Basic Characters of Bacteria

Hope Tan

Size and ShapesSize and Shapes Size:Size:

Unit for measurement Unit for measurement ::

Micron or Micron or micrometer, μm: 1μm=10micrometer, μm: 1μm=10-3-3mmmm

coccus bacillus Spiral

bacterium

Basic shapes of batcteriaBasic shapes of batcteria

Cocci: sphere, 1μm

Bacilli: rods , 0.5 ～ 1 μm in width, 1~3 μm

　 in length

Spiral bacteria: 1~3 μm in length and 0.3~

0.6 μm in width

CoccusCoccus

S. Pneumoniae N. gonorrhoeae Streptococci

Tetrads Sarcina Staphylococcus

Bacillus

S. typhi B. abortus C. diphtheriae

C. Botulinum M. tuberculosis B. anthracis

Spirillum

Vibrio

Spiral bacterium

V. cholerae

H. pylori

Basic structures Cell wall Cell membrane Cytoplasm Nuclear materialSpecial structures Capsule Spore Flagella Pili

Structure of bacteriaStructure of bacteria

Basic structure of bacteriaBasic structure of bacteria

1. Chemical composition ：

A. Common component—— peptidoglycan

Also called mucopeptide or glycopeptide or murein

Cell wallCell wall

• A backbone of N-acetyl glucosamine and N- A backbone of N-acetyl glucosamine and N-

acetyl muramic acid: Both discovered in acetyl muramic acid: Both discovered in

GG++and Gand G-- bacteria. bacteria.• A set of identical tetrapeptide side chain A set of identical tetrapeptide side chain

attached to N-acetyl-muramic acid: different attached to N-acetyl-muramic acid: different

components and binding modes in Gcomponents and binding modes in G++and Gand G--

bacteria.bacteria.• A set of identical peptide cross bridges: only A set of identical peptide cross bridges: only

in Gin G++bacteriabacteria

peptidoglycan

N – acetyl-gulcosamine

N – acetyl-muramic acidβ-1,4 glucosidic bond

① Polysaccharide backbone

PeptidoglycanPeptidoglycan

STRUCTURESTRUCTURE ：：

② Tetrapeptide side chain

③ Peptide cross-bridges

Bond to N – acetyl-muramic acid

Bond to Tetrapeptide side chain and only found in GG+ + bacteria

peptidoglycan for peptidoglycan for GG+ + bacteriabacteria

peptidoglycan for peptidoglycan for GG--bacteriabacteria

Diaminopimelic acid

Function and medical significance of peptidoglycanFunction and medical significance of peptidoglycan ：：

① ① Constructure of tenacious cell wall architectureConstructure of tenacious cell wall architecture

Gram positive bacteria—Gram positive bacteria—threethree-dimensional structure-dimensional structure

Gram negative bacteria—Gram negative bacteria— two two-dimensional structure-dimensional structure

② ② Target of some antibioticsTarget of some antibiotics ：： For exampleFor example ：： Penicilin can inhibit the binding between tetrapeptide

side chain and peptide cross-bridges, while lysozyme can

hydrolyze the β-1,4 glucosidic bond

Penicilin

Lysozyme

Reactive site of some antibiotics in peptidoglycan

Cell wallCell wall

1. 1. Chemical composition ：： A. A. Common component—— peptidoglycan

B. Special componentB. Special component

Gram positive bacteria——teichoic acid Gram positive bacteria——teichoic acid

Special surface proteinsSpecial surface proteins

Teichoic acidTeichoic acid

Structure:

Chemical composition

phosphodiester bondRibitol residue

Glycerine residue

Ribitol type

Polymerizer

Glycerine type

Classfication

According to bonding site on the bacteria,

teichoic acid can be classified into two types

Membrane teichoic acid,

also called lipoteichoic acid (LTA)

Wall teichoic acid

teichoic acidteichoic acid

Membrane teichoic acid

Wall teichoic acid

Peptidoglycan

Teichoicacid

Cellwall

Phospholipid

ProteinCell membrane

Function and medical significance of teichoic Function and medical significance of teichoic acidacid ：：

① Bearing a strong negative charge.

