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 = 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)Cocci (spherical) Rods /bacilli:Rods /bacilli: can be short long robust, thin Spirochaete (helical)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 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 Capsule – gelatinous layer around the bacterium is composed of polysaccharides, proteins – inhibits phagocytosis, helps the adhesion, is used in preparation of vaccines Fimbriae Fimbriae – hair-like filaments, mediate adhesion to receptors Inclusions Inclusions – serve as sources of stored energy (polysaccharides)

Gram-staining (more in practical lessons) Crystal violetCrystal violet – 30 s Iodine solutionIodine solution – 30 s AlcoholAlcohol – decolorize until violet is removed SafraninSafranin – 60 s G+ purple groups G- pink groups

Cell wall Results: different in G- and G+ bacteria principle of Gram staining is still unknown, but it is used for hundred years Iodine purpleG+: 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 StreptococcusBacillusClostridiumListeriaCorynebacteriumYeastsGram-negativesEscherichiaSalmonellaHaemophilusPseudomonasMycoplasma

Flagella flagellinfilaments composed of flagellin movementresponsible 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 axial filamentSpirochaets 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 Bacillus stearothermophilusSo 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.