MI-01

who founded microbiology

Leeuwenhoek (1674)

pasteur

koch

leeuwenhoek

founder of microbiology, not a scientist but a lensemaker, first observed small swimming things in water (animalcule)

pasteur

worked on microbial metabolism, immunity, and identification of causative agents of disease.

Discovery or identification of many medically important pathogenic bacteria and viruses took place between 1875 and early 1900’s

koch

proposed rigorous criteria to identify pathogens. Focused on the identification of disease-causing microbes.

what are some typical shapes of bacterial cells

rods

cocci (spheres)

spirochetes

spirochete shape bacteria

highly motile

can evade immune system + penetrate deep into periodontal pockets

What distinguishes a prokaryotic cell from a eukaryotic cell?

Prokaryotes

• No membrane bound nucleus (DNA still supercoiled)

• No mitochondria or chloroplasts

eukaryotes

Contain a true, membrane bound nucleus

Contain organelles (Mitochondria + Chloroplasts)

eubacteria (“true” bacteria)

Many different groups

Many different shapes

Some are medically important

Multiply by binary fission

No nuclear membrane

Walls contain peptidoglycan, unique to eubacteria

Archaea (primitive bacterial-sized organisms, not bacteria)

  Not medically important

  Chemically different from Eubacteria, no peptidoglycan

  More similar to eukaryotes

  Often found in extreme environments (extremophiles)

many believe Archaea are the progenitors to eukaryotic cells

viruses

Composed of DNA or RNA with a protein coat

Must grow on living cells

Not free-living forms of life

Are obligate, intracellular, parasites

viroids

Composed of RNA without a protein coat

Can cause disease in plants (potato spindle tuber disease)

1/80 the size of a virus (200-400 bases long)

prions

Infectious agent is a protein (smallest infectious agent)

Bovine spongiform encephalopathy (Mad Cow Disease)

only problematic if protein misfolds

Creutzfeld-Jacob Disease in humans

About 1/2 to 1/4 the size of viroids

size of microbes

resolution

ability of microscope to separate two objects

   

light microscope

   Resolution of light microscope is ~0.2 mm (microns)

  - one-fifth of a bacterial cell width

  - Can be used for observing living microorganisms

can see larger structures like nucelus, cell walls, chloroplasts

gram stain can help better visualize

electron microscope

scanning electron microscope (SEM)

allows viewing of three-dimensional view of surfaces

only can see outside surface (cell membrance, cilla, microvilli)

transmission electron microscope (TEM)

looks through the cells or sections of cells

2D

the best approach for looking at cell structure ( all organelles)

cryogenic electron microscope (cryo-em)

can see molecules and large protein complexes like RNA polymerase

simple stains

Stains all protein and cytoplasm

ex: crystal violet

1. fix heat to slide by heat before staining

Differential stains

Stains different bacteria differently

gram stain

most widely used as diagnostic stain

stains differently due to thickness of peptidoglycan layer

**know these steps

IF YOU DONT COUNTERSTAIN GRAN NEG WILL BE COLORLESS

IF YOU DONT DECOLORIZE ALL WILL BE PURPLE

at end colors

gram positive = purple

gran negative = red

arrangements of cells

chains

packets

clusters

chain

cell divides in 1 plane

packets

cell divides in 2+ planes perpendicular to each other

clusters

cell divides in planes at random

cellular organizations

major structural groupings

cellular organizations: genome

arranged in condensed nucleoid structure

cellular organizations: cytosol/ cytoplasm

Around genome is the cytosol or cytoplasm containing the proteins and ribosomes and other smaller molecules of cell

cellular organizations: cell surface

around all of the above

contains membranes, peptidoglycan and all appendages

Medically important: first part to touch infected host cells

cellular organizations: cellular options

bacterial cell wall

Peptidoglycan is unique to bacteria

Peptidoglycan

  -Found in all eubacteria (almost all)

  -A network mesh holding cell together

 lysozyme

(in tears) dissolves peptidoglycan

antibiotics

inhibit peptidoglycan cross-linking

ex: penicillin

gram negative cell wall

•Gram negative cells have thin peptidoglycan layer

•Thin wall allows removal of "gram-stain material"

•Gram negative cells have two membranes, an outer and an inner membrane

gram positive cell wall

Gram positive cells have thick peptidoglycan

Thick wall does not allow removal of "gram-stain material"

Cell wall is stronger than gram-negative cell wall

Gram positive cells have a single cytoplasmic membrane

sensitive to penicillin G or V ( early gen penicillins)

outer membrane (gram negative)

Outer membrane

  Contains lipopolysaccharide (LPS, endotoxin)

  composed of:

  - lipid A core

Outer membrane prevents access of some antibiotics, like early generation penicillins (PenG or PenV), to their target

porins

proteins that allow material to

  enter periplasmic space of cell

periplasm

Material between the two membranes (GRAM NEG ONLYYY)