Basic Structure and Identification of Bacteria Flashcards
How do bacteria reproduce?
Via binary fission (cell division)
Do bacteria have cell walls?
Most bacteria have cell walls, but not all bacteria do. We can use this fact to treat certain bacterial infections.
Do bacteria have a nuclei?
No, bacteria do not have nuclei
What type of DNA do bacteria have?
Circular DNA
What are commensal bacteria?
Bacteria that do not harm their host (Ex. normal flora in the mouth)
What are opportunistic bacteria?
A bacteria that can cause an infection if it gets into part of the body that it is not normally in
What is a pathogenic bacteria?
A bacteria that always harms the host in some way
Do bacteria have prokaryotic or eukaryotic cells?
Bacteria are prokaryotic and humans are eukaryotic
What bacterial enzyme is required to duplicate the circular bacterial DNA and what is the significance of this?
Gyrases –> These enzymes reduces strain while double-stranded DNA is being unwound by elongating RNA-polymerase or helicase
We can target these enzymes with certain medications
How does RNA synthesis differ in bacteria?
Bacteria use prokaryotic polymerases while humans use eukaryotic polymerases
How do humans get folate in their systems?
Since humans cannot make their own folate, we depend on bacteria to do this for us. We can use this knowledge to target certain bacteria, but if we kill the good bacteria we then become completely depend on our diet for folate
What enzymes do bacteria use to make folate?
Dihydropteroate synthase and dihydrofolate reductase
What is LPS?
Lipopolysacharide which only bacteria have (primarily only gram negative bacteria)
Gram positive morphologies (basics)
Thick cell wall which contains Teichoic acid (antibodies attach to this) and thick Peptidoglycan layer
Shapes: Bacillus and Coccus
Gram positive staining
Stains purple as their thick cell walls retain the crystal violet dye even after washing with alcohol
Gram negative morphologies (basics)
Thin cell wall (thin peptidoglycan layer), contains Lipopolysachardies and an Inner AND Outer Membrane
Shapes: Bacillus, Coccus, and can also included curved, corkscrew, and straight shapes
Gram negative staining
Stains red as their thin cell walls do NOT retain the crystal violet dye
Gram variable staining
Can stain purple OR red depending on the conditions
Gram variable morphologies
Have a unique cell wall (example tuberculosis) which causes variables when staining and may be difficult to stain
What are some conditions where you would be unable to see the bacteria via a gram stain?
- Spirochetes: spiral/corkscrew bacteria –> required dark field microscopy or antibody staining to see
- Atypical bacterial (Ex. Chlamydia, Legionella, Mycoplasma) which have no significant cell wall or are intracellular
Single coccus
One round shaped bacteria
Always gram +
Diplococci
Cocci in pairs (groups of two)
Can be gram + or -
Streptococci
Cocci in chains
Usually gram +
Coccus (singular)/Cocci (pleural)
A round shaped bacteria
Staphylococci
Cocci in large groups
Usually gram +
Coccobacilli
Very small oval shaped rods (looks like a mix between coccus and bacilli)
Usually gram -
Bacilli
Rod shaped bacteria
Large bacilli
Large rod shaped bacteria
Usually gram +
Fusiform bacilli
Lumpy rod shaped bacteria
Usually gram -
Short rod-shaped bacilli
Small rod shaped bacteria that somewhat line up
Usually gram -
Vibrios
Curved rod shape
Usually gram -
Peptidoglycan layer
Multilayer of two alternating sugars: N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM), cross-linking done by Penicillin binding proteins (PBPs) which are transpeptidase enzymes also serve as the target for beta lactam antiboitics
Present in both gram (+) and gram (-), but much thicker in gram (+)
Teichoic acid
Found only in gram-positive cell wall
Major antigenic determinants of cell surfaces
Length and nature of side chain differ from species to species
Major components of Gram-Negative Cell Wall
- Small layer of Peptidoglycan
- Periplasmic gel
- Porins: allow diffusion into periplasmic space
- Inner leaflet (ordinary phospholipids)
- Outer membrane
Periplasmic gel
- Component of gram-negative cell wall
- Holds digestive enzymes and facilitates permeability
What is the main component of the outer membrane of gram-negative cells and what does it contain?
-
Lipopolysaccharides (LPS) which is extremly toxin and contains:
- Lipid A –> Toxic component of endotoxin –> Induces TNF and IL-1 through TLR-4
- Core polysacharide
- O antigen - polysaccharide - major surface antigen
Endotoxin
- Part of the bacterial cell structure released upon cell death
- Toxic and potentially fatal
- Relatively heat stable up to 60 degrees celcius
- Less immunogenic - cannot make toxoid/vaccine
- Can cause gram-negative septic shock
- Example: LPS (specifically Lipid A portion)
Exotoxin
- Excreted from living bacteria cell into the environment
- Can be from gram (+) or (-) bacteria
- Most common type = A/B toxins
- Cause systemic effects distant from site of production even after bacteria death (e.g. systemic tetanus from a wound)
- In some diseases, the toxin is the sole virulence factor (tetanus, botulism)
Why is it important to be able to identify a bacteria?
