Burton's Microbiology for the Health Sciences Chapter 4 PDF

Burton's Microbiology for the Health Sciences Chapter 4. Microbial Diversity Part 1: Acellular and Procaryotic Microbes Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Chapter 4 Outline Introduction Acellular Infectious Agents – Viruses – Viroids and Prions The Domain Bacteria...

Burton's Microbiology for the Health Sciences Chapter 4. Microbial Diversity Part 1: Acellular and Procaryotic Microbes Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Chapter 4 Outline Introduction Acellular Infectious Agents – Viruses – Viroids and Prions The Domain Bacteria – Characteristics – Unique Bacteria – Photosynthetic Bacteria The Domain Archaea Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Categories of Microorganisms 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 procaryotic (bacteria and archaea) and those that are eucaryotic (algae, protozoa, and fungi). Viruses, viroids and prions are often referred to as acellular microbes or infectious particles. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Acellular Microbes Viruses – Complete virus particles are called virions. – Most viruses are from 10 to 300 nm in diameter. – Viruses infect humans, animals, plants, fungi, protozoa, algae and bacterial cells. – 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. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Viruses: - These are very different from other groups of M.O.s in terms of their structure and the way in which they function. - Viruses are exceptionally small, varying in size within the range of 20-300 nm in diameter. - They can only be seen by the electron microscope. - Viruses simply consist of a protein coat, called a capsid, made up of a number of protein subunits (capsomeres) that enclose a central core of nucleic acid. - This nucleic acid is either DNA or RNA. - In other M.O.s we expect to find both DNA and RNA, with DNA functioning as the primary genetic material and RNA playing the role of translating DNA information into proteins. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins - In viruses, either DNA or RNA forms a template for the production of new viral nucleic acid and protein. - In addition to the protein coat and nucleic acid, viruses may contain one or two enzymes associated with infection of host cells. - Some viruses are surrounded by an envelope made of lipoprotein derived from the host cell membrane and incorporating viral protein. - Some viral envelopes are covered with spikes made of a carbohydrate-protein complex that functions to attach the viruses to their host cells. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Acellular Microbes, cont. Viruses have 5 properties that distinguish them from living cells: 1. They possess either DNA or RNA – living cells possess both. 2. They are unable to replicate on their own. 3. Unlike cells, they do not divide by binary fission, mitosis, or meiosis. 4. They lack the genes and enzymes necessary for energy production. 5. They depend on the ribosomes, enzymes, and metabolites of the host cell for protein and nucleic acid production. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Acellular Microbes, cont. 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 Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Acellular Microbes, cont. Viruses – There are 4 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 viruses Single-stranded RNA viruses Single-stranded DNA viruses Double-stranded RNA viruses – Most viral genomes are circular molecules, but some are linear. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Comparative sizes of virions, their nucleic acids, and bacteria. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Acellular Microbes, cont. Bacteriophages     Viruses that infect bacteria are known as bacteriophages or simply phages. There are two categories of bacteriophages: virulent bacteriophages and temperate bacteriophages. Virulent bacteriophages always cause what is known as the lytic cycle, which ends with the destruction of the bacterial cell. The 5 steps in the lytic cycle are:      attachment, penetration, biosynthesis, assembly, and; release. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins A partially lysed cell of Vibrio cholerae with attached virions of phage CP-T1. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins The bacteriophage T4 is an assembly of protein components. Viral DNA enters the cell through the core. 20 facets, filled with DNA Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Acellular Microbes, cont. Animal Viruses – The steps in multiplication of animal viruses are: Attachment Penetration Uncoating Biosynthesis Assembly – Animal viruses escape from their host cells either by lysis of the cell or budding. Viruses that escape by budding become enveloped viruses. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Multiplication of Herpes Simplex on HeLa Cells Adsorption Penetration Penetration Uncoating Uncoating Uncoating Penetration Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Acellular Microbes, cont. 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. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Acellular Microbes, cont. 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. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Acellular Microbes, cont. Oncogenic Viruses or Oncoviruses – Viruses that cause cancer. – Examples include Epstein-Barr virus, human papillomaviruses, and HTLV-1. Human Immunodeficiency Virus (HIV) – The cause of acquired immunodeficiency syndrome (AIDS). – It is an enveloped, single-stranded RNA virus. – The primary targets for HIV are CD4+ cells. