Plant and Microbial Science Department, University of Canterbury, Christchurch, New Zealand
Received 22 October 2004; returned 19 November 2004; revised 29 November 2004; accepted 2 December 2004
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Abstract |
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Methods: Fifty-nine isolates representing both invasive and non-invasive pneumococci from multiple locations, serotypes and years were analysed by multilocus sequence typing.
Results: Major international clones, including Spain23F-1, France9V-3 and Taiwan19F-14, were found to be present in New Zealand. A one-allele variant of the Taiwan19F-14 clone (aroE 154, ST 271) was particularly prominent.
Conclusions: Antibiotic-resistant pneumococci have not evolved de novo in New Zealand, but were introduced to the country during the early 1990s.
Keywords: S. pneumoniae , PMEN , MLST
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Introduction |
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New Zealand, as with many other countries, saw a rapid increase in the prevalence of penicillin non-susceptible S. pneumoniae in the late 1990s. In order to explain this observed increase, we sought to determine whether a resistant strain(s) emerged de novo in New Zealand, or if a resistant clone(s) from overseas, which subsequently radiated into New Zealand, was responsible.
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Materials and methods |
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Results and discussion |
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All 11 isolates from the France9V-3 clonal group were recovered from blood cultures. All members of this group with ST 156 were isolated during 1995 or thereafter, and exhibited reduced susceptibility to ß-lactams. However, three single-allele variants (ST 162, ddl 114) were isolated during or prior to 1995 and were all susceptible to penicillin. The pbp2b gene has been shown to be physically linked to the ddl gene, and co-transfer has been demonstrated previously.7
This is supported by the acquisition of ß-lactam resistance also being coupled to a change in the pbp RFLP patterns. None of the New Zealand examples of the France9V-3 clone was found to be multidrug-resistant, although one isolate did express resistance to co-trimoxazole as well as penicillin.
In contrast to the Spain23F-1 clone, which had been prevalent in Spain for at least a decade before its intercontinental spread was first documented,8
the Taiwan19F-14 clone has emerged relatively recently, but seems equally adept at global dissemination. Nineteen isolates of the Taiwan19F-14 clonal group were noted, all of which were serotype 19F with the exception of a single serotype 14 isolate. Curiously, the single-allele variant (ST 271, aroE 154) of the Taiwan19F-14 clone was the most prominent in the current study; of 19 isolates, 13 (68%) were ST 271. This particular variant has previously been described as the major Korean 19F clone (www.mlst.net). Five isolates were from invasive sites (three ST 271 and two ST 236).
The New Zealand Taiwan19F-14 clonal group is resistant to erythromycin, co-trimoxazole and tetracycline and is near uniformly susceptible to chloramphenicol and vancomycin. Two isolates recovered during 19992000, however, had acquired resistance to chloramphenicol. Levels of ß-lactam resistance are variable among this group. In the case of the five ST 236 isolates, the penicillin and cefotaxime MICs were consistently 2 and 1 mg/L (one instance of a cefotaxime MIC of 0.5 mg/L), respectively; however, among the ST 271 isolates MICs were in the range 28 mg/L and 132 mg/L of penicillin and cefotaxime, respectively. The observed MIC variability did not correlate with changes in their respective pbp RFLP profiles (data not shown).
The Taiwan19F-14 clone has emerged only recently. It was first formally identified when multiply antibiotic-resistant S. pneumoniae from Taiwanese hospitals were examined by MLST, showing this clone was present in Taiwan at least as early as 1993.6 In 1995, two serotype 19F isolates were recovered from blood cultures in a London hospital that had the same allelic profile.6 This is the same year that the Taiwan19F-14 clone was observed in New Zealand and coincides with a period of increased prevalence of penicillin-resistant S. pneumoniae throughout the country. The Taiwan19F-14 clone was identified in the USA as early as 19971998.9 Therefore it seems likely that the Taiwan19F-14 strain did in fact originate in Taiwan, or elsewhere in Asia, and began to disseminate globally as early as 1995.
The remaining 12 isolates yielded allelic profiles that matched eight previously defined STs, but do not belong to any of the currently described PMEN clones. These were predominantly invasive, non-resistant isolates, and were representative of multiple serotypes: 9N (ST 66, n=2), 14 (ST 124, n=2; ST 129, n=1; and ST 346, n=1), 19A (ST 199, n=2; and ST 876, n=1), 19F (ST 146, n=1) and 23F (ST 36, n=2). In each instance, these sequence types corresponded to isolates from invasive disease recovered elsewhere in the world. In particular, the ST 124 isolates and one single-allele variant (ddl 145, ST 129) are members of an important clone associated with invasive disease and have been recovered throughout the world, including Sweden, Denmark, Norway, Finland, the UK, Australia and Canada. Another invasive clone, ST 199, and a single-allele variant (spi 17
6, ST 876), has been recovered previously from invasive disease in the UK. The inclusion of antibiotic-susceptible invasive clones in the PMEN database will better allow the distribution of these strains to be monitored worldwide.
Antibiotic-resistant S. pneumoniae in New Zealand can be attributed mainly to the global spread of international resistant clones; in particular the well-described Spain23F-1 and France9V-3 clones, as well as the more recently described Taiwan19F-14 clone. The use of MLST and the PMEN-described clones4 allow effective worldwide surveillance of important pneumococcal clones.
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Footnotes |
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Acknowledgements |
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References |
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