Categories of Microbes

Chapter 4: Microbial Diversity Part 1: Acelluar and Prokaryotic Microbes

Categories of Microbes
Microbes can be divided into those that are truly cellular (bacteria, archaea, algae, protozoa, and fungi) and those that are acellular (viruses, viroids, and prions). Cellular microbes (microorganisms) can be divided into those that are prokaryotic (bacteria and archaea) and those that are eukaryotic (algae, protozoa, and fungi). Viruses, viroids, and prions are often referred to as acellular microbes or infectious particles.

Acelluar Microbes: Viruses
Complete virus particles are called virions. Very small and simples in structure (10 – 300 nm) No type of organism is safe from viral infection Some viruses, called oncogenic viruses or oncoviruses, cause specific types of cancer. A typical virion consists of a genome of either DNA or RNA, surrounded by a capsid (protein coat), which is composed of protein units called capsomeres. Some viruses (enveloped viruses) have an outer envelope composed of lipids and polysaccharides. Very small and simple in structure nm Unable to be seen until electron microscopes were invented NO type of organism is safe from viral infection (Viruses infect humans, animals, plants, fungi, protozoa, algae, and bacterial cells) Oncoviruses-- Cause specific types of cancer Typical viron (virus particles) consists of genome surrounded by a capsid (protein coat) which is composed of capsomeres (small protein units) The necleuid acid and the capsid are referred to as the nucelocapsid (Fig 4-2) Enveloped virues have an outer envelope composed of lipids and polysaccharides

Viral Nucleocapsids and Envelopes

Acellular Microbes: Viruses
Viruses have five properties that distinguish them from living cells: They possess either DNA or RNA, whereas living cells possess both. They are unable to replicate on their own. Unlike cells, 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. Five Specific properties that distinguish them from living cells The vast majority of viruses possess wieher DNA or RNA, unlike living cells, which possess both They are unable to replicate on their own; their replication is directed by the viral nucleic acid once it has been introduced into a host cell Unlike cells, 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 No ribosomes or sites of energy production So they must invade and take over a functioning cell to produce new virions

Viruses that Infect Humans (Fig. 4-1)

Viruses are classified by Type of genetic material (either DNA or RNA) Shape and size of capsid Number of capsomeres Presence or absence of an envelope Type of host it infects Disease it produces Target cell(s) Immunologic/antigenic properties Viruses are classified by the following characteristics Type of genetic material (either DNA or RNA) Shape of the capsid Polyhedral (many sided) Helical (collided tubes) Bullet shaped Spherical or complex (combination of these shapes) Number of capsomeres (that make up the capsid) Size of the capsid Presence or absence of an envelope Type of host that it infects Type of disease it produces Target cell Immunologic or antigeneic properties Table 4-2 Selected groups of viruses with characteristics

Envelope is acquired by certain animal viruses as they escape from the nucleus or cytoplasm of the host cell by budding (fig 4-4) so the membrane is that of the hosts The virus can them alter the membrane with spickes, knobs, and proteins so it can recognize the next host cell to invade

Categories based on genome Double-stranded DNA viruses Single-stranded RNA viruses Single-stranded DNA viruses Double-stranded RNA viruses Most viral genomes are circular molecules, but some are linear. There are four categories of viruses, based on the type of nucleic acid that they possess. Most viral genomes are of the first two types. Double-stranded DNA Signle-stranded RNA Single-stranded DNA Double-stranded RNA Usually circular but some can be linear

Acellular Microbes: Viruese
Origin of Viruses Coevolution theory - coevolved with bacteria and archaea from the primordial soup Retrograde evolution theory – viruses evolved from free- living prokaryotes that invaded other living organisms, and gradually lost functions which were provided by the host cell Escaped gene theory – viruses are a piece of host cell RNA or DNA that have escaped from living cells and are no longer under cell control -- currently most widely accepted Origin of Viruses Coevolution theory - coevolved with bacteria and archaea from the primordial soup Retrograde evolution theory – virulses evolved from free-living prokaryotes that invaded other living organisms, and gradually lost functions wihich were provided by the host cell Escaped gene theory – viruses are a piece of host cell RNA or DNA that have escaped from living cells and are no longer ounder cell control -- currently most widely accepted