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Human Immunodeficiency Virus (HIV) Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Acellular Microbes, cont. Viroids and Prions (smaller and less complex infectious particles than viruses) – Viroids Viroids are short, naked fragments of singlestranded 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: potato spindle tuber and citrus exocortis. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Acellular Microbes, cont. Prions – Prions are small infectious proteins that cause fatal neurologic diseases in animals; examples: Scrapie, Bovine Spongiform Encephalopathy (“Mad Cow Disease”) and Creutzfeldt-Jacob disease. – Of all pathogens, prions are the most resistant to disinfectants. – The mechanism by which prions cause disease remains a mystery. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins The Domain Bacteria Characteristics Bacteria are divided into 3 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. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins The Domain Bacteria Cell Morphology There are 3 basic categories of bacteria, based on shape: – Cocci (round bacteria) – Bacilli (rod-shaped bacteria) – Curved and spiral-shaped bacteria Cocci may be seen singly or in pairs (diplococci), chains (streptococci), clusters (staphylococci), packets of 4 (tetrads), or packets of 8 (octads). The average coccus is about 1 µm in diameter. Some cocci have “coccus” in their name. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Categories of Bacteria Based on the Shape of Their Cells Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Morphologic Arrangements of Cocci Gram-positive Staphylococcus aureus in clusters. SEM of Streptococcus mutans illustrating cocci in chains. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Diagram Showing Various Forms of Bacteria That Might be Observed in GramStained Smears Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins The Domain Bacteria Cell Morphology, cont. Bacilli – Often referred to as rods; 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. – An average sized bacillus is 1 x 3 µm. – Extremely short bacilli are called coccobacilli. – Examples of medically important bacilli: Escherichia, Klebsiella, and Proteus spp. Pseudomonas, Haemophilus, and Bacillus spp. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins The Domain Bacteria Cell Morphology, cont. Curved and Spiral-Shaped Bacteria – Examples of curved bacteria: Vibrio spp. Campylobacter spp. Helicobacter spp. – Examples of spiral-shaped bacteria: Treponema spp. Borrelia spp. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Spiral-Shaped Bacteria Borrelia hermsii in a stained blood smear; a cause of relapsing fever. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins 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 to 10%) Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Domain Bacteria Nutritional Requirements All bacteria need some form of the elements carbon, hydrogen, oxygen, sulfur, phosphorus, and nitrogen for growth. Some bacteria require special elements (e.g., calcium, iron, or zinc). 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. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Domain Bacteria Biochemical and Metabolic Activities As bacteria grow, they produce many waste products and secretions, some of which are enzymes. Pathogenic strains of many bacteria, like 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 lab, 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. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins 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, Treponema pallidum Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Domain Bacteria Genetic Composition Laboratory identification of bacteria is moving toward analyzing the organism’s DNA or RNA – techniques collectively referred to as molecular diagnostic procedures. – The composition of the genetic material (DNA) of an organism is unique to each species. – DNA probes make it possible to identify an isolate without relying on phenotypic characteristics. Through the use of 16S rRNA sequencing, the degree of relatedness between 2 different bacteria can be determined. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins 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 (i.e., they must live within a host cell; they cannot grow on artificial culture media). – Rickettsias have “leaky membranes.” – Chlamydias are “energy parasites,” meaning they prefer to use ATP molecules produced by their host cell. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Rickettsia prowazekii, the cause of epidemic louseborne typhus. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Unique Bacteria, cont. Mycoplasmas – Smallest of the cellular microbes – Lack a cell wall and therefore assume many shapes (they are pleomorphic) – In humans, pathogenic mycoplasmas cause primary atypical pneumonia and genito-urinary infections – Because they have no cell wall, they are resistant to drugs like penicillin that attack cell walls – They produce tiny “fried egg” colonies on artificial media Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins SEM of Mycoplasma pneumoniae Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Photosynthetic Bacteria Photosynthetic bacteria include: purple bacteria, green bacteria, and; Cyanobacteria; – They all use light as an energy source, but not in the same way. – Purple and green bacteria do not produce oxygen, whereas cyanobacteria do. – Photosynthesis that produces oxygen is called oxygenic photosynthesis. – Photosynthesis that does not produce oxygen is called anoxygenic photosynthesis. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins The Domain Archaea Archaea (meaning ancient) were discovered in 1977; they are procaryotic organisms. Genetically, archaea are more closely related to eucaryotes 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). Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins