Part II BACTERIOLOGY Yang Haibo

PROKARYOTES Structure:  have a nucleoid containing DNA surrounded by cytoplasm  proteins can be synthesized  energy can be generated  have cell wall containing peptidoglycan 肽聚糖

Method of replication: by binary fission by binary fission can replicate extracellulary can replicate extracellulary except rickettsiae ， chlamydiae except rickettsiae ， chlamydiae

Nature of the nucleic acid Nature of the nucleic acid contain both DNA and RNA contain both DNA and RNA

Chapter 7 Morphology and Structure of Bacteria

Size and shape  Unit for measurement : Micron or micrometer, Micron or micrometer, μm: 1μm=10-3mm μm: 1μm=10-3mm

Size:  Varies with kinds of bacteria, and also related to their age and external environment.  range from μm in their largest dimension  Approximate 1μm

 Three basic groups: 1.cocci: round 1.cocci: round 2.bacilli: rods 2.bacilli: rods 3. spiral B.: spiral-shape 3. spiral B.: spiral-shape pleomorphic: variable shape pleomorphic: variable shape  The shape is determined by its rigid cell wall  Microscopic appearance: identification Shape

 Coccobacilli: very short rods  Spiral-shaped:  Spirilla: the cells are rigid  Spirochetes: the cells are mor flexible and undulating

arrangement  cocci diplococci: in pairs streptococci: in chains staphylococci: in grapelike clusters  bacilli Some arrange in chains

Structure 1. Basic structure  Cell wall  Cytoplasmic membrane  Cytosol 胞液  nucleiod 2. Specific structure  Capsule 荚膜  Endospores 芽胞  Flagella 鞭毛  Pili 菌毛

cell wall The outermost component common to all bacteria (except mycoplasma) In gram-positive B. : peptidoglygan teichoic acids teichoic acids In gram-negative B. : peptidoglycan outer membrane outer membrane Basic structure

The Cell Envelope Gram Positive Gram Negative

Functions of cell wall  Osmotic protection  maintains the characteristic shape of the cell  The sites of major antigenic determinants  Endotoxin activity of Gram-negative B.

1. Peptidoglycan layer  It is found only in B. cell walls.  provides rigid support for the cell  important in maintaining the characteristic shape of the cell  allows the cell to withstand media of low osmotic pressure osmotic pressure  A good target for antibacterial drugs

Three parts of peptidoglycan layer Carbohydrate backbone: composed of alternating N-acetylglucosamine molecules and N-acetylmuramic acid Tetrapeptide side chains: attached to each of the muramic acid molecules Peptide cross-bridges: between the two tetrapepteds Peptide cross-bridges: between the two tetrapepteds

 The backbone is the same in all B. species  The tetrapeptide side chains and the peptide cross-bridge vary from species to species  The cross-bridge of G- B. consists of a direct peptide linkage between two side chains

In G+ B.:  About 40 sheets of peptidoglycan  Comprise 50% of the cell wall material in G- B.:  Only 1 or 2 sheets  Comprise 5%--10% of the cell wall material

2. Special components of G+ cell walls 2. Special components of G+ cell walls  Teichoic and teichuronic acids 磷壁酸  Polysaccharides 多聚糖

GlN-Mur Gln-Mur GlN-Mur Gln-Mur Cytoplasm GlN-Mur Gln-Mur Lipoteichoic acid Peptidoglycan-teichoic acid Cytoplasmic membrane GRAM POSITIVE CELL WALL GRAM POSITIVE CELL WALL secrete exoenzymes and perform extracellular digestion

(1) Teichoic and teichuronic acid  Wall teichoic acid : linked to peptidoglycan  lipoteichoic acid: linked to the lipid in the cytoplasmic membrane  are antigenic and induce antibodies that are species-specific  mediate adherence

3. Special components of G- cell wall 3. Special components of G- cell wall 3 components:  Lipoprotein 脂蛋白  Outer membrane 外膜  Lipopolysaccharide 脂多糖

