Bacterial CellBacterial Cell StructureStructure

Dr. Majid Zare Bidaki(PhD in Microbiology, Assistant professor)

Birjand University of Medical Science

ReferencesReferences

1. Jawetz, Melnick, & Adelberg; Medical Microbiology, 24th ed.

2. Zinsser, Hans, And Joklik, Wolfgang K.; Medical Microbiology, 17th ed.

3. Baron, Samuel; Medical Microbiology, 4th ed.

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Antonie van LeeuwenhoekAntonie van Leeuwenhoek

First to observe living microbes

his single-lens magnified up to 300X

(1632-1723)

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5

Louis Pasteur (1822-1895) Louis Pasteur (1822-1895)

Showed microbes caused fermentation & spoilage

Disproved spontaneous generation of microbes

Developed aseptic techniques.

Developed a rabies vaccine.

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Robert Koch Robert Koch

Proposed: Germ theory of disease

Developed: pure culture methods.

Identified: cause of anthrax, TB, & Cholera.

(1843-1910)

Acellular and cellular Microorganisms

Acellular: VirusesViruses ViroidsViroids PrionsPrions

Cellular:BacteriaBacteriafungifungiProtista: Protozoa & algaeProtista: Protozoa & algaehelminths (worms) helminths (worms)

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Prokaryotic or EukaryoticProkaryotic or Eukaryotic

Prokaryotes vs EukaryotesProkaryotes vs Eukaryotes

Size smaller Larger

Nucleus - +

Organelles - +

Chromosomes 1 circular Multiple, linear

Ribosomes smaller 70s Larger 80sr

In prokaryotes against Eukaryotes, cell membranes lack In prokaryotes against Eukaryotes, cell membranes lack sterols (e.g. cholesterol)sterols (e.g. cholesterol)

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Scientific nomenclatureScientific nomenclature

Binomial (scientific) nomenclature Gives each microbe 2 namesGenusGenus - noun, always capitalizedspeciesspecies - adjective, lowercase

Both italicized or underlined– Staphylococcus aureus (S. aureus)– Escherichia coli (E. coli)

Bacterial shapesBacterial shapes

Cytoplasmic membrane Cytoplasmic membrane ProtoplastProtoplast

SpheroplastSpheroplast L formsL forms

Gram positiveGram positive Gram negativeGram negative

LipopolysaccharideLipopolysaccharide

Lipid A• Glucosamine disaccharide• Beta hydroxy fatty acids

Core • Heptoses• Ketodeoxyoctonic acid

O-antigenHighly variable

(Hydroxy myritic Acid)

LPS functionLPS functionEndotoxinsEndotoxinsExotoxinsExotoxins

PeptidoglycanPeptidoglycan

Gram positiveGram positive

Gram negativeGram negative

4 groups based on cell wall 4 groups based on cell wall compositioncomposition

1. Gram positive cells

2. Gram negative cells

3. Bacteria without cell walls

4. Bacteria with chemically unique cell walls

Gram positive wall

Gram negative cell wallGram negative cell wall

CytoplasmCytoplasm

CytoplasmCytoplasm

Lipoteichoic acidPeptidoglycan-teichoic acid

Cytoplasmic membrane

Inner (cytoplasmic) membrane

Outer Membrane

LipopolysaccharidePorin

lipoprotein

Peri

plas

mic

spa

ce

r r rrr

r

Gram Positive Cell EnvelopeGram Positive Cell Envelope

rrrr

Lipoteichoic acidPeptidoglycan-teichoic acid

Cytoplasmic membrane

Bacteria classification based on Bacteria classification based on cell wall structurecell wall structure

Grasilicutes (Gram Negative)Grasilicutes (Gram Negative)Firmicutes (Gram Positive)Firmicutes (Gram Positive)Tenricutes (with no Cell wall)Tenricutes (with no Cell wall)Mendosicutes (with no Peptidoglycan in Mendosicutes (with no Peptidoglycan in

cell wall)cell wall)

Major Taxonomic Groups of BacteriaMajor Taxonomic Groups of Bacteria

Gracilicutes – gram-negative cell walls, thin-skinned

Firmicutes – gram-positive cell walls, thick skinned

Tenericutes – lack a cell wall & are softMendosicutes – archaea, primitive procaryotes

with unusual cell walls & nutritional habits

CapsuleCapsule

2 types1. Macro capsule - highly organized, tightly

attached2. Micro capsule, Slime layer or Glycocalyx -

loosely organized and attached

Functions attachment inhibits killing by white blood cells Receptor (K antigen)

2 Types of Capsule2 Types of Capsule

BiofilmsBiofilms

FlagellaFlagella

Fimbrea (Pili)Fimbrea (Pili)

