Gonorrhea, caused by the human pathogen Neisseria gonorrhoeae, is a severe public health problem worldwide with more than 82 million new infections each year. N. gonorrhoeae is transmitted by sexual contact and primarily causes urogenital mucosal infections in men and women. Left untreated, this infection may cause severe complications, especially in females. Eye infections of the newborn can occur. Gonorrhea infections enhance HIV transmission. The highly prevalent antibiotic resistance and the emergence of new drug resistances render treatment of the infections increasingly difficult. Close monitoring of antimicrobial susceptibility of this pathogen is crucial, and enhanced knowledge of molecular mechanisms of gonococcal antimicrobial resistance is urgently needed. There are no vaccines available against N. gonorrhoeae. Control of gonorrhea relies on comprehensive strategies which can be better formulated by understanding, at molecular levels, how N. gonorrhoeae is transmitted in communities.
My research aimed to illustrate the severe burden of antimicrobial resistance in N. gonorrhoeae temporally and geographically in China and to reveal the molecular mechanisms of antibiotic resistance particularly the development of reduced susceptibility to ceftriaxone in N. gonorrhoeae isolates. To determine specific strain distributions, N. gonorrhoeae isolates were characterized using molecular typing methods such as a modified porB-based typing scheme and the N. gonorrhoeae Multi-Antigen Typing (NG-MAST) method, compared to traditional epidemiological approaches. The ultimate goal was to provide information for better formulating disease control strategies for gonorrhea.
In this research, male patients with gonorrhea and their sex partners were recruited in Shanghai (2005 and 2008) and in Urumchi (2007-2008), China. Epidemiological information pertaining to sexual contacts was collected. N. gonorrhoeae isolates were investigated for their antimicrobial susceptibility. Molecular mechanisms of antimicrobial resistance were explored by analysis of potential resistant determinants (gyrA, parC, porB, mtrR, ponA and penA). The molecular data were combined with bioinformatic analysis and traditional epidemiological data.
High percentages of N. gonorrhoeae isolates (11% - 19% in Shanghai, 4.5% in Urumchi) exhibited reduced susceptibility to ceftriaxone (MICs = 0.125-0.25 mg/L), the first line drug recommended for the treatment of gonorrhea in China. The majority of isolates (>98%) were susceptible to spectinomycin, an alternative regimen for gonorrhea treatment; however, the proportion of isolates having intermediate levels of susceptibility increased from 1.9% in 2005 to 9.9% in 2008. The majority of isolates tested were resistant to penicillin (80% - 93%), tetracycline (56% - 65%) and ciprofloxacin (98% - 100%). Plasmid-mediated resistance in N. gonorrhoeae isolates were highly prevalent (51% - 79%) in Shanghai and Urumchi.
Analysis of 60 clinical isolates revealed that reduced susceptibility to ceftriaxone is mediated by porB1b allele and is associated with specific mutations in penicillin binding protein 2 and in the DNA binding and dimerization domains of MtrR. Penicillin binding protein 1 is not involved in reduced susceptibility to ceftriaxone. Although mutation patterns in quinolone resistant determinant regions (QRDRs) varied, the majority of ciprofloxacin resistant isolates had double mutations in GyrA (S91F and D95G/A/N) and most isolates also carried a S87R/N mutation in ParC. The presence of mutations in the QRDR of ParC is correlated with elevated ciprofloxacin MICs.
A modified porB-based molecular typing scheme was developed and involved ~82% of the DNA sequence of gonococcal porB. This typing method proved to have high discriminatory ability (index of discrimination = 0.93 0.96), and was cost effective and easy to perform as compared to the NG-MAST analysis. Using the modified porB-based typing method, N. gonorrhoeae isolates were reliably differentiated, and transmission clusters were identified. Molecular epidemiology using the porB-based method confirmed direct sexual connections and identified sexual networks otherwise unrevealed by the patient self-reporting or traditional case-tracing methods.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:SSU.etd-06202011-231654 |
| Date | 22 June 2011 |
| Creators | Liao, Mingmin |
| Contributors | Reeder, Bruce, Dillon, Jo-Anne R., Blondeau, Joseph, Goldie, Hughes, Howard, Peter |
| Publisher | University of Saskatchewan |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://library.usask.ca/theses/available/etd-06202011-231654/ |
| Rights | unrestricted, I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to University of Saskatchewan or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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