GRAM NEGATIVE CELL WALL GRAM NEGATIVE CELL WALLCytoplasm Inner (cytoplasmic) membrane Outer Membrane (Major permeability barrier) Lipopolysaccharide GlN-Mur Porin Braun lipoprotein Periplasmic space degradative enzyme

(1) lipoprotein  Cross-link the outer membrane and peptidoglycan layers  Stabilize the outer membrane and anchor it to the peptidoglycan layer

(2) Outer membrane  Asymmetrical bilayered structure  Contain prorins 孔蛋白  Large antibiotic molecules penetrate the outer membrane relatively slowly

(3) Lipopolysaccharide (LPS) (3) Lipopolysaccharide (LPS)  Attached to the outer membrane  It is endotoxin of gram-negative B.  the effects are similar irrespective of the organism from which it is derived

GRAM NEGATIVE CELL WALL GRAM NEGATIVE CELL WALLCytoplasm Inner (cytoplasmic) membrane Outer Membrane (Major permeability barrier) Lipopolysaccharide GlN-Mur Porin Braun lipoprotein Periplasmic space degradative enzyme

Three units  Lipid A 脂质 A: responsible for the toxic effects  Core polysaccharide: link to lipid A  Outer polysaccharide: the important somatic antigen of several G- B.

(4) The periplasmic space 周浆间隙  Between the inner and outer membranes  Hydrolytic enzymes: breakdown nontransportable substrates into transportable ones  Detoxifying enzymes: inactivate certain antibiotics

GRAM NEGATIVE CELL WALL GRAM NEGATIVE CELL WALLCytoplasm Inner (cytoplasmic) membrane Outer Membrane (Major permeability barrier) Lipopolysaccharide GlN-Mur Porin Braun lipoprotein Periplasmic space degradative enzyme

GlN-Mur Gln-Mur GlN-Mur Gln-Mur GRAM POSITIVE GRAM NEGATIVE Cytoplasm Cytoplasm GlN-Mur Gln-Mur Lipoteichoic acid Peptidoglycan-teichoic acid Cytoplasmic membrane Inner (cytoplasmic) membrane Outer Membrane Lipopolysaccharide GlN-Mur Porin Braun lipoprotein Periplasmic space

4. L forms  Removal of the B. cell wall, in osmotically protective media, they can grow and divide  May produce chronic infection  Relatively resistant to antibiotic treatment  Can revert to the normal bacillary form

Cytoplasmic membrane Functions: 1. selective permeability and transport of solutes 2. electron transport and oxidative phosphorylation 磷酸化作用 3. Excretion of hydrolytic exoenzymes 4. Secretion of enzymes and toxins

cytosol  Bounded by the cell membrane  Contain plasmid

plasmids  Are extrachromosomal, double- stranded, circular DNA molecules  are capable of replicating independently of the bacterial chromosome  can be integrated into the bacterial chromosome

plasmids  More than one type of plasmid or several copies of a single plasmid may be present in the cell  Can be lost and transfer  Many plasmids carry genes coding for different functions nucloid plasmids

Functions and structures 1. Antibiotic resistance 2. Resistance to heavy metals 3. resistance to ultraviolet light 4. pili (fimbriae) 5. Exotoxins

Nucleoid:  the area in which DNA is located  the DNA is a double strand, circular molecule  the nucleoid contains no nuclear membrane, no nucleolus, no mitotic spindle, and no histones

Specific structure of B.  Capsule  Endospores  Flagella  Pili

A. capsule:capsule  a gelatinous extracellular layer  Synthesized when growing in natural environments  composed of polysaccharede  Capsule: condensed, closely surrounding the cell  Glycocalyx: loose meshwork of fibrils extending outward from the cell

important roles 1. A determinant of virulence of many B. 2. Protected from phagocytosis 3. Are used as the antigens in certain vaccines 4. Play a role in the adherence of B.

