Introduction to Microbiology and bacterial structures Flashcards
What is a microorganism?
The science of microorganisms Microbiology
Microorganisms (or microbes) are organisms that are too small to be seen with the unaided eye —> require a microscope (except for some moulds)
1030 microbes estimated in different habitats (more than stars in the known Universe)
List the major groups of microbes:
Bacteria > Bacteriology
Fungi (yeasts and moulds) > Mycology
Parasites (protozoa, helminths, and ectoparasites) > Parasitology
Micro-algae > Phycology
Viruses and prions > Virology
Microorganism diversity = flow diagram (from moulds)
Generally
Moulds > Protozoa > Yeasts > Bacteria > Viruses > Prions
Define cellular:
formed by cell(s)
A single cell (monocellular) – e.g. bacteria
more cells (pluricellular) – e.g. moulds
Define Acellular:
without a cellular structure (e.g. viruses and prions)
prokaryotic cells
barteria
eukaryotic cells
protozoa, yeasts, moulds
3 domains of bacteria
Bacteria
Archaea
Eukarya
Microorganisms as cellular entities
Bacteria / Archea > Bacteriology
Fungi > Mycology
Parasites > Parasitology
Microalgae > Phycology
acteria / Archea > Bacteriology
Prokaryotes
Mostly unicellular / monocellular
Fungi > Mycology
Eukaryotes
Yeasts > Unicellular
Moulds > Pluricellular
Parasites > Parasitology
Eukaryotes
Protozoa > Unicellular
Helminths > Pluricellular
Microalgae > Phycology
Mostly eukaryotic
Both unicellular and pluricellular
Do microorganisms that have nonliving agent include cells?
NO - not made up of cells
Virus > Virology
Characteristics:
- Acellular (do not have a cellular structure)
- Small infectious particles consist of nucleic acid surrounded by a protective coat of protein(s)
- Coat may be enclosed in a lipid envelope
- They do not divide
- They need to infect a cell to replicate their particles
Prions > Virology
Made up of?
Simpler infectious particles made up of only proteins (no nucleic acids)
What is the Impact of Microbes on the Environment and Human Activities?
(essential for life on earth)
- Organic waste decomposition
(e.g. sewage) - Production of food (e.g. cheese, bread, beer by fermentation)
- Drugs/enzymes synthesis
(e.g. penicillin, insulin, etc.) - Digestion and molecule generation (e.g. vitamins, etc)
- Oxygen generation (photosynthesis)
- Nitrogen fixation (converting atmospheric N2 to ammonia, NH3)
Where are microbes present - human body?
present in body and out of body = NORMAL microbiota
> 100 trillions microorganisms harboured per person (≈10X higher human cells)
Less than _% of microbes cause diseases (pathogens)
1%
The majority of normal microbiota are not harmful and can be helpful to:
a) prevent growth of pathogens
b) produce growth factors (e.g vitamins B and K)
c) breaking down toxic molecules, boosting the immune system and antimicrobial chemicals
What do you call bacteria have one or more shapes?
pleomorphic
Arrangements of Bateria:
Pairs:
diplococci,
diplobacilli
Clusters
(random planes):
staphylococci
Chains (one plane): streptococci, streptobacilli
Groups of four: tetrads
How to name and classify Microorganisms?
Each organism have TWO names - the GENUS and the SPECIES EPITHET
both = written italicised
genus name = CAPITALISED
The specific epithet = lowercase
genus name = can be abbreviated
e.g. Staphylococcus (Genus) aureus (species) – S. aureus (abbreviation)
Escherichia (Genus) coli (species) - E.coli (abbreviation)
Some are named after scientists / or be descriptive: Escherichia coli or E.coli
Honors the discoverer, Theodor Escherich
Describes the bacterium’s habitat—the large intestine, or colon
Vibrio cholerae
Single curved-rod cells (Vibrio)
The agent of cholera (cholerae)
Vibrio cholerae
for info
Single curved-rod cells (Vibrio)
The agent of cholera (cholerae)
Staphylococcus aureus
for info
Arranged in clusters (Staphylo-)
Rounded cells (coccus)
Describes the gold-colored (aureus) colonies
Prokaryotes charictaristics:
Without nucleus
Without membrane-bound organelles
Simple organisation
e.g. Bacteria and Archea
Describe the composition of the plasma membrane;
Phospholipid bilayer that encompasses the cytoplasm
Fluid mosaic model similar to the eukaryotic cells:
40% lipids (mainly phospholipids), 60% proteins
Lacking sterols (cholesterol of human cells)
Contain sterol-like molecules (hopanoids)
Explain the functions of the plasma membrane;
Serves as a selectively permeable barrier:
Controls movements of molecules across the cells
What are the infoldings of the plasma membrane called. Why are they present?
mesosomes
Site for DNA replication and cellular respiration
Functions of the cell wall;
1) Maintain bacterial cell integrity and shape
2) Prevents the cell from bursting when water flows into the cell by osmosis
3) Can contribute to pathogenicity (ability to cause disease)
What is the composition of the cell wall?
Structural difference between these two groups Gram+ = purple
Gram- = red
Why is the cell wall so important?
