Spirochaetes

        Elongated, motile, flexible bacteria twisted spirally along the long axis. A charecteristic feature is the presence of endoflagella-polar flagella, situated between outer membrane and cell wall. They are Gram negative of varying sizes. Many are free living saprophytes, while some are obligate parasites. They may be aerobic, anaerobic, facultative. Reproduction by transverse fission. Human pathogens are: Treponema, Borrelia, Leptospira. The spiral shape and serpentine motility of the spirochaetes depend upon the integrity of these endoflagella. Motility is of 3 types : (i) flexion & extension (ii) cork-screw like rotary movement (iii) translatory motion.