Medical MicrobiologyMedical Microbiology

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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Louis Pasteur Louis Pasteur (1822-1895) (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 names

– GenusGenus - noun, always capitalized– speciesspecies - adjective, lowercase

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

Bacterial shapesBacterial shapes

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Fig. 4.1

Bacterial Cell Structure

13Fig 4.10

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Gram positive Gram negative

Fig 4.16

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CytoplasmCytoplasm

CytoplasmCytoplasm

Lipoteichoic acid Peptidoglycan-teichoic acid

Cytoplasmic membrane

Inner (cytoplasmic) membrane

Outer Membrane

LipopolysaccharidePorin

lipoprotein

Peri

plas

mic

spa

ce

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r r rrr

r

Gram Positive Cell EnvelopeGram Positive Cell Envelope

CytoplasmCytoplasm

rrrr

Lipoteichoic acid

Peptidoglycan-teichoic acid

Cytoplasmic membrane

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PeptidoglycanGeneral structureGeneral structure

in both G+ and G- bacterial cell wall

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Gram positiveGram positive

Gram negativeGram negative

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Cell wall degeneration Cell wall degeneration - Protoplast- Protoplast

- Spheroplast- Spheroplast -L forms-L forms

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Specific Structures in Gram positive and Gram Negative bacteria

• In Gram Positive Bacteria - Teichoic and Lipoteichoic acid (LTA) acids

• In Gram Negative Bacteria - Lipoprotein - Phospholipid - Lipopolysaccharide

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Lipopolysaccharide

Lipid A• Glucosamine disaccharide

• Beta hydroxy fatty acids

Core • Heptoses• Ketodeoxyoctonic acid

O-antigenHighly variable

(Hydroxy myritic Acid)

- Endotoxins: Lipopolysaccharide (LPS) and its functions

- Exotoxins: Enterotoxins, Neurotoxins, ….

- Differences between Endotoxins & Exotoxins

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Bacteria Toxins

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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

Bacteria classification based on cell wall structure

• Grasilicutes (Gram Negative)

• Firmicutes (Gram Positive)

• Tenricutes (with no Cell wall)

• Mendosicutes (with no Peptidoglycan in cell wall)

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Major Taxonomic Groups of Major Taxonomic Groups of BacteriaBacteria

• Gracilicutes – gram-negative cell walls, thin-skinned

• Firmicutes – gram-positive cell walls, thick skinned

• Tenericutes – lack a cell wall & are soft• Mendosicutes – archaea, primitive

procaryotes with unusual cell walls & nutritional habits

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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)

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Biofilms

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2 Types of Capsule:

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lophotrichous

Monotrichous

amphitrichous peritrichous

Flagella

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Fimbrea (Pili)Fimbrea (Pili)

Adhesion to other cells and surfaces

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StructureStructurePili & Sex pili

• Rigid tubular structure made of pielin protein

• Found mostly in Gram negative cells

FunctionsFunctions – Adhesion– joins bacterial cells for DNA transfer (Conjugation)

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ConjugationConjugation

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CytoplasmCytoplasm

• Dense gelatinous solution of sugars, amino acids, & salts

• 70-80% water

• Serves as solvent for materials used in all cell functions

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Chromosome

• 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

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Plasmids

• 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

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Ribosomes

• 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.

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Inclusions, 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--hydroxybutyrate, gas vesicles for floating.

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Endospores vs ExosporesEndospores vs Exospores

Important components in

endospore:

Calcium&

Dipicolinic Acid

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Endospore structureEndospore structure

• Spherical or Oval• Terminal, subterminal or central• Bulging or nobulging

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Grwth in BacteriaGrwth in Bacteria

• Temperature

• Nutrients

• pH

• Osmotic pressure

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• 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

TemperatureTemperature

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Three temperature adaptation groups

Bacterial MetabolismBacterial Metabolism

• Phototropho Photoautotroph (Photolitotroph)o Photoheterotroph (Photoorganotroph)

• Chemotropho Chemoautotroph (Chemolitotropho Chemoheterotroph (Chemoorganotroph)

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Stages of metabolism in Stages of metabolism in chemoheterotrophic bacteriachemoheterotrophic bacteria

• Digestion

• Absorption (Passive and active transportation)

• Preparation for oxidation

• Oxidation

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Oxidation & Reduction

X Y

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e- & H+ Cytochromes, …. Cytochromes, ….

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Oxygen requirements

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Bacterial growthBacterial growth

Binary divisionBinary division

G0

G1

G1

G2

G2

G2

G2

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)

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The curve of bacterial growth in a closed culture

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Con

tinuo

us

Cul

ture

, Che

mos

tat

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

Bacterial growth in a continues culture

Measuring the bacterial Measuring the bacterial growthgrowth

• Measuring the mass of bacteria

• Measuring the number of bacteria

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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

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FermentationFermentation

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Methods in bacterial identificationMethods in bacterial identification

1. Microscopic morphology2. Macroscopic morphology – colony appearance3. Physiological / biochemical characteristics4. Chemical analysis5. Serological analysis6. Genetic & molecular analysis

• G + C base composition• DNA analysis using genetic probes• Nucleic acid sequencing & rRNA analysis

Bacterial Colonies

• Standard Bacterial Count

• Colony-Forming Units

• Plaque-Forming Units

•Spread Plate

• Pour Plate

• Soft-Agar Overlay

MediumMedium

• DefinitionDefinition

• Types 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

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Culture mediaCulture media

• General medium

• Special medium

• Differential medium• Enrichment medium (….. & cold enrichment)

• Transport medium (Stwart, Carry Blair, …)

• Galleries

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Types of culture methodsTypes of culture methods

• Isolation culture

• Spread culture

• Pour plate culture

• Colony count culture

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