Bacterial Structure and Classification Flashcards
- Identify the different shapes and organization of bacteria - Recall the difference between animal and bacterial cells - Recall bacterial structural components and their biological roles - Describe the difference between Gram + and Gram - bacteria - Recall the basis of bacterial classification
The classification of bacteria is mostly determined by ?
structure
Two major shapes of bacteria are
bacilli (rods)
cocci (spheres)
What are chains of cocci called?
streptococci
What are cocci in pairs called?
diplococci
What are grape like clusters of cocci called?
staphylococci
What are the supreme infectious bacteria?
staphylococci
What are the comma-shaped bacteria called?
Vibrio
What does Vibrio Cholerae cause?
watery diarrhea
What are corkscrew-shaped bacteria called?
spirilli
What are some key differences between prokaryotic and eukaryotic cells?
(shape, organelles, DNA, membrane, etc)
Bacteria are smaller, lack organelles, lack nucleus, single/ circular DNA, lack introns and histones, cell wall w/ peptidoglycan.
Bacteria have cell walls composed of peptidoglycan. Why is it important to know this?
Because it is only unique to bacteria, thus serve as a MAJOR target for antimicrobial therapy. Animal cells do not have a cell wall, fungi have cell wall composed of chitin, and plants’ cell wall is made up of cellulose.
Describe the cell wall composition and structure of Gram + bacteria
thick, heavy crossed link. Peptidoglycan is the external layers. 50% is composed of teichoic acid or lipoteichoic acid. (polymers of glycerol Phosphate or ribitol phosphate)
Describe the cell wall composition and structure of Gram - bacteria
thin, lightly crossed-linked
they have a second, outer membrane composed of LPS (lipopolysaccharides). Peptidoglycan layer is the inner layer.
In bacteria cell lipid bilayer membrane, normally what do they lack in the membrane in comparison to eukaryotic cells?
sterol
Besides drug targeting the rigidity and structure of the bacterial cell wall, what are other drug targets?
ribosomes 30S, 50S, 70S.
RNA pol
topoisomerase
What are the purposes of pili? Why is it important in pathogenesis?
“sex pilus” is used to transmit genetic material from one bacterium to another during conjugation. Major role in pathogenesis is to attach bacteria to host cell surfaces. W/o it it is hard to start colonization.
What are flagella?
whip-like structures that allow bacteria to move “swim”.
Note: bacteria bearing H-antigen is used in serotyping.
What are capsules? What is their purpose?
external structures composed of either polysaccharides or polypeptides
To protect encapsulated bacteria from phagocytosis.
What is common to all bacteria that cause meningitis?
they contain capsules.
How can capsules be seen?
They are seen by their ability to exclude dye.
When are spores from Gram + rods released?
in response to stress or nutrient limitation
What are spores?
dehydrated, dormant forms that allowed potential pathogens to survive during harsh conditions. Ex. bacillus species
What is special about the outer membrane of Gram - bacteria?
they are negatively charged because of LPS and allows bacteria to evade phagocytosis, hinders antibiotic uptake, and avoid complement response.
What is the space between the outer and inner membrane of Gram - bacteria?
periplasmic space
True or false, periplasm contains degradative enzymes that can destroy some antibiotics?
True
What is Lipid A and where is it found? Also, what is the innate immune response to it?
It is a toxic phospholipid (endotoxin) found in LPS. It is recognized by the innate immune response to illicit a cytokine storm causing sepsis “septic shock”
What is an important component and major serotyping of gram - bacteria?
O- antigen polysaccharides.
True or False, Gram + bacteria are now the major cause of sepsis?
True, despite not having lipid A; eliciting antigen is not clearly understood.
True or false, some successful pathogen depend on secreting protein from the cell?
True
Describe Type 1 secretion.
Using ABC (ATP binding cassette) transporters to secrete proteins out of the cell from the cytoplasm. (Note Cytoplasm to ECM)
True or False, All Gram - bacteria encode a Type 1 system and Type 2 system.
True
What is clinically significant about Type 1 systems in bacteria?
Antimicrobial drugs can be expelled from the cell, thus promoting resistance to the drug.
Define Type 2 system.
General secretory pathway used to deliver proteins to the PERIPLASM and extracellular spaces. Proteins are 1st secreted to periplasm, then secreted to across the outer membrane.
Type 3 protein secretion systems are found in only _____?
pathogens
How does type 3 secretion system work?
“molecular syringes”; the structure allows “direct injection” of toxins and other virulence factors from the bacteria to the cytosol of the host cell.
The system is made up of hydrophobic segments that span the cytoplasmic and outer membrane of Gram - and plasma membrane of host cell.
List the Gram stain methods and their purpose.
Optional word bank
(word bank: gram iodine, decolorizer, crystal violet, dry/heat fixed bacteria to glass, safranin red)
Pre-steps: Step 1: Step 2 Step 3: Step 4:
Pre-steps: dry/heat fixed bacteria to glass
Step 1:crystal violet, stain peptidoglycan
Step 2: gram iodine, fixed the crystal violet to the cell.