Bacteriophages Viruses that infect bacteria are known as bacteriophages or simply phages. Categorized based on shape, nucleic acid, and events that occur after entry into a host cell Shape: icosahedron, filamentous, complex Nucleic acid: ss DNA, ds DNA, ss RNA, ds RNA Events: virulent vs temperate Viruses that infect bacteria Three categories based on their shape Icosahedron bacteriophages – an almost spherical shape with 20 triangular facets Filamentious bacteriophages – long tbues formed by capsid proteins assembled into a helical structure Complex bacteriophages – icosahedral heads attached to helical tails, they may also posess base plates and tail fibers Can be categorizaed by the type of nucleic acid : Ss DNA, Ds DNA, Ss RNA, Ds RNA Categorized by the events that occur after invasion of the bacterial cell

Virulent bacteriophages vs. temperate bacteriophages. Virulent bacteriophages always cause what is known as the lytic cycle, which ends with the destruction of the bacterial cell. The five steps in the lytic cycle are attachment, penetration, biosynthesis, assembly, and release. Categorized by the events that occur after invasion of the bacterial cell The phages don’t acuall enter the cell but instead inject their genetic Figure 4-8 Virulent always cause lytic cycle Ends with the lysis of the bacteria cells (Table 4-3) (Figure 4-9)

Lytic cycle of bacteriophages Attachment of phase to surface of cell Phage can only attach to bacterial cells that have an appropriate receptor on the surface that the cell surface that the phage recognizes This allows for phages to be strain or species specific Penetration Phage injects its DNA so the DNA can take over the host machinery Biosynthesis Phage genes are expressed resulting in production of viral pieces (DNA and proteins) Assembly Viral pieces are assembled to produce complete viral particles (virions) and complete with DNA in the viral capsids Release The host cell burts open and all of the new virions escape from the cell Lysis is caused by an enzyme coded by a phage gene

Temperate bacteriosphages (lysogenic phages) Do not immediately initiate the lytic cycle Instead, integrates their DNA into the bacterial cell chromosome Phage switches to lytic cycle as a result of environmental clues Temperate phages (lysogenic phages) Do not immediately initiate the lytic cycle but rather their DNA remains integrated into the bacterial cell chromosome, generation after generation If bacterial cell is going to die, the phage turns on the lytic cycle for self-preservation

Uses of bacteriophages Destroy bacterial pathogens Treat bacterial infection Prevent food contamination There has been speculation and experimentation regading their use to destroy bacterial pathogens and treat bacterial infections Renewed research has begun since the emergence of multidrug-resistant bacteria :Phages produce enzmes to destroy or prevent the synthesis of cell walls currently being studied as possible therapeutics FDA has approved the used of phage mixture to prevent Listeria contamination in cergain foods

Animal Viruses Infect animals or humans DNA or RNA Simple or complex Steps in the multiplication of animal viruses are Attachment Biosynthesis Penetration Assembly Uncoating Release Animal viruses Viruses that infect animals or humans DNA or RNA May be simple or complex Steps in Multiplication ( Table 4-4) Attachment Only attach to cells with the appropriate receptors (leads to species or animal specific viruses and certain cells being effected such as respiratory vs gut) Penetration Entire virion usually enters the host cell Uncoating The viral nucleic acid escapes from the capsid within the host cell Biosynthesis The viral nucleic acid dictates what occurs within the host cell Viral genome and proteins produced Some viruses remain latent in host cells and do not intiate biosynthesis right away Assembly Fitting the viruse pieces together to produce complete virions Release Viruses must excape from the cell How they do this depends on the virus – some destroy host cell completely and other bud off host cell and become surrounded by the cell membrane creating an enveloped virus

Latent virus infections Viral infections in which the virus is able to hide from a host’s immune system by entering cells and remaining dormant. Herpes viral infections are examples. Once acquired, herpes virus infections (e.g., those that cause cold sores, genital herpes, and chickenpox/shingles) never completely go away; for example, chickenpox may be followed, years later, by shinglesboth the result of the same virus. Latent viral infections An infected person is always harboring the virus but the infections are limited by the defense systems of the human body A fever, stress, excessive sunlight, age, or disease can weaken the immune system and cause the viral genes to take over the cells and produce more virueses Examplye herpes virus infections (cold sore) Shingles from a different herpes virus that causes chicken pox

