ASTM D6469 standard guide for microbial contamination in fuels and fuel systems
1. Scope
1.1 This guide provides personnel who have a limited microbiological background with an understanding of the symptoms, occurrence, and consequences of chronic microbial contamination. The guide also suggests means for detection and control of microbial contamination in fuels and fuel systems. This guide applies primarily to gasoline, aviation, boiler, industrial gas turbine, diesel, marine, and furnace fuels (see Specifications D396, D910, D975, D1655, D2069, D2880, D3699, D4814, and D6227) and fuel systems. However, the principals discussed herein also apply generally to crude oil and all liquid petroleum fuels.
1.2 This guide is not a compilation of all of the concepts and terminology used by microbiologists, but it does provide a general understanding of microbial fuel contamination.
1.3 The values in SI units are to be regarded as the standard.
1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
2. Referenced Documents
2.1 ASTM Standards:
D130 Test Method for Detection of Copper Corrosion from Petroleum Products by the Copper Strip Tarnish Test
D396 Specification for Fuel Oils
D445 Test Method for Kinematic Viscosity of Transparent of Opaque Liquids (the Calculation of Dynamic Viscosity)
D515 Test Methods for Phosphorus in Water
D664 Test Method for Acid Number of Petroleum Products by Potentiometric Titration
D888 Test Methods for Dissolved Oxygen in Water
D910 Specification for Aviation Gasolines
D974 Test Method for Acid and Base Number by Color-Indicator Titration
D975 Specification for Diesel Fuel Oils
D1067 Test Methods for Acidity or Alkalinity of Water
D1126 Test Method for Hardness in Water
D1293 Test Methods of pH of Water
D1298 Test Method for Density, Relative Density (Specific Gravity), or API Gravity of Crude Petroleum and Liquid Petroleum Products by Hydrometer Method
D1331 Test Methods for Surface and Interfacial Tension of Solutions of Surface-Active Agents
D1426 Test Methods for Ammonia Nitrogen in Water
D1655 Specification for Aviation Turbine Fuels
D1744 Test Method for Water in Liquid Petroleum Products by Karl Fischer Reagent
D1976 Test Method for Elements in Water by Inductively-Coupled Argon Plasma Atomic Emission Spectroscopy
D2068 Test Method for Filter Blocking Tendency of Distillate Fuel Oils
D2069 Specification for Marine Fuels
D2274 Test Method for Oxidation Stability of Distillate Fuel Oil (Accelerated Method)
D2276 Test Method for Particulate Contaminant in Aviation Fuel by Line Sampling
D2880 Specification for Gas Turbine Fuel Oils
D3240 Test Method for Undissolved Water in Aviation Turbine Fuels
D3241 Test Method for Thermal Oxidation Stability of Aviation Turbine Fuels (JFTOT Procedure)
D3242 Test Method for Acidity in Aviation Turbine Fuel
D3325 Practice for Preservation of Waterborne Oil Samples
D3326 Practice for Preparation of Samples for Identification of Waterborne Oils
D3328 Test Methods for Comparison of Waterborne Petroleum Oils by Gas Chromatography
D3414 Test Method for Comparison of Waterborne Petroleum Oils by Infrared Spectroscopy
D3699 Specification for Kerosine
D3867 Test Methods for Nitrite-Nitrate in Water
D3870 Practice for Establishing Performance Characteristics for Colony Counting Methods in Microbiology
D4012 Test Method for Adenosine Triphosphate (ATP) Content of Microorganisms in Water
D4057 Practice for Manual Sampling of Petroleum and Petroleum Products
D4176 Test Method for Free Water and Particulate Contamination in Distillate Fuels (Visual Inspection Procedures)
D4412 Test Methods for Sulfate-Reducing Bacteria in Water and Water-Formed Deposits
D4418 Practice for Receipt, Storage, and Handling of Fuels for Gas Turbines
D4454 Test Method for Simultaneous Enumeration of Total Respiring Bacteria in Aquatic Systems by Microscopy
D4478 Test Methods for Oxygen Uptake
D4814 Specification for Automotive Spark-Ignition Engine Fuel
D4840 Guide for Sampling Chain of Custody Procedures
D4860 Test Method for Free Water and Particulate Contamination in Mid-Distillate Fuels (Clear and Bright Numerical Rating)
D4870 Test Method for Determination of Total Sediment in Residual Fuels
