I – STRUCTURE:
The dotted line represents the envelope. The protoplasmic cylinder is drawn in solid line. The circles are located near the ends of the insertion points periplasmic flagella.
Bacteria belonging to the order of Spirochaetales is flexible, characterized by the helical shape and their mobility is due to internal musculoskeletal system. They are from 5 to 250 microns in length and 0.1 to 30 micronsthick.
spirochaetes are provided with a casing which completely surrounds the protoplasmic cylinder consisting of cytoplasm and nuclear device. This envelope has a structure similar to that of the wall of Gram-negative bacilli.The protoplasmic cylinder is itself limited by a protoplasmic membrane.
The internal skeletal element (also called periplasmic flagella fibrils or axial) is located between the casing and the protoplasmic cylinder. The number of flagella varies with the species from 2 to more than 100 by bacterial body.
Each flagellum is inserted by one of its ends to a basal body intracytoplasmic situated at one pole of the protoplasmic cylinder. Their structure is similar to that of bacterial flagella. But the situation endocellular these flagella allows mobile spirochaetes to stay in an environment with high viscosity that immobilizes other flagellated bacteria.
When observed in dark field microscopy, spirochaetes are animated features movements: displacement, bending, corkscrew movements around their axis.
Some spirochaetes could never be grown in vitro. As for those who are cultivated, there are some which are anaerobic and other aerobic.
II – CLASSIFICATION AND NOMENCLATURE:
The bacteria of the order Spirochaetales are classified into two families:
– Spirochaetaceae family includes four genera Spirochaeta, Cristispira, Treponema and Borrelia
– The family Leptospiraceae consists only of a single genus, Leptospira.
III – HABITAT AND PATHOGENICITY:
The spirochaetes are widespread in nature and found in gifted waters.
Three genera pathogenic to humans:
– The kind Treponema, responsible for syphilis and other treponematoses nonvenereal,
– The genus Leptospira, Agent leptospirosis,
– The genus Borrelia, Agent relapsing fever transmitted by arthropods.