Chap 4 Diversity

DIVERSITY OF MICROORGANISMS Part I Acellular and Prokaryotic Microbes

Acellular Infectious Agents:  

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Viruses Virions are complete viral particles which are very small and simple in structure. Size: 10 to 300nm, or can be up to 1um in length(Ebola virus) 1940: 1st photographs of viruses after the invention of electron microscopes in 1930s

Acellular Infectious Agents:Viruses

Acellular Infectious Agents:Viruses     

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Viruses contain DNA or RNA A protein coat Some are enclosed by an envelope Some viruses have spikes Most viruses infect only specific types of cells in one host Host range is determined by specific host attachment sites and cellular factors

Acellular Infectious Agents:Viruses 

2. 3. 4. 5. 6.

Five specific properties that distinguish viruses from living cells: They possess either DNA or RNA They are unable to replicate on their own They do not divide by binary fission, mitosis, or meiosis They lack the genes and enzymes necessary for energy production They depend on the ribosomes, enzymes, and metabolites of the host cell for protein and nucleic acid production.

Acellular Infectious Agents:Viruses 

2. 3. 4. 5. 6. 7. 8. 9.

Viruses are classified by the following characteristics: Type of genetic material Shape of the capsid Number of capsomeres Size of the capsid Presence or absence of an envelop Type of host that it infects Type of disease it produces Immunologic or antigenic properties

Acellular Infectious Agents:Viruses 

2. 3. 4. 5.

Four categories of viruses based on the type of nucleic acid they possess: Double-stranded RNA viruses Single-stranded RNA viruses Single-stranded DNA viruses Double-stranded DNA viruses

Bacteriophages    4.

5.

6.

Viruses that infect bacteria Obligate intracellular pathogens They may be: Icosahedron: almost spherical shape with 20 facets Filamentous: long tubes formed into helical structure Complex: icosahedral heads attached to helical tails.

Acellular Infectious Agents:Viruses

Acellular Infectious Agents:Viruses

Virulent bacteriophages 

 3. 4. 5. 6. 7.

Cause the lytic cycle, which ends in the destruction of the bacterial cell. The lytic cycle has 5 steps: Attachment (adsorption) Penetration Biosynthesis Assembly Release

Multiplication of Bacteriophages (Lytic Cycle) 

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Attachment Phage attaches by tail fibers to host cell Penetration Phage lysozyme opens cell wall, tail sheath contracts to force tail

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core and DNA into cell Biosynthesis Production of phage DNA and proteins Maturation Assembly of phage particles

Temperate Bacteriophages 

Or lysogenic phages, do not immediately initiate the lytic cycle, but rather, the DNA remains integrated into the bacterial cell chromosome, generation after generation.

Animal Viruses 

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Viruses that infect humans and animals Some maybe DNA viruses, while others may be RNA viruses May be enveloped or may contain enzymes that play a role in viral multiplication of animal viruses.

Animal Viruses 

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Double-stranded DNA, nonenveloped viruses Mastadenovirus 

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Respiratory infections in humans Tumors in animals

Animal Viruses 

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Double-stranded DNA, nonenveloped viruses Papillomavirus (human wart virus) Polyomavirus 

Cause tumors, some cause cancer

Animal Viruses 

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Orthopoxvirus (vaccinia and smallpox viruses) Molluscipoxvirus 

Smallpox, molluscum contagiosum, cowpox

Animal Viruses: (Double-stranded DNA, nonenveloped viruses)   

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Simplexvirus Varicellavirus Lymphocryptovirus Cytomegalovirus Roseolovirus Kaposi's sarcoma Some herpes viruses can remain latent in host cells

Animal Viruses 

Coronavirus 

Upper respiratory infections

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Hepadnavirus (Hepatitis B virus) 

Use reverse transcriptase to produce DNA from mRNA

Animal Viruses 

Enterovirus 

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Enteroviruses include poliovirus and coxsackievirus

Rhinovirus Hepatitis A virus

Animal Viruses: Single-stranded RNA, – strand, one RNA strand  

Vesiculovirus Lyssavirus (rabies virus) 

Cause numerous animal diseases

Animal Viruses: Single-stranded RNA, – strand, one RNA strand 

Filovirus 

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Enveloped, helical viruses Ebola and Marburg viruses

Animal Viruses:Single-stranded RNA  

Lentivirus (HIV) Oncogenic viruses 

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Use reverse transcriptase to produce DNA from viral genome Includes all RNA tumor viruses

Animal Viruses: Double-stranded RNA, nonenveloped 

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Reovirus (Respiratory Enteric Orphan) Rotavirus 

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Mild respiratory infections and gastroenteritis

