Terms You Need to Know

If you want to understand anything here, please know these terms.

Serovars/ Serotype

Serotype or serovar are distinct variations within a species of bacteria or viruses or among immune cells of different individuals. These microorganisms, viruses, or cells are classified together based on their cell surface antigens, allowing the epidemiologic classification of organisms to the sub-species level.

Strain

A strain is a genetic variant or subtype of a micro-organism (e.g., virus or bacterium or fungus). For example, a "flu strain" is a certain biological form of the influenza or "flu" virus.

Gram +ve bacteria

These are bacteria that give a positive result in the Gram stain test. Gram-positive bacteria take up the crystal violet stain used in the test, and then appear to be purple-coloured when seen through a microscope. This is because the thick peptidoglycan layer in the bacterial cell wall retains the stain after it is washed away from the rest of the sample, in the decolorization stage of the test.

Gram -ve bacteria

Gram-negative bacteria are a class of bacteria that do not retain the crystal violet stain used in the Gram staining method of bacterial differentiation, making positive identification possible. The thin peptidoglycan layer of their cell wall is sandwiched between an inner cytoplasmic cell membrane and a bacterial outer membrane. After staining with crystal violet, an alcohol wash is applied which decolorizes the bacteria showing that their peptidoglycan layer is too thin to retain the stain and enabling identification. A counter stain (safranin or fuchsine) is then added which recolorizes the bacteria red or pink.

Bioassay

Bioassays are procedures that can determine the concentration or purity or biological activity of a substance such as vitamin, hormone or plant growth factor by measuring the effect on an organism, tissue, cells, enzyme or receptor.

Nomenclature

This is a body or system of naming things in a particular discipline e.g science. The set or terms are given names in accordance with the naming techniques of that discipline.

Colonies

A microbial colony is defined as a visible cluster of microorganisms growing on the surface of or within a solid medium, presumably cultured from a single cell.

Cocci
(Singular Coccus)

Coccus (plural cocci) can be used to describe any bacterium that has a spherical, ovoid, or generally round shape. It is one of the three distinct bacterial shapes, the other two being bacillus (rod-shaped) and spiral-shaped cells.
Coccus is an English loanword of a Neolatin noun, which in turn stems from the Greek masculine noun kokkos (κόκκος) meaning "berry".

Ø  Diplococci are pairs of cocci (e.g. Streptococcus pneumoniae and Neisseria gonorrhoeae)

Ø  Streptococci are chains of cocci (e.g. Streptococcus pyogenes).

Ø  Staphylococci are irregular (grape-like) clusters of cocci (e.g. Staphylococcus aureus).

Ø  Tetrads are clusters of four cocci arranged within the same plane (e.g. Micrococcus sp.).

Ø  Sarcina is a genus of bacteria that are found in cuboidal arrangements of eight cocci.

Bacillus (Rod- shaped Bacteria)

A bacillus (plural bacilli) is a rod-shaped bacterium. Bacilli are found in many different taxonomic groups of bacteria. However, the name Bacillus, capitalized and italicized, refers to a specific genus of bacteria. The name Bacilli, capitalized but not italicized, can also refer to a less specific taxonomic group of bacteria that includes two orders, one of which contains the genus Bacillus. When the word is formatted with a lowercase and not italicized, 'bacillus', it will most likely be referring to shape and not to the genus at all. The shape bacillus can also be called rods.

Bacilli usually divide in the same plane and are solitary, but can combine to form diplobacilli, streptobacilli, and palisades.

• Diplobacilli: Two bacilli arranged side by side with each other.
• Streptobacilli: Bacilli arranged in chains.
• Coccobacillus: Oval and similar to coccus (circular shaped bacterium).

Aerobic Bacteria

An aerobic organism or aerobe is an organism that can survive and grow in an oxygenated environment.

Aerobic and anaerobic bacteria can be identified by growing them in test tubes of thioglycollate broth:
1: Obligate aerobes need oxygen because they cannot ferment or respire anaerobically. They gather at the top of the tube where the oxygen concentration is highest.
2: Obligate anaerobes are poisoned by oxygen, so they gather at the bottom of the tube where the oxygen concentration is lowest.
3: Facultative anaerobes can grow with or without oxygen because they can metabolise energy aerobically or anaerobically. They gather mostly at the top because aerobic respiration generates more ATP than either fermentation or anaerobic respiration.
4: Microaerophiles need oxygen because they cannot ferment or respire anaerobically. However, they are poisoned by high concentrations of oxygen. They gather in the upper part of the test tube but not the very top.
5: Aerotolerant organisms do not require oxygen as they metabolise energy anaerobically. Unlike obligate anaerobes however, they are not poisoned by oxygen. They can be found evenly spread throughout the test tube.

Anaerobic Bacteria

An anaerobic organism or anaerobe is any organism that does not require oxygen for growth. It may react negatively or even die if oxygen is present. An anaerobic organism may be unicellular (e.g. protozoans, bacteria) or multicellular (e.g. Nereid (worm) polychaetes juvenile Trichinella spiralis (pork worm) parasites).