JAC Advance Access originally published online on September 16, 2008
Journal of Antimicrobial Chemotherapy 2008 62(6):1234-1240; doi:10.1093/jac/dkn392
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Original research |
Breakthrough in penicillin resistance? Streptococcus pneumoniae isolates with penicillin/cefotaxime MICs of 16 mg/L and their genotypic and geographical relatedness
1 Department of Medical Microbiology and Antimicrobial Chemotherapy, Fundación Jiménez Díaz, Madrid, Spain 2 Microbiology Department, School of Medicine, University Complutense, Madrid, Spain 3 PRISM-AG, Madrid, Spain 4 Spanish National Reference Pneumococcal Laboratory, Instituto de Salud Carlos III, Majadahonda, Madrid, Spain 5 IOMC ‘Prof. Dr Alfred Rusescu’, Bucharest, Romania 6 INCDMI Cantacuzino, Bucharest, Romania 7 National Medicines Institute, Warsaw, Poland
Received 17 July 2008; returned 11 August 2008; revised 18 August 2008; accepted 22 August 2008
* Correspondence address. Department of Medical Microbiology and Antimicrobial Chemotherapy, Fundación Jiménez Díaz, Avenida de Reyes Católicos 2, 28040 Madrid, Spain. Tel: +34-91-5447387; Fax: +34-91-5494764; E-mail: fsoriano{at}fjd.es
Objectives: To phenotypically and genotypically characterize 11 strains (isolated in four different centres) exhibiting penicillin MIC of 8–32 mg/L among isolates of the SPICE project. Nine isolates were from Romania (9/162; 5.56%) and two from Poland (2/305; 0.66%).
Methods: In vitro susceptibility was determined in triplicate by microdilution (CLSI guidelines), and additionally, MICs of penicillin, cefotaxime and amoxicillin were confirmed in triplicate by agar dilution. Multilocus sequence typing (MLST), PFGE and gene amplification and sequencing were performed.
Results: For the nine Romanian isolates, MICs were 
16 mg/L for penicillin, cefotaxime and amoxicillin, 32 mg/L for cefuroxime and cefpodoxime, 4–8 mg/L for cefditoren and 128 mg/L for erythromycin and gentamicin. All isolates were non-susceptible to imipenem (MIC = 0.5–1 mg/L) and susceptible to levofloxacin (MIC = 0.5–1 mg/L) and vancomycin (MIC = 0.25–0.5 mg/L). These Romanian strains presented a new cluster in the 595–600 region of PBP2X (YSGIQL
LSTPWF) conferring 98% homology with Streptococcus mitis PBP2X, with a new MurM allele (seven strains) with eight amino acid changes versus R6. PBP nucleotide sequences were highly conserved suggesting a common origin. Allelic profiles of two strains gave sequence type 321, three strains exhibited a single- and four a double-locus variance. MLST-predicted serotype was 23F in all but one strain (19F), but three strains were 19A by Quellung.
Conclusions: The multidrug high resistance (precluding adequate oral therapy in children), its origin, the prevalence found in Romania and the presence of non-vaccine (7-valent) serotypes should worry the medical community because of a possible clonal diffusion that would limit therapeutic alternatives.
Keywords: MurM , multidrug resistance , serotype 23F , serotype 19A