Colorado tick fever

Multiplication of Animal viruses 

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Attachment membrane Penetration Uncoating Biosynthesis proteins Maturation proteins Release or

Viruses attaches to cell By endocytosis or fusion By viral or host enzymes Production of nucleic acid and Nucleic acid and capsid assemble By budding (enveloped viruses) rupture

Multiplication of Animal viruses

Release of an enveloped virus by budding

Inclusion bodies   

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Are remnants or collections of viruses Often seen in infected cells Used as diagnostic tool to identify certain viral diseases Cytoplasmic inclusion bodies: rabies, AIDS, and Guarnieri bodies of smallpox Intranuclear inclusion bodies: herpes and poliomyelitis

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Latent Viral Infections 

Virus remains in asymptomatic host cell for long periods 

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Cold sores caused by herpes simplex virus, and shingles which occurs in person who has had chicken pox (varicella)

Persistent Viral Infections 

Disease processes occurs over a long period, generally fatal 

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

Cancer 

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Activated oncogenes transform normal cells into cancerous cells. Transformed cells have increased growth, loss of contact inhibition, tumor specific transplant and T antigens. The genetic material of oncogenic viruses becomes integrated into the host cell's DNA.

Oncogenic viruses 

Oncogenic DNA Viruses     

Adenoviridae Herpesviridae Poxviridae Papovaviridae Hepadnaviridae

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Oncogenic RNA viruses 

Retroviridae 

Viral RNA is transcribed to DNA which can integrate into host DNA

Viroids 

Plant Viruses 

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Plant viruses enter through wounds or via insects

Viroids 

Viroids are infectious RNA; potato spindle tuber disease

Some Plant viruses

Prions 

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Infectious proteins that cause fatal neurologic diseases in animals. Inherited and transmissible by ingestion, transplant, & surgical instruments Spongiform encephalopathies: Sheep scrapie, Creutzfeldt-Jakob disease, Gerstmann-Sträussler-Scheinker syndrome, fatal familial insomnia, mad cow disease PrPC, normal cellular prion protein, on cell surface PrPSc, scrapie protein, accumulate in brain cells forming plaques

The Domain Bacteria 

Characteristic 6. Biochemical and metabolic s

1. Cell Morphology 2. Staining Reactions 3. Colony morphology 4. Atmospheric requirements 5. Nutritional

activities 7. Specific enzymes that the organism produces 8. Pathogenecity 9. Amino acid sequencing of proteins 10.Genetic

1. Cell Morphology   3.

4.

5.

Size: 0.2um to 10um Shape: Cocci – round or spherical bacteria Bacilli – rectangular or rodshaped bacteria Spirilla – curved and spiralshaped bacteria

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Cocci may be:

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

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1. 2. 3. 4.

Bacilli may be:

Single Diplobacilli Steptobacilli Coccobacilli Ex. Haemophilus 5. Pallisade arrangement Ex. Corynebacterium diptheriae

Examples of medically important bacilli are Enterobacteria -Shigella - Escherichia - Pseudomonas - Klebsiella - Bacillus - Proteus - Clostridium - Salmonella

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Bacillus cereus

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2. 3. 4.

Examples of curved and spiralshaped bacteria: Vibrio cholerae Campylobacter Treponema

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Neisseria

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Cell-wall deficient (CWD) bacteria may lose their cell walls because of adverse growth conditions. Mycoplasma has no cell wall Pleomorphism is the ability to exist in a variety of shapes because of the absence of cell wall.

2. Staining Procedures        

Smearing Fixing Staining Used to observe cell morphology Simple stain Differential stain Gram stain Acid-fast stain

A thin film of a solution of microbes on a slide is a smear.  A smear is usually fixed to attach the microbes to the slide and to kill the microbes. 

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Stains consist of a positive and negative ion. In a basic dye, the chromophore is a cation. In an acidic dye, the chromophore is an anion. Staining the background instead of the cell is called negative staining.

Simple stains Use of a single basic dye is called a simple stain.  A mordant may be used to hold the stain or coat the specimen to enlarge it. 

Differential Staining: Gram Stain 

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The Gram stain classifies bacteria into gram-positive and gramnegative. Gram-positive bacteria tend to be killed by penicillin and detergents. Gram-negative bacteria are more resistant to antibiotics.

Primary stain: Gram – cells Crystal violet

Color of Gram + cellsColor of

Purple

Purple

Mordant: Iodine

Purple

Decolorizing agent: Alcohol-acetone Colorless

Purple

Counterstain: Safranin

Purple

Purple

Red

Differential Stain: Gram Staining

Differential Stains: Acid-fast Stain 

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Cells that retain a basic stain in the presence of acid-alcohol are called acid-fast. Non–acid-fast cells lose the basic stain when rinsed with acidalcohol, and are usually counterstained (with a different color basic stain) to see them.

