Emergence of penicillin-nonsusceptible Streptococcus pneumoniae clones expressing serotypes not present in the antipneumococcal conjugate vaccine.
BACKGROUND
Penicillin-nonsusceptible Streptococcus pneumoniae isolates are confined mainly to a few serogroups. Capsular transformation may serve as a mechanism for spreading antibiotic resistance to new serotypes.


METHODS
Antibiogram and molecular typing, by pulsed-field gel electrophoresis (PFGE), were performed on 46 nasopharyngeal and middle ear fluid (MEF) isolates expressing serotype 11A, 45 MEF isolates expressing serotype 15B/C (recovered during 1998-2003 from Israeli children <5 years old), and 57 MEF isolates expressing serotype 19F (recovered during 1998-2001 from Costa Rican children <7.5 years old).


RESULTS
PFGE patterns showed that 49 (86%) of 57 serotype 19F isolates and 19 (41%) of 46 serotype 15B/C isolates were closely related. The vast majority of these isolates (80% of serotype 19F and 100% of serotype 15B/C isolates) were nonsusceptible to penicillin. Multilocus sequence typing (MLST) data show that the serotype 15B/C isolates belonged to the ST346 cluster, whereas the serotype 19F isolates were a single-locus variant of ST346. For serotype 11A isolates, PFGE patterns and MLST analysis showed that 8 (80%) of the 10 penicillin-nonsusceptible isolates belonged to a single clone--namely, ST156--which was identical to the international Spain9V-3 clone.


CONCLUSIONS
Penicillin-nonsusceptible pneumococcal clones of serotypes not related to those included in the 11-valent conjugate vaccines may derive from capsular transformation of vaccine-related serotypes. Of particular concern was the detection of serotype 11A variants of the successful international Spain9V-3 clone. This phenomenon, although seemingly rare at present, can have implications for the long-term effectiveness of the conjugate vaccines.
Porat
Nurith
N
Pediatric Infectious Disease Unit, Soroka University Medical Center, Beer-Sheva, Israel. npurat@bgumail.bgu.ac.il
Arguedas
Adriano
A
Spratt
Brian G
BG
Trefler
Ronit
R
Brilla
Eduardo
E
Loaiza
Cecilia
C
Godoy
Dan
D
Bilek
Nicole
N
Dagan
Ron
R
D002648:Child; D002675:Child, Preschool; D003364:Costa Rica; D016521:Electrophoresis, Gel, Pulsed-Field; D006801:Humans; D007223:Infant; D007557:Israel; D009305:Nasopharynx / Q000382:microbiology; D010034:Otitis Media with Effusion / Q000382:microbiology; D010403:Penicillin Resistance; D011008:Pneumococcal Infections / Q000382:microbiology; D022242:Pneumococcal Vaccines / Q000276:immunology*; D012703:Serotyping; D013296:Streptococcus pneumoniae / Q000145:classification* / Q000187:drug effects*; D014481:United States
D022242:Pneumococcal Vaccines