Antiviral agents Antibiotics are not effective against viral infections Antiviral agents are drugs that are used to treat viral infections. These agents interfere with virus-specific enzymes and virus production by disrupting critical phases in viral multiplication or inhibiting synthesis of viral DNA, RNA, or proteins. Antiviral agents Antibiotics do not work on viruses, but they may be prescribed to prevent a secondary infection that may follow a virus infection Some antiviral agents have been developed that interfere with virus production and virus specific enzymes

Oncogenic viruses or oncoviruses These viruses cause cancer. Examples include Epstein–Barr virus, human papillomaviruses, Hepatitis B and C, and human herpesvirus 8 Human immunodeficiency virus (HIV) This virus causes acquired immunodeficiency syndrome (AIDS). It is an enveloped, single-stranded RNA retrovirus. The primary targets for HIV are CD4+ cellsthose having CD4 receptors on their surface. Oncogenic Viruses Viruses that cause cancer Epstein-Barr virus causes mononucleosis and three tyeps of human cancers Human herpesvirus 8 causes cancer in AIDS patients Hepatitis B and C viruses can lead to liver cancer HIV Human immunodeficiency virus The cause of AIDS Enveloped, single stranded RNA virus It is a retrovirus HIV is able to attach to and invade cells bearing receptors that the virus recognizes (most important one is CD4) CD4 is found on the helper T cells of the immune system

Plant Viruses Cause plant disease Result in economic losses in excess of $70 billion per year worldwide Infects cocoa tree, rice, barley, tobacco, turnips, cauliflower, potatoes, tomatoes, etc.

Acellular Microbes: Viroids and Prions
Viroids and prions are smaller and less complex infectious particles than viruses Viroids Viroids are short, naked fragments of single- stranded RNA, which can interfere with the metabolism of plant cells. Viroids are transmitted between plants in the same manner as viruses. Examples of plant diseases caused by viroids are potato spindle tuber and citrus exocortis. Does not cause animal disease Viroids and Prions Viroids and prions are even smaller and lexx complex infectious agents than viruses Viroids Short, naked fragments of ss RNA that can interfere with the metabolism of plant cells and stunt the growth of plants, sometimes killing the plants in the process Known to cause disease in potatoes, citris tress, coconut palms, chrysanthemums and tomatoes No animal disease has been discovered to be caused by viroids

Acellular Microbes: Viroids and Prions
Prions are small infectious proteins that cause fatal neurologic diseases in animals and humans Scrapie mad cow disease Kuru Creutzfeldt–Jacob disease Fatal Familial insomnia Of all pathogens, prions are the most resistant to disinfectants. The mechanism by which prions cause disease remains a mystery. All are fatal spongiform encephalopathies Small infectious proteins that cause fatal neurological disease in anmals Scrapie Animals scrape themselves against fence posts and other objects in a effort to relieve the intense itching associated with the disease Also caused chronic wasting disease due to irreversible weight loss Mad cow disease Kuru Once common in natives in Papua, New Guinea where women and children ate human brains as a part of traditional burial custom Since the custom stopped 50 years ago, the disease is nearly eradicated Creutzfeldt-Jakob disease Fatal Familial insomnia (insomnia and dementia follow difficult sleeping) in humans All are fatal spongiform encephalopathies in which the brain become riddled with holes Of all pathogens, prions are belieed to be the most resistant to disinfectants

Domain Bacteria: Characteristics
Bergey’s Manual of Systematic Bacteriology Bacteriologist’s “bible” Domain bacteria contains 23 phyla 32 classes 5 subclasses 77 orders This may only account for <1% to a few percent of the total number of bacteria present in nature 14 suborders 182 families 871 genera 5,007 species Characteristics Bergey’s Manual of Systematic Bacteriiology (bacteriologist’s “bible”) Domain bacteria contains 23 phyla 32 classes 5 subclasses 77 orders 14 suborders 182 families 871 genera 5,007 species This may only account for <1% to a few percent of the toal number of bacteria present in nature