Negative staining is useful for capsules.  Heat is required to drive a stain into endospores.  Flagella staining requires a mordant to make the flagella wide enough to see. 

3. Motility  

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The ability of the organism to move. Bacterial motility is associated with the presence of flagella or axial filaments Some exhibit motility on secreted slime on solid agar Most spiral-shaped bacteria and one half of the bacilli are motile Cocci are generally non-motile Motility can be demonstrated by stabbing organisms into a tube or by the hanging drop technique.

4. Colony Morphology 

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Includes the size, color, overall shape, elevation, and consistency of the colony The features of the colony serve as important “clues” in the identification of bacteria Size of the colony is determined by the organisms’ rate of growth, and it is an important characteristic of a bacteial species Bacterial colony is a mound or pile of bacteria on an agar surface. It contains

5. Atmospheric Requirements It is useful to classify bacteria on the basis of their relationship to oxygen and carbon dioxide  Bacterial isolate can be classified into one of five major groups: 1.) Obligate aerobes – require an atmosphere that contains molecular oxygen in concentrations comparable to that in a room air (20 -21 % oxygen). Ex. Mycobacteria and certain fungi 

2.) Microaerophilic aerobes – require lower concentration (15% oxygen) than that found in room air for multiplication. Ex. Neisseria gonorrhea, Campylobacter species 3.) Obligate anaerobes – is an anaerobe that only grows in anaerobic environment. It will not grow in microaerophilic environment, CO2 incubator, or in air. 4.)Aerotolerant anaerobe – does not require O2, grows better in the absence of O2, but can survive in atmosphere containing molecular oxygen such as air or a CO2 incubator. 5.)Capnophiles – microbes that grow better in increased concentration of CO2.

6. Nutritional Requirements 

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All bacteria need some form of elements such as C,H, O2, S, P, and N for growth Special elements such as K, Ca, Mn, Mg, Co, Cu, Zn, U are needed by certain bacteria. Some have specific vitamin requirements. Others need organic substances

7. Biochemical and Metabolic Activities 

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Bacteria produce waste products and secretions 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 tentatively identified by the enzymes they secrete. Some bacteria are characterized by the production of certain gases such as CO2, H2S, O2, and CH4 Different types of culture media are used in

8. Pathogenecity 

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Disease-producing abilities of pathogens Many pathogens are able to cause disease 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. Amino Acid Sequencing of Proteins 

Comparing amino-acid sequencing of certain bacterial proteins determines the species and its relations to another bacteria.

10. Genetic composition  

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DNA is unique to each species Determining the degree or relationship between two different bacteria can be done by identifying or hybridizing a sequence of bases in portions of DNA or RNA Molecular diagnostic procedures are tests to identify bacteria by analyzing the organisms DNA or RNA

Unique Bacteria Rickettsias  very small parasitic bacteria that live and reproduce within eukaryotic host’s cells  Coccoid, rod-shaped, or pleomorphic Gram-negative bacteria with a bacterial-type cell wall  Contain both DNA and RNA  They are transmitted by arthropod

Chlamydias 

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Most primitive of all bacteria because they lack enzymes required to perform many metabolic activities, particularly production of ATP Transferred by direct contact between hosts C. trachomatis causes blindness

Mycoplasmas  

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Smallest of the cellular microbes They assume many shapes, from coccoid to filamentous because they lack cell walls They are gram-negative and may be free-living or parasitic and pathogenic to animals and some plants They are resistant to treatment with penicillin and other antibiotics

Photosynthetic bacteria 

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Purple bacteria and green bacteria do not produce oxygen but they use light as source of energy Cyanobacteria produce oxygen They may create a “waterbloom”, “a pond scum” which resembles thick layer of bluish-green oil paint. They are able to convert N2 from the air to ammonia in the soil. Some can produce toxins such as neurotoxins, hepatoxins, and cytotoxins.

Different forms of cyanobacteria

Especially large and especially small bacteria 

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Largest: Thiomargarita namibensis and Epulopiscium fishelsonii Nanobacteria have been found in soil, minerals, ocean water, human and animal blood, human dental calculus, arterial plaque and even rocks of extraterrestial origin

Especially large and especially small bacteria 

Thiomargarita

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Epulopiscium

Domain Archaea   

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Discovered in 1977 “Archae” means ancient There is a debate whether archae evolved first than eubacteria. Many are ‘extremophiles” Others are methanogens

END Of Diversity of Acellular and Prokaryotic microbes Quiz on August 19