2. The Gram Stain
Christian Gram (1884) developed gram staining
process.
Stains interact differently with a particular type of
cell wall.
Cells will be either Gram positive / Gram negative.
3. What is a gram (-) bacteria?
• Gram-negative bacteria are a group
of bacteria that do not retain the crystal
violet stain used in the Gram staining method of
bacterial differentiation, making positive
identification possible.
4. Gram negative bacteria
• Gram negative: A group of bacteria that do not retain the crystal
violet dye after the differential staining procedure known as Gram
staining. They appear pink due to the counterstain.
• Gram positive appears purple.
• The difference between Gram negative and Gram positive bacteria
is the cell wall structure, which accounts for the different staining
characteristics
6. Characteristics of gram negative bacteria:
1. Cell membrane (cytoplasmic).
2. Thin peptidoglycan layer (which is much thicker in gram-
positive bacteria)
3. Outer membrane containing lipopolysaccharide (LPS, which
consists of lipid A, core polysaccharide, and O antigen) in its outer
leaflet and phospholipids in the inner leaflet
4. Porins exist in the outer membrane, which act like pores for
particular molecules
5. There is a space between the peptidoglycan layer and the
secondary cell membrane called the periplasmic space
7. Characteristics of gram negative bacteria:
6. The S-layer is directly attached to the outer membrane rather
than the peptidoglycan
7. If present, flagella have four supporting rings instead of two
8. No teichoic acids or lipoteichoic acids are present
9. Lipoproteins are attached to the polysaccharide backbone.
8. Gram Negative
The Gram-negative cell wall is composed of a thin, inner layer of peptidoglycan and an
outer membrane consisting of molecules of phospholipids, lipopolysaccharides (LPS),
lipoproteins and sutface proteins. The lipopolysaccharide consists of lipid A and O
polysaccharide.
9. Characteristics of gram negative bacteria:
Thin peptidoglycan layer
(which is much thicker
in gram-positive
bacteria)
10. Characteristics of gram negative bacteria:
Outer membrane containing lipopolysaccharide (LPS, which
consists of lipid A, core polysaccharide, and O antigen) in its
outer leaflet and phospholipids in the inner leaflet
11. Characteristics of gram negative bacteria:
Porins exist in the outer membrane, which act
like pores for particular molecules
12. Characteristics of gram negative bacteria:
There is a space
between the
peptidoglycan layer
and the secondary
cell membrane called
the periplasmic
space
13. Characteristics of gram negative bacteria:
The S-layer is
directly attached to
the outer membrane
rather than the
peptidoglycan
S Layer – Crystalline layer on top of either gram-positive or gram-negative bugs. The S
Layer may increase virulence, and it may also help in adhesion.
14. Characteristics of gram negative bacteria:
If present, flagella have four
supporting rings instead of
two
15. Characteristics of gram negative bacteria:
No teichoic acids or
lipoteichoic acids are present
16. Characteristics of gram negative bacteria:
Lipoproteins are attached to the polysaccharide backbone.
18. Acetic acid bacteria
derive their energy from the
oxidation of ethanol to acetic
acid during fermentation.
aerobic, rod-shaped bacteria.
Acetic acid bacteria are airborne
and are ubiquitous in nature.
19. Acinetobacter baumannii
It can be an opportunistic
pathogen in humans, affecting
people with compromised
immune systems
Colloquially, A. baumannii is
referred to as 'Iraqibacter' due
to its seemingly sudden
emergence in military
treatment facilities during
the IraqWar.
20. Agrobacterium tumefaciens
s the causal agent of crown
gall disease (the formation
of tumours)in over 140 species
of eudicots.
Economically, A. tumefaciens is a
serious pathogen of walnuts, grape
vines, stone fruits, nut trees, sugar
beets, horse radish, andrhubarb.
