GENOTYPIC AND PHENOTYPIC CHARACTERIZATION OF BORRELIA-BURGDOFERI ISOLATED FROM TICKS AND SMALL ANIMALS IN ILLINOIS

We have characterized 33 isolates of Borrelia burgdorferi from norther n Illinois (32 isolates) and Wisconsin (1 isolate) representing the la rgest series of midwestern isolates investigated to date. The techniqu es used for molecular analysis of strains included (i) genospecies typ ing with species-specific PCR primers, (ii) plasmid profiling by pulse d-field gel electrophoresis of total genomic DNA, (iii) large-restrict ion-fragment pattern (LRFP) analysis by pulsed-field gel electrophores is of MluI-digested genomic DNA (J. Belfaiza, D. Postic, E. Bellenger, G. Baranton, and I. Saint Girons, J. Clin. Microbiol. 31:2873-2877, 1 993), (iv) sodium dodecyl sulfate-polyacrylamide gel electrophoresis o f total proteins, (v) microsequencing of high-performance liquid chrom atography-purified peptides derived from proteins showing high levels of expression, (vi) amino acid composition analysis of proteins, and ( vii) immunological analysis of proteins with a polyclonal antiserum of human origin. Five reference strains as well as two atypical tick iso lates from California (DN127) and New York (25015) were included for c omparison. All of the Illinois and Wisconsin isolates were typed as B. burgdorferi sensu stricto with genospecies-specific PCR primers. The isolates were found to be heterogeneous with regard to their plasmid a nd protein profiles. One isolate from Illinois possessed two large-mol ecular-size plasmids instead of the usual 49-kb plasmid. Fragment patt erns result ting from MluI digestion of genomic DNA from the 33 isolat es and strains DN127 and 25015 were separable into six distinct LRFPs, five of which have not previously been described. Strain 25015 and an isolate from Illinois (CT39) shared an unusual LRFP that is not typic al of other B. burgdorferi sensu stricto strains, suggesting that they may represent a fifth species of B. burgdorferi sensu late. Five of t he 33 isolates and strains DN127 and 25015 showed high-level expressio n of proteins with molecular masses of approximately 22 kDa. Investiga tion of these proteins by microsequencing of individual peptides and t otal amino acid composition analysis indicated that the 22-kDa protein s expressed by the seven strains were polymorphic OspC proteins. By us ing a polyclonal serum of human origin, expression of OspC could be de tected in all 33 Illinois and Wisconsin isolates.