Lecture 22: Important Fields of Microbiology (PDF)

MICR 0490-105 Microbiology Lecture 22 Important Fields of Microbiology  Summary of lecture 3 ⚫ Microbial Pathogenicity ⚫ Microbial Diseases ⚫ Host Immunity ⚫ Microbial Interactions and Symbiosis ⚫ Microbial Ecology ⚫ Microbial Biotechnology ⚫ Applied Environmental M...

MICR 0490-105 Microbiology Lecture 22 Important Fields of Microbiology  Summary of lecture 3 ⚫ Microbial Pathogenicity ⚫ Microbial Diseases ⚫ Host Immunity ⚫ Microbial Interactions and Symbiosis ⚫ Microbial Ecology ⚫ Microbial Biotechnology ⚫ Applied Environmental Microbiology Microbial Pathogenicity ⚫ Infection When a pathogenic microorganism is growing and multiplying on or within a larger organism, the latter, known as the host, is said to have an infection that may result in a disease. ⚫ Pathogen and pathogenicity Any organism that causes disease is known as a pathogen (Greek patho, disease; gennan, to produce), and its ability to cause disease is called pathogenicity. ⚫ Virulence The degree of pathogenicity or how much harm a pathogen can cause i.e. it is the severity of a pathogen. ⚫ Infectious disease An infectious disease is any change from a state of health in which part or all of the host is incapable of carrying on its normal functions due to the presence of a pathogen or its products (e.g., toxins). ⚫ Opportunistic pathogens Resident microbiota, such as those associated with the gut or skin, can become opportunistic pathogens if they infect a host away from their typical niche, especially in a host with a weakened immune system (a compromised host). Microbial Diseases Types of diseases ⚫ When a disease occurs occasionally or at irregular intervals in a human population, it is a sporadic disease (e.g., bacterial meningitis). ⚫ When a disease maintains a steady, low-level frequency at a moderately regular interval, it is an endemic (Greek endemos, dwelling in the same people) disease (e.g., the common cold). ⚫ Hyperendemic diseases gradually increase in frequency beyond the endemic level but not to the epidemic level (e.g., the common cold during winter months). ⚫ An outbreak is the sudden, unexpected occurrence of a disease, usually in a limited segment of a population (e.g., consumption of contaminated produce). ⚫ An epidemic (Greek epidemios, upon the people), on the other hand, is an outbreak affecting many people at once. Influenza is an example of a disease that often achieves epidemic status in a community. ⚫ The influenza virus resides in a reservoir host, an organism that remains healthy while the virus thrives, until it is transmitted to a human host. ⚫ A pandemic (Greek pan, all) is an increase in disease occurrence within a large population over at least two countries around the world. Transmission of diseases ⚫ Transmission occurs either directly or indirectly by four main routes/modes: Airborne disease transmission. Disease transmission via contact. Disease transmission by vehicles. Vector-borne disease transmission. Vertical transmission. Pregnant women can also pass on a pathogen to their unborn child. ⚫ Extensive multiplication within the host will increase the efficiency of transmission. Factors affecting virulence Type of virulence factor. Some virulence factors are stronger than others. Number of virulence factors present in a pathogen. Mode of transmission can increase the pathogen virulence. Ability of a pathogen to live outside its host. The longer the pathogen can survive outside the host, the more its virulence. For example, the causative agents of tuberculosis, diphtheria, and measles can survive for a relatively long time. Ability of virulence factors to transfer between pathogens. Many bacterial virulence factors that facilitate survival are readily transferred between bacteria through conjugation, transduction, or transformation (horizontal gene transfer). Airborne Transmission ⚫ Because air is not a suitable medium for the growth of pathogens, any pathogen that is airborne must have originated from a source such as humans, other animals, plants, soil, food, or water. ⚫ In airborne transmission, the pathogen is suspended in the air in droplets, droplet nuclei, or dust. Droplets form from saliva, mucus, and other body fluids. Because of their size, droplets require close proximity for transfer between hosts (less than 1 meter) and are therefore considered to be transmitted directly. Contact Transmission ⚫ Contact transmission implies the host touching, either