21. Arcobacter
It shows an unusually wide range of
habitats, and some species can be
human and animal pathogens
Symptoms of infections include
diarrhea associated with abdominal
pain, nausea, and vomiting or fever
22. Arcobacter
It shows an unusually wide range of
habitats, and some species can be
human and animal pathogens
Symptoms of infections include
diarrhea associated with abdominal
pain, nausea, and vomiting or fever
23. Bacteroides
obligate anaerobic bacteria
Some species (B. fragilis, for
example) are opportunistic human
pathogens, causing infections of the
peritoneal cavity, gastrointestinal
surgery, and appendicitis via abscess
formation
24. Bdellovibrio
obligate anaerobic bacteria
The Bdellovibrio cell
uses hydrolytic enzymes to break
down the host cell molecules, which
it uses to elongate and form a
filament and gets the host cell
nutrients
26. Gram Negative Spiral Bacteria
Slender and flexible, come in a
lot of different shapes
More rigid than spirochetes
Ex. – Campylobacter jejuni
Symptom – tenesmus: the
sensation of desire to defecate,
which is common and occurs
frequently , with out the
production of significant amounts
of feces (often small amounts of
mucous or blood are alone
passed).
27. Gram Negative Spirochetes
pathogenic
very flexible
tightly coiled, helically coiled
Example
syphilis
Treponema pallidum
28. Gram Negative Spirochetes
Most of pathogenic
Very flexible
Tightly coiled, helically coiled
Example
Lyme disease
Borrelia burgdorferi
(organism gets lodged in
tissues)
31. Gram Negative Aerobic Rods
Pseudomonas aeruginosa
(pigmented)
Needs moisture
Common in hospitals
Opportunistic pathogen –
causes UTI, skin, and lung
infection
32. Gram Negative Facultative Rods
Vibrio
V. cholerae
Most well known of group
Very severe dysentery. Can lose
10-15 liters of water/day. Leads
to hypovolemia – low water, hardly
any water in body
V. vulnificus
Very pathogenic
Can cause flesh eating disease,
if it gets in a wound
V. parahaemolyticus
Found in shellfish – oysters
Halophile – loves salt (will find in
oceans, estuaries)
Self limiting
34. Gram Negative Anaerobic Rods
Fusobacterium
Live in between teeth
and gums
Cause tooth abscesses
and periodontal disease
Teeth have nothing to
anchor – bone is
destroyed
35. Gram Negative Cocci or Coccobaccilli
(plump rods)
Neisseria gonorrhoeae –
Usually a diplococcus in
PMN
Sexually Transmitted
Disease
very antibiotic resistant
36. Gram Negative Cocci or Coccobaccilli
(plump rods)
Neisseria meningitidis
very infectious and
communicable.
37. Gram Negative Cocci or Coccobaccilli (plump
rods)
Acinetobacter baumanni
- opportunistic, UTI, skin,
and upper respiratory
38. Chlamydia Gram Negative Rods
(Transitional)
Very short little rods
Transitional – doesn’t hold stain well
Do not have the ability to synthesize
own ATP, therefore and obligate
intracellular parasite of other
animals (humans)
Can go asymptomatic for a long time
Ex.
C. trachomatis – STD, causes eye
infection
C. psittaci – parrot (associated with
birds)
39. Rickettsia Gram Negative Rod
(Transitional)
Small gram negative rods
Transitional – doesn’t hold
stain well
Can’t synthesize it’s own NAD,
coenzyme A, therefore an
obligate intracellular parasite
Causative agent of Rocky
Mountain Spotted Fever
Example
R. Prowazekii
Lipopolyssacharides - e large molecules consisting of a lipid and a polysaccharide. Porins are involved in the exchange of nutrients over the outer membrane of Gram-negative bacteria but are also involved in pathogenesis
An S-layer (surface layer) is a part of the cell envelope commonly found in bacteria, as well as among archaea.[1] It consists of a monomolecular layer composed of identical proteins or glycoproteins. The main function of teichoic acids is to provide rigidity (stiffness) to the cell-wall by attracting cations such as magnesium and sodium
Teichoic acids are found within the cell wall of most Gram-positive bacteria. Important in phatogenesis and for bacteria resistance