Multilocus Sequence Typing of the Genus Leptospira

Epidemiological studies in rural Thailand have demonstrated that leptospirosis is a major cause of acute febrile illness in this setting. Superimposed on this was a sustained outbreak in northeast Thailand between 1999-2003, the basis for which was unknown. Outbreaks elsewhere in the world are commonly associated with the presence of a dominant, region-specific serovar of Leptospira, and it was postulated here that the Thai outbreak was due to the emergence of a single biologically successful clone. An inherent weakness in defining the population genetic structure of Leptospira is that the commonly used serovar is not a unit of genetic identity. Pulsed-field gel electrophoresis (PFGE) has been described for Leptospira but is an imperfect tool since a number of variable strains appear identical by banding pattern. In response to this, a multilocu~ sequence typing (MLST) was developed for Leptospira interrogans (the most common species associated with human leptospirosis), and this was used to investigate the Thai outbreak. MLST data were also compared with PFGE and serovar typing. MLST was successfully applied to clinical and rodent isolates cultured from Thailand and reference isolates cultured from a more diverse geographical region. MLST demonstrated that the majority ofhuman infection (68%) in Thailand was caused by a single clone ofL. interrogans serovar Autumnalis, termed sequence type (ST) 34. This clone was also found in the rodent population, making a link between maintenance and accidental hosts. STs were compared with those of Leptospira drawn from the reference collection. This indicated a much more diverse population genetic structure for the reference collection. Unlike serovar and PFGE, MLST could differentiate between species and identify genetically related clones of L. interrogans and the highly related species L. kirschneri. MLST of L. interrogans represents a useful new tool for the genetic investigation of this important pathogen.EThOS - Electronic Theses Online ServiceGBUnited Kingdo