Adherence of Streptococcus pneumoniae to polystyrene plates, effect of serum on adhesion, and virulence in the gerbil otitis media model

The adherence of 11 pneumococcal strains to polystyrene was studied and expressed as the number of colony-forming units (CFU) recovered per 106 CFU of initial inoculum. Three strains were considered as strong adherent (>100 CFU/106), three as medium adherent (10–100 CFU/106), and five as low adherent (<10 CFU/106). All serotype 3 strains were low adherent whilst serotypes 23F and 19F behaved as strong or medium adherent. The impact of gerbil sera on adherence of six selected pneumococcal strains (one strong adherent, one medium adherent, and four low adherents) to abiotic material was also studied under two experimental conditions. In the presence of sera, the adherence ability of the strong, medium, and one low adherent strains decreased significantly. On the other hand, the adherence significantly increased in all strains when sera were removed following preincubation of bacteria exposed to sera, although such increase was statistically significant for five of them. Finally, the ability of two (one strong adherent and one low adherent) strains to induce otitis media in gerbils was also evaluated; the strong adherent strain behaved significantly more virulent than the less adherent in terms of ear damage and animal weight loss.