Domain Bacteria: Characteristics
Bacteria are divided into three major phenotypic categories: Those that are Gram-negative and have a cell wall Those that are Gram-positive and have a cell wall Those that lack a cell wall (Mycoplasma spp.) Characteristics of bacteria used in classification and identification include cell morphology, staining reactions, motility, colony morphology, atmospheric requirements, nutritional requirements, biochemical and metabolic activities, enzymes that the organism produces, pathogenicity, and genetic composition. This domain is broadly divided into three categories Gram-negative with a cell wall Gram-positive with a cell wall Lack a cell wall Further categorized by their cellular characteristics and genetic material Many characteristics of bacteria are examined to provide dtat fro identification and classification Cell mshape and morphological arrangement Staining reactions Motility Colony morphology Atmosphereic requirements Nutritional requirements Biochemical and metabolic activites Speicifc enzymes that the organism produces Pathogeneicity Geneti composistion

Domain Bacteria: Cell Morphology
There are three basic categories of bacteria based on shape: Cocci (round bacteria) Bacilli (rod-shaped bacteria) Curved and spiral-shaped bacteria Cell Morphology Size, shape, and morphologic arrangement of various bacteria are observed with compound light microscope Three basic shapes Round or spherical (cocci or coccus) Rectangular or rod-shaped bacteria (calli or bacillus) Curved and spiral-shpaed (spirilla)

Cocci may be seen singly or in pairs (diplococci), chains (streptococci), clusters (staphylococci), packets of 4 (tetrads), or packets of 8 (octads). Medically relevant: Enterococcus, Neisseria, Staphylococcus, Streptococcus After binary fission, the daughter cells may separate completely or remain connected Cocci may be singly or in pairs (diplococcic), chains (streptococci), clusters (staphylococcis), packets of four (tetrads), or packets of eight (octads) depeding on the particular speices an dmanner in which the cells divide (figure 4-17) Medically relevant: Enterococcus, Neisseria, Sephylococcus, Steptococcus

Bacilli They are often referred to as rods; they may be short or long, thick or thin, and pointed or with curved or blunt ends. They may occur singly, in pairs (diplobacilli), in chains (streptobacilli), in long filaments, or branched. Extremely short bacilli are called coccobacilli. Examples of medically important bacilli: Escherichia, Klebsiella, Proteus, Pseudomonas, Haemophilus, and Bacillus spp. Bacilli (rods) may be short or long, thick or thin, pointed or with curved or blunt ends. They may occur single, in pairs (diplobacilli), in chains (streptobacilli), in long filaments, or branched Short rods resemble elongated cocci and are called coccobacilli Listeria monocytogenes and Hamophilus influenze Medically relevant: Escherichia, Bacillus, Clostridium, Shigella, Salmonella

Curve (comma shaped) Medically relevant example: Vibrio usually occur single, but some may form pairs Spiral shape – called spirochetes Vary in length, rigidity, size, number and amplitude of their coils, and tightness of coils Preponema pallidum (syphilis), Borrelia (Lyme disease) Shape can be lost due to adverse growitn conditions Some bacteria can exist in a variety of shapes (pleomorphic) Curved and spiral shapted Curve (comma shaped) Vibrio – one species cause cholera and a second one cused diharrea usually aoccur single, but some may form pairs Spiral shape – called spirochetes Vary in length, rigigdy, size, number and amplitude of their coils, and tightness of coils Preponema pallidum (syphillus), Borrelia (Lyme disease) Shape can be lost due to adverse growitn conditions Some bacteria can exist in a variety of shpapes (pleomorphic

Domain Bacteria: Staining Procedures
Most bacteria are colorless, transparent, and difficult to see Three major categories of staining procedures Simple staining procedure Structural staining procedures Capsule staining Spore staining Flagella staining Differential staining procedures Gram and acid-fast staining procedures Staining Procedure Most bacteria are colorless, transparent, and difficult to see Staning methods have been dievised to enable scientists to examine bacteria Simple stained Structural staining procedures Used to observe bacterial capsules, spores, and flagella Differential staining procedures Gram stain and acid-fast stains because they enable microbiologists to differentiate one group of bacteria from another

Bacterial smears must be fixed prior to staining. The fixation process serves to kill organisms, preserve their morphology, and anchor the smear to the slide. The two most common techniques of fixation: Heat fixationnot a standardized technique; excess heat will distort bacterial morphology Methanol fixationa standardized technique; the preferred method Procedure The bacteria are smeared onto a glass microscope clide Slide is then airdired Then fixed Heat fixation and methanol fixation Fixation kills the organisms, preserves their morphology, and anchors smear to the slide Smear is the stained