D4952 Test Method for Qualitative Analysis for Active Sulfur Species in Fuels and Solvents (Doctor Test)
D5304 Test Method for Assessing Distillate Fuel Storage Stability by Oxygen Overpressure
D5452 Test Method for Particulate Contamination in Aviation Fuels by Laboratory Filtration
D6217 Test Method for Particulate Contamination in Middle Distillate Fuels by Laboratory Filtration
D6227 Specification for Grade 82 Unleaded Aviation Gasoline
D6426 Test Method for Determining Filterability of Distillate Fuel Oils
E 177 Practice for the Use of the Terms Precision and Bias in ASTM Test Methods
E 1259 Test Method for Evaluation of Antimicrobials in Distillate Fuels (Based on Preliminary Screening and Compatibility)
E 1326 Guide for Evaluating Nonconventional Microbio-logical Tests Used for Enumerating Bacteria
2.2 Institute of Petroleum Standards:
IP 385 Determination of the Viable Microbial Content of Fuels and Fuel Components Boiling Below 390°C - Filtration and Culture Method
IP Guidelines for the Investigation of the Microbial Content of Fuel Boiling Below 390°C and Associated Water
IP Proposed Method BY Determination of Fungal Fragment Content of Fuels Boiling Below 390°C
2.3 Government Standards:
40 CFR 79 Fuels and Fuel Additives Registration Regulations
40 CFR 152 Pesticide Registration and Classification Procedures
2.4 Other Standards:
Test Method 2540 D. Total Suspended Solids Dried at 103 - 105°C
3. Terminology
3.1 Definitions:
3.1.1 aerobe, n - an organism that requires oxygen to remain metabolically active.
3.1.1.1 Discussion - Aerobes use oxygen as their terminal electron acceptor in their primary energy-generating metabolic pathways. Aerobes require oxygen for survival, using aerobic metabolic processes to generate energy for growth and survival.
3.1.2 aggressiveness index (A.I.), n - the value computed from the sum of the pH + log alkalinity + log hardness of water sample where both alkalinity and hardness are reported as milligram CaCO3L.
3.1.2.1 Discussion - As A.I. decreases, water becomes more corrosive. At A.I. not less than 12, water is noncorrosive. At 10 not more than A.I. < 12, water is moderately corrosive. At A.I. < 10, water is strongly corrosive.
3.1.3 anaerobe, n - an organism that cannot grow or proliferate in the presence of oxygen.
3.1.3.1 Discussion - Anaerobes use molecules other than oxygen in their primary energy-generating metabolic pathways, such as sulfate, nitrate, ketones, and other high-energy organic molecules. Although anaerobes may survive in the presence of oxygen, anaerobic growth typically occurs only in an oxygen depleted environment.
3.1.4 anoxic, adj - oxygen free.
3.1.5 antimicrobial, n - see biocide.
3.1.6 bacterium (pl. bacteria), n - a single cell microorganism characterized by the absence of defined intracellular membranes that define all higher life forms.
3.1.6.1 Discussion - All bacteria are members of the biological diverse kingdoms Prokaryota and Archaebacteriota. Individual taxa within these kingdoms are able to thrive in environments ranging from sub-zero temperatures, such as in frozen foods and polar ice, to superheated waters in deep-sea thermal vents, and over the pH range <2.0 to> 13.0. Potential food sources range from single carbon molecules (carbon dioxide and methane) to complex polymers, including plastics. Oxygen requirements range from obligate anaerobes, which die on contact with oxygen, to obligate aerobes, which die if oxygen pressure falls below a species specific threshold.
3.1.7 bioburden, n - the level of microbial contamination (biomass) in a system.
3.1.7.1 Discussion - Typically, bioburden is defined in terms of either biomass or numbers of cells per unit volume or mass or surface area material tested (g biomass / mL; g biomass / g; cells / mL sample, and so forth). The specific parameter used to define bioburden depends on critical properties of the system evaluated and the investigator's preferences.
3.1.8 biocide, n - a poisonous substance that can kill living organisms.
3.1.8.1 Discussion - Biocides are further classified as bactericides (kill bacteria), fungicides (kill fungi), and microbiocides (kill both bacterial and fungi). They are also referred to as antimicrobials.
