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Category: Applied and Industrial Microbiology; Clinical Microbiology
Introduction, Page 1 of 2
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Microbiology is the study of microscopic organisms (microorganisms). Microorganisms play important roles in our lives, both for our benefit as well as to our detriment. Of primary consideration are those microorganisms that cause diseases under a variety of circumstances. Other issues include the economic aspects associated with microbial contamination such as food spoilage, plant infections, and surface damage. The control of microorganisms is therefore an important concern, in preventing contamination as well as removing or reducing it when it occurs. A variety of physical and chemical methods are used for these purposes in antisepsis, disinfection, and sterilization applications. Disinfection and sterilization are used for the control of microorganisms on surfaces, in liquids, or in areas, while antisepsis is particularly associated with microbial reduction on the skin or mucous membranes. These antimicrobial applications can include skin washing, wound treatment, product preservation, food and water disinfection, surface disinfection, and product sterilization. Many of these processes have been used historically, being described in ancient texts before we had any true understanding of the nature of microorganisms. Despite this, it is only in the past 160 years, as our knowledge and understanding of microbiology have expanded, that the impact of antiseptics, disinfectants, and sterilization has been truly appreciated. Their utilization has played and continues to play an important role in significantly reducing the incidence of infectious diseases, including gastroenteritis, health care-acquired infections, and pneumonia. Today microorganisms continue to be a significant cause of morbidity, mortality, and economic loss. We continue to be challenged with the identification of new strains of microorganisms such as antibiotic-resistant Enterobacteriaceae (e.g., strains of Escherichia coli and Klebsiella pneumoniae), Clostridium difficile, viruses (e.g., Ebola, influenza, Zika virus, coronaviruses, and parvoviruses), protozoa such as Acanthamoeba and their internal communities of microorganisms, and proteinaceous infectious agents (such as prions).
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A typical helminth life cycle (example: Enterobius vermicularis).
A typical helminth life cycle (example: Enterobius vermicularis).
Typical fungal structures. On the left, filamentous fungus (molds). Hyphae are shown as long lines of unseparated cells, with the development of a fruiting body with attached spores. On the right, typical unicellular fungal (yeast) cells. Cells are generally polymorphic. In two cases, budding cells are shown. Image on right courtesy of CDC-PHIL/Dr. Libero Ajello, 1972 (ID#4219), with permission.
Typical fungal structures. On the left, filamentous fungus (molds). Hyphae are shown as long lines of unseparated cells, with the development of a fruiting body with attached spores. On the right, typical unicellular fungal (yeast) cells. Cells are generally polymorphic. In two cases, budding cells are shown. Image on right courtesy of CDC-PHIL/Dr. Libero Ajello, 1972 (ID#4219), with permission.
Simplified fungal cell envelope. The cross-linked cell wall is associated with the inner cell membrane. The cell wall usually consists of the innermost fibrils of chitin or cellulose, with outer layers of amorphous, cross-linked glucans.
Simplified fungal cell envelope. The cross-linked cell wall is associated with the inner cell membrane. The cell wall usually consists of the innermost fibrils of chitin or cellulose, with outer layers of amorphous, cross-linked glucans.
Life cycle of Toxoplasma gondii.
Life cycle of Toxoplasma gondii.
Simple representation of a mycoplasma cell surface structure.
Simple representation of a mycoplasma cell surface structure.
Basic structure of a bacterial cell, showing the cell surface in greater detail.
Basic structure of a bacterial cell, showing the cell surface in greater detail.
Bacterial cell wall structures. The cell membrane is a similar structure in all types. Gram-positive bacteria have a large peptidoglycan layer (shown as crossed lines) with associated polysaccharides and proteins. Gram-negative bacteria have a smaller peptidoglycan layer linked to an outer membrane. The mycobacterial cell has a series of covalently linked layers, including the peptidoglycan-, arabinogalactan- and mycolic acid-containing components.
Bacterial cell wall structures. The cell membrane is a similar structure in all types. Gram-positive bacteria have a large peptidoglycan layer (shown as crossed lines) with associated polysaccharides and proteins. Gram-negative bacteria have a smaller peptidoglycan layer linked to an outer membrane. The mycobacterial cell has a series of covalently linked layers, including the peptidoglycan-, arabinogalactan- and mycolic acid-containing components.