B. Endospores B. Endospores  formed in response to adverse conditions  sporulation occurs when nutrients are depleted  inside the cell, mother cell autolysis  contains baterial DNA, a small amount of cytoplasm, cell membrane, peptidoglycan, very little water, a thick coat

 a thick, keratinlike coat: responsible for the remarkable resistance of the spore to heat, dehydrateon, radiation and chemicals  is a resting cell, the spore has no metabolic activity and remain dormant for many years

When returned to favorable environment, the spore germinates to produce a single vegetative cell When returned to favorable environment, the spore germinates to produce a single vegetative cell

1. sporulation

2. Properties of endospores  is a resting cell  remarkable resistance to heat, dehydration, radiation and chemicals

3. germination

One spore One spore can germinates into one One spore bacteral cell when exposed to water and the appropriate nutrients (not a means of reproduction

 sterilization cannot be achieved by boiling  patients can be infected by spore- forming organisms

 Are long, whiplike appendages  Semirigid helical rotors  Can cause chemotaxis  Have a characteristic number and location  Many rods have flagella, but most cocci do not C. Flagella

 some are causes of urinary tract infections urethra  Highly antigenic (H antigen )  some are used in identification of B. (by the use of specific antibodies against flagellar proteins)

 Hairlike filaments  Shorter and straighter than flagella  Are found mainly on G- B.  Two classes: ordinary pili sex pili D. Pili

1. Ordinary pili  Mediate the attachment of B.  Act as “colonization antigens”---- adherent---- virulence of certain pathogenic B.

2. Sex pili forms the attachment between the donor and the recipient cells during Bacterial conjugation

Physiological States of F Factor F+ F－F－ donor recipient

Mechanism of F + x F - Crosses F+F+ F-F- F+F+ F-F- F+F+ F+F+ F+F+ F+F+ conjugation

Cytoplasm All bacteria have a cell membrane where oxidative phosphorylation occurs (since there are no mitochondria). Cell membrane Outside the cell membrane is the cell wall which is rigid and protects the cell from osmotic lysis. Cell Wall

A single colony is placed on a slide and dried.  Stage1. Staining with crystal violet.  Stage 2. Fixation with iodine stabilizes crystal violet staining. All bacteria remain purple or blue.  Stage 3. Extraction with alcohol. Decolorizes some bacteria (Gram negative) and not others (Gram positive).  Stage 4. Counterstaining with safranin. Gram positive bacteria are stained with crystal violet and remain purple. Gram negative bacteria are stained pink.

Gram stain morphology  Shape  cocci (round)  bacilli (rods)  spiral or curved (e.g. spirochetes)  Single or multiple cells  clusters (e.g. streptococci)  chains (e.g. streptococci)  Gram positive or negative

Gram Positive Gram Negative

Structure of Lipopolysaccharide

GlN-Mur Gln-Mur GlN-Mur Gln-Mur Cytoplasm GlN-Mur Gln-Mur Lipoteichoic acid Peptidoglycan-teichoic acid Cytoplasmic membrane GRAM POSITIVE CELL WALL GRAM POSITIVE CELL WALL secrete exoenzymes and perform extracellular digestion

GRAM NEGATIVE CELL WALL GRAM NEGATIVE CELL WALLCytoplasm Inner (cytoplasmic) membrane Outer Membrane (Major permeability barrier) Lipopolysaccharide GlN-Mur Porin Braun lipoprotein Periplasmic space degradative enzyme

GlN-Mur Gln-Mur GlN-Mur Gln-Mur GRAM POSITIVE GRAM NEGATIVE Cytoplasm Cytoplasm GlN-Mur Gln-Mur Lipoteichoic acid Peptidoglycan-teichoic acid Cytoplasmic membrane Inner (cytoplasmic) membrane Outer Membrane Lipopolysaccharide GlN-Mur Porin Braun lipoprotein Periplasmic space

1. Flagella are embedded in the cell membrane, extend through the cell envelope and project as a long strand. 2. Flagella consist of a number of proteins including flagellin. 3. They move the cell by rotating with a propeller like action. - Axial filaments in spirochetes have a similar function to flagella.