② Adhesive attraction, relating to pathogenicity

③ They are strongly antigenic, helpful to identify

and type a bacterium

cell wall for cell wall for GG+ + bacteriabacteria

Cell wallCell wall

1. 1. Chemical composition ：： A. A. Common component—— peptidoglycan

B. Special componentB. Special component

Gram positive bacteria——teichoic acidGram positive bacteria——teichoic acid

Special surface proteins Special surface proteins

Gram negative bacteria——outer membraneGram negative bacteria——outer membrane

Outer membraneOuter membraneStructure

Lipopolysaccharide

lipid bilayer

Lipoprotein

Outer membrane

Cell membrane

Periplasmic space

Lipid A

Core polysaccharide

Specific polysaccharide

(O- polysaccharide)

LPSendotoxin

① ① Adsorption and excretionAdsorption and excretion

② ② Barrier function

③ ③ Pathogenicity

④ ④ AntigenicityAntigenicity

⑤ ⑤ Receptor: F pilusReceptor: F pilus, phage, bacteriocin

Function and medical significance of Function and medical significance of outer membraneouter membrane ：：

Cell wall for Cell wall for GG- - bacteriabacteria

Comparison of cell wall between Gram negative Comparison of cell wall between Gram negative and Gram positive bacteriaand Gram positive bacteria

Characters G+ G-

Strength Tenacious Curmbly

Thickness Thick ， 20 ～ 80nm Thin ， 5 ～ 10nm

Layers of peptidoglycan More ， about 50 layers Few ， 1 ～ 3

layers

Content of peptidoglycan High ， 50 ～ 80% of cell

wall dry weight

Little ， 10 ～ 20%

of cell wall dry

weight

Structure of peptidoglycan Three-dimensional Two-dimensional

Content of carbohydrate About 45% 15-20%

Teichoic acid + -

Outer membrane - +

Structures and compositions of cell wall

G + bacterium

Peptidoglycan-rich cell wall

G+ bacterium cell wall

--Peptidoglycan

-- Teichoic acid

Structures and compositions of cell wall

G - bacterium cell wall

--Peptidoglycan

--Outer membrane Lipoprotein

Lipid bilayer

LPS

Lipid-rich

cell wall

• Countering the effects of high intracellular osmotic Countering the effects of high intracellular osmotic

pressure and maintaining the cell’s characteristic pressure and maintaining the cell’s characteristic

shapeshape• Barrier and protection• Participate in substance exchange of bacterial cellParticipate in substance exchange of bacterial cell

Function and medical significance of cell wall

• Determinate some important characters of bacteria Determinate some important characters of bacteria

pathogenicitypathogenicity

immunogenicityimmunogenicity

antibiotics sensitivity

chromaticity : Differentiate bacteria: G + / G ­

2. Wall-less forms of BacteriaWall-less forms of Bacteria (bacteria L form)

Causes： lysozyme, penicilin, antibody, complements,

macrophage, neutrophile granulocyte, bile, UV, etc.

Definition ： bacteria that the cell wall was impaired

but maintain the competence of growth and cell

division

L form of Gram positive bacteria —— protoplast

L form of Gram negative bacteria —— spheroplast

Characteristics ：

• Appearance ： polymorph

• Chromaticity ： Gram negative

• Characteristic of cultivate ： hyperosmotic

pressure, low concentrated agar with

serum,

and it grows very slow

Causes ：

•Lysozyme, penicillin, antibody, complements,

macropages, neutropile granulocyte, bile, UV,

etc.

