Glossary of microbiology

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Dictionary of microbiology

Table of contents:

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# - A

Acute – Sudden onset and repaid progression (when used in reference to a disease or condition).

Aerobic – Bacteria that require oxygen to grow or will grow in the presence of oxygen.

Anaerobic – Bacteria that do not utilize oxygen to grow, or will not grow in the presence of oxygen.

Aqueous – Relating to water. Autoinfection]] – Infection caused by bacteria, viruses, or parasites persisting on or in the body.

aw (Water activity) – The measure of free water in the environment that is available for use by bacterial cells.

B

Bacteriocin – A substance that is produced by specific bacteria that is toxic to closely related strains of the same specific bacteria and either kills or slows the growth of those other specific bacteria.

C

Coliform – Bacteria that most often inhabit the intestine of animals and do not utilize oxygen, but can grow in its presence. Bacteria that are classified as coliforms have the same shape and many of the same characteristics. These bacteria are used as indicators of sanitary quality in many food products.

Colony – A visible growth of microorganisms (bacteria) on a solid nutrient medium. Members of the colony are identical to the original or parent cell.

Colony-forming units (CFUs) – Visible units counted in a plate count, which may be formed from a group of cells rather than from one cell. CFU is used to measure the number of living cells present.

Curing – The addition of salt, sodium, or potassium nitrate (or saltpeter), nitrites, and sometimes sugar, seasonings, phosphates, and cure accelerators (e.g., sodium ascorbate), to pork for preservation, color development, and flavor enhancement.

D

Detection limit – The lowest threshold amount of bacteria that must be present in a sample to be found. Detection level depends upon methods used.

Direct plating – The application of a sample, or dilution thereof, to solid media, usually containing agar and other material used to grow and enumerate bacteria.

D-value – The amount of time needed to destroy one log unit of a specific bacteria at a specific temperature in a specific medium

E

Enrichment – The addition of nutrient-rich broth so that certain bacteria or types of bacteria increase in number to result in a bacterial cell count that is higher than the detection limit. This is used to detect only the presence or absence of the bacteria, not the amount present.

Enterobacteriaceae – Large group of bacteria that are closely related and are commonly found in fecal material of warm-blooded animals. They include coliforms and pathogens such as Salmonella.

F

F-value – Measured in minutes, the D-value of a specific organism at 250 ˚F (121 ˚C) multiplied by the desired log reduction.

Facultative aerobes – Microorganisms that grow best when oxygen is present but do not need it to grow.

Facultative anaerobe – Microorganisms that do not need oxygen to grow, but will use it when it is present.

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G

g (Generation time) – The time it takes for bacterial cell numbers to double.

Germination – The process of a spore becoming a vegetative cell.

Gravid – Pregnant or containing eggs.

H

Heat labile – Destroyed or altered by heat.

Hemolytic anemia – A condition in which red blood cells are destroyed and removed from the bloodstream before their normal lifespan is over. This leads to the blood having a lower than normal number of red blood cells. Hemolytic anemia can lead to many health problems, such as fatigue (tiredness), pain, irregular heartbeats, an enlarged heart, and heart failure.

Hemorrhagic colitis – Abdominal cramps and bloody diarrhea, without fever. Inactivation]] – The destruction of the activity of a pathogenic microorganisms so the microorganism is no longer harmful.

I

Infection – The invasion by, and growth of, pathogenic microorganisms in a host.

Infectivity – The ability to produce infection. Infestation]] – The presence of large numbers of organisms on or in a host causing illness or damage.

Inhibition – The slowing or stopping of bacterial growth. k (Growth rate)]] – The rate at which bacterial cells reproduce.

L

Lag time – The time that bacteria take to become acclimated to a new environment before starting to multiply. Bacteria divide and their numbers grow exponentially: 1 becomes 2 becomes 4 becomes 8, etc.

Lethality – The effectiveness of a treatment to destroy or kill bacteria.

