Transcript Morphology and structure of bacteria

Morphology and structure of
bacteria
Oral Microbiology for dentistry
MUDr. Lenka Černohorská, Ph.D.
Size of bacteria
Pathogenic bacteria: mainly around 1 – 5 μm
(1 μm = 10-3 mm)
Staphylococcus: the diameter circa 1 μm
Even smaller:
rickettsiae (circa 0.5 μm)
chlamydiae (elementary bodies circa 0.3 μm)
mycoplasmas (circa 0.2 – 0.25 μm )
Various shapes of bacteria
• Cocci (spherical)
• Rods /bacilli:
can be short
long
robust, thin
• Spirochaete (helical)
Common bacterial forms
•
•
•
•
•
•
Cocci in chains – streptococci
Cocci in clusters – staphylococci
Cocci in pairs – diplococci (neisseria)
Bacilli in chains
Curved bacilli
Spore-bearing bacilli
Bacterial cell
Structures I. – detail info
Structures II.
Cytoplasm - is enclosed within the cell membrane, contains
organelles. Here occur most cellular activities and metabolic
pathways. The part of the cytoplasm that is not held within
organelles is called the cytosol (a gel, with a network of fibers
dispersed through water)
Capsule – gelatinous layer around the bacterium is composed of
polysaccharides, proteins – inhibits phagocytosis, helps the
adhesion, is used in preparation of vaccines
Fimbriae – hair-like filaments, mediate adhesion to receptors
Inclusions – serve as sources of stored energy (polysaccharides)
Gram-staining (more in practical lessons)
•
•
•
•
Crystal violet – 30 s
Iodine solution – 30 s
Alcohol – decolorize until violet is removed
Safranin – 60 s
G- pink groups
G+ purple groups
Cell wall
Results:
• different in G- and G+ bacteria
• principle of Gram staining is still unknown, but
it is used for hundred years
• G+: Crystal violet attaches to peptidoglycan
(PG) than arise complex with Iodine, complex
is not washed by alcohol, that is why the final
result is purple.
• G-: Little amount of PG inside a cell wall, a
little complex/no complex? is washed by
alcohol, Safranin is needed for visualisation.
Examples of G+ and G– microbes
Gram-positives
Staphylococcus
Streptococcus
Bacillus
Clostridium
Listeria
Corynebacterium
Yeasts
Gram-negatives
Escherichia
Salmonella
Haemophilus
Pseudomonas
Mycoplasma
Flagella
• filaments composed of flagellin
• responsible for movement of bacteria
May be located: (cocci and bacilli)
• at one end:monotrichous, a single flagellum
lophotrichous – many flagella
• all over the outer surface – peritrichous
• Spirochaets move by using the axial filament
– produce undulation motion
Sporulation (bacterial winter sleep)
• In bad conditions some kind of bacteria
sporulate
• Spora contains a high concentration of
calcium dipicolinate, is resistant to heat,
radiation, chemicals, dehydratation, it can
remain for many years
• Better conditions- spore transform itself into
reproducing bacterial cell again.
Sporulation process
septum
Spores - facts
• Spore contains: DNA, small amount of
cytoplasm, cell membrane, peptidoglykan,
very little water, thick keratin-like coat (with
calcium dipicolinate)
Relevance of bacterial spores
• Resistance to heat and chemicals!
• They cannot be easily achieved by boiling
• Other methods of sterilisation like
autoclaving should be used
• So for ex. Bacillus stearothermophilus is
used for evaluation of the sterilisation
efficacy of autoclaves!
Types of spores
1, 4 – central
2, 3, 5 – terminal
6 - lateral
2 – with inclusions
3, 4, 5, 6 – spores deforming a bacterial cell
1, 2 – spores not deforming
Spores
terminal
subterminal
central
Thank you for your attention
More in your textbooks.