Biofilm formation of Streptococcus pneumoniae isolates from nasopharynx and middle-ear effusion

Abstract number: P2203

Tapiainen T., Sevander J., Kaijalainen T., Saukkoriipi A., Renko M., Leinonen M., Uhari M.

Objectives: We aimed to evaluate the biofilm formation of pneumococci in vitro in a large number of clinical isolates obtained from middle ear effusion and nasopharynx.

Methods: In total 153 clinical isolates from children attending an otitis media prevention trial were used. All isolates were serotyped at the National Public Health Institute in Oulu, Finland. Bacteria were grown in BHI until mid-logarithmic phase and diluted 1:100 in BHI or in BHI supplemented with 0.5% glucose or 0.5% fructose. Two hundred ul of diluted bacterial suspension was incubated in triplicate on a polystyrene plate for 18 h at 37°C with 5% CO2. After removal of supernatant and after crystal violet stain (0.4% 50 ul 15 min) wells were washed three times with PBS to remove unattached cells. Optical density was measured at 540 nm after dissolving biofilm in 50 ul of DMSO. To validate the method we used scanning electron microscopy to visualize the structure of biofilms on bottoms of polyvinyl plates. Quantitative PCR was used to measure the number of pneumococcal genomes in biofilm.

Results: Altogether 62 of 153 (41% strains from nasopharynx and middle ear fluid were good biofilm producers (the mean OD >0.5) in nutrition-rich environment after supplementing BHI with 0.5% glucose or 0.5% fructose. The ability to form biofilm in vitro varied among pneumococcal isolates between different serotypes. Pneumococcal serotypes that most effectively produced biofilm were 6A, 14, 6B, 19A, and 19F. The site of isolation did not affect the ability of pneumococcal strains to form biofilm in vitro. In BHI supplemented with 0.5% glucose the OD value of pneumococcal isolates from middle ear effusion was 0.47 (SD 0.11) and 0.50 (SD 0.13) in isolates from nasopharynx (95% CI of the difference -0.08 to 0.021).

Conclusions: The ability of pneumococcal strains isolated from nasopharynx and from middle ear effusion of children to form biofilm in vitro was common. The serotype of pneumococcal isolate seemed to affect its ability to form biofilm. The serotypes that most effectively produced biofilm in our study (6A, 14, 6B, 19F) are among the pneumococcal serotypes that most often cause pneumococcal otitis media in children in our country.

Session Details

Date: 19/04/2008
Time: 00:00-00:00
Session name: 18th European Congress of Clinical Microbiology and Infectious Diseases
Location: Barcelona, Spain
Presentation type:
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