The genus Leptospira is an incredibly varied group of organisms, containing hundreds of serovars and genetic types, which can occupy diverse environments, habitats and life cycles. Contained within the genus are highly pathogenic host-specific strains, and harmless free-living waterborne strains. The historical difficulty is that there is almost no visible difference within the genus – all look pretty much identical. Before the development of DNA analysis, classification has been by serological cross-testing (using serum antibodies to identify similar and different types of bacteria), and in the leptospiral research world this concentration on ‘obsessive labelling’ has got us quite a reputation. Leptospires are often considered too complex an area to get to grips with, due to the huge numbers of tables, lists, groupings and arguments that are published each year.
This is a shame, as the leptospires are in fact a very interesting genus. Apart from the obvious health issues of the pathogenic types, the free-living, innocuous saprophytes have quietly established themselves in some amazingly diverse habitats, including some that have managed to cross the saltwater boundary. Little is known about the genetics, lifestyles and personalities of these non-pathogenic types.
- Domain: bacteria
- Phylum: Spirochaetes
- Class: Spirochaetes
- Order: Spirochaetales
The Order has three families: brachyspiraceae, spirospiraceae and leptospiraceae. Within leptospiraceae there are only three genera, Leptonema, Turneria and Leptospira. The leptospira genus is broken down in the table.
Each serogroup contains one or more serovars. In total there are about 240 recognised serovars for the serogroups in the table – we say ‘about’ as there are always 5 or 10 awaiting confirmation. The definitive listing is available from the Institut Pasteur Genetics Server.
Whilst a great number of serovars are known from human and animal subjects, only a small number cause illness of any severity. The Pasteur grouping places all pathogenic strains under the interrogans block, and non-pathogenic strains under biflexa. The other 8 genonospecies are late additions and (as always with leptospiral research) somewhat break the classification system.
Serovars, as the name implies, are classified using serological testing and not DNA. Over the last decade a lot of DNA work has been done on the leptospira ‘family tree’ and the one clear outcome is that the serogroups and serovars are often genetically diverse. DNA-similar strains can show up in different serogroups, and two serovars in the same group can have major DNA marker variations. The serovar tree is established and will probably remain so, but those working with the bacteria now have to deal with two ‘somewhat different’ ideas of what is related to what.
In 2002 the IUMS confirmed the nomenclature for leptospira as follows:
Genus species serovar Serovar_name : i.e. genus and species italicised, serovar name in plain text, genus and serovar capitalised and species lowercase. Examples include:
Leptospira interrogans serovar Ballum
Leptospira biflexa serovar Codice
L. interrogans serovar Canicola
A serovar is identified based on unique cross-matching, and in many cases there is only one isolate of each serovar. They are each referenced by their discoverer, location and host. Whilst work by the Institut Pasteur and others ensures that an ‘official’ serovar is indeed a new type and not just a case of another one, we can be sure that there are many times more out there than we know about.