Characterization of biofilm matrix, degradation by DNase treatment and evidence of capsule downregulation in Streptococcus pneumoniae clinical isolates.
BACKGROUND
Streptococcus pneumoniae is a common respiratory pathogen and a major causative agent of respiratory infections, including otitis media (OM). Pneumococcal biofilms have been demonstrated on biopsies of the middle ear mucosa in children receiving tympanostomy tubes, supporting the hypothesis that chronic OM may involve biofilm development by pathogenic bacteria as part of the infectious process. To better understand pneumococcal biofilm formation six low-passage encapsulated nasopharyngeal isolates of S. pneumoniae were assessed over a six-eight day period in vitro.


RESULTS
Multiparametric analysis divided the strains into two groups. Those with a high biofilm forming index (BFI) were structurally complex, exhibited greater lectin colocalization and were more resistant to azithromycin. Those with a low BFI developed less extensive biofilms and were more susceptible to azithromycin. dsDNA was present in the S. pneumoniae biofilm matrix in all strains and treatment with DNase I significantly reduced biofilm biomass. Since capsule expression has been hypothesized to be associated with decreased biofilm development, we also examined expression of cpsA, the first gene in the pneumococcal capsule operon. Interestingly, cpsA was downregulated in biofilms in both high and low BFI strains.


CONCLUSIONS
All pneumococcal strains developed biofilms that exhibited extracellular dsDNA in the biofilm matrix, however strains with a high BFI correlated with greater carbohydrate-associated structural complexity and antibiotic resistance. Furthermore, all strains of S. pneumoniae showed downregulation of the cpsA gene during biofilm growth compared to planktonic culture, regardless of BFI ranking, suggesting downregulation of capsule expression occurs generally during adherent growth.
Hall-Stoodley
Luanne
L
Center for Genomic Sciences, Allegheny-Singer Research Institute, Pittsburgh, PA 15212, USA. lstoodle@wpahs.org
Nistico
Laura
L
Sambanthamoorthy
Karthik
K
Dice
Bethany
B
Nguyen
Duc
D
Mershon
William J
WJ
Johnson
Candice
C
Hu
Fen Ze
FZ
Stoodley
Paul
P
Ehrlich
Garth D
GD
Post
J Christopher
JC
D000900:Anti-Bacterial Agents / Q000494:pharmacology; D017963:Azithromycin / Q000494:pharmacology; D001426:Bacterial Proteins / Q000096:biosynthesis / Q000235:genetics; D018441:Biofilms / Q000187:drug effects* / Q000254:growth & development*; D002648:Child; D015169:Colony Count, Microbial; D004269:DNA, Bacterial / Q000302:isolation & purification / Q000378:metabolism*; D003850:Deoxyribonuclease I / Q000378:metabolism*; D020869:Gene Expression Profiling; D006801:Humans; D009305:Nasopharynx / Q000382:microbiology; D013296:Streptococcus pneumoniae / Q000302:isolation & purification / Q000502:physiology*
D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; C500439:CpsA protein, Streptococcus pneumoniae; D004269:DNA, Bacterial; D017963:Azithromycin; D003850:Deoxyribonuclease I