Colony

Fried egg type colony

Granular type colony

Filamentous type colony

Fried egg (L) type

Granular (G) type

Filamentous (F) type

• Reversion: L-form bacteria can revert to its

normal bacteria when the cause was removed at the

early time of formation, the determinant condition is

whether there is peptidoglycan remaining in the cell

wall. And if it is subcultivated for many times in

vitro, it can never be reverted.

•Pathogenicity ： L-form bacteria bearing virulence

（ diagnosis ）• Antibiotic sensitivity ： changed （ cure ）

Basic structure Cell wall Cell membrane Cytoplasm Nuclear materialSpecial structure Capsule Spore Flagella Pili

Structure of bacteriaStructure of bacteria

No cholesterol

Important sturctures：

Cell membraneCell membrane

MesosomesMesosomes Mesosomes are specialized structures formed by

retractable, folded and curled cytoplasmic membrane,

and divided into septal and lateral mesosome. also

called chondroid.

MesosomesMesosomes

Penecillin-binding proteins, (PBP ）

Function

•Material transportation

•Respiration

• Biosynthesis ：

Penicillin-binding protein

• Participate in cell division ： mesosome

Basic structures Cell wall Cell membrane Cytoplasm Nuclear materialSpecial structures Capsule Spore Flagella Pili

Structure of bacteria

Ribosomes: numerous,

15 - 20nm in diameter with

70S; distributed throughout

the cytoplasm; site of protein

synthesis ;sensitive to

streptomycin and

erythromycin

CytoplasmCytoplasm

Composed largely of water, together with proteins,

nucleic acid, lipids and small amount of sugars and salts

Plasmids: extrachromosomal genetic elements

Plasmids are small, circular ， extra-

chromosomal ， double-stranded DNA

molecules. They are capable of self-replication

and contain genes that confer some important

properties, such as antibiotic

resistance ， virulence factors. Plasmids are not

essential for cellular survival.

Inclusions: sources of stored energy, e,g volutin

Inclusions are aggregates of various compounds

that are normally involved in storing energy reserves

or building blocks for the cell.

Inclusions accumilate

when a cell is grown in

the presence of excess

nutrients and they are

often observed under

laboratory conditions.

Basic structures Cell wall Cell membrane Cytoplasm Nuclear materialSpecial structures Capsule Spore Flagella Pili

Structure of bacteria

Lacking nuclear membrane, absence of

nucleoli, hence known as nucleic material

or nucleoid, one to several per bacterium.

Nuclear material

Special structure of bacteria

Basic structures Cell wall Cell membrane Cytoplasm Nuclear materialSpecial structures Capsule Spore Flagella Pili

Structure of bacteria

CapsulesCapsules

These are structures surrounding the outside of the cell wall.

They are not essential to cell

viability and some strains within a

species will produce a capsule, whilst

others do not. Capsules are often

produce in vivo or on a eutrophic

medium and lost during in vitro

culture.

• Antigenicity – Composition: polysaccharide

• Pathogenicity – Protection from phagocyte

– Resistance to drying – Adherence

Function and medical significance

Formation condition

In vivo or eutrophic

Basic structures Cell wall Cell membrane Cytoplasm Nuclear materialSpecial structures Capsule Spore Flagella Pili

Structure of bacteria

FlagellaFlagella

• Some bacterial species are mobile and possess

locomotory organelles - flagella. Flagella consist of

a number of proteins including flagellin

•The diameter of a flagellum is thin, 20 nm, and long

with some having a length 10 times the diameter of

cell. Due to their small diameter, flagella cannot be

seen in the light microscope unless a special stain is

applied. Bacteria can have one or more flagella

arranged in clumps or spread all over the cell.

Classification According to the number and distribution of Flagella, Flagella,

Flagella bacteria can Flagella bacteria can be classified into four types:

Monotrichate

Lophotrichate

Amphitrichate

Peritrichate

• Motility

• Pathogenicity – e.g., Vibrio cholerae

• Antigenicity – protein

– also called as H Ag

Function and significance

Basic structures Cell wall Cell membrane Cytoplasm Nuclear materialSpecial structures Capsule Spore Flagella Pilus

Structure of bacteria

Pili are hair-like

projections of the cell ,

They are known to be

receptors for certain

bacterial viruses.

