Chap 4 Diversity

8/14/2019 Chap 4 Diversity

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DIVERSITY OFMICROORGANISMS

Part I

Acellular and ProkaryoticMicrobes


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Acellular Infectious

Agents:VirusesVirions are complete viral particleswhich are very small and simple instructure.Size : 10 to 300nm, or can be up to1um in length(Ebola virus)1940: 1 st photographs of viruses afterthe invention of electron microscopesin 1930s


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Agents:Viruses


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Agents:VirusesViruses contain DNA or RNAA protein coat Some are enclosed by an envelopeSome viruses have spikesMost viruses infect only specific typesof cells in one hostHost range is determined by specifichost attachment sites and cellular

factors


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Acellular InfectiousAgents:Viruses

Five specific properties thatdistinguish viruses from living cells:

2. They possess either DNA or RNA3. They are unable to replicate on their own4. They do not divide by binary fission,

mitosis, or meiosis

5. They lack the genes and enzymesnecessary for energy production6. They depend on the ribosomes, enzymes,

and metabolites of the host cell for proteinand nucleic acid production.


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Agents:VirusesViruses are classified by thefollowing characteristics :

2. Type of genetic material3. Shape of the capsid4. Number of capsomeres

5. Size of the capsid6. Presence or absence of an envelop7. Type of host that it infects8. Type of disease it produces9. Immunologic or antigenic properties


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Agents:VirusesFour categories of viruses basedon the type of nucleic acid theypossess:

2. Double-stranded RNA viruses3. Single-stranded RNA viruses4. Single-stranded DNA viruses5. Double-stranded DNA viruses


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BacteriophagesViruses that infect bacteriaObligate intracellular pathogens

They may be:4. Icosahedron: almost spherical shape

with 20 facets5. Filamentous: long tubes formed into

helical structure6. Complex: icosahedral heads attached

to helical tails.


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Agents:Viruses


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Agents:Viruses


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Virulent bacteriophagesCause the lytic cycle , which ends in thedestruction of the bacterial cell.

The lytic cycle has 5 steps:3. Attachment (adsorption)4. Penetration

5. Biosynthesis6. Assembly7. Release


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Attachment Phage attaches by tail fibers tohost cell

Penetration Phage lysozyme opens cell wall,

tail sheath contracts to forcetail

core and DNA into cellBiosynthesis Production of phage DNA

and proteins

Maturation Assembly of phage particles

Multiplication of Bacteriophages

(Lytic Cycle)


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Temperate BacteriophagesOr lysogenic phages, do notimmediately initiate the lytic cycle,but rather, the DNA remainsintegrated into the bacterial cellchromosome, generation after

generation.


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Animal Viruses

Viruses that infect humans andanimalsSome maybe DNA viruses, whileothers may be RNA virusesMay be enveloped or may containenzymes that play a role in viralmultiplication of animal viruses.


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Animal Viruses

Double-strandedDNA,

nonenvelopedvirusesPapillomavirus (human wartvirus)Polyomavirus

Cause tumors,

some causecancer


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Animal Viruses

Orthopoxvirus (vaccinia and

smallpox viruses)Molluscipoxvirus

Smallpox, molluscumcontagiosum, cowpox


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Animal Viruses

CoronavirusUpper respiratory

infections

Hepadnavirus (Hepatitis B virus)

Use reversetranscriptase toproduce DNA frommRNA


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Animal Viruses

EnterovirusEnteroviruses

include poliovirusandcoxsackievirus

Rhinovirus

Hepatitis A virus


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Animal Viruses: Single-strandedRNA, strand, one RNA strand

FilovirusEnveloped, helical

virusesEbola andMarburg viruses


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Animal Viruses:Single-stranded RNA

Lentivirus (HIV)Oncogenic viruses

Use reversetranscriptase toproduce DNA fromviral genome

Includes all RNAtumor viruses


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Animal Viruses: Double-strandedRNA, nonenveloped

Reovirus (Respiratory

Enteric Orphan)Rotavirus

Mild respiratoryinfections and

gastroenteritisColorado tickfever


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Multiplication of Animal viruses

Attachment Viruses attaches to cellmembrane

Penetration By endocytosis or fusionUncoating By viral or host enzymesBiosynthesis Production of nucleic acid andproteins

Maturation Nucleic acid and capsidproteins assembleRelease By budding (enveloped viruses)or rupture


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Release of an enveloped virus bybudding


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Inclusion bodies

Are remnants or collections of virusesOften seen in infected cellsUsed as diagnostic tool to identifycertain viral diseasesCytoplasmic inclusion bodies: rabies,AIDS, and Guarnieri bodies of smallpoxIntranuclear inclusion bodies: herpes andpoliomyelitis


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Latent Viral InfectionsVirus remains in asymptomatic host cell forlong periods

Cold sores caused by herpes simplex virus, andshingles which occurs in person who has hadchicken pox (varicella)

Persistent Viral InfectionsDisease processes occurs over a longperiod, generally fatal

Subacute sclerosing panencephalitis (measlesvirus)Progressive encephalitis (Rubella virus)


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Cancer

Activated oncogenes transform normalcells into cancerous cells.