3.1.9 biodeterioration, n - the loss of commercial value or performance characteristics, or both, of a product (fuel) or material (fuel system) through biological processes.
3.1.10 biofilm, n - a film or layer of microorganisms, biopolymers, water, and entrained organic and inorganic debris that forms as a result of microbial growth and proliferation at phase interfaces (liquid-liquid, liquid-solid, liquid-gas, and so forth) (synonym: skinnogen layer).
3.1.11 biomass, n - density of biological material per unit sample volume, area, or mass (g biomass / g (or / mL or / cm2) sample).
3.1.12 biosurfactant, n - a biologically produced molecule that acts as a soap or detergent.
3.1.13 consortium (pl. consortia), n - microbial community comprised of more than one, species that exhibits properties not shown by individual community members.
3.1.13.1 Discussion - Consortia often mediate biodeterioration processes that individual taxa cannot.
3.1.14 depacifying, adj - the process of removing hydrogen ions (protons) from the cathodic surface of an electrolytic cell, thereby promoting continued electrolytic corrosion.
3.1.15 deplasticize, v - the process of breaking down polymers in plastics and similar materials, resulting in loss of the material's structural integrity.
3.1.16 facultative anaerobe, n - a microorganism capable of growing in both oxic and anoxic environments.
3.1.16.1 Discussion - Facultative anaerobes use oxygen when it is present, and use either organic or inorganic energy sources (nitrate, sulfate, and so forth) when oxygen is depleted or absent.
3.1.17 fungus (pl. fungi), n - single cell (yeasts) or filamentous (molds) microorganisms that share the property of having the true intracellular membranes (organelles) that characterize all higher life forms (Eukaryotes).
3.1.18 metabolite, n - a chemical substance produced by any of the many complex chemical and physical processes involved in the maintenance of life.
3.1.19 microbial activity test, n - any analytical procedure designed to measure the rate or results of one or more microorganism processes.
3.1.19.1 Discussion - Examples of microbial activity tests include loss or appearance of specific molecules or measuring the rate of change of parameters, such as acid number, molecular weight distribution (carbon number distribution), and specific gravity.
3.1.20 microbially induced corrosion (MIC), n - corrosion that is enhanced by the action of microorganisms in the local environment.
3.1.21 mold, n - form of fungal growth, characterized by long strands of filaments (hyphae) and, under appropriate growth conditions, aerial, spore-bearing structures.
3.1.21.1 Discussion - In fluids, mold colonies typically appear as soft spheres; termed fisheyes.
3.1.22 obligate aerobe, n - microorganism with an absolute requirement for atmospheric oxygen in order to function.
3.1.22.1 Discussion - Obligate aerobes may survive periods in anoxic environments but will remain dormant until sufficient oxygen is present to support their activity.
3.1.23 obligate anaerobe, n - microrganism that cannot function when atmospheric oxygen is present.
3.1.23.1 Discussion - Obligate anaerobes may survive periods in oxic environments but remain dormant until conditions become anoxic.
3.1.24 oxic, adj - an environment with a sufficient partial pressure of oxygen to support aerobic growth.
3.1.25 shock treatment, n - the addition of an antimicrobial agent sufficient to cause rapid and substantial (several orders of magnitude) reductions in number of living microbes in a fluid or system receiving that concentration.
3.1.26 skinnogen, n - synonymous with biofilm.
3.1.26.1 Discussion - Generally applied to a biofilm formed at the fuel-water interface.
3.1.27 sour, v - to increase the concentration of hydrogen sulfide.
3.1.28 sulfate reducing bacterial (SRB), pl., n - any bacteria with the capability of reducing sulfate to sulfide.
3.1.28.1 Discussion - The term SRB applies to representatives from a variety of bacterial taxa that share the common feature of sulfate reduction (SO4= to S=). SRB are major contributors to MIC.
3.1.29 taxa, pl., n - the units of classification of organisms, based on their relative similarities.
3.1.29.1 Discussion - Each taxonomic unit (group of organisms with greatest number of similarities) is assigned, beginning with the most inclusive to kingdom, division, class, order, family, genus, and species. Bacteria and fungi are often further classified by strain and biovariation.
3.1.30 viable titer, n - the number of living microbes present per unit volume, mass, or area.
3.1.30.1 Discussion - Viable titer is reported in terms of either colony forming units (CFU) or most probable number (MPN) per millilitre, milligram, or centimetre squared.