Chemical nature is pilin

Pilus

Classification:

Ordinary pili or fimbriae: fine, rigid

numerous, related to bacterial adhesion

Sex pili: longer and coarser, only 1-4,

related to bacterial conjugation

Function:

Basic structures Cell wall Cell membrane Cytoplasm Nuclear materialSpecial structures Capsule Spore Flagella Pili

Structure of bacteria

a thick­walled form produced in a bacterial cell. It is very resistant to being killed by heat and various other chemical and physical agents.

Spore

Formation and germination

In vitro or malnutrition

In vivo or eutrophic

Bacteria (vegetative form)

spore （ only one ）

Bacteria (vegetative form, also only one)

Form conditions

(Dormant cell)(Dormant cell)

Multiple layers of resistant coats

Dipicolinic acid or calcium dipicolinate

Low content of water

• Contains a complete nucleus material, ribosomes

and energy-generating components

• Highly resistant to heat, dessication, and chemicals

Reasons

High-pressure steam sterilization is the most effective way to kill the spores

Characteristics:

Coats of sporeCoats of spore

Spore coat

Exosporium

SporewallCore Cortex

Endomembrane

Exomembrane

Medical significance

• Identification of a bacteria: size, appearance

and site

• Standard of sterilization

•Important source of infection —— anthrax,

tetanus, etc.

Bacterial Metabolism and MultiplicationBacterial Metabolism and Multiplication

Bacterial MetabolismBacterial Metabolism

Energy Metabolism Energy Metabolism

Important Metabolic ProductsImportant Metabolic Products

1. Catabolic processes1. Catabolic processes

2. Anabolic processes2. Anabolic processes

Products of anabolic processes and its Products of anabolic processes and its medical significancemedical significance

Pyrogen： a fever-producing substance mainly

synthesized by gram negative bacteria, it is highly

resistant to heat and it has the property of

pyrogenicity. It is a very important microbial

contamination evaluation index of biological products.

Toxins and Invasive Enzymes： Toxins: endotoxin, exotoxin

Invasive Enzymes: hyaluronidase, streptokinase,

streptodornase, and so on.

Pigments Classification—lipo solubility, water solubility

Observation the pigments is helpful to the

identification of a bacteria.

Antibiotics

Substance produced by some microbes

and bearing the property of inhibition or

killing effect to some other microbe or

tumor cells.

Bactericin

Substances produced by some strains of

bacteria and bearing the antibacterial activity to

the bacteria that related to bactericin-produce

one.

Vitamins

The medical significance of these products?

Medical significance

Pathogenicity of bacteria

Treatment of infectious diseases

Identification of bacteria

Products

Pyrogen

Toxin

Invasive enzyme

Antibiotic

Vitamin

Bacteriocin

Pigment

Requirments for Bacteria GrowthRequirments for Bacteria Growth

1. Nutrients: 2. Temperature 3. Hydrogen ion concentration ( pH ) 4. Oxygen Requirements5. Osmotic pressure

1.NutritionNutrition

Factors affecting bacterial growth and division Nutritive material:: Water Carbon source Nitrogen source Minerals Growth factors etc.etc.

Requirments for Bacteria GrowthRequirments for Bacteria Growth

2. Temperature2. Temperature

The temperature suitable for most bacteria growth is

from 20 to 40 centigrade, but the most appropriate

temperature for cultivation of pathogenic bacteria is 37

centigrade.

• Psychrophilic forms（ 15-20 ）• Mesophilic forms （ 30-37 ）： Include all human

pathogens and opportunists.