Step 3: decolorizer, remove crystal violet from gram - stain.
Step 4:safranin red, counter stain for gram -
Disruption of the peptidoglycan cell wall leads to ______?
cell lysis, thus target for antimicrobial therapy.
What is the backbone composition of peptidoglycan?
repeating disaccharides of NAM (N-acetylmuramic acid) and NAG(N-acetylglucosamine)
The long chains of NAM and NAGs are linked to formed long chains by what enzyme?
transglycosylase
What is the bridge that crosslinked the sugar backbones?
pentapeptides (L and D monomers)
What enzymes are involved in forming the pentapeptides cross linked? what is the drug that targets these enzymes?
transpeptidases and carboxypeptidases (aka penicillin binding proteins)
How does the cross link differs between Gram + and Gram - bacteria?
Gram + is like gram - but has inter-crosslinking (pentaglycine) between the pentapeptides cross-links.
Specifically, one of the D-Alanine of the terminal D-alanine pair is removed by carboxypeptidases and the pentaglycine forms a link from L-Lys to D-Ala.
Side Note of pentapeptide that links with the polysaccharides.: L-Ala , D-Glu, L-Lys, D- Ala, D-Ala
FYK (FOR YOUR KNOWLEDGE)
Vancomycins works by inhibiting cell wall formation by binding to D-Ala, D-Ala portion of the pre-cell wall.
Thus, used for serious Gram + multidrug organisms like S. aureus
Cycloserine was an example in the article that incorporates into the pentapeptide side chan and glycopeptide.
Where in the bacteria does cell wall assembly begin?
Cytoplasm! (Note, bacteria has no organelles)
What are lipid carriers and what do they do?
Once NAM-NAG linked to pentapeptides are synthesized, they are attached to lipid carriers via a diphosphate linkage. It is localized in the cytoplasmic membrane and used to transport INDIVIDUAL disaccharides-pentapeptide subunits to the external face of the cytoplasmic membrane.
FYK:
Bacitracin is another drug that block peptidoglycan synthesis by inhibiting the dephosphorylation of the disphosphate linkage of the lipid carrier and the Individual
disaccharides-pentapeptide subunits.
FYK
Innate Immune Response: lysozymes is a natural defense that targets peptidoglycan cell wall. It is a glycosidase and hydrolyzes the bond between NAM and NAG (disrupting the cell wall).
Found in tears and saliva.
Effective against Gram + bacteria
FYK: the periplasmic space is the location of many B-lactamases.
FYK:
Bacteriostatic vs. Bactericidal antibiotics
Static: inhibit growth
cidal: bacteria killing
How do B-lactam antibiotics work?
The B-lactam ring of the drugs is structurally resembles the D-Ala, D-Ala terminal pair ; binds to transpeptidases (enzymes that add pentaglycine crosslinking) and prevents crosslinking.
When does B-lactam resistance occur?
When the B-lactam ring is cleaved by B-lactamases. or contain transpeptidases that do not bind to B-lactams.
Vancomysin resistance occurs when bacteria synthesize D-Ala, D-lactone instead of D-Ala, D-Ala.
Why do B-lactam drugs require cell growth to work?
Because bacteria autolysins cleave the cell wall in order to make room for new subunits to insert. Only then can the drug work.
True or False, B-lactam do not work in non-dividing bacteria.
True
What is special about Mycoplasma bacteria?
They do not have a cell wall
What is special about Chlamydia
NOTHING! IT SUCKS!
PS: it lacks peptidoglycan, even though it contains a double layer like gram - (although not gram -)
Would Mycoplasma or Chlamydia be stained by gram stain?
NO
What bacteria is stained by using carbol fuchsin (red stain)? Why?
Mycobacteria, because it has a waxy coat cell wall containing mycolic acid.
What is an example of bacteria that is said to be acid-fast?
mycobacteria
Describe aerobes bacteria.
requires oxygen and uses respiration for growth
What kind of bacteria is inhibited or killed in presence of oxygen and uses fermentation?
(obligate) anaerobes
What is the name of bacteria that can use oxygen for respiration or fermentation in absence of oxygen for growth?
facultative anaerobes
FYK: these represent the majority of pathogens
What type of bacteria grown in presence of low oxygen concentration?
microaerophilic bacteria
Describe the usefulness of Lancefield antigen
Lancefield antigen is used to distinguish major pathogenic members of certain groups. Ex. Streptococcus pyogenes (Strep Throat) express Group A lancefield antigen; thus called Strep A or GAS. Another Strep express the Group B lancefield antigen, thus is called Strep B.
Define serotyping
Used to distinguish strains within a genus.
Why is serotyping important?
used to determine source and severity of outbreaks.
What is RFLP?
Restriction fragment length polymorphism, it is used to rapidly identify and classify bacteria based the length of specific fragments. (these fragments differ among species and strain) Easier than to genotype the whole DNA genome.
The overall basis of classification includes. List all 8
morphology arrangement staining properties growth properties fermentation properties enzymatic/virulence properties antigenicity genotype
