Bacterial Structure and Characteristics Flashcards
Archaea are an ancient, single cell species that differs from bacteria in 2 ways (one involves cell wall). Name them
They lack peptidoglycan and they don’t cause damage to humans
T/F: Bacteria can conduct dna synthesis in the nucleus and they have a symmetrical membrane
Nah bruh. Bacteria have no nuclear membrane (no nucleus) so they conduct their DNA synthesis in the inner leaflet of the inner membrane
3 ways to classify bacteria include___
By structural components
By cell wall (gram negative vs gram positive vs acid fast)
By genetic makeup
How do you classify bacteria by structural components?
Structural components on the outside of the cell can be found by serology
basically you have an antibody that binds to something on the bacteria and you can find whatever that structure is
0157 E.coli has a structure in the membrane called O antigen that can be found using antibodies against it
How do you classify the cell wall characteristics of bacteria?
By cell wall: do a Gram stain to see if the bug is gram negative or gram positive
Cell wall structure knowing if its gram negative or positive helps decide which antibiotic to use
How do you classifiy a bug by genetic makeup?
sequencing
Another way to classify bacteria is through shape. Name the types of bacterial shapes
Cocci vs spiral vs bacilli – you take tablets for bacillus infection (coz bacilli look like a tablet), there’s snakes around the corner (spiral one look like snakes), cocci are charming (cocci look like little round charms in a line)
Describe the following types of bugs by their growth in O2:
Obligate aerobe
Microaerophile
Obligate anaerobe
Facultative anaerobe
Capnophiles
Obligate aerobes need O2
Microaerophiles need just a tiny bit of O2
Obligate anaerobes don’t like O2 at all
Facultative anaerobes can grow in the presence and absence of O2 but prefer O2. This depends on how the bacteria conducts metabolism (either by using O2 as the terminal electron carrier in the ETC, or some bacteria use nitrogen)
Capnophiles need high CO2
How do you do protein-based mass spec?
Take a single colony, plate it, add some matrix and put in mass spec and it’ll tell you what bug it is
Label the #bugshapes below
See image below
Cocci tend to be gram +ve and those are all the guys thatlook like perfect little circles (have different arrangements)
Bacilli are gram negative
The others are either gram negative or gram positive or don’t fit into any group because of their membranes
Vibrio looks like a coma and delvibrio is a small vibrio that burrows its way into the bacteria and eats the bacteria from inside out
Some bacteria have a stalk that lands on the host cell and attaches there
Other bugs:
Club rod – Corynebacterium
Helical form – Helicobacter pylori
Corkscrew – Borrelia
Filamentous
Spirochete
Enlarged rod
Describe the difference between beta hemolytic, alpha hemolytic and gamma hemolytic Strept
Beta hemolytic Strept secretes toxin that lyses red blood cells
Alpha secretes a toxin that converts hemoglobin to met hemoglobin so it doesn’t conduct complete lysis
(Big Al(pha) is actually pretty mean coz he’ll lyse your globin only to met so he only hurts you half way)
Gamma doesn’t conduct any lysis at all
**note that you can observe this on a blodd agar plate with 5% sheep’s blood and hella nutrients for the bacteria**
External components of a bacterium include ___ and appendages, which serve what function?
What are the components of the cell membrane?
Appendages make the bugs move (fimbriae/pili/flagella)
Glycocalyx: on the outside of the bacteria (capsule or slime layer)
Cell envelope: Cell wall and cell membrane (sometimes outer membrane depending on whether the bug is gram positive or gram negative)
Internal components: see image below
Structures common to all bacteria include___
- Cell membrane/envelope
- Cytoplasm
- Ribosomes
- One (or a few) chromosomes
Structures common to SOME bacteria:
- Flagella
- Pili/Fimbriae
- Capsules
- Slime layers
- Surface coating or glycocalyx
- Endospores
- Plasmids
What’s the difference between gram negative and gram positive bacteria?
Gram-positive bacteria – 2 layers:
Cell wall (peptidoglycan), cytoplasmic membrane. Lipoteichoic acid is also present in gram positives only
Gram-negative bacteria – 3 layers
Cytoplasmic membrane (inner), cell wall (peptidoglycan), outer membrane (on the inner leaflet of the outer membrane = lipoteichoic acid, and on the outer leaflet of the outer membrane = LPS)
What makes acid fast bacteria different from Gram neg and Gram pos?
Acid fast bacteria have the same cytoplasmic membrane and peptidoglycan but they also have 5 sugar residues (arabinogalactam and lipoarabinomannan) that cap the peptidoglycan and some have mycolic acids (big waxes)
If the waxes were exposed the bacteria would be really hydrophobic and easily discovered by macrophages, so instead the bacteria cap the wax as well with another fatty acid
Also, there’s TLR2 recognition (dimerizing with either TLR1 or 6), and you need to do an acid fast stain for these
**main acid fast bacteria = mycobacterium tuberculosis**
T/F: Gram positives are typically round coz the peptidoglycan layer is super flexible
How do gram pos bugs evade killing by complement?
What molecule on the gram pos membrane mediates TLR2 signaling?
Gram positives have a very thick layer of peptidoglycan and because it’s very rigid, that contributes to the round shape of gram positives
These can resist killing by complement because the MAC complex can never reach the membrane so it can’t poke a hole in it and kill the bug
There are also proteins directly embedded in the peptidoglycan that you won’t see in a lipid membrane of gram negatives
TLR2 recognition is via LTA binding
Briefly: how do you do the gram stain?
