller than flagellae

• Usually hundreds arranged over surface

• Promote adherence

Cell wall

• Repetitive structure: pathogen pattern

• Important for immune recognition

• Innate immune cells have pathogen pattern receptors

• Peptidoglycan layers surround cytoplasmic membrane

  • Provides rigidity

  • Helps bacteria survive in hostile conditions

  • EXCEPTION”Mycoplasmas

Gram + and Gram - cell walls

• Gram + will stain but Gram - will not

• G+ has teichoic & lipoteichoic acids

• G- has a LPS on outer memebrane

Alternative cell wall structure

• Mycobacteria

  • Different peptidoglycan

  • Have lipid coat of mycolic acid

  • Described as staining acid-fast

How to tell bacteria apart:

• BY: 

  • Cellular morphology

  • Staining

  • Serotyping

  • Requirements for growth

By morphology:

• Coccus

• Bacillus 

• Spirillum

• Sometimes they also form groups

By staining: 

• 1) simple stains: 

  • Only one stain used, everything stains the same color

  • Just to see if there are bacteria

• 2) differential stains:

  • Gram stain

    • Two groups G+ and G-

  • acid-fast stain

    • Used to stain Mycobacteria (i.e. TB)

Gram stain:

• Most important distinction to know about bacteria

• Used as a major diagnostic test to identify disease-causing bacteria

• Based on cell wall structure

  • Amount on peptidoglycan in bacterial cell wall

Step of Gram staining

• 1 CV fixes bacteria 

• 2 iodine- CV complex precipitates peptidoglycan (PG) mesh

• 3 disruption of PG and associated outer membrane

  • G- have thin PG layer

• 4 counter stain

Gram+ bacteria

• Staphylococcus aureus 

• Streptococcus pneumonia

• Enterococcus faecalis

Gram- bacteria 

• Most commonly isolated bacteria

• Examples: 

  • Neisseria

  • Acinetobacter

  • Haemophilus

  • Pseudomonas 

By requirements:

• For example, do they need oxygen?

  • Aerobic —-- need oxygen

  • Facultative anaerobes —-  can live with or without

  • anaerobic bacteria —- don’t need oxygen

Serotyping

• Using antibodies to detect characteristic antigen on that bacteria

• Useful for organisms that:

  • Are too difficult to detect

  • Too dangerous to grow 

  • Associated with specific syndromes

  • Need to be identified rapidly