Summary
Summary Unit 3.4. - Microbiology
- Course
- Institution
Notes on bacterial properties, aseptic technique, serial dilution and antibiotics
[Show more]
Seller
Follow
elizashaul
Content preview
3.4 MicrobiologyBacterial structure:
Always present Sometimes present
Cell membrane Pili
Cytoplasm Murein cell wall
Mesosome Glycocalyx
Nucleoid Flagellum
Ribosomes
Plasmids
Food granules
Also known as prokaryotes
Come in both heterotrophic and autotrophic forms
They are very important in decaying dead organisms and play an important role in the
nutrient cycle
Disease causing bacteria are pathogens
They reproduce asexually by binary fission (splitting in two) by mitosis
Bacteria can be identified by: Shape, size, staining characteristics plus metabolic, antigenic
and genetic features
Rod shaped bacteria = Bacillus e.g. E.coli
Spherical bacteria = Coccus e.g. staphylococcus
Spiral shaped bacteria = spirillum e.g. Spirillum
Bacteria are grouped in pairs, chains or clusters
Smallest bacteria are archaea and the largest is the sulphur bacterium
Bacteria walls contain peptidoglycan/murein which is molecules of polysaccharides and
polypeptides cross linked and the cross linking provides strength so the wall prevents against
osmotic lysis
Bacteria are either gram positive or gram negative – after staining, gram positive bacteria
are purple and gram-negative bacteria are pink
The difference is that gram positive have a basic cell wall structure whereas gram negative
has an additional lipopolysaccharide layer (fatty layer)
The lack of polysaccharide in gram positive bacteria is what allows it to bind to the stain (it
retains the crystal violet)
Gram positive bacteria are more susceptible to antibiotics and lysozyme (found in human
tears)
Gram positive bacteria example is Staphylococcus aureus
The Gram-negative bacteria have the lipopolysaccharide layer protecting the cell so they are
resistant to lysozyme and antibiotics like penicillin and they don’t retain the crystal violet
stain
Gram negative bacteria example is Salmonella
Gram staining steps:
1. Add crystal violet dye which binds to peptidoglycan so all bacteria stain purple
2. Add iodine which binds crystal violet to peptidoglycan more strongly fixing the stain
in gram positive bacteria
3. Add ethanol which removes unbound crystal violet and lipopolysaccharide so gram
negative bacteria become colourless and gram-positive stay purple
The benefits of buying summaries with Stuvia:
Guaranteed quality through customer reviews
Stuvia customers have reviewed more than 700,000 summaries. This how you know that you are buying the best documents.
Quick and easy check-out
You can quickly pay through credit card or Stuvia-credit for the summaries. There is no membership needed.
Focus on what matters
Your fellow students write the study notes themselves, which is why the documents are always reliable and up-to-date. This ensures you quickly get to the core!
Frequently asked questions
What do I get when I buy this document?
You get a PDF, available immediately after your purchase. The purchased document is accessible anytime, anywhere and indefinitely through your profile.
Satisfaction guarantee: how does it work?
Our satisfaction guarantee ensures that you always find a study document that suits you well. You fill out a form, and our customer service team takes care of the rest.
Who am I buying these notes from?
Stuvia is a marketplace, so you are not buying this document from us, but from seller elizashaul. Stuvia facilitates payment to the seller.
Will I be stuck with a subscription?
No, you only buy these notes for $3.87. You're not tied to anything after your purchase.
Can Stuvia be trusted?
4.6 stars on Google & Trustpilot (+1000 reviews)
66579 documents were sold in the last 30 days
Founded in 2010, the go-to place to buy study notes for 14 years now