Pneumococcal meningitis: is disease severity related to capsular or clonal types?

Abstract number: 1733_1278

Ribes S., Taberner F., Cabellos C., Gerber J., Tubau F., Ardanuy C., Liñares J., Nau R., Gudiol F.

Objectives: Capsular serotype of Streptococcus pneumoniae (Sp) strains is an important virulence factor. A single pneumococcal serotype includes a number of genetically divergent clones. Using the rabbit model of meningitis, we tested whether five different pneumococcal clones belonging to serotypes 23F and 3 caused different disease severity.

Methods: Meningitis was induced by intracisternal inoculation of 106 CFU/mL of five invasive strains of Sp in five groups of rabbits (n ≥10/group). We used three strains of serotype 23F with different degree of penicillin (PEN) susceptibility and sequence type (ST): strain A (ST311, PEN-S), strain B (ST81, PEN-R) and strain C (ST37, PEN-I) and two PEN-S strains of serotype 3: strain D (ST260) and strain E (ST180). Eighteen hours after infection, serial CSF samples were collected over 24 h to determine bacterial counts and inflammatory data levels: lactate, protein and lipoteichoic/teichoic acids (LTAs). Bacteraemia at 0 h and mortality at 24 h were also assessed. Fisher's exact test was used in bacteraemia/mortality studies. ANOVA/T-Student test or Kruskal Wallis/Mann-Whitney tests were performed dependent on whether data were normally distributed or not.

Results: Bacteraemia at 0 h was found in 10/10, 11/13, 8/12, 5/13 and 3/11 of rabbits infected with strains A, B, C, D and E, respectively. Bacterial concentrations at 0 and 6 h were lower in serotype 3 strains than in serotype 23F isolates (p < 0.05). Bacterial counts at 24 h were above 4.5 log CFU/mL in all strains. Lactate at 0, 6 and 24 h, and protein levels at 6 and 24 h were higher in serotype 23F than in serotype 3 strains. Mortality was 50, 30.8, 58.3, 15.4 and 0% for strains A, B, C, D and E, respectively. Among strains belonging to serotype 23F, there were neither marked differences in bacterial counts nor in inflammatory activity. On the contrary, there were statistical differences in CSF bacterial concentrations and in lactate, protein and LTAs levels among strains belonging to serotype 3.

Conclusions: In the rabbit meningitis model, serotype 23F strains (independently of their PEN susceptibility patterns), produced higher bacteraemia and mortality rates, and higher CSF levels of inflammatory parameters than serotype 3 strains. On the other hand, differences noted between two clones of serotype 3 indicated that additional genetic loci other than capsular serotype could be involved in pneumococcal disease severity.

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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