Log unit – An exponential (multiplicative) relationship between units in a numerical scale. The exact relationship is conveyed by the base. Assuming that “log” is “log base 10,” every unit is expressed as the exponential of 10. For example, 1 log10 is equal to 101 (10 to the 1st power) or 10; 2 log10 is equal to 102 (10 x 10) or 100, and so on. Moving 1 unit in the log10 scale is equivalent to multiplying or dividing the preceding number by 10 (multiply if increasing the log number, divide if decreasing the log number). Scientists convert bacterial counts to log scales (or plot on log-log or semilog graphs) because it allows them to see the large changes apart from the irrelevant data inherent in the process of measuring bacteria populations. If two populations of bacteria differ by less than 10 fold (1 log10 unit), the distinction is not likely to be significant. But differences of 10, 100, or 1,000 fold (1, 2 or 3 log10 units) are more likely to be significant and scientifically important.

M

Mesophiles – Bacteria that have optimum growing temperatures between 77 °F (25 °C) and 104 °F (40 °C).

Microaerophiles – Microorganisms that require oxygen at a lower level than is found in normal air to survive.

Microflora – Bacteria, molds, and yeasts. Obligate aerobe]] – Microorganisms that require a high concentration of oxygen to survive.

O

Obligate anaerobe – Microorganisms that must avoid all oxygen to survive.

Oncosphere – The larva of the tapeworm contained within the external embryonic envelope and armed with six hooks. Pathogen]] – Organisms that cause illness. These organisms include bacteria, protozoa, or viruses.

pH

pH – Level of acidity or alkalinity in a product. The pH scale ranges from 1 to 14, with 7 considered neutral, 1 the most acidic, and 14 the most alkaline. Fresh meat usually has a pH near 5.6.

Proglottid – An individual segment of a tapeworm.

Psychrotrophs – Bacteria that have optimum growing temperatures between 68 °F (20 °C) and 86 °F (30 °C), but can grow at temperatures as low as 32 °F (0 °C).

Table of contents:

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.N | .O | .P | .Q | .R | .S | .T | .U | .V | .W | .X | .Y | .Z

S

Scolex – The head of a tapeworm that usually has suckers and/or hooks.

Shocked (heat shocked) – Occurs when a product is heated, but the temperature is not high enough to destroy the bacteria. It results in bacteria that are injured for a while, but in most cases can repair itself and becomes more resistant to heat the next time the product is heated. Heat shocked also can refer to the process by which a spore is induced into germination. When a product is heated thoroughly, the vegetative cells are destroyed, but the spores are undamaged by the heat. The spores then germinate into vegetative cells once the temperature has decreased to an optimum level.

Significant difference – Statistical difference in results.

Spore – A highly resistant, dormant form that some bacteria can change into. Spores are usually very resistant to heat, long periods of dryness, and other adverse conditions that normal vegetative cells cannot survive. Most must be adverse conditions that normal vegetative cells cannot survive. Most must be heat-shocked to germinate into normal, vegetative cells. Most of the time, spores have a toxin associated with them, either within the spore covering, or released at the time of germination, or when becoming a spore (sporulation).

Strain – A specific subset of bacteria. For example, Escherichia is the genus, coli is the species, and O157:H7 is the serotype (strain).

T

Thermotolerant – Bacteria that can withstand higher-than-normal temperatures.

Thermobocytopenia – An abnormal drop in the number of blood cells, called platelets, that are involved in forming blood clots.

Toxin (enterotoxin, mycotoxin, neurotoxin) – A compound produced by a bacterium or fungi (molds and yeasts) that can cause illness in other living organisms. Specific examples include enterotoxins which affect the intestine, mycotoxins (toxins produced by fungi), and neurotoxins that attack the nervous system.

Transdermal synergists – Compounds that work with other compounds against bacteria when applied to the surface of a carcass.

Treatment – The method of processing that is being tested. A good research study will compare various treatments, such as levels of salt in a product, to a control. In this example, the control may be no salt added. All other conditions should remain the same for all samples tested, except the specific treatment.

V

Vegetative cell – The normal bacteria cell. This is in contrast to a spore. Vegetative cells are susceptible to destruction or damage from heat, additives, and other factors that can damage and destroy them relatively easily.

Table of contents:

.A | .B | .C | .D | .E | .F | .G | .H | .I | .J | .K | .L | .M

.N | .O | .P | .Q | .R | .S | .T | .U | .V | .W | .X | .Y | .Z

Also see Microbiology

Dictionary of microbiology

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