Burton's Microbiology for the Health Sciences PDF

Burton’s Microbiology for the Health Sciences Microbial Diversity ❥ Acellular Microbes ✧ Viruses the study of viruses is what we call virology complete virus particles are called virio...

Burton’s Microbiology for the Health Sciences Microbial Diversity ❥ Acellular Microbes ✧ Viruses the study of viruses is what we call virology complete virus particles are called virions viruses infect humans, animals, plants fungi, protozoa, algae, and bacterial cells. a typical virion consist of a genome of either DNA or RNA, surrounded by a capsid (protein coat), which is composed of protein units called capsomeres. some viruses, calles oncogenic viruses or oncoviruses, cause specific types of cancer. Examples: Epstein-Barr virus, human paipillomaviruses, and human T-lymphotrophic virus type 1 (HTLV-1) Human immunodeficiency virus (HIV) the virus causes acquired immunodeficiency syndrome (AIDS) it is an enveloped, single-stranded RNA virus the primary targets for HIV are CD4+ cells—those having CD4 receptors on their surface latent infection (hindi gumagaling) Viruses have five properties that distinguish them form living cells: 1. they possess either DNA or RNA, whereas living cells possess both. 2. they are unable to replicate on their own. Burton’s Microbiology for the Health Sciences 1  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. 💡 They replicate by hyjacking the genetic sequence of people and the mechanism of the body. Antiretroviral = slows down the reproduction Virus Particle Becoming Enveloped 1. Virus-specific glycoproteins are synthesized and transported to the host cell membrane 2. The cytoplasmic domains of membrane proteins bind nucleocapsid. 3. A nucleocapsid is enveloped by the host cell membranes 4. the host cell membrane provides the viral envelope by a process of “budding”. 5. The enveloped virion is released form the host cell. Viruses are classified by: Type of genetic material (either DNA or RNA) shape and size of capsid number of capsomeres presence or absence of envelope type of host it infects disease it produces target cells immunologic/antigenic properties ✧ Bacteriophages Burton’s Microbiology for the Health Sciences 2  viruses that infect bacteria are known as bacteriophages or simply phages —2 categories: Virulent bacteriophages 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. ✧ 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 Example: Herpes viral infections once acquired, herpes virus infections never completely go away; for example, chickenpox may be followed, years later, by shingles—both the result if the same virus. ❥Treatment ✧ Antiviral agents antibiotics are not effective against viral infections—this is very important to remember. 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. The Domain Bacteria Characteristics the study of bacteria is what we call bacteriology bacteria are divided into 3 major phenotypic categories: Burton’s Microbiology for the Health Sciences 3  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 uses 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. Domain Bacteria Morphology these are 3 basic categories of bacteria based on shape: Cocci (round) Bacilli (rod-shaped) 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) Bacilli they are often referred to as rod; they may be short or long, thick or thin, and prointed or with curved or blunt ends. they may occur singly, in paris (diplobacilli). in chains (streptobacilli), in long filaments, or branched extremely short bacilli are called coccobacilli Examples of medically important bacilli: Esterichia, Klebsiella, Proteus, Pseudomonas, Haemophilus, and Bacillus spp. Curved and Spiral-shaped bacteria Examples of curved: Vibrio spp., campylobacter spp., helicobater spp. Burton’s Microbiology for the Health Sciences 4  Examples of spiral-shaped: Treponema spp., Borrelia spp. 💡 Spiral-shaped Bacteria: Borrelia hermsii, the cause of relapsing fever, in a staines blood smear. 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 grows best in the presence of increased concentrations of CO2 (usually 5-10%) Controlling Microbial Growth In Vitro and Inhibiting Microbes In Vivo and In Vitro Factors That Affect Microbial Growth Availability of nutrients All living organisms require nutrients to sustain life. Nutrients are energy sources. Organisms obtain energy by breaking chemical bonds. 1. Moisture Water is essential for life. It is needed to carry out normal metabolic processes. Burton’s Microbiology for the Health Sciences 5  Certain microbial stages (e.g., bacterial endospores and protozoal cysts) can survive a drying process (desiccation). 2. Temperature Every organism has an optimum growth temperature. Thermophiles are microorganisms that grow best at high temperatures. Mesophiles are microbes that grow best at moderate temperatures. Psychrophiles prefer cold temperatures (like deep ocean water). Psychroduric organisms prefer warm temperatures but can endure very cold or even freezing temperatures. 3. pH pH refers to the acidity or alkalinity of a solution. Most microorganisms prefer a neutral or slightly alkaline growth medium (pH 7.0-7.4). Acidophiles prefer a pH of 2 to 5 Alkaliphiles prefer a pH of > 8.5 4. Osmotic pressure and salinity Osmotic pressure is the pressure that is exerted on a cell membrane by solutions both inside and outside the cell. Osmosis is the movement of a solvent, through a permeable membrane, from a lower concentration of solutes (dissolved substances) to a higher concentration of solutes. When the concentration of solutes in the external environment of a cell is greater than that of solutes inside the cell, the solution in which the cell is suspended is said to be hypertonic. Plasmolysis/Crenation is a condition in which the cell membrane and cytoplasm of a cell shrink away from the cell wall; it occurs when bacteria with rigid cell walls are placed in a hypertonic solution. When the concentration of solutes outside a cell is less than that of solutes inside a cell, the solution in which the cell is suspended is Burton’s Microbiology for the Health Sciences 6  said to be hypotonic. If a bacterial cell is placed into a hypotonic solution, it may not burst (because of the rigid cell wall). If it does burst, and escapes the cytoplasm; this process is known as plasmoptysis. A solution is said to be isotonic when the concentration of solutes outside a cell equals the concentration of solutes inside the cell. 5. Gaseous atmosphere Microorganisms vary with respect to the type of gaseous atmosphere that they require. Obligate aerobes prefer the same atmosphere that humans do (~20%-21% Oz and 78%-79% N2, and