1. Scope
1.1 This guide provides personnel who have a limited microbiological background with an understanding of the symptoms, occurrence, and consequences of chronic microbial contamination. The guide also suggests means for detection and control of microbial contamination in fuels and fuel systems. This guide applies primarily to gasoline, aviation, boiler, industrial gas turbine, diesel, marine, and furnace fuels (see Specifications D396, D910, D975, D1655, D2069, D2880, D3699, D4814, and D6227) and fuel systems. However, the principals discussed herein also apply generally to crude oil and all liquid petroleum fuels.
1.2 This guide is not a compilation of all of the concepts and terminology used by microbiologists, but it does provide a general understanding of microbial fuel contamination.
1.3 The values in SI units are to be regarded as the standard.
1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
2. Referenced Documents
2.1 ASTM Standards:
D130 Test Method for Detection of Copper Corrosion from Petroleum Products by the Copper Strip Tarnish Test
D396 Specification for Fuel Oils
D445 Test Method for Kinematic Viscosity of Transparent of Opaque Liquids (the Calculation of Dynamic Viscosity)
D515 Test Methods for Phosphorus in Water
D664 Test Method for Acid Number of Petroleum Products by Potentiometric Titration
D888 Test Methods for Dissolved Oxygen in Water
D910 Specification for Aviation Gasolines
D974 Test Method for Acid and Base Number by Color-Indicator Titration
D975 Specification for Diesel Fuel Oils
D1067 Test Methods for Acidity or Alkalinity of Water
D1126 Test Method for Hardness in Water
D1293 Test Methods of pH of Water
D1298 Test Method for Density, Relative Density (Specific Gravity), or API Gravity of Crude Petroleum and Liquid Petroleum Products by Hydrometer Method
D1331 Test Methods for Surface and Interfacial Tension of Solutions of Surface-Active Agents
D1426 Test Methods for Ammonia Nitrogen in Water
D1655 Specification for Aviation Turbine Fuels
D1744 Test Method for Water in Liquid Petroleum Products by Karl Fischer Reagent
D1976 Test Method for Elements in Water by Inductively-Coupled Argon Plasma Atomic Emission Spectroscopy
D2068 Test Method for Filter Blocking Tendency of Distillate Fuel Oils
D2069 Specification for Marine Fuels
D2274 Test Method for Oxidation Stability of Distillate Fuel Oil (Accelerated Method)
D2276 Test Method for Particulate Contaminant in Aviation Fuel by Line Sampling
D2880 Specification for Gas Turbine Fuel Oils
D3240 Test Method for Undissolved Water in Aviation Turbine Fuels
D3241 Test Method for Thermal Oxidation Stability of Aviation Turbine Fuels (JFTOT Procedure)
D3242 Test Method for Acidity in Aviation Turbine Fuel
D3325 Practice for Preservation of Waterborne Oil Samples
D3326 Practice for Preparation of Samples for Identification of Waterborne Oils
D3328 Test Methods for Comparison of Waterborne Petroleum Oils by Gas Chromatography
D3414 Test Method for Comparison of Waterborne Petroleum Oils by Infrared Spectroscopy
D3699 Specification for Kerosine
D3867 Test Methods for Nitrite-Nitrate in Water
D3870 Practice for Establishing Performance Characteristics for Colony Counting Methods in Microbiology
D4012 Test Method for Adenosine Triphosphate (ATP) Content of Microorganisms in Water
D4057 Practice for Manual Sampling of Petroleum and Petroleum Products
D4176 Test Method for Free Water and Particulate Contamination in Distillate Fuels (Visual Inspection Procedures)
D4412 Test Methods for Sulfate-Reducing Bacteria in Water and Water-Formed Deposits
D4418 Practice for Receipt, Storage, and Handling of Fuels for Gas Turbines
D4454 Test Method for Simultaneous Enumeration of Total Respiring Bacteria in Aquatic Systems by Microscopy
D4478 Test Methods for Oxygen Uptake
D4814 Specification for Automotive Spark-Ignition Engine Fuel
D4840 Guide for Sampling Chain of Custody Procedures
D4860 Test Method for Free Water and Particulate Contamination in Mid-Distillate Fuels (Clear and Bright Numerical Rating)
D4870 Test Method for Determination of Total Sediment in Residual Fuels
D4952 Test Method for Qualitative Analysis for Active Sulfur Species in Fuels and Solvents (Doctor Test)
