Variations in serotypes and susceptibility of adult non-invasive Streptococcus pneumoniae isolates between the periods before (May 2000–May 2001) and 10 years after (May 2010–May 2011) introduction of conjugate vaccines for child immunisation in Spain

Abstract This study explored the serotype distribution and antibiotic susceptibility of adult non-invasive Streptococcus pneumoniae isolates received in the Spanish Reference Laboratory for Pneumococci immediately prior to introduction of the 7-valent pneumococcal conjugate vaccine (PCV7) in June 2001 (May 2000–May 2001) and 10 years afterwards (May 2010–May 2011). Serotyping was performed by Quellung reaction and/or dot-blot assay, and minimum inhibitory concentrations (MICs) were determined by agar dilution. Clinical and Laboratory Standards Institute (CLSI) breakpoints were used for susceptibility interpretation. A total of 1274 isolates were identified (650 in the first period and 624 in the second period). PCV7 serotypes (as a group) showed a decrease ( P 90 values (MIC for 90% of the organisms) of levofloxacin for the remaining PCV7 serotypes of 16 μg/mL. Inversely, non-PCV7 serotypes (as a group) increased from 56.8% to 86.1% ( P P P  = 0.005). Globally, non-susceptibility to penicillin decreased from 54.2% in the first period to 36.9% in the second period ( P 90 for all β-lactams in the second period, with non-susceptibility increasing from 18.2% to 71.4% ( P  = 0.003) for penicillin and from 0.0% to 38.1% ( P  = 0.022) for amoxicillin. Cefditoren showed the highest intrinsic activity (lowest MIC 50 /MIC 90 ) overall and also against serotype 19A. Continuous surveillance of serotype distribution and antibiotic susceptibility among adult non-invasive isolates is necessary to detect emerging serotypes and to continuously assess the intrinsic activity of highly active oral antibiotics such as levofloxacin and cefditoren and of parenteral antibiotics such as cefotaxime.