You must know the bacteria in order to treat it properly
A/B Exotoxins
- Heat labile - toxicity is destroyed at 60 degrees C
- Highly antigenic toxoid (inactivated or just B portion) vaccines
- Examples: Diphtheria and Teanus toxoid
- Composed of two parts:
- A - Active portion: toxic activity inside a target cell
- B - Binding portion: binds to target cell and helps Active portion enter cell (translocation)
What does a positive result mean with regards to gram positive identification with antibiotics?
A positive result means that the bacteria grows in the presence of the mentioned substance.
For example, a positive Novobiocin resistant test means that the bacteria in question can grow in the presence of Novobiocin
Gram Positive Coccus Identification Tests
Catalase test
- Positive test = bubbles/foams –> Likely Staphylococcus
- __Can further test with Coagulase test
- Negative tests –> Streptococcus
- __Can further test with Hemolysis test
Gram Positive Coccus Identification Tests
Coagulase test
- Positive test –> Fibrin clumps
- Indicates that the bacteria is S. aureus
- Negative test –> Doesn’t clump fibrin
- If negative, the next step is to do a Novobiocin resistant test to determine if it is S. saprophyticus or other coagulase negative species
Gram Positive Coccus Identification Test
Bile Esculin Test
- Positive = breaks down esculin in presence of bile
- Indicates that the bacteria is Streptococcus group D
- Negative = does not break down esculin in presence of bile
- Need to run hemolysis test for further verification
Gram Positive Coccus Identification Test
Novobiocin resistant test
- Positive –> Grew in the presence of Novobiocin
- Indicates that the bacteria is S. saprophyticus
- Negative –> Did not grow in the presence of Novobiocin
- Indicates that the bacteria is an other coagulase-negative species
Gram Positive Coccus Identification Test
Bile soluble test
or
Optochin sensitive test
- Positive –> Indicates that the bacteria is S. pneumoniae
- Negative –> Need to run a Bile-Esculin test for further evaluation
Gram Positive Coccus Identification Test
Bacitracin sensitivity test
- Positive = cannot grow in presence of Bacitracin (i.e. is sensitive to Bacitracin)
- This indicates that the bacteria is group A streptococci
- Negative = can grow in presnece of Bacitracin
- Further testing with Hippurate hydrolyzed or CAMP testing required
Gram Positive Coccus Identification Test
Hemolysis Test
- Tests if the organism can lyse RBCs and degrade Hgb
-
Alpha = partial degredation of Hgb = green/greenish color around colony
- Indicates S. pneumoniae or S. mutans
-
Beta = complete degradation of Hgb = clear area around colony (can read print through it)
- Indicates S. pyogenes or S. agalactiae
-
Gamma = no degradation of Hgb = agar is still red around colony
- Indicates Group D Enterococcus, E. faecalis, or S. bovis
What type of morphology do Neisseria meningitidis and Neisseria gonorrhoeae have?
Gram negative diplococci
What type of morphology do Enterobacteriacea have?
Gram negative bacilli
Selective media
Media that only allows certain types of organisms to grow
Differential media
Media that allows identification via color or growth differences on the media
It allows you to differentiate bacteria ;D
What diffeference between humans and bacteria are used as common antibiotic targets?
- Cell wall synthesis
- DNA/RNA synthesis
- Folate synthesis
- Cell membrane
- Protein synthesis (Ribosomes)
What are some examples of antibiotics that target bacterial cell walls?
- B-lactams
- Vancomycin
What are some examples of antibiotics that target DNA/RNA synthesis?
- Fluoroquinolones
- Rifamycins
What are some examples of antibiotics that target folate synthesis?
- Trithoprim
- Sulfonamides
What are some examples of antibiotics that target bacterial cell membranes?
- Daptomycin
What are some examples of antibiotics that target protein synthesis?
- Tetracyclines
- Aminoglycosides
- Macrolides
- Linezolid
Intrinsic antibiotic resistance
- Innate ability of bacteria to resist specific antibiotics
- Bacteria may lack target for antibiotic, drugs cannot get to target, etc.
Acquired antibiotic resistance
- Bacteria acquires ability to resist action of particular Abx
- Commonly via horizontal gene tranfer
- Tranformation
- Conjugation
- Transduction
- Can also be due to random point mutation
General antimicrobial resistancce mechanisms
- Modifying drug target
-
Inactivating a drug
- Example: enzymatic cleavage of Beta Lacatamases
-
Limiting uptake of drug
- Bacteria without cell wall (intrinsic)
- Reduction in number of porin channels
-
Drug efflux
- Mutation modifying transport channel - pumps out Abx
Transformation
Bacterial active uptake of naked DNA in the enviornment which is then recombined with recipient DNA
Transduction
Bacteriophage (virus) infects bacteria and transfers chromsomal DNA fragment or plasmid
Conjugation
Plasmid tranfer via a pilus (“bacterial sex”)