Sample >> fix via heat >> use the blue crystal violet stain >>
In the gram +ve, the iodine treatment basically cross links the peptidoglycan which helps trap the crystal violet inside >> wash off with ethanol >> counter stain with safranin >> gram pos stays purple, gram neg goes pink
Briefly: how do you an acid fast stain?
Acid fast stain: use carbofulschin >> decolorize with alcohol >> then counterstain w/ methylene blue >> should stain red
Peptidoglycan unique to prokaryotes and has only ___ and ___
90% of gram positive is mainly peptidoglycan which is why ___(drug type) work well against gram +ve bugs
The rigidity of peptidoglycan protects against ___; has to broken during replication and re-established
Peptidoglycan unique to prokaryotes and has only NAG and NAM
90% of gram positive is mainly peptidoglycan which is why beta lactams work well against gram +ve bugs
The rigidity of peptidoglycan protects against osmotic pressure; has to broken during replication and re-established
NAG and NAM and crosslinked with the bacterial side chains that go in between one NAG and one NAM to make the membrane stronger
Transglycosylase and transpeptidase are the 2 targets for most of the antibiotics. What do they do?
To insert new Nag and NAM, you have to break a glycosidic linkage and insert a new one via transglycosylase
Once NAM as a 4 aa residue on it, you have to put another 5 via peptide crosslinking which is mediated by transpeptidase
What the main antibiotics that target bacteria? How do they work?
Beta lactam antibiotics:
Penicillin
Cephalosporin
Carbapenem
Monobactam
**you’re in the Hunger Games and you’re in Penem (carbapenem). President Nicillin wants to see blood shed between 2 tributes from the Bactams (whose area is so bad everybody over there got mono) and the Sporins (that all have big heads - cephalo- for some reason)
Some bacteria have beta lactamase that cleaves and opens up the beta lactam rings, which is toxic to the bacteria
Flagella are composed of __ and basically function as a rotating motor. Anticlockwise rotation = __ movement, and clockwise rotation = __ movement
T/F: All bacteria have flagella
Flagella are composed of flagellin and basically function as a rotating motor. Anticlockwise rotation = forward movement, and clockwise = tumbling movement (backwards)
Falsehood. Mainly gram negative bacilli and spirochetes have flagella (not on cocci)
What are the types of bacterial flagella arrangements? (hint: PALM)
Monotrichous (Vibrio): Single (ever since this trich got mono she decided she was gon stay single)
Lophotrichous: Multiple from same spot (like getting multiple lophos of bread from the same tuckshop growing up)
Amphitrichous: Single on each end (too amphitious for its own good so it actually never reaches where it wants to go)
Peritrichous (E. coli): Many in all directions
Two types of flagella movement are ___ and ___ (one you can’t do, and the other bees can do)
Swarming – the bacteria are swarming across the surface
Swimming –basically the bugs are flying
**note that this is FAST movement**
Fimbriae/Pili are for slow movement and are present on __ bacteria
They move via ___ and bugs w/ fimbriae can cause what to happen to RBCs?
T/F: There’s also the same arrangement of pili/fimbriae as there is of flagella
These guys are for slow movement and they’re present in both gram pos and gram neg
These are hooks that grab and pull on surfaces. They move via twitching
These are super fragile and there’s lots of them covering the surface of the cell
Bugs with fimbriae can cause RBC agglutination
They also have sex pili for transferring dna between bacteria
T/F: A slime layer and a capsule are the same thing
Nah. Capsules and slime layers are different but they’re both called glycocalyces. These are also present on gram negs and pos
When is an external matrix considered a slime layer?
An external matrix is considered a slime layer when:
Its easy to take off the membrane
Prevents dehydration and loss of nutrients
Allows bacteria to survive chemical sterilization coz the chemicals stay further from the membrane
e.g. Klebsiella and Strept
**its slimy so its slippery (loosely ass’d with memb), its slippery so its wet (prevents dehydration + loss of nutrients), its an extra blanket so we don’t get blasted by chemicals and die (allows bact to survive chemical sterilization)
When is something considered a capsule?
Something is considered a capsule when:
Polysaccharides are more firmly attached to cell wall (directly to LPS or peptidoglycan)
Provide protection and adhesion (forms biofilm)
Generally have greater pathogenicity coz the capsule resists phagocytosis/anything else in the innate immune system
- Capsule
- Slime layer
- Biofilm
Which bugs (gram neg or pos) have endospores?
What is an endospore?
**basically an endospore is one of those expensive getaway undergound house things that people are making to live in in case of an apocalypse**
Few bacteria sporulate
Spores basically turn the bacteria into a seed in which it can survive under harsh conditions
Endospores can be stable for years and can cause disease once released
Mainly gram positives: Clostridium and Bacillus
Some bacteria can crystalize their nutrients such that when the spore forms, the bacteria will have its own food already there
Plasmids generally have certain characteristics. Name 3.
Describe the following classes of plasmid:
Fertility
Resistance
Col
Degradative
Virulence
Double stranded DNA, usually circular, and transferable
Plasmid classes:
Fertility plasmids - conjugation
Resistance plasmids - resistance against antibiotics (have always been shared between gram negs and gram pos)
Col plasmids - contain genes that code bacteriocins that can kill other bacteria
Degradative plasmids - digestion of unusual substances
Virulence plasmids, which turn the bacterium into a pathogen
**Some bacteria are naturally transformable: throw piece of naked DNA in environment with bacteria and if it likes it, it’ll take it up and even keep it if it really likes it**
