a Pneumococcal Diseases Research Unit of the Medical Research Council, The South African Institute for Medical Research and the University of the Witwatersrand, Johannesburg, South Africa; b Northern Ireland Public Health Laboratory, Belfast City Hospital, Belfast, UK; c Department of International Health, The Rollins School of Public Health, Emory University, Atlanta, GA, USA
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Abstract |
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Introduction |
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Motivated by the emergence of antimicrobial resistance and the spread of resistant organisms worldwide, subtyping methods to differentiate S. pneumoniae strains of the same serogroup/type have been developed and applied. Extensive molecular typing studies from various regions in the world have identified a number of clones of highly penicillin-resistant pneumococci, some of which have spread globally. Predominant among these are the well-characterized Spanish multidrug-resistant serotype 23F and 6B clones and the major penicillin-resistant serotype 9V clone.24
We therefore sought to determine the clonality of FQ resistance of wild-type isolates of S. pneumoniae from different geographical locations in an attempt to provide further insight into the epidemiology of FQ resistance in this important pathogen. A collection of strains was obtained from a study in Northern Ireland and from the Alexander Project, which was established in 1992 to monitor the susceptibility of major lower respiratory tract bacterial pathogens to a variety of antimicrobials and to identify trends in the development of resistance over time.5,6
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Materials and methods |
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MICs of the following antibiotics were determined using broth microdilution methods according to NCCLS guidelines:8 penicillin, chloramphenicol, tetracycline, erythromycin, clindamycin, trimethoprimsulfamethoxazole, rifampicin, cefotaxime, ciprofloxacin, ofloxacin and levofloxacin. MICs of ciprofloxacin, ofloxacin and levofloxacin were confirmed using Etests (AB Biodisk, Solna, Sweden) according to manufacturer's instructions. The term resistance includes intermediate and high-level MICs.
Serotyping of strains was carried out by the Quellung reaction with antisera from the Statens Serum Institut, Copenhagen, Denmark. PCR-based BOX-fingerprinting was carried out on chromosomal DNA by a method adapted from Ertugrul et al.9 Macrorestricted (using SmaI) chromosomal DNA prepared using the method described by Lefevre et al.10 was separated by pulsed-field gel electrophoresis (PFGE) with a Pulsaphor system (Pharmacia, Uppsala, Sweden). Fingerprint patterns were compared with those of 11 international clones.
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Results |
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Discussion |
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Four FQ-resistant isolates (three from France and one from Spain) were identical or closely related (fewer than three band differences) to the well-documented Spain23F-1 clone (Table). This clone has been reported in numerous countries in Europe,2 the USA, South Africa, South America and some regions in the Far East. A recent study in Asia, Europe and North America revealed that 32% of all highly penicillin-resistant isolates belonged to the Spain23F-1 clone.11
These data indicate that FQ resistance may be emerging in pandemic clones of multi-resistant pneumococci, necessitating the need for expanded surveillance for FQ resistance.
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Acknowledgements |
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Notes |
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References |
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Felmingham, D., Grüneberg, R. N. & the Alexander Project Group. (2000). The Alexander Project 19961997: latest susceptibility data from this international study of bacterial pathogens from community-acquired lower respiratory tract infections. Journal of Antimicrobial Chemotherapy 45, 191203.
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McGee, L., McDougal, L., Zhou, J., Spratt, B. G., Tenover, F. C., George, R. et al. (2001). Nomenclature of major antimicrobialresistant clones of Streptococcus pneumoniae defined by the Pneumococcal Molecular Epidemiology Network. Journal of Clinical Microbiology 39, 256571.
8 . National Committee for Clinical Laboratory Standards. (2000). Methods for Dilution Antimicrobial Susceptibility Tests for Bacteria that Grow AerobicallyFifth Edition: Approved Standard M7-A5. NCCLS, Villanova, PA.
9 . Ertugrul, N., Rodriguez-Barradas, M. C., Musher, D. M., Ryan, M. A. K., Agin, C. S., Murphy, S. J. et al. (1997). BOX-polymerase chain reaction-based DNA analysis of nonserotypeable Streptococcus pneumoniae implicated in outbreaks of conjunctivitis. Journal of Infectious Diseases 176, 14015. [ISI][Medline]
10 . Lefevre, J. C., Faucon, G., Sicard, A. M. & Gasc, A. M. (1993). DNA fingerprinting of Streptococcus pneumoniae by pulse-field gel electrophoresis. Journal of Clinical Microbiology 31, 27248. [Abstract]
11 . Davies, T., Goering, R. V., Lovgren, M., Talbot, J. A., Jacobs, M. R. & Appelbaum, P. C. (1999). Molecular epidemiological survey of penicillin-resistant Streptococcus pneumoniae from Asia, Europe and North America. Diagnostic Microbiology and Infectious Disease 34, 712. [ISI][Medline]
Received 18 June 2001; returned 11 August 2001; revised 18 September 2001; accepted 25 September 2001