Physical differences amp clinical signifigance Figure 48b Gram positive bacteria Gramnegative bacteria Figure 48a GramPositive cell walls Teichoic acids Lipoteichoic acid links to plasma membrane ID: 598901
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Slide1
Gram negative vs. Gram Positive
Physical differences & clinical
signifigance
. Slide2
Figure 4.8b
Gram- positive bacteriaSlide3
Gram-negative bacteria
Figure 4.8aSlide4Slide5
Gram-Positive cell walls
Teichoic acids:
Lipoteichoic acid links to plasma membraneWall teichoic acid links to peptidoglycanMay regulate movement of cationsPolysaccharides provide antigenic variationSlide6
Gram Negative: Outer
Membrane (OM)
A bilayer membrane found in gram-negative bacteriaForms the outermost layer of the cell wall; is attached to the peptidoglycan by a continuous layer of lipoprotein moleculesProteins called porins form channels through the OM (transports some proteins)OM has surface antigens and receptorsDoes prevent some molecules from entering (e.g. some antibiotics), but generally isn’t that selectiveSlide7
Gram-Negative Outer Membrane
Figure 4.13cSlide8Slide9
Damage to Cell Walls
Lysozyme digests disaccharide in peptidoglycan.
Penicillin inhibits peptide bridges in peptidoglycan. (effective on Gram-positive cells) . Slide10
Bacterial MembranesSlide11
Gram-Positive
Cell Wall
Thicker layers of peptidoglycan 2-ring basal bodyTeichoic acidDisrupted by lysozymePenicillin sensitiveMore penetrable
Figure 4.13b–c
Thinner layer of peptidoglycan
4
-ring basal body
No
teichoic
acid;
porin
proteins
Endotoxin
Tetracycline
sensitive
Less penetrable
Gram-Negative
Cell WallSlide12
Exotoxins vs. Endotoxins
EXOTOXIN ANIMATION
ENDOTOXIN ANIMATIONSlide13Slide14
The Gram Stain
Table 4.1
Gram-Positive
(b) Gram-NegativeSlide15
Techniques of Light Microscopy
Wet mounts: A drop of medium containing organisms is placed on slide and used to view living microorganisms
Smears: Microorganisms are spread onto the surface of a glass slide and used to view destroyed organismsHeat fixation: destroys the organisms, causes organism to adhere to slide, and alters organism to accept stains (dyes)Slide16
animation
Outline of
Gram Stain procedure
Step 1: applying primary stain
Step 2: apply mordant
Step 3: apply decolorizing agent
Step 4: apply counterstainSlide17
Gram Positive and Gram Negative CellsSlide18
Color of
Gram-positive cells
Color of
Gram-negative cells
Primary stain:
Crystal violet
Purple
Purple
Mordant:
Iodine
Purple
Purple
Decolorizing agent:
Alcohol-acetone
Purple
Colorless
Counterstain:
Safranin
Purple
Red
Gram StainSlide19
Figure 3.12b
Micrograph of Gram-Stained BacteriaSlide20
The Gram Stain Mechanism
Crystal violet-iodine crystals form in cell
Gram-positiveAlcohol dehydrates peptidoglycanCV-I crystals do not leaveGram-negativeAlcohol dissolves outer membrane and leaves holes in peptidoglycanCV-I washes outSlide21
Distinguishing Bacteria by Cell Walls
Gram-positive Bacteria have a relatively thick layer of peptidoglycan (60-90%)
Gram-negative Bacteria have a more complex cell wall with a thin layer of peptidoglycan (10-20%)Acid-fast Bacteria is thick, like that of gram-positive bacteria, but has much less peptidoglycan and about 60% lipid (mycolic acid)… Mycobacteria (TB and leprosy)Slide22
Acid-Fast Bacteria
Found in bacteria that belong to the genus,
Mycobacterium sp. (e.g. tuberculosis, leprosy)Cell wall is mainly composed of lipid, makes them very hardy. Also has slow diffusion = slow growth rate for many (eg: 20 days for M. leprae)Lipid component is mycolic acidAcid-fast bacteria stain gram-positiveSlide23
Color of
Acid-fast
Color of
Non–Acid-fast
Primary stain:
Carbolfuchsin
Red
Red
Decolorizing agent:
Acid-alcohol
Red
Colorless
Counterstain:
Methylene blue
Red
Blue
Acid-Fast StainSlide24
Figure 3.13
Acid-Fast BacteriaSlide25
Q&A
Acid-fast staining of a patient
’s sputum is a rapid, reliable, and inexpensive method to diagnose tuberculosis. What color would bacterial cells appear if the patient has tuberculosis?Slide26
Why doesn
’
t a negative stain color a cell? 3-7Why is fixing necessary for most staining procedures? 3-8Why is the Gram stain so useful? 3-9Slide27
Normal Microbiota
Bacteria were once classified as plants, giving rise to use of the term
flora for microbesThis term has been replaced by microbiotaMicrobes normally present in and on the human body are called normal microbiotaSlide28
Figure 1.7
Normal Microbiota on Human TongueSlide29
Normal Microbiota
Normal microbiota prevent growth of pathogens
Normal microbiota produce growth factors such as folic acid and vitamin KResistance is the ability of the body to ward off diseaseResistance factors include skin, stomach acid, and antimicrobial chemicalsSlide30
Biofilms
Microbes attach to solid surfaces and grow into masses
They will grow on rocks, pipes, teeth, and medical implantsSlide31
Figure 1.8
Biofilms