The phenotypic and genetic biofilm formation characteristics of coagulase-negative staphylococci isolates in children with otitis media

Abstract

Objective: Medical biofilms are involved in a number of chronic infections including otitis media with effusion and chronic rhinosinusitis, which are common pediatric infectious diseases. The purpose of the study was to analyze the phenotypic and genotypic indicators of biofilm formation of coagulase negative staphylococci isolates in children with otitis media with effusion, and in children with chronic rhinosinusitis as a comparison group by using three different detection methods.

Methods: Forty nine children aged from 2 to 6 years old, diagnosed with otitis media with effusion were enrolled to the study. The comparative group consisted of twenty three strains of coagulase-negative staphylococci from the strains collection isolated from nose swabs from children 3 to 7 years old suffering from rhinosinusitis for longer than 12 weeks. Cultured strains were tested for biofilm formation ability with three tests: Congo red agar, tissue culture plate methods and detection of ica operon.

Results: Out of 97 ear effusion specimens, obtained from 49 children suffering from OME, 38 were found positive in conventional culture resulting in isolation of 50 different bacterial species. Nested-PCR method confirmed bacterial presence in 95 (97.9%) cases. Among 50 different bacterial species isolated, 30 (30.9%) CNS and 20 (20.6%) other than CNS species. Detection of slime producing phenotype of CNS was performed with CRA plate test. Among OME isolates, 11 (36.7%) were CRA plate test positive. In case of isolates from CRS, 8 (34.8%) strains revealed black coloration on CRA. Using TCP method, strong adherence to microtiter plate was observed in two Staphylococcus epidermidis strains from OME and two S. epidermidis from CRS. By using the ica operon test, the genotypic ability to form biofilm was identified in 7 (23.3%) S. epidermidis strains cultured from ears effusion and in 3 (13%) strains from nose swabs.

Conclusions: CNS strains revealed genotypic and phenotypic features responsible for the ability to form the biofilm in vivo. The presence of ica genes and phenotypic ability to form a biofilm by CNS strains emphasizes the pathogenic character of these strains in some cases of otitis media with effusion.