Genetic Diversity of Neisseria gonorrhoeae Housekeeping Genes

Abstract

Molecular typing of Neisseria gonorrhoeae strains is an important tool for epidemiological studies of gonococcal infection and transmission. The recently developed multilocus sequence typing (MLST) method is based on the genetic variation among housekeeping genes. As a preliminary investigation for the development of such a method, we characterized the genetic diversity at 18 gonococcal housekeeping gene loci. Approximately 17,500 nucleotides, spanning 18 loci, were sequenced from 24 isolates. Including strain FA 1090, which has been fully sequenced, and three unique glnA sequences from GenBank, the number of alleles identified for the 18 loci ranged from 2 to 18, with a mean of 8.3 alleles per locus. The majority of polymorphic sites were distributed randomly along the genes, consistent with evolution of DNA sequences by point mutation. In addition, several examples of clustered mutations and insertions or deletions were detected, which most likely occurred by recombinational events. While purifying selection is the dominant force driving the evolution of these housekeeping genes, positive selection also appeared to operate on the abcZ and gpdh loci. The 25 completely characterized strains each had a unique allelic profile with as few as three loci (pilA, abcZ, and pip or pgi2). Molecular typing based on the allelic profile of housekeeping genes resolved the isolates better than either porB nucleotide sequencing or typing of the opa gene. The allelic profiles for the pilA, abcZ, and serC loci of paired strains from 16 sexual contacts were identical. A potential MLST for N. gonorrhoeae, based on ϳ500-to 600-bp gene fragments of seven housekeeping gene loci, would include the pilA, abcZ, serC, glnA, gdh, gnd, and pip loci.

Population genetics of microbial pathogens estimated from multilocus sequence typing (MLST) data

“…These analyses yielded comparable mean ρvalues within each species, indicating that LDhat estimates of this parameter are not strongly affected by sample size (see other examples by Jolley et al, 2000;Maggi-Solcà et al, 2001;Feil et al, 2003;Viscidi and Demma, 2003). However, many MLST data sets represent biased samples that are concentrated on disease isolates and confirmation of our results with more population-based samples is desirable.…”

“…The key factors in the evolutionary response of pathogens to their environments can be measured by assessing the genetic diversity (and partitioning of that diversity within versus between populations), the impact of natural selection in shaping that diversity, and the impact of recombination in redistributing that diversity, sometimes into novel combinations. Population studies of pathogens using multilocus sequencing typing (MLST) methods are generally aimed at inferring genetic diversity (usually estimated as the relative contribution of recombination and mutation per allele or per site), selection pressure, and population structure Maynard-Smith et al, 2000;Dingle et al, 2001;Feil et al, 2003;Meats et al, 2003;Viscidi and Demma, 2003) to study the relative impact of genetic drift and natural selection on the evolutionary history of these pathogens.…”

Molecular Epidemiology of Neisseria gonorrhoeae in Amsterdam, The Netherlands, Shows Distinct Heterosexual and Homosexual Networks

“…This (1,10). DNA mutation and/or recombination cannot be ruled out and will certainly occur independent of the typing technique used, as it is known that N. gonorrhoeae opacity and porin proteins are subject to host immune responses (1,24). The persistence of the large clusters during the study period could indicate that reassortment and recombination are not extremely frequent but that, possibly, a very successful (founder) genotype circulated in the population.…”

“…By expanding the current por-opa typing with sequence-based typing methods, such as sequencing of the por IB gene, MLST, or Neisseria gonorrhoeae multiple antigenic sequence typing, the reproducibility of the observed large clusters could be verified. In the study described previously by Viscidi and Demma, such a comparison was done for 25 strains and 18 housekeeping genes (24). There appeared to be no concordance between MLST and por or opa typing, and the diversity of 18 genes, large parts of which were sequenced with MLST, was so high that all sexual partners also differed in strain types.…”

Molecular Typing of Neisseria gonorrhoeae Isolates by Pyrosequencing of Highly Polymorphic Segments of the porB Gene

“…Thus, for epidemiological and clinical purposes a highly discriminating, objective, and reproducible characterization of N. gonorrhoeae strains is essential. The widely used phenotypic characterizations of the bacterium have several limitations (10,12,13,17,24,27,28), and different molecular genetic methods have thus been developed (12,15,18,23,25,26,27,28,30,32).…”