Simple Bacterial Staining Technique
Simple stain Sufficient to determine bacterial shape and morphologic arrangement A dye is applied to the fixed smear, rinsed, dried, and examined Procedure The bacteria are smeared onto a glass microscope clide Slide is then airdired Then fixed Smear is the stained

Gram Stain Divides bacteria into two major groups: Gram-positive (bacteria end up being blue to purple) Gram-negative (bacteria end up being pink to red) The final Gram reaction (positive or negative) depends on the organism’s cell wall structure. The cell walls of Gram-positive bacteria have a thick layer of peptidoglycan, making it difficult to remove the crystal violet–iodine complex. Gram-negative organisms have a thin layer of peptidoglycan, making it easier to remove the crystal violet; the cells are subsequently stained with safranin. Gram Stain Developed by Dr. Hans Christian Gram Most important staining procedure in the laboratory because it distinguishes between Gram-positive and Gram-negative bacteria Figure 4-23 The color of the bacteria at the end of the stain depends on the chemical composition of their cell wall Gram-positive are not decolorized during the decolorization step so they will be blue to purple The thick layer of peptidoglycan in the cell walls of Gram-positive bacteria makes it difficult to remove the crystal violet-iodine complex during the decolorization step Gram-negative removes crystal violoet at decolorization step and the cells were subsequently stained by the safranin (red dye) so they will be pink to red Thin layer of peptidoglycan makes it easier to remove the crystal violet-iodine complex during decolorization The decolorizer also dissolves the lipid in the cell walls of Gram-negative bacteria making it easier to remove the crystal violet-iodine complex

Gram stain Technique

Some bacteria are neither consistently purple nor pink after Gram staining; they are known as Gram-variable bacteria, for example, Mycobacterium spp. Mycobacterium spp. are often identified using the acid-fast stain. The acid-fast stain Carbol fuchsin is the red dye that is driven through the bacterial cell wall using heat. Heat is used to soften the waxes in the cell wall. Because mycobacteria are not decolorized by the acid– alcohol mixture, they are said to be acid-fast. Some bacteria are not consistent in their results so they are referred to as Gram-variable Mycobacterium tuberculosis and M. leprae Acid fast stain Developed by Paul Ehrlich Mycobacterium species are more often identified using this staining procedure Carbol fuchsin (bright red dye) is drivien into the bacterial cell using heat Decolorizing agent then added If decolorization doesn’t work, the color remains and the bacteria are acid-fast Figure 4-32 Used as a laboratory diagnosis for TB in a sputum specimen Most other bacteria are decolorized and are non-acid-fast

Domain Bacteria: Motility
If a bacterium is able to “swim,” it is said to be motile. Bacterial motility is most often associated with flagella and less often with axial filaments. Most spiral-shaped bacteria and about 50% of bacilli are motile; cocci are generally nonmotile. Motility can be demonstrated by stabbing the bacteria into a tube of semisolid medium Motility If the bacterim is able to swim it is motil If it is unable it is nonmotile Motility is most often associated with the presence of flagella or axial filaments a Some bacteria can have a gliding motility on secreted slime Bacteria never possess cilia Spiral shaped bacteria and ½ bacilli are motile by flagella Cocci are generally nonmotile Motility can be determined by growing bacteria in a semisold agar Non motile will only grow on the stab line and motile will grow throughout the medium Figure 4-33

Domain Bacteria: Colony Morphology
A bacterial colony contains millions of organisms. Colony morphology (appearance of the colony) varies from one species to another. Colony morphology includes size, color, overall shape, elevation, and the appearance of the edge or margin of the colony. Colony morphology can also include the results of enzymatic activity on various types of media. As is true for cell morphology and staining characteristics, colony morphology is an important “clue” to the identification (speciation) of bacteria. Colony morphology Single bacteria cell on a medium cannot be seen but after it divides over and over agin, it produes a mound or pile of bacteria known as a colony Morphology (appearance of the colonies) of bacteria vary by species Includes Size Color Overall shpe Elevation Appearance of the edge or margin of the colony Serve as clues for identifying bacteria

