Leptospira spp. - Classification, Characteristics, Morphology, Habitat, Culture

Classification of Leptospira

The classification of Leptospira is:

Domain: Bacteria

Phylum: Spirochaetota

Class: Spirochaetia

Order: Leptospirales

Family: Leptospiraceae

Genus: Leptospira

On the basis of DNA hybridization studies, the genus contains 20 species.

Characteristics of Leptospira

Leptospira includes a small number of species that are pathogenic and saprophytic in nature.

They are spiral-shaped, obligate aerobes, with right-handed helix with hooked ends. It contains two axial filaments and exhibits either spinning motility or rapid back-and-forth movement. Their flagella help them to burrow deep into infected tissues.

Traditionally, this genus contains two species:

• Leptospira interrogans – pathogenic causes human leptospirosis (has more than 260 serovars)

• Leptospira biflexa – saprophytic environmental strains (non-pathogenic) (has more than 60 serovars)

Molecular classification using 16srRNA sequencing separates the genus into three distinct groups:

• pathogens

• environmental pathogens

• other species of uncertain pathogenicity

Morphology of Leptospira

Morphologically, Leptospira is gram-negative, spiral-shaped, measuring about 6-20 μm long and 0.1 μm in diameter with a wavelength of about 0.5 μm. Either one or both ends of the bacterium are usually hooked.

Since Leptospira is very thin, they are observed best with darkfield microscopy.

Habitat of Leptospira

Leptospira can be found in environments, and habitats and is worldwide in distribution, except in Antarctica. The optimum temperature is 6.9–7.4 and it prefers high humidity. Stagnant water bodies such as bogs, shallow lakes, ponds, and puddles, are natural habitats for Leptospira.

Culture of Leptospira

Leptospira spp. can be cultured in Ellinghausen-McCullough-Johnson-Harris (EMJH) medium in aerobic conditions. If the growth medium is supplemented with 0.21% rabbit serum, it can enhance the growth of fastidious strains.

Pathogenic species' growth can be observed in 4–7 days at 13–15 °C while the saprophytic strains grow within 2–3 days at 13 °C. The optimum pH is around 7.2–7.6.