What are the three major categories of bacteria?

Bacteria are tiny organisms and are the most numerous organisms on Earth. Bacteria are everywhere in our lives and have a great impact on people's daily lives. Bacteria are the pathogens of many diseases, and many fatal diseases are caused by bacteria. But bacteria also have many benefits for humans. They can produce antibiotics, lactic acid bacteria, and so on. There are many types of bacteria. So, what are the three major categories of bacteria?

Bacteria are divided into three main categories based on their appearance: cocci, bacilli, and spirals.

1. Coccus

They are spherical or nearly spherical, and some are spear-shaped or kidney-shaped. The diameter of a single coccus is about 0.1.2um.

Due to the different directions of bacterial cell division during reproduction, the degree of bacterial adhesion after division, and the arrangement of bacteria, they can be divided into:

(I) Diplococcus: Diplococcus can be divided into two groups on a plane, such as Pneumococcus and Meningococcus.

(ii) Streptococcus: Split on a plane and arranged in chains, such as hemolytic streptococci.

(III) Micrococcus tetragenus: It divides in two perpendicular planes, forming a square with four cocci, such as Micrococcus tetragenus.

(IV) Sarcina: It divides in three mutually perpendicular planes, with eight overlapping cells forming a cube, such as Sarcina lutea.

(V) Staphylococcus: When the bacteria divide on several irregular planes, they tend to pile up together and form a grape-like arrangement, such as Staphylococcus aureus.

Cocci are a large class of bacteria. Pathogenic cocci that are pathogenic to humans mainly cause suppurative inflammation, also known as pyogenic coccus. Gram-positive bacteria mainly include Staphylococcus, Streptococcus, and Pneumococcus; Gram-negative bacteria include meningococci and gonococci.

2. Bacillus

The size, length, curvature and thickness of various bacilli vary greatly. Most bacilli are of medium size, 2 to 5um long and 0.1um wide. Large bacilli include anthrax bacilli (3 to 5um × 1.1.3um) and small ones include tularemia bacilli (0.0.7um × 0.2um). Most of the bacteria are in the shape of straight rods, and some are slightly curved. The two ends of the bacteria are mostly blunt and round, a few are flat (such as anthrax bacilli), and some are pointed (such as fusobacteria) or have swollen rods (such as diphtheria bacilli). The arrangement is generally scattered, without a certain arrangement form, occasionally in pairs or chains, and some are in special arrangements such as fences or V, Y, and L.

3. Spirillar bacterium

According to the degree of curvature of the bacteria, they can be divided into:

(I) Vibrio bacteria have only one bend, in the shape of an arc or comma. For example, Vibrio cholerae. Vibrio genus is widely distributed in nature, especially in water, with more than 100 species. The main pathogens are Vibrio cholerae and Vibrio parahaemolyticus (pathogenic halophilic bacteria). The former causes cholera; the latter causes food poisoning.

(ii) Spirillum bacteria have several bends, such as the rat-biting thermospirilla. Campylobacter genus is similar in shape to Vibrio, but because of the different GC content from Vibrio, a new genus Campylobacter was established. The main pathogens to humans are Campylobacter jejuni and Campylobacter intestinalis. The former causes acute enteritis and is more common; the latter is an opportunistic pathogen when the human immune system is reduced and is less common.