Genetic characterization of leptospiral isolates

The earliest authentic report of leptospirosis from India dates back to 1929, when Taylor and Goyle isolated 28 strains from 78 suspected cases showing typical signs and symptoms of Weil’s syndrome among prisoners in Andaman Islands. No further information was available since then regarding the status of leptospirosis in these islands till 1988 when outbreaks of Andaman Hemorrhagic Fever that was later proved to be leptospirosis started occurring. Several isolates have been obtained during these outbreaks and attempts were made to characterize these strains serologically and using molecular techniques. The strain CH 31, belonging to the serogroup Grippotyphosa, was originally isolated from a patient in Andaman Islands in 1929. Four isolates, designated as D 22, Mg 47, Mg 51, and Mg 100 were recovered from patients attending primary health center in South Andamans in recent years.

RAPD finger prints of CH31 (isolated in 1929) and four new isolates of leptospires using M16 and P1 primers

All the 5 isolates were serotyped following standard procedures. Genomic DNA of the bacterial strains was extractedand dissolved in MilliQ water and used for RAPD analysis. Three primers i.e. M16, P1 and PB1 were used. Primer PB1 has been used earlier to differentiate between Leptospira species and serovars.

All the isolates belonged to the serogroup Grippotyphosa. Antigenic patterns of all these isolates against the panel of 4 monoclonal antibodies were similar to each other. The antigenic profiles of all the isolates were similar to that of CH 31, indicating a close serological relationship between the isolates.

RAPD fingerprints of the recent isolates D 22, Mg 47, Mg 51, and Mg 100 obtained with the primers M16, P1  (fig. 1.57) and PB1 (fig 1.58) were similar to that of the 1929 isolate CH31. The findings of the present study show the similarity in antigenic and genetic nature of some Leptospira strains isolated over 70 years apart from the Andaman Islands.

RAPD finger prints of CH31 (isolated in 1929) and four new isolates of leptospires using PB1 primers

The primer PB1 used in this study has the ability to discriminate between different species and serovars of leptospires. RAPD fingerprints of the 1929 isolate CH 31, and the recent isolates D 22, Mg 47, Mg 51, and Mg 100 were essentially the same indicating that these recent isolates are genetically similar to the 1929 isolate.

Bacteria, having simple genetic organization and very short generation time, are more susceptible to genetic changes over a period of time, than most of the higher organisms. Our preliminary study however shows that a Leptospira strain has undergone no apparent change in its antigenic and genetic makeup over a time span of over 70 years. This might be because of the fact that genetic exchange mechanisms are lacking in leptospires and these organisms are genetically more refractory than most other bacteria.