• Thermophilic forms （ 50-60 ）

3. hydrogen ion concentrationhydrogen ion concentration ( pH )

The pH value that fit for most bacteria growth is The pH value that fit for most bacteria growth is

from 7.2 to 7.6, but some bacteria grow well in from 7.2 to 7.6, but some bacteria grow well in acidity

environment, while some bacteria just at the opposite.environment, while some bacteria just at the opposite.

According to the appropriate pH value, bacteria

can be classified into three groups just as follows:

• Neutrophiles（ 5 to 8）

• Acidophiles（ below 5.5）

• Alkaliphiles（ above 8.5）

•obligate aerobeobligate aerobe

•microaerophilic bacteriummicroaerophilic bacterium

•facultative anaerobefacultative anaerobe

• obligate anaerobeobligate anaerobe

According to the oxygen requirement,

bacteria can be classified into four classes as

follows:

4.Essential gaseous environment ：： OO22 and CO and CO22

The possible reasons that obligate

anaerobe can not grow aerobically:

1. Deficiency of respiratory enzyme bearing high

redox potential

2. Deficiency of enzymes that degrade toxic oxygen

group, such as superoxide dismutase(SOD), catalase and

peroxidase.

Proliferative way: Binary fission

Bacterial Growth Curve Bacterial Growth Curve

The reproductive speed of most

bacteria is very fast, while some bacteria

such as Mycobacterium tuberculosis

grows very slow.

Reproductive speed：

Generation time ： The time takes for a

population of bacteria to double in number

• many common bacteria ： 20 ～ 60 min

•most common pathogens in the body ： 5 ～ 10

hours

•Mycobacterium tuberculosis in medium: 18～ 20

hours

Bacterial population dynamics—the growth curveBacterial population dynamics—the growth curve

time

Log B

acterial Num

ber

Lag Logarithmic Stationary Decline

Live cell number

Lag phase

• No growth

• Active metabolism

Log phase

• Fast growth

• Typical biological properties

– Staining

– Shapes

– Chemical reactions

– Sensitivity to antimicrobial agents

Stationary phase

• Constant number of live cells

• Atypical morphological properties

• Spores, exotoxins and antibiotics produced

Decline phase

• Decreased number of live cells

• Collapse or atypical cells

Based on the function and the chemical components: Basic Medium

­­contains the basic nutrients for the most bacterial growth; ­­the base of other kind of media. ­­e.g. broth.

Nutrient Medium/Enriched Medium Additional or special nutrients (e.g., serum, growth

factors, trace elements) are added to support some

fastidious bacterial growth.

e.g. blood agar.

Cultivation of Bacteria

Selective Medium The medium that can prevent the certain bacterial growth while permitting others. e.g. SS agar

Differential Medium Some special substrates and indicators are added into the media in order to produce a visual differentiation When several bacteria grow on the same kind of medium. e.g. EMB agar (Eosin­methylene blue agar).

Double sugar iron slant

Citrate slant

Anaerobic Medium A medium for the cultivation of certain anaerobes. The medium contains reducing agent, such as non­saturation fatty acid.

Based on the physical state • Liquid medium:

– Without agar. – for the proliferation of bacteria.

• Solid medium: – 1.5­2.5% agar. – for the isolation and identification of bacteria – e.g., slant, Petri dishes/plates.

• Semisolid medium: – 0.3­0.5% agar. – for the observation of bacterial motility and preservation of bacteria.

Bacterial growth patterns

• In liquid medium: Superficial growth; Turbidity/diffuse; Precipitate growing; (sediment)

• In solid medium:

Confluent growth / Smear ：a cluster of microorganisms growing on a solid medium.

Colony: It is directly visible and arises from a single cell.

• In semi-solid medium: – Only grow along the line of inoculation – Grow diffusely

Bacterial classification

Please self-study

Summary

2.The definitions of plasmid, capsule, flagellum,

pilus, spore, pyrogen, bactericin.

1.The difference between G + cell wall and G ­ cell wall

3. Medical importance of four special structures

4.The characteristics of growth curve