What can children gain from pneumococcal conjugate vaccines?

Viability and virulence of pneumolysin, pneumococcal surface protein A, and pneumolysin/pneumococcal surface protein A mutants in the ear

IMPORTANCE

Understanding how pneumococcal proteins affect the pathology of the middle ear and inner ear is important for the development of new approaches to prevent otitis media and its complications.

OBJECTIVES

To determine the viability and virulence of Streptococcus pneumoniae mutants deficient in pneumolysin (Ply-) and pneumococcal surface protein A (PspA-) in the chinchilla middle ear.

DESIGN

Bullae of chinchillas were inoculated bilaterally with wild-type (Wt), Ply-, PspA-, and Ply-/PspA- strains. Bacterial colony-forming units (CFUs) in middle ear effusions were counted at 48 hours. The CFUs of the PspA- group were also counted at 6 to 36 hours after inoculation. Temporal bone histopathological results were compared.

SETTING AND PARTICIPANTS

Twenty-seven chinchillas in an academic research laboratory.

EXPOSURE

Chinchilla middle ears were inoculated with S pneumoniae to produce sufficient volumes of effusions and noticeable histopathological changes in the ears.

MAIN OUTCOMES AND MEASURES

The CFU counts in the middle ear effusions and histopathological changes were compared to determine the effect of pneumococcal protein mutations on chinchilla ears.

RESULTS

At 48 hours, CFUs in middle ears were increased for the Wt and Ply-/PspA- strains, but Ply- remained near inoculum level. No bacteria were detected in the PspA- group. The CFUs of PspA- decreased over time to a low level at 30 to 36 hours. In vitro, PspA- in Todd-Hewitt broth showed an increase in bacterial growth of 2 logs at 43 hours, indicating PspA- susceptibility to host defenses in vivo. The PspA- and Ply- groups had fewer pathologic findings than the Wt or Ply-/PspA- groups. Histopathological analysis showed significant differences in the number of bacteria in the scala tympani in the Wt group compared with the Ply-, PspA-, and Ply-/PspA- groups. The PspA- strain was the least virulent.

CONCLUSIONS AND RELEVANCE

The PspA- mutant was much less viable and less virulent in the ear than the Wt, Ply-, and Ply-/PspA- strains. There was no significant attenuation in the viability and virulence of the Ply-/PspA- mutant compared with the Wt or single mutants. The viability and virulence of pneumococcal mutants seemed to be protein and organ specific.

Nasopharyngeal carriage rate of Streptococcus pneumoniae in children with sickle cell disease before and after the introduction of heptavalent pneumococcal conjugate vaccine

Children with sickle cell disease (SCD) are at high risk of severe infection with Streptococcus pneumoniae (SP). From 2002, all children aged <5 years in the UK with SCD were recommended 7-valent pneumococcal conjugate vaccine (PCV-7) in infancy and 23-valent pneumococcal polysaccharide vaccine boosting, in addition to regular penicillin prophylaxis. Our objective was to determine the nasopharyngeal (NP) carriage rate of SP in children aged <5 years with SCD before and after vaccination with PCV-7 (by vaccine, cross-protection and non-vaccine serotypes). NP swabs were obtained from 63 children attending the Royal London Hospital or Newham General Hospital paediatric haematology clinic between April 2001 and April 2002. Later, NP swabs were obtained from 43 children attending the clinic between June and December 2004 after a PCV-7 vaccination programme. All SP isolated by culture were serotyped and susceptibility to penicillin measured. In the first study group, 13 samples grew SP with 1 sample containing 2 different serotypes, giving a carriage rate of 21%. Four (31%) were intermediately susceptible to penicillin. In the second group overall NP carriage rate had decreased to 9% (n=4), and the proportion directly or indirectly covered by the PCV-7 vaccine fell from 13/14 to 2/4 (P=0.11). One (25%) of these isolates was intermediately susceptible to penicillin. The introduction of PCV-7 appears to be associated with a shift in distribution of serotypes carried by children with SCD. This may have implications for vaccine effectiveness.

[Nonvaccine Streptococcus pneumoniae serotypes causing acute bacterial meningitis]

The pneumococcal heptavalent conjugate vaccine protects children aged less than 2 years old from invasive pneumococcal disease (IPD). Efficacy is 89-93% in the US population and 71-86% in European studies. The vaccine confers active immunization against the main serotypes causing IPD (4, 6B, 9V, 14, 18C, 19F y 23F). We describe 2 children who presented with pneumococcal meningitis caused by nonvaccine serotypes. As a result of the widespread use of the heptavalent vaccine, there may be a shift in the serotypes causing IPD.

Divide and Conquer: Division of Labor by B-1 B Cells

Capsular polysaccharides enhance bacterial virulence. In this issue of Immunity, demonstrate a division of labor between the B-1 B cell subsets: natural antibodies from B-1a cells limit infection by Streptococcus pneumoniae, whereas B-1b cells generate the anticapsule-induced response that prevents fatal infection.