Transformed cells have increasedgrowth, loss of contact inhibition,tumor specific transplant and T

antigens. The genetic material of oncogenicviruses becomes integrated into the

host cell's DNA.


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Oncogenic viruses

Oncogenic DNAViruses

AdenoviridaeHerpesviridaePoxviridaePapovaviridae

Hepadnaviridae

Oncogenic RNAviruses

RetroviridaeViral RNA istranscribed to DNAwhich canintegrate into host

DNA


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Viroids

Plant VirusesPlant viruses enter through wounds or viainsects

ViroidsViroids are infectious RNA; potato spindle

tuber disease


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Some Plant viruses


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Prions

Infectious proteins that cause fatalneurologic diseases in animals.Inherited and transmissible by ingestion,transplant, & surgical instrumentsSpongiform encephalopathies: Sheepscrapie, Creutzfeldt-Jakob disease,Gerstmann-Strussler-Scheinker syndrome,

fatal familial insomnia, mad cow diseasePrP C, normal cellular prion protein, on cellsurfacePrP Sc , scrapie protein, accumulate in brain

cells forming plaques


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The Domain Bacteria

Characteristics

1. Cell Morphology2. Staining

Reactions

3. Colonymorphology4. Atmospheric

requirements5. Nutritional

6. Biochemical andmetabolicactivities

7. Specific enzymesthat the organismproduces

8. Pathogenecity9. Amino acidsequencing of proteins

10.Genetic


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1. Cell Morphology

Size: 0.2um to 10umShape:

3. Cocci round or sphericalbacteria

4. Bacilli rectangular or rod-shaped bacteria

5. Spirilla curved and spiral-shaped bacteria


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Cocci may be:2. Diplococci (in pairs)3. Streptococci (chains)4. Staphylococci (clusters)5. Tetrads (packets of four)6. Octads (packets of eight)Ex. Enterococcus, Neisseria,

Staphylococcus, Streptococcus.


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Bacilli may be:1. Single2. Diplobacilli3. Steptobacilli4. Coccobacilli

Ex. Haemophilus5. Pallisade

arrangementEx. Corynebacterium

diptheriae


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Examples of medicallyimportant bacilli are

Enterobacteria -Shigella

- Escherichia- Pseudomonas- Klebsiella

- Bacillus- Proteus- Clostridium

- Salmonella

Bacillus cereus


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Examples of curved and spiral-

shaped bacteria:2. Vibrio cholerae3. Campylobacter

4. Treponema


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Neisseria


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Cell-wall deficient (CWD) bacteria maylose their cell walls because of adverse

growth conditions.Mycoplasma has no cell wallPleomorphism is the ability to exist in avariety of shapes because of theabsence of cell wall.


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2. Staining Procedures

SmearingFixing

StainingUsed to observe cell morphologySimple stain

Differential stainGram stainAcid-fast stain


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A thin film of a solution of microbes on a slide is asmear.A smear is usually fixed to

attach the microbes to theslide and to kill the microbes.


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Stains consist of a positive andnegative ion.

In a basic dye, the chromophore isa cation.In an acidic dye, the chromophore

is an anion.Staining the background instead of the cell is called negativestaining .


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Differential Staining: GramStain

The Gram stain classifies bacteriainto gram-positive and gram-negative.Gram-positive bacteria tend tobe killed by penicillin anddetergents.Gram-negative bacteria aremore resistant to antibiotics.


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Primary stain: Color of Gram + cellsColor of Gram cells

Crystal violet Purple Purple

Mordant: Iodine Purple Purple

Decolorizing agent:Alcohol-acetone PurpleColorless

Counterstain:Safranin Purple Red


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Differential Stain: GramStaining


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Differential Stains: Acid-fastStain

Cells that retain a basicstain in the presence of acid-alcohol are calledacid-fast .Nonacid-fast cellslose the basic stainwhen rinsed with acid-

alcohol, and areusually counterstained(with a different colorbasic stain) to seethem.


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Negative staining is usefulfor capsules.Heat is required to drive astain into endospores .Flagella staining requires amordant to make the flagellawide enough to see.


