Emergence of optochin resistance among Streptococcus pneumoniae in Portugal

Abstract number: 1733_660

Aguiar S., Frias M.J., Santos L., Melo-Cristino J., Ramirez M.

Objective: Characterise optochin-resistant strains of Streptococcus pneumoniae associated with pneumococcal infections in Portugal.

Methods: All strains submitted to our laboratory during 1999–2003 were optochin susceptible. Since then, 2 isolates (0.3%) in 2004 and 30 isolates (3.2%) in 2005, recovered from 10 geographically dispersed hospitals, were optochin-resistant. These 32 optochin-resistant S. pneumoniae strains consisted of mixed populations of optochin-susceptible and optochin-resistant isolates. For each isolate, both optochin-resistant and susceptible subpopulations were characterised using a combination of bile solubility, antimicrobial susceptibility, serotyping and macrorestriction profiling, using SmaI and pulsed field gel electrophoresis (PFGE). The BioNumerics software was used to make UPMGA (unweighed pair group method with arithmetic mean) dendrograms of PFGE patterns. The Dice similarity coefficient was used with optimisation and position tolerance settings of 1.0 and 1.5%, respectively.

Results: Subculture of individual colonies of each strain exposed a uniformly optochin-resistant subpopulation and a uniformly optochin-susceptible subpopulation. The optochin-resistant subpopulations were bile soluble and reacted with sera targeting pneumococcal capsular polysaccharides, confirming their identification as S. pneumoniae. The antimicrobial susceptibility profile and serotype was identical in both optochin-susceptible and resistant subpopulations suggesting that they corresponded to variants of the same clone. PFGE analysis of each subpopulations revealed indistinguishable PFGE profiles, further supporting the suggestion that these constitute two variants of the same strain. The 32 strains included in this study presented 19 different serotypes, all previously found among invasive and colonisation pneumococcal strains in Portugal. Furthermore, the diversity of PFGE profiles observed and the identification of internationally disseminated clones (ex: clone England14–9) excludes a clonal origin for these strains.

Conclusion: Accurate identification of S. pneumoniae isolates is essential for the correct diagnosis and adequate therapy of patients with pneumococcal infections. In view of the findings described here we recommend that at least the bile solubility test should be routinely performed in cases of suspected pneumococcal ethiology, even if the isolates are optochin-resistant, to exclude the possibility of S. pneumoniae.

Session Details

Date: 31/03/2007
Time: 00:00-00:00
Session name: European Society of Clinical Microbiology and Infectious Diseases
Location: ICC, Munich, Germany
Presentation type:
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