Characterisation of Yersinia pestis isolates from natural foci of plague in the Republic of Georgia, and their relationship to Y. pestis isolates from other countries.

Forty Yersinia pestis isolates from endemic foci of plague in the Republic of Georgia, and six Y. pestis isolates from neighbouring former Soviet Union countries, were analysed for their biochemical and phenotypic properties, and their genetic relatedness was compared with Y. pestis strains KIM and CO92 by pulsed-field gel electrophoresis (PFGE). In addition, 11 Y. pestis isolates from the USA, together with published nucleotide sequences from Y. pestis strains KIM, CO92 and 91001, were compared with the 46 isolates in the present collection using multilocus sequence typing (MLST), based on sequence data for the 16S rRNA, hsp60, glnA, gyrB, recA, manB, thrA and tmk loci. Four virulence gene loci (caf1, lcrV, psaA and pla) were also sequenced and analysed. Two sequence types (ST1 and ST2), which differed by a single nucleotide, were identified by MLST. With the exception of a single isolate (771G), all of the Georgian Y. pestis isolates belonged to ST2. PFGE also grouped the Georgian Y. pestis isolates separately from the non-Georgian isolates. Overall, PFGE discriminated the Y. pestis isolates more effectively than MLST. The sequences of three of the four virulence genes (lcrV, psaA and pla) were identical in all Georgian and non-Georgian isolates, but the caf1 locus was represented by two allele types, with caf1 NT1 being associated with the non-Georgian isolates and caf1 NT2 being associated with the Georgian isolates. These results suggest that Georgian Y. pestis isolates are of clonal origin.