Domain Bacteria: Atmospheric Requirements
Bacteria can be classified on the basis of their atmospheric requirements, including their relationship to O2 and CO2. With respect to O2, bacterial isolates can be classified as Obligate aerobes Microaerophilic aerobes Facultative anaerobes Aerotolerant anaerobes Obligate anaerobes Capnophilic organisms grow best in the presence of increased concentrations of CO2 (usually 5%–10%) Atmospheric requirements Classiby bacteria based on their releationship with oxygen (O2) and carbon dioxide (CO2) Oxygen bacteria requirements can be divided into five major groups Carbon dioxide Room air contains less than 1% CO2 Capnophiles Grow better in the laboratory in the presence of increased concentrations of CO2 In micro laboratories incubators routinel contain between 5% and 10% CO2 Organisms oxygen requirement has nothing to do with their carbon dioxide requirement

Obligate aerobes Require atmosphere containing molecular oxygen in concentrations comparable to room air for growth and multiplication Mycobacteria and certain fungi fall in this class Microaerophilic aerobes Require oxygen in concentrations lower than that found in room air Neisseria gonorrhoeae Campylobacter – major causes for bacterial diarrhea Facultative anaerobes Capable of surviving in either the presence or absence of oxygen Many of bacteria routinely isolated from clinical specimens Enterobacteriaceae, most streptococci and staphylococci Aerotolerant anaerobes Does not require oxygen, grows better in the absence of oxygen, but can survive in atmospheres containing molecular oxygen The concentration of oxygen that is tolerated varies from species to species Obligate anaerobes Can only grow in an anaerobic environment

Culturing microorganism in thioglycollate broth (THIO) will help determine their oxygen requirements by where they grow

Domain Bacteria: Nutritional Requirements
All bacteria require some form of the elements such as carbon, hydrogen, oxygen, sulfur, phosphorus, and nitrogen for growth. Some bacteria require special elements (e.g., calcium, iron, or zinc) or vitamins Organisms with especially demanding nutritional requirements are said to be fastidious (“fussy”). The nutritional needs of a particular organism are usually characteristic for that species and are sometimes important clues to its identity. Nutritional requirements All bacteria need some form of the elements carbon, hydrogen, oxygen, sulfur, phosphorus, and nitrogen for growth Some special elements (i.e. potassium, copper, cobalt, zinc, and uranium) are required by some bacteria Some need specific vitamins and others need organic substances secretd by other living microorganisms to gorw Organisms with especially demaning nutritional requiements are fastidious Special enriched media must be used to grow these Nutritional requirements can serve as an import clue for microbe determination

Domain Bacteria: Biochemical and Metabolic Activities
As bacteria grow, they produce many waste products and secretions Pathogenic strains of many bacteria, such as staphylococci and streptococci, can be tentatively identified by the enzymes they secrete. In particular environments, some bacteria produce gases such as carbon dioxide or hydrogen sulfide. To identify bacteria in the laboratory, they are inoculated into various substrates (i.e., carbohydrates and amino acids) to determine whether they possess the enzymes necessary to break down those substrates. As bacteria grow, they produce many wast products and secretions Some of these are enzymes that enable them to invade their host and cuase dieses Pathogenic stramins are tentatively identified by the enzymes they secrete Some also produces various gases Different types of culture media is used to determine the bacterial cells metabolic activities

Domain Bacteria: Pathogenicity
Many pathogens are able to cause disease because they possess capsules, pili, or endotoxins, or because they secrete exotoxins and exoenzymes that damage cells and tissues. Frequently, pathogenicity is tested by injecting the organism into mice or cell cultures. Examples of some common pathogenic bacteria: Neisseria meningitidis, Salmonella typhi, Shigella spp., Vibrio cholerae, Yersina pestis, and Treponema pallidum Frequently tested by injecting the organism into mice or cell cultures

Domain Bacteria: Genetic Composition
Laboratory identification of bacteria is moving toward analyzing the organism’s DNA or RNA The composition of the genetic material (DNA) of an organism is unique to each species. Through the use of 16S rRNA sequencing, the degree of relatedness between two different bacteria can be determined. Moving toward the identification of bacteria usin some type of test procudre that analyzes the organism’s DNA or RNA Molecular diagnoistic procedures The DNA composition of an organism is unique to eash species

