Abstract
BackgroundDistinguishing the recent introduction of quinolone resistant gonococci into a population from diversification of resistant strains already in the population is important for planning effective infection control strategies. We applied molecular evolutionary analyses to DNA sequences from 9 housekeeping genes and gyrA, parC and porB of 24 quinolone resistant N. gonorrhoeae (QRNG) and 24 quinolone sensitive isolates collected in Israel during 2000–2001.ResultsPhylogenetic and eBURST analyses and estimates of divergence time indicated QRNG were introduced on 3 separate occasions and underwent limited diversification by mutation, deletion and horizontal gene transfer. Reconstruction of N. gonorrhoeae demography showed a slowly declining effective strain population size from 1976 to 1993, rapid decline between 1994 and 1999, and an increase from 1999 to 2001. This is partially attributable to declining gonorrhea case rates from 1973 to 1994. Additional contributing factors are selective sweeps of antibiotic resistant gonococci and increased transmission from sex workers. The abrupt decline in the mid-1990s heralded an increased incidence of gonorrhea from 1997 to the present. The subsequent increase in effective strain population size since 1999 reflects the increased gonococcal census population and introduction of quinolone resistance strains.ConclusionOur study demonstrates the effective use of population genetic approaches to assess recent and historical population dynamics of N. gonorrhoeae.
Highlights
Distinguishing the recent introduction of quinolone resistant gonococci into a population from diversification of resistant strains already in the population is important for planning effective infection control strategies
An increase in the incidence of gonorrhea was observed in Israel in 1998, accompanied by the appearance of quinolone resistant N. gonorrhoeae (QRNG) isolates [5]
Of 80 isolates collected during this time period that were previously genotyped by molecular probes for the variable regions of the porB gene [6], we selected 24 fluoroquinolone resistant and 24 sensitive strains for more detailed genotyping by sequencing of fragments of multiple housekeeping genes
Summary
Distinguishing the recent introduction of quinolone resistant gonococci into a population from diversification of resistant strains already in the population is important for planning effective infection control strategies. Genetic analysis of porB using molecular probes identified two predominant genotypes among QRNG [6] and pulse field gel electrophoresis demonstrated limited heterogeneity of the resistant strains and clear similarities to resistant strains from southern Israel [7]. These studies suggested recent introduction of QRNG, perhaps from a single source, followed by rapid dissemination through the country. Not all isolates had the identical genotype raising the question of whether there was diversification of the original strain or whether there were multiple introductions of QRNG strains
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