Basic structure of peptidoglycan. Polysaccharides of repeating sugars are cross-linked by peptide bridges. Two different types of peptide bridges, which have been described in Gram-positive and Gram-negative bacterial cell walls, are shown.
Basic structure of peptidoglycan. Polysaccharides of repeating sugars are cross-linked by peptide bridges. Two different types of peptide bridges, which have been described in Gram-positive and Gram-negative bacterial cell walls, are shown.
Cells of M. tuberculosis. Courtesy of Clifton Barry, NIAID.
Cells of M. tuberculosis. Courtesy of Clifton Barry, NIAID.
Basic viral structures.
Basic viral structures.
Typical viral life cycle. Stages include (1) attachment, (2) penetration into the cell, and (3) multiplication. Depending on the virus type, viral particles can be released by cell lysis (4a) or by budding (4b); alternatively, the virus can remain dormant in the cell (4c).
Typical viral life cycle. Stages include (1) attachment, (2) penetration into the cell, and (3) multiplication. Depending on the virus type, viral particles can be released by cell lysis (4a) or by budding (4b); alternatively, the virus can remain dormant in the cell (4c).
E. coli bacteriophages. The T phages are complex DNA viruses; MS2 and ɸ6 are RNA viruses, with ɸ6 being enveloped.
E. coli bacteriophages. The T phages are complex DNA viruses; MS2 and ɸ6 are RNA viruses, with ɸ6 being enveloped.
Theory of prions as infectious proteins. PrPc is the normal form of the protein, and PrPres is the abnormal form.
Theory of prions as infectious proteins. PrPc is the normal form of the protein, and PrPres is the abnormal form.
A representation of the proposed secondary structure changes in the two forms of the prion protein, PrP.
A representation of the proposed secondary structure changes in the two forms of the prion protein, PrP.
The general structure of LPS, a bacterial endotoxin.
The general structure of LPS, a bacterial endotoxin.
Typical fungal aflatoxin structure.
Typical fungal aflatoxin structure.
General microbial resistance to biocides and biocidal processes. This classification can vary depending on the biocide or biocidal process under consideration.
General microbial resistance to biocides and biocidal processes. This classification can vary depending on the biocide or biocidal process under consideration.
A typical time-kill or D-value determination. A known concentration of the test culture is exposed to the biocide (in this case a chemical solution), samples are withdrawn at various times, they are neutralized, and the population of survivors is determined by incubation on growth media. The actual exposure can be conducted at various temperatures, in the presence/absence of test soils, or other test conditions.
A typical time-kill or D-value determination. A known concentration of the test culture is exposed to the biocide (in this case a chemical solution), samples are withdrawn at various times, they are neutralized, and the population of survivors is determined by incubation on growth media. The actual exposure can be conducted at various temperatures, in the presence/absence of test soils, or other test conditions.
Determination of the D value on microbial exposure to a biocide.
Determination of the D value on microbial exposure to a biocide.
Typical survivor curves on biocide exposure. Curve 1 is concave downward, curve 2 is sigmoidal, and curve 3 is concave upward.
Typical survivor curves on biocide exposure. Curve 1 is concave downward, curve 2 is sigmoidal, and curve 3 is concave upward.
Qualitative and semiquantitative population determination.
Qualitative and semiquantitative population determination.
D-value estimation using most probable number estimations.
D-value estimation using most probable number estimations.
Example of biological indicators, including (from left to right) simple inoculated thread, coupons and wires, paper in sealed pouches (center), and two examples of self-contained biological indicators (with a rapid-read example on the far right). Far right image courtesy of 3M Health Care, with permission.
Example of biological indicators, including (from left to right) simple inoculated thread, coupons and wires, paper in sealed pouches (center), and two examples of self-contained biological indicators (with a rapid-read example on the far right). Far right image courtesy of 3M Health Care, with permission.
Example of a chemical indicator color change.
Example of a chemical indicator color change.
The rate of microbial inactivation on exposure to sterilization processes. In this case, the test microorganism (generally bacterial spores) at a starting population of 106 is exposed to the sterilizing agent under two conditions (A and B). The number of microorganisms can be determined over the contact time with or dose of the antimicrobial using a combination of direct enumeration and fraction negative methods (solid lines). Note that the microbial population (y axis) is plotted in a log10 scale. In process A, “tailing” is observed which may not allow the extrapolation of the kill curve to a defined probability of survival (known as a sterility assurance level, SAL). In process B, the kill curve is linear, allowing extrapolation (dotted line) to an SAL of 10−6.