- Only a few bacteria do not posses cell walls (e.g. mycoplasma)
- Target of many antibiotics (anti-bacterial drugs)
What is peptidoglycan/ murein?
Essential components of the bacterial cell wall
Composition of Peptidolycan?
A rigid multi-layered network made up of linear chains
Each chain is a polymer of a repeating identical disaccharide unit (made up of the following 2 monosaccharides) in long rows:
N-acetylglucosamine (NAG)
N-acetylmuramic acid (NAM)
A tetrapeptide chain of 4/5 amino acids is linked to NAM
Chains are linked by peptide cross bridges between tetrapeptide side chains of NAMs
Name a bacteria that does not incl. peptidoglycan?
Archea
The Peptidoglycan formation ; STEP by STEP
1) ubunit: NAG + NAM
2) Repition of the subunit form individual strands/chains
3) Peptidoglycan strands (transpeptidation reaction)
How are peptidoglycan strands formed and what enzyme takes part?
peptide cross-link bridges between tetrapeptide of NAMs of peptidoglycan strands
Bacterial transpeptidase responsible for links - target of β-lactams (e.g. penicillins)
THE link - PEPTIDE bond
Cell wall of Gram +ive bacteria
thick structure (several layers) of peptidoglycan, separated from the plasma membrane by a thin periplasmic space
Cell wall gram +ive =
TEICHOIC ACIDS - what is it made up of?
alcohol and a phosphate group (-ive charge)
What is TEICHOIC ACIDS functions?
Bind to and regulate movement of cations into cell
Regulate cell growth and prevent cell lysis
Linked also to the cell membrane
Cell wall of Gram -ive bacteria
Cell wall is thinner, more complex and more susceptible to mechanical breakage
Composition of cell wall gram -ive
a thin peptidoglycan layer
periplasmic space, containing degradative
enzymes and lipoproteins
outer membrane (the most external)
Composition of the Outer membrane in Gram- bacteria:
Phospholipid bilayer
Lipopolysaccharides (LPS): acting as antigen and endotoxin
Porins: membrane pores that allow the passage of molecules
Lipoproteins
What are the funcitons of Outer membrane in Gram- bacteria:
- Evade phagocytosis and immune system
- Permeability barrier to antibiotics (penicillin), digestive enzymes, etc
What is the process of gram staining?
FIXATION
1) primary staining (crystal violet)
2) Mordant application (Iodine treatment)
3) Decolorisation
4) Counterstaining (counter stain with Safranin)
Distinguishing groups of bacteria according to their cell wall structure
Staining: for better visual observation, to highlight differences or cell components in bacteria
Gram staining - principles
+ive
Gram-positive (cells are stained blue due to the crystal violet-iodine complex – the primary stain/mordant)
Alcohol dehydrates peptidoglycan (thick layer) forming crystals inside and the dye is retained
Gram staining - principles
-ive
Gram-negative (cells stain pink as the counterstain – e.g. safranin)
Alcohol dissolves outer membrane and leaves holes in peptidoglycan
crystal violet-iodine complex washes out; cells are colorless
Safranin (pink) added to stain cells
External to cell wall
Glycocalix
External to cell wall
Glycocalix
Some bacteria have an additional viscous layer/coat (called glycocalyx), composed of a network of polysaccharides, lying outside the cell wall
Components external to cell wall - Glycocalix
Capsule: thick, well organised and firmly attached
Slime layer: thin, unorganised and loosely associated
Functions of components external to cell wall e.g. Glycocalix
- Confer pathogenicity (only capsule)
- Prevent phagocytosis by host phagocytes
- Avoid desiccation by preventing water loss
- Aid in attachment to solid surfaces
Cytoplasm
Location (inside the plasma membrane) of most biochemical activities
Nucleoid
central region containing circular DNA (up to 3500 genes)
Plasmids
small, nonessential, circular DNA (5-100 genes; e.g., antibiotic resistance, production of toxins, digest antibiotics)
They replicate independently
Ribosomes
acterial ribosomes are termed 70S ribosomes (50S + 30S), which distinguish them from the 80S of eukaryotic cells
Selective antibiotic target
Inclusion bodies
granules as reserve deposits of nutrients in the form of high molecular weight polymers. E.g. glycogen, polymeric phosphates, etc.
Name the 5 different classes of antibiotics:
Cell wall
Plasma membrane
Ribosomes
(30S subunits, 50 subunits)
Metabolic Pathways
DNA synthesis + RNA synthesis
Describe the structure of Flagella:
Hairlike filamentous appendages external to the cell
Propel bacteria (process requiring ATP) toward or away from stimuli, detected by chemoreceptors
May also be a sensory organelle (detecting chemicals, temperature, etc)
The composition of Flagella:
3 parts, made of protein flagellin:
Filament: outermost region
Hook: attaches to the filament
Basal body: consists of rod and pairs of rings; anchors flagellum to the cell wall and membrane
Flagella and bacteria movements
Flagella rotate to = “run” or “tumble”
Direction of flagella determines the movements
(tails help movement)
Other bacterial appendages
1) Fimbriae (1-500 per bacteria)
2) Sex Pili
1) Thin hairlike appendages that allow for attachment
Some types are involved in a twitching motility
2) Hair-like tubular structure
Conjugation pili involved in DNA transfer from one cell to another