D5304 Test Method for Assessing Distillate Fuel Storage Stability by Oxygen Overpressure
D5452 Test Method for Particulate Contamination in Aviation Fuels by Laboratory Filtration
D6217 Test Method for Particulate Contamination in Middle Distillate Fuels by Laboratory Filtration
D6227 Specification for Grade 82 Unleaded Aviation Gasoline
D6426 Test Method for Determining Filterability of Distillate Fuel Oils
E 177 Practice for the Use of the Terms Precision and Bias in ASTM Test Methods
E 1259 Test Method for Evaluation of Antimicrobials in Distillate Fuels (Based on Preliminary Screening and Compatibility)
E 1326 Guide for Evaluating Nonconventional Microbio-logical Tests Used for Enumerating Bacteria
2.2 Institute of Petroleum Standards:
IP 385 Determination of the Viable Microbial Content of Fuels and Fuel Components Boiling Below 390°C - Filtration and Culture Method
IP Guidelines for the Investigation of the Microbial Content of Fuel Boiling Below 390°C and Associated Water
IP Proposed Method BY Determination of Fungal Fragment Content of Fuels Boiling Below 390°C
2.3 Government Standards:
40 CFR 79 Fuels and Fuel Additives Registration Regulations
40 CFR 152 Pesticide Registration and Classification Procedures
2.4 Other Standards:
Test Method 2540 D. Total Suspended Solids Dried at 103 - 105°C
3. Terminology
3.1 Definitions:
3.1.1 aerobe, n - an organism that requires oxygen to remain metabolically active.
3.1.1.1 Discussion - Aerobes use oxygen as their terminal electron acceptor in their primary energy-generating metabolic pathways. Aerobes require oxygen for survival, using aerobic metabolic processes to generate energy for growth and survival.
3.1.2 aggressiveness index (A.I.), n - the value computed from the sum of the pH + log alkalinity + log hardness of water sample where both alkalinity and hardness are reported as milligram CaCO3L.
3.1.2.1 Discussion - As A.I. decreases, water becomes more corrosive. At A.I. not less than 12, water is noncorrosive. At 10 not more than A.I. < 12, water is moderately corrosive. At A.I. < 10, water is strongly corrosive.
3.1.3 anaerobe, n - an organism that cannot grow or proliferate in the presence of oxygen.
3.1.3.1 Discussion - Anaerobes use molecules other than oxygen in their primary energy-generating metabolic pathways, such as sulfate, nitrate, ketones, and other high-energy organic molecules. Although anaerobes may survive in the presence of oxygen, anaerobic growth typically occurs only in an oxygen depleted environment.
3.1.4 anoxic, adj - oxygen free.
3.1.5 antimicrobial, n - see biocide.
3.1.6 bacterium (pl. bacteria), n - a single cell microorganism characterized by the absence of defined intracellular membranes that define all higher life forms.
3.1.6.1 Discussion - All bacteria are members of the biological diverse kingdoms Prokaryota and Archaebacteriota. Individual taxa within these kingdoms are able to thrive in environments ranging from sub-zero temperatures, such as in frozen foods and polar ice, to superheated waters in deep-sea thermal vents, and over the pH range <2.0 to> 13.0. Potential food sources range from single carbon molecules (carbon dioxide and methane) to complex polymers, including plastics. Oxygen requirements range from obligate anaerobes, which die on contact with oxygen, to obligate aerobes, which die if oxygen pressure falls below a species specific threshold.
3.1.7 bioburden, n - the level of microbial contamination (biomass) in a system.
3.1.7.1 Discussion - Typically, bioburden is defined in terms of either biomass or numbers of cells per unit volume or mass or surface area material tested (g biomass / mL; g biomass / g; cells / mL sample, and so forth). The specific parameter used to define bioburden depends on critical properties of the system evaluated and the investigator's preferences.
3.1.8 biocide, n - a poisonous substance that can kill living organisms.
3.1.8.1 Discussion - Biocides are further classified as bactericides (kill bacteria), fungicides (kill fungi), and microbiocides (kill both bacterial and fungi). They are also referred to as antimicrobials.
3.1.9 biodeterioration, n - the loss of commercial value or performance characteristics, or both, of a product (fuel) or material (fuel system) through biological processes.