Domain Bacteria: Unique Bacteria
Rickettsias, chlamydias, and mycoplasmas are bacteria, but they do not possess all the attributes of typical bacterial cells. Rickettsias and chlamydias have a Gram-negative type of cell wall and are obligate intracellular pathogens Rickettsias Disease transmitted by arthropods Cause typhus and spotted fever rickettsiosis have “leaky membranes.” Rickettsias, chlamydias, and mycoplasmas are bacteria but they do not possess all the attibutes of typical bacterial cells They are so small they were originally thought to be viruses Rickettsias and chlamydias Gram-negative type cell wall Obligate intracellular pathogens Must be grown in embryonated chick eggs, lab animals, or cell culture – will not grow on media alone Genus Rickettsia Named for Howard T. Ricketts No conndection to the disease caused rickets (which is the result of Vitamin D deficienty) All disease caused by this genus are transmitted by arthropods (lice, fleas, ticks Causes typhus, spotted fiver rickettsiosis Involve the production of a rash Has a leaky cell membrane so must grow in a host cell to retain necessary cellular substances

Chlamydias are “energy parasites,” meaning they prefer to use ATP molecules produced by their host cell. Transferred by aerosols or direct contact Cause trachoma, inclusion conjunctivitis, nongonococcal urethritis, pneumonia, and respiratory disease Chlamydias Energy parasites They can produce ATP but preferentially use ATP molecules produced by the host cells Transferred by aerosols or by direct contact between hosts Cause trachoma (the leading cause of blindess in the world), inclusion conjectivitis and nongonococcal urethritis, pneumonia, and repiratory disease

Mycoplasmas smallest of the cellular microbes. lack a cell wall and therefore assume many shapes (i.e., pleomorphic) May be free living or parasitic Pathogenic to many animals and some plants In humans, pathogenic mycoplasmas cause primary atypical pneumonia and genitourinary infections. Because they have no cell wall, they are resistant to drugs like penicillin that attack cell walls. Smallest of the cellular microbes Lack cell waslls so they assume many shapes May be free living or parasitic Pathogenic to many animals and some plants Cause atepyical pneumonia and genitourinary infections Resisten to treatment with many antibiotics that work by inhibiting cell wall synthesis (PCN) Can be grown on artivicial media

Domain Bacteria: Photosynthetic bacteria
Photosynthetic bacteria include purple bacteria, green bacteria, and cyanobacteria they all use light as an energy source (photosynthesis), but not in the same way. Purple and green bacteria do not produce oxygen (anoxygenic photosynthesis), whereas cyanobacteria do (oxygenic photosynthesis) Cyanobacteria Believed to be the first organisms capable of carrying out oxygenic photosynthesis When appropriate conditions exist in a pond or lake, a water bloom will occur Perform nitrogen fixation Produce toxins Include pruple, green, cyanobacteria (blue-green algea) Three groups all use light as an energy source but they do not all carry out photostynthsis in the same way Purple and green do not produce oxygen (anoxygenic photosynthesis) but cyanobacteria do (oxygenic photosynthesis) Cyanobacteria Many scientist belive cyanotbacteria were the first organisms capable of carry out oxygenic photosynthesis and played a major part in the oxgeneation of the atmosphere When appropriate conditions exist cyanobacteria in a pond or lake water will overgrow, creating a water bloom (pond scum) that resuembles a thick layer of bluish green oil pain Many do nitrogen fixation Some produce toxins that can cause diase and death in wildfife species and humans that consume contaminated water Many scientist are concerned that global warming will lead to increase in these poluation and then toxins

Domain Archaea Archaea (meaning “ancient”)
they are prokaryotic organisms. Genetically, archaea are more closely related to eukaryotes than they are to bacteria. Archaea vary widely in shape; some live in extreme environments, such as extremely acidic, extremely hot, or extremely salty environments. Archaea possess cell walls, but their cell walls do not contain peptidoglycan (in contrast, all bacterial cell walls contain peptidoglycan) Archae means ancient Originally through they evolved before bacteria, but now that is a subject of debate More closely related to eukaryotes genetically Some possess genes otherwise found only in eukaryotes Contains 2 phyla 8 classes 12 orders 21 families 69 genera 217 species Vary in shape Cocci, bacilli, other form long filaments some are extremophoiles Table 4-10 live in extreme environments Some live at the bottom of the ocean in and near thermal vents Methanogens – produce methane Possess cell walls but do not contain peptidoglycan Ribosomes are more similar to eukaryotes than bacteria

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