Clonal relationships of Streptococcus pneumoniae isolates harbouring multiple antibiotic resistance from Belgium

Abstract number: 1733_499

O'Hara F.P., Van Eldere J., Mera R., Miller L., Poupard J., Amrine-Madsen H.

Objectives: Antibiotic resistance has been increasing in many European countries and strains that are non-susceptible to two or more classes of antibiotics (multiple resistance or MR) are particularly troubling. In order to better understand the evolution of resistance in S. pneumoniae, we have identified and characterised the clones present in isolates obtained from a surveillance dataset collected in Belgium.

Methods: A sample of 190 S. pneumoniae isolates from 1997–2004 was selected at random from the larger Belgian surveillance set. For each isolate, PCR was performed on seven housekeeping genes based on the universal Multi Locus Sequence Typing methods. Internal fragments were sequenced, compared to published alleles, and assigned allele numbers. Allele numbers were used to generate allelic profiles, which were compared to published allelic profiles to determine a sequence type (ST). The eBURST algorithm was used to assign STs to clonal complexes (CCs).

Results: The 190 isolates contain 95 unique STs which are divided into 17 CCs and 44 singletons. The 62 MR isolates represent 31 sequence types, but half of these are found within two major clonal complexes (CC156 and CC81). MR is not evenly distributed among CCs; within CCs, the rate of MR varies from 0% (CC53) to 100% (CC81). The clonal composition of the S. pneumoniae population changed over time. In 1997–1999, two CCs, CC156 (representing the PMEN clone Spain9V-3) and CC81 (representing the PMEN clone Spain23F-1), accounted for 25.8% and 13.4% of all isolates, respectively. By 2001–2004, the frequencies of these CCs had dropped to 7.5% and 3.2%. In 1997–1999, CC81 and CC156 accounted for 67.6% of all MR isolates. In 2001–2004, those CCs accounted for only 28.6% of MR isolates. The clonal structure of the different serotype groups varied. Of the 10 most common serotype groups, four were highly clonal, while six contained a variety of CCs representing genetically diverse STs. For example, serogroup 19 covered 7 CCs while serogroup 8 covered 1 CC. MR was much higher in the genetically diverse serotype groups (48.4%) than in those that were highly clonal (4.3%).

Conclusions: The PMEN clones Spain9V-3 and Spain 23F-1 decreased from 1997–2004 in Belgium despite the level of MR increasing over time. The frequency of CCs that harbour MR changes over time. Serotype groups that are genetically diverse such as 19 are more likely to harbour MR.