3.1.10 biofilm, n - a film or layer of microorganisms, biopolymers, water, and entrained organic and inorganic debris that forms as a result of microbial growth and proliferation at phase interfaces (liquid-liquid, liquid-solid, liquid-gas, and so forth) (synonym: skinnogen layer).
3.1.11 biomass, n - density of biological material per unit sample volume, area, or mass (g biomass / g (or / mL or / cm2) sample).
3.1.12 biosurfactant, n - a biologically produced molecule that acts as a soap or detergent.
3.1.13 consortium (pl. consortia), n - microbial community comprised of more than one, species that exhibits properties not shown by individual community members.
3.1.13.1 Discussion - Consortia often mediate biodeterioration processes that individual taxa cannot.
3.1.14 depacifying, adj - the process of removing hydrogen ions (protons) from the cathodic surface of an electrolytic cell, thereby promoting continued electrolytic corrosion.
3.1.15 deplasticize, v - the process of breaking down polymers in plastics and similar materials, resulting in loss of the material's structural integrity.
3.1.16 facultative anaerobe, n - a microorganism capable of growing in both oxic and anoxic environments.
3.1.16.1 Discussion - Facultative anaerobes use oxygen when it is present, and use either organic or inorganic energy sources (nitrate, sulfate, and so forth) when oxygen is depleted or absent.
3.1.17 fungus (pl. fungi), n - single cell (yeasts) or filamentous (molds) microorganisms that share the property of having the true intracellular membranes (organelles) that characterize all higher life forms (Eukaryotes).
3.1.18 metabolite, n - a chemical substance produced by any of the many complex chemical and physical processes involved in the maintenance of life.
3.1.19 microbial activity test, n - any analytical procedure designed to measure the rate or results of one or more microorganism processes.
3.1.19.1 Discussion - Examples of microbial activity tests include loss or appearance of specific molecules or measuring the rate of change of parameters, such as acid number, molecular weight distribution (carbon number distribution), and specific gravity.
3.1.20 microbially induced corrosion (MIC), n - corrosion that is enhanced by the action of microorganisms in the local environment.
3.1.21 mold, n - form of fungal growth, characterized by long strands of filaments (hyphae) and, under appropriate growth conditions, aerial, spore-bearing structures.
3.1.21.1 Discussion - In fluids, mold colonies typically appear as soft spheres; termed fisheyes.
3.1.22 obligate aerobe, n - microorganism with an absolute requirement for atmospheric oxygen in order to function.
3.1.22.1 Discussion - Obligate aerobes may survive periods in anoxic environments but will remain dormant until sufficient oxygen is present to support their activity.
3.1.23 obligate anaerobe, n - microrganism that cannot function when atmospheric oxygen is present.
3.1.23.1 Discussion - Obligate anaerobes may survive periods in oxic environments but remain dormant until conditions become anoxic.
3.1.24 oxic, adj - an environment with a sufficient partial pressure of oxygen to support aerobic growth.
3.1.25 shock treatment, n - the addition of an antimicrobial agent sufficient to cause rapid and substantial (several orders of magnitude) reductions in number of living microbes in a fluid or system receiving that concentration.
3.1.26 skinnogen, n - synonymous with biofilm.
3.1.26.1 Discussion - Generally applied to a biofilm formed at the fuel-water interface.
3.1.27 sour, v - to increase the concentration of hydrogen sulfide.
3.1.28 sulfate reducing bacterial (SRB), pl., n - any bacteria with the capability of reducing sulfate to sulfide.
3.1.28.1 Discussion - The term SRB applies to representatives from a variety of bacterial taxa that share the common feature of sulfate reduction (SO4= to S=). SRB are major contributors to MIC.
3.1.29 taxa, pl., n - the units of classification of organisms, based on their relative similarities.
3.1.29.1 Discussion - Each taxonomic unit (group of organisms with greatest number of similarities) is assigned, beginning with the most inclusive to kingdom, division, class, order, family, genus, and species. Bacteria and fungi are often further classified by strain and biovariation.
3.1.30 viable titer, n - the number of living microbes present per unit volume, mass, or area.
3.1.30.1 Discussion - Viable titer is reported in terms of either colony forming units (CFU) or most probable number (MPN) per millilitre, milligram, or centimetre squared.