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3. Motility The ability of the organism to move.Bacterial motility is associated with thepresence of flagella or axial filamentsSome exhibit motility on secreted slime onsolid agarMost spiral-shaped bacteria and one half of the bacilli are motileCocci are generally non-motileMotility can be demonstrated by stabbingorganisms into a tube or by the hanging droptechnique.


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4. Colony Morphology

Includes the size, color, overall shape,elevation, and consistency of the colony

The features of the colony serve asimportant clues in the identification of bacteriaSize of the colony is determined by theorganisms rate of growth, and it is animportant characteristic of a bacteial speciesBacterial colony is a mound or pile of

bacteria on an agar surface. It contains


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5. AtmosphericRequirements

It is useful to classify bacteria on the basisof their relationship to oxygen and carbon

dioxideBacterial isolate can be classified into one of five major groups:

1.) Obligate aerobes require anatmosphere that contains molecular oxygenin concentrations comparable to that in aroom air (20 -21 % oxygen). Ex.Mycobacteria and certain fungi


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2.) Microaerophilic aerobes require lowerconcentration (15% oxygen) than that foundin room air for multiplication. Ex. Neisseriagonorrhea, Campylobacter species

3.) Obligate anaerobes is an anaerobe thatonly grows in anaerobic environment. It willnot grow in microaerophilic environment,CO2 incubator, or in air.

4.) Aerotolerant anaerobe does not requireO2, grows better in the absence of O2, butcan survive in atmosphere containingmolecular oxygen such as air or a CO2incubator.

5.) Capnophiles microbes that grow better inincreased concentration of CO2.

l


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6. NutritionalRequirements

All bacteria need some form of elements such as C,H, O2, S, P, and N

for growthSpecial elements such as K, Ca, Mn,Mg, Co, Cu, Zn, U are needed by certain

bacteria.Some have specific vitaminrequirements.

Others need organic substances

i h i l d


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7. Biochemical andMetabolic Activities

Bacteria produce waste products andsecretions such as enzymes that enable

them to invade their host and cause disease. The pathogenic strains of many bacteria,such as staph, and strep can be tentativelyidentified by the enzymes they secrete.

Some bacteria are characterized by theproduction of certain gases such as CO2,H2S, O2, and CH4

Different types of culture media are used in


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8. Pathogenecity

Disease-producing abilities of pathogens

Many pathogens are able to causedisease because they have capsules or endotoxins , or because they

secrete exotoxins and exoenzymes that damage cells and tissues.It is tested by injecting the organism

into mice or cell cultures.

9 A i A id S i


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9. Amino Acid Sequencingof Proteins

Comparing amino-acid sequencingof certain bacterial proteins

determines the species and itsrelations to another bacteria.


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10. Genetic composition

DNA is unique to each speciesDetermining the degree or

relationship between two differentbacteria can be done by identifying orhybridizing a sequence of bases inportions of DNA or RNAMolecular diagnostic procedures aretests to identify bacteria by analyzingthe organisms DNA or RNA


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Unique Bacteria

Rickettsiasvery small parasitic bacteria that liveand reproduce within eukaryotichosts cellsCoccoid, rod-shaped, or pleomorphic

Gram-negative bacteria with abacterial-type cell wallContain both DNA and RNA

They are transmitted by arthropod


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Chl di


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Chlamydias

Most primitive of allbacteria because theylack enzymes requiredto perform manymetabolic activities,particularly productionof ATP

Transferred by directcontact between hostsC. trachomatis causes

blindness

M l


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Mycoplasmas

Smallest of the cellular microbes They assume many shapes, from

coccoid to filamentous because theylack cell walls They are gram-negative and may befree-living or parasitic and pathogenicto animals and some plants

They are resistant to treatment withpenicillin and other antibiotics


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Photosynthetic bacteria

Purple bacteria and green bacteria do not produceoxygen but they use light as source of energyCyanobacteria produce oxygen

They may create a waterbloom, a pond scumwhich resembles thick layer of bluish-green oilpaint.

They are able to convert N2 from the air toammonia in the soil.Some can produce toxins such as neurotoxins,hepatoxins, and cytotoxins.


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Especially large and especiallysmall bacteria

Largest: Thiomargarita namibensisand Epulopiscium fishelsonii

Nanobacteria have been found insoil, minerals, ocean water, humanand animal blood, human dental

calculus, arterial plaque and evenrocks of extraterrestial origin


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Especially large and especiallysmall bacteria

Thiomargarita Epulopiscium


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Domain Archaea

Discovered in 1977Archae means ancient

There is a debate whether archaeevolved first than eubacteria.Many are extremophilesOthers are methanogens


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END

OfDiversity of Acellular and

Prokaryotic microbesQuiz on August 19

Chap 4 Diversity

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