Theory:

Depending on the shapes, bacteria are classified into three types.
 
Important!
Spherical shaped - Cocci
Rod-shaped - Bacilli
Spiral shaped - Spirilla
Types of bacteria on basis of shape:
Types
Arrangement of cocci
 Examples
DiplococciArranged in pairsStreptococcus pneumoniae
StreptococciArranged in chainsStreptococcus pyogenes
TetracocciArranged in packets of four cellsAerococcus sp
StaphylococciArranged in grape-like clustersStaphylococcus aureus
Types
Arrangement of bacilli   
Examples
DiplobacilliArranged in pairsKlebsiella sp
Streptobacilli Arranged in chainsStreptobacillus sp
Coccobacilli Arranged in short, stumpy and appear ovoidHaemophilus sp
Types
Arrangement of spirilla
Examples
VibrioComma-shaped bacteriaVibrio cholerae
SpirillaRigid spiral structureHelicobacter pylori
SpirochetesHelical shape and flexible bodiesTreponema pallidum
 
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The main forms of bacteria