Adhesion to other cells and surfaces

StructureStructure

Pili & Sex pili

Rigid tubular structure made of pielin protein

Found mostly in Gram negative cells

FunctionsFunctions Adhesionjoins bacterial cells for DNA transfer (Conjugation)

ConjugationConjugation

CytoplasmCytoplasmdense gelatinous solution of sugars, amino

acids, & salts70-80% waterserves as solvent for materials used in all

cell functions

ChromosomeChromosome

single, circular, double-stranded DNA molecule that contains all the genetic information required by a cell

DNA is tightly coiled around a protein, aggregated in a dense area called the nucleoid

plasmidsplasmids

small circular, double-stranded DNA

free or integrated into the chromosome

duplicated and passed on to offspring

not essential to bacterial growth & metabolism

may encode antibiotic resistance, tolerance to toxic metals, enzymes

& toxins

used in genetic engineering- readily manipulated & transferred

from cell to cell

RibosomesRibosomes

made of 60% ribosomal RNA & 40% protein

consist of 2 subunits: large (50 S) & small (30 S)

procaryotic differ from eucaryotic ribosomes in

size & number of proteins

site of protein synthesis

All bacterial cells have ribosomes.

Inclusions, granulesInclusions, granules

intracellular storage bodies

vary in size, number & content

bacterial cell can use them when

environmental sources are depleted

Examples: glycogen, sulfur and polyphosphate granules,

poly-b-hydroxybutyrate, gas vesicles for floating.

endosporesendospores

Important components in endospore: Important components in endospore:

CalciumCalciumDipicolinic AcidDipicolinic Acid

The Endospore structureThe Endospore structure

Spore structureSpore structure

Spherical or Oval

Terminal, subterminal or central

Bulging or nobulging

Growth in BacteriaGrowth in Bacteria

Temperature

Nutrients

pH

Osmotic pressure

Minimum temperature – lowest temperature that

permits a microbe’s growth and metabolism

Maximum temperature – highest temperature

that permits a microbe’s growth and metabolism

Optimum temperature – promotes the fastest

rate of growth and metabolism

Temperature Temperature

3 temperature adaptation groups

Bacterial MetabolismBacterial Metabolism

PhototrophPhotoautotroph (Photolitotroph) Photoheterotroph (Photoorganotroph)

ChemotrophChemoautotroph (ChemolitotrophChemoheterotroph (Chemoorganotroph)

Stages of metabolism in Stages of metabolism in chemoheterotrophic bacteriachemoheterotrophic bacteria

Digestion

Absorption (Passive and active transportation)

Preparation for oxidation

Oxidation

Oxidation & ReductionOxidation & Reduction

X Ye- & H+ Cytochromes, …. Cytochromes, ….

Oxygen requirementsOxygen requirements

Bacterial growth Bacterial growth

Binary divisionBinary division

Microbial growth calculationMicrobial growth calculation

b = a X 2n

G (Generation time) = T / n

(n = The number of generations, T = The total time of growth for the population)

The curve of bacterial growth in a closed The curve of bacterial growth in a closed cultureculture

Growth Curve

Bacterial growth in a Bacterial growth in a continues culturecontinues culture

Con

tinuo

us C

ultu

re, C

hem

osta

t

Chemostats are a means of keeping a culture in log phase indefinitely.

Measuring the bacterial growthMeasuring the bacterial growth

• Measuring the mass of bacteria

• Measuring the number of bacteria

FermentationFermentation

Incomplete oxidation of glucose or other carbohydrates in the absence of oxygen

Uses organic compounds as terminal electron acceptors

Yields a small amount of ATP

Production of ethyl alcohol by yeasts acting on glucose

Formation of acid, gas & other products by the action of various bacteria on pyruvic acid

FermentationFermentation

Methods in bacterial identificationMethods in bacterial identification

1. Microscopic morphology

2. Macroscopic morphology – colony appearance

3. Physiological / biochemical characteristics

4. Chemical analysis

5. Serological analysis

6. Genetic & molecular analysis G + C base composition DNA analysis using genetic probes Nucleic acid sequencing & rRNA analysis

Bacterial ColoniesBacterial Colonies

• Standard Bacterial Count

• Colony-Forming Units

• Plaque-Forming Units

•Spread Plate

• Pour Plate

• Soft-Agar Overlay

MediumMedium

DefinitionDefinitionTypes based on solidity:Types based on solidity:

1. Liquid medium (Name broth)

BHI, TSB, SF, NB, …

2. Solid medium (Name agar)

Blood agar, Nutrient agar, chocolate agar, Columbia agar, EMB

3. Semi-solid medium

SIM

Culture mediaCulture media

General medium

Special medium

Differential medium

Enrichment medium (….. & cold enrichment)

Transport medium (Stwart, Carry Blair, …)

Galleries

Types of culture methodsTypes of culture methods

Isolation culture

Spread culture

Pour plate culture

Colony count culture