Interaction of phase variation, host and pressure/gas composition: pneumococcal gene expression of PsaA, SpxB, Ply and LytA in simulated middle ear environments.
OBJECTIVE
Streptococcus pneumoniae, a leading cause of otitis media (OM), undergoes spontaneous intra-strain variations in colony morphology. Transparent (T) variants are more efficient in colonizing the nasopharynx while opaque (O) variants exhibit greater virulence during systemic infections. This study was intended to delineate the underlying molecular mechanisms by which the predominant S. pneumoniae variant efficiently infects the middle ear (ME) mucosa.


METHODS
Human ME epithelial cells were preconditioned for 24h under one of the three gas/pressure conditions designed to simulate those for (1) normal ME (NME), (2) ME with Eustachian tube obstruction (ETO) and (3) ME with tympanostomy tube placement (TT), and then were incubated with ∼ 10(7)CFU/ml of either T or O variants of S. pneumoniae (6A) for 3h. Relative expression levels of genes encoding virulence factors, PsaA (surface adhesion), SpxB (pyruvate oxidase), Ply (pneumolysin), and LytA (autolysin) were assessed separately in epithelium-attached and supernatant bacteria 3h post infection using real-time PCR.


RESULTS
Basal levels of the virulence molecules in inocula were comparable between two variants. However, relative expression levels of the gene transcripts were significantly induced in epithelium-attached T variants 3h after infection. Comparing with NME and TT conditions, ETO environment produced the largest effect on the differential expression of the virulence genes in the infected ME epithelial cells between T (induced) and O (suppressed) phenotypic pneumococci.


CONCLUSIONS
T variant is a predominant phenotype responsible for the pathogenesis of pneumococcal OM.
Li-Korotky
Ha-Sheng
HS
Division of Pediatric Otolaryngology, Children's Hospital of Pittsburgh, Pittsburgh, PA 15201, USA. Ha-Sheng.Li@chp.edu
Lo
Chia-Yee
CY
Zeng
Fan-Rui
FR
Lo
David
D
Banks
Juliane M
JM
D018829:Adhesins, Bacterial / Q000235:genetics*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D002478:Cells, Cultured; D017077:Culture Media, Conditioned; D004432:Ear, Middle / Q000166:cytology / Q000382:microbiology; D004847:Epithelial Cells / Q000382:microbiology / Q000502:physiology; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial / Q000235:genetics / Q000502:physiology*; D006801:Humans; D008074:Lipoproteins / Q000235:genetics*; D008954:Models, Biological; D009238:N-Acetylmuramoyl-L-alanine Amidase / Q000235:genetics* / Q000378:metabolism; D010033:Otitis Media / Q000235:genetics* / Q000382:microbiology; D010641:Phenotype; D011771:Pyruvate Oxidase / Q000235:genetics; D012680:Sensitivity and Specificity; D013296:Streptococcus pneumoniae / Q000235:genetics* / Q000378:metabolism; D013301:Streptolysins / Q000235:genetics* / Q000378:metabolism; D037521:Virulence Factors / Q000096:biosynthesis / Q000235:genetics
D018829:Adhesins, Bacterial; D001426:Bacterial Proteins; D017077:Culture Media, Conditioned; D008074:Lipoproteins; C085000:PsaA protein, Streptococcus; D013301:Streptolysins; D037521:Virulence Factors; C032290:plY protein, Streptococcus pneumoniae; D011771:Pyruvate Oxidase; C119964:LytB protein, Streptococcus; D009238:N-Acetylmuramoyl-L-alanine Amidase
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