directly, or indirectly, the source or reservoir of the pathogen. Direct contact transmission requires an actual physical interaction with the infectious source (figure 34.2). ⚫ It is frequently called person-to-person contact. Person-to-person transmission occurs primarily by: touching, kissing, or sexual contact (e.g., gonorrhea, mononucleosis); by contact with oral secretions or body lesions (e.g., herpes and boils); by nursing mothers (e.g., HIV, staphylococcal infections); and through the placenta (e.g., syphilis; see Vertical Transmission) or during birth (e.g., group B streptococcus). Vehicle Transmission ⚫ Materials that indirectly transmit pathogens from a source are called vehicles. ⚫ Vehicles that can spread/transmit pathogens to many hosts are considered common vehicles e.g. fomites, air, food, water and biological materials. ⚫ A fomite, spreads the pathogen to multiple hosts. Examples of fomites include surgical instruments, drinking vessels, stethoscopes, bedding, eating utensils, and clothing. ⚫ Aerosolized agents traveling greater than 1 meter to reach a new host are using the air as a vehicle. Sources of pathogens A single source containing pathogens (e.g., blood, drugs, intravenous fluids) can contaminate a common vehicle that causes multiple infections. Multiple sources containing pathogens. Vector-Borne Transmission ⚫ Living organisms that can transmit a pathogen are called vectors. ⚫ Most vectors are: Arthropods (e.g., insects, ticks, mites, fleas). Vertebrates (e.g., dogs, cats, skunks, bats). ⚫ Vector-borne transmission often permit extensive reproduction and spread of the pathogen across hosts. ⚫ If pathogen levels are very high in the host, a vector such as a biting insect has a better chance of picking up the pathogen and transferring it to a new host. These pathogens are highly virulent such as in the case of malaria, typhus, and sleeping sickness. ⚫ Generally, vectors remains healthy at least long enough for pathogen transmission. Vertical Transmission ⚫ Vertical transmission of pathogens occurs when an unborn child acquires a pathogen from its infected mother. ⚫ Babies born with an infectious disease are said to have a congenital (Latin, congenitus; born together) infection. ⚫ Examples of congenital infections include gonorrhea, syphilis, herpes, German measles, and toxoplasmosis. Host Immunity  Host body reaction to Infection ⚫ The human body is equipped with mechanisms to get rid of any foreign molecules called antigens e.g. pathogenic microorganisms, viruses, toxins that enter the body. ⚫ These mechanisms are called body immune responses. ⚫ The ability of the host to get rid of foreign molecules and resist infection/disease is called immunity. ⚫ The study of the immune response to infection/disease is called immunology. ⚫ When a pathogenic microorganism is growing and multiplying on or within a larger organism, the latter, known as the host, is said to have an infection that may result in a disease. ⚫ There are two different yet complementary components of the immune response: Innate immunity ⚫ It is the first line of defence against any foreign material encountered by the host. ⚫ It includes general mechanisms such as skin, mucus, constitutively produced antimicrobial chemicals, and proteins of the complement system. ⚫ The complement system proteins help to: recruit white blood cells (WBCs, leukocytes) lysing microbial cells promoting phagocytosis (engulfment and killing) of microbial invaders. ⚫ Phagocytosis takes place by different types of WBCs that can attack, engulf and kill foreign invaders. ⚫ Phagocytosis was discovered by Metchnikoff in 1884.  Adaptive immunity ⚫ It is the second line of defence. ⚫ It includes specific mechanisms each against specific foreign invaders. ⚫ Activated by cells and chemicals of innate immunity. ⚫ Amplify a variety of cellular and chemical responses. ⚫ The effectiveness of adaptive immune responses increases if the host encounters the specific foreign agent again i.e. the adaptive immune system can remember the invaders. ⚫ Adaptive immunity cells: (discovered in 1950) Certain WBCs called T lymphocytes. Certain WBCs called B lymphocytes that differentiate into plasma cells that produce antibodies. Microbe-microbe Interactions and Symbiosis Symbiosis ⚫ Symbiosis is the stable association of one microorganism with another. ⚫ The symbiotic interactions can be beneficial, neutral, or has a negative impact. ⚫ The symbiotic interactions may shift with