Summary auto-generated
This study examined the population genetics and molecular epidemiology of Serpulina pilosicoli, a spirochete bacterium that causes intestinal spirochaetosis, using 164 isolates from humans and animals in Papua New Guinea villages. Researchers employed multilocus enzyme electrophoresis (MLEE) and pulsed-field gel electrophoresis (PFGE) to characterize genetic diversity. The 164 isolates were divided into 33 electrophoretic types (ETs), with four dominant ETs containing 65% of isolates. Among 145 human isolates, genetic diversity was low (0.18), and only 5 of 15 enzyme loci were polymorphic. However, PFGE analysis revealed extensive strain diversity, identifying 99 distinct types. Statistical analysis indicated a recombinant population structure lacking linkage disequilibrium, suggesting extensive genetic recombination. When individuals were resampled after 6 weeks, 47% carried the same PFGE type, while others had different strains. Notably, identical PFGE patterns were found in isolates from both humans and dogs from different villages, suggesting natural cross-species transmission and zoonotic potential. The research demonstrates that despite low genetic diversity at the MLEE level, S. pilosicoli exhibits considerable strain diversity in geographically restricted populations.
Key findings
- Serpulina pilosicoli showed a recombinant population structure with minimal linkage disequilibrium, indicating extensive genetic recombination among isolates
- PFGE analysis revealed 99 distinct strain types among 164 isolates, demonstrating greater discriminatory power than MLEE and indicating substantial strain diversity in a geographically restricted area
- Identical PFGE patterns were found in isolates from both humans and dogs from different villages, providing evidence of natural cross-species transmission of S. pilosicoli between animals and humans
- Only 47% of resampled individuals carried the same PFGE type after 6 weeks, suggesting either persistent infection with single strains or frequent reinfection with different strains
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Abstract
The population genetics of Serpulina pilosicoli and its molecular epidemiology in villages in the Eastern Highlands province of Papua New Guinea were investigated. Multilocus enzyme electrophoresis (MLEE) was used to analyse 164 isolates from humans and animals. These were divided into 33 electrophoretic types (ETs), four of which contained 65% of the isolates. The mean genetic diversity (n = number of ETs) for 145 human isolates was 0·18, and the mean number of alleles at five polymorphic loci was 2·6. The species appeared to be recombinant, as there was a lack of linkage disequilibrium, and 25% of all the possible combinations of alleles was present in the population. PFGE analysis using the enzymes Mlul and Sall divided 157 of the isolates into 99 PFGE types, demonstrating the existence of considerable strain diversity in a geographically restricted area. The two techniques were in excellent agreement; however, PFGE was more discriminatory for strain typing than was MLEE. Nine out of 19 (47·4%) culture-positive individuals were colonized by the same PFGE type of S. pilosicoli when retested after 6 weeks. For three individuals, the PFGE profiles of the second isolate differed from the first in only one or two DNA bands, while the other seven individuals were colonized with distinct PFGE types on each occasion. In two cases, strains with the same PFGE pattern were isolated from humans and dogs, suggesting that cross-species transmission of S. pilosicoli may occur naturally and that the infection can be zoonotic.