The rate of microbial inactivation on exposure to sterilization processes. In this case, the test microorganism (generally bacterial spores) at a starting population of 106 is exposed to the sterilizing agent under two conditions (A and B). The number of microorganisms can be determined over the contact time with or dose of the antimicrobial using a combination of direct enumeration and fraction negative methods (solid lines). Note that the microbial population (y axis) is plotted in a log10 scale. In process A, “tailing” is observed which may not allow the extrapolation of the kill curve to a defined probability of survival (known as a sterility assurance level, SAL). In process B, the kill curve is linear, allowing extrapolation (dotted line) to an SAL of 10−6.
Basic structures of surfactants/soaps and micelles (a water-in-oil micelle is shown).
Basic structures of surfactants/soaps and micelles (a water-in-oil micelle is shown).
Examples of single-chamber (left) and multiple-chamber (right) washer-disinfector machines. Washer-disinfectors come in a variety of shapes and sizes depending on their required use. Images courtesy of STERIS, and ©2017 Getinge AB, with permission.
Examples of single-chamber (left) and multiple-chamber (right) washer-disinfector machines. Washer-disinfectors come in a variety of shapes and sizes depending on their required use. Images courtesy of STERIS, and ©2017 Getinge AB, with permission.
Various types of cleaning chemistries. Image courtesy of STERIS, with permission.
Various types of cleaning chemistries. Image courtesy of STERIS, with permission.
Examples of various types of microorganisms
Examples of various types of microorganisms
Some advantages and disadvantages of microorganisms
Some advantages and disadvantages of microorganisms
Comparison of general prokaryotic and eukaryotic structures a
Comparison of general prokaryotic and eukaryotic structures a
Helminths associated with disease
Helminths associated with disease
Examples of common fungi
Examples of common fungi
Classification of protozoa, based on their motility mechanisms and microscopic morphologies
Classification of protozoa, based on their motility mechanisms and microscopic morphologies
Examples of pathogenic mycoplasmas
Examples of pathogenic mycoplasmas
General differentiation of bacteria types based on their microscopic morphology and reaction to Gram staining
General differentiation of bacteria types based on their microscopic morphology and reaction to Gram staining
Examples of Gram-positive bacteria
Examples of Gram-positive bacteria
Examples of Gram-negative bacteria
Examples of Gram-negative bacteria
Cell wall structures in mycobacteria and other related organisms
Cell wall structures in mycobacteria and other related organisms
Examples of extremophile archaea
Examples of extremophile archaea
Viral families with examples of classifications
Viral families with examples of classifications
Examples of viral diseases
Examples of viral diseases
Examples of bacterial, fungal, and algal toxins
Examples of bacterial, fungal, and algal toxins
Examples of bacterial exotoxins and their clinical effects
Examples of bacterial exotoxins and their clinical effects
Examples of surrogate microorganisms used to test and verify the antimicrobial activity of biocide products and processes
Examples of surrogate microorganisms used to test and verify the antimicrobial activity of biocide products and processes
Examples of standardized suspension tests
Examples of standardized suspension tests
Examples of standardized carrier tests
Examples of standardized carrier tests
Examples of simulated-use and/or in-use tests and/or guidelines. Simulated testing uses an artificial inoculum and in-use testing uses the normal bioburden present on a surface or device
Examples of simulated-use and/or in-use tests and/or guidelines. Simulated testing uses an artificial inoculum and in-use testing uses the normal bioburden present on a surface or device
Bacterial endospore species used to monitor and validate sterilization processes
Bacterial endospore species used to monitor and validate sterilization processes
Examples of biological indicator standards
Examples of biological indicator standards
An example of the classification of chemical indicators (in accordance with ISO 11140-1)
An example of the classification of chemical indicators (in accordance with ISO 11140-1)
Examples of chemical indicator standards
Examples of chemical indicator standards
Examples of guidelines, standards, and requirements for antisepsis, disinfection, and sterilization
Examples of guidelines, standards, and requirements for antisepsis, disinfection, and sterilization
Various constituents of formulated biocidal product
Various constituents of formulated biocidal product
Examples of process variables in various disinfection and sterilization techniques
Examples of process variables in various disinfection and sterilization techniques
Various components of cleaning formulations
Various components of cleaning formulations
Examples of common water contaminants and their consequences
Examples of common water contaminants and their consequences