environmental conditions and community structure. ⚫ The symbiotic interactions can be facultative or obligatory. ⚫ Facultative interaction means that the microbe has alternative lifestyles. This is illustrated by Rhizobium spp. that inhabit soil as free-living bacteria, but also thrive within the nodules (i.e. symbiont) of leguminous plants. ⚫ Viruses exemplify obligatory interactions—that is, a host cell is an absolute requirement for viral replication and it cannot live outside the host cell. Likewise, many bacteria that live within eukaryotic cells are obligate intracellular symbionts. Mutualism ⚫ Mutualism defines the relationship in which some mutual benefit takes place to both partners. ⚫ Mutualism is an obligatory relationship in which the microorganisms are dependent on each other and cannot survive when separated. Cooperation ⚫ Cooperation is a non-obligatory relationship in which some mutual benefit takes place to both partners. Antagonism ⚫ Antagonism is a relationships in which one microorganism negatively impacts another by using defensive strategy. Microbial Ecology Biogeochemical cycling ⚫ Biogeochemical cycling of nutrients in the environment that involves: movement of nutrients (from one location to another), transformation (chemical changes via non-biological agents e.g. light) biotransformation (chemical change via organisms and microorganisms) of nutrients (inorganic and organic). Microbial Biotechnology Microbial biotechnology It is the field of microbiology that harnesses the capacity of microbes to synthesize compounds that have important applications in medicine, agriculture, food preparation, and other industrial processes. These compounds are commonly called natural products. Also, microbial biotechnology shows how microorganisms (or their genes) are optimized for industrial manufacturing. Antibiotics More than 65% of all antibiotics are produced by members of the genus Streptomyces and by filamentous fungi. Antibiotics are secreted by these microbes and are used clinically either in their native state or are chemically modified to produce semisynthetic derivatives. Amino Acids Amino acids such as lysine and glutamic acid are used in the food industry as nutritional supplements in bread products and as flavour-enhancing compounds such as monosodium glutamate (MSG). Organic Acids ⚫ Most processed foods contain organic acids such as citric, acetic, and lactic acids that are principally used as preservatives. ⚫ Citric acid (citrate), is produced from Aspergillus niger growing under high sugar concentrations. Enzymes ⚫ Industrial enzymes are used in a variety of processes in the pharmaceutical, agricultural, food, and consumer products industries, with a global market of about $5 billion annually. ⚫ The vast majority of the enzymes are bacterial and fungal in origin, and are classified as hydrolases. These enzymes break down natural polymers such as starches and proteins. ⚫ In many industrial biocatalysis processes, enzyme-catalyzed reactions substitute for chemical treatments, offering benefits like reduced cost, reduced toxic by- products, and improved quality and safety. Biofuels ⚫ Microbial energy conversion includes the microbial transformation of organic materials into biofuels, such as ethanol and hydrogen, that can fuel cars or other machines. ⚫ Corn is the substrate most commonly used for generating ethanol in the United States, while sugar cane and palm oil are used in other countries. ⚫ As an alternative to plant starch from corn, cellulose from crop residue is being developed for biofuel production. Applied Environmental Microbiology Applied environmental microbiology deals with the following topics: Purification and sanitary analysis of drinking water. ⚫ Drinking water is purified from all harmful molecules and particles. ⚫ Microorganisms and viruses are removed from drinking water by: [i] Filtration [ii] Chlorination Wastewater treatment. ⚫ Wastewater produced from the use of humans are treated by physical, chemical and microbial methods. Bacterial production of electricity. ⚫ Some heterotrophic microorganisms oxidize organic material and can pass the electrons to an electrode. A microbial fuel cell (MFC) captures these electrons to generate electricity. Bioremediation of polluted environments. ⚫ Harmful organic (e.g. crude oil and plastics) and inorganic (e.g. heavy metals) compounds found in the environment can be removed/remediated by living organisms especially microorganisms.