Distinguishing importation from diversification of quinolone-resistant Neisseria gonorrhoeae by molecular evolutionary analysis
1 Department of Integrative Biology, Brigham Young University, Provo, UT, USA
2 Department of Microbiology and Molecular Biology, Brigham Young University, Provo, UT, USA
3 Division of Bacterial, Parasitic and Allergenic Products, Center for Biologics Evaluation and Research, United States Food and Drug Administration, Bethesda, MD, USA
4 Infectious Diseases Unit, Edith Wolfson Hospital, Tel Aviv, Israel
5 Division of Infectious Diseases, Department of Medicine, Johns Hopkins University School of Medicine, Baltimore MD, USA
6 Stanley Division, Department of Pediatrics, Johns Hopkins University School of Medicine, Baltimore MD, USA
BMC Evolutionary Biology 2007, 7:84 doi:10.1186/1471-2148-7-84Published: 1 June 2007
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. 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.
Phylogenetic 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.
Our study demonstrates the effective use of population genetic approaches to assess recent and historical population dynamics of N. gonorrhoeae.